Patent Application
20190191501
Embodiments of the subject matter described herein relate generally to apparatus and methods of defrosting a load using radio frequency (RF) energy.
Conventional capacitive food defrosting (or thawing) systems include large planar electrodes contained within a heating compartment. After a food load is placed between the electrodes and the electrodes are brought into contact with the food load, low power electromagnetic energy is supplied to the electrodes to provide gentle warming of the food load. As the food load thaws during the defrosting operation, the impedance of the food load changes. Accordingly, the power transfer to the food load also changes during the defrosting operation. The duration of the defrosting operation may be determined, for example, based on the weight of the food load, and a timer may be used to control cessation of the operation.
Although good defrosting results are possible using such systems, the dynamic changes to the food load impedance may result in inefficient defrosting of the food load. In addition, inaccuracies inherent in determining the duration of the defrosting operation based on weight may result in premature cessation of the defrosting operation, or late cessation after the food load has begun to cook. What are needed are apparatus and methods for defrosting food loads (or other types of loads) that may result in efficient and even defrosting throughout the load and cessation of the defrosting operation when the load is at a desired temperature.
A more complete understanding of the subject matter may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures.
The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the words “exemplary” and “example” mean “serving as an example, instance, or illustration.” Any implementation described herein as exemplary or an example is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, or the following detailed description.
Embodiments of the subject matter described herein relate to solid-state defrosting apparatus that may be incorporated into stand-alone appliances or into other systems. As described in greater detail below, embodiments of solid-state defrosting apparatus include both “unbalanced” defrosting apparatus and “balanced” apparatus. For example, exemplary “unbalanced” defrosting systems are realized using a first electrode disposed in a cavity, a single-ended amplifier arrangement (including one or more transistors), a single-ended impedance matching network coupled between an output of the amplifier arrangement and the first electrode, and a measurement and control system that can detect when a defrosting operation has completed. In contrast, exemplary “balanced” defrosting systems are realized using first and second electrodes disposed in a cavity, a single-ended or double-ended amplifier arrangement (including one or more transistors), a double-ended impedance matching network coupled between an output of the amplifier arrangement and the first and second electrodes, and a measurement and control system that can detect when a defrosting operation has completed. In various embodiments, the impedance matching network includes a variable impedance matching network that can be adjusted during the defrosting operation to improve matching between the amplifier arrangement and the cavity.
Generally, the term “defrosting” means to elevate the temperature of a frozen load (e.g., a food load or other type of load) to a temperature at which the load is no longer frozen (e.g., a temperature at or near 0 degrees Celsius). As used herein, the term “defrosting” more broadly means a process by which the thermal energy or temperature of a load (e.g., a food load or other type of load) is increased through provision of RF power to the load. Accordingly, in various embodiments, a “defrosting operation” may be performed on a load with any initial temperature (e.g., any initial temperature above or below 0 degrees Celsius), and the defrosting operation may be ceased at any final temperature that is higher than the initial temperature (e.g., including final temperatures that are above or below 0 degrees Celsius). That said, the “defrosting operations” and “defrosting systems” described herein alternatively may be referred to as “thermal increase operations” and “thermal increase systems.” The term “defrosting” should not be construed to limit application of the invention to methods or systems that are only capable of raising the temperature of a frozen load to a temperature at or near 0 degrees Celsius.
According to an “unbalanced” embodiment, the first electrode 170 is arranged proximate to a cavity wall (e.g., top wall 111), the first electrode 170 is electrically isolated from the remaining cavity walls (e.g., walls 112-115 and door 116), and the remaining cavity walls are grounded. In such a configuration, the system may be simplistically modeled as a capacitor, where the first electrode 170 functions as one conductive plate (or electrode), the grounded cavity walls (e.g., walls 112-115) function as a second conductive plate (or electrode), and the air cavity (including any load contained therein) function as a dielectric medium between the first and second conductive plates. Although not shown in
According to a “balanced” embodiment, the first electrode 170 is arranged proximate to a first cavity wall (e.g., top wall 111), a second electrode 172 is arranged proximate to an opposite, second cavity wall (e.g., bottom wall 112), and the first and second electrodes 170, 172 are electrically isolated from the remaining cavity walls (e.g., walls 113-115 and door 116). In such a configuration, the system also may be simplistically modeled as a capacitor, where the first electrode 170 functions as one conductive plate (or electrode), the second electrode 172 functions as a second conductive plate (or electrode), and the air cavity (including any load contained therein) function as a dielectric medium between the first and second conductive plates. Although not shown in
According to an embodiment, during operation of the defrosting system 100, a user (not illustrated) may place one or more loads (e.g., food and/or liquids) into the defrosting cavity 110, and optionally may provide inputs via the control panel 120 that specify characteristics of the load(s). For example, the specified characteristics may include an approximate weight of the load. In addition, the specified load characteristics may indicate the material(s) from which the load is formed (e.g., meat, bread, liquid). In alternate embodiments, the load characteristics may be obtained in some other way, such as by scanning a barcode on the load packaging or receiving a radio frequency identification (RFID) signal from an RFID tag on or embedded within the load. Either way, as will be described in more detail later, information regarding such load characteristics enables the system controller (e.g., system controller 312, 912,
To begin the defrosting operation, the user may provide an input via the control panel 120. In response, the system controller causes the RF signal source(s) (e.g., RF signal source 320, 920,
During the defrosting operation, the impedance of the load (and thus the total input impedance of the cavity 110 plus load) changes as the thermal energy of the load increases. The impedance changes alter the absorption of RF energy into the load, and thus alter the magnitude of reflected power. According to an embodiment, power detection circuitry (e.g., power detection circuitry 330, 930,
The defrosting system 100 of
Similar to the defrosting system 100, each of defrosting systems 210, 220 includes a defrosting cavity, a control panel 214, 224, one or more RF signal sources (e.g., RF signal source 320, 920,
In addition, according to an embodiment, each of the defrosting systems 210, 220 may have sufficient thermal communication with the freezer or refrigerator compartment 212, 222, respectively, in which the system 210, 220 is disposed. In such an embodiment, after completion of a defrosting operation, the load may be maintained at a safe temperature (i.e., a temperature at which food spoilage is retarded) until the load is removed from the system 210, 220. More specifically, upon completion of a defrosting operation by the freezer-based defrosting system 210, the cavity within which the defrosted load is contained may thermally communicate with the freezer compartment 212, and if the load is not promptly removed from the cavity, the load may re-freeze. Similarly, upon completion of a defrosting operation by the refrigerator-based defrosting system 220, the cavity within which the defrosted load is contained may thermally communicate with the refrigerator compartment 222, and if the load is not promptly removed from the cavity, the load may be maintained in a defrosted state at the temperature within the refrigerator compartment 222.
Those of skill in the art would understand, based on the description herein, that embodiments of defrosting systems may be incorporated into systems or appliances having other configurations, as well. Accordingly, the above-described implementations of defrosting systems in a stand-alone appliance, a microwave oven appliance, a freezer, and a refrigerator are not meant to limit use of the embodiments only to those types of systems.
Although defrosting systems 100, 200 are shown with their components in particular relative orientations with respect to one another, it should be understood that the various components may be oriented differently, as well. In addition, the physical configurations of the various components may be different. For example, control panels 120, 214, 224 may have more, fewer, or different user interface elements, and/or the user interface elements may be differently arranged. In addition, although a substantially cubic defrosting cavity 110 is illustrated in
User interface 380 may correspond to a control panel (e.g., control panel 120, 214, 224,
Some embodiments of defrosting system 300 may include temperature sensor(s), IR sensor(s), and/or weight sensor(s) 390. The temperature sensor(s) and/or IR sensor(s) may be positioned in locations that enable the temperature of the load 364 to be sensed during the defrosting operation. When provided to the system controller 312, the temperature information enables the system controller 312 to alter the power of the RF signal supplied by the RF signal source 320 (e.g., by controlling the bias and/or supply voltages provided by the power supply and bias circuitry 326), to adjust the state of the variable impedance matching network 370, and/or to determine when the defrosting operation should be terminated. The weight sensor(s) are positioned under the load 364, and are configured to provide an estimate of the weight of the load 364 to the system controller 312. The system controller 312 may use this information, for example, to determine a desired power level for the RF signal supplied by the RF signal source 320, to determine an initial setting for the variable impedance matching network 370, and/or to determine an approximate duration for the defrosting operation.
The RF subsystem 310 includes a system controller 312, an RF signal source 320, first impedance matching circuit 334 (herein “first matching circuit”), power supply and bias circuitry 326, and power detection circuitry 330, in an embodiment. System controller 312 may include one or more general purpose or special purpose processors (e.g., a microprocessor, microcontroller, Application Specific Integrated Circuit (ASIC), and so on), volatile and/or non-volatile memory (e.g., Random Access Memory (RAM), Read Only Memory (ROM), flash, various registers, and so on), one or more communication busses, and other components. According to an embodiment, system controller 312 is coupled to user interface 380, RF signal source 320, variable impedance matching network 370, power detection circuitry 330, and sensors 390 (if included). System controller 312 is configured to receive signals indicating user inputs received via user interface 380, and to receive signals indicating RF signal reflected power (and possibly RF signal forward power) from power detection circuitry 330. Responsive to the received signals and measurements, and as will be described in more detail later, system controller 312 provides control signals to the power supply and bias circuitry 326 and to the RF signal generator 322 of the RF signal source 320. In addition, system controller 312 provides control signals to the variable impedance matching network 370, which cause the network 370 to change its state or configuration.
Defrosting cavity 360 includes a capacitive defrosting arrangement with first and second parallel plate electrodes that are separated by an air cavity within which a load 364 to be defrosted may be placed. For example, a first electrode 340 may be positioned above the air cavity, and a second electrode may be provided by a portion of a containment structure 366. More specifically, the containment structure 366 may include bottom, top, and side walls, the interior surfaces of which define the cavity 360 (e.g., cavity 110,
Essentially, defrosting cavity 360 includes a capacitive defrosting arrangement with first and second parallel plate electrodes 340, 366 that are separated by an air cavity within which a load 364 to be defrosted may be placed. The first electrode 340 is positioned within containment structure 366 to define a distance 352 between the electrode 340 and an opposed surface of the containment structure 366 (e.g., the bottom surface, which functions as a second electrode), where the distance 352 renders the cavity 360 a sub-resonant cavity, in an embodiment.
In various embodiments, the distance 352 is in a range of about 0.10 meters to about 1.0 meter, although the distance may be smaller or larger, as well. According to an embodiment, distance 352 is less than one wavelength of the RF signal produced by the RF subsystem 310. In other words, as mentioned above, the cavity 360 is a sub-resonant cavity. In some embodiments, the distance 352 is less than about half of one wavelength of the RF signal. In other embodiments, the distance 352 is less than about one quarter of one wavelength of the RF signal. In still other embodiments, the distance 352 is less than about one eighth of one wavelength of the RF signal. In still other embodiments, the distance 352 is less than about one 50th of one wavelength of the RF signal. In still other embodiments, the distance 352 is less than about one 100th of one wavelength of the RF signal.
In general, a system 300 designed for lower operational frequencies (e.g., frequencies between 10 MHz and 100 MHz) may be designed to have a distance 352 that is a smaller fraction of one wavelength. For example, when system 300 is designed to produce an RF signal with an operational frequency of about 10 MHz (corresponding to a wavelength of about 30 meters), and distance 352 is selected to be about 0.5 meters, the distance 352 is about one 60th of one wavelength of the RF signal. Conversely, when system 300 is designed for an operational frequency of about 300 MHz (corresponding to a wavelength of about 1 meter), and distance 352 is selected to be about 0.5 meters, the distance 352 is about one half of one wavelength of the RF signal.
With the operational frequency and the distance 352 between electrode 340 and containment structure 366 being selected to define a sub-resonant interior cavity 360, the first electrode 340 and the containment structure 366 are capacitively coupled. More specifically, the first electrode 340 may be analogized to a first plate of a capacitor, the containment structure 366 may be analogized to a second plate of a capacitor, and the load 364, barrier 362, and air within the cavity 360 may be analogized to a capacitor dielectric. Accordingly, the first electrode 340 alternatively may be referred to herein as an “anode,” and the containment structure 366 may alternatively be referred to herein as a “cathode.”
Essentially, the voltage across the first electrode 340 and the containment structure 366 heats the load 364 within the cavity 360. According to various embodiments, the RF subsystem 310 is configured to generate the RF signal to produce voltages between the electrode 340 and the containment structure 366 in a range of about 90 volts to about 3,000 volts, in one embodiment, or in a range of about 3000 volts to about 10,000 volts, in another embodiment, although the system may be configured to produce lower or higher voltages between the electrode 340 and the containment structure 366, as well.
The first electrode 340 is electrically coupled to the RF signal source 320 through a first matching circuit 334, a variable impedance matching network 370, and a conductive transmission path, in an embodiment. The first matching circuit 334 is configured to perform an impedance transformation from an impedance of the RF signal source 320 (e.g., less than about 10 ohms) to an intermediate impedance (e.g., 50 ohms, 75 ohms, or some other value). According to an embodiment, the conductive transmission path includes a plurality of conductors 328-1, 328-2, and 328-3 connected in series, and referred to collectively as transmission path 328. According to an embodiment, the conductive transmission path 328 is an “unbalanced” path, which is configured to carry an unbalanced RF signal (i.e., a single RF signal referenced against ground). In some embodiments, one or more connectors (not shown, but each having male and female connector portions) may be electrically coupled along the transmission path 328, and the portion of the transmission path 328 between the connectors may comprise a coaxial cable or other suitable connector. Such a connection is shown in
As will be described in more detail later, the variable impedance matching circuit 370 is configured to perform an impedance transformation from the above-mentioned intermediate impedance to an input impedance of defrosting cavity 320 as modified by the load 364 (e.g., on the order of hundreds or thousands of ohms, such as about 1000 ohms to about 4000 ohms or more). In an embodiment, the variable impedance matching network 370 includes a network of passive components (e.g., inductors, capacitors, resistors). According to a more specific embodiment, the variable impedance matching network 370 includes a plurality of fixed-value lumped inductors (e.g., inductors 412-414, 712-714, 812-814,
According to an embodiment, RF signal source 326 includes an RF signal generator 322 and a power amplifier (e.g., including one or more power amplifier stages 324, 325). In response to control signals provided by system controller 312 over connection 314, RF signal generator 322 is configured to produce an oscillating electrical signal having a frequency in the ISM (industrial, scientific, and medical) band, although the system could be modified to support operations in other frequency bands, as well. The RF signal generator 322 may be controlled to produce oscillating signals of different power levels and/or different frequencies, in various embodiments. For example, the RF signal generator 322 may produce a signal that oscillates in a range of about 10.0 megahertz (MHz) to about 100 MHz and/or from about 100 MHz to about 3.0 gigahertz (GHz). Some desirable frequencies may be, for example, 13.56 MHz (+/−5 percent), 27.125 MHz (+/−5 percent), 40.68 MHz (+/−5 percent), and 2.45 GHz (+/−5 percent). In one particular embodiment, for example, the RF signal generator 322 may produce a signal that oscillates in a range of about 40.66 MHz to about 40.70 MHz and at a power level in a range of about 10 decibels (dB) to about 15 dB. Alternatively, the frequency of oscillation and/or the power level may be lower or higher.
In the embodiment of
In an embodiment, each amplifier stage 324, 325 is implemented as a power transistor, such as a field effect transistor (FET), having an input terminal (e.g., a gate or control terminal) and two current carrying terminals (e.g., source and drain terminals). Impedance matching circuits (not illustrated) may be coupled to the input (e.g., gate) of the driver amplifier stage 324, between the driver and final amplifier stages 325, and/or to the output (e.g., drain terminal) of the final amplifier stage 325, in various embodiments. In an embodiment, each transistor of the amplifier stages 324, 325 includes a laterally diffused metal oxide semiconductor FET (LDMOSFET) transistor. However, it should be noted that the transistors are not intended to be limited to any particular semiconductor technology, and in other embodiments, each transistor may be realized as a gallium nitride (GaN) transistor, another type of MOSFET transistor, a bipolar junction transistor (BJT), or a transistor utilizing another semiconductor technology.
In
Defrosting cavity 360 and any load 364 (e.g., food, liquids, and so on) positioned in the defrosting cavity 360 present a cumulative load for the electromagnetic energy (or RF power) that is radiated into the cavity 360 by the first electrode 340. More specifically, the cavity 360 and the load 364 present an impedance to the system, referred to herein as a “cavity input impedance.” The cavity input impedance changes during a defrosting operation as the temperature of the load 364 increases. The cavity input impedance has a direct effect on the magnitude of reflected signal power along the conductive transmission path 328 between the RF signal source 320 and electrodes 340. In most cases, it is desirable to maximize the magnitude of transferred signal power into the cavity 360, and/or to minimize the reflected-to-forward signal power ratio along the conductive transmission path 328.
In order to at least partially match the output impedance of the RF signal generator 320 to the chamber input impedance, a first matching circuit 334 is electrically coupled along the transmission path 328, in an embodiment. The first matching circuit 334 may have any of a variety of configurations. According to an embodiment, the first matching circuit 334 includes fixed components (i.e., components with non-variable component values), although the first matching circuit 334 may include one or more variable components, in other embodiments. For example, the first matching circuit 334 may include any one or more circuits selected from an inductance/capacitance (LC) network, a series inductance network, a shunt inductance network, or a combination of bandpass, high-pass and low-pass circuits, in various embodiments. Essentially, the fixed matching circuit 334 is configured to raise the impedance to an intermediate level between the output impedance of the RF signal generator 320 and the chamber input impedance.
As will be described in conjunction with
According to an embodiment, power detection circuitry 330 is coupled along the transmission path 328 between the output of the RF signal source 320 and the electrode 340. In a specific embodiment, the power detection circuitry 330 forms a portion of the RF subsystem 310, and is coupled to the conductor 328-2 between the output of the first matching circuit 334 and the input to the variable impedance matching network 370, in an embodiment. In alternate embodiments, the power detection circuitry 330 may be coupled to the portion 328-1 of the transmission path 328 between the output of the RF signal source 320 and the input to the first matching circuit 334, or to the portion 328-3 of the transmission path 328 between the output of the variable impedance matching network 370 and the first electrode 340.
Wherever it is coupled, power detection circuitry 330 is configured to monitor, measure, or otherwise detect the power of the reflected signals traveling along the transmission path 328 between the RF signal source 320 and electrode 340 (i.e., reflected RF signals traveling in a direction from electrode 340 toward RF signal source 320). In some embodiments, power detection circuitry 330 also is configured to detect the power of the forward signals traveling along the transmission path 328 between the RF signal source 320 and the electrode 340 (i.e., forward RF signals traveling in a direction from RF signal source 320 toward electrode 340). Over connection 332, power detection circuitry 330 supplies signals to system controller 312 conveying the magnitudes of the reflected signal power (and the forward signal power, in some embodiments) to system controller 312. In embodiments in which both the forward and reflected signal power magnitudes are conveyed, system controller 312 may calculate a reflected-to-forward signal power ratio, or the S11 parameter. As will be described in more detail below, when the reflected signal power magnitude exceeds a reflected signal power threshold, or when the reflected-to-forward signal power ratio exceeds an S11 parameter threshold, this indicates that the system 300 is not adequately matched to the cavity input impedance, and that energy absorption by the load 364 within the cavity 360 may be sub-optimal. In such a situation, system controller 312 orchestrates a process of altering the state of the variable matching network 370 to drive the reflected signal power or the S11 parameter toward or below a desired level (e.g., below the reflected signal power threshold and/or the reflected-to-forward signal power ratio threshold), thus re-establishing an acceptable match and facilitating more optimal energy absorption by the load 364.
More specifically, the system controller 312 may provide control signals over control path 316 to the variable matching circuit 970, which cause the variable matching circuit 370 to vary inductive, capacitive, and/or resistive values of one or more components within the circuit, thus adjusting the impedance transformation provided by the circuit 370. Adjustment of the configuration of the variable matching circuit 370 desirably decreases the magnitude of reflected signal power, which corresponds to decreasing the magnitude of the S11 parameter and increasing the power absorbed by the load 364.
As discussed above, the variable impedance matching network 370 is used to match the input impedance of the defrosting cavity 360 plus load 364 to maximize, to the extent possible, the RF power transfer into the load 364. The initial impedance of the defrosting cavity 360 and the load 364 may not be known with accuracy at the beginning of a defrosting operation. Further, the impedance of the load 364 changes during a defrosting operation as the load 364 warms up. According to an embodiment, the system controller 312 may provide control signals to the variable impedance matching network 370, which cause modifications to the state of the variable impedance matching network 370. This enables the system controller 312 to establish an initial state of the variable impedance matching network 370 at the beginning of the defrosting operation that has a relatively low reflected to forward power ratio, and thus a relatively high absorption of the RF power by the load 364. In addition, this enables the system controller 312 to modify the state of the variable impedance matching network 370 so that an adequate match may be maintained throughout the defrosting operation, despite changes in the impedance of the load 364.
The variable matching network 370 may have any of a variety of configurations. For example, the network 370 may include any one or more circuits selected from an inductance/capacitance (LC) network, an inductance-only network, a capacitance-only network, or a combination of bandpass, high-pass and low-pass circuits, in various embodiments. In an embodiment, the variable matching network 370 includes a single-ended network (e.g., network 600,
The variable matching network 370 may have any of a wide variety of circuit configurations, and non-limiting examples of such configurations are shown in
Variable impedance matching network 400 includes an input node 402, an output node 404, first and second variable inductance networks 410, 411, and a plurality of fixed-value inductors 412-415, according to an embodiment. When incorporated into a defrosting system (e.g., system 300,
Between the input and output nodes 402, 404, the variable impedance matching network 400 includes first and second, series coupled lumped inductors 412, 414, in an embodiment. The first and second lumped inductors 412, 414 are relatively large in both size and inductance value, in an embodiment, as they may be designed for relatively low frequency (e.g., about 4.66 MHz to about 4.68 MHz) and high power (e.g., about 50 watts (W) to about 500 W) operation. For example, inductors 412, 414 may have values in a range of about 200 nanohenries (nH) to about 600 nH, although their values may be lower and/or higher, in other embodiments.
The first variable inductance network 410 is a first shunt inductive network that is coupled between the input node 402 and a ground reference terminal (e.g., the grounded containment structure 366,
In contrast, the “cavity matching portion” of the variable impedance matching network 400 is provided by a second shunt inductive network 416 that is coupled between a node 422 between the first and second lumped inductors 412, 414 and the ground reference terminal. According to an embodiment, the second shunt inductive network 416 includes a third lumped inductor 413 and a second variable inductance network 411 coupled in series, with an intermediate node 422 between the third lumped inductor 413 and the second variable inductance network 411. Because the state of the second variable inductance network 411 may be changed to provide multiple inductance values, the second shunt inductive network 416 is configurable to optimally match the impedance of the cavity plus load (e.g., cavity 360 plus load 364,
Finally, the variable impedance matching network 400 includes a fourth lumped inductor 415 coupled between the output node 404 and the ground reference terminal. For example, inductor 415 may have a value in a range of about 400 nH to about 800 nH, although its value may be lower and/or higher, in other embodiments.
As will be described in more detail in conjunction with
According to an embodiment, the variable impedance matching network 400 embodiment of
For each parallel inductor/switch combination, substantially all current flows through the inductor when its corresponding switch is in an open or non-conductive state, and substantially all current flows through the switch when the switch is in a closed or conductive state. For example, when all switches 511-514 are open, as illustrated in
Starting from the maximum inductance state in which all switches 511-514 are open, the system controller may provide control signals 521-524 that result in the closure of any combination of switches 511-514 in order to reduce the inductance of the network 500 by bypassing corresponding combinations of inductors 501-504. In one embodiment, each inductor 501-504 has substantially the same inductance value, referred to herein as a normalized value of I. For example, each inductor 501-504 may have a value in a range of about 10 nH to about 200 nH, or some other value. In such an embodiment, the maximum inductance value for the network 500 (i.e., when all switches 511-514 are in an open state) would be about N×I, plus any trace inductance that may be present in the network 500 when it is in the maximum inductance state. When any n switches are in a closed state, the inductance value for the network 500 would be about (N−n)×I (plus trace inductance). In such an embodiment, the state of the network 500 may be configured to have any of N+1 values of inductance.
In an alternate embodiment, the inductors 501-504 may have different values from each other. For example, moving from the input node 530 toward the output node 532, the first inductor 501 may have a normalized inductance value of I, and each subsequent inductor 502-504 in the series may have a larger or smaller inductance value. For example, each subsequent inductor 502-504 may have an inductance value that is a multiple (e.g., about twice) the inductance value of the nearest downstream inductor 501-503, although the difference may not necessarily be an integer multiple. In such an embodiment, the state of the network 500 may be configured to have any of 2N values of inductance. For example, when N=4 and each inductor 501-504 has a different value, the network 500 may be configured to have any of 16 values of inductance. For example, but not by way of limitation, assuming that inductor 501 has a value of I, inductor 502 has a value of 2×I, inductor 503 has a value of 4×I, and inductor 504 has a value of 8×I, Table 1, below indicates the total inductance value for all 16 possible states of the network 500 (not accounting for trace inductances):
Referring again to
Although the above example embodiment specifies that the number of switched inductances in the network 500 equals four, and that each inductor 501-504 has a value that is some multiple of a value of I, alternate embodiments of variable inductance networks may have more or fewer than four inductors, different relative values for the inductors, a different number of possible network states, and/or a different configuration of inductors (e.g., differently connected sets of parallel and/or series coupled inductors). Either way, by providing a variable inductance network in an impedance matching network of a defrosting system, the system may be better able to match the ever-changing cavity input impedance that is present during a defrosting operation.
In Smith chart 600, point 601 corresponds to the point at which the load (e.g., the cavity 360 plus load 364,
It should be noted that the combination of impedance transformations provided by embodiments of the variable impedance matching network keep the impedance at any point within or very close to the lower right quadrant of the Smith chart 600. As this quadrant of the Smith chart 600 is characterized by relatively high impedances and relatively low currents, the impedance transformation is achieved without exposing components of the circuit to relatively high and potentially damaging currents. Accordingly, an alternate definition of an “inductor-only” matching network, as used herein, may be a matching network that enables impedance matching of a capacitive load using solely or primarily inductive components, where the impedance matching network performs the transformation substantially within the lower right quadrant of the Smith chart.
As discussed previously, the impedance of the load changes during the defrosting operation. Accordingly, point 601 correspondingly moves during the defrosting operation. Movement of load point 601 is compensated for, according to the previously-described embodiments, by varying the impedance of the first and second shunt inductances 410, 411 so that the final match provided by the variable impedance matching network still may arrive at or near the optimal matching point 606. Although a specific variable impedance matching network has been illustrated and described herein, those of skill in the art would understand, based on the description herein, that differently-configured variable impedance matching networks may achieve the same or similar results to those conveyed by Smith chart 600. For example, alternative embodiments of a variable impedance matching network may have more or fewer shunt and/or series inductances, and or different ones of the inductances may be configured as variable inductance networks (e.g., including one or more of the series inductances). Accordingly, although a particular variable inductance matching network has been illustrated and described herein, the inventive subject matter is not limited to the illustrated and described embodiment.
A particular physical configuration of a defrosting system will now be described in conjunction with
The defrosting system 700 is contained within a containment structure 750, in an embodiment. According to an embodiment, the containment structure 750 may define three interior areas: the defrosting cavity 774, a fixed inductor area 776, and a circuit housing area 778. The containment structure 750 includes bottom, top, and side walls. Portions of the interior surfaces of some of the walls of the containment structure 750 may define the defrosting cavity 774. The defrosting cavity 774 includes a capacitive defrosting arrangement with first and second parallel plate electrodes 770, 772 that are separated by an air cavity within which a load 764 to be defrosted may be placed. For example, the first electrode 770 may be positioned above the air cavity, and a second electrode 772 may be provided by a conductive portion of the containment structure 750 (e.g., a portion of the bottom wall of the containment structure 750). Alternatively, the second electrode 772 may be formed from a conductive plate that is distinct from the containment structure 750. According to an embodiment, non-electrically conductive support structure(s) 754 may be employed to suspend the first electrode 770 above the air cavity, to electrically isolate the first electrode 770 from the containment structure 750, and to hold the first electrode 770 in a fixed physical orientation with respect to the air cavity.
According to an embodiment, the containment structure 750 is at least partially formed from conductive material, and the conductive portion(s) of the containment structure may be grounded to provide a ground reference for various electrical components of the system. Alternatively, at least the portion of the containment structure 750 that corresponds to the second electrode 772 may be formed from conductive material and grounded. To avoid direct contact between the load 764 and the second electrode 772, a non-conductive barrier 756 may be positioned over the second electrode 772.
When included in the system 700, the weight sensor(s) 790 are positioned under the load 764. The weight sensor(s) 790 are configured to provide an estimate of the weight of the load 764 to the system controller 730. The temperature sensor(s) and/or IR sensor(s) 792 may be positioned in locations that enable the temperature of the load 764 to be sensed both before, during, and after a defrosting operation. According to an embodiment, the temperature sensor(s) and/or IR sensor(s) 792 are configured to provide load temperature estimates to the system controller 730.
Some or all of the various components of the system controller 730, the RF signal source 720, the power supply and bias circuitry (not shown), the power detection circuitry 780, and portions 710, 711 of the variable impedance matching network 760, may be coupled to a common substrate 752 within the circuit housing area 778 of the containment structure 750, in an embodiment. For example, some of all of the above-listed components may be included in an RF module (e.g., RF module 1300,
The first electrode 770 is electrically coupled to the RF signal source 720 through a variable impedance matching network 760 and a transmission path 748, in an embodiment. As discussed previously, the variable impedance matching network 760 includes variable inductance networks 710, 711 (e.g., networks 410, 411,
For enhanced understanding of the system 700, the nodes and components of the variable impedance matching network 760 depicted in
Between the input and output nodes 702, 704 (e.g., input and output nodes 402, 404,
In an embodiment, the first lumped inductor 712 has a first terminal that is electrically coupled to the input node 702 (and thus to the output of RF signal source 720), and a second terminal that is electrically coupled to a first intermediate node 721 (e.g., node 421,
The first variable inductance network 710 (e.g., network 410,
The description associated with
For example,
User interface 980 may correspond to a control panel (e.g., control panel 120, 214, 224,
The RF subsystem 910 includes a system controller 912, an RF signal source 920, a first impedance matching circuit 934 (herein “first matching circuit”), power supply and bias circuitry 926, and power detection circuitry 930, in an embodiment. System controller 912 may include one or more general purpose or special purpose processors (e.g., a microprocessor, microcontroller, ASIC, and so on), volatile and/or non-volatile memory (e.g., RAM, ROM, flash, various registers, and so on), one or more communication busses, and other components. According to an embodiment, system controller 912 is operatively and communicatively coupled to user interface 980, RF signal source 920, power supply and bias circuitry 926, power detection circuitry 930 (or 930′ or 930″), variable matching subsystem 970, sensor(s) 990 (if included), and pump 992 (if included). System controller 912 is configured to receive signals indicating user inputs received via user interface 980, to receive signals indicating RF signal reflected power (and possibly RF signal forward power) from power detection circuitry 930 (or 930′ or 930″), and to receive sensor signals from sensor(s) 990. Responsive to the received signals and measurements, and as will be described in more detail later, system controller 912 provides control signals to the power supply and bias circuitry 926 and/or to the RF signal generator 922 of the RF signal source 920. In addition, system controller 912 provides control signals to the variable matching subsystem 970 (over path 916), which cause the subsystem 970 to change the state or configuration of a variable impedance matching circuit 972 of the subsystem 970 (herein “variable matching circuit”).
Defrosting cavity 960 includes a capacitive defrosting arrangement with first and second parallel plate electrodes 940, 950 that are separated by an air cavity within which a load 964 to be defrosted may be placed. Within a containment structure 966, first and second electrodes 940, 950 (e.g., electrodes 140, 150,
The first and second electrodes 940, 950 are separated across the cavity 960 by a distance 952. In various embodiments, the distance 952 is in a range of about 0.10 meters to about 1.0 meter, although the distance may be smaller or larger, as well. According to an embodiment, distance 952 is less than one wavelength of the RF signal produced by the RF subsystem 910. In other words, as mentioned above, the cavity 960 is a sub-resonant cavity. In some embodiments, the distance 952 is less than about half of one wavelength of the RF signal. In other embodiments, the distance 952 is less than about one quarter of one wavelength of the RF signal. In still other embodiments, the distance 952 is less than about one eighth of one wavelength of the RF signal. In still other embodiments, the distance 952 is less than about one 50th of one wavelength of the RF signal. In still other embodiments, the distance 952 is less than about one 100th of one wavelength of the RF signal.
In general, a system 900 designed for lower operational frequencies (e.g., frequencies between 10 MHz and 100 MHz) may be designed to have a distance 952 that is a smaller fraction of one wavelength. For example, when system 900 is designed to produce an RF signal with an operational frequency of about 10 MHz (corresponding to a wavelength of about 30 meters), and distance 952 is selected to be about 0.5 meters, the distance 952 is about one 60th of one wavelength of the RF signal. Conversely, when system 900 is designed for an operational frequency of about 300 MHz (corresponding to a wavelength of about 1 meter), and distance 952 is selected to be about 0.5 meters, the distance 952 is about one half of one wavelength of the RF signal.
With the operational frequency and the distance 952 between electrodes 940, 950 being selected to define a sub-resonant interior cavity 960, the first and second electrodes 940, 950 are capacitively coupled. More specifically, the first electrode 940 may be analogized to a first plate of a capacitor, the second electrode 950 may be analogized to a second plate of a capacitor, and the load 964, barrier 962, and air within the cavity 960 may be analogized to a capacitor dielectric. Accordingly, the first electrode 940 alternatively may be referred to herein as an “anode,” and the second electrode 950 may alternatively be referred to herein as a “cathode.”
Essentially, the voltage across the first and second electrodes 940, 950 heats the load 964 within the cavity 960. According to various embodiments, the RF subsystem 910 is configured to generate the RF signal to produce voltages across the electrodes 940, 950 in a range of about 90 volts to about 3000 volts, in one embodiment, or in a range of about 3000 volts to about 10,000 volts, in another embodiment, although the system may be configured to produce lower or higher voltages across electrodes 940, 950, as well.
An output of the RF subsystem 910, and more particularly an output of RF signal source 920, is electrically coupled to the variable matching subsystem 970 through a conductive transmission path, which includes a plurality of conductors 928-1, 928-2, 928-3, 928-4, and 928-5 connected in series, and referred to collectively as transmission path 928. According to an embodiment, the conductive transmission path 928 includes an “unbalanced” portion and a “balanced” portion, where the “unbalanced” portion is configured to carry an unbalanced RF signal (i.e., a single RF signal referenced against ground), and the “balanced” portion is configured to carry a balanced RF signal (i.e., two signals referenced against each other). The “unbalanced” portion of the transmission path 928 may include unbalanced first and second conductors 928-1, 928-2 within the RF subsystem 910, one or more connectors 936, 938 (each having male and female connector portions), and an unbalanced third conductor 928-3 electrically coupled between the connectors 936, 938. According to an embodiment, the third conductor 928-3 comprises a coaxial cable, although the electrical length may be shorter or longer, as well. In an alternate embodiment, the variable matching subsystem 970 may be housed with the RF subsystem 910, and in such an embodiment, the conductive transmission path 928 may exclude the connectors 936, 938 and the third conductor 928-3. Either way, the “balanced” portion of the conductive transmission path 928 includes a balanced fourth conductor 928-4 within the variable matching subsystem 970, and a balanced fifth conductor 928-5 electrically coupled between the variable matching subsystem 970 and electrodes 940, 950, in an embodiment.
As indicated in
In an alternate embodiment, as indicated in a dashed box in the center of
According to an embodiment, RF signal source 920 includes an RF signal generator 922 and a power amplifier 924 (e.g., including one or more power amplifier stages). In response to control signals provided by system controller 912 over connection 914, RF signal generator 922 is configured to produce an oscillating electrical signal having a frequency in an ISM (industrial, scientific, and medical) band, although the system could be modified to support operations in other frequency bands, as well. The RF signal generator 922 may be controlled to produce oscillating signals of different power levels and/or different frequencies, in various embodiments. For example, the RF signal generator 922 may produce a signal that oscillates in a range of about 10.0 MHz to about 100 MHz and/or from about 100 MHz to about 3.0 GHz. Some desirable frequencies may be, for example, 13.56 MHz (+/−5 percent), 27.125 MHz (+/−5 percent), 40.68 MHz (+/−5 percent), and 2.45 GHz (+/−5 percent). Alternatively, the frequency of oscillation may be lower or higher than the above-given ranges or values.
The power amplifier 924 is configured to receive the oscillating signal from the RF signal generator 922, and to amplify the signal to produce a significantly higher-power signal at an output of the power amplifier 924. For example, the output signal may have a power level in a range of about 100 watts to about 400 watts or more, although the power level may be lower or higher, as well. The gain applied by the power amplifier 924 may be controlled using gate bias voltages and/or drain bias voltages provided by the power supply and bias circuitry 926 to one or more stages of amplifier 924. More specifically, power supply and bias circuitry 926 provides bias and supply voltages to the inputs and/or outputs (e.g., gates and/or drains) of each RF amplifier stage in accordance with control signals received from system controller 912.
The power amplifier may include one or more amplification stages. In an embodiment, each stage of amplifier 924 is implemented as a power transistor, such as a FET, having an input terminal (e.g., a gate or control terminal) and two current carrying terminals (e.g., source and drain terminals). Impedance matching circuits (not illustrated) may be coupled to the input (e.g., gate) and/or output (e.g., drain terminal) of some or all of the amplifier stages, in various embodiments. In an embodiment, each transistor of the amplifier stages includes an LDMOS FET. However, it should be noted that the transistors are not intended to be limited to any particular semiconductor technology, and in other embodiments, each transistor may be realized as a GaN transistor, another type of MOS FET transistor, a BJT, or a transistor utilizing another semiconductor technology.
In
For example, as indicated in the dashed box in the center of
Defrosting cavity 960 and any load 964 (e.g., food, liquids, and so on) positioned in the defrosting cavity 960 present a cumulative load for the electromagnetic energy (or RF power) that is radiated into the interior chamber 962 by the electrodes 940, 950. More specifically, and as described previously, the defrosting cavity 960 and the load 964 present an impedance to the system, referred to herein as a “cavity input impedance.” The cavity input impedance changes during a defrosting operation as the temperature of the load 964 increases. The cavity input impedance has a direct effect on the magnitude of reflected signal power along the conductive transmission path 928 between the RF signal source 920 and the electrodes 940, 950. In most cases, it is desirable to maximize the magnitude of transferred signal power into the cavity 960, and/or to minimize the reflected-to-forward signal power ratio along the conductive transmission path 928.
In order to at least partially match the output impedance of the RF signal generator 920 to the chamber input impedance, a first matching circuit 934 is electrically coupled along the transmission path 928, in an embodiment. The first matching circuit 934 is configured to perform an impedance transformation from an impedance of the RF signal source 920 (e.g., less than about 10 ohms) to an intermediate impedance (e.g., 50 ohms, 75 ohms, or some other value). The first matching circuit 934 may have any of a variety of configurations. According to an embodiment, the first matching circuit 934 includes fixed components (i.e., components with non-variable component values), although the first matching circuit 934 may include one or more variable components, in other embodiments. For example, the first matching circuit 934 may include any one or more circuits selected from an inductance/capacitance (LC) network, a series inductance network, a shunt inductance network, or a combination of bandpass, high-pass and low-pass circuits, in various embodiments. Essentially, the first matching circuit 934 is configured to raise the impedance to an intermediate level between the output impedance of the RF signal generator 920 and the cavity input impedance.
According to an embodiment, and as mentioned above, power detection circuitry 930 is coupled along the transmission path 928 between the output of the RF signal source 920 and the electrodes 940, 950. In a specific embodiment, the power detection circuitry 930 forms a portion of the RF subsystem 910, and is coupled to the conductor 928-2 between the RF signal source 920 and connector 936. In alternate embodiments, the power detection circuitry 930 may be coupled to any other portion of the transmission path 928, such as to conductor 928-1, to conductor 928-3, to conductor 928-4 between the RF signal source 920 (or balun 974) and the variable matching circuit 972 (i.e., as indicated with power detection circuitry 930′), or to conductor 928-5 between the variable matching circuit 972 and the electrode(s) 940, 950 (i.e., as indicated with power detection circuitry 930″). For purposes of brevity, the power detection circuitry is referred to herein with reference number 930, although the circuitry may be positioned in other locations, as indicated by reference numbers 930′ and 930″.
Wherever it is coupled, power detection circuitry 930 is configured to monitor, measure, or otherwise detect the power of the reflected signals traveling along the transmission path 928 between the RF signal source 920 and one or both of the electrode(s) 940, 950 (i.e., reflected RF signals traveling in a direction from electrode(s) 940, 950 toward RF signal source 920). In some embodiments, power detection circuitry 930 also is configured to detect the power of the forward signals traveling along the transmission path 928 between the RF signal source 920 and the electrode(s) 940, 950 (i.e., forward RF signals traveling in a direction from RF signal source 920 toward electrode(s) 940, 950).
Over connection 932, power detection circuitry 930 supplies signals to system controller 912 conveying the measured magnitudes of the reflected signal power, and in some embodiments, also the measured magnitude of the forward signal power. In embodiments in which both the forward and reflected signal power magnitudes are conveyed, system controller 912 may calculate a reflected-to-forward signal power ratio, or the S11 parameter. As will be described in more detail below, when the reflected signal power magnitude exceeds a reflected signal power threshold, or when the reflected-to-forward signal power ratio exceeds an S11 parameter threshold, this indicates that the system 900 is not adequately matched to the cavity input impedance, and that energy absorption by the load 964 within the cavity 960 may be sub-optimal. In such a situation, system controller 912 orchestrates a process of altering the state of the variable matching circuit 972 to drive the reflected signal power or the S11 parameter toward or below a desired level (e.g., below the reflected signal power threshold and/or the reflected-to-forward signal power ratio threshold), thus re-establishing an acceptable match and facilitating more optimal energy absorption by the load 964.
More specifically, the system controller 912 may provide control signals over control path 916 to the variable matching circuit 972, which cause the variable matching circuit 972 to vary inductive, capacitive, and/or resistive values of one or more components within the circuit, thus adjusting the impedance transformation provided by the circuit 972. Adjustment of the configuration of the variable matching circuit 972 desirably decreases the magnitude of reflected signal power, which corresponds to decreasing the magnitude of the S11 parameter and increasing the power absorbed by the load 964.
As discussed above, the variable matching circuit 972 is used to match the input impedance of the defrosting cavity 960 plus load 964 to maximize, to the extent possible, the RF power transfer into the load 964. The initial impedance of the defrosting cavity 960 and the load 964 may not be known with accuracy at the beginning of a defrosting operation. Further, the impedance of the load 964 changes during a defrosting operation as the load 964 warms up. According to an embodiment, the system controller 912 may provide control signals to the variable matching circuit 972, which cause modifications to the state of the variable matching circuit 972. This enables the system controller 912 to establish an initial state of the variable matching circuit 972 at the beginning of the defrosting operation that has a relatively low reflected to forward power ratio, and thus a relatively high absorption of the RF power by the load 964. In addition, this enables the system controller 912 to modify the state of the variable matching circuit 972 so that an adequate match may be maintained throughout the defrosting operation, despite changes in the impedance of the load 964.
The variable matching circuit 972 may have any of a variety of configurations. For example, the circuit 972 may include any one or more circuits selected from an inductance/capacitance (LC) network, an inductance-only network, a capacitance-only network, or a combination of bandpass, high-pass and low-pass circuits, in various embodiments. In an embodiment in which the variable matching circuit 972 is implemented in a balanced portion of the transmission path 928, the variable matching circuit 972 is a double-ended circuit with two inputs and two outputs. In an alternate embodiment in which the variable matching circuit is implemented in an unbalanced portion of the transmission path 928, the variable matching circuit may be a single-ended circuit with a single input and a single output (e.g., similar to matching circuit 400,
The variable matching circuit 972 may have any of a wide variety of circuit configurations, and non-limiting examples of such configurations are shown in
Circuit 1000 includes a double-ended input 1001-1, 1001-2 (referred to as input 1001), a double-ended output 1002-1, 1002-2 (referred to as output 1002), and a network of passive components connected in a ladder arrangement between the input 1001 and output 1002. For example, when connected into system 900, the first input 1001-1 may be connected to a first conductor of balanced conductor 928-4, and the second input 1001-2 may be connected to a second conductor of balanced conductor 928-4. Similarly, the first output 1002-1 may be connected to a first conductor of balanced conductor 928-5, and the second output 1002-2 may be connected to a second conductor of balanced conductor 928-5.
In the specific embodiment illustrated in
According to an embodiment, the third variable inductor 1021 corresponds to an “RF signal source matching portion”, which is configurable to match the impedance of the RF signal source (e.g., RF signal source 920,
In contrast, the “cavity matching portion” of the variable impedance matching network 1000 is provided by the first and second variable inductors 1011, 1016, and fixed inductors 1015, 1020, and 1024. Because the states of the first and second variable inductors 1011, 1016 may be changed to provide multiple inductance values, the first and second variable inductors 1011, 1016 are configurable to optimally match the impedance of the cavity plus load (e.g., cavity 960 plus load 964,
The fixed inductors 1015, 1020, 1024 also may have inductance values in a range of about 50 nH to about 800 nH, although the inductance values may be lower or higher, as well. Inductors 1011, 1015, 1016, 1020, 1021, 1024 may include discrete inductors, distributed inductors (e.g., printed coils), wirebonds, transmission lines, and/or other inductive components, in various embodiments. In an embodiment, variable inductors 1011 and 1016 are operated in a paired manner, meaning that their inductance values during operation are controlled to be equal to each other, at any given time, in order to ensure that the RF signals conveyed to outputs 1002-1 and 1002-2 are balanced.
As discussed above, variable matching circuit 1000 is a double-ended circuit that is configured to be connected along a balanced portion of the transmission path 928 (e.g., between connectors 928-4 and 928-5), and other embodiments may include a single-ended (i.e., one input and one output) variable matching circuit that is configured to be connected along the unbalanced portion of the transmission path 928.
By varying the inductance values of inductors 1011, 1016, 1021 in circuit 1000, the system controller 912 may increase or decrease the impedance transformation provided by circuit 1000. Desirably, the inductance value changes improve the overall impedance match between the RF signal source 920 and the cavity input impedance, which should result in a reduction of the reflected signal power and/or the reflected-to-forward signal power ratio. In most cases, the system controller 912 may strive to configure the circuit 1000 in a state in which a maximum electromagnetic field intensity is achieved in the cavity 960, and/or a maximum quantity of power is absorbed by the load 964, and/or a minimum quantity of power is reflected by the load 964.
The series arrangement of inductors 1111-1114 may be considered a first variable inductor (e.g., inductor 1011,
In an embodiment, sets of corresponding inductors in the two paths between input 1101 and output 1102 have substantially equal values, and the conductive state of the switches for each set of corresponding inductors is operated in a paired manner, meaning that the switch states during operation are controlled to be the same as each other, at any given time, in order to ensure that the RF signals conveyed to outputs 1102-1 and 1102-2 are balanced. For example, inductors 1111 and 1116 may constitute a first “set of corresponding inductors” or “paired inductors” with substantially equal values, and during operation, the states of switches 1131 and 1136 are controlled to be the same (e.g., either both open or both closed), at any given time. Similarly, inductors 1112 and 1117 may constitute a second set of corresponding inductors with equal inductance values that are operated in a paired manner, inductors 1113 and 1118 may constitute a third set of corresponding inductors with equal inductance values that are operated in a paired manner, and inductors 1114 and 1119 may constitute a fourth set of corresponding inductors with equal inductance values that are operated in a paired manner.
For each parallel inductor/switch combination, substantially all current flows through the inductor when its corresponding switch is in an open or non-conductive state, and substantially all current flows through the switch when the switch is in a closed or conductive state. For example, when all switches 1131-1134, 1136-1139, 1141, and 1143 are open, as illustrated in
Starting from the maximum inductance state in which all switches 1131-1134, 1136-1139 are open, the system controller may provide control signals 1151-1154, 1156-1159 that result in the closure of any combination of switches 1131-1134, 1136-1139 in order to reduce the inductance of the network 1100 by bypassing corresponding combinations of inductors 1111-1114, 1116-1119.
Similar to the embodiment of
As also explained in conjunction with
Assuming that the trace inductance through series inductors 1111-1114 in the minimum inductance state is about 10 nH, and the range of inductance values achievable by the series inductors 1111-1114 is about 10 nH (trace inductance) to about 400 nH, the values of inductors 1111-1114 may be, for example, about 10 nH, about 20 nH, about 40 nH, about 80 nH, and about 160 nH, respectively. The combination of series inductors 1116-1119 may be similarly or identically configured. Of course, more or fewer than four inductors 1111-1114 or 1116-1119 may be included in either series combination between input and output nodes 1101-1/1102-1 or 1101-2/1102-2, and the inductors within each series combination may have different values from the example values given above.
Although the above example embodiment specifies that the number of switched inductances in each series combination between corresponding input and output nodes equals four, and that each inductor 1111-1114, 1116-1119 has a value that is some multiple of a value of I, alternate embodiments of variable series inductance networks may have more or fewer than four inductors, different relative values for the inductors, and/or a different configuration of inductors (e.g., differently connected sets of parallel and/or series coupled inductors). Either way, by providing a variable inductance network in an impedance matching network of a defrosting system, the system may be better able to match the ever-changing cavity input impedance that is present during a defrosting operation.
As with the embodiment of
It should be understood that the variable impedance matching circuits 1000, 1100 illustrated in
According to various embodiments, the circuitry associated with the single-ended or double-ended variable impedance matching networks discussed herein may be implemented in the form of one or more modules, where a “module” is defined herein as an assembly of electrical components coupled to a common substrate. For example,
According to an embodiment, the PCB 1204 houses an RF input connector 1238 (e.g., coupled to back side 1208 and thus not visible in the view of
In addition, the PCB 1204 houses circuitry associated with a double-ended variable impedance matching network (e.g., network 972, 1000, 1100,
A plurality of switches or relays (e.g., not visible in the view of
In various embodiments, the circuitry associated with the RF subsystem (e.g., RF subsystem 310, 910,
According to an embodiment, the PCB 1302 houses the circuitry associated with the RF subsystem (e.g., subsystem 310 or 910,
In the embodiment of
RF module 1300 also includes a plurality of connectors 1316, 1326, 1338, 1380, in an embodiment. For example, connector 1380 may be configured to connect with a host system that includes a user interface (e.g., user interface 380, 980,
Embodiments of an RF module (e.g., module 1300,
Now that embodiments of the electrical and physical aspects of defrosting systems have been described, various embodiments of methods for operating such defrosting systems will now be described in conjunction with
The method may begin, in block 1402, when the system controller (e.g., system controller 312, 912,
According to various embodiments, the system controller optionally may receive additional inputs indicating the load type (e.g., meats, liquids, or other materials), the initial load temperature, and/or the load weight. For example, information regarding the load type may be received from the user through interaction with the user interface (e.g., by the user selecting from a list of recognized load types). Alternatively, the system may be configured to scan a barcode visible on the exterior of the load, or to receive an electronic signal from an RFID device on or embedded within the load. Information regarding the initial load temperature may be received, for example, from one or more temperature sensors and/or IR sensors (e.g., sensors 390, 792, 990,
In block 1404, the system controller provides control signals to the variable matching network (e.g., network 370, 400, 972, 1000, 1100,
As also discussed previously, a first portion of the variable matching network may be configured to provide a match for the RF signal source (e.g., RF signal source 320, 920,
It has been observed that a best initial overall match for a frozen load (i.e., a match at which a maximum amount of RF power is absorbed by the load) typically has a relatively high inductance for the cavity matching portion of the matching network, and a relatively low inductance for the RF signal source matching portion of the matching network. For example,
According to an embodiment, to establish the initial configuration or state for the variable matching network in block 1404, the system controller sends control signals to the first and second variable inductance networks (e.g., networks 410, 411,
Assuming, however, that the system controller does have a priori information regarding the load characteristics, the system controller may attempt to establish an initial configuration near the optimal initial matching point. For example, and referring again to
Referring again to
In block 1414, power detection circuitry (e.g., power detection circuitry 330, 930, 930′, 930″,
In block 1416, the system controller may determine, based on the reflected power measurements, and/or the reflected-to-forward signal power ratio, and/or the S11 parameter, whether or not the match provided by the variable impedance matching network is acceptable (e.g., the reflected power is below a threshold, or the ratio is 10 percent or less, or the measurements or values compare favorably with some other criteria). Alternatively, the system controller may be configured to determine whether the match is the “best” match. A “best” match may be determined, for example, by iteratively measuring the reflected RF power (and in some embodiments the forward reflected RF power) for all possible impedance matching network configurations (or at least for a defined subset of impedance matching network configurations), and determining which configuration results in the lowest reflected RF power and/or the lowest reflected-to-forward power ratio.
When the system controller determines that the match is not acceptable or is not the best match, the system controller may adjust the match, in block 1418, by reconfiguring the variable impedance matching network. For example, this may be achieved by sending control signals to the variable impedance matching network, which cause the network to increase and/or decrease the variable inductances within the network (e.g., by causing the variable inductance networks 410, 411, 1011, 1016, 1021 to have different inductance states, or by switching inductors 501-504, 1111-1114, 1116-1119, 1121, 1123,
Once an acceptable or best match is determined, the defrosting operation may commence. Commencement of the defrosting operation includes increasing the power of the RF signal supplied by the RF signal source (e.g., RF signal source 320, 920,
In block 1422, power detection circuitry (e.g., power detection circuitry 330, 930, 930′, 930″,
In block 1424, the system controller may determine, based on one or more reflected signal power measurements, one or more calculated reflected-to-forward signal power ratios, and/or one or more calculated S11 parameters, whether or not the match provided by the variable impedance matching network is acceptable. For example, the system controller may use a single reflected signal power measurement, a single calculated reflected-to-forward signal power ratio, or a single calculated S11 parameter in making this determination, or may take an average (or other calculation) of a number of previously-received reflected signal power measurements, previously-calculated reflected-to-forward power ratios, or previously-calculated S11 parameters in making this determination. To determine whether or not the match is acceptable, the system controller may compare the received reflected signal power, the calculated ratio, and/or S11 parameter to one or more corresponding thresholds, for example. For example, in one embodiment, the system controller may compare the received reflected signal power to a threshold of, for example, 5 percent (or some other value) of the forward signal power. A reflected signal power below 5 percent of the forward signal power may indicate that the match remains acceptable, and a ratio above 5 percent may indicate that the match is no longer acceptable. In another embodiment, the system controller may compare the calculated reflected-to-forward signal power ratio to a threshold of 10 percent (or some other value). A ratio below 10 percent may indicate that the match remains acceptable, and a ratio above 10 percent may indicate that the match is no longer acceptable. When the measured reflected power, or the calculated ratio or S11 parameter is greater than the corresponding threshold (i.e., the comparison is unfavorable), indicating an unacceptable match, then the system controller may initiate re-configuration of the variable impedance matching network by again performing process 1410.
As discussed previously, the match provided by the variable impedance matching network may degrade over the course of a defrosting operation due to impedance changes of the load (e.g., load 364,
According to an embodiment, in the iterative process 1410 of re-configuring the variable impedance matching network, the system controller may take into consideration this tendency. More particularly, when adjusting the match by reconfiguring the variable impedance matching network in block 1418, the system controller initially may select states of the variable inductance networks for the cavity and RF signal source matches that correspond to lower inductances (for the cavity match, or network 411,
In an alternate embodiment, the system controller may instead iteratively test each adjacent configuration to attempt to determine an acceptable configuration. For example, referring again to Table 1, above, if the current configuration corresponds to state 12 for the cavity matching network and to state 3 for the RF signal source matching network, the system controller may test states 11 and/or 13 for the cavity matching network, and may test states 2 and/or 4 for the RF signal source matching network. If those tests do not yield a favorable result (i.e., an acceptable match), the system controller may test states 10 and/or 14 for the cavity matching network, and may test states 1 and/or 5 for the RF signal source matching network, and so on.
In actuality, there are a variety of different searching methods that the system controller may employ to re-configure the system to have an acceptable impedance match, including testing all possible variable impedance matching network configurations. Any reasonable method of searching for an acceptable configuration is considered to fall within the scope of the inventive subject matter. In any event, once an acceptable match is determined in block 1416, the defrosting operation is resumed in block 1414, and the process continues to iterate.
Referring back to block 1424, when the system controller determines, based on one or more reflected power measurements, one or more calculated reflected-to-forward signal power ratios, and/or one or more calculated S11 parameters, that the match provided by the variable impedance matching network is still acceptable (e.g., the reflected power measurements, calculated ratio, or S11 parameter is less than a corresponding threshold, or the comparison is favorable), the system may evaluate whether or not an exit condition has occurred, in block 1426. In actuality, determination of whether an exit condition has occurred may be an interrupt driven process that may occur at any point during the defrosting process. However, for the purposes of including it in the flowchart of
In any event, several conditions may warrant cessation of the defrosting operation. For example, the system may determine that an exit condition has occurred when a safety interlock is breached. Alternatively, the system may determine that an exit condition has occurred upon expiration of a timer that was set by the user (e.g., through user interface 380, 980,
If an exit condition has not occurred, then the defrosting operation may continue by iteratively performing blocks 1422 and 1424 (and the matching network reconfiguration process 1410, as necessary). When an exit condition has occurred, then in block 1428, the system controller causes the supply of the RF signal by the RF signal source to be discontinued. For example, the system controller may disable the RF signal generator (e.g., RF signal generator 322, 922,
It should be understood that the order of operations associated with the blocks depicted in
The connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in an embodiment of the subject matter. In addition, certain terminology may also be used herein for the purpose of reference only, and thus are not intended to be limiting, and the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context.
As used herein, a “node” means any internal or external reference point, connection point, junction, signal line, conductive element, or the like, at which a given signal, logic level, voltage, data pattern, current, or quantity is present. Furthermore, two or more nodes may be realized by one physical element (and two or more signals can be multiplexed, modulated, or otherwise distinguished even though received or output at a common node).
The foregoing description refers to elements or nodes or features being “connected” or “coupled” together. As used herein, unless expressly stated otherwise, “connected” means that one element is directly joined to (or directly communicates with) another element, and not necessarily mechanically. Likewise, unless expressly stated otherwise, “coupled” means that one element is directly or indirectly joined to (or directly or indirectly communicates with) another element, and not necessarily mechanically. Thus, although the schematic shown in the figures depict one exemplary arrangement of elements, additional intervening elements, devices, features, or components may be present in an embodiment of the depicted subject matter.
An embodiment of a thermal increase system is coupled to a cavity for containing a load. The thermal increase system includes an RF signal source configured to supply an RF signal, a transmission path, an impedance matching network, power detection circuitry, and a controller. The transmission path is electrically coupled between the RF signal source and first and second electrodes that are positioned across the cavity. The impedance matching is electrically coupled along the transmission path, and the impedance matching network comprises a network of variable passive components. The power detection circuitry is configured to detect reflected signal power along the transmission path. The controller is configured to modify, based on the reflected signal power, one or more values of one or more of the variable passive components of the impedance matching network to reduce the reflected signal power.
An embodiment of a method of operating a thermal increase system that includes a cavity includes supplying, by an RF signal source, one or more RF signals to a transmission path that is electrically coupled between the RF signal source and first and second electrodes that are positioned across the cavity. The method further includes detecting, by power detection circuitry, reflected signal power along the transmission path, and modifying, by a controller, one or more values of one or more of variable passive components of an impedance matching network that is electrically coupled along the transmission path to reduce the reflected signal power.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of filing this patent application.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17306854.5 | Dec 2017 | EP | regional |
