Patent Grant
11632829
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, exemplary defrosting systems are realized using a first electrode disposed in a cavity, an amplifier arrangement (including one or more transistors), an 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 an embodiment, the impedance matching network is 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 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, 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 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 330,
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 340,
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 380,
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 340,
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 320 may correspond to a control panel (e.g., control panel 120, 214, 224,
System controller 330 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 330 is coupled to user interface 320, RF signal source 340, variable impedance matching network 360, power detection circuitry 380, and sensors 390 (if included). System controller 330 is configured to receive signals indicating user inputs received via user interface 320, and to receive forward and reflected power measurements from power detection circuitry 380. Responsive to the received signals and measurements, and as will be described in more detail later, system controller 330 provides control signals to the power supply and bias circuitry 350 and to the RF signal generator 342 of the RF signal source 340. In addition, system controller 330 provides control signals to the variable impedance matching network 360, which cause the network 360 to change its state or configuration.
Defrosting cavity 310 includes a capacitive defrosting arrangement with first and second parallel plate electrodes that are separated by an air cavity within which a load 316 to be defrosted may be placed. For example, a first electrode 370 may be positioned above the air cavity, and a second electrode may be provided by a portion of a containment structure 312. More specifically, the containment structure 312 may include bottom, top, and side walls, the interior surfaces of which define the cavity 310 (e.g., cavity 110,
Defrosting cavity 310 and any load 316 (e.g., food, liquids, and so on) positioned in the defrosting cavity 310 present a cumulative load for the electromagnetic energy (or RF power) that is radiated into the cavity 310 by the first electrode 370. More specifically, the cavity 310 and the load 316 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 316 increases. As will be described in conjunction with
The first electrode 370 is electrically coupled to the RF signal source 340 through a variable impedance matching network 360 and a transmission path 348, in an embodiment. As will be described in more detail later, the variable impedance matching circuit 360 is configured to perform an impedance transformation from an impedance of the RF signal source 340 to an input impedance of defrosting cavity 340 as modified by the load 316. In an embodiment, the variable impedance matching network 360 includes a network of passive components (e.g., inductors, capacitors, resistors). According to a more specific embodiment, the variable impedance matching network 360 includes a plurality of fixed-value lumped inductors (e.g., inductors 412-414, 712-714, 812-814,
According to an embodiment, RF signal source 350 includes an RF signal generator 342 and a power amplifier (e.g., including one or more power amplifier stages 344, 346). In response to control signals provided by system controller 330, RF signal generator 342 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 342 may be controlled to produce oscillating signals of different power levels and/or different frequencies, in various embodiments. For example, the RF signal generator 342 may produce a signal that oscillates in a range of about 3.0 megahertz (MHz) to about 300 MHz. Some desirable frequencies may be, for example, 13.56 MHz (+/−5 percent), 27.125 MHz (+/−5 percent), and 40.68 MHz (+/−5 percent). In one particular embodiment, for example, the RF signal generator 342 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 than the above-given ranges or values.
In the embodiment of
In an embodiment, each amplifier stage 344, 346 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 344, between the driver and final amplifier stages 346, and/or to the output (e.g., drain terminal) of the final amplifier stage 346, in various embodiments. In an embodiment, each transistor of the amplifier stages 344, 346 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
Power detection circuitry 380 is coupled along the transmission path 348 between the output of the RF signal source 340 and the input to the variable impedance matching network 360, in an embodiment. In an alternate embodiment, power detection circuitry 380 may be coupled to the transmission path 349 between the output of the variable impedance matching network 360 and the first electrode 370. Either way, power detection circuitry 380 is configured to monitor, measure, or otherwise detect the power of the forward signals (i.e., from RF signal source 340 toward first electrode 370) and the reflected signals (i.e., from first electrode 370 toward RF signal source 340) traveling along the transmission path 348.
Power detection circuitry 380 supplies signals conveying the magnitudes of the forward and reflected signal power to system controller 330. System controller 330, in turn, may calculate a ratio of reflected signal power to forward signal power, or the S11 parameter. As will be described in more detail below, when the reflected to forward power ratio exceeds a threshold, this indicates that the system 300 is not adequately matched, and that energy absorption by the load 316 may be sub-optimal. In such a situation, system controller 330 orchestrates a process of altering the state of the variable impedance matching network until the reflected to forward power ratio decreases to a desired level, thus re-establishing an acceptable match and facilitating more optimal energy absorption by the load 316.
As mentioned above, 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 316 to be sensed during the defrosting operation. When provided to the system controller 330, the temperature information enables the system controller 330 to alter the power of the RF signal supplied by the RF signal source 340 (e.g., by controlling the bias and/or supply voltages provided by the power supply and bias circuitry 350), to adjust the state of the variable impedance matching network 360, and/or to determine when the defrosting operation should be terminated. The weight sensor(s) are positioned under the load 316, and are configured to provide an estimate of the weight of the load 316 to the system controller 330. The system controller 330 may use this information, for example, to determine a desired power level for the RF signal supplied by the RF signal source 340, to determine an initial setting for the variable impedance matching network 360, and/or to determine an approximate duration for the defrosting operation.
As discussed above, the variable impedance matching network 360 is used to match the input impedance of the defrosting cavity 310 plus load 316 to maximize, to the extent possible, the RF power transfer into the load 316. The initial impedance of the defrosting cavity 310 and the load 316 may not be known with accuracy at the beginning of a defrosting operation. Further, the impedance of the load 316 changes during a defrosting operation as the load 316 warms up. According to an embodiment, the system controller 330 may provide control signals to the variable impedance matching network 360, which cause modifications to the state of the variable impedance matching network 360. This enables the system controller 330 to establish an initial state of the variable impedance matching network 360 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 316. In addition, this enables the system controller 330 to modify the state of the variable impedance matching network 360 so that an adequate match may be maintained throughout the defrosting operation, despite changes in the impedance of the load 316.
According to an embodiment, the variable impedance matching network 360 may include a network of passive components, and more specifically a network of fixed-value inductors (e.g., lumped inductive components) and variable inductors (or variable inductance networks). As used herein, the term “inductor” means a discrete inductor or a set of inductive components that are electrically coupled together without intervening components of other types (e.g., resistors or capacitors).
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 312,
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 310 plus load 316,
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 100 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 310 plus load 316,
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 716 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 716 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 716. The weight sensor(s) 790 are configured to provide an estimate of the weight of the load 716 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 716 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 740, 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. According to an embodiment, the system controller 730 is coupled to the user interface, RF signal source 740, variable impedance matching network 760, and power detection circuitry 780 through various conductive interconnects on or within the common substrate 752. In addition, the power detection circuitry 780 is coupled along the transmission path 748 between the output of the RF signal source 740 and the input 702 to the variable impedance matching network 760, in an embodiment. For example, the substrate 752 may include a microwave or RF laminate, a polytetrafluorethylene (PTFE) substrate, a printed circuit board (PCB) material substrate (e.g., FR-4), an alumina substrate, a ceramic tile, or another type of substrate. In various alternate embodiments, various ones of the components may be coupled to different substrates with electrical interconnections between the substrates and components. In still other alternate embodiments, some or all of the components may be coupled to a cavity wall, rather than being coupled to a distinct substrate.
The first electrode 770 is electrically coupled to the RF signal source 740 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 740), and a second terminal that is electrically coupled to a first intermediate node 720 (e.g., node 420,
The first variable inductance network 710 (e.g., network 410,
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 902, when the system controller (e.g., system controller 330,
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,
In block 904, the system controller provides control signals to the variable matching network (e.g., network 360, 400,
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 340,
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 904, 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 914, power detection circuitry (e.g., power detection circuitry 380,
In block 916, the system controller may determine, based on 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 ratio is 10 percent or less, or compares 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 forward and 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-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 918, by reconfiguring the variable inductance 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 to have different inductance states). After reconfiguring the variable inductance network, blocks 914, 916, and 918 may be iteratively performed until an acceptable or best match is determined in block 916.
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 340) to a relatively high power RF signal, in block 920. Once again, the system controller may control the RF signal power level through control signals to the power supply and bias circuitry (e.g., circuitry 350,
In block 922, power detection circuitry (e.g., power detection circuitry 380,
In block 924, the system controller may determine, based on 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 calculated reflected-to-forward signal power ratio or S11 parameter in making this determination, or may take an average (or other calculation) of a number of previously-calculated reflected-to-forward power ratios or S11 parameters in making this determination. To determine whether or not the match is acceptable, the system controller may compare the calculated ratio and/or S11 parameter to a threshold, for example. For example, in one 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 calculated ratio or S11 parameter is greater than the 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 910.
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 316,
According to an embodiment, in the iterative process 910 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 918, 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 916, the defrosting operation is resumed in block 920, and the process continues to iterate.
Referring back to block 924, when the system controller determines, based on 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 calculated ratio or S11 parameter is less than the threshold, or the comparison is favorable), the system may evaluate whether or not an exit condition has occurred, in block 926. 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 320,
If an exit condition has not occurred, then the defrosting operation may continue by iteratively performing blocks 922 and 924 (and the matching network reconfiguration process 910, as necessary). When an exit condition has occurred, then in block 928, 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 342,
As indicated above, the defrosting system may be configured to determine when a defrosting operation has completed. More specifically, the defrosting system may be configured to estimate a time when a previously-frozen load has reached a desired state of defrost. For example, a desired state of defrost may be a state in which the average temperature of the load is in a range of about −4 degrees Celsius to about −2 degrees Celsius. Alternatively, a desired state of defrost may be a state in which the average temperature of the load is in a range of about −2 degrees Celsius to about 0 degrees Celsius. A desired state of defrost may be a state when the load is at another temperature or temperature range, as well.
According to an embodiment, a method of determining completion of a defrosting operation is based on observations of the rates of impedance changes for the load throughout a defrosting operation in comparison with observed typical impedance change rates of known loads during defrosting operations. To facilitate understanding of the method embodiments, a chart illustrating a typical impedance change response for a typical load is provided in
As trace 1110 indicates, the rate of change of reflected-to-forward power ratio or S11 parameter (e.g., as measured by power detection circuitry 380 and calculated by system controller 330,
As will be described in detail below in conjunction with
Referring first to
In block 1204 (substantially similar to block 904,
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 340) to a relatively high power RF signal, in block 1212 (substantially similar to block 920,
According to an embodiment, if the system controller is in possession of a starting temperature measurement for the load (e.g., received from a temperature or IR sensor 390, 792,
In block 1218 (substantially similar to block 924,
Referring back to block 1218, when the system controller determines, based on 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 calculated ratio or S11 parameter is less than the threshold, or the comparison is favorable), then the system controller may calculate, in block 1220, the rate of change of the reflected-to-forward power ratio (or the rate of change of the S11 parameter). For example, the rate of change may be calculated by performing a mathematical calculation (e.g., calculating an average or standard deviation) using a number, X, of the most recently calculated ratios, where X may be an integer in a range of 2 to 10, for example. In other words, the system controller calculates the rate of change of the reflected-to-forward power ratio (or the rate of change of the S11 parameter) by performing the mathematical calculation on a sliding window of the X most recently calculated ratios.
According to another embodiment, the system controller may quantify the rate of change of the reflected-to-forward power ratio (or the rate of change of the S11 parameter) in terms of how frequently the matching network is re-configured (i.e., in block 1210). A low frequency of re-configuring the matching network implies that the reflected-to-forward power ratio is not changing significantly at a rapid rate. Conversely, a high frequency of re-configuring the matching network implies that the reflected-to-forward power ratio is changing significantly at a rapid rate.
In block 1222, the system controller makes a determination of whether or not the rate of change of the reflected-to-forward power ratio (or the rate of change of the S11 parameter) is greater than the plateau rate. Alternatively, the system controller may make a determination of whether the frequency at which the matching network is re-configured exceeds a threshold (thus implying that the rate of change is greater than the plateau rate). As discussed previously in conjunction with
When the system controller determines that the rate of change is greater than the plateau rate, an assumption is made that the load temperature is still within the sub-plateau temperature range (e.g., range 1120,
To this end, and continuing with block 1250 of
According to an embodiment, the system determines the limit to correspond to an amount of time (or a number of counts) that it will take the system to provide enough RF power to the load to increase the temperature of the load to a desired defrost cessation temperature (e.g., the upper plateau temperature limit 1132,
In block 1252 (substantially similar to block 922,
In block 1254 (substantially similar to block 924,
In addition, the system controller may increment the plateau region timer (although this may be done continuously, as well), or may increment the plateau region counter (e.g., indicating a number of times that the reflected-to-forward power ratio has been calculated.
When the calculated ratio or S11 parameter is greater than the 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 performing process 1256 (substantially similar to process 910,
Referring again to block 1254, when the calculated ratio or S11 parameter is not greater than the threshold (i.e., the comparison is favorable), indicating an acceptable match, then the system controller may make a determination, in block 1260, of whether or not the plateau region timer/counter is less than the limit (or the timer has not expired).
If the plateau region timer/counter is not less than the limit (or has expired), then the system controller may determine that the defrosting process has completed. When the system controller has determined that the defrosting process has completed, then in block 1266, 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 342,
If the plateau region timer/counter is less than the limit (or has not expired), then in block 1262 (substantially similar to block 1220, described above), the system controller may calculate the rate of change of the reflected-to-forward power ratio (or the rate of change of the S11 parameter). Again, for example, the rate of change may be calculated by performing a mathematical calculation (e.g., calculating an average or standard deviation) using a number, X, of the most recently calculated ratios. According to another embodiment, the system controller may quantify the rate of change of the reflected-to-forward power ratio (or the rate of change of the S11 parameter) in terms of how frequently the matching network is re-configured (i.e., in block 1256).
In block 1264, the system controller makes a determination of whether or not the rate of change of the reflected-to-forward power ratio (or the rate of change of the S11 parameter) is greater than the plateau rate. Alternatively, the system controller may make a determination of whether the frequency at which the matching network is re-configured exceeds a threshold (thus implying that the rate of change is greater than the plateau rate).
When the system controller determines that the rate of change is not greater than the plateau rate (or the rate of change compares favorably with the plateau rate), an assumption is made that the load temperature is still within the plateau temperature range (e.g., range 1130,
Again, when the system controller has determined that the defrosting process has completed, then in block 1266, the system controller causes the supply of the RF signal by the RF signal source to be discontinued, and the system controller may send signals to the user interface (e.g., user interface 320,
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 method of performing a thermal increase operation (or a defrosting operation) on a load that is positioned within a cavity of a thermal increase system includes providing, by an RF signal source through a transmission path, an RF signal to an electrode that is proximate to the cavity. The method further includes repeatedly taking forward RF power measurements and reflected RF power measurements along the transmission path, repeatedly determining, based on the forward RF power measurements and the reflected RF power measurements, a calculated rate of change, and repeatedly comparing the calculated rate of change to a threshold rate of change. When a determination is made that the calculated rate of change compares favorably with the threshold rate of change, the method further includes continuing to provide the RF signal to the electrode until a determination is made that the thermal increase operation is completed. When the determination is made that the thermal increase operation is completed, provision of the RF signal to the electrode is ceased.
The RF signal may be an oscillating signal having a frequency between 3.0 megahertz and 300 megahertz. The RF signal may be an oscillating signal having a frequency selected from 13.56 megahertz (+/−5 percent), 27.125 megahertz (+/−5 percent), and 40.68 megahertz (+/−5 percent). Determining the calculated rate of change may comprise: calculating a plurality of ratios of the reflected RF power measurements to the forward RF power measurements; and determining the calculated rate as a rate at which the plurality of ratios changes over time. Determining the calculated rate of change may comprise: calculating a plurality of ratios of the reflected RF power measurements to the forward RF power measurements; calculating a plurality of S11 parameters from the plurality of ratios; and determining the calculated rate as a rate at which the plurality of S11 parameters changes over time. The threshold rate of change may be a rate of change that is consistent with the load having a temperature that is within a plateau temperature range. The plateau temperature range may include a range of temperatures between −16 degrees Celsius and −3 degrees Celsius. The plateau temperature range may include a range of temperatures between −8 degrees Celsius and −4 degrees Celsius. Making the determination that the thermal increase operation is completed may comprise determining whether a timer has expired. The thermal increase system may include a variable impedance matching network between the RF signal source and the electrode, and wherein making the determination that the thermal increase operation is completed comprises determining whether a rate at which the variable impedance matching network is re-configured to improve matching between the RF signal source and the cavity plus the load. The thermal increase system may include a variable impedance matching network between the RF signal source and the first electrode, the method further comprising: repeatedly calculating ratios of the reflected RF power measurements to the forward RF power measurements; repeatedly comparing the ratios to a threshold; and when a ratio of a reflected RF power measurement to a forward RF power measurement compares unfavorably with the threshold, re-configuring the variable impedance matching network to improve matching between the RF signal source and the cavity plus the load.
An embodiment of a thermal increase system (or defrosting system) is configured to perform a thermal increase operation (or defrost operation) on a load positioned within a cavity of the thermal increase system. The system includes an RF signal source configured to produce an RF signal, and a transmission path between the RF signal source and an electrode that is positioned proximate to the cavity, where the transmission path is configured to convey the RF signal from the RF signal source to the electrode. The system further includes power detection circuitry coupled to the transmission path and configured repeatedly to take forward RF power measurements and reflected RF power measurements along the transmission path, and a system controller coupled to the power detection circuitry. The system controller is configured to repeatedly determine, based on the forward RF power measurements and the reflected RF power measurements, a calculated rate of change, and to repeatedly compare the calculated rate of change to a threshold rate of change. When a determination is made that the calculated rate of change compares favorably with the threshold rate of change, the system controller is configured to enable the RF signal source to continue to provide the RF signal to the electrode until a determination is made that the thermal increase operation is completed. When the determination is made that the thermal increase operation is completed, the system controller is configured to cause the RF signal source to cease provision of the RF signal to the electrode.
The system controller may be configured to determine the calculated rate of change by: calculating a plurality of ratios of the reflected RF power measurements to the forward RF power measurements; calculating a plurality of S11 parameters from the plurality of ratios; and determining the calculated rate as a rate at which the plurality of S11 parameters changes over time. The threshold rate of change may be a rate of change that is consistent with the load having a temperature that is within a plateau temperature range. The plateau temperature range may include a range of temperatures between −16 degrees Celsius and −3 degrees Celsius. The plateau temperature range may include a range of temperatures between −8 degrees Celsius and −4 degrees Celsius. The system may further comprise: a timer, wherein making the determination that the thermal increase operation is completed comprises determining whether the timer has expired. The system may further comprise: a variable impedance matching network coupled between the RF signal source and the electrode, wherein the system controller is configured to make the determination that the thermal increase operation is completed by determining a rate at which the variable impedance matching network is re-configured to improve matching between the RF signal source and the cavity plus the load. The system may further comprise: a variable impedance matching network between the RF signal source and the first electrode, wherein the system controller is configured to repeatedly calculate ratios of the reflected RF power measurements to the forward RF power measurements, repeatedly compare the ratios to a threshold, and when a ratio of a reflected RF power measurement to a forward RF power measurement compares unfavorably with the threshold, to re-configure the variable impedance matching network to improve matching between the RF signal source and the cavity plus the load.
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 |
|---|---|---|---|
| 16306022 | Aug 2016 | EP | regional |
This application is a continuation of co-pending, U.S. patent application Ser. No. 15/454,345, filed on Mar. 9, 2017, which claims priority under 35 U.S.C. 119(b) to European Patent Application Number 16306022.1, filed on Aug. 5, 2016.
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| Number | Date | Country | |
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| Number | Date | Country | |
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| Parent | 15454345 | Mar 2017 | US |
| Child | 16812274 | US |
