Patent Grant
10165630
The embodiments described herein relate to radio frequency antenna for radiating electromagnetic energy into a reservoir filled with a target material such as hydrocarbons.
Radio-frequency (RF) antennas may be used in various applications where it is desired to radiate electromagnetic (EM) energy into a reservoir filled with a target material in order to change one or more of the target material's characteristics. For example, radiation of EM energy may initiate or enhance a chemical process or reaction, heat the target material, or help to perform an analysis of the target material's physical properties or composition. EM radiation may be used at different stages of oil production: heating the soil to decrease viscosity of oil, improve oil's mobility, or upgrade the bitumen or heavy oil in a process on the surface or underground.
The RF antenna and its environment form a connected system, and the RF antenna's performance greatly depends on the EM properties of the surrounding target material. The input impedance of the RF antenna characterizes its ability to deliver high RF power to the target material. The RF antenna is a part of an electrical circuit that typically comprises an RF generator, impedance matching circuits, and a feed transmission line. If there is a mismatch between the RF antenna's input impedance and its feed system, at least one part of the EM power will be reflected from the antenna back to the RF generator. This EM power reflection reduces the amount of power delivered by the RF antenna to the target material in the reservoir and increases losses and/or heating in the transmission line and the RF generator. This typically leads to a decrease in the overall system efficiency.
To reduce or eliminate the EM power reflection, impedance matching circuits are generally used between the RF antenna and the RF generator. The matching circuits tend to be expensive and complex and typically operate optimally only within a narrow frequency range. Instead, dynamic or adaptive impedance matching circuits that match the antenna to the feed transmission line over a wider range of frequencies and/or values of input impedance, may be used. However, the cost and complexity of such dynamic matching circuits is significantly higher than that of the regular matching circuits.
It would be desirable to reduce the EM power reflection from the RF antenna delivering the RF power into surrounding target material by improving the impedance matching between the RF antenna and the feed transmission line without the use of an impedance matching circuit.
In a first aspect, there is provided a radio frequency antenna for radiating electromagnetic energy into a reservoir filled with a target material, the antenna being operatively connected to a feed transmission line. In at least one embodiment, the antenna may include a waveguide having an inner waveguide layer a waveguide dielectric layer, and an outer waveguide layer; at least one slot formed in the outer waveguide layer, the at least one slot being adapted to radiate the electro-magnetic energy into the reservoir; and a sleeve portion enclosing at least a portion of the waveguide, the sleeve portion having at least first and second dielectric layers where the permittivity of the second dielectric layer is higher than the permittivity of the first dielectric layer and the first dielectric layer is positioned in closer proximity to the waveguide than the second dielectric layer; such that when the antenna is inserted into the reservoir, the input impedance of the antenna remains matched to the feed transmission line for a wide range of target materials.
In at least one embodiment, the at least one slot and at least one of the first and second dielectric layers may be dimensioned and positioned relative to each other such that the reflectivity coefficient of the antenna may be less than approximately −10 dB.
In at least one embodiment, at least one of the first and second dielectric layers may have permittivity and thickness such that the reflectivity coefficient of the antenna may be less than approximately −10 dB.
In at least one embodiment, the thickness of at least one of the first and second dielectric layers may be equal to a thickness factor multiplied by the wavelength of the electro-magnetic wave in the waveguide dielectric layer, the thickness factor being in the approximate range of 1/15 to ¼.
In at least one embodiment, the thickness of at least one of the first and second dielectric layers may be equal to a thickness factor multiplied by the wavelength of the electro-magnetic wave in the waveguide dielectric layer, the thickness factor being in the approximate range of 1/30 to 1. In at least one embodiment, the radius of the at least first and second dielectric layers may be variable along the length of the antenna.
In at least one embodiment, a most inner dielectric layer of the sleeve portion may be air. In at least one embodiment, at least one of the at least first and second dielectric layers may be made at least in part of ceramic material. In at least one embodiment, at least one of the at least first and second dielectric layers may be concentric.
In at least one embodiment, the at least one slot may have helical form. In at least one embodiment, a plurality of slots may be formed in the outer waveguide layer. In at least one embodiment, the slots may be formed along the waveguide with dimensions and relative distribution such that uniform near-field radiation may be provided along the length of the antenna.
In at least one embodiment, each of the plurality of slots may be formed with identical dimensions. In at least one embodiment, each of the plurality of slots may have identical shapes. In at least one embodiment, the slots may be equally distributed along the length of the waveguide. In at least one embodiment, the slots may be unequally distributed along the length of the waveguide. In at least one embodiment, at least one of the first and second dielectric layers may be concentric.
In at least one embodiment, the waveguide may have an input portion operatively connected to the feed transmission line and an output portion connected to a termination.
In at least one embodiment, the slots that are in closer proximity to the input portion of the waveguide may have smaller dimensions and may be positioned farther apart than slots that are in closer proximity to the output portion of the waveguide.
In at least one embodiment, the antenna may be adapted to operate: (a) in a resonant mode when a permittivity ratio is less than or about 1 and (b) in a travelling wave mode when the permittivity ratio is more than about 1, wherein the permittivity ratio is the ratio of a permittivity of the target material in the reservoir to the permittivity of the waveguide dielectric layer.
In at least one embodiment, the waveguide may be of the type selected from the group consisting of: a coaxial waveguide, a hollow cylindrical waveguide and a rectangular waveguide.
In at least one embodiment, the lateral dimension of the waveguide may be approximately equal to the lateral dimension of the feed transmission line. In at least one embodiment, the feed transmission line and the waveguide may be both coaxial cables.
In at least one embodiment, the antenna may be adapted to operate at a center frequency of about 30 MHz to about 10 GHz.
In at least one embodiment, the waveguide dielectric layer may be air.
In at least one embodiment, the antenna may comprise a plurality of segments.
In at least one embodiment, the termination of the radio-frequency antenna may be selected from the group consisting of: a short termination, an open termination, and a matched termination. In at least one embodiment, the radio-frequency antenna may further comprise a connecting transmission line operatively connected between the antenna and the feed transmission line.
In at least one embodiment, the target material in the reservoir may be selected from the group consisting of: air, dry oil sand, wet oil sand, water, soil, soil sands, shale, ore, and a combination thereof.
In at least one embodiment, the target material in the reservoir may have a relative dielectric permittivity about 1 to about 90 and electric conductivity about 0 S/m to about 5 S/m.
In at least one embodiment, at least one portion of the antenna may be inserted into the reservoir or at least one portion of the antenna may be outside of the reservoir.
For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings which show at least one exemplary embodiment, and in which:
The skilled person in the art will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the applicants' teachings in anyway. Also, it will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
Numerous embodiments are described in this application, and are presented for illustrative purposes only. The described embodiments are not intended to be limiting in any sense. The invention is widely applicable to numerous embodiments, as is readily apparent from the disclosure herein. Those skilled in the art will recognize that the present invention may be practiced with modification and alteration without departing from the teachings disclosed herein. Although particular features of the present invention may be described with reference to one or more particular embodiments or figures it should be understood that such features are not limited to usage in the one or more particular embodiments or FIGS. with reference to which they are described.
The terms “an embodiment”, “embodiment”, “embodiments”, “the embodiment”, “the embodiments”, “one or more embodiments”, “some embodiments”, and “one embodiment” mean “one or more (but not all) embodiments of the present invention(s)”, unless expressly specified otherwise.
The terms “including”, “comprising” and variations thereof mean “including but not limited to”, unless expressly specified otherwise. A listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms “a”, “an” and “the” mean “one or more”, unless expressly specified otherwise.
Further, although process steps, method steps, algorithms or the like may be described (in the disclosure and/or in the claims) in a sequential order, such processes, methods and algorithms may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of processes described herein may be performed in any order that is practical. Further, some steps may be performed simultaneously.
When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article.
It should be noted that terms of degree such as “substantially”, “about” and “approximately” when used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of the modified term if this deviation would not negate the meaning of the term it modifies.
Furthermore, the recitation of any numerical ranges by end points herein includes all numbers and fractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.90, 4, and 5). It is also to be understood that all numbers and fractions thereof are presumed to be modified by the term “about” which means a variation up to a certain amount of the number to which reference is being made if the end result is not significantly changed.
In addition, as used herein, the wording “and/or” is intended to represent an inclusive-or. That is, “X and/or Y” is intended to mean X or Y or both, for example. As a further example, “X, Y, and/or Z” is intended to mean X or Y or Z or any combination thereof.
The antenna 100 may be designed to be operatively connected to a feed transmission line 120. In at least one embodiment, the input portion 190 of the waveguide 130 of the antenna 100 may be operatively connected to the feed transmission line 120. In this way the feed transmission line 120 may deliver RF power from an RF generator 124 to the antenna 100.
In at least one embodiment, at least a portion of the antenna 100 may be positioned within the reservoir 110 (i.e. after being inserted into the reservoir 110). In at least one embodiment, at least a portion of the antenna 100 may be positioned outside the reservoir 110. In at least one embodiment, the antenna 100 may be at a certain distance from the reservoir 110.
For example, the target material 115 may be enclosed in a holder made of EM transparent material (such as, e.g. ceramic). The antenna 100 may be placed close to such reservoir 110, or even touching its surface. In this case, the antenna 110 may radiate a portion of its energy into the reservoir 110.
In at least one embodiment, the target material 115 in the reservoir 110 may include materials such as air, dry oil sand, wet oil sand, water, soil, soil sands, other industrial material, shale, ore, brine, clay, drilling mud, crude oil or a geologic formation containing oil, heavy oil, bitumen, other hydrocarbons, and/or a combination thereof.
For example, the target material 115 in the reservoir 110 may have a relative dielectric permittivity of about 1 to about 90; about 1.5 to about 90; about 2 to about 80; about 2 to about 60; about 2 to about 70; about 2 to about 57; about 2 to about 50; of about 50 to about 60; of about 10 to about 60.
For example, the target material 115 in the reservoir 110 may have a relative dielectric permittivity of at least about 1.5; at least about 2; at least about 10; at least about 30; at least about 50; not greater than about 60; not greater than about 70; not greater than about 80; not greater than about 90; not greater than about 58.
For example, the target material 115 in the reservoir 110 may be lossy (i.e. the electromagnetic field may be absorbed by the target material 115). For example, the target material 115 in the reservoir 110 may have conductivity of about 0 S/m to about 5 S/m. For example, the target material 115 in the reservoir 110 may have conductivity of about 0 S/m to about 1 S/m; of about 0 S/m to about 4 S/m; of about 1 S/m to about 4 S/m; of about 0 S/m to about 3 S/m. For example, the conductivity of the dry sand may be about 2.5 E−5 S/m, wet oil sand material may have conductivity of about 0.01 S/m, or about 0.002 S/m, or about 0.005 S/m (depending on the amount of water).
The reservoir 110 may be a container (e.g. a metal container), or a reactor, directly interacting with the target material 115. Alternatively, the reservoir 110 does not have to have walls, rather it could be partially comprised of surrounding materials such as a soil, etc. surrounding the target material 115.
In at least one embodiment, the waveguide 130 may be of a type of a coaxial cable, a hollow waveguide, a cylindrical waveguide, or a rectangular waveguide. For example, the waveguide 130 may have any type of cross-section, including, but not limited to cylindrical, rectangular, or elliptical.
For example, the waveguide 130 may be of the same type and/or have the same at least one cross-sectional dimension as the transmission line 120. In at least one embodiment, the widest dimension of the cross-section of the waveguide 130 may be approximately equal to the widest dimension of the feed transmission line 120. In at least one embodiment, both the waveguide 130 and the feed transmission line 120 may be coaxial cables.
In at least one embodiment, the waveguide 130 may comprise a waveguide core 132, an inner waveguide layer 135, a waveguide dielectric layer 140, and an outer waveguide layer 145.
As shown at
In at least one embodiment, the waveguide 130 may also comprise other waveguide layers. For example, the waveguide 130 may comprise a plurality of waveguide dielectric layers made of the same or different dielectric materials. The waveguide 130 may also comprise other layers made of at least one type of a conductor. Each of the plurality of waveguide layers may at least partially enclose one or more other waveguide layers. It should be understood that different dielectric materials may be used both in longitudinal and radial directions.
The waveguide core 132 may be made of air and/or a dielectric material. For example, the waveguide core 132 may have relative permittivity of about 1 to about 30. It should be noted that the relative permittivity is defined herein as a ratio of the permittivity of a certain material to the permittivity of vacuum. For example, the waveguide core 132 may be made of liquid (e.g. for cooling purpose), and/or other gas, and/or solid.
The inner waveguide layer 135 may be made of a first conductor. The first conductor may be a metal, such as, for example: copper, aluminum, steel. For example, the inner waveguide layer 135 may have conductivity of 106 S/m to about 6×107 S/m.
For example, the outer waveguide layer 145 may be made of a second conductor. For example, the second conductor may be: copper, aluminum, steel. For example, the outer waveguide layer 145 may have conductivity of 106 S/m to about 6×107 S/m.
For example, the waveguide dielectric layer 140 may be made of air and/or a dielectric material such as, for example, fiberglass, PEEK, teflon, different types of ceramic (e.g.: Alumina, Zirconia), hydrocarbon liquid (e.g.: toluene, saraline, benzene, etc.). For example, the waveguide dielectric layer 140 may have relative permittivity of about 2 to about 40. For example, the waveguide dielectric layer 140 may have relative permittivity of at least about 1.5; at least about 2; at least about 10, at least about 20; at least about 30; not greater than about 40; not greater than about 50; not greater than about 60; and not greater than about 80.
The waveguide 130 may be adapted to receive EM energy (RF power) from the transmission line 120 and to transmit it from the input portion of the waveguide 190 to the output portion of the waveguide 192.
In at least one embodiment, the waveguide 130 (and the antenna 100) may be longer than at least two wavelengths λ of the EM wave in the waveguide 130, where, for example, the wavelength λ is calculated in the waveguide dielectric layer 140.
In at least one embodiment, the at least one slot 170 may be formed in the waveguide 130 of the antenna 100. In at least one embodiment, the at least one slot 170 may be formed in the outer waveguide layer 145, as shown in
For example, the slots 170 may be located at any portion of the outer waveguide layer 145, such as sidewalls and/or top walls and/or bottom walls of the waveguide 130.
In at least one embodiment, the outer waveguide layer 145 may comprise a plurality of slots 170. For example, each of the plurality of slots 170 may be formed with identical dimensions and/or identical shapes.
Referring again to
In at least one embodiment, at least three of the slots 170 may be equally and/or unequally distributed along the length of the waveguide 130. For example, the slots 170 may be distributed equally at one portion of the waveguide 130 and may be distributed unequally at another portion of the waveguide 130.
In at least one embodiment, the slots 170 may be distributed uniformly with a certain distance between each other, or with a varying distance between each other.
For example, some portions of the antenna 100 may have the density of slots 170 higher than the other portions in order to radiate more EM energy. For example, increasing the distance between the slots 170 (decreasing the density of the slots 170) in one portion of the waveguide 130 may decrease the EM radiation from the waveguide 130 (and therefore in the corresponding portion of the antenna 100). Decreasing the distance between the slots 170 in one portion of the waveguide 130 (increasing the density of slots 170) increases the EM radiation in that portion of the waveguide 130 (and therefore in the corresponding portion of the antenna 100).
It should be understood that the input portion 190 of the waveguide 130, which is operatively connected to the feed transmission line 120, may have more RF power than the output portion 192 of the waveguide 130, which is operatively connected to a termination 184.
The antenna 100 is said to operate in a “slow mode” when the phase velocity of the wave present inside the antenna 100 is lower than the phase velocity of the wave that is radiated into the reservoir's target material 115. When the antenna 100 operates in a “slow mode”, slots 170 may be positioned periodically, with the periodic distance determining a frequency range in which the radiation is possible. For example, the m-th harmonic may radiate in the frequency range between −m11 and −m*f2, where f1=c/(P*(sqrt(er)+1)) and f2=c/(P*(sqrt(er)−1)), where P is the periodic distance, c is the velocity of light in vacuum, er is the relative permittivity of the dielectric inside the antenna 100 or effective relative permittivity of the multiple dielectrics inside the antenna 100.
In at least one embodiment, there may be a few sections with different periods, but within each section the period may be constant. It should be noted that slow or fast wave refers to slow or fast wave phase velocity, as it compares with the phase velocity of the wave radiated out.
The antenna 100 is said to operate in a “fast mode” when the wave present inside the antenna 100 is higher than the speed of the wave outside the antenna 100. When the antenna 100 operates in a fast mode, any type of slot distribution and/or density of slots 170 may be used.
In at least one embodiment, each or at least one portion of the waveguide 130, with the portion's length approximately equal to about a wavelength λ, of the EM wave in the waveguide 130, may contain at least two slots 170. For example, if the wavelength λ=1 m, there may be at least two slots 170 positioned every meter along the waveguide 130.
In at least one embodiment, the slots 170 of the antenna 100 may be designed such that about all or at least 90% of the RF energy may be radiated into the reservoir 110 by the time the RF energy reaches the output portion 192 of the antenna 100.
In at least one embodiment, each slot 170 may be designed with small enough dimensions such that it radiates only a small portion of the RF energy into the target material 115, and therefore does not cause a noticeable disturbance of the EM wave inside the waveguide 130. This may permit the antenna to maintain properties (for example, characteristic impedance) that are close to the properties of the feed transmission line 120, and accordingly assist with maintaining impedance matching of the antenna 100 with the feed transmission line 120.
For example, each slot 170 may have width lower than or about λ/20, where λ is the wavelength of the EM wave inside the waveguide. For example, when the antenna 100 has a plurality of slots 170, the length of each slot 170 may be about λ/20 to about λ/2.
For example, the distance between the slots may be about λ/20 to about λ. Generally, the wider, longer or more frequent slots 170 are, the more energy may be radiated by them. Density, length and width of the slots 170, as well as their tilt angle may be adjusted to achieve desired radiation pattern and to make sure that most of the EM power is radiated by the time the EM wave reaches the output portion of the antenna 100.
For example, the length of the slot 170 may be about as long as the antenna 100 (e.g. a horizontal slot). The length of this type of slot 170 may be about multiple wavelengths of the EM wave inside the waveguide. For example, the length of the slot 170 may be longer than the length of the antenna 100, when e.g. the slot 170 is helical.
Further, different shapes, dimensions and relative distribution of slots 170 may help to achieve a specific radiation profile of the EM wave in the reservoir 110. In at least one embodiment, the slots 170 may be formed along the waveguide 130 with dimensions, and/or shapes, and/or relative distribution such that uniform near-field radiation may be achieved along the length of the antenna 100. For example, specific combination of shapes, and/or dimensions, and/or relative distribution may help to achieve high power concentration at a certain distance from the waveguide 130.
In at least one embodiment, the input portion 190 of the waveguide 130 may be designed to have fewer slots 170 than in the output portion 192 of the waveguide 130. In at least one embodiment, the density of slots at the input portion 190 of the waveguide 130 may be lower than the density of slots 170 at the output portion 192 of the waveguide 130.
In at least one embodiment, the input portion 190 of the waveguide 130 may have less slots 170 and/or smaller slots, while the output portion 192 of the waveguide 192 may have more slots 170 and/or the slots may have higher density and/or larger sizes.
In at least one embodiment, the slots 170 that are in closer proximity to the input portion 190 of the waveguide 190 may have smaller dimensions and/or may be positioned farther apart than slots 170 that are in closer proximity to the output portion 192 of the waveguide 130.
In at least one embodiment, the slots 170 may be distributed along the waveguide 130 such that the electromagnetic energy provided at the output portion 192 of the waveguide 130 may be at least about 10 times lower than the electromagnetic energy provided at the input portion 190 of the waveguide 130.
In at least one embodiment, the at least one slot 170 may be vertical and/or horizontal.
In at least one embodiment, the sleeve portion 150 of the antenna 100 may enclose at least one portion of the waveguide 130. For example, as shown in
In at least one embodiment, the sleeve portion 150 may comprise two or more dielectric layers. In at least one embodiment, the sleeve portion 150 may comprise an inner (first) dielectric layer 152 and an outer (second) dielectric layer 154. In at least one embodiment, the outer (second) dielectric layer 154 may enclose at least one portion of the inner (first) dielectric layer 152.
In at least one embodiment, the dielectric layers of the sleeve portion 150 may be concentric. In at least one embodiment, the dielectric layers of the sleeve portion 150 may be non-concentric. The presence of the non-concentric dielectric layers may assist with achieving an axially asymmetric radiation pattern.
For example, as shown in
The radius Ri and/or the thickness wi of at least one dielectric layer of the sleeve portion 150 may be variable or constant along at least one portion of the length of the antenna 100. For example, variation of the radius R, and/or the thickness wi of the at least one dielectric layer along the length of the dielectric sleeve portion 150, may help to achieve axially asymmetric radiation pattern. The variable thickness and radius of the at least one dielectric layer may be designed to achieve a specific pattern of the radiation intensity along the antenna 100 and/or to achieve axially asymmetric radiation pattern.
The terms “inner dielectric layer” and “outer dielectric layer” are used herein to describe any two dielectric layers of the sleeve portion 150, wherein the “inner dielectric layer” is positioned in closer proximity to the waveguide 130 than the “outer dielectric layer”. At any position along the antenna 100, a radius of the “inner dielectric layer” may be smaller than the radius of the “outer dielectric layer”.
The term “the most inner dielectric layer” is used herein to describe a layer of the sleeve portion 150, which is the closest to the waveguide 130, that is which has the smallest radius of all dielectric layers of the sleeve portion 150. For example, at
The term “the most outer dielectric layer” is used herein to describe a layer of the sleeve portion 150, which is the furthest of the waveguide 130, that is which has the largest radius of all dielectric layers of the sleeve portion 150. For example, at
In at least one embodiment, impedance matching of the antenna 100 to the transmission line 120 may be achieved when a reflection coefficient of the antenna 100 is not greater than about −10 dB. For example, the power reflected from the antenna 100 back to the transmission line 120 may be not greater than about 10%.
In at least one embodiment, the antenna 100 as described herein may not require an impedance matching circuit in order to maximize the power transfer between the feed transmission line 120 and the antenna 100. In at least one embodiment, an input impedance of the antenna 100 may be matched to the impedance of the feed transmission line 120.
In at least one embodiment, the impedance matching (for example, when the reflection coefficient is not greater than about −10 dB) may be achieved at frequencies in a wide impedance matching frequency range. In at least one embodiment, the impedance matching may be achieved when the relative dielectric permittivity of the target material 115 is within the ranges described herein. For example, the impedance matching (for example, when the reflection coefficient is not greater than about −10 dB) may be achieved even when the properties of the target material 115 (e.g. relative dielectric permittivity) are changed. For example, the input impedance of the antenna 100 may remain matched to the feed transmission line 120 over an impedance matching frequency range. For example, the input impedance of the antenna 100 may remain matched to the feed transmission line 120 both when the target material 115 has a first relative dielectric permittivity and when the target material 115 has a second relative dielectric permittivity. For example, the input impedance of the antenna 100 may remain matched to the feed transmission line 120 for a wide range of target materials 115, where the type and/or properties of the target material 115 are as described herein.
For example, the properties of the target material 115 may be changed due to radiation of EM energy, by the antenna 100, into the target material 115. When the properties of the target material 115 change, the input impedance of the antenna 100 may remain matched to the feed transmission line 120.
In at least one embodiment, the input impedance of the antenna 100 may remain matched to the feed transmission line 120 when the antenna 100 radiates into two (or more) different types of target material 115. When the antenna 100 is inserted into the reservoir 110, the input impedance of the antenna 100 may remain matched to the feed transmission line 120 regardless of the type and/or properties of target material 115 in the reservoir 110.
The impedance of the antenna 100 may remain matched to the feed transmission line 120 over the impedance matching frequency range as described herein.
In at least one embodiment, the antenna's input impedance may be matched to the feed transmission line 120 in the presence of a wide range of target material 115 as described herein. In at least one embodiment, the input impedance of the antenna 100 may remain matched to the feed transmission line 120 over a wide frequency range, regardless of the type and/or properties (for example, relative dielectric permittivity) of the target material 115 in the reservoir 110. In at least one embodiment, the antenna 100 may be matched to a broad range of target materials 115 with dielectric and/or electrical properties as described herein. In at least one embodiment, the antenna's input impedance may continue to be matched to the feed transmission line 120 when the properties of the target material 115 change.
In at least one embodiment, the antenna 100 may be adapted to operate at a center frequency of about 30 MHz to about 10 GHz, of about 100 MHz to about 10 GHz, of about 1 GHz to about 3 GHz. For example, the bandwidth of the RF signal may be at least 10% of the center frequency.
In at least one embodiment, the impedance matching frequency range may be about 1 GHz wide, about 1.5 GHz wide, about 2 GHz wide, about 4 GHz wide, about 5 GHz wide. In at least one embodiment, the impedance matching frequency range may be about 2 GHz wide to about 3 GHz wide, about 1.7 GHz wide to about 3 GHz wide, about 1.8 GHz wide to about 3 GHz wide, about 2 GHz wide to about 4 GHz wide, about 2 GHz wide to about 5 GHz wide, about 1.5 GHz wide to about 5 GHz wide.
In at least one embodiment, the impedance matching frequency range may be at least about 2% of the center frequency, at least about 5% of the center frequency, at least about 10% of the center frequency, at least about 20% of the center frequency, at least about 50% of the center frequency.
For example, the impedance of the antenna 100 may be matched to the feed transmission line 120 due to the size and/or distribution of the slots 170.
In at least one embodiment, the slots 170 may be dimensioned (for example, length/height, thickness/width) and positioned (for example, distance between the slots and/or tilt angle) relative to each other such that a reflectivity coefficient of the antenna 100 may be less than about −10 dB.
As a further example, the slots 170 may be positioned and dimensioned such that the reflectivity coefficient of the antenna 100 may be less than about −5 dB.
In at least one embodiment, the thickness and properties (such as, for example, electrical and/or dielectric properties) of the dielectric layers of the sleeve portion 150 may help to achieve the reflection coefficient of the antenna 100 of lower than or about −10 dB.
In at least one embodiment, a combination of the sizes and properties of the dielectric layers of the sleeve portion 150 as well as sizes and shapes of the slots 170 may help to achieve the reflection coefficient of the antenna 100 of about or lower than −10 dB.
In at least one embodiment, the dielectric sleeve portion 150 may stabilize the impedance of the antenna 100 and reduce reflectivity, and therefore reduce the reflection coefficient of the antenna 100 with respect to changes in the properties of the processed target material 115, which surrounds the antenna 100 in the reservoir 110.
In at least one embodiment, the dielectric sleeve portion 150, together with appropriate distribution of slots 170, may form a system that allows for impedance matching over a wide impedance matching frequency range and for various target materials 115.
When RF antennas are designed for communication, the slot distribution and the slot size in such RF communication antennas may be designed to ensure appropriate far field radiation pattern and gain of the antenna 100, including radiation of full power (or at least 90% or at least 95%). The uniformity of radiation in the near field, as well as distribution of the electromagnetic field in the near field is typically not an issue for the RF antennas designed for communications and only a far field pattern is important. Near-field is a concept understood by those skilled in the art.
The antenna 100 as described herein, in at least one embodiment, needs to have a uniform radiation in the near field. Additionally, the antenna 100 needs to have low reflection (less than −10 dB) and full power radiation (or at least 90% or at least 95%). The slot size, slot distribution and slot positions may be designed to ensure all of the three objectives satisfied simultaneously. For example, the distribution of the slots 170 may be designed to ensure approximately uniform radiation intensity in the near field along the length of the antenna 100. The size and the shape of the slots 170 of the antenna 100 may be designed to ensure low disturbance and full radiation of the RF power by the time it reaches the output portion of the antenna 100, and to achieve the uniform radiation in the near field along the length of the antenna 100.
In at least one embodiment, the at least one slot 170 and at least one of the first and the second dielectric layers of the sleeve portion 150 may be dimensioned and/or positioned relative to each other such that the reflectivity coefficient of the antenna may be less than about −10 dB. In at least one embodiment, at least one of the first and the second dielectric layers of the sleeve portion 150 may have permittivity and thickness such that the reflectivity coefficient of the antenna 100 may be not greater than about −10 dB.
The impedance of the antenna 100 may be matched to the feed transmission line 120 due to the size and/or distribution of the slots 170, and/or the thickness and/or electrical or dielectric properties of the sleeve portion 150.
The antenna 100 as disclosed herein may operate in two different modes: (1) a resonant mode and (2) a traveling wave mode. When the wavelength in the target material 115 is longer or approximately equal to the wavelength of the EM wave in the waveguide dielectric layer 140 of the antenna 100, the antenna 100 may operate in the resonant mode. In this mode, a good match of the antenna 100 to the feed transmission line 120 is achieved over a large number of relatively narrow frequency bands. Central frequencies and bandwidths of those frequency bands may be controlled by adjusting the (1) slot distribution and density, (2) thickness of the dielectric layers of the dielectric sleeve portion 150 and (3) the EM properties of the dielectric layers of the dielectric sleeve portion 150.
When the wavelength of the EM wave in the target material 115 is shorter than the wavelength inside the antenna's waveguide dielectric layer 140, the antenna 100 may operate in the traveling mode. In this case, a good match of the antenna 100 to the feed transmission line 120 may be achieved over a single broad impedance matching frequency range. The thickness and the EM properties of the dielectric layers of the sleeve portion 150, as well as design of the slots 170, can affect the bandwidth of the antenna 100 in this case.
To achieve impedance matching for a broad range of target materials 115 (for example, from air to brine), the dielectric sleeve portion 150 and distribution of slots 170 in the antenna 100 may need to be designed such that impedance matching is achieved in both resonant and traveling wave modes.
The permittivity ratio may be calculated as a ratio of a permittivity (dielectric constant) of the target material 115 in the reservoir 110 to the permittivity (dielectric constant) of the waveguide dielectric layer 140.
In at least one embodiment, the antenna 100 may operate in a resonant mode when the permittivity ratio is less than or about 1.0. In at least one embodiment, the antenna 100 may operate in a travelling wave mode when the permittivity ratio is more than about 1.0.
To improve impedance matching of the antenna 100 to the transmission line 120, and to achieve the reflectivity of the antenna 100 of less than or about −10 dB over the impedance matched frequency range for the broadest range of target materials 115 as described herein, the at least two dielectric layers of the sleeve portion 150 may need to have thicknesses and permittivity as described herein.
In at least one embodiment, the thickness wi of at least one i-th dielectric layer of the dielectric sleeve portion 150 may be a function of a wavelength λ, where λ, is the wavelength of the electromagnetic wave in the waveguide dielectric layer 140.
For example, the thickness of the at least one dielectric layer of the dielectric sleeve portion 150 may be about λ/30 to about λ, about λ/15 to about λ/8, about λ/15 to about λ/4, about λ/30 to about λ/8, about λ/30 to about λ/4.
For example, the thickness of at least one dielectric layer may be approximately equal to a thickness factor k, multiplied by the wavelength of the electromagnetic wave in the dielectric material of the at least one dielectric layer: wi=k*λ. For example, the thickness factor k may be about 1/30 (about 0.03333) to about 1, about 1/15 (about 0.06667) to about ⅛ (about 0.125), about 1/15 (about 0.06667) to about ¼ (about 0.25), about 1/30 (about 0.03333) to about ⅛ (about 0.125), about 1/30 (about 0.03333) to about ¼ (about 0.25).
In at least one embodiment, the permittivity of the outer dielectric layer 154 of the sleeve portion 150 may be higher than the permittivity of the inner dielectric layer 152. For example, a wavelength of propagation in the outer dielectric layer 154 of the sleeve portion 150 may be shorter than the wavelength of propagation in the inner dielectric layer 152. For example, the permittivity of the outer dielectric layer 154 may be at least 20% higher than the permittivity of the inner dielectric layer 152.
In at least one embodiment, if the sleeve portion has more than two dielectric layers, the permittivity of any outer dielectric layer may be higher than the permittivity of any inner dielectric layer. For example, the permittivity of any outer dielectric layer may be at least 20% higher than the permittivity of any inner dielectric layer.
In at least one embodiment, a ratio of the permittivity of the outer dielectric layer 154 to the permittivity of the inner dielectric layer 152 may be about 2 to about 40, about 5 to about 40. For example, the most inner dielectric layer (152 or 252) may have the lowest permittivity of the dielectric layers of the sleeve portion 150 or 250. For example, the most outer dielectric layer (154 or 256) may have the highest permittivity of the dielectric layers of the sleeve portion 150 or 250.
In at least one embodiment, the most inner dielectric layer 152 or 252 may have the same EM characteristics, such as permittivity and/or conductivity, as the waveguide dielectric layer 140 or 240.
For example, at least one dielectric layer of the sleeve portion 150 may be air. For example, the most inner dielectric layer 152 or 252 may be air.
For example, when one of the dielectric layers is made of air, fixtures such as, e.g., centralizers may be used at the input and output portions the antenna 100 (and/or along the length of the antenna) to provide a certain radius of the dielectric layer made of air. The centralizers may be made of metal and/or dielectric materials.
In at least one embodiment, the permittivity of at least one dielectric layer of the dielectric sleeve portion 150 or 250 may be about 2 to about 20, about 5 to about 10, about 7 to about 20; about 2 to about 40; not greater than about 20; not greater than about 30; not greater than about 40; at least about 1.5; at least about 2; at least about 5; at least about 10. In at least one embodiment, at least one dielectric layer of the dielectric sleeve portion 150 (or 250) may be in immediate contact with the outer waveguide layer 145 (or 245) of the antenna 100.
For example, at least one dielectric layer of the dielectric sleeve portion 150 may be made of Teflon (PTEE), PEEK, fiberglass, glass, and/or different types of ceramics, such as, for example and not limited to, Alumina, Zirconia.
It should be understood that various other combinations of thicknesses and EM parameters of dielectric layers of the dielectric sleeve portion 150 may be used, especially if the antenna 100 is expected to operate in respect of a limited range of target materials 115.
When the target material 115 of the reservoir 110 is heated by the antenna 100, the antenna 100 may be in a direct contact with the heated target material 115, which may contain various liquids, sand grains, mud, steam etc. In at least one embodiment, the dielectric sleeve portion 150 may also protect the antenna 100 from the target material 115 in the reservoir 110. The most outer dielectric layer 154 (or 256) of the dielectric sleeve portion 150 (or 250) may need to seal the internal structure of the antenna 100 (or 200) and to protect it from the influence of target material 115 and processed target material 115 that are contained in the reservoir 110.
In at least one embodiment, the sleeve portion 150 may be made of the material that can tolerate temperature of about 300 degrees C. In at least one embodiment, the sleeve portion 150 may be made of the material that can tolerate temperature of about 100 degrees C.; of about 200 degrees C.; of about 300 degrees C.; of about 500 degrees C.; of about 1000 degrees C. In at least one embodiment, at least one of the dielectric layers of the dielectric sleeve portion 150 may be made at least in part of ceramic material. For example, the most outer dielectric layer 154 of the sleeve portion 150 may be made of ceramic material. For example, the ceramic material may withstand temperature as high as 1000 C and more and seal the internal structure of the antenna 100 from the influence of processed target material 115, or various target materials 115, that is/are contained in the reservoir 110. For example, the ceramic material may withstand steam.
In at least one embodiment, the length of the antenna 100 may be at least about two wavelengths of the EM wave inside the waveguide dielectric layer 140. For example, the antenna 100 may be long enough such that more than 80% of the RF power that passed through the input portion 190 of the waveguide 130, may be radiated before the EM wave (power) reaches the output portion 192 of the waveguide 130.
Referring again to
For example, the antenna 100 may radiate almost all of the EM power before the EM wave reaches the output portion 192 of the waveguide 130. In this case, the type of the termination 184 may not be important. For example, such operation mode may be possible in an example embodiment where the length of the antenna 100 is many wavelengths of the EM wave inside the waveguide dielectric layer 140 of the antenna 100.
In some exemplary embodiments, a small but significant portion of the EM power may reach the output portion 192 of the waveguide 130. In that case, the termination 184 may be important for the overall performance of the antenna 100. For example, a short termination 192 may reflect the EM wave with a reflection coefficient of −1. For example, an open termination 192 may reflect the EM wave with +1 reflection coefficient.
A matched termination (matched load termination) may not reflect anything, but may absorb all the EM power instead. In this case, the output portion 192 of the waveguide 130 may get heated at a rate that may be proportional to the EM power reaching it.
In at least one embodiment, the antenna 100 may have the same cross-sectional dimensions as the feed transmission line 120. For example, the diameter of the waveguide 130 may be approximately equal to the diameter of the feed transmission line 120. For example, the shape of the cross-section of the waveguide 130 may be the same as the shape of the feed transmission line 120. In at least one embodiment, the antenna 100 may have the waveguide 130 of the same type as the feed transmission line 120.
In at least one embodiment, the waveguide 130 of the antenna 100 may have the shape and/or the cross-sectional dimensions and/or the type different from the shape and/or cross-sectional dimensions and/or the type of the feed transmission line 120. In this case, an adaptor which may comprise a connecting transmission line may be used to connect the feed transmission line 120 and the antenna 100.
In at least one embodiment, the cross-sectional size of the feed transmission line 120 may be larger than the cross-sectional size of the waveguide 130 and/or antenna 100. In this case, a transition and/or adaptor may need to be used.
In at least one embodiment, the adapter may be a two port device, with a first port having the cross-sectional size and shape of the feed transmission line 120, and a second port having the cross-sectional size and shape of the waveguide 130. For example, the first port of the adapter may be operatively connected to the feed transmission line 120 and the second port of the adapter may be operatively connected to the input portion of the waveguide 190.
In at least one embodiment, the purpose of the adaptor may be to guide the EM wave from the feed transmission line 120 to the waveguide 130 with minimal reflection. For example, the reflection of less than −20 dB, i.e. the power reflection of less than 1%, may be required.
For example, the connecting transmission line may have a form of a tapered transition, a step transition, a quarter-wavelength transformer, or a combination thereof. For example, other types of the connecting transmission line may be used.
For example, if the system operates at an industrial frequency of 2.45 GHz, the feed transmission line 120 may be a WR-340 rectangular waveguide, while the antenna's waveguide 130 may be made of a 1⅝″ air-filled coaxial cable. In that case, a waveguide to coax adapter (WR-340 to EIA 1⅝″) may need to be used to connect the antenna 100 to the feed transmission line 120.
For example, in between of the first and the second port, a tapered coaxial cable may be used with the outer conductor being a truncated cone with lower radius and larger radius. For example, the adapter may be a step transition, i.e. a coax with a radius between r1 and r2, such that its characteristic impedance (Z3) satisfies Z3=sqrt(Z1*Z2), where Z1 and Z2 are characteristic impedances of the coax 1 and 2, respectively. The length of the transition coax may be a quarter of the wavelength.
For example, the adapter may have one or more steps. It should be noted that the adapter may have other designs.
In at least one embodiment, the antenna 100 may further comprise a flange 180 and/or a feed choke 182, positioned at the input portion of the waveguide 130. For example, the flange 180 and/or a thread may be used to connect the antenna 100 with the feed transmission line 120 or the connecting transmission line.
In at least one embodiment, no choke may be required to stop the leakage current from propagating along the outer walls of the feed transmission line 120.
Referring back to
Suppressing the leakage current may be especially important when the surrounding target material 115 is lossless or has a very low electrical loss, or when the target materials is expected to have very low electrical loss at some point during the operation of the antenna 100. In at least one embodiment, the choke 182, or the metal plate, may be positioned either on the feed transmission line 120 or on the antenna 100, for example, on the antenna's side of the flange 180 or of another connection used. In at least one embodiment, the choke 182 or the metal plate may be positioned closer to the feed transmission line 120 than the closest slot 170. In at least one embodiment, the antenna 100 may have no choke.
In at least one embodiment, the antenna 100 may operate as a monopole antenna if at least one portion of the reservoir 110 is made of a conductor (e.g. a metal) which acts as a ground plane. In such example of embodiment, the antenna 100 may not need a choke 182.
In at least one embodiment, the antenna 100 may comprise a plurality of segments. This may help to manufacture and to assemble the antenna 100.
Operation of Exemplary Implementations
In a first operational example, an antenna 100 with an a coaxial waveguide 130 with the waveguide dielectric layer 140 filled with air with a radius of the inner waveguide layer (135) of about 9.53 mm and a radius of the outer waveguide layer (145) of about 20.4 mm was analyzed in frequency range of 0 to 3 GHz. The length of the antenna (100) was about 560 mm, which corresponded to approximately 5.6 wavelengths at about 3 GHz. The antenna was terminated with a short circuit. The antenna's dielectric sleeve portion 150 had two ¼″-thick, cylindrical, concentric dielectric layers. The inner dielectric layer 152 (the layer immediately next to the waveguide) was air, while the outer dielectric layer 154 was alumina.
The reflection coefficient of the antenna 100 operating in sands with various degrees of moisture may be expected to fall between the solid and dashed lines shown in
For comparison,
A number of embodiments have been described herein. However, it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the embodiments as defined in the claims appended hereto.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4490727 | Kowols | Dec 1984 | A |
| 7182151 | Stump | Feb 2007 | B2 |
| 7194297 | Talpade et al. | Mar 2007 | B2 |
| 20080073079 | Tranquilla | Mar 2008 | A1 |
| 20140110395 | Parsche | Apr 2014 | A1 |
| 20140266951 | Okoniewski et al. | Sep 2014 | A1 |
| 20150322759 | Okoniewski | Nov 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 2895595 | Dec 2015 | CA |
| Entry |
|---|
| Mario Pauli et al., “Impedance Matching of a Coaxial Antenna for Microwave In-situ Processing of Polluted Soils”, retrieved from Journal of Microwave Power and Electromagnetic Energy, 45 (2), 2011, pp. 70-78. |
| International Search Report and Written Opinion dated May 10, 2017 in corresponding International Patent Application No. PCT/CA2017/050104. |
| Number | Date | Country | |
|---|---|---|---|
| 20170231035 A1 | Aug 2017 | US |
