Dielectric heating is the process in which a high-frequency alternating electric field heats a dielectric material, such as water molecules. At higher frequencies, this heating is caused by molecular dipole rotation within the dielectric material, while at lower frequencies in conductive fluids, other mechanisms such as ion-drag are more important in generating thermal energy.
In dielectric heating, microwave frequencies are typically applied for cooking food items and are considered undesirable for drying laundry articles because of the possible temporary runaway thermal effects random application of the waves in a traditional microwave. Radio frequencies and their corresponding controlled and contained e-field are typically used for drying of textiles.
When applying an RF electronic field (e-field) to a wet article, such as a clothing material, the e-field may cause the water molecules within the e-field to dielectrically heat, generating thermal energy that effects the rapid drying of the articles.
In one aspect, the disclosure relates to a radio frequency (RF) applicator including an anode having multiple digits extending from an anode trunk, and a cathode having multiple digits extending from a cathode trunk and a gap in cathode trunk defining a space, the cathode encompassing the multiple digits of the anode. At least a subset of the anode digits and at least a subset of the cathode digits being interdigitated, and wherein the anode trunk passes through the space in the cathode.
In another aspect, the disclosure relates to a method of drying clothes using an e-field generated between an anode and cathode of a radio frequency (RF) applicator, the method including applying an RF signal to the anode having multiple digits extending from an anode trunk to form an e-field between the anode and cathode, the cathode having multiple digits extending from a cathode trunk and a gap in cathode trunk defining a space, the cathode encompassing the multiple digits of the anode, wherein at least a subset of the anode digits and at least a subset of the cathode digits being interdigitated, and wherein the anode trunk passes through the space in the cathode.
In the drawings:
While this description may be primarily directed toward a laundry drying machine, the invention may be applicable in any environment using a radio frequency (RF) signal application to dehydrate any wet article.
As illustrated in
The drying surface 22 may be in the form of a supporting body 18, such as a non-conductive bed, having an upper surface for receiving wet laundry and which forms the drying surface 22. Preferably, the drying surface 22 is a planar surface though other surfaces may be implemented.
A portion of the cathode element 16 may substantially encompass the anode element 14 to ensure, upon energizing of the RF generator 20, the formation of the e-field between the anode and cathode elements 14, 16 instead of between the anode element 14 and the Faraday cage 26.
The Faraday cage 26 may be a conductive material or a mesh of conductive material forming an enclosure that heavily attenuates or blocks transmission of radio waves of the e-field into or out of the enclosed volume. The enclosure of the Faraday cage 26 may be formed as the volume sealed off by a rectangular cuboid. The six rectangular faces of the cuboid may be formed as the four rigid walls 29, 31, 33, 35 lining the RF dryer 10, a bottom surface (not shown) and a top surface that is formed in the lid 27 of the RF dryer when the lid is in the closed position. Other geometrical configurations for the enclosure including, but not limited to, any convex polyhedron may be implemented and the example shown in
Referring now to
By controlling the spacing C of the anode element 14 and the cathode element 16 to be less than the spacing A, B of the cathode element 16 and the Faraday cage 26, the anode element 14 may be electrically shielded from the Faraday cage 26 with at least a portion of the cathode element 16.
Referring to
The cathode element 16 may further include at least one terminal 52, a first comb element 36 having a first trunk 38 from which extend a first plurality of digits 40 and a second comb element 42 having a second trunk 44 from which extend a second plurality of digits 46. The anode and cathode elements 14, 16 may be fixedly mounted to a supporting body 18 in such a way as to interdigitally arrange the first plurality of digits 32 of the anode element 14 and the first plurality of digits 40 of the first comb element 36 of the cathode element 16.
The anode and cathode elements 14, 16 may be fixedly mounted to the supporting body 18 in such a way as to interdigitally arrange the second plurality of digits 34 of the anode element 14 and the second plurality of digits 46 of the second comb element 42 of the cathode 16. Each of the conductive anode and cathode elements 14, 16 remain at least partially spaced from each other by a separating gap, or by non-conductive segments. The supporting body 18 may be made of any suitable low loss, fire retardant materials, or at least one layer of insulating materials that isolates the conductive anode and cathode elements 14, 16 and may also be formed with a series of perforations to allow for airflow through the anode and cathode elements. The supporting body 18 may also provide a rigid structure for the RF laundry dryer 10, or may be further supported by secondary structural elements, such as a frame or truss system. The anode and cathode elements 14, 16 may be fixedly mounted to the supporting body 18 by, for example, adhesion, fastener connections, or laminated layers. Alternative mounting techniques may be employed.
The anode and cathode elements 14, 16 are preferably arranged in a coplanar configuration. The first trunk element 38 of the cathode element 16 and the second trunk element 44 of the cathode element 16 will be in physical connection by way of a third interconnecting trunk element 48 that effectively wraps the first and second comb elements 36, 42 of the cathode element 16 around the anode element 14. In this way, the anode element 14 has multiple digits 32, 34 and the cathode element 16 encompasses the multiple digits 32, 34 of the anode element 14. The cathode trunk elements 38, 44, 48 and the digits 41, 47 proximal to the anode terminal 50 encompass the anode digits 32, 34. In a preferred embodiment of the invention, at least one of the digits of the cathode 16 encompasses the anode digits 32, 34. Additionally, the cathode element 16 has multiple digits 40, 46 with at least some of the anode digits 32, 34 and cathode digits 40, 46 being interdigitated.
The gap between the digits 41, 47 proximal to the anode terminal 50 form a space 66 in the cathode element 16. The trunk 30 of the anode element 14 from which the anode digits 32, 34 branch may pass through the space 66 in the cathode to connect to the terminal 50. At either side of the gap, the cathode element 14 may have a cathode terminal 52, 53 electrically coupled to ground 54.
The RF applicator 12 may be configured to generate an e-field within the radio frequency spectrum between the anode 14 and cathode 16 elements. The anode element 14 of the RF applicator 12 may be electrically coupled to an RF generator 20 and an impedance matching circuit 21 by a terminal 50 on the anode element 14. The cathode element 16 of the RF applicator may be electrically coupled to the RF generator 20 and an impedance matching circuit 21 by one or more terminals 52, 53, 55 of the cathode element 16. The cathode terminals 52, 53, 55 and their connection to the RF generator 20 and impedance matching circuit 21 may be additionally connected to an electrical ground 54. In this way, the RF generator 20 may apply an RF signal of a desired power level and frequency to energize the RF applicator 12 by supplying the RF signal to the portion of the anode passing through the gap in the cathode element 16. One such example of an RF signal generated by the RF applicator 12 may be 13.56 MHz. The radio frequency 13.56 MHz is one frequency in the band of frequencies between 13.553 MHz and 13.567 MHz, which is often referred to as the 13.56 MHz band. The band of frequencies between 13.553 MHz and 13.567 MHz is one of several bands that make up the industrial, scientific and medical (ISM) radio bands. The generation of another RF signal, or varying RF signals, particularly in the ISM radio bands, is envisioned.
The impedance matching circuit 21, by electrically coupling the RF generator 20 and the RF applicator 12 to each other, may provide a circuit for automatically adjusting the input impedance of the electrical load to maximize power transfer from the RF generator 20 to the RF applicator 12, where the electrical load is substantially determined by the wet textiles and the anode and cathode elements 14, 16. There are a number of well-known impedance matching circuits for RF applications including L-type, Pi-type, and T-type networks of which any may be implemented without limitation in an embodiment of the invention.
The aforementioned structure of the RF laundry dryer 10 operates by creating a capacitive coupling between the pluralities of digits 32, 40 and 34, 46 of the anode element 14 and the cathode element 16, at least partially spaced from each other. During drying operations, wet textiles to be dried may be placed on the drying surface 22. During, for instance, a predetermined cycle of operation, the RF applicator 12 may be continuously or intermittently energized to generate an e-field between the capacitive coupling of the anode and cathode digits which interacts with liquid in the textiles. The liquid residing within the e-field will be dielectrically heated to effect a drying of the laundry.
During the drying process, water in the wet laundry may become heated to the point of evaporation. As water is heated and evaporates from the wet laundry, the impedance of the electrical load; that is the impedance of the laundry and the RF applicator 12, may vary with respect to time as the physical characteristics of laundry load change. As previously described, the impedance matching circuit 21 may adjust the impedance of the electrical load to match the impedance of the RF generator 20 which typically holds at a steady value such as 50 Ohms. Also, as previously described, impedance matching may provide efficient transfer of power from the RF generator 20 to the RF applicator 12. To aid in the maximum power transfer of the power from the RF generator 20 to the RF applicator, the e-field must be formed between the anode and cathode elements 14, 16. Significantly, the anode element 14 should be shielded from the Faraday cage 26 to prevent unwanted electromagnetic leakage where some amount of the e-field is formed between the anode element 14 and the Faraday cage 26.
Cathode and anode connections 210, 212 respectively, may be provided along any of the digits of cathode and anode elements 116, 114. For example, as shown in
Additionally, the design of the anode and cathode may be controlled to allow for individual energizing of particular RF applicators in a single or multi-applicator embodiment. The effect of individual energization of particular RF applicators results in avoiding anode/cathode pairs that would result in no additional material drying (if energized), reducing the unwanted impedance of additional anode/cathode pairs and electromagnetic fields, and an overall reduction to energy costs of a drying cycle of operation due to increased efficiencies. Also, allowing for higher power on a particular RF applicator with wet material while reducing power on an RF applicator with drier material may result in a reduction of plate voltage and, consequently, a lower chance of arcing for an RF applicator.
For purposes of this disclosure, it is useful to note that microwave frequencies are typically applied for cooking food items. However, their high frequency and resulting greater dielectric heating effect make microwave frequencies undesirable for drying laundry articles. Radio frequencies and their corresponding lower dielectric heating effect are typically used for drying of textiles. In contrast with a conventional microwave heating appliance, where microwaves generated by a magnetron are directed into a resonant cavity by a waveguide, the RF applicator 12 induces a controlled electromagnetic field between the anode and cathode elements 14, 16. Stray-field or through-field electromagnetic heating; that is, dielectric heating by placing wet articles near or between energized applicator elements, provides a relatively deterministic application of power as opposed to conventional microwave heating technologies where the microwave energy is randomly distributed (by way of a stirrer and/or rotation of the load). Consequently, conventional microwave technologies may result in thermal runaway effects that are not easily mitigated when applied to certain loads (such as metal zippers, etc). Stated another way, using a water analogy where water is analogous to the electromagnetic radiation, a microwave acts as a sprinkler while the above-described RF applicator 12 is a wave pool. It is understood that the differences between microwave ovens and RF dryers arise from the differences between the implementation structures of applicator vs. magnetron/waveguide, which renders much of the microwave solutions inapplicable for RF dryers.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
This application claims priority to and is a continuation of U.S. patent application Ser. No. 13/974,092, filed Aug. 23, 2013, now U.S. Pat. No. 9,784,499, issued Oct. 10, 2017, which is incorporated herein by reference in its entirety.
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