Cooking appliance and method for operating a cooking appliance

Abstract

Cooking appliance (10) with a cooking chamber (12), at least one microwave source (16), a control and evaluation unit (28) and at least one antenna (18) for supplying microwaves (23), wherein the control and evaluation unit (28) controls the polarization (24, 26) of the microwaves (23) supplied into the cooking chamber (12), characterized in that a polarization-sensitive sensor (30) is provided which is coupled to the control and evaluation unit (28) and detects the polarization direction (24, 26) of the microwave radiation within the cooking chamber (12), and wherein the control and evaluation unit (28) detects the microwave absorption of a food being cooked (14) by measurements via the polarization-sensitive sensor (30).

Description

[0001] The invention relates to a cooking appliance for preparing food and a method for operating a cooking appliance.

[0002] Cooking appliances used in commercial or professional kitchens may have a microwave source that couples microwaves into a cooking chamber. These microwaves can be used for research purposes or to cook food in the chamber, at least as a supplement to another cooking method. The microwaves emitted by the microwave source are typically fed into the cooking chamber via an antenna. From the antenna, the microwaves strike the food being cooked and are absorbed or partially reflected. The reflected microwaves are then reflected again by the inner walls of the cooking chamber before striking the food once more and being at least partially absorbed.

[0003] It is known that the microwaves emitted by the antenna are not distributed homogeneously within the cooking chamber, resulting in uneven heating of the food. Food located close to the antenna is exposed to a higher concentration of microwaves, shielding food further away. Therefore, it is known from the prior art to use a stirrer located within the cooking chamber to swirl the microwave field generated by the input microwaves. This is intended to create a more uniformly distributed microwave field within the cooking chamber, thus ensuring more homogeneous cooking of the food.

[0004] From US patent 2014 / 0063676A1, a cooking appliance is known which has an antenna system with multiple antennas, each of which, due to its geometry, can feed differently polarized microwave beams into a cooking chamber.

[0005] DE 10 2014 104 796 A1 shows a cooking accessory that is sensitive to polarization.

[0006] From US patent 2012 / 0152939A1, a cooking appliance is known which has a control that controls the polarization of the supplied microwave beams.

[0007] US Patent 6 884 979 B1 describes a cooking appliance that can adjust the polarization of the supplied microwaves by changing the orientation of the antennas.

[0008] The object of the invention is to improve the homogeneous heating of the food being cooked using microwave energy.

[0009] The object of the invention is achieved by a cooking appliance comprising a cooking chamber, at least one microwave source, a control and evaluation unit, and at least one antenna for supplying microwaves, wherein the control and evaluation unit controls the polarization of the microwaves supplied to the cooking chamber, in particular selectively changing the polarization direction of the supplied microwaves, wherein a polarization-sensitive sensor is provided which is coupled to the control and evaluation unit and detects the polarization direction of the microwave radiation within the cooking chamber. The control and evaluation unit detects the microwave absorption of food being cooked by measurements via the polarization-sensitive sensor.

[0010] The basic idea of ​​the invention is to selectively change the polarization of the microwaves fed into the cooking chamber in order to selectively influence the absorption and reflection behavior of the food being cooked. It is known that the absorption of incident microwaves by the surface of the food being cooked depends strongly on the polarization direction of the microwave electric field with respect to the surface of the food. This effect can be selectively used by the control and evaluation unit to selectively modify the local effect of the injected microwaves. The change in the absorption and reflection behavior of the food when the polarization of the injected microwaves is altered occurs particularly when the microwaves strike the surface of the food at a large angle.Especially in larger cooking chambers, the concept of incident waves can be applied, and cooking appliances used in commercial or professional kitchens typically have such a chamber. For example, the polarization direction of the input microwaves, particularly the linear polarization, can be changed from a parallel orientation to a perpendicular polarization direction to reduce the absorption of the input microwaves by the surface of the food being cooked. This correspondingly increases the reflection at the surface of the food, allowing the cooking result to be specifically influenced by changing the polarization.

[0011] The polarization-sensitive sensor detects the microwaves reflected from the surface of the food being cooked, thus providing information about the food's absorption characteristics. This polarization-sensitive sensor can be an antenna. For example, it can be an antenna that also serves to feed microwaves into the cooking chamber. This antenna can then be called a measuring antenna. For this purpose, it is made polarization-sensitive. The polarization of the microwaves is determined by the antenna that has been repurposed as a measuring antenna.

[0012] The microwaves fed in by at least one antenna exhibit linear polarization. This polarization refers to the electric field component of the microwaves.

[0013] In general, the polarization direction of the microwaves emitted by the antenna can be adjusted via the geometry of the respective antenna, in particular the linear polarization.

[0014] Furthermore, the control and evaluation unit can regulate the polarization of the supplied microwaves based on the data acquired by the sensor. This allows for more homogeneous heating of the food, as the microwave absorption of the food can be determined based on the detected microwaves within the cooking chamber. Based on this, the control and evaluation unit can influence the polarization direction of the supplied microwaves to selectively modify the absorption behavior of the food. This ensures that less absorbent areas of the food are supplied with polarized microwave radiation, thereby increasing energy input, and vice versa.

[0015] Another aspect involves at least two antennas, positioned on opposite sides of the cooking chamber or on a shared side. The more antennas are provided, the more precisely the cooking chamber can be monitored with spatial resolution, and the more accurately the microwaves can be directed onto the food being cooked. Furthermore, microwaves with mutually orthogonal polarization directions can be fed into the cooking chamber via the two antennas. This is particularly important when the two antennas are located on the same side of the cooking chamber. This ensures that the food on that side of the cooking chamber can be cooked with both a first polarization direction and a second polarization direction perpendicular to the first, resulting in correspondingly different absorption characteristics.The polarization direction of the injected microwaves can be adjusted via the geometry of the antennas.

[0016] In particular, at least one antenna is designed to feed in microwaves of a first polarization direction as well as microwaves of a second polarization direction, which is perpendicular to the first polarization direction. This reduces the number of antennas required, as only one antenna is needed per side of the cooking chamber to feed microwaves with mutually perpendicular polarization directions into the cooking chamber. With only one antenna per side of the cooking chamber, the cooking result can thus be influenced by a targeted change in the polarization of the fed-in microwaves. Such an antenna typically has two connections. Depending on the selected active connection, through which the microwaves emanating from the microwave source are fed to the antenna, microwaves with a defined polarization direction are fed from the antenna into the cooking chamber.

[0017] Furthermore, the object of the invention is achieved by a method for operating a cooking appliance of the aforementioned type, wherein the polarization of the supplied microwaves is controlled by the control and evaluation unit, in particular the polarization direction is selectively changed. The polarization of the microwave radiation within the cooking chamber is processed by the control and evaluation unit to determine the microwave absorption of the food being cooked. This makes it possible to cook the food in the cooking chamber homogeneously by actively changing or rotating the polarization direction of the supplied microwaves in order to selectively influence the absorption or reflection behavior of the food.

[0018] The microwave absorption of the food being cooked can be monitored based on the polarization direction of the microwaves. This makes it possible not only to control but also to regulate the microwave input, as the polarization direction is adjusted based on the microwave absorption of the food being cooked, which is indirectly detected by a sensor, in order to obtain a desired microwave absorption value.

[0019] The polarization of the injected microwaves can be changed to reduce microwave absorption by food near the at least one feeding antenna. By changing the polarization direction from parallel to perpendicular, absorption by the food can be significantly reduced when the injected microwaves are at an angle. This makes it possible to decrease the absorption of food located directly adjacent to the feeding antenna, so that food located further away from the feeding antenna is exposed to a relatively higher microwave energy.

[0020] Furthermore, the amount of food being cooked can be determined based on the polarization of the microwave radiation within the cooking chamber. For this purpose, the polarization direction of the reflected microwaves is analyzed, whereby the amount of food being cooked within the chamber can be determined with spatial resolution if multiple sensors are provided, which are specifically assigned to certain areas of the cooking chamber.

[0021] Another aspect allows the type of food being cooked to be determined based on the polarization of the microwave radiation within the cooking chamber. This is because the absorption and reflection properties of the injected microwaves depend on the surface of the food. Flat or liquid foods have a relatively even surface, resulting in homogeneous reflection across the entire surface. This can be determined based on the polarization and intensity of the reflected microwaves.

[0022] In particular, the cooking process can be determined based on the polarization of the microwave radiation within the cooking chamber. This can be observed, among other reasons, because the surface of the food changes depending on its state, resulting in altered polarization of the reflected microwaves. For this purpose, the data acquired by the control and evaluation unit can be stored in a memory, allowing the stored values ​​to be compared and trends to be evaluated. This enables monitoring of the cooking process.

[0023] In general, the polarization direction of the electric field component of microwaves is important.

[0024] Further advantages and features of the invention will become apparent from the following description and the drawings, to which reference is made. The drawings show: - Fig. 1 a schematic representation of a cooking appliance according to the invention in a first embodiment, - Fig. 2 a reduced schematic representation of a cooking appliance according to the invention in a second embodiment, - Fig. 3. A diagram of the absorption of polarized microwaves at a food surface as a function of the angle of incidence. - Fig. 4 a schematic representation of an incident microwave with a second polarization direction, and - Fig. 5 a schematic representation of an incident microwave with a first polarization direction.

[0025] In the Fig. Figure 1 shows a cooking appliance 10 which has a cooking chamber 12 in which food 14 can be cooked.

[0026] Furthermore, the cooking appliance 10 has at least one microwave source 16 which generates microwaves to cook the food 14 located in the cooking chamber 12. The microwaves generated by the microwave source 16 are fed into the cooking chamber 12 via antennas 18, which are either located in the cooking chamber 12 or directly adjacent to it.

[0027] Microwave source 16 could, for example, be a magnetron.

[0028] In the first embodiment shown, two antennas 18 are arranged on opposite sides 20 and 22 of the cooking chamber. Each of the two antennas 18, assigned to one of the two sides 20 and 22, can feed microwaves 23 with a first polarization direction 24 or microwaves 23 with a second polarization direction 26 into the cooking chamber 12. Thus, the cooking appliance 10 shown has an antenna arrangement with four channels, since four antennas 18 are provided.

[0029] The polarization direction of the microwaves 23 fed in by the antennas 18 depends on the design of the antennas 18, in particular their geometry.

[0030] The cooking appliance 10 further comprises a control and evaluation unit 28, which can be coupled to the microwave source 16 and / or to the antennas 18 in order to actively control the polarization of the microwaves 23 fed into the cooking chamber 12 by the control and evaluation unit 28 controlling the respective antenna 18, so that the controlled antenna 18 is supplied with microwaves 23 via the microwave source 16, which the antenna 18 can feed into the cooking chamber 12.

[0031] For example, the microwave source 16 can be coupled to the antennas 18 in such a way that the control and evaluation unit 28 enables or blocks the microwave radiation supplied to the antennas 18 by the microwave source 16. This requires that the antennas 18 are controlled synchronously. The polarization is controlled by the difference in phase and amplitude of the respective signals at the antennas 18. Depending on whether the antennas 18 are enabled or blocked, which, due to their design or geometry, feed in a specific polarization direction, the control and evaluation unit 28 can selectively control the polarization of the microwaves 23 fed into the cooking chamber 12.

[0032] The microwave radiation emitted by the microwave source 16 is modulated by the antennas 18 into linearly polarized microwaves 23 due to their design, so that the microwaves 23 fed into the cooking chamber 12 have a specific polarization 24, 26. The polarization of the microwave radiation is defined when emitted by the antennas 18. In the feed line to the antennas 18, the polarization of the microwave radiation is neither relevant nor defined.

[0033] The microwaves 23 fed in by the antennas 18 strike the surface of the food 14 and are absorbed or reflected differently by the food 14 depending on their polarization direction and the angle of incidence on the surface. This is in the Fig. Figure 3 shows a diagram illustrating the absorption of microwaves as a function of the angle of incidence of the microwaves on the surface of the food being cooked.

[0034] The diagram shows the absorption behavior of microwaves of the first polarization direction 24, which corresponds to a parallel polarization direction of the electric field, and of microwaves of the second polarization direction 26, which corresponds to a perpendicular polarization direction of the electric field.

[0035] From the Fig. Figure 3 clearly shows that the absorption properties differ considerably at a large angle of incidence of the microwaves on the surface of the food being cooked, since in the first polarization direction 24 (parallel) the microwave radiation is almost completely absorbed by the food being cooked 14, whereas in the second polarization direction 26 (perpendicular) the microwave radiation is almost not absorbed by the food being cooked 14 and is therefore almost completely reflected.

[0036] The impact of the injected microwaves 23 with the first polarization direction 24 or the second polarization direction 26 on the surface of the food being cooked 14 is in the Fig. 4 and Fig. Figure 5 is shown schematically. In the two figures, the injected microwaves 23 are represented by their electric field component E, their magnetic field component H, and the wave propagation direction k. Furthermore, the food being cooked 14 is partially shown, and the surface of the food being cooked is shown in certain areas, by the normal n perpendicular to the surface of the food being cooked.

[0037] In the Fig. 4. The electric field component E of the injected microwave 23 is polarized perpendicular to the plane formed by the normal n and the vector k of the wave propagation direction. In contrast, the electric field component E of the injected microwave 23 is polarized in the Fig. 5 is polarized parallel to the corresponding plane formed by n and k. The food 14, with its surface, corresponds at least partially to the plane to which the normal n is perpendicular.

[0038] Furthermore, the cooking device 10 has a polarization-sensitive sensor 30, which is arranged in the cooking chamber 12.

[0039] The polarization-sensitive sensor 30 is coupled to the control and evaluation unit 28 and detects the microwave radiation present in the cooking chamber 12, in particular the microwaves reflected by the food being cooked 14. The polarization-sensitive sensor 30 can specifically detect the polarization direction of the electric field of the microwaves present in the cooking chamber 12.

[0040] Alternatively or additionally, the polarization-sensitive sensor 30 can be one of the antennas 18, which, depending on the circuit, functions as a feed-in antenna 18 or as a polarization-sensitive sensor 30 via the control and evaluation unit 28. Accordingly, the four-channel antenna arrangement can be used not only for feeding in the microwaves but also for measuring the microwaves within the cooking chamber 12.

[0041] Depending on the design or geometry of the respective antenna 18, it can only detect microwaves with a polarization direction corresponding to its geometry.

[0042] Furthermore, the cooking device 10 can have a memory 32, which is also coupled to the control and evaluation unit 28. The data acquired by the sensors 30 can be stored in the memory 32. The control and evaluation unit 28 can access the memory 32 to extrapolate the acquired data and generate trends.

[0043] In general, the control and evaluation unit 28 controls the polarization of the supplied microwaves 23 based on the data acquired by the sensor 30, so that the microwave absorption of the food 14 can be inferred from the microwave reflection of the food 14. The more sensors 30 are provided in the cooking chamber 12, the more spatially resolved the microwave absorption of the food 14 can be determined.

[0044] Should the control and evaluation unit 28 detect that a food item 14 located near a feeding antenna 18 has high microwave absorption, the control and evaluation unit 28 can switch on the other antenna 18 on that side 20, 22 of the cooking chamber and switch off the previous antenna 18 or interrupt its microwave supply. As a result, microwaves 23 now being fed to the food item 14 with a different polarization direction, perpendicular to the previous polarization direction, strike the food item 14, causing it to exhibit a changed microwave absorption (see Fig. 3).

[0045] For example, the food 14 located close to the feed antenna 18 is initially cooked with microwaves 23 of the first polarization direction 24. Due to the high absorption of the food 14 located close to the feed antenna 18, the remaining food 14, located further away, is effectively shielded from the fed microwaves 23 and has absorbed correspondingly fewer microwaves.

[0046] To still achieve a homogeneous cooking result, the control and evaluation unit 28 switched off the initially feeding antenna 18 and switched on the other antenna 18, which is assigned to the same side 20, 22 of the cooking chamber. Microwaves of the second polarization direction 26 now strike the food 14 located directly on the corresponding side 20, 22 of the cooking chamber. The absorption behavior of the food 14 is correspondingly worse due to the deliberately changed polarization direction of the fed microwaves 23. Because of the lower microwave absorption, the fed microwaves 23 of the second polarization direction 26 are reflected more strongly by the directly adjacent food 14, which results in the food 14, which is located further away from the feeding antenna 18, being exposed to higher microwave energy, thus cooking it more thoroughly.

[0047] Overall, this makes it possible to cook all the food 14 more homogeneously within the cooking chamber 12. For this purpose, the polarization direction of the supplied microwaves 23 is specifically controlled, whereby the microwave absorption of the food 14 can be detected by measurements via the sensors 30, in particular the antennas 18.

[0048] Furthermore, the cooking appliance 10 can determine the load within the cooking chamber 12, since the detected polarization direction of the microwaves in the cooking chamber 12 allows conclusions to be drawn about the distribution of the food 14 within the cooking chamber 12 and thus about the load. For this purpose, a good spatial resolution is particularly useful, which can be ensured by several sensors 30.

[0049] Furthermore, the type of food being cooked 14 can be determined using the polarization direction of the microwaves reflected and detected by sensor 30 within the cooking chamber 12. For example, a liquid food 14 has a substantially homogeneous surface, which has a correspondingly homogeneous reflection behavior. In contrast, a solid food 14 would have a scattering reflection behavior of the microwaves, which would be detected by the control and evaluation unit 28 when the microwaves in the cooking chamber 12 are detected. In general, the scattering of the supplied microwaves 23 is sensitive to the orientation of the food 14 in the cooking chamber 12 and to its surfaces, which serve as reflective surfaces. This is particularly evident from the Fig. 3, in which absorption is shown as a function of the angle of incidence.

[0050] Furthermore, the polarization of microwave radiation detected by the sensors 30 within the cooking chamber 12 allows conclusions to be drawn about the state of the food being cooked 14, since a change in state alters the surface of the food. This is evident, for example, in a corresponding change in the absorption or reflection behavior of the food being cooked 14, which is detected by the sensor 30 and evaluated by the control and evaluation unit 28.

[0051] The targeted control of the supplied microwaves 23 and the measurement of the microwaves within the cooking chamber 12 is possible because the typically used wavelength of the supplied microwaves 23 has a frequency of approximately 2.45 GHz, which corresponds to a free wavelength of approximately 12.2 cm. This free wavelength is relatively small compared to the dimensions of the cooking chamber 12 in cooking appliances 10 used in professional or commercial kitchens, thus enabling targeted control.

[0052] In the Fig. Figure 2 shows a second embodiment of the cooking device 10 in a reduced schematic representation, in which essentially the cooking chamber 12 of the cooking device 10 is shown.

[0053] In this embodiment, each side 20, 22 of the cooking chamber is assigned only one antenna 18. This antenna 18 is designed such that it can feed both microwaves 23 with the first polarization direction 24 and microwaves 23 with the second polarization direction 26 into the cooking chamber 12. For this purpose, each antenna 18 has two connections through which microwaves are supplied to the antenna 18. The two connections of the antenna 18 are each connected to a line 34, 36.

[0054] In addition, each of the lines 34, 36 has a switch 38, 40 which can be controlled by the control and evaluation unit 28, so that only microwaves are supplied to the antenna 18 via the first connection or the second connection.

[0055] Depending on the connection controlled by the control and evaluation unit 28, the antenna 18 feeds in microwaves 23 with the first polarization direction 24 or the second polarization direction 26. If the other of the two connections has been activated by the control and evaluation unit 28, microwaves with the second polarization direction 26 or the first polarization direction 24 are fed in via the antenna 18.

[0056] By activating lines 34 and 36, particularly via switches 38 and 40, the control and evaluation unit 28 can selectively control or change the polarization of the injected microwaves 23, since the polarization of the injected microwaves 23 changes due to the activation of the antenna 18 connection. The polarization direction orthogonal to that activated by the control and evaluation unit 28 is largely suppressed.

[0057] The one in Fig. The antenna arrangement of the cooking appliance 10 shown in Figure 2 is therefore designed as a two-channel antenna, wherein each of the two antennas 18 is able to feed in and detect microwaves with both polarization directions 24, 26, provided that the antennas 18 function as polarization-sensitive sensors 30.

[0058] The antenna arrangement of a cooking appliance 10 can also be multi-channel. It is only important that each side of the cooking chamber 12 is assigned antennas 18 in such a way that the food 14 can be exposed to both mutually perpendicular polarization directions 24, 26 from each side of the cooking chamber.

[0059] According to the invention, a cooking appliance 10 is thus created which has a control and evaluation unit 28 that selectively controls or changes the polarization direction 24, 26 of the microwaves 23 fed into the cooking chamber 12 in order to enable homogeneous cooking of the food 14 in the cooking chamber 12. The cooking appliance 10 controls the polarization direction 24, 26 of the microwaves present in the cooking chamber 12, i.e., the reflected microwaves, and also actively controls the polarization direction 24, 26 of the fed-in microwaves 23. In particular, the control and evaluation unit 28 can regulate the polarization direction 24, 26 of the fed-in microwaves 23 in order to obtain a desired microwave absorption value of the food 14.

Claims

[1] Cooking appliance (10) with a cooking chamber (12), at least one microwave source (16), a control and evaluation unit (28) and at least one antenna (18) for supplying microwaves (23), wherein the control and evaluation unit (28) controls the polarization (24, 26) of the microwaves (23) supplied into the cooking chamber (12), characterized by , that a polarization-sensitive sensor (30) is provided which is coupled to the control and evaluation unit (28) and detects the polarization direction (24, 26) of the microwave radiation inside the cooking chamber (12), and wherein the control and evaluation unit (28) detects the microwave absorption of a cooking food (14) by measurements via the polarization-sensitive sensor (30). [2] Cooking appliance (10) according to claim 1, characterized by , that the control and evaluation unit (28) controls the polarization (24, 26) of the injected microwaves (23) depending on the data recorded by the sensor (30). [3] Cooking appliance (10) according to any one of the preceding claims, characterized by , that at least two antennas (18) are provided, which are assigned to opposite sides of the cooking chamber (20, 22) or to a common side of the cooking chamber (20, 22). [4] Cooking appliance (10) according to any one of the preceding claims, characterized by , that at least one antenna (18) is designed such that it can feed in microwaves (23) of a first polarization direction (24) as well as microwaves (23) of a second polarization direction (26) perpendicular to the first. [5] Method for operating a cooking appliance (10) according to one of the preceding claims, wherein the polarization (24, 26) of the supplied microwaves (23) is controlled by the control and evaluation unit (28), characterized by , that the polarization (24, 26) of the microwave radiation within the cooking chamber (12) is processed by the control and evaluation unit (28) to determine the microwave absorption of the food being cooked (14). [6] Method according to claim 5, characterized by , that the type of food being cooked (14) is determined based on the polarization (24, 26) of the microwave radiation within the cooking chamber (12). [7] Method according to claim 5 or 6, characterized by , that the state of the food being cooked (14) is determined due to the polarization (24, 26) of the microwave radiation within the cooking chamber (12).

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