JPH05172884A - Microwave detector - Google Patents

Abstract

(57) [Abstract] [Purpose] The structure is simple, the size is small, and the amount of microwave energy absorbed by an object to be heated is detected directly, easily, and accurately. Further, the electromagnetic wave absorption efficiency and heat dissipation are high, the response speed is excellent, and destruction due to discharge between terminal electrodes or between leads does not occur. [Structure] The bridge circuit 38 includes a microwave sensor 10 and a temperature sensor 50 which are provided in the heating chamber 17, respectively.
The output of the bridge circuit 38 is connected to the controller 30 that controls the magnetron 18 that generates microwaves toward the heating chamber 17. Microwave sensor 1
Reference numeral 0 is provided with a first radio wave absorber 12 that absorbs microwaves, and a first thermistor element 11 provided at a position of the radio wave absorber 12 that does not receive microwaves, and the temperature sensor 50 is a radio wave that reflects microwaves. The reflector 55 and the first reflector provided at a position where the microwave of the radio reflector 55 is not received.
Second thermistor element 5 having the same configuration as the thermistor element 11
1 and 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave detector suitable for detecting a heating condition or a finishing condition of an object to be heated in a microwave heating device such as a microwave oven.

[0002]

2. Description of the Related Art Microwave ovens are equipped with various functions such as a function for thawing frozen food by microwave heating and a function for warming cold food. The microwave oven automatically controls the output of a magnetron that generates microwaves by detecting the heating or finishing state of this type of food with a microwave detector. Conventionally, a microwave heating device is provided with a device for detecting a microwave transmitted or reflected without being absorbed by an object to be heated by using an antenna as a microwave detector for controlling the magnetron (for example, JP Sho 59
-207595, Same as 59-207596, Same as 62-79
394), which is provided with a humidity sensor for detecting water vapor generated from food in the exhaust duct (for example, Japanese Unexamined Patent Application Publication No. Sho 6-96).
2-123226) or a temperature sensor comprising a thermistor for detecting the temperature of the heating chamber (for example, JP-A-60-170188, JP-A-61-263092).
Etc. have been proposed.

However, in the case of detecting by the above microwave detecting device, the detection circuit is complicated and expensive, and the sensor is attached to the heating chamber, so that it is easily destroyed thermally, and the directivity of the antenna is strong and the object to be heated is heated. There is a problem that the detection output is easily affected by the shape of the object. Further, when the humidity sensor is used for detection, there is a problem that the heating condition cannot be accurately detected when the object to be heated is wrapped with wraps or aluminum foil. Further, when the temperature sensor is used for detection, the temperature sensor is far from the object to be heated, so that the temperature of the object to be heated cannot be directly measured, and the temperature sensor has a drawback that it is only a guide for cooking. In order to solve the above-mentioned various problems, the present applicant has applied for a patent for a microwave sensor having a radio wave absorber in the temperature sensing portion of a thermistor element and a microwave heating device using the same (Japanese Patent Application No. 3-2).
44449). As shown in FIG. 3, the microwave sensor 10 includes terminal electrodes 11 formed at both ends of the temperature sensing portion 11a.
The thermistor element 11 in which a pair of leads 11c are attached to b is made by immersing the radio wave absorber powder and an organic substance or an inorganic substance together with a resin, leaving the leads 11c, and immersing them in a coating liquid prepared. As a result, the temperature sensing portion 11a of the thermistor element 11 is covered with the substance 12a containing the radio wave absorber powder. This microwave sensor 10 directly detects the amount of microwave energy when the substance 12a generates heat when microwaves arrive and the resistance value of the thermistor element 11 changes. In the microwave heating device, the microwave sensor and a temperature sensor composed of a thermistor element that constitutes the sensor are provided side by side in the heating chamber, and the output of the bridge circuit including these microwave sensor and temperature sensor is directed to the heating chamber. Connected to a controller that controls the magnetron that generates microwaves.
Since the temperature of the heating chamber is detected by the temperature sensor, a voltage corresponding to the amount of microwave energy is substantially obtained in the bridge circuit.

[0004]

However, the microwave sensor manufactured by the above manufacturing method has the following points to be improved. First, the radio wave absorption efficiency is not high due to the presence of organic or inorganic substances. Second, since the outer shape is oval or spherical, the area for receiving microwaves is not wide enough and the heat dissipation is low, resulting in a slow response speed. Third, the leads are susceptible to microwaves, which can cause discharges between the leads and damage the sensor. Further, in the temperature sensor of the conventional microwave heating device, the leads are likely to receive the microwave as in the case of the microwave sensor, which causes discharge between the leads and the sensor is easily broken. In order to avoid this, if the temperature sensor is arranged at a position where the microwave of the heating chamber is not received, the temperature of the heating chamber detected by this temperature sensor and the temperature of the heating chamber detected by other than the microwave of the microwave sensor are substantially. However, there is a problem that it is difficult to obtain an accurate microwave energy amount from the bridge circuit. It is an object of the present invention to provide a microwave detector that can directly and easily detect the amount of microwave energy absorbed by an object to be heated and that has a simple structure and is small in size. Another object of the present invention is to provide a microwave detector which has a high electromagnetic wave absorption efficiency and a high heat dissipation property, an excellent response speed, and which is not damaged by discharge between terminal electrodes or between leads.
Still another object of the present invention is to provide a microwave detector capable of accurately detecting the amount of microwave energy from a bridge circuit.

[0005]

In order to achieve the above object, as shown in FIGS. 1 and 2, the present invention provides a bridge circuit 38 by a microwave sensor 10 and a temperature sensor 50 provided in a heating chamber 17, respectively. And the output of the bridge circuit 38 is connected to a controller 30 that controls the magnetron 18 that generates microwaves toward the heating chamber 17, and is the microwave detector of the microwave heating device.
The microwave sensor 10 has a first microwave absorption unit.
The temperature sensor 50 includes a radio wave absorber 12 and a first thermistor element 11 provided at a position that does not receive microwaves of the radio wave absorber 12, and the temperature sensor 50 includes a radio wave reflector 55 that reflects microwaves and a radio wave reflector 55. The second thermistor element 51 is provided at a position where the microwave is not received by the body 55 and has the same configuration as the first thermistor element 11.

The present invention will be described in detail below. In the microwave detector of the present invention, as shown in FIGS. 1 and 2, the microwave sensor 10 and the temperature sensor 50 form a bridge circuit 38. The microwave sensor 10 includes a first thermistor element 11 and a first radio wave absorber 12, and the temperature sensor 50 includes a radio wave reflector 55 and a second thermistor element 51 having the same configuration as the first thermistor element 11. First
And the second thermistor element includes a bead type, a disk type,
Known elements such as rod type, thick film type, thin film type, chip type, and electrode integrated type can be used. This radio wave reflector 55
Is a second electromagnetic wave absorber 52 having the same configuration as the first electromagnetic wave absorber 12.
And a surface 52a of the radio wave absorber 52 that receives microwaves.
It is preferable to provide a metal coating material 53 that reflects microwaves. This metal coating 53 is made of Al, Ag, Au,
1 or 2 selected from the group consisting of Cu, Pt and Pd
It is preferably a thin film composed of at least one kind of metal material. The electromagnetic wave absorbers 12 and 52 are formed in a flat plate shape having a larger area than at least the temperature sensing portions 11a and 51a of the thermistor elements 11 and 51, and one surface 12a of the electromagnetic wave absorber 12 is a microwave absorbing surface. It is preferable that the temperature-sensitive parts 11a and 51a of the thermistor elements 11 and 51 are bonded to the other surfaces 12b and 52b of the absorbers 12 and 52.

The radio wave absorber is preferably a ceramic having either or both magnetic properties and dielectric properties. The radio wave absorber 12 is formed by compressing and molding a ceramic powder of a magnetic material or a dielectric material into a flat plate with a binder and firing the compact, or by kneading the ceramic powder with a binder and a solvent to prepare a slurry. Like the bulk type thermistor element, this slurry is formed into a sheet, punched into a square plate or a disc, and fired to obtain a predetermined size. As the electromagnetic wave absorber having magnetism, there is ferrite or ceramics containing ferrite as a main component,
Dielectric wave absorbers include SiC, Al ₂ O ₃ ,
B ₄ C, SrTiO ₃ , ZrO ₂ , Y ₂ O ₃ , PZT and P
One or more ceramics selected from the group consisting of LZT can be mentioned. Further, as a radio wave absorber having both magnetism and dielectric property, disclosed in JP-A-1-291406 is a magnetic material powder containing ferrite fine powder having a particle size of 50 μm or less and BaTiO ₃ having a particle size of 10 μm or more.
A material obtained by mixing a dielectric material powder containing a perovskite-type compound as described above and firing the mixture at 1000 to 1500 ° C., forming a reaction phase between ferrite particles or between ferrite particles and perovskite-type compound particles. Then, ceramics having both a magnetic loss and a very large dielectric loss can be mentioned.

Microwave sensor 10 and temperature sensor 50
The manufacturing method of the temperature sensor 11 of the thermistor elements 11 and 51 is
a and 51a are flat wave absorbers 12 and 5 made of an insulating adhesive such as epoxy resin having excellent thermal conductivity and heat resistance
It is adhered to the one side 12b, 52b of No. 2. Thermistor element 1
If there is no lead in 1, 51, its terminal electrode 11b,
51b and leads 11 to the terminal electrodes 11b and 51b.
If the c and 51c are connected, this lead 11
The temperature sensitive parts 11a and 51a of the thermistor elements 11 and 51 are bonded to the positions where c and 51c do not receive microwaves, respectively. The temperature sensor 50 is further made by forming a thin metal coating material 53 on the surface 52a of the radio wave absorber 52 that receives microwaves by a vapor deposition method, a sputtering method, or the like. As shown in FIG. 2, the microwave sensor 10 and the temperature sensor 50 form a bridge circuit 38 together with the resistors 36 and 37, and the output of the circuit 38 is connected to the controller 30 that controls the magnetron 18. The microwave sensor of the present invention can be applied not only to a microwave heating device for home use such as a microwave oven but also to microwave detection of a microwave heating device for industrial use.

[0009]

When a high frequency radio wave arrives at the microwave sensor 10 and the temperature sensor 50, the metal coating material 53 reflects it at the temperature sensor 50, but the flat radio wave absorption surface 12a of the radio wave absorber 12 absorbs it. Generate heat. The thermistor element 51 that constitutes the temperature sensor 50 has an electric resistance value that changes depending on the temperature of the heating chamber due to radiant heat of the object to be heated. On the other hand, the thermistor element 1 that constitutes the microwave sensor 10
In No. 1, the electric resistance value changes due to heat generation corresponding to the microwave energy amount in addition to the temperature of the heating chamber. Radio wave absorber 12
Since is made of ceramics, it has high thermal conductivity, that is, high thermal responsiveness and excellent heat resistance. In particular, if a highly heat-resistant material such as SiC or Al ₂ O _{3 is} used, it will not be subjected to thermal shock even at high temperatures and will be highly reliable. Moreover, since the terminal electrodes 11b and 51b or the leads 11c and 51c are hidden behind the electromagnetic wave absorbers 12 and 52 and do not receive microwaves, destruction due to discharge does not occur between the electrodes or between the leads, and the microwave sensor 10 is Stable detection of wave energy.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIGS. 1 and 2, in this example, the microwave heating device is a microwave oven. A door 14 is provided on the front surface of the microwave oven main body 13 so as to be openable and closable, and an operation panel 16 is installed in the vicinity thereof. In addition to the cooking start switch 16a and the cooking stop switch 16b, the operation panel 16 includes a large number of cooking selection switches 16c, 16d, ..., 16
n and the like are provided. Further, the microwave sensor 10 and the temperature sensor 50, which have already been described in detail, are arranged side by side on the ceiling of the heating chamber 17 of the microwave oven. Both sensors 10 and 50 are provided with slits 15a and 15 formed in the frame 15 of the ceiling, respectively.
The leads 11c and 51c of both the sensors 10 and 50 are fixed to the heating chamber 17 in a.
It is provided at a position where microwaves from 8 are not received.

The thermistor elements 11 and 51 are glass-filled type elements each having a size of 1.4 mmφ × 1.5 mm, and are made of a sintered body of a metal oxide containing Mn, Co and Ni as main components. 11a and 51a, and leads 11c and 51c are soldered to both ends thereof. The resistance value of each of the thermistor elements 11 and 51 at 25 ° C. is 100 kΩ, and the B constant is 3960K.
Each of the radio wave absorbers 12 and 52 is a sintered body of SiC, and has a length of 10 mm, a width of 5 mm, and a thickness of 0.5 mm. One surface 12 of the radio wave absorbers 12, 52
The thermistor element 1 with the lead is provided in the center of b and 52b.
The temperature sensitive parts 11a and 51a of 1,51 are adhered by an epoxy resin. The other surface 12a of the radio wave absorbers 12, 52,
Reference numeral 52a is a surface that receives radio waves, and a vapor deposition film 53 of aluminum is formed on this surface 52a. A radio wave reflector 55 is configured by the radio wave absorber 52 and the vapor deposition film 53.

A magnetron 18 for generating a microwave of 2450 MHz is provided at the back of the heating chamber 17, and a blower fan 19 and a fan motor 20 are provided behind it. Beaker 2 with water at the bottom of heating chamber 17
A turntable 2 mounted with 1 and rotated by a motor 23
Two are provided. Intake port 2 near the fan motor 20
4, and an exhaust port 26 is provided in the ceiling of the heating chamber 17. As shown in FIG. 2, the microwave oven has a CP.
A controller 30 including U and memory is provided. .., 16n of the above-described cooking selection switches 16c, 16d, ..., 16n of the operation panel 16 are stored with the cooking program corresponding to the calorific value of the food to be heated. These switches 16c and 16 are used as inputs to the controller 30.
In addition to d, ..., 16n, switches 16a, 16b are connected. Further, a detection circuit 31 for detecting the heating status or the finishing status of the food 1 is connected to the input of the controller 30 via A / D converters 33 and 34.

The detection circuit 31 has a bridge circuit 38 in which a series circuit of the resistor 36 and the microwave sensor 10 and a series circuit of the resistor 37 and the temperature sensor 50 are connected in parallel.
And an amplifier 39 whose input terminals are connected to the output terminals A and B of the bridge circuit 38. The resistance values of the resistors 36 and 37 are the same as those of the thermistor elements 11 and 51.
It is kΩ. A DC power supply 41 is connected to the input terminal of the bridge circuit 38 via a current control resistor 40. The magnetron 18 described above is connected to the control output of the controller 30 via the drive circuit 42, and the motors 20 and 23 described above are connected to the control output of the controller 30 via the drive circuit 43.

Next, the amount of water in the beaker 21 is adjusted to 0, 100, 200, 3 by using the microwave oven configured as described above.
The voltage Vs between the terminals A and B of the bridge circuit 38 was measured when the voltage was changed in five steps from 00, 400 and 500 mL. The results are shown in Table 1.

[0015]

[Table 1]

As is clear from Table 1, the output voltage Vs decreased as the amount of water in the beaker 21 increased. Therefore, the amount of microwave energy reaching the microwave sensor 10, that is, the amount of microwave energy leaked without being absorbed by the object to be heated corresponds to the amount of water, and the sensor 10 accurately detects the microwave generated from the magnetron 18. You can see that Also, the leads 11c of the sensors 10 and 50,
Since 51c is provided at a position where microwaves are not received, no discharge occurs between the leads 11c and between the leads 51c,
Stable output was obtained.

[0017]

As described above, according to the microwave detector of the present invention, the amount of microwave energy is converted into heat energy by the radio wave absorber, and this is detected by the thermistor element. It is possible to directly and simply detect the amount of microwave energy absorbed by the. Since this microwave detector does not require an antenna or a waveguide as in the past, it has a simple structure and can be miniaturized. Further, since the radio wave absorber is made of ceramics, it has high thermal conductivity, that is, high thermal response, and excellent heat resistance. Especially SiC, Al ₂
If a high heat-resistant material such as O _{3 is} used, it will not be subject to thermal shock even at high temperatures and will be highly reliable. Further, since the thermistor element is hidden behind the electromagnetic wave absorber and does not receive the microwave, the microwave detector stably detects the microwave energy amount. Further, since the bridge circuit in which the microwave sensor and the temperature sensor are combined is used as the microwave detector, the temperature of the heating chamber can be measured as in the conventional case in addition to the microwave.
In particular, if a metal coating material is provided on the surface of the microwave absorber that constitutes the microwave sensor to receive microwaves to form a temperature sensor, the thermal effect from the ambient heat source of the microwave sensor can be removed, and as a result, the heated object It is possible to accurately detect heating or finish.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a microwave heating device including a microwave detector of the present invention.

FIG. 2 is a diagram showing the electric circuit configuration thereof.

FIG. 3 is a sectional view of a conventional microwave sensor.

[Explanation of symbols]

 10 microwave sensor 11,51 thermistor element 11a, 51a temperature sensing part 11b, 51b terminal electrode 11c, 51c lead 12,52 radio wave absorber 12a one side of radio wave absorber 12b, 52b other side of radio wave absorber 17 heating Chamber 18 Magnetron 30 Controller 50 Temperature sensor 52a Microwave receiving surface 53 Metal coating 55 Radio wave reflector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sakae Mori 2270 Yokoze, Yokose-cho, Chichibu-gun, Saitama Sanryo Materials Co., Ltd. Ceramics Laboratory

Claims (9)

[Claims] 1. A bridge circuit (3) comprising a microwave sensor (10) and a temperature sensor (50) respectively provided in a heating chamber (17).
8), and the output of this bridge circuit (38) is the heating chamber.
A microwave detector of a microwave heating device connected to a controller (30) for controlling a magnetron (18) that generates microwaves toward (17), wherein the microwave sensor (10) detects microwaves. First to absorb
A radio wave absorber (12) and a first thermistor element (11) provided at a position that does not receive microwaves of the radio wave absorber (12), and the temperature sensor (50) reflects microwaves Reflector
(55) and a second thermistor element (51) having the same structure as the first thermistor element (11) provided at a position where the microwave of the radio wave reflector (55) is not received. Microwave detector. 2. A second electromagnetic wave absorber (52) having the same structure as that of the first electromagnetic wave absorber (12), and this electromagnetic wave absorber (52).
The microwave detector according to claim 1, further comprising a metal coating material (53) for reflecting the microwave on a surface (52a) for receiving the microwave. 3. The electromagnetic wave absorber (12, 52) is formed in a flat plate shape having a larger area than at least the temperature sensing section (11a, 51a) of the thermistor element (11, 51), and the electromagnetic wave absorber (12) is One surface (12a) is a microwave absorbing surface, and the other surface (12b, 52b) of the radio wave absorber (12, 52) has a temperature sensing part (11a, 51a) of the thermistor element (11, 51). 3. The microwave detector according to claim 2, wherein) is bonded. 4. The microwave detector according to claim 2, wherein the radio wave absorber (12, 52) is made of ceramics having either or both magnetic properties and dielectric properties. 5. The microwave detector according to claim 4, wherein the magnetic ceramics is ferrite. 6. The dielectric ceramic is SiC,
Al ₂ O ₃ , B ₄ C, SrTiO ₃ , ZrO ₂ , Y ₂ O ₃ , P
The microwave detector according to claim 4, which is one or more ceramics selected from the group consisting of ZT and PLZT. 7. The microwave detector according to claim 4, wherein the ceramic having both magnetism and dielectric properties is a composite of ferrite and BaTiO ₃ . 8. The metal coating material (53) is made of Al, Ag, Au, C.
The microwave detector according to claim 2, wherein the microwave detector is made of one or more metal materials selected from the group consisting of u, Pt, and Pd. 9. The microwave detector according to claim 2, wherein the metal coating material (53) is a thin film.