JPH06337277A - Microwave detector - Google Patents

Abstract

PURPOSE:To provide a downsized microwave detector having simple constitution which can detect microwave quickly. CONSTITUTION:The microwave detector 15 is equipped with a first thermister 10 comprising a thermister element 11 connected with leads 12, 13. The leads 12, 13 are located at positions irradiated with microwave M so that high frequency current is induced upon irradiation with microwave to cause self-heating of the thermister element 11. When a second thermister 20 connected with leads for measuring the ambient temperature having same constitution as the first thermister 10 is disposed at a position close to the first thermister 10 but not irradiated with microwave, detection error can be removed when the ambient temperature is increased through radiation. When the leads 12, 13 are irradiated with microwave M, high frequency current is induced therein to cause self-heating of the thermister element 11 thus varying the resistance of the thermister 10.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a microwave detector having a thermistor with a lead. More specifically, the present invention relates to a microwave detector suitable for an automatic cooking sensor of a microwave oven or for various devices using microwaves.

[0002]

2. Description of the Related Art Conventionally, a detector of this type is provided in a high-frequency heating device and has a quarter of the oscillation frequency of a magnetron.
A thawing sensor has been proposed which includes an antenna shorter than the wavelength and a detection circuit for detecting the electric wave received by this antenna, and which detects the heating progress state of the object to be heated (Japanese Patent Laid-Open No. 1-248490). In addition, a thermistor whose impedance is matched to the waveguide is attached to the end of the waveguide, the transmission power of the waveguide is absorbed by this thermistor, and the microwave is detected from the temperature rise of the thermistor.
An ultra-high frequency power detector using a thermistor is disclosed (for example, “Thermistor and its application” by Hiroyoshi Kato, No. 10).
Pages 0 to 102, issued March 10, 1955, OHM
Paperback). Furthermore, the present applicant has applied for a patent for a microwave sensor having a radio wave absorber in the temperature sensing portion of the thermistor element (Japanese Patent Laid-Open No. 5-52889). This microwave sensor detects the temperature rise of the radio wave absorber caused by microwave irradiation with a thermistor.

[0003]

However, the above-mentioned decompression sensor requires a wave detection circuit, and has a drawback that the detection circuit becomes complicated. Further, the ultra-high frequency power detector using the thermistor has a problem that it cannot be downsized because it requires a waveguide. Further, since the microwave sensor is composed of a combination of a radio wave absorber and a thermistor, there is a problem that the thermal response is slow and the detection of microwaves is not quick as compared with the thermistor alone. An object of the present invention is to provide a microwave detector which has a simple structure, can be miniaturized, and can rapidly detect microwaves.

[0004]

As shown in FIGS. 1 and 3, the microwave detector 15 of the present invention includes a thermistor element body 1.
A first thermistor 10 with a lead, in which leads 12 and 13 are connected to 1, is provided. Its characteristic structure is the lead 1
2, 13 are provided at positions where the microwave M is irradiated,
This is because the thermistor element body 11 is configured to self-heat by inducing a high frequency current during microwave irradiation.

As shown in FIG. 3, if a second thermistor 20 with a lead for measuring an ambient temperature, which has the same structure as the first thermistor 10, is provided at a position near the first thermistor 10 where the microwave M is not irradiated, It is preferable because a detection error when the environmental temperature is rising due to radiant heat or the like can be eliminated. It is preferable that the thermistors 10 and 20 are bead type thermistors or glass-enclosed thermistors because the microwave detector can be downsized. Furthermore,
The leads 12, 13 and 22, 23 of the thermistors 10 and 20 are coated with 20 to 28% of Cu on the outside of a core of Ni58% and Fe42% alloy dumet wire (dumet).
It is preferable that the thermal expansion coefficient of the wire is close to that of the thermistor element body. The diameter of these leads is at least about 0.05 mm, and the length of the leads in the portion that receives microwaves is such that it is difficult for the leads to spark when receiving microwaves.

[0006]

When the leads 12 and 13 are irradiated with the microwave M, a high frequency current is induced in the leads 12 and 13. The high frequency current causes the thermistor element body 11 to self-heat,
The resistance value of the thermistor 10 changes. The output of the microwave detector is preferably detected by connecting each of the two thermistors 10 and 20 to an ohmmeter and converting each resistance of the thermistor into a temperature. The output of the microwave detector may be obtained from the voltage output by configuring a bridge circuit as shown in FIG.

When the angle φ formed by the wiring directions of the leads 12 and 13 with respect to the direction E of the linearly polarized electric field formed by the microwave M is in the range of 0 ° to 60 °, this angle φ is 0. The most high-frequency current is induced at 6 °,
At 0 °, the high frequency current decreases. When the angle exceeds 60 °, almost no high-frequency current flows and the microwave detection function deteriorates.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIGS. 1 and 3, the microwave detector 15 includes two thermistors 10 and 20 with leads and is attached to a window hole 31 of a housing 30 of a microwave oven. The thermistor 10 is arranged at a position where the microwave M is irradiated, and the thermistor 20 is arranged at a position for measuring the environmental temperature and where the microwave M is not irradiated. Specifically, the thermistors 10 and 20 are arranged in a printed circuit board 40 of a glass cloth epoxy substrate having a horizontally long square hole 41 formed in the center thereof so as to cut the square hole 41 vertically.

These thermistors 10 and 20 are small NTC bead type thermistors and have the same structure. Leads 12, 13 and 22, 23 made of a pair of dumet wires are connected to both ends of the bead-shaped thermistor bodies 11 and 21, respectively. In this example, these are GA13 series thermistors manufactured by Mitsubishi Materials Corp., the resistance value at 25 ° C. is 2 kΩ, and the B constant is 3470K. Thermistor body 1
1 and 21 are each 1.6 mm in diameter and 2.5 mm in length
And the total length of the thermistor including the lead is 20
mm.

The thermistor elements 11 and 21 are arranged at the center of the square hole 41 in the z direction, and the leads 12, 13 and 22,
Each end of 23 is soldered to the electrode pads 42 and 43 on the substrate 40, respectively. These leads 12, 13
22 and 23 are in the height direction of the microwave oven, that is, z in the figure.
They are arranged parallel to the direction (see FIG. 4, φ = 0 °). The portion of the leads 12 and 13 exposed from the square hole 41 is longer than the length of the square hole 51 of the box 50 described later in the z direction. Four enamel-coated leads 44 are soldered to the two sets of electrode pads 42 and 43 perpendicularly to the substrate 40.

The printed circuit board 40 on which the thermistors 10 and 20 are mounted is adhered to the bottom surface of the box 50 with an adhesive. The inside dimension of the box 50 is 40 mm in length, 40 mm in width, and 10 mm in thickness. The box 50 is selected from copper, stainless steel, aluminum or the like having good electric conductivity in order to have a function as a microwave shielding plate for the thermistor 20. In this example, it is made of aluminum. The bottom surface of the box 50 faces the inside of the microwave oven, and there is a square hole 51 smaller than the square hole 41 of the printed circuit board 40 for exposing only the thermistor 10.
Is formed. The square hole 51 has a length of 5 to 15 mm in the z direction (lead direction) of the drawing, and a length of 10 mm to the y direction of the drawing.
It is 30 mm. In this example, the size of the square hole 51 is 10 mm
(Z direction) × 15 mm (y direction).

The bottom surface of the box 50 is covered with a plate 60 from the outside. The plate 60 is a heat-resistant thin plate that transmits microwaves, and is selected from mica, Teflon, polystyrene and the like. In this example, it is mica. The plate 60 prevents water vapor, oil drops, etc. generated in the microwave oven from adhering to the thermistor 10. The opening of the box 50 is covered with a lid 70 made of an insulating material so that dust or the like does not enter the box and adhere to the thermistors 10 and 20. The lid 70 is the lead 44 described above.
Has four holes 71 having a diameter of 1 mm.

The microwave detector 15 is assembled by passing four bolts 81 through the four corners of the plate 60, the box 50 and the lid 70 and screwing them with nuts 82. The microwave detector 15 thus assembled is fitted into the window hole 31 of the housing 30 of the microwave oven having the same area as the outer shape of the detector. Specifically, the upper flange 34 and the lower flange 35 are fixed to the hole edge of the window hole 31 with screws 32 and 33. After inserting the box 50 into these flanges 34 and 35, the upper flange 34 and the lower flange 35 are attached to the upper surface and the lower surface of the box 50. Screws 36 and 3 through flanges 34 and 35, respectively
By tightening 7, the microwave detector 15 becomes a window hole 3
It is fixed to 1.

Next, the two pairs of leads 44, 44 drawn from the hole 71 of the lid 70 were connected to an ohmmeter (not shown). Then, the microwave M was applied to the microwave detector 15 from a magnetron of a microwave oven (not shown). Here, the output of the microwave oven was switched to four stages of 50 W, 100 W, 200 W and 460 W, and the microwave M was irradiated for 1 minute each. A high-frequency current was induced in these leads 12 and 13 by the irradiation of microwaves, and the thermistor element body 11 of the thermistor 10 self-heated according to the output of the microwave oven and its resistance value decreased. On the other hand, the thermistor 20
The resistance value of the thermistor element body 21 was decreased due to an increase in the environmental temperature near the thermistor 10. The resistance of the thermistors 10 and 20 was measured with a resistance meter, and the temperature was determined from the thermistor characteristics. The output of the detector is a value obtained by subtracting the temperature of the thermistor 20 from the temperature of the thermistor 10. The results are shown in FIG.

Further, the thermistor element body 1 of the thermistor 10
In order to check the degree of self-heating of No. 1, in the height direction of the microwave oven, that is, in the z direction (direction E of the electric field of the microwave M) in the figure.
The angle φ formed by the wiring directions of the leads 12 and 13 of the thermistor 10 with respect to is 0 ° shown in FIG. 4 and 4 shown in FIG.
Change the detector mounting angle to 5 ° and 90 ° (not shown), and set the output of the microwave oven to 50 W and 10
The microwave M was irradiated for 1 minute each by switching to four stages of 0 W, 200 W and 460 W. The results are shown in FIG. As is apparent from FIGS. 6 and 7, at φ = 0 ° and φ = 45 °, the output of the detector increases with the increase of the output of the microwave oven, although it is nonlinear. It was found that the detector 15 functions as a microwave detector. In the above example, in order to check the output of the detector, the resistance meter was connected to each of the two pairs of leads 44, 44, but the output of the detector may be measured by the bridge circuit shown in FIG. In this circuit, a resistor R ₁ is connected in series to the thermistor 10 and a resistor R ₂ is connected in series to the thermistor 20, and these are connected in parallel to form both terminals a and b as input terminals. The connection point B between the thermistor 10 and the resistor R ₁
Is connected to the terminal c, the terminal d is connected to the connection point C between the thermistor 20 and the resistor R ₂ , and both terminals c and d are output terminals.
By applying the DC voltage V _IN to the input terminals a and b and measuring the output voltage V _OUT of the output terminals c and d at this time, the difference in resistance between the two thermistors 10 and 20, that is, the substantial microwave. The temperature rise value due to is calculated.

[0016]

As described above, the conventional microwave detector requires a complicated detection circuit and a waveguide occupying a lot of space, whereas the microwave detector of the present invention has a basic structure. Since it is a thermistor with leads, it has an excellent effect that a simple circuit configuration requires a small space. In addition, since a high-frequency current is induced in the lead to cause the thermistor element to self-heat and the microwave intensity is detected from the amount of change in its resistance value, microwaves can be quickly generated unlike the detector using a conventional electromagnetic wave absorber. Can be detected.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a microwave detector according to an embodiment of the present invention.

FIG. 2 is a detection circuit diagram including the microwave detector.

FIG. 3 is an assembled perspective view of the microwave detector.

FIG. 4 is a view on arrow A in FIG.

5 is a view corresponding to FIG. 4 in which the microwave detector is tilted at 45 ° with respect to the z direction.

FIG. 6 is an output characteristic diagram of the microwave detector with respect to the output of the microwave oven.

FIG. 7 is an output characteristic diagram of the detector when the microwave detector is tilted with respect to the z direction.

[Explanation of symbols]

 M microwave E direction of electric field of microwave 10 first thermistor with lead 11 thermistor element 12, 13 lead 15 microwave detector 20 second thermistor with lead 21 thermistor element 22, 23 lead

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masami Koshimura 2270 Yokose, Yokose-cho, Chichibu-gun, Saitama Sanryo Materials Co., Ltd.

Claims (4)

[Claims] 1. A thermistor element body (11) is provided with a first thermistor (10) with leads, to which leads (12, 13) are connected, and the leads (12, 13) are irradiated with microwaves (M). A microwave detector provided at a position and configured to induce a high-frequency current when the microwave is applied to cause the thermistor element body (11) to self-heat. 2. A microwave in the vicinity of the first thermistor (10)
The second thermistor (2) with a lead having the same configuration as the first thermistor (10) for measuring the ambient temperature is provided at a position where (M) is not irradiated.
0) The microwave detector according to claim 1, wherein the microwave detector is provided. 3. The microwave detector according to claim 2, wherein the first and second thermistors (10, 20) are bead type thermistors or glass-enclosed thermistors. 4. The microwave detector according to claim 3, wherein the leads (12, 13) of the first thermistor (10) and the leads (22, 23) of the second thermistor (20) are each made of Dumet wire.