JP2001255224A - Physical quantity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a physical quantity sensor detecting the physical quantity in a distal place. SOLUTION: A magnetic field is generated in a coil 12 by an oscillation output from an external oscillator 10, the ambient temperature of a coil 13 is converted into frequency by a physical quantity detecting part 2 comprising the coil 13 wound around a magnetic material 14 having a temperature sensing characteristic, and electromagnetically connected to the coil 12 and a capacitor 15 connected in parallel to the coil 13, the frequency of the physical quantity detecting part 2 is detected by receiving the magnetic field generated by the coil 13, and the physical quantity is measured based on the detected frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a physical quantity sensor for converting a physical quantity such as temperature, pressure, acceleration and the like into a frequency and detecting the frequency at a remote position.

[0002]

2. Description of the Related Art In the case of a conventional physical quantity sensor, for example, a temperature sensor, a thermometer as a temperature sensor is directly brought into contact with a measured object to measure the temperature of the measured object. However, when the object to be measured is at a remote position and cannot directly contact the temperature sensor, temperature detection becomes difficult.

[0003]

In such a case, the temperature is detected using an infrared sensor or the like. However, this method has a problem that only the surface temperature of the measured object can be detected. For example, there is a problem that it is extremely difficult to detect the temperature of a deep part of a living body or the like. The same applies to pressure, acceleration, and the like, not limited to temperature.

When measuring a physical quantity at a remote location,
Due to the transmission of the detected physical quantity, there is a problem that the physical quantity sensor becomes large and it becomes difficult to detect the temperature in the deep part of the living body.

It is an object of the present invention to provide a physical quantity sensor capable of detecting a physical quantity at a remote position.

[0006]

A physical quantity sensor according to the present invention includes a first coil for generating a magnetic field by receiving an oscillation output from an external oscillator, a second coil electromagnetically coupled to the first coil, and a second coil. A physical quantity detecting means including a capacitor connected in parallel with the second coil and detecting a physical quantity to convert the output into a frequency based on the detected physical quantity; and a third coil including a third coil electromagnetically coupled to the second coil. Receiving means for receiving the magnetic field generated by the second coil by the coil and detecting the frequency of the magnetic field generated by the second coil.

According to the physical quantity sensor according to the present invention, the physical quantity detecting means comprising the second coil and the capacitor, which receives the oscillation output from the external oscillator and electromagnetically couples with the magnetic field generated by the first coil, is provided with the second quantity. A current flows at a frequency based on the inductance of the coil and the capacitance of the capacitor, and the second coil generates a magnetic field at the frequency of the current. Therefore, the frequency of the current flowing through the physical quantity detecting means can be detected by receiving the magnetic field generated by the second coil by the third coil and measuring the frequency. That is, if the detected physical quantity changes, the frequency of the current flowing through the physical quantity detecting means changes, and the physical quantity can be measured based on this frequency.

When a coil wound around a magnetic material having a temperature-sensitive characteristic and converting an ambient temperature into an inductance based on the ambient temperature is used as the second coil, the characteristic of the magnetic material changes depending on the temperature. Since the inductance of the second coil changes depending on the ambient temperature, the temperature can be measured based on the frequency of the current flowing through the physical quantity detection means.

When a capacitor having a temperature characteristic is used as the capacitor dielectric, the capacitance of the capacitor changes depending on the ambient temperature of the capacitor. Therefore, the temperature is measured based on the frequency of the current flowing through the physical quantity detecting means. can do.

When the physical quantity detecting means includes a fourth coil connected in parallel to the second coil, and the fourth coil is a magnetostrictive thin film coil that changes inductance based on the external force when an external force is applied, , Acceleration and the like can be measured.

When the physical quantity detecting means is provided with an element whose capacitance changes when an external force is applied, pressure and stress can be measured.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a physical quantity sensor according to the present invention will be described.

FIG. 1 is a block diagram showing a configuration of a physical quantity sensor according to an embodiment of the present invention, and illustrates a case where temperature is measured as a physical quantity.

Reference numeral 1 denotes an energy supply circuit,
The oscillation output of the external oscillator 10 is amplified by the amplifier 11, applied to the coil 12, and generates a magnetic field in the coil 12.

Reference numeral 2 denotes a physical quantity detecting section corresponding to the physical quantity detecting means, which constitutes a tank circuit composed of a coil 13 and a capacitor 15 connected in parallel to the coil 13, and the inductance L of the coil 13 changes according to the detected physical quantity. It is configured as follows.

In the case of the physical quantity sensor according to the embodiment of the present invention, since the temperature is measured, a soft magnetic material whose magnetic permeability changes with temperature or a temperature-sensitive ferrite used for a temperature switch or the like is used. A coil 13 is wound around a magnetic material 14 having a temperature-sensitive characteristic, and a capacitor 15 is connected to the coil 13 in parallel.

Therefore, if the inductance L of the coil 13 changes depending on the ambient temperature, and the capacitance of the capacitor 15 is C, the tank circuit composed of the inductance L and the capacitance C, that is, the resonance frequency frx of the physical quantity detection unit 2 is as follows: 1) It changes based on the equation.

Frx = 1 / {2π (LC) ^1/2 } (1) Therefore, the resonance current flowing through the coil 13 becomes maximum when the frequency of the magnetic field applied from the coil 12 matches the resonance frequency frx. Further, the intensity of the magnetic field generated by the coil 13 at that time also becomes maximum.

On the other hand, reference numeral 3 denotes a receiving unit corresponding to the receiving means, and a coil 17 electromagnetically coupled to the coil 13;
The frequency at which the strength of the magnetic field received by the coil 17 is maximum,
That is, the temperature is detected by detecting the maximum frequency of the current flowing through the coil 17 with the receiving circuit 18. Here, the maximum frequency of the current flowing through the coil 17 is
, And the temperature can be detected by the maximum frequency detected by the receiving circuit 18.

As described above, by measuring the frequency at which the intensity of the magnetic field received by the coil 17 is maximum, the resonance frequency frx can be detected, and the temperature can be detected based on the maximum frequency. .

According to the physical quantity sensor according to the embodiment of the present invention configured as described above, it is possible to measure a local temperature at a remote position and in real time.

Next, the elements used in the physical quantity sensor according to the embodiment of the present invention will be specifically described.

The coil 12 has a diameter of, for example, 200 m.
An air-core coil having a diameter of 27 μH and a diameter of 16 mm and a length of 16 turns wound with an insulated conductor was used. As the magnetic material 14 around which the coil 13 is wound, a temperature-sensitive ferrite having a Curie temperature of 55 ° C. was used. This magnetic material 14 has a diameter of 4 m.
Fifteen disk-shaped thermosensitive ferrites having a thickness of 1.6 mm and a thickness of 1.6 mm were laminated, and a 2,000-turn winding was formed therearound with an insulated conductor to form a coil 13.

In this configuration, the inductance L of the coil 13 changes depending on the temperature, and changes between 18 mH and 8 mH in the temperature range of 35 ° C. to 60 ° C. as shown in FIG. On the other hand, the resistance R of the coil 13 changed between 42 ohms (Ω) and 47 ohms (Ω). As the capacitor 15, a 55.3 pF capacitor was used.

In the case of the above configuration, the distance between the coil 12 and the coil 13 is 130 mm,
The distance between the coil 3 and the coil 17 was 130 mm, and the capability of remote sensing of temperature was measured. As a result, as shown in FIG. 3, it became clear that the frequency of the magnetic field received by the coil 17 changes depending on the ambient temperature of the coil 13. As a result, as shown in FIG. 2, the resonance frequency frx calculated from the inductance L with respect to the ambient temperature of the coil 13 measured in advance using the above equation (1) matches the resonance frequency frx, and a desired temperature measurement can be performed. It was shown that there is.

From the above results, in this case, the temperature can be measured in a temperature range of 35 ° C. to 60 ° C. at a remote position and in real time.

According to the physical quantity sensor according to one embodiment of the present invention, in order to convert a temperature into a frequency and measure it,
Even if the position of the physical quantity detector 2 fluctuates during the measurement and the state of the electromagnetic coupling changes during the measurement, there is a great feature that the temperature measurement is not affected at all.

In this case, the physical quantity detecting unit 2 is several mm.
The energy supply circuit 1 and the receiving unit 3 can be formed on a corner base, and the physical quantity detection unit 2 including this base can be inserted into the living body deep by installing the energy supply circuit 1 and the receiving unit 3 to detect the temperature of the living body deep part. Becomes possible.

The distance between the coil 12 and the coil 13 is 500 mm, and the distance between the coil 13 and the coil 17 is 500 mm.
mm, the temperature could be measured in the temperature range of 35 ° C to 60 ° C.

In the physical quantity sensor according to the embodiment of the present invention described above, the temperature is measured using the change in the inductance L of the coil 13 due to the temperature. Alternatively, the capacitance C of the capacitor 15 may be changed according to the temperature by using a capacitor 15 using a dielectric whose permittivity changes according to the temperature.
FIG. 4 shows an example of a temperature change of the dielectric constant of the dielectric. By forming the capacitor 15 using this dielectric material, the capacitance C changes according to the temperature, and the resonance frequency frx changes. Even if this is used, the temperature can be measured by the temperature change of the capacitance C as in the case of the temperature change of the inductance L.

In the above description, the case of temperature detection has been described as an example, but a case where the present invention is applied to acceleration detection instead of temperature detection will be described.

As shown in FIG. 5, in the acceleration sensor 30 having the cantilever 31, the inductance L
Forming a magnetostrictive thin-film coil 32 made of a material which changes due to strain, for example, cobalt, iron, silicon, boron,
By disposing the magnetostrictive thin-film coil 32 at the root of the cantilever 31, it is possible to convert the distortion of the root of the cantilever 31 based on the received acceleration into a change in inductance.

For this reason, in the case of acceleration measurement, as shown in FIG.
A is used. The physical quantity detection unit 2A is configured by connecting a magnetostrictive thin-film coil 32 in parallel with the air-core coil 13 in the physical quantity detection unit 2.

Here, the reason why the magnetostrictive thin-film coil 32 is connected in parallel to the air-core coil 13 is that the magnetostrictive thin-film coil 32 has a small size, so that the magnetic field generated by the resonance current is small.
Since the measured physical quantity cannot be transmitted to the coil 17, an air-core coil 13 having a large size and a high electromagnetic coupling efficiency is used for electromagnetic coupling with the coil 12 and transmission of a magnetic field to the coil 17. The resonance circuit is mainly composed of the magnetostrictive thin-film coil 32 and the capacitor 15, and the acceleration can be detected by the magnetostrictive thin-film coil 32 and the capacitor 15. In this case, the transmission to the coil 17 is performed, so that the acceleration at a more remote position can be measured.

Next, the case of pressure measurement will be described.

In the case of pressure measurement, the air-core coil 13
The pressure and the stress can be measured by using the physical quantity detection unit 2 including the pressure sensor in which the distance between the opposing electrode plates changes due to the pressure received instead of the capacitor 15 and the capacitance C changes. .

In the example of the pressure sensor shown in FIG. 7, polycrystalline silicon Si and n
^The case where each of the ⁺ -doped layers is used as an electrode is shown. The capacitance C changes based on the pressure applied to polycrystalline Si and n ⁺ , and by using this instead of the capacitor 15, the pressure and the stress are reduced. Can also be measured.

In the above, temperature measurement, acceleration measurement,
Although the case of pressure / stress measurement has been exemplified, a physical quantity detection unit that can convert a measured physical quantity into an inductance change, or a capacitance change, even with other physical quantities,
It is applicable to this physical quantity sensor.

[0039]

As described above, according to the physical quantity sensor according to the present invention, the physical quantity to be measured is converted into a frequency and detected, and the physical quantity can be detected regardless of the position where the physical quantity detection unit is placed. it can. Furthermore, when the physical quantity detecting unit is minimal, it is composed of one coil and one capacitor, so that the physical quantity detecting unit can be reduced in size and can detect a physical quantity at a position where measurement was impossible conventionally. Furthermore, since the operating energy of the physical quantity detection unit is magnetically applied from the outside, it is not necessary to provide an energy source inside the physical quantity detection unit, and the physical quantity can be detected at a remote position.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a physical quantity sensor according to one embodiment of the present invention.

FIG. 2 is a temperature characteristic diagram of inductance of a coil in which a winding is formed on a temperature-sensitive magnetic material used in a physical quantity sensor according to one embodiment of the present invention.

FIG. 3 is a temperature characteristic diagram of a physical quantity detection unit in the physical quantity sensor according to one embodiment of the present invention.

FIG. 4 is a temperature characteristic diagram of a dielectric constant of a dielectric material of a capacitor used in the physical quantity sensor according to the embodiment of the present invention.

FIG. 5 is a schematic diagram showing an example of an acceleration sensor used for a physical quantity sensor according to one embodiment of the present invention.

FIG. 6 is a block diagram illustrating a configuration example of a physical quantity sensor according to an embodiment of the present invention when an acceleration sensor is used for a physical quantity detection unit.

FIG. 7 is a schematic diagram showing an example of a pressure sensor used for a physical quantity sensor according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Energy supply circuit 2, 2A ... Physical quantity detection part 3 ... Reception part 10 ... External oscillator 11 ... Amplifier 12, 13, 17
... Coil 14 ... Magnetic material 15 ... Capacitor 18 ... Receiving circuit 30 ... Acceleration sensor 31 ... Cantilever 32 ... Magnetostrictive thin film coil

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01P 15/11 G01P 15/11 15/125 15/125 (72) Inventor Mitsuteru Inoue Igacho, Okazaki City, Aichi Prefecture 20-8, Jizogairi (72) Inventor Kim Egaku 4-5, Matsunamicho, Yagiyama, Taishiro-ku, Sendai, Miyagi Prefecture A72, Tohoku University Yagiyama Hall A301 48-cho, Ryowa Electronics Co., Ltd. (72) Inventor Tetsuo Yoshida 6-7-1, Koriyama, Taishiro-ku, Sendai-shi, Miyagi F-term (reference) 2F055 AA05 BB20 CC01 DD05 EE25 FF43 GG11

Claims (5)

[Claims] A first coil for generating a magnetic field by receiving an oscillation output from an external oscillator; a second coil electromagnetically coupled to the first coil; and a capacitor connected in parallel to the second coil. A physical quantity detecting means for detecting the included physical quantity and converting the output to a frequency based on the detected physical quantity; and a third coil electromagnetically coupled to the second coil, the magnetic field generated by the second coil by the third coil. Receiving means for detecting the frequency of a magnetic field generated by the second coil upon reception. 2. The physical quantity sensor according to claim 1, wherein the second coil is a coil wound around a magnetic material having a temperature-sensitive characteristic and converting the ambient temperature into an inductance based on the ambient temperature. Physical quantity sensor. 3. The physical quantity sensor according to claim 1, wherein a dielectric having a temperature characteristic of a dielectric constant is used as a dielectric of the capacitor, and an ambient temperature is converted into a capacitance based on the ambient temperature. Physical quantity sensor. 4. The physical quantity sensor according to claim 1, wherein the physical quantity detecting means is connected to a fourth coil connected in parallel to the second coil.
Wherein the fourth coil is a magnetostrictive thin-film coil that changes inductance based on the external force when an external force is applied. 5. The physical quantity sensor according to claim 1, wherein the physical quantity detecting means includes an element whose capacitance changes when an external force is applied.