JP5055172B2 - Capacitive proximity sensor - Google Patents

Description

  The present invention relates to a capacitance-type proximity sensor that detects the approach of a detection object such as a human body by a change in capacitance, and more particularly to a capacitance-type proximity sensor that includes a plurality of electrodes.

  In this type of capacitive proximity sensor, two electrodes are formed in a flat plate shape, and both the flat plate electrodes face each other in parallel. In both electrodes, electric lines of force from one electrode enter another electrode to constitute a capacitor. When the human body or the like of the detection object approaches the electrode, the electric lines of force emitted from the electrode are deformed, and the capacitance between the electrodes changes. The approach of the detection target is detected by a change in capacitance.

JP 2006-78422 A

[Issues of background technology]
It is desirable that the capacitive proximity sensor can detect a detection object at a position far from the electrode in the detection region on the front side of the electrode, that is, has a long detectable distance.
Further, it is desirable that the detectable distance is short in the regions on the opposite side and the rear side of the electrode. It is desirable that there are few malfunctions.

[Idea for solving problems]
In the capacitive proximity sensor as described above, when the human body of the detection object approaches the electrode, the electric lines of force from one electrode enter the ground through the human body and do not enter the other electrode. The capacitance between them changes. From this, it is surmised that the lines of electric force between the two electrodes extend far and the detectable distance becomes longer when the number of the lines at a far position is large. If both electrodes are flat plates of the same shape and the same size and face each other, it is assumed that the number of lines of electric force between the electrodes is difficult to increase at a distant position.
Accordingly, the inventors have conceived that one of the electrodes has a linear shape with a small surface area and the other has a planar or plate shape with a large surface area.

[Experiment (see FIGS. 1 to 5)]
In the capacitive proximity sensor, an experiment was conducted using a linear electrode and a planar electrode.

1) Electrode (see FIGS. 1 to 3)
In Example 1 of the electrode, as shown in FIG. 1, the linear electrode 1 is a linear electric wire having a diameter of 0.22 mm and a length of 300 mm. The planar electrode 2 is a belt-shaped or rectangular flat plate having a width of 30 mm and a length of 300 mm. Linear electrode 1, parallel align the planar electrode 2 and the longitudinal direction, arranged in the width direction center position location of the planar electrode 2, are spaced 3mm between the planar electrode 2. On both sides of the linear electrode 1, the linear electrode 1 is not hidden by the planar electrode 2, and the linear electrode 1 and the planar electrode 2 appear, which is a front region and a detection region. On the planar electrode 2 side, the linear electrode 1 is hidden behind the planar electrode 2 and is a rear region.

In the electrode example 2, as shown in FIG. 2, the linear electrode 1 is the same electric wire as in the electrode example 1. The planar electrode is folded back to the front side by extending the upper and lower sides of the flat plate of the planar electrode 2 in the electrode example 1 vertically. The front plate 4 is connected to the upper and lower edges of the rear plate 3 having the same shape and the same size as the planar electrode 2 in the electrode example 1 via the upper plate and the lower plate, respectively. The relative positions of the rear plate 3 and the linear electrode 1 are the same as those of the planar electrode 2 and the linear electrode 1 in the electrode example 1. The two front plates 4 are juxtaposed with the rear plate 3, positioned above and below the linear electrode 1, and spaced by 3 mm from the linear electrode 1. The planar electrodes are the folded plates 3 and 4. The linear electrode 1 side of both electrodes is a front region and a detection region. The rear plate 3 side of the planar electrodes 3 and 4 is a rear region.

  In the comparative example, as shown in FIG. 3, two planar electrodes 2 in the electrode example 1 are juxtaposed, and a space of 3 mm is placed between them.

2) Electrical circuit (see FIGS. 4 and 5)
As the electric circuit, various circuits capable of detecting a change in capacitance can be used, but a series resonance circuit is used. In this circuit, as shown in FIG. 4, a transmission source E, a coil L having interwinding capacitance C1, an electrode 6 and an electrode 7 constituting a capacitor C2, and a resistor R are connected in series. The inter-winding capacitance C1 and the coil L constitute a parallel resonance circuit. The coil L and the capacitor C2 constitute a series resonance circuit. The source E and the resistor R are grounded. The voltage V across the resistor R is detected. The relationship between the detection voltage V and the AC frequency of the transmission source E is indicated by a solid line in the diagram of FIG. The series resonance frequency is lower than the parallel resonance frequency.

  When the human body whose detection target is grounded approaches the electrode 6 or the electrode 7, the capacitance of the capacitor C2 decreases, while the human body forms the capacitor C, and the capacitor C is parallel to the capacitor C2 and the resistor R connected in series. Will be connected to. The capacitor C by the human body has a capacitance several times that of the capacitance decrease of the capacitor C2. For example, the capacitance of the capacitor C is 2 to 3 pF, and the decrease in the capacitance of the capacitor C2 is about 0.7 pF. In the series resonant circuit, the capacitance increases and the series resonant frequency decreases as the human body approaches. The relationship between the detection voltage V and the AC frequency of the transmission source E is such that the characteristic curve of series resonance moves to the lower frequency as shown by the broken line in the diagram of FIG.

  The transmission source E transmits a sine wave alternating current, sets the transmission frequency slightly higher than the series resonance frequency, and sets the detection voltage V to 8 V in an initial state where there is no human hand of the detection target. When a human hand approaches the electrode 6 or the electrode 7, the detection voltage V decreases from the initial setting of 8V.

3) Experimental method and experimental results (see Fig. 6)
In the electrode example 1, the linear electrode 1 is connected to the resistor R to be the electrode 7, and the planar electrode 2 is connected to the coil L to be the electrode 6. The transmission frequency is 54 kHz and the transmission voltage is 0.5 mV. Then, the detection voltage V becomes 8V in the initial state where the detection target has no human hand. In this initial setting, the detection voltage V is measured by placing the human hand of the detection object at each distance from the linear electrode 1 in the front region. In the rear region, a human hand is placed at each distance from the planar electrode 2 to detect the detection voltage V.

  Then, the experimental result is shown by a thick solid line in FIG. When a human hand approaches a distance of slightly more than 200 mm from the linear electrode 1 in the front region, the detection voltage V starts to decrease from the initial setting of 8V. Human hands begin to be detected. As the human hand approaches the linear electrode 1, the detection voltage V decreases rapidly. In the rear area, when the human hand approaches a distance of less than 200 mm from the planar electrode 2, the detection voltage V starts to decrease. Human hands begin to be detected. As the human hand approaches the planar electrode 2, the detection voltage V decreases rapidly. The detectable distance is longer in the front region on the linear electrode 1 side than in the rear region on the planar electrode 2 side.

  When the linear electrode 1 is replaced with the electrode 6 and the planar electrode 2 is replaced with the electrode 7, the detection voltage V is set to 8V as an initial setting, so that the transmission frequency is 57 kHz and the transmission voltage is 0.4 mV. The experimental results are almost the same as in the above case.

  In the electrode example 2, the linear electrode 1 is connected to the resistor R to be the electrode 7, and the planar electrodes 3 and 4 are connected to the coil L to be the electrode 6. The transmission frequency is 55 kHz and the transmission voltage is 0.4 mV. In the initial state, the detection voltage V becomes 8V. The experimental result is shown by a thin solid line in FIG. When a human hand approaches a distance of about 300 mm from the linear electrode 1 in the front region, the detection voltage V starts to decrease. Human hands begin to be detected. As the human hand approaches the linear electrode 1, the detection voltage V decreases rapidly. Further, when the human hand approaches the distance of about 200 mm from the planar electrode 2 in the rear region, the detection voltage V starts to decrease. As the human hand approaches the planar electrode 2, the detection voltage V decreases rapidly. The detectable distance in the front region on the linear electrode 1 side is significantly longer than the rear region on the planar electrodes 3 and 4 side. Further, the detectable distance in the front region is significantly longer than that in the electrode example 1.

  When the linear electrode 1 is replaced with the electrode 6 and the planar electrodes 3 and 4 are replaced with the electrode 7, the transmission frequency and the transmission voltage are not changed, and the experimental results are the same.

In the comparative example, one planar electrode 2 is an electrode 7 and the other planar electrode 2 is an electrode 6. The transmission frequency is 63 kHz and the transmission voltage is 0.6 mV. In the initial state, the detection voltage V becomes 8V. The experimental result is shown by a broken line in FIG. The detectable distance between the front region and the rear region is about 160 to 170 mm. The detectable distance in the front region is shorter than that in electrode example 1 and electrode example 2.
After all, in electrode example 1 and electrode example 2, the detectable distance of the front detection area is long.

[Shielding electrode (see FIGS. 7 to 9)]
In electrode example 1 and electrode example 2, the detectable distance of the rear region is shorter than that of the front region, but it is not yet sufficient to reduce malfunctions. Therefore, in order to further reduce the detectable distance of the rear region, a shielding electrode is provided. In the electrode example 1, as shown in FIG. 7, the planar shielding electrodes 8 face each other in parallel with a space behind the planar electrode 2. The shield electrode 8 is a belt-like or rectangular flat plate. Also in the electrode example 2, as shown in FIG. 8, the planar shielding electrodes 8 face each other in parallel with a space behind the planar electrodes 3 and 4. The shield electrode 8 is grounded.

  Then, in the electrode example 1, the linear electrode 1 of the electrode 7 and the planar electrode 2 of the electrode 6 constitute a capacitor C2, while the planar electrode 2 of the electrode 6 and the shielding electrode 8 constitute a capacitor C3. Also in the electrode example 2, the linear electrode 1 of the electrode 7 and the planar electrodes 3 and 4 of the electrode 6 constitute a capacitor C2, while the planar electrodes 3 and 4 of the electrode 6 and the shielding electrode 8 constitute a capacitor C3. In the series resonant circuit shown in FIG. 4, a capacitor C3 is connected in parallel to a capacitor C2 and a resistor R connected in series as shown in FIG.

  In the electrode example 1 and the electrode example 2 with the shielding electrode, the detectable distance of the rear region is shortened by the shielding electrode 8.

[Other electrode examples (see FIGS. 10 and 11)]
The electrode example 3 is a modification of the planar electrode of the electrode example 2. The rear side plate 3, the upper side plate, and the lower side plate in the planar electrode of the electrode example 2 are eliminated. As shown in FIG. 10, the planar electrode of the electrode example 3 is only the upper and lower front side plates 4. The electrode example 3 includes an upper and lower front side plate 4, a planar sheet electrode, and a wire electrode 1. The planar electrodes of only the upper and lower front plates 4 are easier to manufacture than the planar electrodes of the folded plate of the electrode example 2.

In addition, the electrode example 4 is a modification of the planar electrode of the electrode example 3. As shown in FIG. 11, the lower edge of the upper front plate 4 and the upper edge of the lower front plate 4 in the planar electrode of the electrode example 3 are connected by a groove plate 5 having a groove-shaped cross section. The channel plate 5 protrudes to the rear side of the shielding electrode 8 side. The planar electrode of the electrode example 4 is composed of upper and lower front plates 4 and a groove plate 5 and is a bent plate. The electrode example 4 includes the planar electrodes 4 and 5 of the bent plate and the linear electrode 1 of the electric wire. The planar electrodes 4 and 5 of the folded plate are easier to manufacture than the planar electrodes of the folded plate of the electrode example 2.

[Non-operation due to raindrops (see FIGS. 12 and 9)]
In the capacitive proximity sensor, a sensing unit having an electrode built therein is disposed outdoors, and raindrops or the like may adhere near the electrodes 6 and 7 of the sensing unit. Even if raindrops or the like that are not detection objects are attached, it is desired that they do not operate.

  In the electric circuit shown in FIG. 9, when raindrops outside the detection object are closest to the electrodes 6 and 7, for example, within 1 mm, the raindrops act as a dielectric between the electrodes 6 and 7, The capacitance of the capacitor C2 due to both electrodes 6 and 7 is greatly increased. If raindrops are not closest between the electrode 6 and the shield electrode 8, the capacitance of the capacitor C3 does not change. Ungrounded raindrops and the like do not constitute a capacitor C unlike a grounded human body.

  That is, when an ungrounded raindrop or the like is closest to the electrodes 6 and 7, the series resonance circuit has an increased capacitance and a lower series resonance frequency. At the same time, due to the increase in the capacitance of the capacitor C2, the impedance of the series connection portion of the capacitor C2 and the resistor R decreases. The impedance of the connection portion of the capacitor C3 does not change. Then, in the series connection portion of the capacitor C2 and the resistor R, the current increases and the detection voltage V increases. Eventually, the relationship between the detection voltage V and the AC frequency of the transmission source E is such that the characteristic curve of the series resonance moves to a lower frequency and a higher detection voltage as shown by a chain line in the diagram of FIG. Moving.

  In the diagram of FIG. 12, at the transmission frequency slightly higher than the initial series resonance frequency indicated by the solid line, the initial characteristic curve indicated by the solid line and the characteristic curve at the time of raindrop adhesion indicated by the chain line intersect. In the vicinity of the transmission frequency, the detection voltage does not change or hardly changes due to adhesion of raindrops. There is a transmission frequency that is insensitive to the attachment of raindrops. If the transmission frequency is set to an insensitive transmission frequency, it will not malfunction due to adhesion of raindrops.

  In order to prevent malfunction due to raindrops or the like, the sensing unit is configured such that raindrops or the like are not closest between the electrode 6 and the shield electrode 8.

[Other electrical circuits (see FIG. 13)]
As shown in FIG. 13, the other electric circuit replaces “coil L having interwinding capacitance C1” and “capacitor C2 composed of electrode 6 and electrode 7” in the electric circuit shown in FIG. ing. The series connection circuit and series resonance circuit of the coil L and the capacitor C2 are the same as those in the electric circuit shown in FIG.

1) to form a capacitor with one electrode and the other electrode, the human body of the detection object to the electrode approaches the electrostatic capacitance is changed, to detect the approach of a detection object based on a change in capacitance In capacitive proximity sensors,
One electrode makes it less linear shape surface area and the other electrode, the greater the surface shape of the surface area, the linear electrode and the planar electrode, Resshi parallel spaced, face linear electrode The side that is not hidden by the electrode is the front detection area ,
The linear electrode is an electric wire, and the planar electrode has both sides of the flat plate folded forward, the rear plate on the rear side, the front plate on both sides of the front side, and the linear electrode between the front plate on both sides and the front plate Arranged in the same direction, the linear electrodes are equidistant from the front and rear plates on both sides,
A series resonance circuit is configured by connecting a capacitor and a coil composed of linear electrodes and planar electrodes in series, and the voltage or current of the series resonance circuit is detected, and the approach of the detection target is detected by a change in the detection voltage or detection current. It is characterized by having a configuration .
2) In the above capacitive proximity sensor,
On the rear side of the planar electrode, the shield electrodes are arranged to face each other with a space therebetween, and the shield electrode is grounded .
3) In the above capacitive proximity sensor,
The series resonance circuit sets the transmission frequency higher than the series resonance frequency, and when the human body of the detection object approaches in the detection area on the front side, the series resonance frequency decreases and the detection voltage or detection current decreases. When a raindrop or the like that is not close, the series resonance frequency is lowered and the impedance is decreased, and the detection voltage or the detection current is not changed or hardly changed .
4) In the capacitive proximity sensor of 2) or 3 ) above,
A coil is arranged on one end side of the planar electrode , the planar electrode and the coil are connected by an electric wire,
An electric wire, a linear electrode, a planar electrode, a shielding electrode, and a coil in which a planar electrode and a coil are connected are buried and fixed in an electrical insulator.
5) In the capacitive proximity sensor of 2), 3) or 4) above,
Connect the sensor and electrical circuit with a cable,
The sensing unit contains a linear electrode, a planar electrode, a shielding electrode and a coil,
The electric circuit unit is characterized in that a transmission source of a series resonance circuit, a circuit or a device for detecting a change in detection voltage or detection current is incorporated .

  The capacitive proximity sensor has a long detectable distance in the front detection area. The detectable distance is short in the rear area. There are few malfunctions.

  In the capacitive proximity sensor of the embodiment, as shown in FIG. 14, the sensing unit 11 having a built-in electrode with a shielding electrode is connected to the electric circuit unit 31 with cables of shielded wires 19 and 20.

  As shown in FIGS. 14 to 16, the sensing unit 11 includes a shielding electrode 12, an insulating sheet 13, a planar electrode 14, a linear electrode 17, and a coil 18.

The shielding electrode 12 is a metal plate which is a belt-like or rectangular flat plate, and an insulating sheet 13 is overlapped on one plate surface. The insulating sheet 13 is an electrical insulator, is substantially the same shape and size as the shielding electrode 12, and is aligned with the shielding electrode 12 in the length direction. A planar electrode 14 is superimposed on one surface of the insulating sheet 12. The planar electrode 14 is a metal plate of a folded plate of the form shown in FIG. 8, and has a rear plate 15 on the rear side and front plates 16 on both sides of the front side. The rear plate 15 is a strip or rectangular flat plate that is slightly smaller than the shielding electrode 12 and the insulating sheet 13, and is aligned with the insulating sheet 13 in the length direction. An insulating sheet 13 is sandwiched between the shielding electrode 12 and the rear plate 15 of the planar electrode 14. Between the front plates 16 on both sides, the linear electrodes 17 are arranged with the front plate 16 aligned in the length direction. The linear electrode 17 is a round metal wire or a linear electric wire, and has substantially the same length as the planar electrode 14 and is located at an equal distance from the front side plate 16 and the rear side plate 15 on both sides. The shielding electrode 12, the planar electrode 14, and the linear electrode 17 are arranged in parallel at intervals.

  One end of the coil 18 and the cables 19 and 20 are arranged on one end side of the planar electrode 14. The coil 18 has an inductance L and an interwinding capacitance C1. The cables 19 and 20 bundle two shield wires 19 and 20 together. The coil 18 has one end connected to the planar electrode 14 with an electric wire 21 and the other end connected to the core of the shield wire 19. The other shield wire 20 connects the core wire to the linear electrode 17. The shielded mesh wires of both shield wires 19 and 20 are connected to the shield electrode 12.

  The shield electrode 12, the insulating sheet 13, the planar electrode 14, the linear electrode 17, the coil 18, one end of the electric wire 21 and the cables 19 and 20 are immersed in the synthetic resin liquid, and the synthetic resin liquid is cured and molded into the case 22. is doing. The case 22 is an electrical insulator of a synthetic resin molded product and has a flat plate shape of a belt shape or a rectangular shape. The linear electrode 17 side of the case 22 is a detection region where the linear electrode 17 is not hidden by the planar electrode 14 and is a front region. On the shielding electrode 12 side, the linear electrode 17 is hidden behind the planar electrode 14 and is a rear region.

The planar electrode 14 and the linear electrode 17 constitute a capacitor C2. The planar electrode 14 and the shielding electrode 12 constitute a capacitor C3. The shielding electrode 12, the planar electrode 14 , the linear electrode 17 , the coil 18, and the electric wire 21 are buried and fixed in the case 22. The stray capacitance and stray inductance in the vicinity of them are difficult to change. It is difficult for the LC series resonance characteristic to shift due to a change in stray capacitance.

  The electric circuit unit 31 includes a transmission source E, a resistor R, a circuit or device for detecting a change in the voltage V across the resistor R, and the other ends of the cables 19 and 20. The transmission source E has one end connected to one end of the resistor R and the other end connected to the core of the shield wire 19. The other end of the resistor R is connected to the core wire of the shield wire 20. The shielded mesh wires of both shield wires 19 and 20 are connected between the transmission source E and the resistor R. The source E and the resistor R are grounded. In the electric circuit, as shown in FIG. 17, a coil 18 having an inductance L and a capacitor C <b> 2 including a planar electrode 14 and a linear electrode 17 are connected in series. This is the same as the LC series resonance circuit shown in FIG. The transmission frequency of the transmission source E is set to a transmission frequency slightly higher than the series resonance frequency and a transmission frequency insensitive to adhesion of raindrops and the like.

  In the detection region on the front side of the case 22, the detectable distance is long with respect to the human body of the detection target. It becomes about 200 mm. In the area behind the case 22, there is almost no human body detection. Even if raindrops or the like outside the detection target adhere to the front surface of the case 22, the operation does not occur.

[Modification]
In the above embodiments SL, linear electrodes 17, although the cross-sectional shape is circular, to shape.

  The present invention is used to prevent the approach and collision between a moving body and a human body, prevent the human body from approaching a dangerous location, prevent the human body from entering a prohibited area, and confirm the location of the human body.

The perspective view of Experimental example 1 of the electrode of the capacitive proximity sensor of this invention. The perspective view of Experimental example 2 of the same electrode. The perspective view of the comparative example of an electrode. The figure of the experiment example of the electric circuit of the electrostatic capacitance type proximity sensor. The diagram which shows the relationship between the detection voltage in the electric circuit of the experiment example, and the frequency of a transmission source. The diagram which shows the relationship between the detection voltage in the experiment example, and the distance of a detection target object. The perspective view of Example 1 of the electrode with a shielding electrode of the same capacitive proximity sensor. The perspective view of Example 2 of the electrode with a shielding electrode of the same capacitive proximity sensor. The figure of the example of the electric circuit of the electrode with the shielding electrode. The perspective view of the other example of the electrode with the same shielding electrode. The perspective view of the further another example of the electrode with the shielding electrode. FIG. 6 is a diagram similar to FIG. 5, showing non-operation due to insensitive transmission frequency, adhesion of raindrops, and the like. The figure of the other example of the electric circuit of the electrode with the same shielding electrode. The schematic diagram of the capacitive proximity sensor of the embodiment of the present invention. The case fracture | rupture front view of the sensing part of the electrostatic capacitance type proximity sensor. FIG. 16 is an enlarged sectional view taken along line AA in FIG. 15. The electric circuit diagram of the same capacitive proximity sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Linear electrode, Electric wire 2 Planar electrode, Flat plate, Metal plate 3, 4 Planar electrode, Folded plate, Metal plate 3 Rear plate of planar electrode 4 Front plate of planar electrode, Planar electrode 4, 5 Planar shape Electrode, bent plate, metal plate 5 planar electrode groove plate 6 electrode 7 electrode 8 shielding electrode, flat plate, metal plate 11 sensing unit 12 shielding electrode, flat plate, metal plate 13 insulating sheet, electrical insulator 14 planar electrode, Folded plate, metal plate 15 rear electrode 16 planar electrode front plate 17 linear electrode, round bar metal wire, electric wire 18 coil 19, 20 cable, cable shield wire 19 shield wire 20 shield wire 21 electric wire 22 Case, Synthetic Resin Molded Electrical Insulator 31 Electric Circuit Part E Transmission Source L Coil, Inductance C1 Capacitance between windings of coil C2 Capacitor by electrode C3 Capacitor by shielding electrode C Capacitor by human body Resistors V voltage, the detection voltage

Claims (5)

To form a capacitor with one electrode and the other electrode, the human body of the detection object to the electrode approaches the electrostatic capacitance is changed, to detect the approach of a detection object based on a change in capacitance In capacitive proximity sensors,
One electrode makes it less linear shape surface area and the other electrode, the greater the surface shape of the surface area, the linear electrode and the planar electrode, Resshi parallel spaced, face linear electrode The side that is not hidden by the electrode is the front detection area ,
The linear electrode is an electric wire, and the planar electrode has both sides of the flat plate folded forward, the rear plate on the rear side, the front plate on both sides of the front side, and the linear electrode between the front plate on both sides and the front plate Arranged in the same direction, the linear electrodes are equidistant from the front and rear plates on both sides,
A series resonance circuit is configured by connecting a capacitor and a coil composed of linear electrodes and planar electrodes in series, and the voltage or current of the series resonance circuit is detected, and the approach of the detection target is detected by a change in the detection voltage or detection current. A capacitive proximity sensor characterized by having a configuration . 2. The capacitive proximity sensor according to claim 1, wherein the shield electrodes are arranged to face each other in parallel on the rear side of the planar electrode, and the shield electrode is grounded. The series resonance circuit sets the transmission frequency higher than the series resonance frequency, and when the human body of the detection object approaches in the detection area on the front side, the series resonance frequency decreases and the detection voltage or detection current decreases. 3. The configuration according to claim 1, wherein when a raindrop or the like that is not close approaches, the series resonance frequency decreases and the impedance decreases, and the detection voltage or detection current does not change or hardly changes. Capacitive proximity sensor. A coil is arranged on one end side of the planar electrode , the planar electrode and the coil are connected by an electric wire,
The electrostatic capacity type proximity according to claim 2 or 3 , characterized in that an electric wire, a linear electrode, a planar electrode, a shielding electrode, and a coil in which a planar electrode and a coil are connected are buried and fixed in an electrical insulator. Sensor. Connect the sensor and electrical circuit with a cable,
The sensing unit contains a linear electrode, a planar electrode, a shielding electrode and a coil,
5. The capacitive proximity sensor according to claim 2, wherein the electric circuit unit includes a transmission source of a series resonance circuit, a circuit or a device for detecting a change in a detection voltage or a detection current .

Images