JP2004354331A - Electrical field sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrical field sensor which increases sensitivity by amplifying a voltage to be applied between electrodes of an electro-optical crystal and applying a sufficient voltage between the electrodes of the electro-optical crystal. <P>SOLUTION: The electrical field received with a receiving electrode 43 is amplified by an amplifier 25, and applied between the first and second electrodes 12 and 14 of the electro-optical crystal 11 to thereby change the polarization of a laser beam incident from a laser source 13 to the electro-optical crystal 11 via a first optical system 15. This polarization change is converted into the intensity change of the light by a second optical system 17, converted into an electrical signal by a photodetector 19, and output as an electrical field detection signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric field sensor that detects an electric field transmitted through an electric field transmission medium using an electro-optic (EO) crystal.
[0002]
[Prior art]
The sensitivity of an electric field sensor using an electro-optic crystal is proportional to the voltage applied between a pair of electrodes provided on the side surface of the electro-optic crystal so as to sandwich the electro-optic crystal.
[0003]
FIG. 3 is a diagram showing a configuration of a receiving terminal 100 in which such an electric field sensor is applied to detect a data signal transmitted as an electric field from a transmitter to a human body. In the figure, a data signal output from a signal electrode 33 of a data signal generator 31 constituting a transmitter 3 is induced as an electric field in a human body 5 as an electric field transmission medium via a transmission electrode 41 and propagates in the human body 5. Then, it is received by the receiving electrode 43.
[0004]
The electric field received by the receiving electrode 43 is coupled to the electro-optic crystal 11 via the first electrode 12 provided on one side of the electro-optic crystal 11, and provided on the other side of the electro-optic crystal 11. Is pulled into the second electrode 14. When an electric field is coupled to the electro-optic crystal 11 through the first electrode 12, the birefringence, which is an optical characteristic, changes depending on the intensity of the electric field.
[0005]
On the other hand, the electro-optic crystal 11 is output from the laser light source 13, converted into parallel light by the first optical system 15, and the laser light whose polarization state is adjusted is incident from between the first and second electrodes 12 and 14. However, the polarization of the incident laser light is changed according to the intensity of the electric field coupled via the first electrode 12 as described above. The laser light having undergone the polarization change in accordance with the electric field strength in this manner exits from the electro-optic crystal 11 and enters the second optical system 17. The second optical system 17 converts a change in the polarization of the laser light incident from the electro-optic crystal 11 into a change in the intensity of the light and supplies the change to the photodetector 19. The photodetector 19 converts an optical output from the second optical system 17 into an electric signal and outputs the electric signal as an electric field detection signal. The laser light source 13 and the photodetector 19 operate by being supplied with a voltage from the first power supply circuit 21, and the ground of the first power supply circuit 21 is connected to the circuit ground 23 of the receiving terminal 100.
[0006]
[Patent Document 1]
Japanese Patent Application No. 2001-295139
[Patent Document 2]
Japanese Patent Application No. 2001-295121
[Problems to be solved by the invention]
Since the sensitivity of the electric field sensor is proportional to the voltage applied between the electrodes, it is desirable that the voltage between the electrodes is sufficiently high. However, as described above, the first electrode 12 of the electro-optic crystal 11 is , The human body 5, and the signal electrode 33 of the transmitter 3 via the transmission electrode 41, whereas the second electrode 14 of the electro-optic crystal 11 is not connected to the ground electrode 35 of the transmitter 3, and Since the absolute potential of the circuit ground 23 of the receiving terminal 100 actually fluctuates greatly and becomes noise, the second electrode 14 of the electro-optic crystal 11 is also insulated from the circuit ground 23 of the receiving terminal 100. However, the voltage applied between the electrodes of the electro-optic crystal 11 is generally very small, and there is a problem that the sensitivity of the electric field sensor is insufficient.
[0009]
The present invention has been made in view of the above, and its purpose is to amplify a voltage applied between electrodes of an electro-optic crystal and apply a sufficient voltage between the electrodes of the electro-optic crystal, An object of the present invention is to provide an electric field sensor with increased sensitivity.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention according to claim 1 is an electric field sensor for detecting an electric field transmitted through an electric field transmission medium using an electro-optic crystal, wherein the electric field transmitted through the electric field transmission medium is used. And a pair of electrodes provided on the side surface of the electro-optic crystal so as to sandwich the electro-optic crystal, a light source that generates light of a single wavelength, and convert the light from the light source into parallel light. A first optical system that enters between the electrodes of the electro-optic crystal, and a second optical system that converts parallel light that enters from the first optical system and passes through the electro-optic crystal into a change in light intensity; A gist comprising: a photoelectric conversion means for converting a light output from the second optical system into an electric signal; and an amplifier for amplifying an electric field received by the reception electrode and applying the electric field between the electrodes of the electro-optic crystal. And
[0011]
According to the present invention, since the electric field received by the receiving electrode is amplified by the amplifier and applied between the electrodes of the electro-optic crystal, the amplified electric field is sufficiently large between the electrodes of the electro-optic crystal. When a voltage is applied, the sensitivity as an electric field sensor can be significantly improved.
[0012]
According to a second aspect of the present invention, in the first aspect of the invention, a first power supply circuit for supplying operating power to the light source and the photoelectric conversion means and a circuit ground of the first power supply circuit are insulated. And a second power supply circuit for supplying operating power to the amplifier.
[0013]
According to the second aspect of the present invention, since the second power supply circuit for supplying the operating power to the amplifier is insulated from the circuit ground of the first power supply circuit, the amplifier is affected by the fluctuation of the circuit ground. Without this, the electric field from the receiving electrode can be amplified.
[0014]
Further, according to a third aspect of the present invention, in the first or second aspect of the invention, a side surface of the electro-optic crystal is a pair of opposed side surfaces, and the electrodes are provided on each of the pair of side surfaces. The gist of the present invention is a pair of electrodes.
[0015]
According to a fourth aspect of the present invention, in the first aspect of the present invention, a signal having a predetermined low frequency in an electric field received at the receiving electrode is connected between the receiving electrode and an input of an amplifier. The gist of the present invention is to have a high-pass filter that removes a component and passes only a predetermined high frequency to supply the high-pass filter to the amplifier.
[0016]
According to the fourth aspect of the present invention, since a predetermined low frequency component is removed by a high-pass filter and only a predetermined high frequency is input to the amplifier, noise caused by potential fluctuation of the human body is mixed into the input of the amplifier. And only a normal valid signal is output from the amplifier.
[0017]
According to a fifth aspect of the present invention, in the fourth aspect, the high-pass filter includes a capacitor.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a receiving terminal to which an electric field sensor according to an embodiment of the present invention is applied, together with a transmitter. In the embodiment shown in the figure, an amplifier 25 is connected to the first and second electrodes 12 and 14 provided on the side surfaces of the electro-optic crystal 11 in the conventional circuit configuration shown in FIG. The only difference is that a second power supply circuit 27 for supplying power is added. Other configurations and operations are the same as those in FIG. 3, and the same components are denoted by the same reference numerals. Note that a configuration including the electro-optic crystal 11, the amplifier 25, and the second power supply circuit 27 is referred to as an electric field processing unit 20, and the entire receiving terminal including the electric field processing unit 20 is denoted by reference numeral 1.
[0019]
The amplifier 25 is composed of an operational amplifier, has a non-inverting input terminal indicated by a “+” sign connected to the receiving electrode 43, and is supplied with a voltage corresponding to an electric field received from the human body 5 at the receiving electrode 43. ing. The output terminal of the amplifier 25 is connected to the first electrode 12, and the inverting input terminal indicated by the “−” symbol is connected to the second electrode 14.
[0020]
The second power supply circuit 27 that supplies the operating power to the amplifier 25 is insulated from the first power supply circuit 21 and the circuit ground 23 of the receiving terminal 1.
[0021]
In the present embodiment configured as described above, the data signal transmitted from the transmitter 3 via the signal electrode 33 is received by the reception electrode 43 via the transmission electrode 41 and the human body 5, The voltage is supplied to the amplifier 25, amplified, and applied as a sufficiently large voltage to the electro-optic crystal 11 via the first and second electrodes 12, 14, so that the sensitivity as an electric field sensor can be remarkably improved. More specifically, the laser light incident on the electro-optic crystal 11 from the laser light source 13 via the first optical system 15 is sufficiently large to be applied to the electro-optic crystal 11 via the first and second electrodes 12 and 14. The light undergoes a large change in polarization due to the voltage, is converted into a change in light intensity by the second optical system 17, is converted into a large electric signal by the photodetector 19, and is output as a sufficient electric field detection signal.
[0022]
The first optical system 15 is composed of a collimating lens that converts the laser light into parallel light, and a wave plate that adjusts the polarization state of the laser light from the collimating lens. A polarization beam splitter that separates the laser light incident from 11 into a P-wave and an S-wave and converts it into a change in light intensity is configured. The photodetector 19 is configured by a photodiode.
[0023]
FIG. 2 is a diagram showing an electric field processing unit 20a used in a receiving terminal 1 similar to FIG. 1 to which an electric field sensor according to another embodiment of the present invention is applied.
[0024]
The electric field processing unit 20a of the embodiment shown in FIG. 2 corresponds to the electric field processing unit 20 of FIG. 1, and is provided in the receiving terminal 1 instead of the electric field processing unit 20 in FIG. 1 is different from the electric field processing unit 20 of FIG. 1 in that a capacitor 29 constituting a new high-pass filter is connected to a non-inverting input terminal of the amplifier 25 indicated by a “+” sign. The operation is the same as in FIG.
[0025]
The electric field processing unit 20a in the embodiment of FIG. 2 includes the electro-optic crystal 11, the first and second electrodes 12, 14, the amplifier 25, the capacitor 29, and the second power supply circuit 27. 1, a laser light source 13, a first optical system 15, a second optical system 17, and a photodetector 19 are connected, and a non-inverting input terminal of the amplifier 25 indicated by a “+” symbol is a capacitor 29. Is connected to the receiving electrode 43 via the receiving electrode 43, and further connected to the signal electrode 33 of the transmitter 3 via the human body 5 and the transmitting electrode 41 from the receiving electrode 43.
[0026]
As described above, the non-inverting input terminal of the amplifier 25 is connected to the human body 5 via the capacitor 29 and the receiving electrode 43. It is generally said that the human body 5 has a slowly changing potential. The capacitor 29 is connected to the input of the amplifier 25 as a high-pass filter in order to prevent noise due to the noise from being mixed into the input of the amplifier 25. Therefore, noise due to the slowly varying potential of the human body 5 is removed by the capacitor 29 and is not input to the amplifier 25, and only a valid data signal of a high frequency from the transmitter 3 passes through the capacitor 29 and passes through the amplifier 25. , And the amplifier 25 outputs only a normal signal without noise.
[0027]
The frequency component of the potential fluctuation of the human body 5 is expected to be 1 kHz or less, and the data signal output from the transmitter 3 generally has a wide frequency component. In many cases, the upper limit of the cutoff frequency fc of the capacitor 29 is about 100 kHz, and the capacitor 29 may have a capacitance of 1 μF or more.
[0028]
【The invention's effect】
As described above, according to the present invention, the electric field received by the receiving electrode is amplified by the amplifier and applied between the electrodes of the electro-optic crystal. When a voltage is applied, the sensitivity as an electric field sensor can be significantly improved.
[0029]
Further, according to the present invention, since the second power supply circuit that supplies the operating power to the amplifier is insulated from the circuit ground of the first power supply circuit, the amplifier is not affected by the fluctuation of the circuit ground, The electric field from the receiving electrode can be amplified.
[0030]
Furthermore, according to the present invention, a predetermined low frequency component is removed by a high-pass filter, and only a predetermined high frequency is input to the amplifier, so that noise due to fluctuations in human body potential is prevented from being mixed into the input of the amplifier. Only a normal valid signal is output from the amplifier.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a receiving terminal to which an electric field sensor according to an embodiment of the present invention is applied, together with a transmitter.
FIG. 2 is a diagram showing an electric field processing unit used in a receiving terminal similar to FIG. 1 to which an electric field sensor according to another embodiment of the present invention is applied.
FIG. 3 is a diagram showing a configuration of a receiving terminal to which a conventional electric field sensor is applied, together with a transmitter.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 receiving terminal 3 transmitter 5 human body 11 electro-optic crystal 13 laser light source 15 first optical system 17 second optical system 19 photodetector 21 first power supply circuit 23 circuit ground 25 amplifier 27 second power supply circuit 29 capacitor 43 receiving electrode

Claims (5)

An electric field sensor for detecting an electric field transmitted through an electric field transmission medium using an electro-optic crystal,
A receiving electrode for receiving an electric field transmitted through the electric field transmission medium,
A pair of electrodes provided on side surfaces of the electro-optic crystal so as to sandwich the electro-optic crystal,
A light source that emits light of a single wavelength,
A first optical system that converts light from the light source into parallel light and enters between the electrodes of the electro-optic crystal;
A second optical system that converts parallel light incident from the first optical system and passing through the electro-optic crystal into a change in light intensity;
Photoelectric conversion means for converting the light output from the second optical system into an electric signal;
An electric field sensor comprising: an amplifier that amplifies an electric field received by the receiving electrode and applies the electric field between the electrodes of the electro-optic crystal. A first power supply circuit for supplying operating power to the light source and the photoelectric conversion means;
The electric field sensor according to claim 1, further comprising: a second power supply circuit that is insulated from a circuit ground of the first power supply circuit and supplies operating power to the amplifier. The electric field sensor according to claim 1, wherein a side surface of the electro-optic crystal is a pair of opposed side surfaces, and the electrodes are a pair of electrodes provided on each of the pair of side surfaces. A high-pass filter connected between the reception electrode and an input of the amplifier, for removing a predetermined low frequency component in an electric field received by the reception electrode, and passing only a predetermined high frequency to supply the amplifier. The electric field sensor according to claim 1, wherein: The electric field sensor according to claim 4, wherein the high-pass filter is configured by a capacitor.

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