JP2012208117A - Detection sensor for three-dimensional component of underground electromagnetic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a horizontal electric field component of feeble underground electromagnetic waves with long wavelength with sufficient sensitivity in a narrow borehole for observation provided underground.SOLUTION: As a detection sensor for horizontal electric field component, many short dipole antenna elements consisting of a pair of linear conductors whose full length is smaller than an inner diameter of a borehole for observation are arranged in parallel with the depth direction by separating them from one another for predetermined separation distance or more, elements on one side of the respective short dipole antenna elements are connected to an input of one side of a differential amplifier via a capacitor C, elements on the other side are connected to on input on the other side of the differential amplifier via the capacitor C, respectively, potential difference between the elements on both sides of the respective short dipole antennas is added by detecting the potential difference by the total value of electric charges to be inducted by capacitance C(<<C) between the input on one side and the input on the other side of the differential amplifier by the potential difference between the elements on both sides of the respective short dipole antennas, and detection sensitivity and directional characteristics equivalent to those of long dipole antennas are obtained.

Description

  The present invention relates to an underground electromagnetic wave three-dimensional component detection sensor for detecting a three-dimensional component of an underground electromagnetic wave in a narrow observation borehole.

The inventor is researching a subsurface electromagnetic wave observation system that detects a weak electromagnetic pulse in the ground and identifies the source of the electromagnetic pulse originating in the ground due to crustal deformation, etc. by detecting the arrival direction of the pulse. (For example, refer to Patent Document 1).
In FIG. 6, the structure of the conventional underground electromagnetic wave observation system disclosed by patent document 1 is shown.
This system includes a search coil 12 that detects magnetic field components in the east-west direction, a search coil 14 that detects magnetic field components in the north-south direction, and a vertical dipole antenna 16 that detects electric field components in the vertical direction. And a signal processing unit 20 that performs AD conversion on the signal detected by the sensor unit 10 and calculates the arrival direction by computer analysis, and is located in a narrow observation borehole that extends over 100 m from the ground in the depth direction. The sensor unit 10 is inserted into the sensor to detect underground electromagnetic waves. The east-west magnetic field component detected by the east-west magnetic field sensor 12 and the north-south magnetic field component detected by the north-south magnetic field sensor 14 are detected. The arrival direction of the underground electromagnetic wave in the horizontal plane is calculated, and the phase information of the vertical electric field component detected by the electric field sensor 16 at the same time Underground electromagnetic waves to identify whether the electromagnetic waves coming from any direction in the horizontal plane from.

JP 2005-274371 A JP 2009-156661 A JP 2010-164327 A

As described above, in the conventional underground electromagnetic wave observation system, although the arrival direction of the underground electromagnetic wave in the horizontal plane can be obtained, the vertical direction of the incoming electromagnetic wave cannot be specified. It cannot be separated whether it is from the inside or from the ground (for example, from lightning).
Moreover, when the electromagnetic wave generated by lightning on the ground was observed using this underground electromagnetic wave observation system, it was observed that the polarization plane of the electromagnetic wave might be an elliptically polarized wave that rotates with time. An electromagnetic wave propagates through a medium by combining a time-varying electric field and a magnetic field, and in order to accurately determine the three-dimensional arrival direction of the electromagnetic wave whose polarization plane rotates, It is necessary to simultaneously detect the three magnetic field components.

  Normally, a coil is used to detect the magnetic field component of electromagnetic waves. However, in order to increase detection sensitivity, the search coil can be miniaturized by using a ferromagnetic coil as a core and providing a number of windings. Can do. Therefore, a sensor for detecting a three-dimensional magnetic field component of an electromagnetic wave can be configured by arranging search coils in three directions orthogonal to each other as shown in FIG. 7, and can be inserted into a narrow observation borehole to A three-dimensional magnetic field component can be detected.

On the other hand, in order to detect an electric field component of electromagnetic waves, a linear dipole antenna having a pair of linear conductors on a straight line is usually used. Therefore, in order to detect a three-dimensional electric field component of electromagnetic waves, it is necessary to provide linear dipole antennas in three directions orthogonal to each other.
The electric field is the potential gradient per unit length in space, but the electric field detected by the dipole antenna is the difference between the potential at the midpoint of the element on one side of the dipole antenna and the potential at the midpoint of the element on the other side. Therefore, in order to increase the detection sensitivity, it is necessary to increase the length of the element of the dipole antenna so that the potential difference between the midpoints of the elements on both sides of the dipole antenna is increased.

  However, in order to detect a three-dimensional electric field component of an electromagnetic wave in a small-diameter observation borehole provided for inserting a sensor into the ground, a vertical dipole antenna is used to detect a vertical electric field component. Although it is possible to cope with this problem, the detection of the electric field component in the horizontal direction has a limitation that the length of the element of the dipole antenna cannot be made longer than the diameter of the observation borehole as shown in FIG. There is a problem that it is difficult to obtain a practical detection sensitivity.

On the other hand, as a sensor that simultaneously detects electric field components in three directions orthogonal to each other in a three-dimensional space, for example, Patent Document 2 discloses an electric field detection in which conductive electrodes are arranged on each surface of a cubic or spherical metal casing. A three-dimensional electric field sensor having a portion is disclosed.
However, in such a conventional three-dimensional electric field sensor, in order to detect the electric field component of a weak electromagnetic wave having a long wavelength such as the underground electromagnetic wave targeted by the present invention, the area of each detection electrode is increased, It is also necessary to increase the distance between the detection electrodes to be detected, and it is difficult to detect the electric field component of the underground electromagnetic wave in a narrow observation borehole.
In addition, since the planar or spherical detection electrode induces an electric field having a directional component in a wide angle range, it is difficult to accurately detect the direction of arrival of electromagnetic waves coming from far away.

In addition, as a system for detecting the arrival direction of electromagnetic waves in a borehole provided in the ground, for example, Patent Document 3 discloses a signal using a dipole array antenna in which a plurality of dipole antennas are arranged on the outer periphery in the vertical direction of the borehole. A borehole radar system for estimating the arrival direction of a received wave from the phase difference between the two is disclosed.
This borehole radar system radiates electromagnetic waves from the transmitting antenna into the ground, and receives the scattered waves and reflected waves from the underground cracks, faults, groundwater, etc. with the receiving antenna provided in the other borehole, and detects the direction of arrival By doing so, it is intended to estimate the three-dimensional position of cracks, faults, underground water, etc. in the ground, and since a dipole antenna tuned to the wavelength of the electromagnetic wave transmitted from the transmitting antenna can be used as the receiving antenna, The detection sensitivity can be kept high.
However, the underground electromagnetic wave to be detected in the present invention is an electromagnetic wave generated in the natural world due to crustal movement or the like, and the detection target is a low-frequency electromagnetic wave having a long wavelength of 50 kHz or less, but has a wide frequency range and is of a tuning type. The receiving antenna cannot be used.
In the above-described borehole radar system, since the horizontal arrival direction is detected by the phase difference of the signals reaching the dipole array antenna, the electric field components in the horizontal two directions of the underground electromagnetic wave cannot be detected separately. . Furthermore, in the above-described borehole radar system, it is necessary to raise and lower the transmitting antenna and the receiving antenna in the depth direction in order to detect the position in the depth direction such as cracks, faults, and groundwater in the ground. The direction of arrival of the generated electromagnetic wave in the vertical direction cannot be detected instantaneously.
As described above, the above-described dipole array antenna of the borehole radar system cannot be used for the purpose of detecting the three-dimensional electric field component of the electromagnetic wave generated in the natural world which is the object of the present invention. It is impossible to separate whether it originates in the ground or the ground.

  Therefore, the main object of the present invention is to provide a three-dimensional underground electromagnetic wave component that can detect a horizontal electric field component of a weak electromagnetic wave with a long wavelength with high sensitivity in a narrow observation borehole provided in the ground. It is to provide a detection sensor.

An underground electromagnetic wave three-dimensional component detection sensor according to the present invention includes a three-dimensional electric field sensor that detects a three-dimensional electric field component of an underground electromagnetic wave in a narrow observation borehole provided in the ground, The three-dimensional electric field sensor is a short dipole antenna comprising a pair of linear conductors whose overall length is smaller than the inner diameter of the observation borehole as a horizontal electric field component detection sensor for detecting electric field components in two horizontal directions among the three-dimensional electric field components. Corresponding to each of the short dipole antenna arrays, and a plurality of short dipole antenna arrays arranged in parallel in the depth direction. A differential increment that adds the potential difference between the potential and the potential induced in the other element to each of the arranged short dipole antennas. It is obtained by a vessel.
According to this invention, as a horizontal electric field component detection sensor for detecting electric field components in two horizontal directions, a plurality of short dipole antennas having a pair of linear conductors whose overall length is smaller than the diameter of the observation borehole are parallel to the depth direction. Since the difference between the potential induced in one element of each short dipole antenna and the potential induced in the other element is added by a differential amplifier, it is inserted into a narrow observation borehole. An underground electromagnetic wave three-dimensional component detection sensor that can detect the horizontal electric field component of the underground electromagnetic wave with high sensitivity can be configured.

The ground electromagnetic wave three-dimensional component detection sensor according to the present invention is such that the horizontal electric field component detection sensor is an input on one side of the differential amplifier with respect to the detection direction of each of the arranged short dipole antennas. Connected to the input on one side of the corresponding differential amplifier through a capacitor having a sufficiently large capacitance with respect to the capacitance between the input on the other side and the input on the other side, and The element on the other side with respect to the detection direction is connected to the input on the other side of the corresponding differential amplifier via a capacitor having the same capacitance as the capacitor used for connecting the element on the one side, The differential amplifier corresponding to each short dipole antenna array has a potential induced in an element on one side with respect to the detection direction of each short dipole antenna arranged. A potential difference due to the total value of charges induced in the capacitance between the input on one side and the input on the other side of the differential amplifier is detected by the potential difference with the potential induced in the element on the side. It is.
According to the present invention, in the horizontal electric field component detection sensor, the element on one side of each short dipole antenna is sufficiently large with respect to the capacitance between the input on one side and the input on the other side of the differential amplifier. Connect to the input of one side of the differential amplifier via a capacitor with capacitance, and differentially connect the device on the other side via a capacitor with the same capacitance as the capacitor used to connect the device on one side The differential amplifier is connected to the input on the other side of the amplifier, and the differential amplifier is a charge induced in the electrostatic capacitance between the input on one side and the other side of the differential amplifier due to the potential difference between the elements on both sides of each short dipole antenna. By detecting the potential difference based on the sum of the values, the potential difference between the elements on both sides of each short dipole antenna is added, so that no current is drawn from each dipole antenna element. It is possible to prevent disturbing the weak spatial electric field around the short dipole antenna, it is possible to obtain a detection sensitivity which is proportional to the number of elements of the short dipole antenna arranged.

The ground electromagnetic wave three-dimensional component detection sensor according to the present invention is configured such that the horizontal electric field component detection sensor is configured to store charges between the arranged short dipole antennas and the adjacent short dipole antennas by the short dipole antenna elements. In other words, they are arranged with a separation distance at which the influence of charge accumulation by adjacent short dipole antenna elements can be ignored.
According to the present invention, the horizontal electric field component detection sensor ignores the effect of charge accumulation by the adjacent short dipole antenna with respect to charge accumulation by each short dipole antenna between each short dipole antenna and the adjacent short dipole antenna. Since the arrangement is performed with a possible separation distance, detection sensitivity proportional to the number of elements of the short dipole antenna to be arranged can be obtained.

In the ground electromagnetic wave three-dimensional component detection sensor according to the present invention, the short dipole antenna array for detecting the electric field component in the two horizontal directions is each of the short dipole antennas arranged in the short dipole antenna array in the two horizontal directions. Are arranged in a direction orthogonal to each of the horizontal planes spaced apart from each other in the depth direction.
According to the present invention, the short dipole antenna array in two horizontal directions is arranged such that the respective elements of each short dipole antenna are arranged in directions orthogonal to each other in each horizontal plane spaced apart from each other in the depth direction. Therefore, it is possible to detect the electric field component in the two horizontal directions within the same volume, increase the space utilization efficiency of the short dipole antenna array in the two horizontal directions, and reduce the overall volume of the underground electromagnetic wave three-dimensional component detection sensor. be able to.

The ground electromagnetic wave three-dimensional component detection sensor according to the present invention is characterized in that the three-dimensional electric field sensor is a vertical electric field component detection sensor for detecting a vertical electric field component in a three-dimensional detection direction, and the electric field component detection in the two horizontal directions. A long dipole antenna having a length corresponding to the total length of a plurality of short dipole antennas, a potential induced in one element with respect to a detection direction of the long dipole antenna, and an induction in the other element And a vertical direction electric field component detection differential amplifier for detecting a potential difference between the detected electric potentials, wherein the element on one side with respect to the detection direction of the long dipole antenna is for detecting the vertical direction electric field component The differential amplification for detecting the electric field component in the vertical direction through a capacitor having a sufficiently large capacitance with respect to the capacitance between the input on one side and the input on the other side of the differential amplifier Connected to one input of the long dipole antenna, the element on the other side with respect to the detection direction of the long dipole antenna is the same as the capacitor used to connect the input on one side of the differential amplifier for detecting the vertical electric field component The vertical direction electric field component detection differential amplifier is connected to the other side input of the vertical direction electric field component detection differential amplifier through a capacitor having capacitance, and the vertical direction electric field component detection differential amplifier is connected to the detection direction of the long dipole antenna. The electrostatic capacitance between the input on one side and the input on the other side of the vertical direction electric field component detecting differential amplifier due to the potential difference between the potential induced in the one side element and the potential induced in the other side element The potential difference due to the electric charge induced in is detected.
According to the present invention, a length corresponding to the total length of a plurality of short dipole antennas for detecting electric field components in two horizontal directions as a vertical electric field component detecting sensor for detecting a vertical electric field component in the three-dimensional detection direction. In the same manner as the short dipole antenna array, the element on one side with respect to the detection direction of the long dipole antenna is the one on the one side of the differential amplifier for detecting the vertical electric field component. Connected to the input on one side of the differential amplifier for detecting the electric field component in the vertical direction through a capacitor having a sufficiently large capacitance between the input and the input on the other side of the long dipole antenna The element on the other side with respect to the detection direction is a differential amplifier for detecting the electric field component in the vertical direction via a capacitor having the same capacitance as the capacitor used for connecting the element on the one side. The vertical direction electric field component detection differential amplifier is connected to the other side input, and the vertical electric field component detection differential amplifier is connected to the other side input by the potential difference between the elements on both sides of the long dipole antenna. Since the potential difference between the elements on both sides of the long dipole antenna is detected by detecting the potential difference due to the electric charge induced by the capacitance between the vertical electric field component and the horizontal two-direction electric field component. Equivalent detection sensitivity and directivity can be obtained, and the three-dimensional electric field component of the underground electromagnetic wave can be detected evenly.

In the underground electromagnetic wave three-dimensional component detection sensor according to the present invention, the long dipole antenna is formed of a cylindrical conductor, and a ground-side cylindrical conductor of the long dipole antenna includes a connection point of the long dipole antenna. A connection coaxial cable for connecting the input side of the vertical electric field component detection differential amplifier; and at the ground end of the ground side element of the long dipole antenna, the vertical electric field component detection differential amplifier An input on one side is connected to a shield part of the connecting coaxial cable, an input on the other side of the differential electric field component detecting differential amplifier is connected to a core part of the connecting coaxial cable, and the long dipole antenna In the underground end of the ground side element, the ground side element of the long dipole antenna is passed through the capacitor having a sufficiently large capacitance. The connecting coaxial cable core wire is connected to the shield portion of the connecting coaxial cable, and the underground element of the long dipole antenna is connected to the capacitor having the same capacitance as the capacitor having a sufficiently large capacitance. Connected to the part.
According to the present invention, the long dipole antenna is formed of a cylindrical conductor, the coaxial cable for connection is provided in the cylindrical conductor of the ground side element, and the long dipole antenna is connected to the vertical electric field component detecting differential amplifier. Pass the cable through the ground side element of the long dipole antenna, and connect the ground side element of the long dipole antenna to the input on one side of the differential amplifier for detecting the vertical electric field component through the capacitor. The coaxial cable core is used for connection from the underground side element of the long dipole antenna to the other side input of the differential amplifier for detecting the vertical electric field component through the capacitor. As a result, the input on the other side of the vertical direction electric field component detection differential amplifier from the underground element of the long dipole antenna via the capacitor Connecting lines for connecting is shielded by the shield of the coaxial cable connection, the electrical coupling between the ground-side element of the long dipole antenna is suppressed. This provides a long dipole antenna that has the original directivity and signal-to-noise ratio of a dipole antenna in a narrow borehole vertical dipole antenna that must be laid along the ground-side element. Can do.

In the underground electromagnetic wave three-dimensional component detection sensor according to the present invention, the long dipole antenna is formed of a triple coaxial cable, and an outer shield portion of the triple coaxial cable is used as an antenna element. At the ground end of the ground-side triple coaxial cable of the long dipole antenna, an input on one side of the vertical direction electric field component detection differential amplifier is connected to an inner shield portion of the ground-side triple coaxial cable, and the vertical field The input on the other side of the differential amplifier for component detection is connected to the core of the ground-side triple coaxial cable, and the ground-side triple coaxial cable is connected to the ground end of the ground-side triple coaxial cable of the long dipole antenna. An outer shield part of the ground side triple coaxial cable through a capacitor having a sufficiently large capacitance, The outer shield portion of the underground side triple coaxial cable of the dipole antenna is connected to the core portion of the ground side triple coaxial cable via a capacitor having the same capacitance as the capacitor having a sufficiently large capacitance. It is.
According to the present invention, the long dipole antenna is formed of a triple coaxial cable in which the outer shield part and the inner shield part are insulated, and the outer shield part of the triple coaxial cable is used as an antenna element. Use the inner shield part of the ground side triple coaxial cable to connect to the input on one side of the differential amplifier for detecting the vertical electric field component from the ground side element through the capacitor. From the underground side element of the long dipole antenna to the capacitor Because the core part of the ground side triple coaxial cable is used for connection with the other side input of the differential amplifier for detecting the electric field component in the vertical direction through the base, the underground side element of the long dipole antenna is passed through the capacitor. Therefore, the connection line connected to the input on the other side of the differential amplifier for detecting the electric field component in the vertical direction is blocked by the inner shield part of the ground side triple coaxial cable. Is electrically coupled with the ground-side element of the long dipole antenna is suppressed. This provides a long dipole antenna that has the original directivity and signal-to-noise ratio of a dipole antenna in a narrow borehole vertical dipole antenna that must be laid along the ground-side element. Can do.

The underground electromagnetic wave three-dimensional component detection sensor according to the present invention is a search coil for detecting a three-dimensional magnetic field component of the underground electromagnetic wave corresponding to each of the detection directions of the three-dimensional electric field component of the underground electromagnetic wave by the three-dimensional electric field sensor. And a direction-of-arrival calculation means for calculating the direction of arrival of underground electromagnetic waves based on the three-direction electric field component of the three-dimensional electric field sensor and the three-direction magnetic field component of the three-dimensional magnetic field sensor. It is a thing.
According to this invention, in addition to the three-dimensional electric field sensor, the three-dimensional magnetic field sensor provided with a search coil for detecting the magnetic field component of the underground electromagnetic wave corresponding to each of the three-dimensional detection directions of the three-dimensional electric field sensor, Since the arrival direction of the underground electromagnetic wave is calculated based on the three-direction electric field component by the three-dimensional electric field sensor and the three-direction magnetic field component by the three-dimensional magnetic field sensor, the polarization plane of the underground electromagnetic wave is rotating. However, the three-dimensional arrival direction of the underground electromagnetic wave can be accurately detected, and whether the detected electromagnetic wave originates from the ground or from the ground can be correctly separated.

  According to the present invention, there is an effect that a horizontal electric field component of a weak underground electromagnetic wave having a long wavelength can be detected with high sensitivity in a narrow observation borehole provided in the ground.

  The above object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

It is a schematic block diagram of the underground electromagnetic wave three-dimensional component detection sensor concerning one Embodiment of this invention. (1) shows a circuit configuration of the horizontal electric field component detection sensor, (2) shows a circuit configuration of the vertical electric field component detection sensor, and (3) shows an arrangement configuration of antenna elements of the electric field three-dimensional component detection sensor. It is basic principle explanatory drawing of the horizontal electric field component detection sensor of the underground electromagnetic wave three-dimensional component detection sensor concerning one Embodiment of this invention. (1) shows the arrangement of antenna elements for theoretically elucidating the directional characteristics of a short dipole antenna array, (2) shows the circuit configuration of a current-driven electric field detection sensor, and (3) shows charge addition 1 shows a circuit configuration of a type electric field detection sensor. It is a figure which shows the measurement experimental data of the detection potential by the horizontal electric field component detection sensor of the underground electromagnetic wave three-dimensional component detection sensor concerning one Embodiment of this invention. (1) shows the appearance of the magnetic shield box used in the measurement experiment, and (2) measures the change in detected potential in the direction perpendicular to the electric field application electrodes installed on the left and right wall surfaces in the shield box using four types of dipole antennas. The results are shown. It is a figure which shows the measurement experimental data of the detection potential by the horizontal electric field component detection sensor of the underground electromagnetic wave three-dimensional component detection sensor concerning one Embodiment of this invention. (3) shows a spatial region that affects the detection potential of each antenna element that causes a change in the detection potential depending on the element spacing of the short dipole antenna. It is a figure which shows the measurement experimental data of the detection potential by the horizontal electric field component detection sensor of the underground electromagnetic wave three-dimensional component detection sensor concerning one Embodiment of this invention. (4) shows the measurement result of the detection potential change on the center line between the electrodes, and (5) shows the measurement result of the detection potential change due to the antenna element spacing in the measurement environment. It is a figure which shows the measurement data of the directional characteristic by the horizontal electric field component detection sensor of the underground electromagnetic wave three-dimensional component detection sensor concerning one Embodiment of this invention. (1) shows the measurement situation of the directivity of the horizontal electric field component, and (2) shows the measurement result of the directivity of the horizontal electric field component. It is a figure which shows the measurement data of the directional characteristic by the vertical electric field component detection sensor of the underground electromagnetic wave three-dimensional component detection sensor concerning one Embodiment of this invention. (1) shows the measurement situation of the directivity of the vertical electric field component, and (2) shows the measurement result of the directivity of the vertical electric field component. It is a schematic block diagram of the underground electromagnetic wave three-dimensional component detection sensor concerning other embodiment of this invention. It is a schematic block diagram of the conventional underground electromagnetic wave observation system. It is a schematic block diagram of the magnetic field 3 direction component detection sensor of underground electromagnetic waves. It is a figure which shows the problem of the electric field component detection sensor of underground electromagnetic waves.

  The presence of an oscillating electric field in the space means that a displacement current flows along the direction of the changing electric field. Therefore, the electric field component of the electromagnetic wave induces a current in the linear dipole antenna element parallel to the displacement current, and causes the current to flow through the resistance connected to the collection point (connection point) of the antenna elements on both sides. It can be detected by reading the potential difference across the resistor. Therefore, the antenna theory teaches that in order to detect many induced currents, the element length should be increased to ¼ of the wavelength of the varying electric field to be detected.

  However, when detecting an electromagnetic wave in the natural world whose wavelength is unknown, it is often limited by the size of the space where the antenna can be installed. In particular, when observing underground electromagnetic waves, an observation borehole for inserting a sensor is provided in the ground, and a dipole antenna formed in a three-dimensional direction is inserted into the borehole. However, the horizontal length is particularly limited, and it is difficult to obtain practical detection sensitivity.

The space that contributes to the current induction of the linear dipole antenna is a cylindrical region formed around the antenna element. Accordingly, in a horizontal dipole antenna on the ground, by increasing the length of the antenna element as necessary, the cylindrical region contributing to current induction can be lengthened, and the detection sensitivity can be increased.
For this reason, a vertical dipole antenna having a pair of long antenna elements is used as a sensor for detecting a vertical electric field component in an observation borehole. It is considered that necessary detection sensitivity can be obtained by securing a necessary space area.

Here, the underground electromagnetic wave is an electromagnetic wave having a long wavelength as described above, and it is considered that the electric field component of the underground electromagnetic wave to be detected is uniformly applied to the entire observation borehole. A large number of short cylindrical spaces corresponding to the inner diameter of the borehole are provided in the depth direction, and by adding the electric field components detected in each short cylindrical space, a cylindrical region equivalent to a long horizontal dipole antenna is obtained. It is thought that it can be obtained.
Thus, by adding the electric field components induced in many short horizontal dipole antennas provided in parallel in the observation borehole, it is possible to obtain detection sensitivity equivalent to that of the long horizontal dipole antenna. Is the basic idea of the present invention.

That is, the horizontal electric field component detection sensor of the present invention is basically a dipole antenna array in which short horizontal dipole antennas are arranged in parallel in the depth direction, and adds up the potential difference between the elements on both sides of each short dipole antenna. Therefore, the detection performance equivalent to that of a long dipole antenna is to be obtained.
In a normal array antenna, the purpose is to direct a sharp electromagnetic beam in a specific direction by controlling the signal phase between each antenna element. In the present invention, a signal phase difference is given between each antenna element. In this case, the structure is characterized in that it is not necessary to consider the wavelength at all.

  Therefore, the directivity characteristics of the dipole antenna array in which short dipole antennas are arranged in parallel coincide with the directivity characteristics of a single short dipole antenna, and the total induced current of N short dipole antennas arranged in parallel is It can be obtained as N times the induced current of the short dipole antenna. In this way, a number of short dipole antennas whose overall length is smaller than the inner diameter of the observation borehole are arranged in parallel, and by adding the currents induced in each short dipole antenna, they are inserted into narrow boreholes and horizontal electromagnetic waves A sensor for detecting an electric field component can be configured.

FIG. 2B shows a current-driven electric field component detection sensor according to an embodiment of the electromagnetic wave three-dimensional component detection sensor of the present invention. The current-driven electric field component detection sensor has N short dipole antenna elements (110 _A1 , 110 _B1 ), (110 _A2 , 110 _B2 ) made of a pair of linear conductors whose overall length is smaller than the inner diameter of the observation borehole. ,... (110 _AN , 110 _BN ) are arranged in parallel, and a short dipole antenna array 110 and a differential amplifier 120 for adding the potential difference between the elements on both sides of each short dipole antenna. Elements on one side (110 _A1 , 110 _A2 ,..., 110 _AN ) of each short dipole antenna are connected to an input 120 _A on one side of the differential amplifier 120 via input resistors R, respectively. The elements on the other side of the dipole antenna (110 _B1 , 110 _B2 ,..., 110 _BN ) are connected to the input 120 _B on the other side of the differential amplifier 120 via input resistors R, respectively. The other side input 120 _B is connected to the output 120 _{C of the} differential amplifier via the feedback resistor R, and the one side input 120 _A of the differential amplifier is grounded via the matching resistor R.
With such a configuration, the output voltage V _o obtained at the output 120 _C of the differential amplifier is a potential induced in the elements on both sides of each short dipole antenna, assuming that the relationship of the above equation (2) is satisfied. When the potential difference and V, V o _{= N} × V becomes, N times the voltage output of a single short dipole antenna is obtained.

However, as a result of actually arranging N short dipole antennas and performing addition using a differential amplifier as shown in FIG. 2B, a voltage proportional to the number of elements of the short dipole antenna may not be obtained. confirmed. This is because, in the circuit as shown in FIG. 2 (2), the current induced in each short dipole antenna is sucked up to the differential amplifier side via the input resistor, feedback resistor, and matching resistor. This is considered to be caused by the disturbance of the weak spatial electric field detected by the antenna.
Therefore, a more preferred embodiment will now be described in which the potential difference between the potentials induced on the elements on both sides of each short dipole antenna can be added without disturbing the spatial electric field of each short dipole antenna.

FIG. 2 (3) shows a charge addition type electric field detection sensor according to another embodiment of the electromagnetic wave three-dimensional component detection sensor of the present invention. In the charge addition type electric field detection sensor, the connection points of both elements of each short dipole antenna are connected in series by capacitors C ₁ , C ₀ , C ₁ , and the voltage at both ends of the capacitor C ₀ is obtained by a high input impedance differential amplifier. It is based on measurement.

Electric charges are accumulated in the elements on both sides of the short dipole antenna due to the alternating electric field E appearing in the space, and since the elements on both sides are conductors, equipotentials are formed respectively. Assuming that the potentials of the elements on both sides are V _A and V _B , a potential difference V (V = V _B −V _A ) is generated at the connection point.
Further, since the capacitors C1, Co, and C1 are connected in series, the same charge Q is stored in each capacitor, and potential differences V1, V ₀ , and V _{1 that} are inversely proportional to the capacitance are generated at both ends of each capacitor. Here, since the relationship of C ₁ V ₁ = C ₀ V ₀ is established, V ₁ = (C ₀ / C ₁ ) V ₀ , and the potential difference V at the connection point between the dipole antenna elements is
In this way, by adding the charges induced to the input capacitor C ₀ of the high input impedance differential amplifier through the two capacitors C ₁ due to the potential difference due to the charges accumulated in the elements on both sides of each dipole antenna. The potential difference between the elements on both sides of each short dipole antenna can be added without disturbing the spatial electric field of each dipole antenna.

That is, as shown in FIG. 2 (3), fitted with a condenser C ₁ of the same capacitance to the connection point of the elements of the N short dipole antenna arranged, the other end of each capacitor of the common capacitor to connect to the C _0. The capacitors C ₁ , C ₀ , and C ₁ are connected in series in this way because an independent electric field supply source (a kind of power source) is used for each short dipole antenna in which the electric field E generated uniformly in the space is arranged. This is because the potential V = E × l (l is the distance between the centers of the antenna elements on both sides) is given to each short dipole antenna.
Thus, although both ends to the charge Q of the capacitor C ₁ is generated, the capacitor C ₀ charge N × Q corresponding to the number of elements N of the dipole are accumulated. As a result, a potential difference N × V appears at both ends (between C and D) of the capacitor C ₀ , and as a result, a voltage N × V that is N times the voltage V detected by a single short dipole antenna can be obtained.
Note that the condition for obtaining such an approximate relationship of the electric charge addition type electric field detection sensor is C ₀ << C ₁ , and therefore the capacitor C ₀ does not need to be actually provided, and a stray capacitance by a connection cable or the like is used. be able to.

  Next, based on the above-described theory, a measurement experiment was conducted to verify whether an electric field detection sensor using a short dipole antenna array can obtain an electric field detection performance equivalent to that of a long dipole antenna. The results are shown in FIGS. 3 and 4a.

In the case of a charge addition type electric field detection sensor, since a differential amplifier with a high input impedance is used, the commercial power supply frequency component is largely mixed in a normal environment, which makes measurement difficult.
For this reason, the measurement was performed in a magnetic shield box made of permalloy alloy having an internal volume of 60 cm × 60 cm × 60 cm.
FIG. 3 a (1) shows the appearance of the magnetic shield box in which the measurement experiment was performed. In the magnetic shield box, 50 cm x 50 cm copper plate electrodes are placed 50 cm apart on the left and right wall surfaces in parallel, a short dipole antenna for measurement is placed near the center between both electrodes, and a signal is applied between the copper plate electrodes. A measurement experiment was conducted.
As an applied signal, a signal of 1 Vpp (2 Vpp between both ends) was applied to both electrodes so as to have a balanced electric field in an alternating manner with respect to both elements of the dipole antenna used for measurement. .

Prior to the electric field detection measurement experiment using the short dipole antenna array, first, a measurement experiment was performed to confirm the spatial potential distribution in the region sandwiched between the copper plate electrodes in the magnetic shield box by a single short dipole antenna. It was.
In this measurement experiment, a single short dipole antenna having one element in the electric charge addition type electric field detection sensor shown in FIG. 2 (3) is placed on the axis connecting the centers of both electrodes (in the left-right direction). Relative spatial potential in the axial direction by measuring the potential difference between both elements of the short dipole antenna at each point, and integrating in the axial direction with reference to the value at the axial center. Distribution was obtained.
In this measurement experiment, measurement was performed on four types of single short dipole antennas each having a one-side element length of 2 cm, 3 cm, 4 cm, and 5 cm formed of a copper wire having a linear shape of 0.8 mmφ.
FIG. 3 a (2) shows the measurement result of the spatial potential distribution in the axial direction in the space obtained by the measurement experiment using the short dipole antenna having the four element lengths.
In each potential distribution, it is considered that the potential gradient is constant (uniform electric field) in the vicinity of the center. As a result of dividing the gradient by the respective element lengths, in the short dipole antenna having all the element lengths, approximately 2. It shows that the electric field strength is 4 mV / m.
From this, it was verified that the space electric field can be correctly measured by the charge-added short dipole antenna regardless of the element length.

Next, in a short dipole antenna array, a measurement experiment was performed to confirm the dependence of the detected electric field on the antenna element spacing of the short dipole antenna.
As described above, in a single dipole antenna element placed in a region where a spatial electric field exists, charges corresponding to the structure are accumulated. If the length is short, it is considered that sufficient charges cannot be accumulated in the mutual elements. FIG. 3 b (3) shows the relationship between the diameter of the surrounding cylindrical effective region contributing to charge accumulation in the antenna element of such a dipole antenna and the element spacing. Therefore, if the element spacing D of the antenna elements is shorter than the diameter of the cylinder, a part of the cylinder shares an area with the adjacent cylinder, and sufficient charge cannot be supplied to the antenna element.
In order to confirm the dependence of the electric field detection on the element spacing of such a short dipole antenna array, the following measurement experiment was performed.

In order to confirm the dependence of the electric field detection on the element spacing of the short dipole antenna array, ideally a wide measurement space with a uniform electric field is required. In this measurement experiment, the above-described magnetic shield box was used because it was difficult to measure due to the mixing of.
In a narrow space such as a magnetic shield box, since the space region where the uniform electric field is formed is narrow, it is impossible to confirm the element spacing dependency of the spatial electric field in the entire short dipole antenna array. Therefore, two single short dipole antennas were used, and the measurement was performed while changing the element spacing between the two to confirm the validity of FIG. 3b (3). Prior to this measurement, the spatial electric field distribution in the measurement region in the magnetic shield box was measured.
In this measurement, a short dipole antenna with an element length of 5 cm on one side was used and moved in 5 mm increments in the direction perpendicular to the central axis at the center of the copper plate electrode, and the change in the detected potential difference (relative electric field value) was measured. .
As a result, as shown in FIG. 3 c (4), an electric field region that is seen to be uniform is obtained in the range of about 7 cm from the central axis, but small in the region close to the wall surface such as the back of the shield box or the door surface, It was found to be a non-uniform electric field. Such a non-uniform electric field cannot obtain correct element spacing dependency when the element spacing of the short dipole antenna array becomes large. Therefore, the antenna element spacing dependency of the two short dipole antennas was measured as follows.

A measurement experiment for confirming the dependency of the electric field detection on the element spacing of the short dipole antenna array was performed using a two-element short dipole antenna array in which two short dipole antennas were arranged in parallel.
The two-element short dipole antenna array used for the measurement has an element length on each side of each short dipole antenna of 5 cm, and the center between the antenna elements of the two short dipole antennas is the center of the axis between the electrodes for applying an external electric field. Then, along the measurement region shown in FIG. 3c (4), the element interval of the two short dipole antennas was changed from the minimum interval of 3.5 cm to the maximum interval of 27 cm in increments of 1 cm.
Measurements after detecting solely by both short dipole antenna, connected to a length of the connection line of the element spacing through the capacitor C ₁ from each element of the two short dipole antennas, separately connected point side of each short dipole antenna The voltage was measured by using the average value as the output voltage of the dipole antenna array.

FIG. 3c (5) shows the measurement results. In the figure, the mark indicated by ● is the output voltage of the short dipole antenna array, and the mark indicated by + is a plot of the sum of the output voltage values of the two short dipole antennas measured independently.
FIG. 3 c (5) shows the measured values on a scale from 0 V, and the output voltage value in the state of a short dipole antenna array is far away from the total output voltage of a single short dipole antenna. You can see that it is not.
However, in the vicinity of an interval of 5 cm, the output voltage in the state of a short dipole antenna array appears about 10% less than the sum of the output voltages of a single short dipole antenna, and such a situation appears up to an element interval of 13 cm. ing.
As described in the explanation of FIG. 3b (3), this indicates that the region contributing to the charge supply to the two short dipole antennas is shared, so that sufficient charge cannot be supplied to the two elements. Yes.
In FIG. 3c (5), even when the element spacing is 15 cm and 16 cm, the measured value and the total value are deviated, and the cause is unknown. However, it is considered that the two values coincide with each other by separating them by approximately 14 cm or more. be able to.
For this reason, the element interval of the short dipole antenna array according to one embodiment of the present invention is set to 14 cm.

Next, a measurement experiment was conducted to confirm the directivity characteristics of the short dipole antenna array.
In this measurement experiment, a 9-element short dipole antenna array with an element interval of 5 cm was connected to a differential amplifier as shown in FIG. 2 (3), and the short dipole antenna array was placed in the magnetic shield box of FIG. 3a (1). Then, the change in the detection voltage when the center position of the short dipole antenna array was rotated was measured.
FIG. 4a (1) shows the measurement situation of the directivity of the horizontal electric field component, and FIG. 4a (2) shows the measurement result of the directivity of the horizontal electric field component.
As a result, it was confirmed that the directivity characteristics of the short dipole antenna array coincided with the directivity characteristics of the single short dipole antenna expressed by the above equation (2). As a result, in the short dipole antenna array in which the short dipole antennas are arranged in parallel, the potential difference between the elements on both sides of each short dipole antenna element is summed up to obtain a potential difference substantially equal to that of the long dipole antenna. The theory that the characteristics of a small dipole antenna exhibited by a single short dipole antenna can be obtained.

Hereinafter, an embodiment of the underground electromagnetic wave three-dimensional component detection sensor of the present invention actually configured based on the theoretical examination of the electric field detection sensor using the short dipole antenna array as described above and the measurement experiment result demonstrating it will be described. To do.
FIG. 1 shows a schematic configuration of a ground electromagnetic wave three-dimensional component detection sensor according to an embodiment of the present invention. FIG. 1A shows a circuit configuration of a horizontal electric field component detection sensor that detects electric field components in two horizontal directions, and FIG. 1B shows a circuit configuration of a vertical electric field component detection sensor that detects an electric field component in the vertical direction. FIG. 1 (3) shows the arrangement of antenna elements in the electric field three-dimensional component detection sensor. In the underground electromagnetic wave three-dimensional component detection sensor according to this embodiment, the above-described short dipole antenna array is used as the horizontal electric field component detection sensor, and a single long dipole antenna is used as the vertical electric field component detection sensor. .

FIG. 1 (1) shows a circuit configuration of a horizontal electric field component detection sensor that detects electric field components in two horizontal directions among the three electric field components of an electromagnetic wave in the ground, and a pair whose overall length is smaller than the inner diameter of the observation borehole. The four east-west short dipole antennas ( _111A1 , _111B1 ), ( _111A2 , _111B2 ), ( _111A3 , _111B3 ), ( _111A4 , _111B4 ) made of a linear conductor Are arranged in parallel to each other to form a short dipole antenna array for detecting an east-west electric field component. Similarly, four north-south short dipole antennas (112 _A1 , 112 _B1 ), (112 _{A2, 112 B2), (112} A3, 112 B3), (112 A4, 112 South direction and arranged in parallel to _B4) in the depth direction Forming a short dipole antenna array for detecting an electric field component.
The elements on one side (111 _A1 , 111 _A2 , 111 _A3 , 111 _A4 ) with respect to the detection direction of the short dipole antenna in the east-west direction are respectively connected to the input 121 _A on one side and the input 121 _B on the other side of the differential amplifier 121. The east-west short dipole antenna is connected to the input 121 _A on one side of the differential amplifier 121 for detecting the electric field component in the east-west direction through a capacitor C ₁ having a sufficiently large capacitance relative to the capacitance C ₀ between the two. The elements on the other side (111 _B1 , 111 _B2 , 111 _B3 , 111 _B4 ) with respect to the detection direction are respectively connected via the capacitor C ₁ having the same capacitance as the capacitor used for connecting the one element. This is connected to the input 121 _B on the other side of the differential amplifier 121 for detecting the east-west electric field component. As a result, electric charges based on the potentials induced on the elements on both sides of each short dipole antenna are formed at both ends of the capacitor C ₀ between the inputs 121 _A and 121 _B of the differential amplifier 121 for detecting the east-west electric field component as described above. Is induced, and a voltage four times the potential difference between the elements on both sides of each short dipole antenna is input to the east-west electric field component detection differential amplifier 121, and the potential difference detected by each short dipole antenna. 4 times the potential difference is detected.
Similarly, the elements on one side (112 _A1 , 112 _A2 , 112 _A3 , 112 _A4 ) with respect to the detection direction of the short dipole antenna in the north-south direction are respectively connected to the input 122 _A and the input on the other side of the differential amplifier 122. via the capacitor C ₁ having a sufficiently large capacitance with respect to 122 capacitance C ₀ between _B is connected to one side of the input 122 _a north-south field component detecting differential amplifier 122, the north-south direction The other element (112 _B1 , 112 _B2 , 112 _B3 , 112 _B4 ) with respect to the detection direction of the short dipole antenna element is a capacitor C having the same capacitance as the capacitor used to connect the one element. ₁ is connected to the input 122 _B on the other side of the differential amplifier 122 for detecting the north-south direction electric field component. As a result, the both ends of the capacitor C ₀ between the inputs 122 _A and 122 _B of the north-south direction electric field component detection differential amplifier 122 are based on the potentials induced on the elements on both sides of each short dipole antenna as described above. A charge four times the charge is induced, and a voltage four times the potential difference between the elements on both sides of each short dipole antenna is input to the north-south direction electric field component detection differential amplifier 122 and detected by each short dipole antenna. A potential difference that is four times the potential difference is detected.

The capacitor _{C 0} between the input 122 _A and 122 _B of the input 121 capacitor _C between _A and 121 _{B 0} and north-south direction electric field component detecting differential amplifier 122 in the east-west direction electric field component detecting differential amplifier 121 , it is not necessary to provide in practice, as described above, respectively from both sides of the element through the capacitor C ₁ in the east-west direction electric field component detecting differential amplifier 121 and the north-south direction electric field component detecting differential amplifier 122 for each short dipole antenna It can be substituted by stray capacitance by a connection cable or the like connected to the input.

FIG. 1 (2) shows a circuit configuration of a vertical electric field component detection sensor that detects a vertical electric field component among three electric field components of an underground electromagnetic wave.
Since the vertical electric field component detection sensor is not restricted by the inner diameter of the observation borehole as in the two horizontal electric field component detection sensors, a single long dipole antenna (113 _A , 113 _B ) is used, and the horizontal electric field component is detected. In order to have detection characteristics equivalent to the detection characteristics of the detection sensor, the detection circuit has a circuit configuration that performs differential amplification by capacitor coupling in the same manner as the horizontal electric field component detection sensor.
That is, the ground-side element 113 _A of the long dipole antenna is sufficient for the capacitance C ₀ between the input 123 _A on one side and the input 123 _B on the other side of the vertical direction electric field component detection differential amplifier 123. large electrostatic via the capacitor C ₁ having a capacity is connected to one side of the input 123 _a vertical electric field component detecting differential amplifier 123, underground side device 113 _B long dipole antenna, one side of the element Is connected to the other input 123 _B of the vertical direction electric field component detection differential amplifier 123 via the capacitor C ₁ having the same capacitance as the capacitor used for the connection of the vertical direction electric field component detection differential amplifier. 123, a vertical direction electric field component detection differential is generated by a potential difference between a potential induced in one element of the long dipole antenna and a potential induced in the other element. Potential difference due to one side of the input and the other side of the induced charge on the electrostatic capacitance C ₀ between the input is detected width 123.

In the vertical electric field component sensor, narrow in the borehole for using vertical dipole antenna long, antenna elements ₍₁₁₃ A, 113 _B) and the connection for connecting the vertical electric field component detecting differential amplifier 123 cable the elongated dipole antenna becomes to laying along on the ground element 113 _a, a long die pole antenna by connection cables only on the ground element 113 _a is laid in proximity of the elongated dipole antenna There has been a problem that an unbalanced voltage is generated between the elements on both sides and becomes a noise source.
In the present invention, the ground In order to solve such a problem, long dipole antenna of the antenna elements ₍₁₁₃ A, 113 _B) and the vertical electric field component of the connection cable for connecting the sensing differential amplifier 123 long dipole antenna The configuration is such that the connection cable does not affect the electrical characteristics of the ground-side element of the long dipole antenna.
Specifically, a long dipole antenna is formed by a triple coaxial cable (triaxial cable) in which a double shield is applied and an outer shield and an inner shield are insulated, and the outer shield portion is used as an antenna element. in the ground side triple underground end of the coaxial cable length dipole antenna, the outer shield part 113 _a of the ground-side triple coaxial cable forming the ground antenna element of a long dipole antenna, the ground-side 3 through the capacitor C ₁ connected to the inner shield part 113 _E heavy coaxial cable, the outer shield portion 113 _B of the underground side triple coaxial cable to form an underground antenna element of a long dipole antenna, the ground-side triple coaxial through the capacitor C ₁ connected to the core wire portion 113 _F of the cable, terrestrial ground-side triple coaxial cable long dipole antenna In, one side of the input 123 _A vertical electric field component detecting differential amplifier, the connecting cable 113 through a _C connected to the inner shield part 113 _E of the ground-side triple coaxial cable, the vertical electric field component for detecting difference the other side of the input 123 _B of the dynamic amplifier, and to be connected to the core wire portion 113 _F of the ground-side triple coaxial cable via a connecting cable 113 _D.
In this way, the long dipole antenna is formed of a triple coaxial cable, the outer shield part of the triple coaxial cable is used as an antenna element, and the signal detected by the outer shield part of the ground side triple coaxial cable is the ground side triple. The signal detected by the outer shield part of the underground triple coaxial cable is guided to the input on one side of the differential amplifier for detecting the vertical electric field component via the inner shield part of the coaxial cable. The signal detected by the underground antenna element is shielded by the inner shield part of the ground-side triple coaxial cable, and is guided to the ground side. The antenna element is no longer affected.
The connection cables (113 _C and 113 _D ) that connect the ground end of the ground side triple coaxial cable of the long dipole antenna and the input of the vertical direction electric field component detection differential amplifier maintain an electrical equilibrium state with respect to the ground. For this reason, the inner shield part 113 _E and the core wire part 113 _{F of} the ground side triple coaxial cable are connected to two thin coaxial cables of the same type, and the one-side input 123 _{A of the} vertical direction electric field component detection differential amplifier respectively. and it is connected to the other side input 123 _B.
Further, the capacitor C ₀ between the inputs 123 _A and 123 _B of the vertical electric field component detection differential amplifier 123 does not have to be actually provided as described above, and the capacitor C ₁ is provided from the elements on both sides of the long dipole antenna. It is possible to substitute a stray capacitance by a connection cable or the like connected to the vertical electric field component detection differential amplifier 123 via the.

Here, a measurement experiment for confirming directivity characteristics was performed on the vertical electric field component detection sensor according to the embodiment. In this measurement experiment, a dipole antenna having an element length of 20 cm on one side is connected to a differential amplifier by the connection method of FIG. 1 (2), and this dipole antenna is the same as the short dipole antenna array in FIG. 3a (1). The change in the detection voltage was measured when the dipole antenna was rotated around the center position in the magnetic shield box.
FIG. 4 b (1) shows the measurement situation of the directivity of the vertical electric field component, and FIG. 4 b (2) shows the measurement result of the directivity of the vertical electric field component.
As a result, it was confirmed that the vertical electric field component detection sensor configured as shown in FIG. 1 (2) can obtain symmetrical directivity characteristics similar to those of an ideal minute dipole antenna.

FIG. 1 (3) shows how the antenna elements of the east-west electric field component detection sensor, the north-south electric field component detection sensor, and the vertical electric field component detection sensor as described above can be arranged and inserted into the observation borehole 1. It shows whether to form a three-dimensional electric field sensor that detects the three-direction electric field component of the underground electromagnetic wave.
As described above, in the short dipole antenna array for horizontal electric field component detection, when the short dipole antennas are arranged so that the cylindrical effective regions contributing to the antenna potential shown in FIG. Since the electric field detection performance corresponding to the number of dipole antennas cannot be obtained, the short dipole antenna elements adjacent to the short dipole antenna elements are charged with respect to charge accumulation between the short dipole antenna elements and the adjacent short dipole antenna elements. Arrange them at a separation distance where the effect of charge accumulation can be ignored. In this embodiment, the separation distance between the antenna elements of the short dipole antenna array was set to 14 cm based on the result of the measurement experiment of the dependency of the electric field detection on the element distance of the short dipole antenna array.
Since the observation borehole actually used here has an inner diameter of 19 cm, the total length of each of the short dipole antennas of the two short dipole antenna arrays for detecting the horizontal electric field component is 17 cm.
In addition, since the total length of the long dipole antenna for detecting the vertical electric field component has the same detection sensitivity as that of the horizontal electric field component detection sensor, the length of each short dipole antenna of the short dipole antenna array for detecting the horizontal electric field component is long. It was set to 68 cm multiplied by the number of antenna elements.

Under such conditions, in order to construct a three-dimensional electric field sensor that detects a three-dimensional electric field component in the observation borehole, as shown in FIG. 1 (3), each short dipole antenna ( 111 _A1 , 111 _B1 ), (111 _A2 , 111 _B2 ), (111 _A3 , 111 _B3 ), (111 _A4 , 111 _B4 ) antenna elements, and short dipole antennas of the short dipole antenna array in the north-south direction ( 112 _A1 , 112 _B1 ), (112 _A2 , 112 _B2 ), (112 _A3 , 112 _B3 ), and (112 _A4 , 112 _B4 ) antenna elements are separated from each other in the depth direction. In each case, the long dipole antennas (113 _A , 113 _B ) are arranged below the short dipole antenna array for detecting horizontal electric field components.

In this embodiment, the short dipole antenna array for horizontal electric field component detection uses 0.8 mmφ copper wires for each antenna element and is arranged as shown in FIG. each antenna element is fixed to the substrate, each of the central end side via the capacitor C ₁ by wiring the connection cable of each antenna element, and to connect the input side of the corresponding horizontal electric field component detecting differential amplifier .
That is, the horizontal electric field component detection sensor includes rectangular printed circuit boards 131 _A and 131 _B having a short side slightly smaller than half of the inner diameter of the observation borehole, and short sides of half the inner diameter of the observation borehole. A slightly smaller rectangular north-south direction antenna element fixing printed circuit board 132 _A , 132 _B, and circular support plates 133 ₁ , 133 that fix the printed circuit boards 131 _A , 131 _B and the printed circuit boards 132 _A , 132 _B in a direction orthogonal to _{each other} . ₂ , the elements on both sides of each short dipole antenna in the east-west direction are fixed to the east-west antenna element fixing printed boards 131 _A , 131 _B with a predetermined separation distance in the depth direction, respectively, and the north-south direction antenna element fixing the printed board ₁₃₂ a, 132 on both sides of each short dipole antenna north-south direction _B By fixing each at a predetermined distance in the depth direction element, it is possible to form a short dipole antenna array for detecting a horizontal electric field component.
In addition, the long dipole antenna for detecting the vertical electric field component connects the ground side triple coaxial cable and the underground side triple coaxial cable with the insulating support plate 134, and detects the horizontal electric field component at the ground end of the ground side triple coaxial cable. The sensor antenna element is fixed to the printed circuit boards 131 _A , 131 _B , 132 _A , 132 _B and suspended in the vertical direction, and is used from the ground end of the ground-side triple coaxial cable. It was made to connect with the input side of the differential amplifier for vertical direction electric field component detection via the connection cable (113C, 113D).

The elements on both sides of each short dipole antenna of the short dipole antenna array in the east-west direction for the short dipole antenna array in the east-west direction, the short dipole antenna array in the north-south direction, and the long dipole antenna in the vertical direction thus formed. the east-west direction electric field component detecting differential amplifier 121 which is connected via the capacitor C ₁ from the north-south direction is connected via the capacitor C ₁ from both sides of the element of each short dipole antenna north-south direction of short dipole antenna array the electric field component detecting differential amplifier 122, comprises a vertical electric field component detecting differential amplifier 123 is connected from both sides of the elements in the vertical direction of the long dipole antenna via the capacitor C _1, for detecting the east-west direction electric field component In the differential amplifier 121 and the north-south direction electric field component detection differential amplifier 122 Each short dipole antennas on both sides of the device adds the potential difference of the induced voltage in the charge adding type field detection is performed, the electric field component output V _WE and the field component output V _NS north-south east-west direction of the underground electromagnetic waves In the vertical direction electric field component detection differential amplifier 123, the electric field detection is performed by differential amplification by capacitor coupling similar to the east-west direction electric field component detection differential amplifier 121 and the north-south direction electric field component detection differential amplifier 122. done, the electric field component output V _UD in the vertical direction of the underground electromagnetic wave is outputted.

  As described above, the horizontal electric field component detection sensor is configured by arranging the same number of antenna elements with the same length of the antenna elements of the short dipole antenna array in the two horizontal directions. By using a long dipole antenna having a length obtained by multiplying the length of the short dipole antenna of the component detection sensor by the number of elements, an orthogonal three-direction electric field sensor having the same detection sensitivity for each three-dimensional electric field component can be easily realized. it can.

In the above embodiment, the vertical electric field component detection sensor has been described on the assumption that the long dipole antenna is formed by a triple coaxial cable. However, the antenna element is formed by a cylindrical conductor (for example, a cylindrical pipe) and is coaxial within the cylindrical conductor. A cable may be provided.
That is, in the ground-side cylindrical conductor of the long dipole antenna, a connection coaxial cable for connecting the connection point of the long dipole antenna and the input side of the vertical direction electric field component detecting differential amplifier is provided. of the underground end of the ground side element, the ground-side element of the long dipole antenna, connected to the shield portion of the coaxial cable connected via the capacitor C _1, the underground side element of the long dipole antenna, a capacitor C ₁ Connected to the core of the coaxial cable for connection, and at the ground end of the ground-side element of the long dipole antenna, connect the input on one side of the differential amplifier for detecting the vertical electric field component to the shield part of the coaxial cable for connection. By connecting the input on the other side of the vertical electric field component detection differential amplifier to the core portion of the connecting coaxial cable, the same effect as in the above embodiment It can form a vertical electric field component detecting sensors exhibited.

Further, by combining the three-dimensional electric field sensor for detecting the three-direction electric field component of the underground electromagnetic wave as described above with the three-dimensional magnetic field sensor for detecting the three-direction magnetic field component of the underground electromagnetic wave, Even when the plane of polarization of the rotation is rotating, it is possible to configure a ground electromagnetic wave three-dimensional component detection sensor capable of accurately detecting the three-dimensional arrival direction.
FIG. 5 shows a schematic configuration of a ground electromagnetic wave three-dimensional component detection sensor according to another embodiment of the present invention. In the underground electromagnetic wave three-dimensional component detection sensor of this embodiment, the sensor unit 100 inserted into the observation borehole 1 and the signal processing for calculating the arrival direction of the underground electromagnetic wave by processing the signal detected by the sensor unit 100 Part 200 is provided.

The sensor unit 100 includes a three-dimensional magnetic field sensor that detects the three-direction magnetic field component of the underground electromagnetic wave in addition to the three-dimensional electric field sensor that detects the three-direction electric field component of the underground electromagnetic wave illustrated in FIG.
The three-dimensional magnetic field sensor corresponds to each of the three-dimensional detection directions of the electric field component of the underground electromagnetic wave by the three-dimensional electric field sensor, and the search coil 141 for detecting the east-west magnetic field component for detecting the east-west magnetic field component of the underground electromagnetic wave. And an east-west magnetic field component detection differential amplifier 151 that amplifies the potential difference between both ends of the search coil 141 and outputs an east-west magnetic field component of the underground electromagnetic wave, and a search that detects the north-south magnetic field component of the underground electromagnetic wave. A differential amplifier 152 for detecting the north-south direction magnetic field component that amplifies the potential difference between both ends of the coil 142 and the search coil 142 and outputs the north-south direction magnetic field component of the underground electromagnetic wave, and detects the vertical magnetic field component of the underground electromagnetic wave. Search coil 143 for detecting the vertical direction magnetic field component for amplifying the potential difference between both ends of the search coil 143 and the search coil 143 to output the vertical magnetic field component of the underground electromagnetic wave It comprises a vessel 153.

  The signal processing unit 200 receives the three-direction electric field component detected by the three-dimensional electric field sensor of the detection unit 100 and the three-direction magnetic field component detected by the three-dimensional magnetic field sensor, and samples each input sensor signal. LPF (low-pass filter) 210 for preventing aliasing distortion at the time, AD converter 220 that cuts out and samples an electromagnetic wave pulse under conditions set for a signal that has passed through LPF 210, and AD conversion The computer 220 includes a computer 230 that performs a calculation process of calculating the arrival direction by taking the signal sampled in the device 220, and a display 240 that displays the arrival direction obtained by the computer 230.

Here, a process of calculating the arrival direction of the underground electromagnetic wave from the electric field three-direction component and the magnetic field three-direction component detected by the underground electromagnetic wave three-dimensional component detection sensor will be described.
Therefore, the arrival direction of the underground electromagnetic wave can be obtained by the following signal processing.

1) The six electromagnetic field components detected by the above-described underground electromagnetic wave three-dimensional component detection sensor are E _x , E _y , E _z , H _x , H _y , and H _z , which are variable electromagnetic fields, and various First, the detected signal of the electromagnetic field 6 component is decomposed into frequency components, and the amplitude and phase for each frequency are calculated.
2) Since there is a phase difference between the signals of the electromagnetic field 6 component in one frequency component, a reference signal is determined from among the signals, and components having a phase difference of π / 2 or more are in reverse phase Therefore, a negative sign is attached. As a result, six electromagnetic field components including positive and negative signs are obtained, and the pointing vector for one frequency component is determined by substituting it into the equation (4).
4) Since the reverse of the propagation direction represents the arrival direction, it is set as the arrival direction of one frequency component of the electromagnetic wave pulse detected in the ground.
5) Repeat the above steps 2) to 4) for other frequency components, and determine the direction of arrival for all frequency components.
6) Color coding is performed for each frequency calculated for one detected electromagnetic wave pulse, and the direction of the wave source is clarified by drawing the arrival azimuth lines on the same three-dimensional map.

In the above embodiment, the case where the number of elements of the short dipole antenna is 4 in each short dipole antenna array of the horizontal electric field component detection sensor has been described, but the expected electromagnetic field satisfies the plane wave approximation ( Since there is no limit in the depth direction as long as it is sufficiently far from the wave source, a large number of antenna elements can be arranged to increase detection sensitivity.
For example, when the element length of one side of each short dipole antenna is 5 cm, a short dipole antenna array is configured using 20 short dipole antennas, so that it is equivalent to a long dipole antenna having a side length of 1 m. Detection sensitivity can be obtained.

  In the above embodiment, each short dipole antenna of the short dipole antenna array of the horizontal electric field component detection sensor has been described as having the same length, but the present invention is not limited to this, Even a short dipole antenna array in which short dipole antennas with non-uniform lengths are combined has the effect of the present invention.

  In the above embodiment, each of the short horizontal dipole antennas in the two horizontal directions has been described as being arranged in a direction orthogonal to each of the horizontal planes spaced apart from each other, but the present invention is limited to this. Rather, as long as each short dipole antenna array in each detection direction is arranged in parallel with the depth direction with a predetermined separation distance, an orthogonal three-direction electric field sensor having the same detection sensitivity for each three-dimensional electric field component is used. The effect of the present invention can be achieved.

  Further, in the above embodiment, in the short dipole antenna array of the horizontal electric field component detection sensor, between the short dipole antennas and the adjacent short dipole antennas, the short dipole antenna elements adjacent to the charge accumulation by the short dipole antenna elements are used. Although the description has been given assuming that the arrangement is performed with a separation distance at which the influence of charge accumulation can be ignored, the present invention is not limited to this, and the distance between each short dipole antenna of the short dipole antenna array and the adjacent short dipole antenna May be shorter than a predetermined separation distance. In this case, detection sensitivity proportional to the number of antenna elements of the short dipole antenna array cannot be obtained, but this can be dealt with by increasing the number of elements accordingly.

In the above-described embodiment, the electric field addition type electric field detection is performed as the horizontal electric field component detection sensor. However, the present invention is not limited to this, and one side of each short dipole antenna in the differential amplifier. As long as the potential difference between the potential induced in this element and the potential induced in the other element is added, the effect of the present invention can be obtained.
In the current-driven electric field detection described above, since the current induced in each short dipole antenna is sucked up to the differential amplifier side, the weak spatial electric field detected by each short dipole antenna is disturbed, and the short dipole Although it has been confirmed that detection sensitivity proportional to the number of elements of the antenna cannot be obtained, this case can be dealt with by increasing the number of elements accordingly.

  In the above embodiment, each antenna element of each short dipole antenna array of the horizontal electric field component detection sensor has been described as being fixed using a perforated printed board, but the present invention is not limited to this. As long as each short dipole antenna can be arranged in parallel, any fixing method may be used.

As described above, according to the present invention, a plurality of short dipole antennas composed of a pair of linear conductors whose overall length is smaller than the inner diameter of the observation borehole are arranged in parallel in the depth direction, and both sides of each short dipole antenna are arranged. By adding the potential difference of the potential induced in the element, it becomes possible to obtain the same detection sensitivity and directional characteristics as a long dipole antenna, and the horizontal level of weak underground electromagnetic waves with long wavelengths in a narrow observation borehole An underground electromagnetic wave three-dimensional component detection sensor capable of detecting an electric field component with high sensitivity can be configured.
Furthermore, in addition to such a three-dimensional electric field component detection sensor, by combining a three-dimensional magnetic field component detection sensor for detecting a three-dimensional magnetic field component of the underground electromagnetic wave, an accurate three-dimensional electromagnetic wave can be detected in a narrow observation borehole. Dimensional azimuth can be detected, and even when the plane of polarization of the detected underground electromagnetic wave is rotating, it is possible to correctly separate whether it is from the ground or from the ground It becomes.
In addition, by installing such underground electromagnetic wave three-dimensional component detection sensors at a plurality of locations, it becomes possible to accurately identify the position of the source of the weak electromagnetic pulse generated due to, for example, crustal movement, etc. It is possible to construct a ground electromagnetic wave observation system useful in the field of

  The present invention is not limited to the above-described embodiments. As long as the effects of the present invention are achieved, the constituent elements described in the embodiments are appropriately replaced, new constituent elements are added, or some of the constituent elements are added. Needless to say, the constituent elements may be deleted.

1 Borehole for observation 110 _{A1 to} 110 _AN short dipole antenna one side element 110 _{B1 to} 110 _BN short dipole antenna other side element 120 differential amplifier 111 _{A1 to} 111 _A4 east-west short dipole antenna one side element 111 _{B1 to} 111 _B4 east-west direction The other side element of the short dipole antenna 121 The differential amplifier for detecting the electric field component in the east-west direction 112 _{A1 to} 112 _{A4 The} one side element of the short dipole antenna in the north-south direction 112 _{B1 to} 112 _{B4 The} other side element of the short dipole antenna in the north-south direction 122 The difference for detecting the north-south direction electric field component Dynamic Amplifier 113 _A Vertical Long Dipole Antenna Outer Shield Part of Ground Side Triple Coaxial Cable 113 _B Vertical Long Dipole Antenna Base Outer Side Triple Coaxial Cable Outer Shield Part 113 _C Vertical Long Die Pole antenna ground side element connection cable 113 _D Vertical long dipole antenna underground side element connection cable 113 _E Vertical long dipole antenna Ground side triple coaxial cable inner shield part 113 _F Vertical long dipole antenna ground side Triple coaxial cable core line 123 Vertical direction electric field component detection differential amplifier 131 _A , 131 _B East-west direction antenna element fixing printed circuit board 132 _A , 132 _B North-south direction antenna element fixing printed circuit board 133 ₁ , 133 ₂ Circular support Plate 134 Vertically long dipole antenna insulation support plate 100 Sensor part 141 East-west magnetic field component detection search coil 151 East-west magnetic field component detection differential amplifier 142 North-South magnetic field component detection search coil 152 North-South magnetic field component detection difference Dynamic amplifier 143 Search coil for detecting vertical magnetic field component 153 Differential amplifier for detecting vertical magnetic field component 200 Signal processor 210 Low-pass filter 220 AD converter 230 Computer 240 Display

Claims (8)

An underground electromagnetic wave three-dimensional component detection sensor comprising a three-dimensional electric field sensor for detecting a three-dimensional electric field component of an underground electromagnetic wave in a narrow observation borehole provided in the ground,
The three-dimensional electric field sensor is a horizontal electric field component detection sensor that detects electric field components in two horizontal directions among three-dimensional electric field components.
A short dipole antenna array in which a plurality of short dipole antennas each consisting of a pair of linear conductors whose overall length is smaller than the inner diameter of the observation borehole are arranged in parallel in the depth direction;
Corresponding to each of the short dipole antenna arrays, a potential difference between a potential induced in one element and a potential induced in the other element with respect to the detection direction of the arranged short dipole antennas, A differential amplifier for summing up each of the arranged short dipole antennas;
An underground electromagnetic wave three-dimensional component detection sensor, comprising: The horizontal electric field component detection sensor is
The element on one side with respect to the detection direction of each of the arranged short dipole antennas is sufficiently large in capacitance with respect to the capacitance between the input on one side and the input on the other side of the differential amplifier. Connected to the input on one side of the differential amplifier through a capacitor having
The element on the other side with respect to the detection direction of each of the arranged short dipole antennas is connected to the other side of the differential amplifier via a capacitor having the same capacitance as the capacitor used to connect the one side element. Connected to the side input,
The differential amplifier is arranged on one side of the differential amplifier by a potential difference between a potential induced in one element and a potential induced in the other element with respect to the detection direction of each of the arranged short dipole antennas. 2. The underground electromagnetic wave three-dimensional component detection sensor according to claim 1, wherein a potential difference due to a total value of electric charges induced in a capacitance between the input of the first input and the other input is detected. The horizontal electric field component detection sensor is
A space is provided between the arranged short dipole antennas and the adjacent short dipole antennas so that the influence of the charge accumulation by the adjacent short dipole antenna elements can be ignored with respect to the charge accumulation by the respective short dipole antenna elements. The ground electromagnetic wave three-dimensional component detection sensor according to claim 2, wherein the sensor is arranged. The short dipole antenna array for detecting electric field components in the two horizontal directions is
Each of the short dipole antennas arranged in the horizontal two-direction short dipole antenna array is arranged in a direction orthogonal to each of the horizontal planes spaced apart from each other in the depth direction. The underground electromagnetic wave three-dimensional component detection sensor according to claim 3. The three-dimensional electric field sensor corresponds to a total length of a plurality of short dipole antennas for detecting electric field components in two horizontal directions as a vertical electric field component detecting sensor for detecting a vertical electric field component among the three-dimensional electric field components. And a vertical electric field component detection for detecting a potential difference between a potential induced in one element and a potential induced in the other element with respect to the detection direction of the long dipole antenna. A differential amplifier for use,
The element on one side with respect to the detection direction of the long dipole antenna has a static electricity sufficiently large with respect to the capacitance between the one side input and the other side input of the vertical direction electric field component detection differential amplifier. Connected to one side input of the vertical direction electric field component detection differential amplifier through a capacitor having a capacitance;
The element on the other side with respect to the detection direction of the long dipole antenna has the same capacitance as the capacitor used to connect the element on the one side, and the differential amplifier for detecting the electric field component in the vertical direction Connected to the input on the other side of
The vertical electric field component detecting differential amplifier includes the vertical electric field by a potential difference between a potential induced in one element and a potential induced in the other element with respect to a detection direction of the long dipole antenna. The potential difference due to the charge induced in the capacitance between the input on one side and the input on the other side of the differential amplifier for component detection was detected.
The underground electromagnetic wave three-dimensional component detection sensor according to claim 4, wherein The long dipole antenna is formed of a cylindrical conductor, and a connection point of the long dipole antenna and an input side of the differential electric field component detecting differential amplifier are provided in the ground side cylindrical conductor of the long dipole antenna. It has a coaxial cable for connection to connect,
At the ground end of the ground-side element of the long dipole antenna, an input on one side of the vertical direction electric field component detection differential amplifier is connected to a shield part of the connection coaxial cable, and the vertical direction electric field component detection difference Connect the input on the other side of the dynamic amplifier to the core portion of the coaxial cable for connection,
At the underground end of the ground-side element of the long dipole antenna, the ground-side element of the long dipole antenna is connected to the shield portion of the connection coaxial cable via the capacitor having a sufficiently large capacitance, The underground element of the long dipole antenna is connected to the core portion of the connection coaxial cable via a capacitor having the same capacitance as the capacitor having a sufficiently large capacitance.
The underground electromagnetic wave three-dimensional component detection sensor according to claim 5, wherein: The long dipole antenna is formed of a triple coaxial cable, and an outer shield part of the triple coaxial cable is an antenna element,
At the ground end of the ground-side triple coaxial cable of the long dipole antenna, an input on one side of the vertical direction electric field component detection differential amplifier is connected to an inner shield portion of the ground-side triple coaxial cable, and the vertical Connecting the input on the other side of the differential electric field component detecting differential amplifier to the core portion of the ground side triple coaxial cable;
At the underground end of the ground-side triple coaxial cable of the long dipole antenna, an outer shield portion of the ground-side triple coaxial cable is connected to the ground-side triple coaxial cable via the capacitor having a sufficiently large capacitance. Connected to the inner shield part, the outer shield part of the base-side triple coaxial cable of the long dipole antenna is connected to the ground side 3 via a capacitor having the same capacitance as the capacitor having a sufficiently large capacitance. Connected to the core of the heavy coaxial cable
The underground electromagnetic wave three-dimensional component detection sensor according to claim 5. The apparatus further includes a three-dimensional magnetic field sensor provided with a search coil for detecting a three-dimensional magnetic field component of the underground electromagnetic wave corresponding to each detection direction of the three-dimensional electric field component of the underground electromagnetic wave by the three-dimensional electric field sensor. And
The arrival direction calculating means for calculating the arrival direction of the underground electromagnetic wave based on the three-direction electric field component by the three-dimensional electric field sensor and the three-direction magnetic field component by the three-dimensional magnetic field sensor is provided. The underground electromagnetic wave three-dimensional component detection sensor according to claim 7.