JP2000028743A - Buried object prospecting method and non-contact high- frequency current sensor for detecting cavity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily identify an underground cavity from another object. SOLUTION: A high-frequency signal generator 14 of a sensor 10 outputs a high-frequency signal to a directivity coupler 32 in synchronization with a trigger signal from a control device 56. The directivity coupler 32 divides an input signal into a transmission signal and a reference signal before outputting. A transmission signal is fed to a pair of transmission antennas 16 and 18 via a plurality of power splitters. The transmission antennas 16 and 18 are arranged close to the ground, and current flows into the ground when a high-frequency signal is applied. Antennas 20 and 22 are arranged between the transmission antennas 16 and 18, detects the voltage drop between the transmission antennas 16 and 18, and transmits a reception signal to a mixer 36 via a power combiner 50. The mixer 36 adds a reference signal from the directivity coupler 32 to the reception signal for synthesizing an IF signal and transmits it to the control device 56 via an IF amplifier/filter 54.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for measuring electric conductivity in the ground and detecting a hollow or the like in the ground, and more particularly to measuring the electric conductivity of Chiryu in a non-contact manner, TECHNICAL FIELD The present invention relates to a method for searching for a buried object and a sensor for measuring conductivity, which can detect a cavity or the like of an object.

[0002]

2. Description of the Related Art When road works such as burying pipes in the ground are performed, they are backfilled and paved so as not to impede traffic. At this time, it is checked whether or not the backfill has been completely performed and a cavity is not formed in the ground. Conventionally, when a non-destructive exploration of a cavity under a pavement of a road is performed, an underground radar that radiates an electromagnetic wave into the ground and receives the reflected wave to detect the presence or absence of the cavity has been used. The feature of this underground radar is that accurate information on the position and size of an underground object having a different dielectric constant from that of the soil can be obtained.

[0003]

However, since electromagnetic waves radiated into the ground are reflected not only from cavities but also from metals and the like, it is necessary to determine whether the object reflecting the electromagnetic waves is a cavity or another object. You need to judge. Then, the distinction between the cavity and another object is performed by examining the phase of the reflected wave. However, this phase is delicate and changes depending on the attenuation of electromagnetic waves in the ground, the shape and size of the object, and the like. Furthermore, since electromagnetic waves are reflected only on the surface of the object when the frequency increases, there is a problem that the volume information of the object is lacking. For this reason, for example, even if there is a cavity directly under the pavement, it is difficult to identify this. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the related art, and has as its object to make it easy to distinguish an underground cavity from other objects.

[0004]

In order to achieve the above object, a method for exploring a buried object according to the present invention comprises applying a high-frequency voltage between a plurality of antennas arranged in close proximity to a measurement object to thereby detect the object. , A voltage drop between the antennas is detected, the conductivity of the object to be measured is measured, and the presence or absence of an embedded object is determined. It is desirable that the electric field generated by the antenna to which the high-frequency voltage is applied be directed in a direction perpendicular to the surface to be measured.

[0005] A conductivity measuring sensor according to the present invention for carrying out the above-described searching method includes a plurality of transmitting antennas arranged close to the object to be searched, and a high-frequency voltage applied between the plurality of transmitting antennas. It has a signal generator to be applied and a receiving antenna arranged between the plurality of transmitting antennas and detecting a voltage drop between adjacent transmitting antennas. The transmitting antennas are 180
A multipole having a plurality of electrodes to which the different high-frequency voltages are applied is formed in a multipole such as a double pole, a quadrupole, or an octupole, and the plurality of electrodes are arranged in a line in a direction orthogonal to a surface to be searched. ,
It can be configured to generate an electric field having directivity in a direction orthogonal to the surface to be searched.

[0006]

The present invention configured as described above makes use of the difference in electric conductivity between the cavity and another object (for example, metal). That is, when a high-frequency voltage is applied between two transmitting antennas arranged close to the ground surface, a high-frequency current flows through the ground because the soil has a slight electrical conductivity. When there is no cavity between the two transmitting antennas, a constant voltage drop occurs between the two transmitting antennas due to the current flowing in the ground. However, if there is a cavity in the ground, that part is insulated and the voltage drop is small. Further, when a good conductor such as a metal having high electric conductivity exists in the ground, a current flows intensively therethrough, so that a voltage drop between the transmitting antennas becomes large. Therefore, by detecting the voltage drop between the transmitting antennas, it is possible to determine whether a cavity exists between the two antennas or whether a good conductor such as a metal exists. If the electric field generated by the transmitting antenna is made directional in a direction perpendicular to the surface to be searched, the electric field can be applied deeper into the ground, and the ability to detect buried objects such as cavities can be enhanced. Can be.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method for detecting an embedded object and a sensor for measuring conductivity according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of a conductivity measuring sensor according to an embodiment of the present invention. FIG.
1, the sensor 10 has an antenna unit 12 and a high-frequency signal generator 14. The antenna unit 12 includes a pair of transmission antennas 16 and 18 arranged close to the ground to be searched (measurement target) and a pair of transmission antennas 16 and 1.
It is composed of a pair of receiving antennas 20 and 22 inserted and arranged between the receiving antennas 8. Then, each transmitting antenna 16, 18
Are formed in a multipole having a plurality of electrodes (four electrodes in this embodiment) to which high-frequency voltages whose phases are shifted by 180 degrees from each other are applied, as will be described in detail later.

The high-frequency signal generator 14 has a frequency of 10 to 100 M
A high-frequency signal of an appropriate frequency between Hz, specifically, a frequency at which the wavelength is sufficiently longer than the representative dimension of the search area (search depth) is output. The directional coupler 32 is connected to the output side of the high-frequency signal generator 14. The directional coupler 32 divides the high-frequency signal output from the high-frequency signal generator 14, outputs a part of the high-frequency signal as a transmission signal to the power splitter 34, and partially uses a mixer 36 as a reference signal for detecting a reception signal. Give to.

The power splitter 34 divides the input signal into two, sets the phase of one of the divided signals to the phase of the signal input from the directional coupler 32 and the signal of 0 degree phase, and A 180-degree phase signal is obtained by shifting the phase by 180 degrees with respect to the phase of the input signal. Then, the power splitter 34 transmits the 0-degree phase signal to the transmitting antenna 1.
The signal is input to the power splitter 38 on the 6th side, and the 180-degree phase signal signal is input to the power splitter 40 on the transmitting antenna 18 side. Similarly to the power splitter 34, the power splitters 38 and 40 divide the signal and output a signal having the same phase as that of the input signal and a signal whose phase is shifted by 180 degrees, and convert these signals into power splitters 42, 44 and 46. , 48
To send to. And these power splitters 42 ~
48 also outputs a signal having the same phase as the input signal and a signal whose phase is shifted by 180 degrees.
6 and 18 are applied to the constituent electrodes.

On the other hand, the receiving antennas 20 and 22 are connected to a power combiner 50. The power combiner 50 includes a 0-degree phase signal received by the receiving antenna 20;
The 180-degree phase signal received by the receiving antenna 22 is combined into one signal and input to the mixer 36 via the amplifier 52. Then, the mixer 36 inputs the received signal obtained by adding the reference signal from the directional positive coupler 34 to the output signal of the amplifier 52 to the control device 56 via the intermediate frequency (IF) amplifier / filter 54. Has become. A rotary encoder 58 is connected to the control device 56,
A signal is input from the rotary encoder 58 as the sensor 10 is moved. Then, the control device 56 counts the output signal of the rotary encoder 58, and counts the signal for each predetermined movement distance of the sensor 10 (for example, 1 cm).
Each time), a trigger signal is given to the high-frequency signal generator 14 to output a transmission signal. Further, a signal processor / display 60 is connected to the controller 56, and performs signal processing on the detection signal (IF signal) output from the IF amplifier / filter 54 and the distance above based on the output of the rotary encoder 58. vessel·
The signal is transmitted to the filter 56 so that the state of the voltage drop between the transmitting antennas 16 and 18 can be displayed.

[0011] As shown in FIG.
A metal plate 64 for reflecting an electric field on the upper end of the insulating plate 62
Are attached, and the insulating plate 62 and the metal plate 64 are fixed perpendicularly to each other and integrated. The insulating plate 62 has four mounting plates 66, 68, 70,
72 is fixed orthogonally to the insulating plate 62 and the metal plate 64. And each of the mounting plates 66, 68, 70, 72
The transmitting antennas 16 and 18 are mounted on mounting plates 66 and 72 at both ends, with the mounting intervals p (40 cm in this embodiment). Also, the mounting plate 6
6 and 70 attached to the mounting plate 72
, Receiving antennas 20 and 22 are attached. The intervals between the mounting plates 66 to 72, that is, the intervals between the antennas need not be equal.

The transmitting antennas 16 and 18 have four electrodes formed of metal rods arranged in a line in a vertical direction perpendicular to the metal plate 64 and at regular intervals in parallel with the metal plate 64. The length L and the thickness (diameter) D of the metal rod constituting the antenna can be set according to the size of the antenna. However, the thickness is desirably 10 cm or less, and may be a square bar instead of a round bar. In this embodiment, the one having a length of 1 m and a diameter of 3 cm is used. Further, the width B of the insulating plate 62, that is, the metal plate 6
The distance B from the lower surface of 4 to the lower end of the insulating plate 62 is 20 cm in the embodiment.

One transmitting antenna 16 has electrodes 74 and 76 to which a signal (high-frequency voltage) having a phase of 0 degree is applied at its upper and lower ends, and an electrode 78 disposed between these electrodes 74 and 76. , 80 are provided with a signal having a phase of 180 degrees. The other transmitting antenna 18 is configured such that a 180-degree phase signal is applied to the upper and lower electrodes 82 and 84, and a 0-degree phase signal is applied to the electrodes 86 and 88 arranged in the middle. The receiving antenna 20 attached to the mounting plate 68 detects, for example, a voltage drop between the transmitting antennas 16 and 18 due to the 0-degree phase signal given to the transmitting antenna 16, and the receiving antenna 22 attached to the mounting plate 70 A voltage drop between the transmitting antennas 16 and 18 for the 180-degree phase signal given to the transmitting antenna 16 is detected.

The operation of the embodiment configured as described above is as follows.
It is as follows. First, the sensor 10 is attached to, for example, the lower part of the vehicle, and the antenna unit 12 is positioned several cm to 10 cm from the ground.
cm so that it is parallel to the ground. Then, the vehicle is caused to travel in the search range at a speed of, for example, 40 km / h or less. As a result, the rotary encoder 58 rolls on the ground, and outputs a pulse signal to the control device 56 at each predetermined rotation angle. Then, the control device 56
Counts the output pulses of the rotary encoder 58 and gives a trigger signal to the high-frequency signal generator 14 every predetermined traveling distance (for example, 2 cm) of the vehicle. High frequency signal generator 14
Are synchronized with a trigger signal from the control device 56 to 10-1.
A high-frequency transmission signal of a frequency suitable for searching for a fixed embedded object (cavity) of 00 MHz is generated and supplied to the directional coupler 32.

Here, the high-frequency signal output from the high-frequency signal generator 14 and having a frequency suitable for exploring a buried object means that the wavelength is sufficiently longer than a representative dimension of a measurement area (depth from the ground) of the sensor 10. This is a frequency signal. This is for the following reason. The high-frequency signal output from the high-frequency signal generator 14 travels underground as radio waves. However, an area not far from the sensor 12 (for example, the sensor 12
At a distance within a few times the representative dimension of the measurement area), it can be considered equivalent to the presence of a static electric field if the wavelength is sufficiently longer than the representative dimension of the measurement area. Then, when measuring under conditions where this static electric field cannot be assumed,
The phase of the high-frequency signal changes according to the distance between the transmitting antennas 16 and 18 and the distance from the antenna to the buried object, and it becomes impossible to easily determine the drop in the potential between the transmitting antennas 16 and 18. That is, the information of the measurement is insufficient.

The directional coupler 32 is a high-frequency signal generator 1
4 is divided, a part of the signal is input to the power splitter 34 as a transmission signal, and a part is input to the mixer 36 as a reference signal for reception. The power splitter 34
The input signal is divided into two, and one of the power splitters 38, 42, 4 is converted into a 0-degree phase signal having the same phase as the input signal.
4 to one transmitting antenna 16, and the other to the other transmitting antenna 18 via power splitters 40, 46 and 48 as a 180-degree phase signal whose phase is shifted by 180 degrees from the input signal.

The transmitting antenna 16 is supplied with a 0-degree phase signal to the upper and lower electrodes 74 and 76, for example, and the intermediate electrode 7
A signal having a phase of 180 degrees is given to 8,80. That is, as shown in FIG. 3, for example, when a (+) voltage is applied to the electrodes 74 and 76, a (-) voltage is applied to the electrodes 78 and 80. Also, the transmitting antenna 18
Are the upper and lower electrodes 82, 84, opposite to the transmitting antenna 16.
Are supplied with a 180-degree phase signal, and the intermediate electrodes 86 and 88
Is supplied with a signal having a phase of 0 degrees. The transmitting antennas 16 and 18 having four electrodes generate an electric field similar to that of the octupole due to the reflection effect of the metal plate 64, and have an electric field having a directivity in a direction orthogonal to the ground 90 which is the surface to be searched. Are formed in the underground 92 to be searched.

Since the signal (voltage) applied to the transmitting antenna 16 and the signal applied to the transmitting antenna 18 have a phase difference of 180 degrees, a potential difference occurs between the two and a current flows as indicated by an arrow 94. . The electric field generated by the transmitting antennas 16 and 18 which are substantially octupoles has directivity in the direction orthogonal to the ground 90 because the four electrodes are arranged in a line in the direction orthogonal to the ground 90. And the electric current 94 flows deeper into the underground 92. Note that reference numerals 96 and 98 shown in FIG.
Indicates an equipotential surface of the electric field generated by the transmitting antennas 16 and 18.

The receiving antennas 20 and 22 arranged between the transmitting antennas 16 and 18 input a received signal corresponding to a change in potential to the power combiner 50. The power combiner 50 combines the signals from the receiving antennas 20 and 22,
The signal is output to the mixer 36 via the amplifier 52. Then, the mixer 36 adds the directional coupler 32 to the output signal of the amplifier 52.
, And synthesizes an IF signal, which is input to the control device 56 via the IF signal amplifier / filter 54.
Further, the controller 56 sends the IF signal transmitted through the filter to the signal processor / display 60 together with the position (traveling distance) information obtained based on the output signal of the rotary encoder 58. The signal processor obtains the state of the voltage drop between the transmitting antennas 16 and 18 from the input IF signal, and displays it on the display together with the position information. This makes it possible to easily determine whether or not a cavity exists in the underground 92.

In other words, when there is no cavity or metal between the transmitting antennas 16 and 18 having electric conductivity different from that of the soil, the voltage drop between the antennas 16 and 18 is constant. The presence of an insulator with low conductivity reduces the detected voltage drop, and the presence of metal with higher electrical conductivity than soil increases the voltage drop. , Water and other objects. Moreover,
In the embodiment, since the transmitting antennas 16 and 18 are multipole, an electric field that can be searched deeper into the underground 92 can be formed, and a cavity existing deep in the underground 92 can also be detected. be able to. Further, in the embodiment, the antenna unit 12 has the transmitting antennas 16 and 1.
Since the metal plate 64 is provided on the upper portion of the sensor 8, the directivity of the electric field can be enhanced by the reflection of the metal plate 64, and no electric field is generated above the metal plate 64, so that the sensor 10 is mounted on a vehicle or the like. It is not affected by the electric field.

The sensor 10 according to the embodiment is used in combination with an underground radar, the position and size of the buried object are specified by the underground radar, and the type of the buried object is determined using the sensor 10 according to the embodiment. By identifying, it is possible to more effectively search for a cavity or the like. Further, in the above-described embodiment, the case where the object to be searched is the underground 92 has been described, but the object to be searched may be concrete or ceramic as long as a current flows.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Depth 5c in soil 102 in experimental tank 100
As a sample, a cylindrical plastic container having a diameter of 10 cm and a height of 6 cm, in which salt water 104, clay 106 and air 106 were sealed, and a copper plate 110 having a diameter of 15 cm were buried at positions m. Then, an antenna unit 12 similar to that shown in FIG. 2 was prepared, and the antenna unit 12 was moved at a speed of about 10 cm / sec in the direction of arrow 112 in FIG. Done. However, as for the dimensions of the electrodes, the length L is 16 cm, the diameter is 1.5 cm, and the vertical dimension B of the transmitting antennas 16 and 18 is 4 cm. The pitch p between the antennas is 7 cm. The frequency used for the search is 250 MHz, and the output of the high-frequency signal generator 14 is 1 mW.

FIG. 5 shows a search result, in which the horizontal axis represents the moving distance (unit: cm) of the antenna unit 12, and the vertical axis represents the output (unit: μUnit) of the sensor 10. In FIG. 5, the antenna unit 12 is moved with the soil 102 as a reference, that is, with the receiving antennas 20 and 22 in contact with the soil 102. As is clear from FIG.
As the electric conductivity of the buried object increases, the negative value of the absolute value increases, indicating a large voltage drop. In the case of air (cavity) which is an insulator, a positive value having a large absolute value is shown.

[0024]

As described above, according to the present invention, a high-frequency voltage is applied between a plurality of transmitting antennas arranged close to an object to be searched, and a current flows through the object to be searched. By detecting the state of the voltage drop, it is possible to easily detect the presence of a buried object having an electric conductivity different from that of the object to be searched. And when the electric field generated by the antenna is given directivity in the direction perpendicular to the surface to be searched,
An electric field can be applied even deeper in the ground, and the ability to detect a cavity can be enhanced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a conductivity measuring sensor according to an embodiment of the present invention.

FIG. 2 is a detailed explanatory diagram of an antenna unit according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of an electric field generated by the antenna unit according to the embodiment.

FIG. 4 is an explanatory view of an earthen tub used in the example.

FIG. 5 is a diagram showing a result of exploring the earth tank shown in FIG. 4 by an antenna unit according to an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Sensor 12 Antenna part 14 Signal generator (high-frequency signal generator) 16, 18 Transmitting antenna 20, 22 Receiving antenna 32 Directional coupler 36 Mixer 56 Control device 60 Signal processor / display

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasunari Mori 3-1-1, Tamano, Tamano-shi, Okayama Mitsui Engineering & Shipbuilding Co., Ltd. (72) Inventor Takayoshi Yumai 3-1-1, Tamano, Tamano-shi, Okayama No. Mitsui Engineering & Shipbuilding Co., Ltd.

Claims (4)

[Claims] 1. A high-frequency voltage is applied between a plurality of antennas arranged close to a measurement target to cause a current to flow through the measurement target, and a voltage drop between the antennas is detected to determine the conductivity of the measurement target. A method for exploring a buried object, comprising measuring to determine the presence or absence of a buried object. 2. The method according to claim 1, wherein the antenna generates an electric field directed in a direction perpendicular to a surface of the object to be measured. 3. A plurality of transmitting antennas arranged close to an object to be searched, a signal generator for applying a high-frequency voltage between the plurality of transmitting antennas, and an adjacent transmitting antenna arranged between the plurality of transmitting antennas. A sensor for measuring conductivity, comprising a receiving antenna for detecting a voltage drop between antennas. 4. The transmitting antennas are 180 ° out of phase with each other.
The multi-pole having a plurality of electrodes to which the different high-frequency voltages are applied, the plurality of electrodes being arranged in a line in a direction perpendicular to a surface to be searched. Conductivity measurement sensor.