JP3366124B2 - Underground exploration equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underground buried object exploration apparatus for exploring underground buried objects.

[0002]

2. Description of the Related Art An underground buried object exploration radar is known as a means for quickly and nondestructively measuring pipes and underground structures buried underground. It transmits radio waves from one antenna,
The other antenna receives the reflected wave reflected from the underground buried object and displays it on the display. However, in general commercially available antennas, the directions of the transmitting antenna and the receiving antenna are parallel, so not only the echo of the underground buried object but also the echo from the ground surface is received, and It will be greatly affected.

In order to prevent the influence of the earth's surface, the transmitting and receiving antennas should be orthogonal to each other.
Proposed in No. 05530. This is to connect two transmitting antennas with a 180 ° hybrid circuit to form a transmitting antenna set, and to connect two receiving antennas with a 180 ° hybrid circuit to form a receiving antenna set. Are orthogonal to each other. By doing so, it is possible to strongly capture the reflected wave from the position rotated by 45 ° with respect to the axis made orthogonal by the transmitting and receiving antenna group. Therefore, the entire image of the underground buried object can be captured by rotating the antenna.

[0004]

However, in such a conventional antenna, it is necessary to rotate the antenna even when the directionality of the underground buried object is not required and when the buried object is detected. It had a mechanically complicated structure. The present invention has been made in view of such a situation, and is intended to obtain the maximum reflection of an underground buried object without rotating the antenna.

[0005]

In order to solve such a problem, the invention of claim 1 is to set a transmitting antenna set at one end and the other end of a metal plate and a receiving antenna provided at a 90.degree. A first transmitting / receiving antenna composed of an antenna set, a second transmitting / receiving antenna having the same structure as that of the first transmitting / receiving antenna, which is provided at a position on a metal plate rotated by 45 ° about a central portion of the metal plate, and a first transmitting / receiving antenna And a switching unit for alternately switching the second transmitting / receiving antenna, and the first and second
It is obtained by a signal processing unit for obtaining the square sum of the scattering matrix elements obtained from each of the transmitting and receiving antennas.
According to a second aspect of the present invention, in the first aspect of the invention, the signal transmitted from the antennas forming the transmitting antenna set is in a frequency band including a high frequency signal having a diameter of the metal plate as a half wavelength.

[0006]

According to the invention of claim 1, the sum of squares of the signal detected by the first transmitting / receiving antenna and the signal detected by the second transmitting / receiving antenna becomes a value independent of the angle,
It shows the maximum value of the reflection of the buried object. Claim 2
In the invention, the metal plate resonates with the radio wave transmitted from the transmitting antenna.

[0007]

1 is a block diagram showing an embodiment of the present invention, in which a transceiver 1 supplies a high frequency signal for transmission and a switching signal for antenna switching to an antenna switching device 2,
The antenna switching device 2 alternately switches the supplied high-frequency signal according to the switching signal and supplies the high-frequency signal to the transmitting 180 ° hybrid circuit 4 and the transmitting 180 ° hybrid circuit 5. When the 180 ° hybrid circuit 4 is selected, the supplied high frequency signal is supplied to the transmitting antenna 10 and the transmitting antenna 11 in the opposite phase, and they are radiated into the ground as radio waves. Further, when the 180 ° hybrid circuit 5 is selected, the transmitting antenna 12 is similarly set.
And 13 emit radio waves. In this case, the transmitting antennas 10 to 13 are placed near the surface of the earth, from which radio waves are radiated into the ground. The 180 ° hybrid circuit 4
Transmitting antenna 10 and transmitting antenna 11 coupled by
Form one transmitting antenna set, and the transmitting antennas 12 and 13 combined by the 180 ° hybrid circuit 5 form the other transmitting antenna set. In addition, the signals received by the receiving antenna 14 and the receiving antenna 15 are 180
In the hybrid circuit 6, the signals from one of the receiving antennas are combined in opposite phases and are combined and supplied to the antenna switching device 3, and the signals received by the receiving antennas 16 and 17 are also processed in the 180 ° hybrid circuit 7. It is supplied to the antenna switching device 3. The antenna switching device 3 is switched in synchronization with the transmission side by the switching signal supplied from the transceiver 1, and supplies the reflected signal obtained by the switching to the transceiver 1. The receiving antennas 14 and 15 connected by the 180 ° hybrid circuit 6 form one receiving antenna set, and the receiving antennas 16 and 17 connected by the 180 ° hybrid circuit 7 form the other receiving antenna set. There is.

In FIG. 1, antenna switching devices 2 and 180
° Hybrid circuits 4 and 5, transmitting antennas 10-1
Reference numeral 3 constitutes a transmitting antenna system 20. The antenna switch 3, the 180 ° hybrid circuits 6 and 7, and the receiving antennas 14 to 17 form a receiving antenna system 21.

In this example, as shown in the plan view of FIG. 2, the transmitting antenna and the receiving antenna are attached to opposite sides of an octagon, and a metal plate is attached to the transmitting antenna group composed of the transmitting antennas 10 and 11. A receiving antenna set composed of the receiving antennas 14 and 15 is attached at a position rotated by 90 ° around the central portion. The transmitting antenna set and the receiving antenna set shown in satin in FIG. 2 are one transmitting / receiving antenna. The other transmitting antenna 12 shown by hatching at a position rotated by 45 ° around the central portion of the metal plate with respect to the transmitting and receiving antenna shown by this satin finish.
And 13, and the other transmitting / receiving antenna including receiving antennas 16 and 17 is provided. In this example, the antenna is attached to an octagonal metal plate, but it may be a circular metal plate.

FIG. 3 is a block diagram showing the internal structure of the transceiver 1. The rotary encoder 1j generates the distance pulse shown in FIG. 4A for each unit distance as the vehicle travels, and the control circuit 1k outputs the pulse. In response to the signal, the VCO 1a is shown in FIG.
The control voltage shown in (b) is supplied, and the switching signal shown in FIG. 4 (c) is supplied to the transmitting antenna system 20 and the receiving antenna system 21. The VCO 1a is swept according to the supplied voltage level, and as an example, generates a swept high frequency signal in the range of DC to 700 MHz. As shown in (b), the control voltage generates the same signal twice during the period in which the distance pulse is generated, and the switching signal is generated in synchronization with the first control voltage as shown in (c). ing.
In this example, it is assumed that the antenna selectors 2 and 3 of FIG. 1 select the 180 ° hybrid circuits 4 and 6 when the switching signal is generated. The frequency swept by the VCO 1a should include a frequency corresponding to a wavelength twice the diameter of the metal plate on which the antenna is attached near the center, and the metal plate will resonate at that frequency and transmit a strong electric wave. Therefore, even if the antenna used is a small one that resonates at the higher frequency of the swept frequency band, it can efficiently radiate radio waves up to the vicinity of the resonance frequency, and can be made compact and lightweight.

The signal output from the VCO 1a is supplied to the mixer 1c via the directional coupler 1b, where it is combined with the low frequency signal generated by the oscillator 1d to be an amplitude modulated wave and supplied to the transmitting antenna system 20. It The transmitting antenna system 20 alternately transmits the transmitting antenna group of the transmitting antennas 10 and 11 of FIG. 2 and the transmitting antenna group of the transmitting antennas 12 and 13 located at a position rotated by 45 ° alternately by the switching signal supplied from the control circuit 1k. Radio waves are radiated from the selected transmission antenna set.

The radiated radio wave is reflected by the underground buried object 4 and received by the receiving antenna system 21.
The radio waves transmitted by the 0 and 11 transmitting antenna groups are shown in FIG.
The signal received by the receiving antenna set of the receiving antennas 14 and 15 of FIG. 2 is used, and the radio wave transmitted by the transmitting antenna set of the transmitting antennas 12 and 13 is received by the receiving antenna set of the receiving antennas 16 and 17 of FIG. The transmitting antenna system 20 and the receiving antenna system 21 are controlled by a control signal from the control circuit 1k so that the one used.

The received signal is the signal generated by the oscillator 1d and delayed by the delay line 1f, thereby the mixer 1
g. Then, the output signal of the mixer 1g is branched by the directional coupler 1b and further combined by the mixer 1h by the signal delayed by the delay line 1e.
i and the signal processing device 1m.

In the signal processing device 1m, the conversion of the scattering matrix component by the rotation of the measurement direction for performing the signal processing by the known scattering matrix is obtained by the following equations (1a) to (1c).

[Equation 1] A detailed description is omitted because the coordinate rotation processing by the scattering matrix is complicated, but assuming the X and Y axes orthogonal to the ground surface, Sxy transmits radio waves in the X direction and transmits the Y direction polarized wave. Sxx is the component that detects the reflected wave, Sxx is the component that detects the X-direction polarized wave by transmitting the X-direction polarized wave, and Syy is the Y-direction polarized wave that is the Y-direction polarized wave. Is a component that has detected, and the calculation for obtaining them is the coordinate rotation processing by the scattering matrix. Note that θ is the angle that the antenna makes with the X axis.

By the way, in the present proposal, since the other receiving antenna set is attached by rotating it by an angle of π / 4 with respect to the one receiving antenna set, θ in equation (1a) is satisfied.
By setting = θ ± π / 4, the following expression (2) is obtained.

[Equation 2] Sxx, Syy, and Sxy are as shown in FIG.
Sxy represents the X coordinate lowered from the yy points P and Q on the X axis, and Sxy represents the Y coordinate.

Since the phase of the expression (2) differs from that of the expression (1) by 90 °, the sum of squares of the respective reception components is calculated as follows.
It becomes like (3).

[Equation 3] In order to obtain the sum of squares, the reception input represented by the equation (1) and the reception input represented by the equation (2) are respectively stored in the memory, and the data necessary for the calculation are read and used.

That is, since the equation (3) is not a function of θ, the maximum value R of the reflected wave can be obtained as shown in FIG. 5 without rotating the antenna.

In this way, the maximum value of the reflected wave can be obtained without rotating the antenna, but in the case of an elongated object such as a buried pipe, it may not be known in which direction it is buried. . In such a case, if the antenna is rotated as in the conventional case, the magnitude of the reflected wave changes, so that the direction in which the buried object is buried can be known.

In FIG. 3, if the high-frequency oscillation frequency oscillated by the VCO 1a is fi and the low-frequency oscillation frequency for modulation oscillated by the oscillator 1d is f0, the output of the diplexer 1i is expressed by equation (4). ACOS (2πf ₀ t ₀ + θ ₀ ) COS (2πf _i t ₀ + θ _i ) ・ ・ ・ ・ (4)

Here, A is the magnitude of reflection, t ₀ is the time until the radio wave radiated from the transmitting antenna is reflected by the underground buried object and returns to the receiving antenna, and θ ₀ is shown in FIG. In order to determine the phase of the amplitude-modulated wave shown, the phase determined by adjustment of the delay line 1f, θ _i is the signal from both inputs of the mixer 1h in FIG. 3, that is, the signal from the directional coupler 1b and the signal transmitted from the directional coupler 1b. It is the phase difference of the signals that pass through the antenna system 20 and the receiving antenna system 21 and reach the mixer 1h.
Determined by adjusting e.

The delay line 1f is for adjusting the phase. If the envelope is adjusted so that the position of the node of the envelope is close to the ground surface, the amplitude near the ground surface becomes small and reflection on the ground surface is suppressed. To be Usually, the reflected wave is large on the ground surface, attenuates as the depth increases, and the amplitude of the reflected wave decreases. Therefore, if the position of the envelope node is adjusted so that it is close to the ground surface, the amplitude on the ground surface will be small, the influence of reflected waves from the ground surface will be small, and the amplitude will be amplified in the depth direction. Will be. In this case, the position of the knot depends on whether or not there is an embedded object near the ground surface, but if there is no embedded object, the ground surface should be located at the node of the envelope curve. When the buried object of the depth is removed and the measurement is performed, the distance L1 may be adjusted so that the vicinity of the buried object position becomes a node. Normally, θ ₀ = π / 2 is set in the vicinity to eliminate the influence of reflection near the ground surface.

The oscillation frequency f0 of the oscillator 1d determines the size of the time domain data to be displayed, that is, the position of L2 in FIG. 6 corresponding to the depth of the echo. The position of the antinode of the envelope is the depth to be measured. Adjust to the position. That is,
Adjust so that the measured value is approximately π / 4 from the position of the envelope node. As a result, the reflected wave from the measurement position is amplified. The delay line 1e is a directional coupler 1b.
The time until the radio wave emitted from the transmitting antenna system 20 via the receiver is directly received by the receiving antenna system 21 and supplied to the multiplier 1h, and reaches the multiplier 1h from the directional coupler 1b through the delay line 1e. Adjust so that the times are the same. In this way, the signal received by the receiving antenna 21 through the ground surface has the same phase as the signal supplied through the delay line 1e, and therefore the frequency component of the signal transmitted from the mixer 1h is DC. Become an ingredient. On the other hand, since the phase of the radio wave reflected from the ground is delayed, the multiplier 1
The frequency component of the difference output from h becomes the frequency corresponding to the phase delay. Therefore, a reflection signal from a deeper position has a higher frequency component. Thereby, the depth of the buried object can be known from the detected frequency component.

[0023]

As described above, the invention of claim 1 is
Since the transmitting and receiving antennas of a set are arranged in a state of being rotated by 45 ° and the sum of squares of reflected waves due to the radio waves alternately radiated from each antenna is obtained, the maximum reflection of the underground buried object can be obtained without rotating the antennas. It has the effect that The invention of claim 2 is the same as the invention of claim 1,
Since the VCO generates a signal including a radio wave having a frequency having a wavelength twice the diameter of the metal plate to which the antenna is attached, the metal plate resonates at that frequency, and even a small antenna can use a low frequency. Since it is possible to realize the weight reduction and to reduce the frequency of the radio wave, it is possible to measure at a deeper position.

[Brief description of drawings]

FIG. 1 is a block diagram showing a signal system for driving an antenna to which the present invention is applied.

FIG. 2 is a plan view showing an embodiment of the configuration of the antenna of the present invention.

3 is a block diagram showing a configuration of a transceiver in FIG.

FIG. 4 is a time chart showing the sweeping state of the VCO of FIG. 2 and the timing of signals for driving the antenna switching device of FIG.

FIG. 5 is a diagram showing a coordinate rotation of a scattering component.

FIG. 6 is a diagram showing a waveform of an envelope curve in the ground.

[Explanation of symbols]

1 ... Transceiver, 2,3 ... Antenna switch, 4-7 ... 18
0 ° hybrid circuit, 10 to 13 ... Transmitting antenna, 1
4 to 17 ... Receiving antenna, 20 ... Transmitting antenna system, 21
… Receiving antenna system.

Claims (2)

(57) [Claims] 1. An underground buried object exploration apparatus for exploring an underground condition by a reflected wave reflected from an underground buried object, wherein an antenna is provided on one end and the other end of a circular or regular octagonal metal plate, respectively. And a transmission antenna configured by connecting the two antennas by a hybrid circuit (4) that supplies signals having opposite phases to one antenna (10) and the other antenna (11). It said gold rotated 90 degrees with respect to the set and before Kioku credit antenna assembly and said transmitting antenna assembly about said metal plate central portion takes the same structure
A receiving antenna set (14, 14) arranged at a position on the base plate to receive a reflected wave of a signal transmitted from the transmitting antenna set.
15 and 6), and a first transmission / reception antenna having the same structure as the first transmission / reception antenna with respect to the center of the metal plate.
And ° rotated second transceiver antenna disposed at a position on the metal plate (12,13,5,16,17,7), switches the first transceiver antenna and said second transmitting and receiving antennas alternately a switching unit (2,3), the signal processing device for determining the square sum of the scattering matrix elements obtained from each of said first and second transmitting and receiving antenna (1
m) is provided with the underground buried object exploration device. 2. The method of claim 1, signals transmitted from antennas constituting the transmitting antenna assembly is ground, characterized in that the diameter of the metal plate is a frequency band including a high frequency signal to be a half wavelength Buried object exploration device.