JPH0149911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried object detection device for detecting buried objects underground.

A conventional device of this type is shown in FIG. In FIG. 1, 1 is an oscillator, 2 is a transmitting antenna, 3 and 4 are receiving antennas, 5 and 6 are detectors with mutually polarized polarities, 7 is a differential comparator, 8 is an indicator, and 9 is the above-mentioned transmitting antenna. 2 and a container for storing and fixing receiving antennas 3 and 4, 10 a foreign object or buried object, and 11 a homogeneous object such as soil or sand.

Next, the operation of the above conventional device will be explained. Radio waves generated by an oscillator 1 are transmitted from a transmitting antenna 2 and received by receiving antennas 3 and 4. The radio waves received by the receiving antennas 3 and 4 are transmitted to the buried object 10.
Otherwise, the radio waves are the radio waves reflected from the homogeneous object 11 and the radio waves directly received from the transmitting antenna 2. At this time, since the receiving antennas 3 and 4 are arranged so that the distance D ₀ from the transmitting antenna 2 is the same, the strength of the radio waves of the receiving antennas 3 and 4 is equal to that between the container 9 and the homogeneous object 11. Even if the distance L ₀ changes, it changes by the same amount at the same time. Receiving antenna 3
The radio waves received by and 4 are converted into DC signals with different polarities and the same magnitude by detectors 5 and 6, which have opposite polarities, and these two signals are applied to a differential comparator 7, whose output is If there is no buried object 10, it will always be zero. Next, when the container 9 is moved in the direction of the arrow V, the reception antenna 4 is affected by the presence of the buried object 10, causing a change in the indicator 8, which has been in an equilibrium state until now. Further, when the transmitting antenna 2 is near the buried object 10, the receiving antennas 3 and 4 are again in an equilibrium state and the indicator 8 indicates zero. Furthermore,
When the receiving antenna 3 approaches the buried object 10, it becomes unbalanced and the indicator 8 changes. Therefore, the presence of the buried object 10 can be known from the change in the indicator 8.

By the way, radio waves are emitted from the transmitting antenna 2 and directly reach the receiving antennas 3 and 4 placed at a distance D ₀ from the transmitting antenna 2, and radio waves are emitted from the transmitting antenna 2 and reflected by the homogeneous object 11 to the receiving antenna. The radio waves reaching 3 and 4 are received by antenna 3.
and 4 to cause interference, and a standing wave is generated due to the distance L ₀ between the transmitting antenna 2 and the homogeneous object 11. Therefore, if the distance L ₀ between the transmitting antenna 2 or receiving antennas 3 and 4 and the homogeneous object 11 changes, the receiving antennas 3 and 4 will change even though the power of the radio waves being transmitted from the transmitting antenna 2 is constant. The strength of the radio waves received varies.

The above-mentioned standing wave is emitted from the transmitting antenna 2 by the distance D ₀ between the transmitting antenna 2 and the receiving antennas 3 and 4, the distance L ₀ between the transmitting antenna 2 or the receiving antenna 3 or 4, and the homogeneous object 11, and It is inevitably determined by the frequency of the radio waves. Similarly,
Distance between transmitting antenna 2 and receiving antennas 3 and 4 D ₀
It is also inevitably determined by the distance M ₀ between the transmitting antenna 2 or the receiving antenna 3 or 4 and the buried object 10, and the frequency of the radio waves emitted from the transmitting antenna 2.

According to experiments, the standing waves at the positions of the receiving antennas 3 and 4 were measured by changing the distance _L0 between the homogeneous object 11 and the container 9 that houses and fixing the transmitting antenna 2 and the receiving antennas 3 and 4. The magnitude of the standing wave in the case of only the homogeneous object 11 and the buried object 10
There will come a point where the magnitude of the standing waves becomes the same.

The reason for this can be explained by the spacing in the configurations of Figure 5 A and B.
This will be explained using FIG. 6, which shows experimental results when L ₀ is varied. First, in the configuration shown in FIG. As a result, the distance L ₀ between the transmitting antenna 2 and receiving antennas 3 and 4 and the homogeneous medium 11 and the detector 5,
6 changes as shown by the solid line in FIG.

Next, the buried object 10 is buried as shown in FIG. 5B,
As in the case of FIG. 5A, when the distance L ₀ is increased, the distance changes greatly as shown by the dotted line in FIG. 6. However, from FIG. 6, the specific values of distance L ₀ L ₀ 1, L ₀ 2,
In L ₀ 3, L ₀ 4, and L ₀ 5, dotted lines indicate the outputs of the detectors 5 and 6 when there is a buried object 10, and
The solid lines showing the outputs of the detectors 5 and 6 when there is no buried object overlap, and the outputs of the detectors 5 and 6 are the same regardless of whether there is a buried object or not.

Note that when the container 9 in FIG. 1 is moved in the V direction, the distance L ₀ is constant and if there is only a homogeneous object 11, the magnitude of the output of the detectors 5 and 6 due to the standing wave is constant. .

Since the conventional buried object detection device described above is configured as described above, the container 9 is moved in the direction of arrow V,
One receiving antenna 4 is in the state shown in FIG. 5B,
When the other receiving antenna 3 is in the state shown in FIG. 5A, the distance L ₀ becomes the specific value L ₀ 1, shown in FIG.
At L ₀ 2, L ₀ 3, L ₀ 4, and L ₀ 5, the outputs of the detectors 5 and 6 are the same, so no signal appears on the indicator 8, indicating zero. Therefore, in the conventional buried object detection device described above, even though the buried object 10 is present, the distance L ₀ between the container 9 and the homogeneous object 11 is
There is a drawback that depending on the size of the buried object 10, there is a distance _L0 at which the buried object 10 cannot be detected. Furthermore, if the receiving system is arranged symmetrically on both sides of the transmitting system using a large number of antennas, and the detection polarities of the signals obtained from each antenna are set to opposite polarities, the distance between the container 9 and the homogeneous object 11 will be The above-mentioned problem of standing waves caused by a certain size of ₀ was not solved, and there were further drawbacks such as radio waves interfering with each other between multiple antennas.

This invention was made to eliminate the drawbacks of the conventional device as described above, and solves the problem of standing waves by using two or more different frequencies simultaneously or intermittently. The present invention aims to provide a buried object detection device that can perform buried object detection with high reliability.

The features of the present invention include a signal generating unit including at least two oscillators with different oscillation frequencies, two or more transmitting antennas with different frequencies for transmitting signals from the signal generating unit, and one transmitting antenna. an antenna unit composed of two or more sets each including two receiving antennas having the same frequency as the transmitting antenna, a circuit for detecting and amplifying the signal received by each of the receiving antennas, and a circuit for detecting and amplifying the signal received by each of the receiving antennas; It is equipped with a signal processing section consisting of a differential amplifier circuit that outputs only the difference between signals, a logic circuit that ORs the output signals of the differential amplifier circuit for each different frequency, and an indicator that indicates the output of the logic circuit. let me,
Two receiving antennas, which form a pair with the above-mentioned transmitting antenna and have the same frequency as the above-mentioned transmitting antenna, are arranged in a row at symmetrical positions on both sides of the above-mentioned transmitting antenna. Even if the distance to the detection surface changes, the signal from the buried object is generated by one of the sets of different frequencies, so that no matter the distance between the container that houses and fixes the antenna section and the detection surface, It is also possible to detect signals from buried objects, and since each set of antennas has a different frequency, it is possible to prevent interference between each set of antennas.

Another feature of the invention is that instead of at least two oscillators with different oscillation frequencies, one oscillator that continuously or intermittently oscillates two or more different frequencies is used as a transmitting antenna and a receiving antenna. The advantage is that a device capable of operating at two or more different frequencies can be used, and in this case as well, signals from the buried object can be detected at any distance between the container that houses and fixes the antenna section and the surface to be detected.

Embodiments of the buried object detection device according to the present invention will be described below with reference to the drawings.

FIG. 2 shows a first embodiment of the invention. In this figure, a ₁ is the signal generation section, b ₁ is the antenna section, and c ₁
is a signal processing section, 20a and 20b are oscillators, 21a
and 21b are resistive attenuators, 22a and 22b are transmitting antennas, 23a, 23b, 24a and 24b are receiving antennas, 25a, 25b, 26a and 26b are detection amplifier circuits, 27a and 27b are differential amplifier circuits, 2
8 is a logic circuit, and 30 is an indicator.

Next, the operation of the above embodiment will be explained. The radio waves oscillated by the oscillator 20a are transmitted through the resistance attenuator 21a.
or the transmitting antenna 22 while being oscillated by the oscillator 20a without attaching the resistive attenuator 21a.
It is fired from a. Radio waves emitted from the transmitting antenna 22a are received by the receiving antennas 23a and 24a, sent to the respective detection amplifier circuits 25a and 26a, and further converted into DC signals by the detection amplifier circuits 25a and 26a, and then sent to the differential amplifier circuit 27a. sent to. The differential amplifier circuit 27a is the detection amplifier circuit 25a.
and 26a, and the difference between the two signals is processed by a logic circuit 28 using an OR circuit.
sent to.

On the other hand, the radio waves oscillated by the oscillator 20b at a frequency different from that of the oscillator 20a pass through the resistance attenuator 21b, or remain oscillated by the oscillator 20b without attaching the resistance attenuator 21b and are sent to the transmitting antenna 22.
It is fired from b. Radio waves emitted from the transmitting antenna 22b are received by the receiving antennas 23b and 24b, sent to the respective detection amplifier circuits 25b and 26b, and further converted into DC signals by the detection amplifier circuits 25b and 26b, and then sent to the differential amplifier circuit 27b. sent to. The differential amplifier circuit 27b is the detection amplifier circuit 25b.
and 26b, and the difference signal between the two signals is applied to the logic circuit 2 using an OR circuit.
Sent to 8. The logic circuit 28 is a differential amplifier circuit 27
When a signal is generated at either a or 27b, it is activated and produces an output, which activates the indicator 30 to notify the presence of a buried object.

Next, the case of detecting a buried object will be explained with reference to FIG. FIG. 3 shows a transmitting antenna 22a, a set of receiving antennas 23a and 24a arranged in a row symmetrically on both sides of the transmitting antenna 22a, a transmitting antenna 22b having a different frequency from the set, and a receiving antenna 22b arranged symmetrically in a row on both sides of the transmitting antenna 22a. The arrangement of a pair of antennas 23b and 24b is shown. In FIG. 3, the container A is located parallel to the detected surface 40 at a distance L ₁ , and is located at a distance M ₁ from the buried object 41 .

First, if the buried object 41 is not near the container A, it is emitted from the transmitting antenna 22a and
The strength of the radio waves reflected at 0 and sent to the receiving antennas 23a and 24a is the same, and the strength of the radio waves reflected at the transmitting antenna 2
Since the intensities of the radio waves emitted from 2a and directly sent to receiving antennas 23a and 24a are the same, the outputs of detection amplifier circuits 25a and 26a are the same, and therefore the output of differential amplifier circuit 27a is zero. Furthermore, although the frequency of the radio waves emitted from the transmitting antenna 22b is different from that of the radio waves emitted from the transmitting antenna 22a, the radio waves emitted from the transmitting antenna 22b are reflected by the detection surface 40, and are transmitted to the receiving antenna 23b and 2.
The strength of the radio waves sent to 4b is the same, and the strength of the radio waves emitted from the transmitting antenna 22b and directly sent to the receiving antennas 23b and 24b is also the same, so the outputs of the detection amplifier circuits 25b and 26b are the same, and the difference is The output of the dynamic amplifier circuit 27b becomes zero. Therefore, since the outputs of the differential amplifier circuits 27a and 27b are zero, the output of the logic circuit 28 is zero, and the indicator 30 does not indicate anything.

Next, when the container A moves in the X direction and the receiving antennas 24a and 24b come close to the top of the buried object 41, first, the signal is emitted from the transmitting antenna 22a, changes under the influence of the buried object 41, and changes to the receiving antenna. 24
The radio waves sent to the antenna 22a and the radio waves emitted from the transmitting antenna 22a and directly sent to the receiving antenna 24a are combined by the detection amplifier circuit 26a to generate a signal corresponding to the standing wave. Also, radio waves emitted from the transmitting antenna 22a, reflected by the detection surface 40 without being affected by the buried object 41, and sent to the receiving antenna 23a, and radio waves emitted from the transmitting antenna 22a and sent directly to the receiving antenna 23a. The signals are combined by the detection amplifier circuit 25a to generate a signal corresponding to the standing wave. At this time, the outputs of the detection amplifier circuits 25a and 26a vary depending on the size of the distance _L1 between the container A and the detection surface 40, but at a certain size of the distance _L1 , the detection Amplification circuits 25a and 26a
There are places where the outputs are the same, and even though the receiving antenna 24a is near the top of the buried object 41, no signal indicating the existence of the buried object 41 appears in the output of the differential amplifier circuit 27a.

However, since the radio waves emitted from the transmitting antenna 22b have a different frequency from the radio waves emitted from the transmitting antenna 22a, the radio waves emitted from the transmitting antenna 22b change due to the influence of the buried object 41 and are sent to the receiving antenna 24b. A signal corresponding to a standing wave generated by combining the radio waves emitted from the transmitting antenna 22b and sent directly to the receiving antenna 24b in the detection amplifier circuit 26b is sent to the detection amplifier circuit 2.
When the distance L ₁ between the container A and the detection surface 40 makes the outputs of 5a and 26a the same, the detection amplifier circuit 2
This wave is generated with a different magnitude from the standing wave generated at 6a. On the other hand, radio waves are emitted from the transmitting antenna 22b, are not affected by the buried object 41, are reflected by the detection surface 40, and are sent to the receiving antenna 23b,
It is emitted from the transmitting antenna 22b and sent to the receiving antenna 2.
The radio waves sent directly to the detection amplifier circuit 25b
The signal corresponding to the standing wave generated by the synthesis is generated with a magnitude different from that of the signal corresponding to the standing wave generated in the detection amplifier circuit 25a at the same time as described above.
In this case, the magnitude of the signal corresponding to the standing wave of the detection amplifier circuit 26b is affected by the buried object 41, and therefore differs from the magnitude of the signal corresponding to the standing wave of the detection amplifier circuit 25b. Therefore, the detection amplifier circuit 25
Even if the outputs of a and 26a are the same and the output of the differential amplifier circuit 27a is zero, the detection amplifier circuits 25b and 26
Since the outputs of the terminals b are different, a signal is generated in the differential amplifier circuit 27b, which is activated by the logic circuit 28 and sends a signal to the indicator 30 to notify the presence of the buried object 41.

Furthermore, when the container A moves in the X direction and the transmitting antennas 22a and 22b come close to the top of the underground structure 41, first, the signal is emitted from the transmitting antenna 22a, changes due to the influence of the buried structure 41, and changes to the receiving antenna 22a.
A signal corresponding to a standing wave generated by combining the radio waves sent to the antenna 22a and the radio waves emitted from the transmitting antenna 22a and directly sent to the receiving antenna 24a in the detection amplifier circuit 26a is emitted from the transmitting antenna 22a and is transmitted directly to the receiving antenna 24a. The radio waves that change under the influence of and are sent to the receiving antenna 23a and the transmitting antenna 22
The output of the differential amplifier circuit 27a is zero because it has the same magnitude as the signal corresponding to the standing wave generated by combining the radio wave emitted from the radio wave a and the radio wave directly sent to the receiving antenna 23a in the detection amplifier circuit 25a. In addition, the detection amplifier circuit 26b combines the radio waves emitted from the transmitting antenna 22b, changed by the influence of the buried object 41, and sent to the receiving antenna 24b, and the radio waves emitted from the transmitting antenna 22b and sent directly to the receiving antenna 24b. A signal corresponding to the standing wave generated by the transmission is emitted from the transmitting antenna 22b and
A signal corresponding to a standing wave generated by combining the radio wave changed under the influence of 1 and sent to the receiving antenna 23b and the radio wave emitted from the transmitting antenna 22b and sent directly to the receiving antenna 23b in the detection amplifier circuit 25b. Since they are the same size, differential amplifier circuit 2
The output of 7b is zero. Therefore, the differential amplifier circuit 2
Since the outputs of 7a and 27b are zero, logic circuit 2
8 becomes zero, and the indicator 30 indicates zero.

Furthermore, when the container A moves in the X direction and the receiving antennas 23a and 23b come close to the top of the buried object 41, the signal is first emitted from the transmitting antenna 22a and reaches the detection surface 40 without being affected by the buried object 41. Radio waves reflected and sent to the receiving antenna 24a and radio waves emitted from the transmitting antenna 22a and receiving antenna 24a
The detection amplifier circuit 26a synthesizes the radio waves sent directly to the detection amplifier circuit 26a to generate a signal corresponding to the standing wave. Also,
A radio wave emitted from the transmitting antenna 22a, changed by the influence of the buried object 41, and sent to the receiving antenna 23a, and a radio wave emitted from the transmitting antenna 22a and sent directly to the receiving antenna 23a are combined by the detection amplifier circuit 25a and are stationary. Generates a signal corresponding to the wave. At this time, the distance L 1 between the container A and the detection surface 40 when the receiving antennas 24a and 24b are near the top of the buried object 41, and the distance L ₁ between the container A and the detection surface 40 when the receiving antennas 23a and 23b are near the top of the buried object 41. Container A
Since the distance L ₁ between the detection surface 40 and the detected surface 40 is the same, the outputs of the detection amplifier circuits 25a and 26a are the same. Therefore, the receiving antenna 23a is connected to the buried object 41.
Although the differential amplifier circuit 27 is near the top of
The output of a becomes zero, and no signal indicating the existence of the buried object 41 appears.

However, since the radio waves emitted from the transmitting antenna 22b have a different frequency from the radio waves emitted from the transmitting antenna 22a, they are emitted from the transmitting antenna 22b, are not affected by the buried object 41, are reflected by the detection surface 40, and are transmitted to the receiving antenna 24b. and the radio waves emitted from the transmitting antenna 22b and directly sent to the receiving antenna 24b are detected by the detection amplifier circuit 2.
At the same time as above, the signal corresponding to the standing wave synthesized at 6b is sent to the detection amplifier circuits 25a and 26a.
A signal corresponding to the standing wave generated in the detection amplifier circuit 26a when the distance _L1 between the container A and the detection surface 40 is the same, and the output is the same, is generated with a different magnitude. On the other hand, the radio waves emitted from the transmitting antenna 22b, changed by the influence of the buried object 41, and sent to the receiving antenna 23b, and the radio waves emitted from the transmitting antenna 22b and directly sent to the receiving antenna 23b are transmitted to the detection amplifier circuit 25b. The signal corresponding to the standing wave generated by the synthesis is generated with a magnitude different from that of the standing wave generated in the detection amplifier circuit 25a at the same time as described above. In this case, since the magnitude of the signal corresponding to the standing wave of the detection amplifier circuit 25b is affected by the buried object 41, the detection amplifier circuit 26b
It also differs from the magnitude of the signal corresponding to the standing wave. Therefore, the receiving antennas 23a and 23b are connected to the buried object 41.
Even though it is near the top of the detection amplifier circuit 25
Even if the outputs of a and 26a are the same and the output of the differential amplifier circuit 27a is zero, the detection amplifier circuits 25b and 26
Since the outputs of the terminals b are different, a signal is generated in the differential amplifier circuit 27b to inform the existence of the buried object 41, which activates the logic circuit 28 and sends a signal to the indicator 30 to inform the existence of the buried object 41. become.

As described above, even if there is a buried object, the detection amplifier circuit 25
Although we have explained the case where the outputs of a and 26a are the same, the distance L ₁ between the container A and the detection surface 40
When the value changes, a point naturally occurs where the magnitudes of the outputs of the detection amplifier circuits 25b and 26b become the same. However, in this case, the detection amplifier circuits 25a and 26a
Since the outputs of are generated differently, it is possible to obtain the same effect even though the operations are opposite to those described above.

In the first embodiment, the signal generating section _a1 has a configuration in which the two oscillators 20a and 20b are separated, but it is possible to use one oscillator (for example, a sweep oscillator) continuously or intermittently. to generate two or more different frequencies, and the antenna part _b1 is
Transmitting antenna 22a and receiving antennas 23a and 24
a group and a transmitting antenna 2 having a different frequency from the group.
2b and a set of receiving antennas 23b and 24b, one set includes one wideband transmitting antenna and two wideband receiving antennas that operate at different frequencies, and the transmitting antenna of the signal processing unit _c1 and A configuration may be adopted in which one set of circuit configurations of the receiving antenna are provided to operate in the same manner as in the first embodiment. This case is considered as the second embodiment of the present invention.
As shown in the figure. In FIG. 4, a ₂ is a signal generation section, b ₂ is an antenna section, c ₂ is a signal processing section, 50 is an oscillator that continuously or intermittently oscillates two or more different frequencies, 51 is a resistance attenuator, and 52 are transmitting antennas operating at two or more different frequencies, 53a and 5
3b is a receiving antenna that operates on two or more different frequencies; 54a and 54b are detection amplifier circuits that operate on two or more different frequencies; 55 is a differential amplifier circuit;
6 is an indicator. In this case, there are times when no output appears on the indicator 56 even though there is a buried object at a specific frequency, but at that time, the buried object is always detected at another frequency and indicated on the indicator 56. Become. Further, since the continuous or intermittent change in the oscillation frequency of the oscillator 50 is extremely high compared to the speed at which the antenna part b ₂ is moved relative to the buried object (which is usually moved manually), the change in the oscillation frequency of the oscillator 50 is substantially It is possible to obtain the same effects as in the first embodiment in which detection is performed by simultaneously using radio waves of different frequencies.

As described above, according to the present invention, radio waves of two or more different frequencies are emitted and received simultaneously or in a time-division manner, so that even if there is a buried object, the container A and the surface to be detected are ₄₀ , there will be no point where the buried object could not be detected, and this device can be used at any distance, so the buried object will not be overlooked and can be reliably detected. Furthermore, when detecting buried objects, there is no need to worry about the distance between the container and the surface to be detected, which has the effect of making the detection work easier and faster.

[Brief explanation of drawings]

FIG. 1 is a system block diagram showing a conventional buried object detection device, FIG. 2 is a system block diagram showing a first embodiment of the buried object detection device according to the present invention, and FIG. 3 is a system block diagram showing the structure of the first embodiment. 4 is a system block diagram of a buried object detection device showing a second embodiment of the present invention, and FIG. 5 is a conventional device in which the antenna faces a homogeneous object or a buried object. FIG. 6 is a graph showing the detector output when the distance L ₀ is changed in the case of FIG. 5. a ₁ , a ₂ ... signal generation section, b ₁ , b ₂ ... antenna section,
c ₁ , c ₂ ... signal processing section, 20a, 20b, 50 ... oscillator, 21a, 21b, 51 ... resistance attenuator, 22
a, 22b, 52...transmission antenna, 23a, 23
b, 24a, 24b, 53a, 53b...receiving antenna, 25a, 25b, 26a, 26b354
a, 54b...detection amplifier circuit, 27a, 27b, 5
5... Differential amplifier circuit, 28... Logic circuit, 30, 56
...Indicator, A...Container, 40...Detected surface, 41...Buried object.

Claims (1)

[Scope of Claims] 1. A signal generating unit including at least two oscillators with different oscillation frequencies, two or more transmitting antennas with different frequencies for transmitting signals from the signal generating unit, and the one transmitting antenna. an antenna unit consisting of two or more sets each including two receiving antennas having the same frequency as the transmitting antenna; a circuit for detecting and amplifying the signal received by each of the receiving antennas; and a circuit for detecting and amplifying the signal received by each of the receiving antennas, and a signal processing unit comprising a differential amplifier circuit that outputs only the difference between the signals, a logic circuit that takes the logical sum of the output signals of the differential amplifier circuit for each different frequency, and an indicator that indicates the output of the logic circuit. 2, which is paired with the transmitting antenna and has the same frequency as the transmitting antenna.
The receiving antennas are arranged one in a row at symmetrical positions on both sides of the transmitting antenna, so that even if the distance to the detection surface of the container in which the antenna part is housed and fixed changes, it is possible to detect any of the different frequencies. A buried object detection device characterized by having a configuration in which a signal from the buried object is generated by a set of receiving antennas. 2. A signal generator consisting of one oscillator that continuously or intermittently oscillates two or more different frequencies, one transmitting antenna that operates at two or more different frequencies to transmit the signal from the signal generator, and An antenna section consisting of two receiving antennas operating at two or more different frequencies forming a pair with a transmitting antenna, two detection amplifier circuits operating at two or more different frequencies received by each of the receiving antennas, and the detection The signal processing unit includes a differential amplifier circuit that outputs the difference between two signals of the amplifier circuit and an indicator that indicates the output of the differential amplifier circuit, and the two receiving antennas are connected to each other on both sides of the transmitting antenna. The antenna parts are arranged in a line in symmetrical positions, and even if the distance between the container in which the antenna part is housed and fixed and the detected surface changes, a signal from the buried object is generated at one of the different frequencies. A buried object detection device.