JP3558491B2 - Apparatus and method for transmitting and receiving pulsed signals into the ground - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention measures the propagation speed of radio waves inside the embankment to detect the degree of compaction of the embankment, or transmits an electric signal into the ground and receives its reflected wave to investigate buried objects underground. The present invention relates to a transmission / reception device and a transmission / reception method of a pulse-like electric signal to the ground used for the purpose of, for example, transmitting the electric signal in the form of a ringing wave after propagation through the ground. The present invention relates to a transmission / reception device and a transmission / reception method for improving measurement accuracy by improving accuracy.
[0002]
[Prior art]
Conventionally, as disclosed in a patent application (Japanese Patent Application Laid-Open No. 9-89807) entitled "Method and Apparatus for Measuring Degree of Compaction of Soil" related to the earlier application of the present applicant, the density of embankment, and 2. Description of the Related Art A measuring device for measuring the degree of compaction is known. This measuring device utilizes the principle that the relative permittivity of an embankment increases as its water content (moisture content) and density increase, and as a result, the propagation speed of radio waves decreases as the water content and density of the embankment increase. It was done.
[0003]
According to this measuring device, a pulse-like electric signal is propagated inside the embankment to be measured, and the time difference between the transmission time of the pulse-like electric signal and the reception time of the reception signal after propagation in the ground ( The propagation speed of the radio wave inside the embankment is measured from the required propagation time, and the dry density and compaction degree of the embankment are measured from the propagation speed and the separately measured or estimated water content of the embankment.
[0004]
In addition, a patent application (Japanese Patent Publication No. Hei 3-47474) entitled "Underground Exploration Apparatus" previously filed by the present applicant transmits a pulse-like electric signal into the ground, and An underground radar apparatus for detecting a buried object underground by receiving a generated reflected wave is disclosed.
[0005]
The above-mentioned electric signal transmitting and receiving device for transmitting and receiving pulse-like electric signals underground for the purpose of measuring the degree of compaction of the embankment and exploring underground objects is fundamentally similar to a radar device installed on a ship or the like. Have the following features. First, since radio waves propagating in the ground are greatly attenuated by as much as 10 dB per meter, the measurement range cannot be so long, and is limited to at most several meters. Second, radio waves propagating in the ground have different propagation paths and speeds depending on frequency components.
[0006]
The first feature is that the measurable range is narrow, so the time interval between transmission and reception of radio waves is extremely short. For example, if the relative dielectric constant in the ground is about 16, the propagation distance of 1 meter is required. The time is about 13 nsec. As described above, in this type of measuring apparatus, the time interval from transmission to reception is short, and in order to secure the required resolution, an isolated pulse to be transmitted needs to be extremely sharp with a half width of about 1 nsec. .
[0007]
The sharp isolated pulse having a half width of about 1 nsec as described above includes an extremely wide range of frequency components from DC to a maximum of about 2 GHz. By the way, according to the patent application (Japanese Patent Application Laid-Open No. 9-89807) related to the earlier application of the present applicant, similar to the skin effect that the penetration depth of the propagation path from the ground surface decreases as the frequency component increases. The phenomenon is disclosed.
[0008]
That is, as illustrated in FIG. 3, as a propagation path of a radio wave formed through the underground near the ground surface between the transmitting antenna TX and the receiving antenna RX arranged substantially parallel to the ground surface G, a high-frequency component, A so-called multi-path (multi-path) having different depths and path lengths such as fh, fl, and fm is formed for each of the low-frequency components and the intermediate frequency components. As described above, since a multipath having a different propagation path length is formed for each frequency component, the waveform (B) of the received signal is different from the waveform (A) of the transmitted signal as illustrated in FIG. When the frequency components are combined under different delay times via different propagation paths, a ringing waveform having a large distortion is generated.
[0009]
Further, the water having a large relative dielectric constant contained in the soil increases the relative dielectric constant of the soil. The relative permittivity of this water shows a large value of about 80 for the DC component, but in the GHz band, it approaches the dielectric relaxation frequency of water as the frequency increases, so this relative permittivity decreases as the frequency component increases It is estimated that it will continue. This suggests that the propagation speed of radio waves in the ground increases as the frequency component increases.
[0010]
According to a patent application (Japanese Patent Application No. 9-116189) entitled "Radar Antenna" related to the applicant's earlier application, an underground radar for transmitting and receiving a sharp pulse-like electric signal having a half width of about 1 nsec is disclosed. It is also disclosed that the waveform of the reflected electric signal reflected and received by the buried object becomes a ringing waveform similarly to the reception waveform (B) of FIG. 2 due to the limitation of the frequency band of the antenna.
[0011]
In a transmission / reception apparatus for an electromagnetic wave such as a laser beam propagating in the air instead of in the ground, the waveform of the received reflected wave is slowed down, but still maintains a pulse shape similar to the transmission waveform. According to a patent application entitled “Laser radar” (Japanese Patent Laid-Open Publication No. Hei 6-214025) related to the earlier application of the present applicant, the present point of time of the peak value of the received pulse amplified to be substantially constant is detected as the reception time. An arrangement is disclosed. Another patent application entitled “Laser radar” (Japanese Patent Application Laid-Open No. Hei 6-235765) related to the earlier application of the present applicant has disclosed a method of detecting a peak value of a received pulse and detecting a fixed ratio to the peak value, for example, A configuration is disclosed in which a value of 1/2 is dynamically set as a threshold, and a point in time when the amplitude of the received pulse exceeds the threshold is set as a reception point.
[0012]
[Problems to be solved by the invention]
As described above, in the transmission / reception device for pulsed electric signals into the ground, the reception waveform of the transmitted or reflected waves in the ground may cause multipath formation due to a phenomenon similar to the skin effect, or the frequency dependence of the propagation speed. The ringing waveform has a large distortion as illustrated in FIG. 2B based on various factors such as the characteristics and the band limiting characteristics of the antenna. In this case, what kind of characteristic point on such a waveform has appeared is determined as the time of reception, and how to detect the appearance of such a characteristic point with high accuracy is determined. It becomes a problem.
[0013]
[Means for Solving the Problems]
According to the transmitting and receiving apparatus and the transmitting and receiving method of the pulsed electric signal into the ground according to the present invention which solves the above-mentioned problems of the prior art, a transmitting circuit that generates and outputs a pulsed electric signal of a predetermined transmission cycle, A transmitting antenna disposed substantially parallel to the ground and transmitting a pulsed electric signal output from the transmitting circuit to the ground, and a receiving antenna disposed substantially parallel to the ground and receiving the electric signal propagated through the ground And a receiving circuit for detecting a reception time point from a waveform of the received electric signal received by the receiving antenna. The receiving circuit samples and holds the received electric signal at a sampling period slightly longer than a predetermined transmission period, thereby extending a time axis of the received electric signal. a variable gain amplifier circuit for amplifying an electric signal, an a / D converter circuit for converting the waveform of the amplified received electrical signals into digital waveform signals, the maximum value of the amplitude of the first occurrence in the digital waveform signal Controlling the amplification gain of the variable gain amplifier circuit so as to keep the gain substantially at a predetermined value, and detecting the time when the amplitude of the digital signal first reaches a threshold of a predetermined ratio with respect to the predetermined value as the reception time. A detection unit.
Signal transmitting and receiving device.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
According to a preferred embodiment of the present invention, the predetermined threshold is set to a value of 3 to 4% of the predetermined value.
[0015]
【Example】
FIG. 1 is a functional block diagram showing the configuration of an apparatus for measuring the dry density of an embankment including an apparatus for transmitting and receiving a pulsed signal to the ground according to an embodiment of the present invention, and 1 is a digital signal processor (DPS). 2) a timing control circuit, 3 a transmission circuit, 4 a balun transformer, and 5 a transmission antenna. Further, 6 is a receiving antenna, 7 is a balun transformer, 8 is a high frequency amplifier circuit, 9 is a sample and hold circuit, 10 is a band pass filter circuit, 11 is a low frequency amplifier circuit, 12 is a variable gain amplifier circuit, and 13 is an A / A A D conversion circuit, 14 is a D / A conversion circuit, and 15 is a moisture content measuring unit using gamma rays, neutron rays, and the like.
[0016]
When the timing control circuit 2 is activated by the digital signal processor 1 and starts operating, the timing control circuit 2 supplies a transmission trigger pulse having a constant period T (20 μsec in this embodiment) to the transmission circuit 3 and the period of the transmission trigger pulse. A sampling pulse having a period (T + τ) larger than T by a small amount τ (τ≪T, 0.1 nsec in this example) is supplied to the sample and hold circuit 9 with a delay of (T + τ) from the first transmission trigger pulse. .
[0017]
Upon receiving the transmission trigger pulse supplied from the timing control circuit 2, the transmission circuit 3 uses a sharp isolated pulse of high power (in this embodiment, an isolated pulse having a half width of about 1 nsec and a peak value of about 200 volt) as a transmission pulse. appear. The transmission pulse is supplied to a planar transmission antenna 5 called a bow-tie antenna or the like through a balun transformer 4 that converts two lines into four lines. Referring to FIG. 3, the transmission pulse is radiated from the transmission antenna 5 (TX), which is held substantially parallel to the ground, into the ground through a narrow gap between the transmission antenna 5 and the ground.
[0018]
Referring to FIG. 3, the transmission pulse radiated into the ground propagates on the surface of the ground almost in parallel with the ground, and then a narrow space between the receiving antenna 6 (RX) held substantially in parallel with the ground and the ground. The signal is received by the receiving antenna 6 (RX) via the gap. The reception signal received by the reception antenna 6 passes through a balun transformer 7 for converting four lines into two lines, and after being amplified by a high frequency amplifier circuit 8, is supplied to a sample and hold circuit 9, and is supplied to a timing control circuit 2. And is held in synchronization with the sampling pulse of the period (T + τ) supplied from.
[0019]
The received signal is sampled and held, and its time axis is expanded by (T / τ) times (in this embodiment, 20 μsec / 0.1 nsec = 2 × 10 ⁵ = 200,000 times). It becomes. A predetermined number (2,000 in this embodiment) of the transmission pulses are continuously transmitted in the above-mentioned fixed transmission cycle (20 μsec in this embodiment), so that one reception signal waveform expanded in the time axis is obtained. can get. Therefore, the time required to obtain one such received signal waveform that has been extended on the time axis is 40 msec, and the detection range of the received signal is 200 nsec (= 0.1 nsec / number × 2000) from the transmission of the transmission pulse. Range.
[0020]
By receiving 200,000 times longer axis extension, the received signal waveform that has been converted into a low frequency signal of the frequency band of several kHz, through the band pass filter circuit 10, which is fixed in a low-frequency amplifier circuit 11 amplifies After receiving the low frequency amplification of the gain, it is supplied to a variable gain amplification (AGC) circuit 12 where it is subjected to variable gain amplification controlled by the digital signal processor 1. The received signal waveform expanded on the time axis which has been amplified by the variable gain is supplied to an A / D conversion circuit 13, where it is converted into a digital signal while being sampled at a period of 5 μsec. Supplied to
[0021]
The digital signal processor 1 receives the received signal waveform supplied from the A / D conversion circuit 13 and expanded on the time axis and digitized. The received signal waveform is as illustrated in FIG. 2C, and the digital signal processor 1 detects the first maximum value Vpf appearing in such a received signal waveform. As a specific example, the digital signal processor 1 determines the maximum value in the interval from when the amplitude of the received signal exceeds the positive threshold value Vth to when the amplitude of the received signal again becomes lower than the threshold value Vth. Is detected as the maximum value Vpf.
[0022]
The digital signal processor 1 compares the first appearing maximum value Vpf with a predetermined peak value Vpp (1 volt in this embodiment) being preset through the input circuit (IN) 1a. The digital signal processor 1 increases the gain to be newly set in the variable gain amplifier circuit 12 when the comparison result is Vpf <Vpp, and decreases the gain when the comparison result is Vpf> Vpp. Output a signal. This gain control signal is converted into an analog signal by the D / A conversion circuit 14 and set in the variable gain control circuit 12.
[0023]
The digital signal processor 1 changes the gain control signal when Vpf and Vpp become substantially equal due to the above-described variable gain control. Specifically, when the absolute value of the difference between the two becomes smaller than a predetermined minute amount, the digital signal processor 1 changes the gain control signal. Stop. In this state, the digital signal processor 1 sets the threshold Vth (30 mvolts to 40 mvolts) in which the amplitude of the rising portion of the digitized received signal waveform that has been extended on the time axis is set as 3 to 4% of the peak value Vpp. ) Is detected as the point in time tr of the reception pulse.
[0024]
As shown in FIG. 3, the digital signal processor 1 determines the center of the transmission antenna 5 (TX) and the reception antenna 6 ( By dividing the distance d from the center of RX), the propagation time of the transmitted pulse in the ground is calculated. The digital signal processor 1 calculates the dry density of the ground surface and the compaction degree from the calculated propagation speed and the water content of the ground measured by the water content measuring unit 15, and comprises a display device and the like. Output circuit (OUT) 1b.
[0025]
The apparatus and method for transmitting and receiving an electric signal to the ground according to the present invention have been described above by taking as an example the apparatus and method for measuring the dry density and compaction degree of soil. However, the transmitting / receiving device of the present invention can be applied to a device for measuring a physical quantity related to soil properties other than the dry density and compaction degree of the soil.
[002 6 ]
【The invention's effect】
As described in detail above, the transmitting and receiving apparatus and the transmitting and receiving method of the pulsed electric signal into the ground according to the present invention are based on the maximum value of the first appearing amplitude instead of the peak value of the received signal. As a configuration to set the threshold for detecting the reception time point while controlling the amplification gain to keep this at a constant value, high measurement accuracy is realized based on the high-frequency component that appears first in the received signal it can.
[002 7 ]
That is, when the underground is used as a propagation path, the lower frequency components reach the receiving antenna via a deeper and longer propagation path farther from the surface of the ground or with a delay at a small propagation speed. The waveform of the received signal formed by combining low frequency components becomes complicated, and the peak value appearing later than the first rise of the received signal has large fluctuations with respect to the point of occurrence and the amplitude. Therefore, instead of using the peak value accompanied by such a large fluctuation as the reference value, the detection accuracy at the time of reception can be improved by using the first maximum value appearing earlier as the reference value.
[002 8 ]
In addition, since the control of the variable gain amplifier circuit is performed by a control / detection unit realized by a digital signal processor or the like, the first local maximum value, instead of the peak value appearing in the received signal , is set to a substantially predetermined value. The complicated function of controlling the amplification gain so as to keep it can be easily realized with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration of an apparatus for measuring a dry density of an embankment including an apparatus for transmitting and receiving a pulsed electric signal to the ground according to an embodiment of the present invention.
FIG. 2 is a waveform diagram exemplifying a transmission pulse waveform transmitted from a transmission antenna to the ground and a reception pulse waveform received by a reception antenna after propagating in the ground.
FIG. 3 is a conceptual diagram for explaining that a penetration depth into the ground and a propagation path length are different depending on each frequency component included in a transmission pulse signal.
[Explanation of symbols]
1 Digital signal processor
2 Timing control circuit
3 Transmission circuit
5 Transmit antenna
6 Receiving antenna
9 Sample and hold circuit
12 Variable gain amplifier circuit
15 Moisture content measurement section

Claims (4)

A transmission circuit that generates and outputs a pulse-like electric signal of a predetermined transmission cycle, a transmission antenna that is disposed substantially parallel to the ground and transmits the pulse-like electric signal output from the transmission circuit to the ground, A receiving antenna that is arranged substantially parallel to the ground and receives an electric signal transmitted through the ground, and a receiving circuit that detects a reception time point from a waveform of the received electric signal received by the receiving antenna. In a transmitting and receiving device for a pulse-like electric signal,
The receiving circuit,
A sample and hold circuit that extends the time axis of the received electric signal by sampling and holding the received electric signal at a sampling period slightly longer than the predetermined transmission period,
A variable gain amplifier circuit for amplifying the received electric signal whose time axis has been extended,
An A / D conversion circuit for converting the waveform of the amplified received electric signal into a digital waveform signal;
The amplification gain of the variable gain amplifying circuit is controlled so that the maximum value of the amplitude first appearing in the digital waveform signal is kept substantially at a predetermined value, and the amplitude of the digital signal is set to a threshold value of a predetermined ratio to the predetermined value. And a control / detection unit for detecting a time point at which the signal reaches the first time as the reception time point. The transmission / reception device according to claim 1, wherein the predetermined threshold is set to a value of 3 to 4% of the predetermined value. A transmission circuit that generates and outputs a pulse-like electric signal of a predetermined transmission cycle, a transmission antenna that is disposed substantially parallel to the ground and transmits the pulse-like electric signal output from the transmission circuit to the ground, A receiving antenna that is arranged substantially parallel to the ground and receives the electric signal propagated in the ground, a receiving circuit that detects a reception time point from a waveform of the received electric signal received by the receiving antenna, and a transmission circuit that transmits the electric signal. An apparatus for measuring the propagation speed of an underground pulsed electric signal, comprising a calculating unit that calculates a propagation speed of an underground electric signal from an elapsed time until a reception time,
The receiving circuit,
A sample and hold circuit that extends the time axis of the received electric signal by sampling and holding the received electric signal at a sampling period slightly longer than the predetermined transmission period,
A variable gain amplifier circuit for amplifying the received electric signal whose time axis has been extended,
An A / D conversion circuit for converting the waveform of the amplified received electric signal into a digital waveform signal;
The amplification gain of the variable gain amplifying circuit is controlled so that the maximum value of the amplitude first appearing in the digital waveform signal is kept substantially at a predetermined value, and the amplitude of the digital waveform signal is set at a predetermined ratio to the predetermined value. A control / detection unit for detecting a time point at which a threshold value is first reached as the reception time point, the apparatus for measuring the propagation speed of an underground pulsed electric signal. A pulse-like electric signal of a predetermined transmission cycle is transmitted into the ground from a transmitting antenna arranged substantially parallel to the ground, and an electric signal propagated in the ground is received by a receiving antenna arranged substantially parallel to the ground. Receiving, in a method of transmitting and receiving a pulsed electric signal to the ground to detect the reception time point from the waveform of the received electric signal received,
When receiving the electric signal propagated underground,
Extending the time axis of the received electric signal by sampling and holding the received electric signal at a sampling period slightly longer than the predetermined transmission period,
The received electric signal whose time axis is extended is amplified by a variable gain amplifier circuit,
The amplified waveform of the received electric signal is converted into a digital waveform signal,
The amplification gain of the variable gain amplifying circuit is controlled so that the maximum value of the amplitude first appearing in the digital waveform signal is kept substantially at a predetermined value, and the amplitude of the digital waveform signal is set at a predetermined ratio to the predetermined value. A method of transmitting and receiving a pulsed electric signal to the ground, wherein a time point when a threshold value is first reached is detected as the reception time point.

Images