JP3511026B2 - Calibration method of relative permittivity of electromagnetic wave probe and electromagnetic wave probe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for calibrating the relative permittivity of an electromagnetic wave probe and an electromagnetic probe, and more particularly, to a novel method for accurately and easily calibrating the relative permittivity at an inspection site. Regarding technology.

BACKGROUND ART Conventionally, an electromagnetic wave probe for radiating an electromagnetic wave from an antenna and receiving and analyzing a reflected wave from an object to perform an exploration has been developed and used for the purpose of exploring a buried object such as a buried pipe or a land mine.

Such an electromagnetic wave probe radiates a high frequency electromagnetic wave from the antenna at a predetermined cycle, determines the distance to the object by receiving and analyzing the reflected wave, and determines the physical properties of the object through which the electromagnetic wave passes. Non-destructive measurement of exploration target.

Generally, the spacecraft can display the spacecraft search results in various modes. For example, as shown in FIG. 11, one received signal at a certain search position can be displayed as a received waveform on a screen with the horizontal axis representing the time axis and the vertical axis representing the amplitude axis. Alternatively, by storing and holding the respective received signals at a plurality of search positions at predetermined intervals in the horizontal direction of the search target, and subjecting the plurality of received signals to predetermined signal processing, the vertical axis represents the depth and the horizontal axis represents the horizontal axis. Search position (number of scans)
It is possible to generate a two-dimensional cross-sectional image (or pulse echo image) of the search target, and display the cross-sectional image as shown in FIG. The signal processing may be a pulse compression process or a synthetic aperture process.

During exploration, the characteristics of the high-frequency circuit change depending on various conditions such as temperature and humidity.Therefore, it is necessary to calibrate or set the probe manually or automatically based on the received waveform beforehand. Is essential to do.

By the way, when the image display shown in FIGS. 11 and 12 is performed based on the received signal, it is necessary to clarify the starting point of the received signal. If the starting point of the received signal shown in FIG. 11 fluctuates, the reflected wave P on the ground surface and the reflected wave P1 due to the buried object fluctuate in the time axis direction, and due to this, in the depth axis direction on the cross-sectional image of FIG. The fluctuation of d occurs. For this reason, the sectional image becomes complicated, and the depth and physical properties of the buried object cannot be accurately determined.

Therefore, the conventional probe uses a specific point (for example, the first peak point of amplitude) P ₀ of the surface wave P in the received signal shown in FIG.
Many have an automatic tracking function of capturing as a reception start point and automatically performing tracking processing based on the captured reception start point P ₀ .

In addition, as a trend of recent spacecraft, there are many specialized machines specialized for the purpose of landmine survey, buried object survey, wall surface survey, etc. There are many things that exclude adjustment and calibration as much as possible.

However, in the conventional probe, since the electromagnetic wave radiated from the antenna has a very wide band and contains many harmonics and low frequencies, the received signal also contains many frequency components in the wide band, The received signal had a complicated waveform. For this reason, the first peak point P ₀ of the surface wave P cannot be accurately captured, causing a problem of capturing an incorrect point, and the automatic tracking function for performing stable search is an unstable element. Was a factor that produced.

In addition, the automatic tracking circuit fluctuates due to ambient temperature fluctuations and fluctuations in circuit members, which causes fluctuations in the tracking zone, resulting in fluctuations in measurement results even though the products have the same specifications. Was occurring.

Furthermore, a wideband transmitted electromagnetic wave is reflected at various phase points at all points in the medium, and a received wave is formed by a composite wave of a large number of reflected waves, but since it is a wideband, the period of the received waveform and It is not possible to correlate with the relative permittivity or resistivity of the medium, and by analyzing only a single received waveform observed at a specific measurement point on the ground surface,
It was impossible to measure the relative permittivity of the medium.

The present inventor has found that the band of the transmitted wave is very narrow (for example,
When the center frequency is 1 GHz, the band is about 20 MHz) and the radiation is performed in a pulse shape. The reflected wave of the electromagnetic wave in the narrow band is detected by the reception antenna, and the detection signal is detected by a new detection circuit to detect the reception waveform. It has been found that a predetermined correlation occurs between the period and the relative permittivity of the medium. That is, the pulsed narrow-band electromagnetic wave has a propagation velocity and an attenuation rate according to the relative permittivity of the medium in the process of propagating in the medium. Further, a reflected wave is generated at every point in the medium, and a received wave is formed by combining the large number of reflected waves. Here, assuming that a reflected wave is generated for each unit distance in the depth direction of the medium, each reflected wave propagates in the medium at a speed according to the relative permittivity of the medium, so that each received wave is received by a receiving antenna on the ground. A predetermined phase shift occurs in the reflected wave according to the relative permittivity of the medium. The received waveform formed by combining a large number of reflected waves contains a signal component corresponding to the average relative permittivity for each depth of the search target. For example, the cycle of each phase of the received waveform changes according to the average dielectric constant for each depth of the search target, or the noise component of each phase of the received wave is the average for each depth of the search target. It corresponds to the dielectric constant. Therefore, based on these signal components, it is possible to observe the change in the dielectric constant for each depth in the exploration target.

However, even if the change in permittivity can be observed, the relative permittivity for each depth of the object to be searched cannot be obtained from the received waveform unless there is a reference for the change.

The present invention is proposed in view of such circumstances, and in an electromagnetic wave probe capable of observing the permittivity for each depth of the probe in the received waveform, the relative permittivity can be easily calibrated prior to the probe. An object of the present invention is to provide a method for calibrating the relative permittivity of an electromagnetic wave probe that can be used. Another object of the present invention proposed at the same time is to provide an electromagnetic wave probe capable of effectively implementing this relative permittivity calibration method.

DISCLOSURE OF THE INVENTION The relative permittivity calibration method of the present invention proposed to achieve the above-mentioned object is a transmitting antenna that radiates an electromagnetic wave, a receiving antenna that receives a reflected wave of the radiated electromagnetic wave, and detection of the receiving antenna. A reception unit that generates a reception signal based on a signal, and a signal processing unit that processes the reception signal and outputs an analysis signal, the signal processing unit analyzes the reception signal by a frequency conversion with different signal periods. In the electromagnetic wave exploration device having a frequency conversion constant setting unit, the period of the analysis signal when electromagnetic waves are radiated from the transmitting antenna to the reference ratio. The setting means is adjusted so as to match a predetermined reference time according to the dielectric constant. In the present invention, the average relative permittivity for each depth in the exploration target, and the average period for each phase of the analysis signal waveform,
It can be suitably applied to an electromagnetic wave probe having a predetermined correlation, and more preferably, the average period for each phase of the analysis signal waveform is approximately the square root of the average relative dielectric constant for each depth in the probe target. It is preferably used in an electromagnetic wave probe equipped with a signal processing circuit that generates a proportional signal waveform for analysis. Further, the present invention can be suitably applied to a device that radiates a narrow band pulsed electromagnetic wave by optimizing a transmission antenna or a transmission circuit. In the above basic invention, the receiving unit can be mainly composed of a high-frequency circuit, and the main function of the receiving unit can be to detect the reflected wave, and the received signal which is the output signal of this receiving unit. Is preferably in the KHz band to a dozen MHz band. In addition, the receiving unit and the signal processing unit (signal processing circuit),
The circuit may be configured on another substrate, or may be integrally configured on the same substrate.

The frequency conversion in the present invention is a general term for the process of equivalently changing the frequency by changing the correspondence between the analysis signal and the time axis, and the process of changing the analysis signal itself in the time axis direction. It includes all processes for changing the unit time on the time axis. For example, if the analysis signal is an analog signal, a double balanced mixer (Double B
The signal for analysis can be frequency-converted by a frequency conversion circuit such as a balanced mixer. Further, when the analysis signal is represented by a set of digital data obtained by A / D converting the reception signal, the digital data group is treated as being sampled at a timing different from the actual sampling timing. (In other words, by changing the unit time between each sampling data), the analysis signal is frequency-converted. The frequency conversion constant setting means may have an appropriate configuration. For example, when the period adjusting means is constituted by the frequency conversion circuit as described above, the setting means is a variable resistor or a variable resistor provided in the circuit. When the period adjusting means is constituted by a microcomputer that operates based on a predetermined program, the setting means is a rewritable memory and rewrites data in the memory. The program and the input means such as a switch for inputting data can be used.

The calibration of the relative permittivity in the probe is to make the signal period of the received signal in the medium having the relative permittivity correspond to the time axis.

Here, assuming that the relative permittivity of the medium is ε _r and the propagation velocity of the electromagnetic wave in the air is C ₀ , the propagation distance (depth) D of the electromagnetic wave and the time t are generally related by the following equation. To establish.

That is, the propagation distance (depth) can be calculated by finding the propagation time.
Is required.

By the way, when the analysis signal based on the received signal is displayed on the screen as a received waveform with the horizontal axis as the time axis and the vertical axis as the amplitude axis, the relative position of the analysis signal is Even if there is a correlation between the cycle for each phase and the time axis on the screen, there is no standard, so, for example,
When an analysis signal containing the surface reflected wave and the reflected wave from the embedded object is displayed on the screen, the waveform shape can be discriminated, but even the embedded object can be detected based on the time between the surface reflected wave and the object reflected wave. The distance (depth) cannot be obtained. Further, since the period of the received signal at the reference relative permittivity is not determined, the relative permittivity cannot be specified for the received signals of different periods, and the physical property cannot be analyzed. That is, since the reference time for signal processing is not determined, the period of the analysis signal cannot be associated with the time axis in the signal processing unit.

Therefore, for an analysis signal based on a reflected wave that has passed through a medium having a predetermined relative permittivity, by calibrating the correspondence between the period and the time axis, the analysis signal waveform between arbitrary points displayed on the screen is displayed. The propagation time can be obtained from the time axis. As a result, the period of the analysis signal in the signal processing unit and the time axis can be associated with each other, and the signal processing based on the calibrated time axis can be performed.

According to the calibration method of the present invention, the setting unit of the cycle adjusting unit is adjusted and set so that the cycle of the analysis signal (the cycle of the surface reflected wave) when the electromagnetic wave is radiated to the air coincides with the reference time. By this, the state calibrated with the medium of the reference relative dielectric constant is equivalently created.

According to this calibration method, no special device or procedure for calibration is required, and the calibration operation can be performed simply by displaying the analysis signal when performing anti-radiation and adjusting the period. Accurate and easy calibration can be performed on site.

Further, according to this calibration method, even if the cycle of the analysis signal fluctuates due to the temperature fluctuation of the internal circuit of the probe, etc., the cycle of the analysis signal in the fluctuation state is made to match the reference time. Calibration is done. As a result, as long as the temperature or the like does not change abruptly, the fluctuation error between the cycles corresponding to the relative permittivity in the analysis signal is canceled out, and the measurement with a small error can be performed. Further, since the calibration is performed using the analysis signal of the radiation to the air, the influence of the dielectric substance on the transmitting antenna can be eliminated as much as possible, and the calibration can be performed more accurately.

When making the period of the analysis signal coincide with the reference time, it is preferable to make the period coincide with the surface reflected wave. Here, the surface reflected wave at the time of radiation to the air is based on the first reflection by the electromagnetic wave radiated from the transmitting antenna, and includes, for example, the reflection of the antenna substrate or the like.

In the present invention, the signal processing unit is configured to generate and output an analysis signal having a predetermined relationship between the period and the relative permittivity, based on a received signal having a different period according to the relative permittivity of the medium. be able to.

An electromagnetic wave passing through a medium having a different relative permittivity causes a change in propagation velocity depending on the passing medium, and accordingly, a received signal undergoes a frequency change (period change) according to the relative permittivity of the medium.

Therefore, for example, it is possible to output an analysis signal that has been processed by the signal processing unit so as to have linearity between the period of the received signal and the square root of the relative dielectric constant.

This clarifies the correlation between the period of the analysis signal and the relative permittivity, calculates the average relative permittivity for each depth based on the analysis signal, and based on the calculated average relative permittivity. Depth analysis can be performed easily.

The present invention proposed at the same time is a method for deriving a reference time in the relative permittivity calibration method of the present invention, in which electromagnetic waves are radiated from a transmitting antenna toward a reference dielectric having a predetermined relative permittivity and a calibration distance. Adjusting the setting means so that the time between the reflected waves at the reference dielectric surface and the calibration distance contained in the analysis signal coincides with the time when the electromagnetic wave propagates the calibration distance in the reference dielectric, and then from the transmitting antenna The period of the analysis signal when radiation to the air is performed is determined as a reference time.

Here, the time that the electromagnetic wave propagates in the calibration distance within the reference dielectric means the time that the electromagnetic wave travels back and forth between the surface of the reference dielectric and the calibration distance.

According to the method of deriving the reference time, the period of the reflected wave when the calibration is performed by the reference dielectric and the anti-air radiation is performed in the calibrated state is used as the reference time for the calibration.

The above-described calibration method of the present invention uses the reference time thus obtained, and in the state calibrated with the reference dielectric constant, the period of the analysis signal at the time of radiation to the air is used as the reference time for the calibration. The excellent idea of the present invention can be recognized in the point of utilization.

The present invention proposed at the same time, a transmitting antenna that radiates an electromagnetic wave, a receiving antenna that receives a reflected wave of the radiated electromagnetic wave, a receiving unit that generates a received signal based on a detection signal of the receiving antenna, and the receiving unit. The signal processing unit includes a signal processing unit that processes a signal and outputs a signal for analysis, a storage unit that stores measurement condition data including a reference relative permittivity value, and a calculation unit. The signal processing unit outputs a received signal by frequency conversion. Includes a cycle adjustment unit that converts into an analysis signal with a different cycle,
The period adjusting unit is an electromagnetic wave probe having a means for setting a frequency conversion constant. In the electromagnetic wave probe of the present invention, the setting means, the period of the analysis signal when electromagnetic waves are radiated from the transmitting antenna to the air, so as to match the reference time predetermined according to the reference relative permittivity. It can be configured to be adjustable. Further, the signal processing unit generates a reception signal in the exploration as an analysis signal calibrated according to the relative permittivity, and the arithmetic unit determines a predetermined analysis signal based on the measurement condition data stored in the storage unit. It can be configured to generate analysis data that has been subjected to calculation.

The above-described method of calibrating the relative permittivity can be used in this electromagnetic wave probe.

By calibrating the relative permittivity by, for example, optimizing the predetermined circuit constants of the signal processing unit, the correspondence between the analysis signal at the relative permittivity and the time axis is calibrated. The unit generates and outputs an analysis signal obtained by performing a cycle adjustment process on the received signal according to the setting of the setting unit. The period of this analysis signal has a fixed relationship with the relative permittivity of a medium such as underground.

The generated analysis signal is sent to the calculation means, and necessary calculation is performed based on the measurement condition data stored in the storage means to generate analysis data necessary for displaying the search result. The measurement condition data includes data such as an arithmetic processing program to be added to the analysis signal corresponding to the reference relative permittivity value and the search result display mode.

Further, the signal processing unit may be configured to generate and output an analysis signal having a predetermined relationship between the period and the relative permittivity, similarly to the electromagnetic wave probe that performs the relative permittivity calibration method. It is possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a main configuration of an electromagnetic wave probe according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a sampling state of a received signal in a medium having a low relative dielectric constant.

FIG. 3 is an explanatory diagram showing a sampling state of a received signal in a medium having a high relative dielectric constant.

FIG. 4 is an explanatory diagram showing a procedure for calibrating the relative permittivity of the present invention using the indicator of the probe shown in FIG.

FIG. 5 is a front view showing a reference dielectric (dry Masa soil).

FIG. 6 is an explanatory diagram showing a procedure for matching the calibration distances based on the analysis signal in the reference dielectric.

FIG. 7 is an explanatory diagram showing a procedure for making the period of the surface reflected wave of the analysis signal at the time of radiation to the air coincide with the reference time.

FIG. 8 is an explanatory diagram showing a procedure for matching the calibration distances shown in FIG. 6 by performing surface wave processing.

FIG. 9 is a front view showing a reference dielectric (epoxy resin).

FIG. 10 is an explanatory diagram showing a procedure for matching the calibration distances based on the analysis signal in the reference dielectric.

FIG. 11 is an explanatory diagram of a conventional tracking zone in an analysis signal.

FIG. 12 is an explanatory diagram showing a change that occurs in a cross-sectional image due to a change in the tracking zone.

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, there are various methods for changing the cycle of a received signal by frequency conversion in the cycle adjusting section.

For example, with the received signal fixed, the time axis corresponding to the received signal is adjusted by the setting means of the cycle adjustment unit.
As a result, the correspondence between the received signal and the time axis can be calibrated, and as a result, the analysis signal in which the received signal is frequency-converted can be generated.

On the other hand, with the time axis fixed, it is also possible to perform frequency conversion (period conversion) on the received signal itself by the cycle adjustment unit according to the setting of the setting means, and thereby the correspondence between the received signal and the time axis can be calibrated. The analyzed signal can be generated.

There are various methods for performing frequency conversion (period conversion) on the received signal itself.

For example, it is possible to obtain an analysis signal in which the frequency is changed by subjecting the received signal to heterodyne processing.

Further, it is also possible to convert the received signal into digital received data once by analog-digital conversion, and subject the converted received data to digital processing to obtain an analysis signal in which the frequency is changed.

Here, in the present invention, it is preferable that the transmission signal radiated from the transmission antenna and the detection signal of the reception antenna belong to a microwave band of several hundred MHz to approximately 1 GHz. It is difficult to directly perform signal processing on the detection signal itself of the receiving antenna.

Therefore, for example, the receiving unit repeatedly performs a series of processes for generating a reception signal by repeating sampling a predetermined number of times while gradually shifting the sampling point of the reception antenna detection signal that is repeatedly received at predetermined intervals. You can also do it.

In other words, the peak value hold or average value hold is performed while sampling the amplitude of the receiving antenna detection signal that is repeatedly received, and the original receiving antenna detection signal is detected by envelope detection of these peak values or average values. It is possible to generate a reception signal suitable for signal processing in which the frequency is reduced by the receiving unit. And
The signal processing unit can perform period adjustment for calibration on the generated reception signal.

A triangular wave signal (sawtooth wave) for sampling
It is possible to output a pulse-shaped control signal including a pulse controller from the pulse controller and sample the received signal by this control signal. Further, the rise time of the triangular wave signal in the control signal is determined by the potential change amount (ΔV) of the detection signal.
When the relative permittivity of the medium is large and the period of the received signal is large, the received waveform can be observed in a relatively long time width (observation window) by varying the relative permittivity of the medium. When the cycle of the received signal is small, the received waveform can be observed in a relatively short time width (observation window). In addition, by using a diode bridge with a diode (for example, a Schottky barrier diode) whose frequency characteristic relatively varies greatly in the vicinity of the frequency of the transmitted wave or the received wave, and by the correlation between the response characteristic of the diode and the frequency characteristic,
By configuring a reception circuit that can change each sampling point, the reception signal is sampled while sensitively detecting the change in ΔV of the detection signal, and when the relative permittivity of the medium is large and the cycle of the reception signal is large. Can observe the received waveform in a relatively long time width (observation window), and can observe the received waveform in a relatively short time width (observation window) when the relative permittivity of the medium is small and the period of the received signal is small. it can.

By the way, when the calibration is performed with the predetermined relative permittivity as described above, the analysis signal passing through the medium having the different relative permittivity has a different cycle according to the relative permittivity.

Therefore, a time (depth) is obtained from the analysis signal by converting the correction cycle according to the cycle by creating a correction data table indicating the relationship between the cycle of the analysis signal and the real time by measurement in advance. be able to. In addition, by holding the correction data table in the signal processing unit,
It is also possible to generate and output an analysis signal that has undergone signal processing so that the cycle of the received signal and the real time have a predetermined relationship.

Next, a method of deriving the reference time in the relative permittivity calibration method of the present invention will be specifically described. In the description, the time taken for the electromagnetic wave to propagate within the reference dielectric within the calibration distance refers to the time required for the electromagnetic wave to travel back and forth between the surface of the reference dielectric and the calibration distance.

The time t required for the electromagnetic wave to travel back and forth by the calibration distance D in the reference dielectric having the reference relative permittivity ε _r is expressed by the following equation. However, the propagation velocity of electromagnetic waves in the atmosphere is C ₀
And

Therefore, in the reflected wave when the electromagnetic wave is radiated to the reference dielectric, the setting means is set so that the time between the reflected wave on the surface of the reference dielectric and the reflected wave at the calibration distance matches the propagation time t required for the calibration distance D. Adjust. As a result, the correspondence between the analysis signal and the time axis in the signal processing unit is calibrated. In this calibration state, the reference time is determined by performing radiation to the air and determining the period of the reflected wave.

After the reference time is obtained in this way, it is possible to reproduce the state equivalently calibrated with the reference relative permittivity simply by matching the period when the anti-air radiation is performed with the reference time.

The derivation of the reference time can be performed by the user of the electromagnetic wave probe, but a large-scale reference dielectric is required. Therefore, it is assumed that the manufacturer of the spacecraft will basically derive the reference time, and if the reference time is obtained for each antenna that can be replaced and installed in the spacecraft, the reference time can be specified to the user side. The user can accurately and easily calibrate the relative permittivity.

As the reference dielectric, “dry Masato” having a relative permittivity ε _r = 12 and a calibration distance of 50 cm is inexpensive and practical, but a medium having another relative permittivity may be used as the reference dielectric. good. Note that the Masa soil is gravelly soil made of weathered granite.

By the way, when "dry Masato" is used as the reference dielectric, the relative permittivity may change due to the humidity inside the Masato. Therefore, an epoxy resin material (relative dielectric constant = 3.5 to 4.
It is necessary to control the relative permittivity of “dry Masato” using a reference dielectric such as 5) or a melamine resin material (relative permittivity = 6.5 to 7).

For example, when managing the relative permittivity of “dry Masato” using an epoxy resin with a predetermined calibration distance as a reference dielectric, first calibrate the epoxy resin so that the calibration distance (calibration time) is the same. To do. This calibration procedure is the same as the calibration in the above-mentioned “dry Masato”.

Then, the calibration distance (calibration time) is measured in “dry Masato”. By confirming that the measured value is within the predetermined error range, it is possible to manage the relative permittivity of "dry Masato".

As the above-mentioned reference dielectric, for example, the relative dielectric constant is 12
If you want to make a structure with a calibration distance of 50 cm using the "dry Masato", fill the inside of the box made of wood with dry Masato, and install an acrylic plate etc. on the top of the box to make "Masato" It is possible to provide a structure that makes it easier to see the state of, and to form a target calibration distance in this structure.

It is also possible to equivalently form a reference dielectric having a predetermined relative dielectric constant and a calibration distance by appropriately combining media having different relative dielectric constants.

Next, a configuration will be described in which the signal processing unit generates and outputs an analysis signal having a predetermined relationship between the period and the relative permittivity for a received signal having a different period depending on the relative permittivity of the medium.

The period T of the electromagnetic wave passing through the medium is the relative permittivity ε of the medium.
It is expressed by the following equation using _r , the propagation velocity C ₀ of the electromagnetic wave in the atmosphere, and the frequency f of the electromagnetic wave.

Therefore, for example, the period in the medium having the relative permittivity ε _r = 12 is approximately 1 / the period of the medium having the relative permittivity ε _r = 45.
This is twice the frequency, and the received signal undergoes frequency fluctuation (periodic fluctuation) according to the relative permittivity of the medium.

Therefore, _{assuming that} the period of the analysis signal when the relative permittivity ε _r0 = 12 is T ₀ and the period of the analysis signal when the relative permittivity ε _r = 45 is T, for example, It is possible to generate an analysis signal, which is obtained by subjecting the received signal to signal processing, by the signal processing unit so that the relationship is established. That is, it is possible to generate an analysis signal having linearity between the analysis signal and the square root of the relative permittivity.

By this processing, the correspondence between the period of the analysis signal and the relative permittivity becomes clear, and in particular, the signal processing when displaying as a cross-sectional image becomes extremely easy.

Next, an embodiment of the electromagnetic wave probe according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, the electromagnetic wave probe 1 includes an antenna unit AT, a signal processing unit 10, a calculation unit 11, and a storage unit 1.
2 and the display unit 13.

The antenna unit AT has a transmitting antenna T that radiates an electromagnetic wave at a predetermined cycle and a receiving antenna R that receives a reflected wave of the radiated electromagnetic wave adjacent to each other and integrated therein.

The signal processing unit 10 includes a transmission unit 10b that supplies an impulse or a bias voltage to the transmission antenna T, a reception unit 10c that performs necessary preprocessing on the detection signal captured by the reception antenna R, and a transmission from the reception unit 10c. The received signal is provided with a period adjusting unit 10d that generates an analysis signal in which a period adjustment is performed by frequency conversion, and a setting unit 10e that variably sets a frequency conversion constant of the period adjusting unit 10d. It should be noted that each component of the signal processing unit 10 is connected to the signal processing circuit 10a, and receives a necessary control signal or the like to operate.

The calculation means 11 performs digital processing, and
It has a digital conversion unit and has a function of converting an analog analysis signal transmitted from the signal processing unit 10 into digital data. Then, the analysis signal transmitted from the cycle adjustment unit 10d is subjected to arithmetic processing based on the measurement condition data stored in the storage unit 12 to generate analysis data.

For example, according to the display mode set by the probe 1,
The analysis data is generated by performing the corresponding arithmetic processing on the analysis signal, and the search result is displayed based on the generated analysis data.

Further, the display unit 13 receives the analysis data that has been subjected to the arithmetic processing transmitted from the arithmetic means 11 and performs display control, and a display device that performs display based on the display signal output from the display controller 13a. 13b
And a display adjustment unit 13c for adjusting the display position of the display 13b.

The cycle adjusting unit 10d receives the analog reception signal transmitted from the receiving unit 10c, and changes the cycle of the reception signal according to the setting of the setting unit 10e to change the correspondence with the time axis.

In this embodiment, these adjustment processes are mainly performed by analog processes.

In other words, the analysis signal output from the period adjusting unit 10d is displayed on the display unit 13 via the calculating unit 11, and the semi-fixed resistor (not shown) of the setting unit 10e is adjusted to adjust the analysis signal time. The period is adjusted by changing the sweep speed in the axial direction, that is, the relative permittivity is calibrated.

The probe 1 of this embodiment is centered on a probe in a medium having a relative permittivity of about 3 to 50, and requires an analysis signal having linearity between the square root of the relative permittivity and the period of the received signal. And The frequency of the received signal is approximately 500 MHz
Since it is 1.5 GHz, it is difficult to directly perform signal processing on the received signal.

Therefore, in this embodiment, prior to the process of the period adjusting unit 10d, the preprocessing for reducing the frequency of the received signal and obtaining the analysis signal having the period according to the relative permittivity of the passing medium. Is performed by the receiving unit 10c.

The operation of the receiving unit 10c will be described with reference to FIGS.

When a reflected wave due to radiation to the air is received and the received signal is displayed as a received waveform on a predetermined time axis and amplitude axis, an attenuated waveform as shown in FIG. 2 is obtained. On the other hand, when a reflected wave from a medium having a relative permittivity ε _r is received, the propagation speed of the electromagnetic wave is lower than that in the atmosphere. Therefore, if the same time axis as in FIG. The received signal has a long required time.

Therefore, in the receiving unit 10c, the non-linear portion of the frequency characteristic and the ON characteristic of the Schottky barrier diode (hereinafter, referred to as SBD) is positively combined to be used, so that the relative permittivity of the medium and the period can be predetermined. An analysis signal having the relationship of is output in front.

That is, depending on the characteristics of the SBD, the received signal is sampled at each time interval according to the slope (ΔV / Δt) of the output level V with respect to the time t of the received signal, and the peak position hold or the average position hold is performed and the predetermined number of At the time when the reception signal is completely received, the operation for repeating the series of processes for generating the analysis signal with the reduced frequency is performed.

When an exploration test of the stratum is conducted with the spacecraft 1 having this configuration, linearity approximately proportional to the square root of the relative permittivity is obtained between the relative permittivity of the medium and the period of the analysis signal generated in advance. I found out.

In other words, if the period of the received signal is short, the period of the analysis signal with a reduced frequency generated is also short, and conversely, if the period of the received signal is long, the period of the generated analysis signal is also long. It is possible to apply pretreatment to the.

Further, as shown in FIGS. 2 and 3, the sampling time interval (t
By changing (1, t2), there is no inconvenience that sampling ends in the middle of the attenuation signal even in a reception signal in a medium having a large relative dielectric constant, and
An analysis signal with a reduced frequency was obtained.

In the present embodiment, the signal processing circuit 1 of the signal processing unit 10
The receiving unit 10c receives the control signal transmitted from 0a and generates the receiving signal by analog processing.
It is also possible to generate the received signal by digital processing.

Next, a method of calibrating the relative permittivity in the probe 1 will be described.

First, electromagnetic waves are radiated from the transmitting antenna T to the air, and the analysis signal received by the receiving antenna R and generated by the signal processing unit 10 is displayed on the display 13b as shown in FIG.

The setting means 10e is adjusted so that the cycle of the surface reflected wave Wo in the analysis signal matches the reference time t that is predetermined according to the reference relative permittivity. As a result, the period of the analysis signal at the reference relative permittivity and the time axis are associated with each other, and the calibration of the relative permittivity is completed.

After the relative permittivity is calibrated, the display adjustment unit 13c is adjusted and set so that the first peak point P ₀ of the amplitude of the surface reflected wave W ₀ of the analysis signal W coincides with the start point (left end) of the time axis. . As a result, the starting point of the analysis signal W is set to the transmission antenna T.
The origin of the analysis signal in the exploration analysis is clarified by making it approximately coincident with the electromagnetic wave radiated from.

By the above calibration and adjustment, the relative permittivity of the probe 1 is calibrated and the probe preparation is completed.

After the relative permittivity is calibrated in this way, the received signal received by the receiving antenna R is then subjected to frequency conversion by the period adjusting unit 10d according to the setting of the setting unit 10e. A search signal is generated, and an exploration analysis process is performed using the analysis signal obtained by performing a calculation process on the generated analysis signal by the calculation unit 11.

In other words, when the reflected wave in the medium having the relative permittivity ε _r = 12 is received, the period of the analysis signal displayed on the display 13b and the time axis are associated with each other, and the signal processing unit 1
The time standard in the signal processing of 0 becomes clear.

Since the relative permittivity of the present invention is extremely easy to calibrate, for example, if the calibration is performed every predetermined time, a more accurate survey can be performed.

Further, as described above, in the receiving unit 10c of the signal processing unit 10, the period of the analysis signal at the reference dielectric constant is used as a reference, and the reception signal in the medium having a different dielectric constant is approximately proportional to the square root of the dielectric constant. An analysis signal having a specified period is generated.

In the calculation means 11, according to the measurement condition data stored in the storage means 12, processing necessary for displaying the search result is applied to the analysis signal to generate analysis data and sent to the display unit 13.

As a result, various displays necessary for determining the exploration result can be displayed based on the analysis data, and the buried object can be easily estimated.

In the present embodiment, the receiving unit 10c generates an analysis signal having a period substantially proportional to the square root of the relative permittivity. However, the receiving unit 10c generates an analysis signal with a reduced frequency, and the calculation is performed. It is also possible for the means 11 to generate analysis data having a period approximately proportional to the square root of the relative permittivity.

As described above, according to the relative permittivity calibration method of the present invention, it is possible to easily perform it by simply matching the period of the analysis signal at the time of radiation to the air with the reference time without using a special device. It is possible to conduct various explorations.

Moreover, since the correspondence between the relative permittivity and the depth is clear, it is easy to estimate the exploration state from the cross-sectional image, and the exploration workability is improved.

Further, even when the antenna unit AT having a different radiation frequency is exchanged for the search, it is possible to immediately calibrate the relative permittivity according to the reference time presented in advance by the manufacturer.

Next, a method of deriving the reference time, which is the basis of the above-described relative permittivity calibration, will be described with reference to FIG. Note that the time required for the electromagnetic wave to propagate through the calibration distance at the reference relative permittivity (round-trip propagation time of the calibration distance) t is calculated in advance.

As shown in FIG. 5, the relative permittivity ε _r = 12 and the calibration distance d
The antenna AT of the probe 1 is brought into contact with the reference dielectric body 20 of "dry Masato" of 50 cm to radiate an electromagnetic wave, and the received signal is displayed on the display 13b as an analysis signal.

FIG. 6 shows the analysis signal W, which includes the surface reflected wave W ₀ and the reflected wave W1 at the calibration distance d (50 cm).

The period adjusting unit 10d is configured so that the time t ₀ between the surface reflected wave W ₀ and the reflected wave W1 coincides with the propagation time t of the calibration distance.
The setting means 10e is adjusted. As a result, the relative permittivity ε
Calibration of relative permittivity at _r = 12, that is, analysis signal W
Calibration of the cycle and time axis is completed.

In this way, radiation to air is performed with the relative permittivity calibrated, and the reference time t can be obtained by reading the period t of the surface reflected wave of the analysis signal from the time axis as shown in FIG.

In FIG. 6, when the starting point of the reflected wave W1 is unclear, the signal processing circuit 10a extracts the difference signal component between the analysis signals W by the surface wave processing (the surface wave processing mode of the probe 1). ), The starting point can be easily grasped.

That is, as shown in FIG. 8, the difference signal component subjected to the surface wave processing is displayed as the analysis signal W ′, and the reference dielectric 2
A metal plate or the like is brought into contact with or separated from the position of the calibration distance d of 0 (the lower surface of the reference dielectric 20). By observing the analysis signal W ′ at this time, the reflected wave W1 ′ is displayed as a variable element, so that the starting point can be easily grasped. Therefore, the calibration can be easily performed by adjusting the time between the origin of the surface reflected wave W _{0 and} the origin of the reflected wave W1 ′ to t ₀ .

As described above, the reference time which is the basis for the calibration of the relative permittivity is set at a low cost by using “dry Masato” or the like.
Can be easily derived by.

If the manufacturer of the probe 1 needs to provide the reference dielectric 20, the user does not need to provide the reference dielectric 20, and the user can surely calibrate the reference dielectric 20 simply by indicating the reference time in the instruction manual.

Next, a method of managing the relative permittivity of the reference dielectric 20 using “dry Masato” will be described.

As shown in FIG. 9, the antenna AT of the probe 1 is brought into contact with the reference dielectric 21 made of an epoxy resin having a relative permittivity ε _r = 4.0 and a calibration distance d1 = 20 cm to radiate an electromagnetic wave, and a reception signal thereof is received. Is displayed on the display 13b as a signal for analysis.

FIG. 10 shows the analysis signal W, which includes the surface reflected wave W ₀ and the reflected wave W1 at the calibration distance (50 cm).

The period adjusting unit 10 adjusts the time t ₀ between the surface reflected wave W ₀ and the reflected wave W 1 to match the propagation time t of the calibration distance.
The d setting means 10e is adjusted. This calibrates the relative permittivity when the relative permittivity ε _r = 4.0, that is, the period of the analysis signal W and the time axis.

With the relative permittivity ε _r = 4.0 calibrated, as shown in FIG. 5, the relative permittivity ε _r = 12 and the calibration distance d =
The antenna AT of the explorer 1 is brought into contact with the reference dielectric 20 of 50 cm of "dry Masato" to radiate an electromagnetic wave, and the received signal is displayed on the display 13b as an analysis signal.

As shown in FIG. 6, the analysis signal W includes the surface reflected wave W ₀ and the reflected wave W1 at the calibration distance (50 cm).

The time t ₀ between the surface reflected wave W ₀ and the reflected wave W1 is read from the time axis, the error with the propagation time t of the calibration distance at the relative permittivity ε _r = 12 is calculated, and the error is within a predetermined range. For example, it is assumed that the relative dielectric constant of the reference dielectric 20 is maintained.

However, if the error exceeds a predetermined value, the soil of the reference dielectric 20 is dried to adjust the error to be within the error range.

The surface reflected wave W ₀ and the reflected wave W included in the analysis signal
When the time between 1 and 1 is read from the time axis, the display adjustment unit 13c may be adjusted to move the analysis signal to a position where it is easy to read the time.

In FIG. 1, the signal processing unit 10 and the computing means 1 are shown.
Although 1 is shown as another configuration, it is also possible to employ a configuration in which the arithmetic means 11 uses a CPU that is common to the signal processing circuit 10a of the signal processing unit 10.

It is also possible to digitize the processing of the cycle adjusting unit 10d and the setting means 10e.

Next, as an application example of the electromagnetic wave probe, a method of measuring an average relative dielectric constant for each depth in a medium (underground) will be described.

This method of measuring the relative dielectric constant can include the following steps (a) to (d).

(A) A step of detecting all peak positions (positive side peak and negative side peak) of a waveform propagating an electromagnetic wave.

(B) With the propagation velocity at each peak position as the positive peak and the zero cross point, and the negative peak and the zero cross point, the time width of each section is sequentially measured to change the propagation period, that is, the dielectric constant. Is calculated from the following formula: relative permittivity = (measurement period time / reference period time) ² × reference calibration relative permittivity (where, this relative permittivity is an average value for each section).

(C) In the verification of the propagation period of each section, the frequency spectrum is analyzed by setting the signal component to zero in other sections, and its normalization is calculated by the sum of squares of the maximum spectrum (excluding the DC component) to obtain the dominant frequency, Confirming the correlation of Δf = Δε _r .

(D) A step of displaying the relative permittivity obtained for each section by color bar classification and displaying it on the display device as a permittivity distribution map in the depth direction of the formation.

To confirm the above-mentioned correlation, since a 512-point discrete period can be obtained by a Fourier analysis of 2 ¹⁰ decomposition, the measurable period obtained by the reference period (5 msec, 0.5 msec at maximum)
Since the reference period corresponds to 10 discrete periods, the discrepancy between the permittivity ratio and the discrete period is verified), and the linear correlation with the permittivity is evaluated.

By displaying the permittivity (relative permittivity) thus obtained by color bar classification and displaying it as a permittivity distribution map / depth map in the depth direction of the stratum, it is easy for an experienced explorer to understand The state, permittivity, stratum, etc. can be identified. Furthermore, if a cursor is placed on the color bar and the analyzed section distance is searched, the average permittivity of the section, the total depth, etc. can be observed simultaneously, dramatically simplifying electromagnetic wave exploration and increasing functionality. Can be achieved.

As described above, according to the relative permittivity calibration method of the present invention, a special device is not required, and the period of the analysis signal based on the received signal obtained by the radiation to the air is set to be equal to the reference time. The relative dielectric constant can be immediately calibrated, the workability at the exploration site is improved, and the precise exploration can be performed.

Further, according to the method of deriving the reference time of the present invention that is proposed at the same time, it is possible to easily obtain the reference time by using the reference dielectric.

Further, according to the electromagnetic wave probe of the present invention that is proposed at the same time, the relative permittivity calibration method of the present invention can be effectively implemented.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01V 3/12 G01S 7/03 G01S 13/88

Claims (6)

(57) [Claims] 1. A transmission antenna that radiates an electromagnetic wave, a reception antenna that receives a reflected wave of the radiated electromagnetic wave, a reception unit that generates a reception signal based on a detection signal of the reception antenna, and the reception signal is processed. And a signal processing unit for outputting an analysis signal, the signal processing unit having a period adjusting unit for converting the received signal into the analyzing signal having a different signal period by frequency conversion, and the period adjusting unit. Is an electromagnetic wave probe having a means for setting a frequency conversion constant, so that the period of the analysis signal when electromagnetic waves are radiated from the transmitting antenna to the air matches the reference time predetermined according to the reference relative permittivity. A method for calibrating the relative permittivity of an electromagnetic wave probe, comprising adjusting the setting means. 2. The method for calibrating the relative permittivity of an electromagnetic wave probe according to claim 1, wherein the signal processing unit determines the period and the relative permittivity based on a received signal having a different period according to the relative permittivity of the medium. A method for calibrating a relative permittivity of an electromagnetic wave probe, comprising generating and outputting an analysis signal having a predetermined relationship with a coefficient. 3. The method for calibrating the relative permittivity of an electromagnetic wave probe according to claim 1, wherein the reference time radiates an electromagnetic wave from the transmitting antenna toward a reference dielectric having a predetermined relative permittivity and a calibration distance. Then, after adjusting the setting means so that the time between reflected waves at the reference dielectric surface and the calibration distance included in the analysis signal coincides with the time during which the electromagnetic wave propagates the calibration distance in the reference dielectric, the transmission is performed. A method for calibrating the relative permittivity of an electromagnetic wave probe, which is the period of the analysis signal when radiation from the antenna to the air is performed. 4. A transmission antenna that radiates an electromagnetic wave, a reception antenna that receives a reflected wave of the radiated electromagnetic wave, a reception unit that generates a reception signal based on a detection signal of the reception antenna, and the reception signal is processed. And a signal processing unit for outputting a signal for analysis, a storage unit for storing measurement condition data including a reference relative permittivity value, and a calculation unit, wherein the signal processing unit frequency-converts the received signal into a signal cycle of There is a period adjusting unit for converting into a different analysis signal, the period adjusting unit has a frequency conversion constant setting means, the setting means, the period of the analysis signal when electromagnetic waves are radiated from the transmitting antenna to the air Is configured to be adjustable so as to match a predetermined reference time according to the reference relative permittivity. 5. The electromagnetic wave probe according to claim 4, wherein the signal processing unit generates a received signal in the probe as an analysis signal calibrated according to a relative permittivity, and the arithmetic unit is stored in a storage unit. An electromagnetic wave exploring device, which generates analysis data by performing a predetermined calculation on the analysis signal based on the measured condition data. 6. The electromagnetic wave probing machine according to claim 4, wherein the signal processing unit sets a predetermined value between the period and the relative permittivity for a received signal having a different period according to the relative permittivity of the medium. An electromagnetic wave explorer characterized by generating and outputting an analysis signal having the relationship of