JPH03115806A - Method for measuring thickness in laminated structure - Google Patents

Abstract

PURPOSE:To highly accurately measure thickness of each layer by a method wherein a pulse wave is radiated to a laminated structure, a synthesized reflection wave is decomposed and extracted as reflection waves of a surface and respective layers, their time differences are detected, and the difference and the dielectric constant of each layer are used to calculate the thickness. CONSTITUTION:A pulse wave is radiated to a pavement where a surface At, a sub grade St and a road bed Mt are laminated, and a synthesized reflection wave of waveforms reflected on the surface and borders of the respective layers is received. Reflection waveforms W11 to W13 of the surface and the respective layers are decomposed and extracted from the synthesized deflection wave. With a time axis of the waveforms W11 as a reference, respective time differences D1 to D3 of the reflection waveforms W11 to W13 are calculated. An equation I is used to calculate thickness L of a layer based on the time difference D and a dielectric constant epsilon of each layer which is obtained as data in advance. Thus thickness of a layer can be measured at high accuracy quickly and continuously.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention uses pulse waves (electromagnetic waves) to measure the thickness of each layer of a laminated structure, such as a paved road. Regarding the measurement method.

[Prior Art] Conventionally, when measuring the thickness of concrete in a single-story building or bricks in a blast furnace, a pulse wave is emitted, and then the surface of the concrete, brick, etc. is determined from the reflected waves obtained. A method is well known in which the thickness of the concrete, brick, etc. is measured from the waveform that remains after removing reflected waves (including crosstalk).

In this case, when measuring relatively thin concrete,
As shown in Figure 7, first, make sure that the conc IJ is sufficiently thick.
-) Emit a pulse wave to the surface of T, and store the reflected wave W1 obtained here. Next, a pulse wave is emitted to the concrete Ta to be measured, and the reflected wave W2 from the surface is
and the reflected wave W from the bottom surface are combined to obtain a composite reflected wave W.

Then, the reflected wave W is read out from the combined reflected wave W4 and subtracted, thereby creating only the reflected wave W3 from the bottom surface.

[Problem to be solved by the invention] However, the surface layer (ascon) At shown in FIG.
When measuring the thickness of a laminated paved road, etc. consisting of a subgrade (crushed stone) sr and a subgrade (soil) Mt, the subgrade St and the subgrade M
The signal level of the reflected wave W6 from the boundary of t is low, especially when
When the roadbed St is thin, it is affected by the reflected wave W1 from the bottom of the surface layer At, and therefore it is difficult to measure the thickness. That is, the reflected wave W6 from the surface is subtracted from the composite reflected wave W, and then the reference reflected wave W from the bottom of the surface layer At is calculated.
When determining and subtracting , the reference reflected wave W7 changes depending on the thickness of the roadbed St, and the thickness of the roadbed St changes.
An error will occur in the measurement of the reflected wave W6 from the interface between the roadbed Mt and the roadbed Mt.

As described above, it is difficult to measure the thickness of the subgrade St in a laminated paved road, that is, the depth to the subgrade Mt, using conventional methods for measuring the thickness of a laminated structure. Furthermore, there is currently no method for measuring the thickness of each layer of a laminated pavement road.

The present invention has been made in view of the above points, and after a pulse wave is radiated to a laminated structure, for example, a paved road consisting of multiple layers, each of the synthesized reflected waves obtained from the boundaries of each layer is An object of the present invention is to provide a method for measuring the thickness of a layer in a laminated structure, in which the thickness of a layer can be measured with high precision, quickly, and continuously.

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the method for measuring the thickness of a laminated structure according to the present invention, after a pulse wave is radiated to the laminated structure, a pulse wave is emitted to the laminated structure, and then the thickness is In a thickness measurement method for a laminated structure in which the thickness of each layer is measured based on such synthetic reflected waves, the time difference (D
) is formed; a second process of determining the dielectric constant of each layer; and a time difference (D) between the respective layers; and a third step of determining the thickness L (mm) of each of the layers with respect to the corresponding dielectric constant.

[Operation] In the method for measuring the thickness of a laminated structure described above, a pulse wave emitted to the laminated structure passes through the surface and each layer, and then is reflected at the bottom (boundary) of each layer, forming a composite reflected wave. Ru. Then, the composite reflected wave is decomposed and extracted into reflected waves related to the surface and the boundaries of each layer, and then, with the reflected waves from the surface as a reference, a time difference in each of the reflected waves is detected, and the time difference is detected. The thickness of each layer is calculated by calculating the dielectric constant of each layer (substance) obtained in advance as data.

[Example] Next, an example of thickness measurement method in a laminated structure according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view showing the structure of a laminated pavement road used for explanation of the embodiment, FIG. 2 is a waveform diagram showing the phase state and the synthesized reflected waves formed at the boundaries of each layer of the laminated pavement road, and FIG. The figure is a diagram used to explain the processing process, and Figures 4 (a) and b) are simulation flowcharts in the processing process.
Figure 5 (a), diagram provided to explain the processing process until June, No. 6
The figure is a configuration diagram showing a buried object exploration device to which an embodiment is applied.

First, with reference to FIG. 6, a buried object detection device to which the method for measuring thickness in a laminated structure of the present invention is applied, for example, when measuring each layer of a laminated paved road will be explained.

This example has a cart Dc and a main body display section 10.

For example, a transmitting antenna 12 whose directivity (beam turn) is formed in the direction of the paved road M and a receiving antenna 14 are disposed on the trolley Dc.

Note that the portion indicated by the symbol Tx is a reflective object such as a water/sewage pipe or a communication goobunope cavity.

The main body display section 10 includes a control section 16 that performs system control, and a transmitter 18 that is supplied with a synchronization trigger signal (S,) from the control section 1G and sends out a pulse signal to the transmission antenna 12.
It has The transmitting antenna 12 generates a pulse signal into a pulse wave (electromagnetic wave) PTw and radiates it underground.

Next, there is a sample and hold circuit 20 to which a received signal related to the reflected wave Plill from the reflective object T's is supplied from the receiving antenna 14. The principle of the sample and hold circuit 20 is the same as that of a sampling oscilloscope, and samples a high frequency signal that repeats at a constant cycle using a sampling signal S1 from the control unit 1G, and converts it into a low frequency signal S2 that is easy to handle. Furthermore, low frequency signal S2
It has a low frequency amplifier 22 that amplifies the signal to a predetermined value, an A/D converter 24, and a signal processor 26. The signal processor 26 has a built-in microcomputer, and performs various signal processing on the digitized reflected wave signal for the purpose of improving the S/N ratio and resolution. Furthermore, it performs display on a cathode ray tube and sends data to other terminal equipment such as a data recorder, color hard copy device, host computer, etc. Note that an operating means 26a such as a keyboard for performing the above-mentioned signal processing is provided in series. Said A/
The D converter 24 and the signal processor 26 each include a control section 16.
Control signals (clock signals, etc.) necessary for synchronization etc. from S<
, Ss are supplied.

Note that reference numeral 30 is a color cathode ray tube, which visually displays reflected waves in various formats.

This embodiment is a processing process related to the signal processor 26, for example, a thickness measuring method in a laminated structure when measuring the thickness of each layer under a laminated pavement road, and the details thereof will be explained below.

First, the surface layer (ascon) At that is the object to be measured.

FIG. 1 shows the configuration (cross section) of a paved road on which a subgrade (crushed stone) St and a subgrade (soil) Mt are laminated. Next, the relative permittivity of each of the above layers is shown in Table 1 below.

Table 1 As shown in Table 1, the dielectric constants are different for each layer. Then, the pulse wave PT sent out from the transmitting antenna 12
W is reflected at the boundary between the surface Ma of the paved road M, the bottom surface of each of the surface layer At and the roadbed St.

Here, the reflected wave PRw received by the receiving antenna I4 is shown in FIG. As can be easily understood from the figure, the reflected wave PRw is a composite of the waveforms of the emitted pulse wave that passes through the surface Ma, the surface layer At, and the roadbed St, and is reflected at each boundary. . Here, the components (waveform) of the composite reflected wave Wt are as follows.

Synthetic reflected wave Wt = waveform WIG 10 waveform W1° 10 waveform W, 2
+Waveform W 13 Waveform W, , : This is a waveform that wraps around from the transmitting system to the receiving system.

Waveform W11: This is a reflected wave from the surface Ma.

Waveform W1□: This is a reflected wave from the interface between the surface layer At and the roadbed St.

Waveform W13: This is a reflected wave from the boundary surface between the roadbed St and the roadbed Mt.

Next, the time differences (phase differences) Do to D3 of the waveforms WIG to WH3 are as follows (see FIG. 2).

Do: No time difference occurs (one point on the time axis of this waveform is taken as the reference point).

Dl: transmitting antenna 12, receiving antenna 14, surface Ma
It is determined by the distance between the three points.

D2: Determined by the thickness of the surface layer At.

D3: Determined by the thickness of the roadbed St.

In such a principle (characteristic), the surface layer At, the roadbed St
, the thickness of each layer of the roadbed Mt is determined as follows.

First, waveforms WIO to WIF are obtained from the composite reflected wave Wt.
Then, the time difference between the waveforms Wl+ to W13 is determined using one point on the time axis of the waveform who as a reference.

In such processing, each processed waveform signal is stored in a storage unit (not shown) in the signal processor 26, and then processed (
This is accomplished by performing the following continuous processing after reading out the stored waveform and the waveform formed here.

Here, if each time difference is D and the dielectric constant of the layer is ε, then the thickness L (mm) of the layer is given by the following equation (1).

The extraction of each of waveforms W16 to W+3 will be described below.

The waveform WIO wraps around from the transmitting system to the receiving system (crosstalk), and is a unique waveform of the device determined by the characteristics of the electrical circuit of the device.

Therefore, it is sufficient to use the measured waveform W1o.

Regarding the waveform W11 of the surface layer At, first, the distance between the transmitting antenna 12 and the receiving antenna 14 is constant, and furthermore, the distance between the transmitting antenna 12 and the receiving antenna 14 and the surface Ma is constant depending on the wheel diameter of the truck Dc. It is. Further, the relative dielectric constants of air and the surface layer At are constant and do not vary in normal measurements. Therefore, it is sufficient to measure and use the waveform W11 of a representative part based on experience.

To generate the waveform Wl□, first, as shown in FIG. 3, the aforementioned waveform WI0 and waveform W11 are subtracted from the composite reflected wave Wt to form a composite wave of the waveform W12 and the waveform w13.

Here, the waveform W12 from the interface between the surface layer At and the roadbed St is
As shown in FIG. 3, the time difference D2 is determined from an initial characteristic point (peak or zero cross) in the waveform w12 that does not include the influence of the waveform Wlff from the interface between the subgrade St and the subgrade Mt. I can do Koki.

In this way, when the time difference D2 is actually measured, the surface layer At
The waveform wI□ from the interface between the roadbed St and the roadbed St can be obtained from a simulation according to the following procedure (see FIG. 4(a), et al.).

■ Relative permittivity ε of air. and surface layer At (ascon) relative permittivity ε, and the interface permeability coefficient To between air and surface layer At.

■ Relative permittivity ε1 of surface layer At (ascon) and roadbed St
The interface reflection coefficient R0 between the surface layer At and the roadbed St is obtained from the dielectric constant ε2 of .

■ Waveform W. Forms an input waveform that can be considered the same as

■ Find the magnitude IW+zl of the waveform W1□.

W+21 =WIOX ('ro)2XR■ Shift the phase by D+ +D2.

■ Form a waveform of waveform W12.

The waveform W13 is a waveform W from the composite reflected wave Wt. , waveform W
11 and the theoretically determined waveform W+2. As a result, waveform W1. The time difference in Fig. 5 (a) and (b) 1. : Can be determined from characteristic points (peaks or zero crossings) as shown. Note that FIG. 5, etc.) are waveforms W, 1 to W1.
This is a schematic representation of the reflection state of .

Therefore, the thickness of the roadbed St (mm) is the above (1
) is obtained by L2 = 1/2 V-Ds.

In the above example, a case has been described in which the thickness of the roadbed St is determined, but the present invention is not limited to this. For example, after obtaining a composite reflected wave from the surface of four or more laminated pavement roads and the boundaries of the bottom of each layer, and further extracting each waveform, the extracted waves are calculated based on the reflected wave from the surface. The present invention also includes detecting a time difference between waveforms and calculating the thickness of each layer by calculating the time difference and the dielectric constant of each layer obtained in advance as data.

In addition, it goes without saying that it can be used to measure the thickness of each layer in various types of laminated structures, as well as the above-mentioned laminated pavement roads.

[Effects of the Invention] As described above, according to the method for measuring the thickness in a laminated structure of the present invention, a composite reflected wave is decomposed and extracted into reflected waves related to the surface and the boundaries of each layer. Next, the time difference between the respective reflected waves is detected using the reflected wave from the surface as a reference, and the thickness of each layer is calculated by calculating the time difference and the dielectric constant of each layer (substance) obtained in advance as data. is calculated.

As a result, after a pulse wave is emitted onto a laminated structure, such as a laminated pavement road, the thickness of each layer can be measured rapidly and continuously with high precision from the combined reflected waves at the boundaries of each layer. In addition, it enables the appropriate selection of construction methods when maintaining and repairing laminated pavement roads, and also has the advantage of being able to quickly measure the maintenance status of thickness, etc., at the time of completion. have

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a laminated paved road, which is used to explain an embodiment of the method for measuring thickness in a laminated structure of the present invention, and FIG. 2 is a cross-sectional view of each layer of the laminated paved road shown in FIG. A waveform diagram showing the combined reflected wave and phase state formed at the boundary, Figure 3 is a diagram used to explain the processing process, Figure 4 (a),
Figures 5(a) and ('b) are diagrams used to explain the processing process, and Figure 6 is a flowchart of the simulation in the processing process and a reference diagram related to the simulation. FIG. 7 and FIG. 8 are diagrams illustrating a conventional buried object exploration device. 10...Main display unit 14...Receiving antenna 26...Signal processor At...Surface (ascon) Dc...Bogie Mt...Road bed (soil) W 16-W Hz... Waveform 12...Transmission antenna 16...Control unit Do"=Ds...Time difference St...Roadbed (crushed stone) Wt...Synthetic reflected wave

Claims (2)

[Claims] (1) In a thickness measurement method for a laminated structure in which the thickness of each layer is measured based on the resulting synthesized reflected waves related to the boundaries of each layer after a pulse wave is radiated to the laminated structure, Time difference (D) based on the reflected wave from the wave surface
) is formed; a second process of determining the dielectric constant of each layer; and a time difference (D) between the respective layers; A third process of determining the thickness L (mm) of each layer with the corresponding dielectric constant as L=1/2×(3×10^1^0)/√ε×D; A method for measuring thickness in a laminated structure, comprising: (2) In the method for measuring thickness in a laminated structure according to claim 1, the first step employs extraction of initial feature points on the time axis of the waveform, subtraction between waveforms, and simulation related to the relative dielectric constant of each waveform. A method for measuring thickness in a laminated structure.