JP6817628B2 - Vibration radar device and data analysis device - Google Patents

Description

The present invention mainly relates to a vibration radar device and a data analysis device for precisely measuring the corrosion state of a reinforcing bar of reinforced concrete.

Most of the reinforced concrete (RC: Reinforced-Concrete) structures constructed during the high-growth period of Japan have passed more than 40 years, and there is concern that the maintenance cost will increase enormously. RC structures prevent the oxidation of reinforcing bars by keeping the concrete alkaline, but when the reinforcing bars are corroded and expanded due to the invasion of chloride ions, fine cracks occur in the concrete, causing peeling of the concrete and significant strength. It causes a decrease. In addition to external factors such as earthquakes, such concrete has a risk of spontaneous collapse, so it is necessary to detect such a risk in advance and take immediate measures. It is necessary to inspect and measure the corrosion and expansion of the reinforcing bar in order to detect the danger in advance.

Prior art documents close to the technical field of the present invention are shown in Patent Document 1 and Patent Document 2.
Patent Document 1 discloses a measurement method in which a reinforcing bar is vibrated by a fluctuating magnetic field as a non-destructive inspection method for a structure containing a magnetostrictive body.
Patent Document 2 describes an acoustic diagnosis / measurement device using pulsed electromagnetic force, and as a method for diagnosing / measuring them, the reinforcing bar is diagnosed by measuring the waveform of the reinforcing bar inside the concrete vibrated by the pulsed electromagnetic force. The method is disclosed.

JP-A-2002-90350 Japanese Patent No. 3738424

In the existing inspection methods for reinforced concrete, cracks and rust juice are first visually confirmed, and then the natural potential method and the polarization resistance method, which involve the squeezing out of the reinforcing bars, have been applied. However, the natural potential method is only used for evaluating the presence or absence of corrosion, and it is difficult to accurately evaluate the amount of corrosion. In addition, the polarization resistance method is used to evaluate the corrosion rate. As described above, a firm method for non-destructively evaluating the current amount of corrosion of reinforcing bars in concrete has not been established at this time.

On the other hand, as a research on the evaluation of corrosion of reinforcing bars in the past, there is a method of measuring the temperature of the concrete surface by applying an alternating magnetic field to the reinforcing bars from the outside to generate heat by eddy currents. However, this method is difficult to apply in a solar radiation environment.
Further, as a study closest to the present invention, there is a method called an electromagnetic pulse method. The electromagnetic pulse method is a method in which a pulse current of about several ms is applied to an exciting coil from the outside of concrete, the reinforcing bar is momentarily vibrated, and vibration due to an impact using the reinforcing bar as a sound source is measured by an elastic wave sensor on the surface. When the reinforcing bar is corroded and the restraint with concrete is weakened, the elastic wave amplitude obtained is smaller than that of a healthy reinforcing bar, so that it is expected to be applied to the evaluation of the reinforcing bar.

In addition, this electromagnetic pulse method is also used for evaluation of cracks between reinforced concrete as one of the impact elastic wave methods using reinforcing bars as a vibration source. However, since the electromagnetic pulse method measures the pulse vibration from the reinforcing bar with an elastic wave sensor installed on the surface, there is a drawback that the measurement data is affected by the contact state of the sensor. In addition, elastic waves are generally affected by the inhomogeneity between reinforcing bars and concrete due to the propagation of elastic waves, such as being strongly damped by cracks in concrete. For this reason, it is essentially difficult to obtain direct information on the vibration of the reinforcing bar that reflects the corrosion status around the reinforcing bar by the electromagnetic pulse method, and it is not always effective in evaluating the corrosion of the reinforcing bar. ..
Further, in the evaluation of cracks and peeling of concrete, for the same reason, it is difficult in principle to search for horizontal cracks generated by corrosion of reinforcing bars deeper than cracks.

The present invention has been made in view of the above circumstances, and can accurately identify the corroded part of the reinforcing bar of the RC building without being influenced by external factors such as cracks in concrete. An object of the present invention is to provide a vibration radar device and a data analysis device.

In order to solve the above problems, the vibration radar device of the present invention is based on a vibration low frequency signal source that generates a low frequency signal for vibration of the reinforcing bars existing inside the concrete and a low frequency signal. It includes an exciting coil that excites the reinforcing bar and a high-frequency generator that generates a high-frequency signal for radar waves. Further, a frequency setting unit that sets the frequency of the high-frequency signal, a transmitting antenna that transmits a radar wave based on the high-frequency signal to the reinforcing bar, a receiving antenna that receives the radar wave reflected from the reinforcing bar, and a signal received from the receiving antenna. It includes an orthogonal detector that inputs a high-frequency signal and performs orthogonal detection, and a switch provided between the excitation low-frequency signal source and the exciting coil. The quadrature detector outputs an unmodulated component signal when the switch is off and a Doppler modulated component signal when the switch is on.

According to the present invention, a vibration radar device and a data analysis device capable of non-destructively and accurately identifying a corroded part of a reinforcing bar of an RC building without being influenced by external factors such as cracks in concrete. Can be provided.
Issues, configurations and effects other than those described above will be clarified by the description of the following embodiments.

It is the schematic which shows the whole structure and the measuring method of the vibration radar apparatus which concerns on embodiment of this invention. It is a block diagram of the vibration radar apparatus which concerns on embodiment of this invention. It is a front view and a side view of a bowtie slot antenna. It is a block diagram which shows the software function of a data analysis apparatus. It shows a state in which the excitation coil of the excitation radar device according to the embodiment of the present invention, the transmission bow tie slot antenna, and the reception bow tie slot antenna are arranged on a sound reinforced concrete column and a reinforced concrete column in which the corrosion of the reinforcing bar has progressed. , It is a schematic cross-sectional view. The conceptual diagram of this invention is shown. It is the schematic which shows the state of the reinforced concrete specimen and the exciting coil produced. It is a graph which shows the unmodulated signal waveform and the vibrating Doppler signal waveform obtained in the sound specimen and the specimen which was subjected to electrolytic corrosion for 21 hours. It is a partially enlarged view of the unmodulated signal waveform and the vibrating Doppler signal waveform obtained in a sound specimen and a specimen subjected to electrolytic corrosion for 21 hours. It is a partially enlarged view of the unmodulated signal waveform and the vibration Doppler signal waveform obtained in 1. It is a graph showing the result of showing the spatial average and standard deviation of the vibration displacement by the error bar, and the graph showing the average value and the standard deviation of the peak delay time of the Doppler waveform with respect to the unmodulated component by the error bar.

The vibration radar device according to the embodiment of the present invention is a kind of method for obtaining direct information on the vibration of the reinforcing bar, which is a problem in the electromagnetic pulse method. The reinforcing bar in the concrete is vibrated by the exciting coil, and the electromagnetic wave radar is used. The vibration is non-destructively measured by the existing Doppler displacement measurement method. Concrete is a medium that is more homogeneous to electromagnetic waves than elastic waves, and is less susceptible to internal cracks. Further, unlike the contact type elastic wave sensor, the vibration displacement can be measured without contact, so that the influence of the installation method can be reduced.

Further, since the vibration radar device according to the embodiment of the present invention uses a high-resolution electromagnetic wave radar method having a resolution of about 1 cm in concrete, the reinforcing bar and the radar reflector other than the reinforcing bar such as iron rust and concrete are used. Temporal separation can be easily performed. The electromagnetic pulse method is based on the transmission measurement of elastic waves, and it is not possible to discuss the vibration of only the reinforcing bar part. However, since this method can identify the reinforcing bar from the state of the radar response, only the part where the reinforcing bar exists is discussed independently. The points that can be done are very different. In addition, the vibration displacement of the reinforcing bar can be quantitatively evaluated by the principle of Doppler radar, and it is possible to effectively grasp the phenomenon that the vibration displacement of the reinforcing bar decreases due to the weakening of the restraint of concrete due to the corrosion of the reinforcing bar. ..

Further, from the viewpoint of capturing the state of vibration of the reinforcing bar itself, corrosion products such as red rust are generated from the reinforcing bar as the reinforcing bar is corroded, and a cross-sectional defect of the reinforcing bar occurs. Since this affects the skeleton strength of the structure, it is also important to evaluate the cross-sectional defect. In this method, it is possible to measure the radar response when there is no vibration and when there is vibration by exciting the reinforcing bar at a single frequency.

For example, in a sound reinforcing bar without corrosion, the radar response when there is no vibration and the radar response when there is vibration pass through the same propagation path, so that there is no difference in the arrival time of the waveform.
However, when the diameter of the reinforcing bar becomes small due to the cross-sectional defect due to corrosion, the radar reflection response is measured as an expanded reinforcing bar including corrosion products when no vibration is applied. On the other hand, at the time of vibration, the corrosion product does not vibrate, and only the reinforcing bar having a missing cross section vibrates. From this, it can be expected that the reflected response of the rebar reflected wave arrives with a delay.

Since the vibration radar device according to the embodiment of the present invention can measure this state, the amount of corrosion is evaluated not only from the vibration displacement but also from the time difference of the reinforcing bar reflection response during no vibration and vibration. Is possible.
As a result, the amount of corrosion of the reinforcing bars and the distribution of horizontal cracks can be measured without being affected by the heterogeneity between the reinforcing bars and concrete due to the increase in vibration displacement due to the decrease in the restraint of the reinforcing bars due to a wide range of horizontal cracks that span multiple reinforcing bars. It is possible to develop industrial application fields that are not available in existing methods.

[Vibration radar device: overall configuration and measurement method]
FIG. 1 is a schematic view showing an overall configuration and a measurement method of the vibration radar device 101 according to the embodiment of the present invention.
The exciting coil 103 and the bowtie slot antenna 104 are pressed and fixed to the positions to be measured on the columns 102 of the RC structure made of reinforced concrete. In this state, a high frequency signal of about 1 GHz to 13 GHz is output from the network analyzer 105. Further, a low frequency signal of about 50 Hz is generated from the vibration low frequency signal source 106. The personal computer 107 controls the frequency of the high-frequency signal output by the network analyzer 105 (network analyzer) and the on / off of the switch 108 connected to the excitation low-frequency signal source 106.

The high-frequency signal output from the network analyzer 105 is amplified by the RF power amplifier 109 and input to the down-conversion circuit 110. Further, the low frequency signal output from the vibration low frequency signal source 106 is also input to the down conversion circuit 110 via the switch 108. Based on the addition theorem, the down-conversion circuit 110 lowers the frequency of the high-frequency signal amplified by the RF power amplifier 109 by the amount of the low-frequency signal output from the vibrating low-frequency signal source 106. Therefore, when the switch 108 is on, the down-conversion circuit 110 outputs a high-frequency signal whose frequency is lowered by the frequency of the low-frequency signal, and when the switch 108 is off, the down-conversion circuit 110 outputs a high-frequency signal whose frequency is lowered by the frequency of the low-frequency signal. Outputs an unmodulated high frequency signal.

On the other hand, the low frequency signal output from the excitation low frequency signal source 106 is input to the frequency divider 111 via the switch 108. The frequency divider 111 divides the input low frequency signal by half the frequency.
The low frequency signal output from the frequency divider 111 is input to the AF power amplifier 112. The AF power amplifier 112 is a class D power amplifier of about 200 W class.
The high-power low-frequency current output from the AF power amplifier 112 flows to the exciting coil 103. When a large low-frequency alternating current flows through the exciting coil 103, a strong low-frequency magnetic force is generated in the core 103a of the exciting coil 103 made of a laminated steel plate. The low-frequency magnetic force reaches the reinforcing bar 208 (see FIG. 2) existing in the concrete, which constitutes the column 102, and vibrates the reinforcing bar 208.

The high-frequency signal output from the down-conversion circuit 110 is supplied to the transmission bowtie slot antenna 104a (see FIG. 2), which is a transmission antenna arranged directly below the exciting coil 103. Radio waves are emitted from the transmission bowtie slot antenna 104a to which a high-frequency signal is applied. The radio waves of 1 to 13 GHz transmitted from the transmission bowtie slot antenna 104a reach the reinforcing bar 208 existing in the concrete and are reflected by the reinforcing bar 208.
The radio wave reflected by the reinforcing bar 208 reaches the receiving bow tie slot antenna 104b (see FIG. 2), which is a receiving antenna arranged directly under the exciting coil 103 and on the side of the transmitting bow tie slot antenna 104a. A high-frequency signal is emitted from the receiving bowtie slot antenna 104b that has received the radio waves. The high frequency signals of 1 to 13 GHz received by the receiving bowtie slot antenna 104b are input to the network analyzer 105.

The network analyzer 105 internally performs orthogonal detection of the high-frequency signal output to the RF power amplifier 109 and the high-frequency signal of 1 to 13 GHz received by the receiving bowtie slot antenna 104b. Then, the obtained data is output to the personal computer 107.
The personal computer 107 analyzes a data obtained from the network analyzer 105 to detect a slight change contained in the high-frequency signal received by the receiving bowtie slot antenna 104b, and quantifies the vibration displacement of the reinforcing bar 208. To do.

The vibration displacement detection of the reinforcing bar 208 embedded in the column 102 by the exciting coil 103 and the bow tie slot antenna 104 is effective only at the place where the exciting coil 103 and the bow tie slot antenna 104 are fixed. Therefore, after the measurement is performed at one location of the pillar 102, the exciting coil 103 and the bowtie slot antenna 104 are then displaced from the location, and the measurement is performed at another location. That is, the exciting coil 103 and the bowtie slot antenna 104 scan the pillar 102.

[Vibration radar device 101: block diagram]
FIG. 2 is a block diagram of the vibration radar device 101 according to the embodiment of the present invention.
The network analyzer 105 generates a high frequency signal in the GHz band. In addition, it receives a high-frequency signal, performs signal processing described later, and outputs the generated data to an external device such as a personal computer 107.
The reference frequency generator 201 built into the network analyzer 105 generates a high frequency transmission frequency. Here, in the reinforcing bar 208 existing outside the network analyzer 105, frequency modulation of several tens of Hz occurs with respect to a high frequency in the GHz band due to the Doppler effect described later. Therefore, the reference frequency generator 201 is preferably a reference frequency generator circuit using a crystal oscillator or the like, which has low phase noise and ultra-high stability.

The high frequency generator 202 is an oscillation circuit based on a well-known PLL circuit, and generates a high frequency signal whose phase is synchronized with the reference signal generated by the reference frequency generator 201.
The frequency setting unit 203 sets the frequency of the signal generated by the high frequency generation unit 202. As will be described later, since it is necessary to perform frequency subtraction from 1 GHz to 13 GHz for the signal generated by the high frequency generation unit 202, the frequency setting unit 203 can be controlled by using an external device such as a personal computer 107. A function of arbitrarily setting the frequency of the signal generated by the high frequency generating unit 202 is realized.

The high frequency signal output by the network analyzer 105 is amplified by the RF power amplifier 109. The high frequency signal power amplified by the RF power amplifier 109 is input to the orthogonal distributor 204 of the down conversion circuit 110.
The orthogonal distributor 204 outputs two types of signals from the input high-frequency signal, one is the side that outputs the signal as it is (phase 0 °) and the other is the side that delays the phase by 90 ° (phase 90 °).
The high frequency signal having a phase of 0 ° is input to the first multiplier 205. On the other hand, the low frequency signal output from the vibration low frequency signal source 106 is input to the first multiplier 205 through the switch 108.
The high frequency signal having a phase of 90 ° is input to the second multiplier 206. On the other hand, the low frequency signal output from the vibration low frequency signal source 106 is input to the second multiplier 206 through the switch 108 and the 90 ° phase shifter 215.

The vibration low frequency signal source 106 generates, for example, a sine wave (sine wave) of about 50 Hz. The excited low frequency signal source 106 may be created by a circuit, or a compressed audio file may be created and played endlessly by a semiconductor audio player.

The output signals of the first multiplier 205 and the second multiplier 206 are added by the synthesizer 207. The synthesizer 207 adds the output signals of the first multiplier 205 and the second multiplier 206. Then, the frequency f of the high frequency signal is lower by frequency f _v of the low frequency signal. The purpose of the down-conversion circuit 110 is to shift the frequency f of the high-frequency signal in the negative direction to the frequency f _v of the low-frequency signal.
When the switch 108 is off, no low frequency signal is applied to the first adder and the second adder, so the high frequency signal output from the RF power amplifier 109 passes through as it is. Therefore, the frequency of the high frequency signal at this time remains f.
When the switch 108 is on, the low-frequency signal is applied to the first adder and the second adder, the frequency of the high frequency signal outputted from the RF power amplifier 109 is reduced by the frequency f _v of the low frequency signal .. Therefore, the frequency of the time of a high-frequency signal is f-f _v.

The high-frequency signal output from the up-conversion circuit 110 is supplied to the transmission bowtie slot antenna 104a arranged directly below the exciting coil 103. Then, a radio wave is emitted from the transmission bowtie slot antenna 104a to which the high frequency signal is applied. The radio waves of 1 to 13 GHz transmitted from the transmission bowtie slot antenna 104a reach the reinforcing bar 208 existing in the concrete and are reflected by the reinforcing bar 208.

On the other hand, the low frequency signal output from the excitation low frequency signal source 106 is input to the frequency divider 111 via the switch 108. The frequency divider 111 divides the input low frequency signal by half the frequency.
The low frequency signal output from the frequency divider 111 is input to the AF power amplifier 112. The high-power low-frequency current output from the AF power amplifier 112 flows to the exciting coil 103. When a large low-frequency alternating current flows through the exciting coil 103, a strong low-frequency magnetic force is generated in the core 103a of the exciting coil 103 made of a laminated steel plate. The low frequency magnetic force reaches the reinforcing bars 208 existing in the concrete and drives the reinforcing bars 208.

Since the reinforcing bar 208 is not a magnet, the reinforcing bar 208 is attracted to the core 103a of the exciting coil 103 in any case even if the magnetic pole of the exciting coil 103 is changed from N to S and vice versa. That is, the reinforcing bar 208 is vibrated at a frequency twice that of the alternating current applied to the exciting coil 103. Therefore, a frequency divider 111 that halves the frequency is required.
Instead of providing a frequency divider 111 that doubles the output frequency to the input frequency between the switch 108 and the AF power amplifier 112, a multiplier that doubles the output frequency to the input frequency is downed with the switch 108. It may be provided between the conversion circuits 110.

FIG. 3A is a front view of the bowtie slot antenna 104. FIG. 3B is a side view of the bowtie slot antenna 104.
The transmitting bowtie slot antenna 104a and the receiving bowtie slot antenna 104b have the same shape.
In the bowtie slot antenna 104, a bowtie (bow tie) -shaped slot 301a is formed in a rectangular parallelepiped housing 301 formed of a copper plate. A feeding point 302a provided at the tip of the cable 302 is formed in the central portion of the slot 301a. Due to its shape, the bow tie slot antenna 104 is characterized in that the fluctuation of SWR (Standing Wave Ratio) is small in a wide frequency band. Therefore, it is suitable for the vibration radar device 101 according to the embodiment of the present invention.

Returning to FIG. 2, the explanation of the block diagram will be continued.
When the rebar 208 irradiated with the high frequency signal is driven by the exciting coil 103 when the switch 108 is on, the high frequency signal irradiated and reflected by the rebar 208 undergoes frequency modulation due to the Doppler effect. That is, the reinforcing bar 208 produces an effect similar to a multiplier. Then, in the high-frequency signal of frequency "f-f _v" further signal of ± f _v is applied.
Unmodulated component: ff _v
Positive modulation component: f-f _v + f _v = f
Negative direction modulation component: f-f _v- f _v = f-2f _v
Of these, f, which is a positive modulation component, is required for data processing described later.

The radio wave reflected by the reinforcing bar 208 reaches the receiving bowtie slot antenna 104b located directly below the exciting coil 103 and on the side of the transmitting bowtie slot antenna 104a.
A high-frequency signal is emitted from the receiving bowtie slot antenna 104b that has received the radio waves. The high frequency signal of 1 to 13 GHz received by the receiving bowtie slot antenna 104b is input to the network analyzer 105.

The high-frequency signal received by the receiving bowtie slot antenna 104b and the high-frequency signal generated by the high-frequency generator 202 are input to the orthogonal detector 209 built in the network analyzer 105. Then, the well-known orthogonal detection is performed, and the complex amplitude of the received high frequency signal composed of the I component signal and the Q component signal is output.
The high frequency component of the I component signal is removed by the first LPF210. At this point, only the I component of the frequency f, which is a positive modulation component synchronized with the frequency f of the high frequency signal received by the receiving bowtie slot antenna 104b and the high frequency signal generated by the high frequency generator 202, is selectively obtained. Be done.

Similarly, the high frequency component of the Q component signal is removed by the second LPF211. At this point, only the Q component of the frequency f, which is a positive modulation component synchronized with the frequency f of the high frequency signal received by the receiving bowtie slot antenna 104b and the high frequency signal generated by the high frequency generator 202, is selectively obtained. Be done.
That is, the orthogonal detector 209, the first LPF210, and the second LPF211 obtain only the vibrating Doppler component included in the high-frequency signal obtained from the receiving bowtie slot antenna 104b.

The first A / D converter 212 converts the output signal of the first LPF210 into digital data. Similarly, the second A / D converter 213 converts the output signal of the second LPF211 into digital data. These data are stored as files in the non-volatile storage 214 of the personal computer 107.
The personal computer 107 acquires the data when the switch 108 is off and the data when the switch 108 is on while shifting the frequency of the high frequency signal output by the high frequency generation unit 202 to about 1 to 13 GHz. The data thus obtained represent the transfer function between the transmitting bowtie slot antenna 104a and the receiving bowtie slot antenna 104b.

[Data analysis device: block diagram]
In the vibration radar device 101 shown in FIG. 2, when the switch 108 is turned off, an unmodulated complex response (a normal inter-antenna transmission characteristic, which is called an unmodulated component) is obtained. Also, when turned on, the response of only the vibrating reflector is obtained (Doppler component). In this case, the reflection response from an object other than the magnetic material that does not contribute to the magnetic attraction cannot be obtained. The method of obtaining the vibration amplitude and delay time difference of the reinforcing bar reflection from the unmodulated component and the Doppler component is shown below.

FIG. 4 is a block diagram showing a software function of the data analysis device 401. This function can be realized on the personal computer 107 shown in FIGS. 1 and 2.
The unmodulated component data group 402 is a set of I component data and Q component data when the switch 108 is off.
The unmodulated component data group 402 is input to the radar waveform acquisition unit 403. The radar waveform acquisition unit 403 performs an inverse Fourier transform on the unmodulated component data group 402 and outputs impulse response data (radar waveform).

The impulse response data is input to the differential processing unit 404. The differential processing unit 404 performs a differential operation on the impulse response data which is a radar waveform, and outputs the differential radar waveform data. The same result can be obtained by multiplying the unmodulated component data group 402 by the frequency of the high frequency signal and then performing the inverse Fourier transform in the radar waveform acquisition unit 403 without providing the differential processing unit 404.

The differential radar waveform data is input to the first reinforcing bar reflected wave peak amplitude acquisition unit 405. The first reinforcing bar reflected wave peak amplitude acquisition unit 405 extracts the reflected waveform corresponding to the arrival time of the reflected wave of the reinforcing bar 208 in the time waveform for each frequency of the high frequency signal constituting the differential radar waveform data, and the amplitude of the peak. Extract the value.
Further, the differential radar waveform data is input to the first reinforcing bar reflected wave peak time acquisition unit 406. The first reinforcing bar reflected wave peak time acquisition unit 406 extracts the arrival time of the reflected wave of the reinforcing bar 208 in the time waveform for each frequency of the high frequency signal constituting the differential radar waveform data.

The Doppler modulation component data group 407 is a set of I component data and Q component data when the switch 108 is on.
The Doppler modulation component data group 407 is input to the radar waveform acquisition unit 403. The radar waveform acquisition unit 403 performs an inverse Fourier transform on the Doppler modulation component data group 407 and outputs impulse response data (radar waveform).
The impulse response data is input to the second reinforcing bar reflected wave peak amplitude acquisition unit 408. The second reinforcing bar reflected wave peak amplitude acquisition unit 408 extracts the reflected waveform corresponding to the arrival time of the reflected wave of the reinforcing bar 208 in the time waveform for each frequency of the high frequency signal constituting the impulse response data, and the amplitude value of the peak. Is extracted.
Further, the impulse response data is input to the second reinforcing bar reflected wave peak time acquisition unit 409. The second reinforcing bar reflected wave peak time acquisition unit 409 extracts the arrival time of the reflected wave of the reinforcing bar 208 from the time waveform for each frequency of the high frequency signal constituting the impulse response data.

The unmodulated component peak amplitude value obtained from the first reinforcing bar reflected wave peak amplitude acquisition unit 405 and the Doppler component peak amplitude value obtained from the second reinforcing bar reflected wave peak amplitude acquisition unit 408 are input to the vibration amplitude acquisition unit 410. .. The vibration amplitude acquisition unit 410 outputs the peak amplitude by subtracting the unmodulated component peak amplitude value from the Doppler component peak amplitude value, multiplying by 2π, and further dividing by the propagation velocity of the electromagnetic wave of the column 102.
The unmodulated component peak arrival time obtained from the first reinforcing bar reflected wave peak time acquisition unit 406 and the Doppler component peak arrival time obtained from the second reinforcing bar reflected wave peak time acquisition unit 409 are input to the delay time difference acquisition unit 411. .. The delay time difference acquisition unit 411 calculates the difference between the unmodulated component peak arrival times from the Doppler component peak arrival time, and outputs the peak delay time difference.

Corrosion measurement of the reinforcing bar 208 is performed on the entire column 102 by scanning the column 102. If there is a portion where corrosion is significant inside the column 102, the peak amplitude and the peak delay difference value are different from those of the other portions. Further, if a healthy pillar 102 without corrosion is separately measured in advance, the peak amplitude and the peak delay difference value are stored as sample values, and the pillar 102 to be measured is scanned, the healthy pillar 102 is used as a reference. The degree of corrosion of the pillar 102 to be measured and the location where the corrosion is remarkable can be detected with high accuracy.

[principle]
FIG. 5A shows a state in which the exciting coil 103 of the excitation radar device 101 according to the embodiment of the present invention, the transmitting bow tie slot antenna 104a, and the receiving bow tie slot antenna 104b are arranged on a sound reinforced concrete pillar 102. It is a sectional view.
In FIG. 5B, the exciting coil 103 of the excitation radar device 101 according to the embodiment of the present invention, the transmission bow tie slot antenna 104a, and the reception bow tie slot antenna 104b are arranged on the reinforced concrete column 102 in which the corrosion of the reinforcing bar 208 has progressed. It is a schematic cross-sectional view which shows the state.

As shown in FIG. 5B, as the corrosion of the reinforcing bar 208 progresses, red rust 501 (ferric oxide) and the like are generated around the reinforcing bar 208. Then, red rust is generated between the concrete and the reinforcing bar 208, so that the concrete expands and cracks C502 are generated. Then, the vibration amplitude of the reinforcing bar 208 is increased as compared with the sound reinforced concrete (from the amplitude V503 to V504). In addition, since the dynamic elastic modulus around the reinforcing bar 208 decreases, the Doppler effect changes.
In this way, the exciting coil 103 vibrates the reinforcing bar 208 at a low frequency, and the vibration displacement is measured using the radar wave in the GHz band to measure the change in the dynamic modulus around the reinforcing bar 208. ..

The vibration radar device 101 according to the embodiment of the present invention is based on the reflection response measurement of a single frequency radio wave in the GHz band, and while inserting the frequency into a wide band, pulse vibration like a conventional radar device. Instead, the reinforcing bar 208 is vibrated by a continuous wave, and the Doppler response of the reflected radio wave accompanying the vibration is measured.
As described with reference to FIG. 2, the reference frequency generator 201 requires high frequency stability in order to modulate the excitation frequency of several tens of Hz to the transmission frequency in the GHz band.

A single high frequency frequency set by the frequency setting unit 203 is generated in the high frequency generating unit 202. When the switch 108 is off, the high-frequency signal that has passed through the down-conversion circuit 110 as it is is transmitted as a radio wave from the transmission bowtie slot antenna 104a, reflected on the reinforcing bar 208, and then received by the reception bowtie slot antenna 104b. After that, it is orthogonally detected by the orthogonal detector 209 and stored in the non-volatile storage 214 as a complex amplitude response accompanying radio wave propagation between the antennas. Further, by changing the frequency stepwise in the high frequency generating unit 202, it is possible to acquire a complex transfer function over a wide band.

On the other hand, the vibrating low frequency signal source 106 generates a single frequency of about 50 Hz, which is the vibration frequency of the reinforcing bar 208. The low-frequency signal output from the excited low-frequency signal source 106 is supplied to the down-conversion circuit 110 via the switch 108. Then, the high-frequency signal output from the high-frequency generation unit 202 is frequency-transitioned by the frequency of the low-frequency signal.
When the low frequency signal whose frequency is halved by the frequency divider 111 is amplified by the AF power amplifier 112 and a current is applied to the exciting coil 103, the reinforcing bar 208 is oscillated by magnetic attraction. Since the reinforcing bar 208 attracts the reinforcing bar 208 at both the positive and negative peaks of the sinusoidal alternating magnetic field, it vibrates at twice the frequency applied to the coil. As the reinforcing bar 208 vibrates, the high frequency signal from the transmitting antenna undergoes FM modulation due to the Doppler effect. As a result, the spectrum appears at a frequency that is an integral multiple of the vibration frequency, but since the vibration amplitude of the reinforcing bar 208 is about 1/100 or less with respect to the wavelength of the electromagnetic wave, only the first-order positive and negative Doppler frequency components dominate. It becomes. Therefore, the reflected wave reflected by the reinforcing bar 208 has a frequency component of the transmission frequency ± the excitation frequency in addition to the high frequency transmission frequency.

At the time of measuring the Doppler component, since the transmission frequency is shifted in advance by the vibration frequency of the reinforcing bar 208, the Doppler component becomes the same as the original high frequency transmission frequency and is detected by the orthogonal detector 209. Therefore, if the cutoff frequencies of the first LPF210 and the second LPF211 in the orthogonal detector 209 are sufficiently narrowed compared to the vibration frequency, the I and Q signals output from the orthogonal detector 209 are affected by the unmodulated component. Instead, the frequency response of only the signal component affected by the Doppler effect will be measured.

Further, the transfer functions of the unmodulated and Doppler components obtained by controlling the switch 108 on and off are converted into radar waveforms by inverse Fourier transform in the data analysis apparatus 401 shown in FIG. The Doppler component is theoretically equivalent to the transfer function obtained by multiplying the unmodulated component by the low frequency vibration frequency component. Therefore, the unmodulated component is differentiated by the differentiation processing unit 404, and then the reinforcing bar reflected wave component of both time waveforms is taken out, and the first reinforcing bar reflected wave peak amplitude acquisition unit 405 and the first reinforcing bar reflected wave peak time acquisition unit 406 are used. The amplitude and arrival time of the peak waveform are measured.

The vibration amplitude of the reinforcing bar 208 is estimated by using a constant term that depends on the medium to the ratio of the peak amplitude of the unmodulated component and the Doppler component. Further, the delay time difference can be estimated as the arrival time difference in the delay time difference acquisition unit 411 from the difference in the peak time of the reinforcing bar reflection portion of the non-modulation component and the Doppler component.

FIG. 6 shows a conceptual diagram of the present invention.
Now, the transmitting antenna 601 at the origin irradiates a radio wave of a single frequency f as a sensing wave toward the measurement target, and the reflected wave reflected from the reflector 602 at the point (x, z) is received by the same antenna. It shall be. At the same time, when the measurement target is vibrated at a sufficiently low single frequency _fv , the vibration target vibrates uniformly, and the z-direction displacement u (t) of the reflector 602 is generally expressed by Eq. (1).

[Experiment]
An experiment was conducted to verify the vibration radar device 101 according to the above-described embodiment.
The network analyzer 105 outputs a single frequency f, orthogonally detects input signals of the same frequency, measures a complex response between input / output ports, and sweeps the frequency f. This makes it possible to measure the transfer function. An image canceling mixer (ICM) was used for the down-conversion circuit 110. In this system, a frequency response of 301 points was obtained by sweeping the frequency from 1 to 13 GHz. The IF bandwidth corresponding to the cutoff frequency of the detector was set to 10 Hz. A cavity back bowtie slot antenna was used as the transmitting and receiving antenna. The applied frequency of the coil was 25 Hz, and the vibration frequency was 50 Hz.

The exciting coil 103 for exciting the reinforcing bar 208 uses an enamel wire having a diameter of 1 mm, and is wound around a U-shaped 100-layer laminated steel plate core by 500 times. The impedance of the exciting coil 103 was a resistance component of 2.4 Ω and an inductance component of 200 mH, and each was 30 Ω at a frequency of 25 Hz. A class D amplifier (DCP2000, Sound House Inc.) was used as the vibration amplifier. A voltage of 400 V was applied to the coil, and a current of 20 App was applied. The received signal was synchronously added five times. Using this measurement system, a wire having a diameter of 5 mm was vibrated in the air, and the vibration displacement was measured from 40 mm above the wire. As a result, the proposed method and the vibration displacement obtained by the laser displacement meter are in good agreement, and the displacement estimated by this measurement has sufficient accuracy.

FIG. 7 is a diagram showing a state of the produced reinforced concrete specimen and the exciting coil 103.
The reinforcing bar 208 used has a diameter of 16 mm, and the reinforcing bar cover D701 has a diameter of 1 cm. The exciting coil 103 was arranged on the concrete in parallel with the reinforcing bar 208 as shown in FIG. Further, as shown in FIG. 7, a transmission bowtie slot antenna 104a and a reception bowtie slot antenna 104b are arranged in the hollow portion formed by the U-shaped core 103a of the excitation coil 103, and under the excitation coil 103. The displacement of the vibration of the existing reinforcing bar 208 was measured. The distance between the feeding points of the antenna was set to 4 cm.

In order to evaluate the relationship between the corrosion of the reinforcing bar 208 and the vibration displacement, a sound specimen of the reinforcing bar 208 was used in an electrolytic corrosion experiment, and a total of three specimens in which the reinforcing bar 208 was corroded by energization for 21 hours and 42 hours were used. An experiment was conducted.
FIG. 8A is a graph showing an unmodulated signal waveform and a vibrating Doppler signal waveform obtained in a sound specimen. The amplitude of the unmodulated signal waveform (unmodulated component) is set to 1/500 of the measured value in order to match the scale with the amplitude of the vibrating Doppler signal waveform (Doppler component). From FIG. 8A, the reflected wave from the reinforcing bar 208 can be confirmed in the vicinity of 0.4 ns in both cases. Since the distance between the transmitting and receiving antennas is 4 cm, the propagation distance between the transmitting antenna, the reinforcing bar, and the receiving antenna is geometrically about 4.5 cm, and the arrival time of the reinforcing bar from the cover 1 cm is about 0.4 ns. The electromagnetic wave propagation velocity in the concrete is about 11250,000 m / s. The unmodulated waveform was differentiated, and the vibration displacement was obtained from the obtained electromagnetic wave propagation velocity by the equation (7), and the reinforcing bar 208 had a vibration displacement of about 5.5 μm even if it was not corroded.
FIG. 8B is a graph showing the unmodulated signal waveform and the vibrating Doppler signal waveform obtained in the specimen subjected to electrolytic corrosion for 21 hours.
Compared with FIG. 8A, the amplitudes of both the DC component and the vibrating Doppler component decreased due to the influence of moisture due to electrolytic corrosion, but when the vibration displacement was obtained in the same manner, the vibration amplitude increased to about 7 μm.

FIG. 9A is a partially enlarged view of the unmodulated signal waveform and the vibration Doppler signal waveform obtained in the sound specimen shown in FIG. 8A.
FIG. 9B is a partially enlarged view of the unmodulated signal waveform and the vibrating Doppler signal waveform obtained in the specimen subjected to the electrolytic corrosion for 21 hours shown in FIG. 8B.
Looking at FIGS. 9A and 9B, in the specimen subjected to electrolytic corrosion for 21 hours at around 0.4 nsec, the peak of the vibrating Doppler component (P902, P904) with respect to the peak of the unmodulated component (P901, P903) It can be confirmed that the position is slightly delayed.

Next, the spatial distribution of the vibration displacement was measured by moving the 10 cm section every 1 cm while maintaining the positional relationship between the exciting coil 103 and the bow tie slot antenna 104 along the reinforcing bar 208. This measurement was performed on the uncorroded reinforcing bar 208 specimen, the reinforcing bar 208 specimen subjected to 21 hours of electrolytic corrosion, and the reinforcing bar 208 specimen subjected to 42 hours of electrolytic corrosion, respectively, and the average of the vibration displacements thereof was performed. The values and standard deviations were calculated.
FIG. 10A is a graph showing the results of showing the spatial average and standard deviation of the vibration displacement with error bars. The vertical axis represents the vibration displacement (μm) of the reinforcing bar 208, and the horizontal axis represents the electrolytic corrosion time (h).
As shown in FIG. 10A, the average value of the vibration displacement (μm) of the reinforcing bar 208 tended to increase as the electrolytic corrosion time (h) increased.

FIG. 10B is a graph showing the average value and standard deviation of the peak delay time of the Doppler waveform with respect to the unmodulated component by error bars. The vertical axis shows the delay time difference (psec), and the horizontal axis shows the electrolytic corrosion time (h).
As shown in FIG. 10B, it can be seen that the peak of the Doppler component is delayed as the electrolytic corrosion time (h) increases. The delay time of 10 psec is equivalent to a change in the propagation path of about 1 mm from the propagation speed of the radio wave. From this, it is considered that the reflected position recedes due to the cross-sectional defect due to the corrosion of the reinforcing bar 208, and the reinforcing bar reflected wave of the Doppler component arrives later than the unmodulated component.

In the vibration radar device 101 according to the above-described embodiment, a radar wave in the GHz band is used as a medium for analysis, but ultrasonic waves in the 0.1 to 1.0 MHz band are used as a medium for analysis. However, it is possible in principle. In this case, an ultrasonic transducer will be used instead of the antenna. As other circuits and functional blocks, basically the same as those in the above-described embodiment can be used.

In this embodiment, the vibration radar device 101 and the data analysis device 401 are disclosed.
The exciting coil 103 is brought into contact with the column 102 of the RC building, and the reinforcing bar 208 inside the column 102 is vibrated at a low frequency. The reinforcing bar 208 is irradiated with a radar wave and the reflected wave is received. Then, by analyzing the complex component data obtained by orthogonal detection, the peak amplitude and peak time delay of the Doppler component and the unmodulated component are observed. From the above, it is possible to measure the corrosive state of completely non-destructive reinforced concrete.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and other modifications and applications are provided as long as they do not deviate from the gist of the present invention described in the claims. including.
For example, the above-described embodiment describes in detail and concretely the configurations of the apparatus and the system in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those including all the described configurations. Further, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and further, it is possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add / delete / replace a part of the configuration of each embodiment with another configuration.
In addition, each of the above configurations, functions, processing units, and the like may be realized by hardware, for example, by designing a part or all of them with an integrated circuit. In addition, each of the above configurations, functions, and the like may be realized by software for the processor to interpret and execute a program that realizes each function. Information such as programs, tables, and files that realize each function is stored in memory, hard disk, volatile or non-volatile storage such as SSD (Solid State Drive), or recording medium such as IC card and optical disk. be able to.
In addition, control lines and information lines are shown as necessary for explanation, and not all control lines and information lines are shown in the product. In practice, it can be considered that almost all configurations are interconnected.

101 ... Excitation radar device, 102 ... Pillar, 103 ... Excitation coil, 103a ... Core, 104 ... Bowtie slot antenna, 104a ... Transmission bowtie slot antenna, 104b ... Reception bowtie slot antenna, 105 ... Network analyzer, 106 ... Amplitude low frequency signal source, 107 ... personal computer, 108 ... switch, 109 ... RF power amplifier, 110 ... down conversion circuit, 111 ... frequency divider, 112 ... AF power amplifier, 201 ... reference frequency generator, 202 ... high frequency generator , 203 ... Frequency setting unit, 204 ... Orthogonal distributor, 205 ... First multiplier, 206 ... Second multiplier, 207 ... Synthesizer, 208 ... Reinforcing bar, 209 ... Orthogonal detector, 210 ... First LPF, 211 ... Second LPF, 212 ... First A / D converter, 213 ... Second A / D converter, 214 ... Non-volatile storage, 215 ... 90 ° phase shifter, 301 ... Housing, 302 ... Cable, 401 ... Data analyzer, 402 ... Unmodulated component data group, 403 ... Radar waveform acquisition unit, 404 ... Differential processing unit, 405 ... First reinforcing bar reflected wave peak amplitude acquisition unit, 406 ... First reinforcing bar reflected wave peak time acquisition unit, 407 ... Doppler modulation component data group, 408 ... Second reinforcing bar reflected wave peak amplitude acquisition unit, 409 ... Second reinforcing bar reflected wave peak time acquisition unit, 410 ... Vibration amplitude acquisition unit, 411 ... Delay time difference acquisition unit, 501 ... Red rust, 601 ... transmit antenna, 602 ... reflector

Claims (2)

A vibrating low-frequency signal source that generates a low-frequency signal to vibrate the reinforcing bars existing inside the concrete,
An exciting coil that excites the reinforcing bar based on the low frequency signal,
A high-frequency generator that generates high-frequency signals for radar waves,
A frequency setting unit that sets the frequency of the high-frequency signal and
A transmitting antenna that transmits the radar wave based on the high frequency signal to the reinforcing bar, and
A receiving antenna that receives the radar wave reflected from the reinforcing bar, and
A quadrature detector which performs quadrature detection signal received from the receiving antenna and the high frequency signal is input,
A switch provided between the exciting low frequency signal source and the exciting coil
Equipped with
The orthogonal detector outputs an unmodulated component signal when the switch is off and a Doppler modulated component signal when the switch is on.
Vibration radar device. A vibrating low-frequency signal source that generates a low-frequency signal for vibrating the reinforcing bars existing inside the concrete, an exciting coil that vibrates the reinforcing bars based on the low-frequency signal, and a high frequency for radar waves. A high-frequency generating unit that generates a signal, a frequency setting unit that sets the frequency of the high-frequency signal, a transmitting antenna that transmits the radar wave based on the high-frequency signal to the reinforcing bar, and the radar wave reflected from the reinforcing bar. A data analysis device that processes data output from a vibration radar device including a receiving antenna for receiving, a signal received from the receiving antenna, and an orthogonal detector that inputs the high frequency signal and performs orthogonal detection. ,
The data analysis device is
Acquiring the peak amplitude of the reflected wave of the first reinforcing bar, which acquires the maximum amplitude from the unmodulated component data group acquired from the orthogonal detector in a state where the exciting radar device does not vibrate the reinforcing bar with the exciting coil. Department and
The first reinforcing bar reflected wave peak time acquisition unit that acquires the maximum time from the unmodulated component data group, and
Acquisition of the peak amplitude of the reflected wave of the second reinforcing bar, which acquires the maximum amplitude from the Doppler modulation component data group acquired from the orthogonal detector while the excitation radar device is exciting the reinforcing bar with the exciting coil. Department and
A second reinforcing bar reflected wave peak time acquisition unit that acquires the maximum time from the Doppler modulation component data group, and
The unmodulated component peak amplitude value obtained from the first reinforcing bar reflected wave peak amplitude acquisition unit is subtracted from the Doppler component peak amplitude value obtained from the second reinforcing bar reflected wave peak amplitude acquisition unit, and multiplied by 2π. A vibration amplitude acquisition unit that obtains the peak amplitude by dividing by the propagation velocity of electromagnetic waves in the concrete in which the reinforcing bar is embedded, and
The difference in the unmodulated component peak arrival time obtained from the first reinforcing bar reflected wave peak time acquisition unit is calculated from the Doppler component peak arrival time obtained from the second reinforcing bar reflected wave peak time acquisition unit, and the peak delay time difference is output. , A data analysis device including a delay time difference acquisition unit.

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