JP7652056B2 - Measuring device and measuring method - Google Patents

Description

The present invention relates to a measurement device and a measurement method that simultaneously measures the thickness and longitudinal wave sound velocity of an object using ultrasound.

Technologies for simultaneously measuring the thickness and sound speed of an object include Patent Document 1 and Non-Patent Documents 1 and 2.

Patent document 1 describes how ultrashort pulse coherent light is made to interfere in a transparent thin film, and the sound speed is calculated from the interference undulations caused by the elastic waves inside the film. It also describes how the thickness of the thin film is calculated from the obtained sound speed and the propagation time of the elastic waves in the thin film.

Non-Patent Document 1 describes a method of irradiating an object with ultrasonic waves, measuring the waves reflected from the front and back surfaces of the object, and calculating the thickness and sound speed of the object based on the time difference.

Non-Patent Document 2 describes a method of irradiating a thin film on a substrate with ultrasonic waves, measuring the combined wave of reflected waves from the front and back surfaces of the thin film, and calculating the thickness and sound speed of the thin film based on the frequency spectrum of the amplitude.

Japanese Patent Application Publication No. 5-346309

Graciet, C., Hosten, B., Proceedings of IEEE Ultrasonics Symposium(1994), pp.1219-1223 Zhao, Y., Lin, L., Li, M.K., NDT&E International, Vol.43, No.7(2010), pp.579-585

However, the method in Patent Document 1 requires the laser light to interfere within the object, so there is a problem in that it cannot be applied to opaque objects.

In addition, in Non-Patent Document 1, it was necessary to measure the waves reflected from the front surface and the back surface separately, and this was not applicable when the target object was thin.

In Non-Patent Document 2, there is no need to separate the waves reflected from the front surface and the back surface, but it is necessary to separate the waves reflected from the substrate. This makes it difficult to apply to thin substrates. In addition, because both the thickness and longitudinal wave sound velocity of the object depend on the amplitude, a high-frequency, wideband ultrasonic sensor is required to separate them based on the amplitude and simultaneously calculate the thickness and longitudinal wave sound velocity with high accuracy. For this reason, the method in Non-Patent Document 2 can only be applied to the water immersion ultrasonic method and the contact ultrasonic method.

The object of the present invention is to provide a measurement device and a measurement method that can simultaneously and accurately measure the thickness and longitudinal wave sound velocity of an object.

The present invention is a measuring device that simultaneously measures the thickness and longitudinal wave sound velocity of an object, comprising: a transmitting unit that irradiates the object with ultrasonic waves; a receiving unit that receives ultrasonic waves, which are transmitted waves or reflected waves from the object, as electrical signals of a time waveform; a converting unit that converts the electrical signals into amplitude and phase frequency spectra; and an analyzing unit that calculates the frequency spectrum of the amplitude and phase when the thickness and longitudinal wave sound velocity of the object are set to predetermined values using an analytical formula, repeatedly determines the compatibility of the frequency spectrum of the amplitude and phase obtained by the converting unit with the frequency spectrum of the amplitude and phase obtained by the analytical formula by changing the thickness of the object and the longitudinal wave sound velocity used in the analytical formula, and calculates the thickness of the object and the longitudinal wave sound velocity used in the analytical formula as a solution when the frequency spectrum of the amplitude and phase obtained by the converting unit and the frequency spectrum of the amplitude and phase obtained by the analysis are most compatible, and the analytical formula is a formula that takes into account the medium existing between the transmitting unit and the object, and the medium, and takes into account the phase change of the ultrasonic waves.

The present invention also provides a measurement method for simultaneously measuring the thickness and longitudinal wave sound velocity of an object, comprising: irradiating an ultrasonic wave from a transmitting unit to the object; receiving an ultrasonic wave, which is a transmitted wave or a reflected wave from the object, as an electrical signal of a time waveform at a receiving unit; converting the electrical signal into an amplitude and phase frequency spectrum; calculating the amplitude and phase frequency spectrum when the thickness and longitudinal wave sound velocity of the object are set to predetermined values using an analytical formula; repeatedly determining the compatibility between the amplitude and phase frequency spectrum converted from the electrical signal and the amplitude and phase frequency spectrum by the analytical formula by changing the thickness of the object and the longitudinal wave sound velocity used in the analytical formula; and calculating the thickness and longitudinal wave sound velocity of the object used in the analytical formula as a solution when the amplitude and phase frequency spectrum converted from the electrical signal and the amplitude and phase frequency spectrum by the analysis are most compatible; and the analytical formula is a formula that takes into account the medium existing between the transmitting unit and the object and from the object to the receiving unit, and takes into account the phase change of the ultrasonic wave due to the medium.

In the present invention, compatibility can be determined by RMSE, maximum likelihood estimation, or machine learning.

In the present invention, the medium may be air.

In the present invention, the receiving unit may receive a transmitted wave from an object.

In the present invention, the analytical formula may be a formula calculated using a distributed constant circuit model.

In the present invention, the object may be one layer of a laminate composed of multiple layers.

The present invention makes it possible to measure the thickness and longitudinal wave velocity of an object simultaneously with high accuracy.

FIG. 1 is a diagram showing the configuration of a measurement apparatus according to a first embodiment. FIG. 4 is a flowchart showing a measurement method according to the first embodiment. FIG. 2 is a diagram showing a distributed constant circuit model between a transmitting sensor 2 and a receiving sensor 3. A graph showing the relationship between longitudinal wave speed and amplitude and phase. Graph showing the relationship between thickness and amplitude and phase. A graph showing the relationship between longitudinal wave speed and amplitude and phase. Graph showing the relationship between thickness and amplitude and phase. 1 is a graph showing the time waveform of a transmitted wave. Graph showing the frequency spectrum of the amplitude of the transmitted wave. Graph showing the frequency spectrum of the phase of a transmitted wave.

(About the configuration of the measuring device)
The measurement device of the first embodiment is a measurement device capable of simultaneously measuring the thickness and longitudinal wave sound velocity of an object 10. Fig. 1 is a diagram showing the configuration of the measurement device of the first embodiment. As shown in Fig. 1, the measurement device of the first embodiment has a transmission/reception source 1, a transmission sensor 2, a reception sensor 3, a Fourier transform unit 4, and an analysis unit 5.

The object 10 may be a single layer of material, or one layer of a material consisting of multiple layers. In the first embodiment, even a thin material in which the reflected waves from the front and back cannot be separated can be measured. For example, in a structure in which two thin materials are joined with a thin adhesive, the thickness of the adhesive and the longitudinal wave sound velocity can be measured simultaneously. Figure 1 shows a three-layer laminate 14 of a first adherend 11, an adhesive 12, and a second adherend 13, of which the adhesive 12 is the object 10.

The transmission/reception source 1 is connected to a transmission sensor 2, a reception sensor 3, and a Fourier transform unit 4. The transmission/reception source 1 is a device that controls the transmission and reception of ultrasonic waves.

The transmitting sensor 2 is connected to the transmitting/receiving source 1. The transmitting sensor 2 is a device that converts the transmitting signal (electrical signal) from the transmitting/receiving source 1 into ultrasonic waves, and emits the ultrasonic waves into the air to irradiate the laminate 14. The center frequency of the ultrasonic waves is, for example, 50 kHz to 100 MHz. The bandwidth is, for example, 10 kHz to 20 MHz. The wavelength of the ultrasonic waves may be longer than the thickness of the target object 10. Therefore, low-cost sensors can be used for the transmitting sensor 2 and the receiving sensor 3.

The receiving sensor 3 is connected to the transmission/reception source 1. It is a device that receives ultrasonic waves that pass through the laminate 14 and propagate through the air, and converts them into an electrical signal (time waveform). The converted electrical signal is input to the transmission/reception source 1. Note that in the first embodiment, the transmitted waves of the laminate 14 are received, but it is also possible to receive reflected waves from the laminate 14. However, the reflected waves from the laminate 14 are stronger than the transmitted waves, and care must be taken to ensure that the reception intensity at the receiving sensor 3 does not become saturated.

The transmitting sensor 2 and the receiving sensor 3 are arranged facing each other with a gap between them. The laminate 14 is placed between the transmitting sensor 2 and the receiving sensor 3 so that the ultrasonic waves from the transmitting sensor 2 are incident perpendicularly.

The Fourier transform unit 4 is connected to the transmission/reception source 1 and the analysis unit 5. The Fourier transform unit 4 is a device that performs a Fourier transform on the electrical signal (time waveform) from the transmission/reception source 1 to convert it into a frequency spectrum of amplitude and phase and outputs it. The time waveform may also be converted into a frequency spectrum of amplitude and phase by a method other than the Fourier transform. For example, the amplitude and phase may be measured directly using a detector or the like. In that case, the input signal is preferably a continuous wave.

The analysis unit 5 is connected to the Fourier transform unit 4. The analysis unit 5 is a device that calculates the thickness and longitudinal wave sound velocity of the object 10 from the frequency spectrum of the amplitude and phase from the Fourier transform unit 4. The specific calculation method will be described later.

In the first embodiment, the space between the transmitting sensor 2 and the receiving sensor 3 and the object is air, and measurements are taken using an airborne ultrasonic method, but the medium is not limited to air and may be any medium, such as water.

In addition, a mechanism for moving the transmitting sensor 2 and the receiving sensor 3, or a mechanism for moving the object 10, may be provided, and the thickness distribution and longitudinal wave sound velocity distribution of the object 10 may be measured by changing the position at which the ultrasonic waves are irradiated onto the object 10.

(Measurement method)
Next, a method for measuring the thickness and longitudinal wave velocity of the object 10 using the measurement device of the first embodiment will be described.

First, a transmission signal is sent from the transmission/reception source 1 to the transmission sensor 2, where it is converted into ultrasonic waves, which are then irradiated onto the laminate 14. The ultrasonic waves that have passed through the laminate 14 are then received by the receiving sensor 3, which converts the ultrasonic waves into an electrical signal with a time waveform. The received time waveform is converted into a time waveform of voltage values by the transmission/reception source 1, and is further converted into a frequency spectrum of amplitude and phase by the Fourier transform unit 4. The time when the transmission signal is sent by the transmission/reception source 1 is set as the origin. For example, this can be determined by issuing a trigger signal simultaneously with the transmission.

Next, in the analysis unit 5, the thickness of the object 10 and the longitudinal wave sound velocity are simultaneously calculated from the frequency spectrum of the amplitude and phase. The details will be explained with reference to the flowchart in Figure 2.

First, the frequency spectrum of amplitude and phase is summarized in the form of a complex number shown in the following formula (1) (step S1 in FIG. 2 ): In formula (1), V _m (f) is a measurement signal at frequency f expressed as a complex number, A _m (f) is a measurement value of the amplitude at frequency f, θ _m (f) is a measurement value of the phase at frequency f, and j is an imaginary unit.

Next, V _m (f) is divided by the measurement signal V _m0 (f) of the reference test piece, which was obtained in advance, to calculate the specific complex transmittance Tr' _m (f) (step S2 in FIG. 2). The reference test piece is a material with known thickness, longitudinal wave velocity, and density, and is preferably a flat plate with little attenuation.

Next, the complex transmittance Tr _c (f) of the laminate 14 at a certain thickness and longitudinal wave sound velocity is analytically calculated (step S3 in FIG. 2). The details of the analytical model will be described later, but the model also takes into account the air layer between the transmitting sensor 2 and the receiving sensor 3 and the target object 10. Tr _c (f) is expressed by the following formula (2). In formula (2), A _c (f) is the analytical value of the amplitude at frequency f, θ _c (f) is the analytical value of the phase at frequency f, and j is the imaginary unit.

Next, Tr _c (f) is divided by the complex transmittance Tr _c0 (f) of the reference test piece that has been analytically determined in advance to calculate the specific complex transmittance Tr′ _c (f) (step S4 in FIG. 2).

The reason why V _m (f) and Tr _c (f) are converted into ratios to the reference test piece is as follows. The measurement signal corresponds to the product of the transmission signal and the complex transmittance, and the measurement signal and the complex transmittance have different units and scales. Therefore, V _m (f) and Tr _c (f) cannot be compared as they are. Therefore, by making V _m (f) and Tr _c (f) into ratios to the reference test piece, dimensionlessness and scale adjustment are performed, making it possible to compare the two.

Next, the RMSE of Tr' _m (f) and Tr' _c (f) is calculated by the following equation (3) (step S5 in FIG. 2).

In equation (3), n is the total number of frequencies, and fi is the i-th frequency. For example, if n is 10 or more, the thickness and longitudinal wave sound velocity can be measured simultaneously with sufficient accuracy. n is preferably 50 or more. There is no particular restriction on how to select the n frequencies, but it is advisable to select them at equal frequency intervals, for example. It is also advisable to select frequencies so as not to include frequencies near the resonant frequency of the object 10. This is because the reception strength of the receiving sensor 3 is strong near the resonant frequency, and there is a risk of saturation.

Steps S3 to S5 are repeated by changing the thickness and longitudinal wave velocity used in the analysis, and the RMSE is calculated for all combinations of thickness and longitudinal wave velocity determined in advance (step S6 in Figure 2).

Next, the thickness and longitudinal wave velocity used in _Tr'c (f) when the RMSE was smallest are output as the thickness and longitudinal wave velocity of the object 10 (step S7 in FIG. 2). If the density and Poisson's ratio of the object 10 are known, it is possible to calculate the Young's modulus from the longitudinal wave velocity.

In other words, steps S3 to S6 are to evaluate the degree of compatibility between Tr' _m (f) and Tr' _c (f) by RMSE, to find the most compatible Tr' _c (f) by changing the combination of thickness and longitudinal wave speed in a brute force manner, and to use the combination of thickness and longitudinal wave speed used for that Tr' _c (f) as the solution. However, the index of compatibility between Tr' _m (f) and Tr' _c (f) is not limited to RMSE, and the method of selecting the most compatible one is not limited to the above. For example, the most compatible Tr' _c (f) may be found by maximum likelihood estimation or machine learning.

(About the analytical formula)
Next, the analytical formula used to calculate the complex transmittances Tr _c (f) and Tr _c0 (f) will be described.

The complex transmittances Tr _c (f) and Tr _c0 (f) are calculated by an analytical formula derived based on a distributed constant circuit model. The distributed constant circuit model is a model that expresses the relationship between input and output signals in a circuit element using a formula called S-parameters that express the reflection, transmission, and propagation characteristics of the circuit element. The matrix S, which is an S-parameter, is given by the following formula (4).

The derivation of the analytical formula using the distributed constant circuit model will be described below. Fig. 3 shows the section from the transmitting sensor 2 to the receiving sensor 3 in the first embodiment as a distributed constant circuit model. As shown in Figure 3, the S parameters are _S1 for the air layer between the transmitting sensor 2 and the laminate 14, _S12 for the interface between the air layer and the first adherend 11, _S2 for the first adherend 11, S23 for the interface between the first adherend 11 and the adhesive 12, _S3 for the adhesive 12, _S3 for the interface between the adhesive 12 and the second adherend 13, _S4 for the second adherend ₁₃ , _S45 for the interface between the second adherend 13 and the air layer, and _S5 for the air layer between the second adherend 13 and the receiving sensor 3, and this is a circuit model in which the elements are connected in series in the order of _S1 , _S12 , _S2 , _S23 , _S3 , _S34 , _S4 , _S45 , and _S5 .

The S parameters of each layer and interface are expressed by the following equations (5) and (6).

In formula (5), _cn is the longitudinal wave speed of the ultrasonic wave in the n-th layer, and _tn is the thickness of the n-th layer. Here, _cn is expressed by the following formula (7).

In formula (7), E _n is the Young's modulus of the nth layer, ρ _n is the density of the nth layer, and ν _n is the Poisson's ratio of the nth layer. If the density and Poisson's ratio of the material are known, as in formula (7), the Young's modulus can be calculated from the longitudinal wave sound velocity.

In addition, in equation (6), Γ _{(n+1) n} indicates the reflectance when ultrasonic waves propagate from the nth layer to the (n+1)th layer, and Tr _{(n+1) n} indicates the reflectance when ultrasonic waves propagate from the nth layer to the (n+1)th layer.

Γ _{(n+1) n} and Tr _{(n+1) n} are expressed by the following equations (8) and (9).

In equations (8) and (9), Z _n is the acoustic impedance of the n-th layer and is expressed by the following equation (10).

By converting the S-parameters to the T-parameters, the cascade connection can be expressed simply by matrix multiplication. The conversion from the S-parameters to the T-parameters is expressed by Equation (11). Moreover, the overall T-parameter (T _all ) from the transmitting sensor 2 to the receiving sensor 3 is expressed by Equation (12).

In formula (12), T _n is the T parameter of the nth layer, and T _{n (n+1)} is the T parameter of the interface between the nth layer and the (n+1)th layer.

The T parameter T _all obtained by equation (12) is converted back into an S parameter to calculate the overall S parameter S _all from the transmitting sensor 2 to the receiving sensor 3. The conversion from T _all to S _all is expressed by equation (13).

As can be seen by comparing with formula (6), the component S _all 21 of S _all is the complex transmittance from the transmitting sensor 2 to the receiving sensor 3, and corresponds to _Trc (f). In this manner, the analytical formula for _Trc (f) using the distributed constant circuit model is obtained. Note that the component S _all 11 of S _all corresponds to the complex reflectance.

The analytical formula for Tr _c (f) calculated as described above takes into consideration the relationship between the amplitude and phase of the reflected wave and the transmitted wave at each interface. In other words, the overlapping manner of the reflected wave and the transmitted wave is taken into consideration. Therefore, even if the object 10 is thin enough that the reflected wave and the transmitted wave overlap, the thickness can be calculated with high accuracy.

Furthermore, as in equation (12), the air layers between the transmitting sensor 2 and the receiving sensor 3 and the object 10 are considered as _T1 and _T5 , respectively, and the phase change of the ultrasonic wave in the air layers is taken into consideration. Therefore, the thickness of the object is strongly reflected in the phase of the complex transmittance Tr _c (f), and the compatibility between Tr' _m (f) and Tr' _c (f) can be more appropriately evaluated.

The analytical formula does not necessarily have to be based on a distributed constant circuit model, and any formula can be used as long as it takes into account the air layer between the transmitting sensor 2 and the receiving sensor 3 and the target object 10, and the phase change of the ultrasonic wave in that air layer. For example, a model that analyzes the amplitude and phase of the reflected wave and transmitted wave from the propagation formula of the sound pressure and particle velocity in each layer, and the relational formula of the sound pressure and particle velocity between each layer, may be used.

As described above, in the first embodiment, not only the amplitude of the ultrasonic waves but also the phase is measured and used, and the analysis is performed taking into account the phase change that occurs when the ultrasonic waves propagate through the medium (air) between the transmitting sensor 2, the receiving sensor 3, and the object 10. Therefore, the thickness of the object 10 and the longitudinal wave sound velocity can be measured simultaneously with high accuracy.

In addition, in the first embodiment, the thickness and longitudinal wave sound velocity can be determined with high accuracy even at low frequencies, so it can also be used in non-contact airborne ultrasonic methods. In addition, the thickness and longitudinal wave sound velocity can be measured simultaneously even for thin layers in a multilayer structure. For example, the thickness and longitudinal wave sound velocity of an adhesive in an adhesive joint can also be measured. Therefore, even for an object 10 for which it is difficult to simultaneously measure the thickness and longitudinal wave sound velocity using contact or water immersion methods, measurement is possible according to the first embodiment, and the range of objects for which the thickness and longitudinal wave sound velocity can be measured simultaneously is wider than in the past.

Next, we will explain the results of various experiments related to the first embodiment.

(Experiment 1)
4 and 5 show the results of the analysis without considering the air layer, and the amplitude and phase of the complex transmittance are calculated. Also, FIG. 6 and FIG. 7 show the results of the analysis with the air layer in mind, and the amplitude and phase of the complex transmittance are calculated. FIG. 4(a) and FIG. 6(a) show the relationship between the longitudinal wave sound velocity and the amplitude, and FIG. 4(b) and FIG. 6(b) show the relationship between the longitudinal wave sound velocity and the phase. The thickness of the adhesive was 100 μm, and the longitudinal wave sound velocity was 400 to 1200 m/S. FIG. 5(a) and FIG. 7(a) show the relationship between the thickness and the amplitude, and FIG. 5(b) and FIG. 7(b) show the relationship between the thickness and the phase. The longitudinal wave sound velocity of the adhesive was 1500 m/S, and the thickness was 0 to 800 μm. 4 to 7, the first adherend 11 is an Al plate having a thickness of 1 mm, the second adherend 13 is a steel plate having a thickness of 0.8 mm, the density of the adhesive 12 is 1264 kg/m ³ , and the Poisson's ratio is 0.3. The frequency of the ultrasonic waves is 330 kHz. In addition, in Figures 6 and 7, the distance between the transmitting sensor 2 and the receiving sensor 3 is 30 mm, and the distance from the transmitting sensor 2 to the object 10 (the distance to the first adherend 11) is 14 mm. The sound speed of air is 340 m/s, and the acoustic impedance is 408 kg/(s·m ² ).

In conventional methods that measured thickness and longitudinal wave speed by considering only the amplitude, there was no need to consider the air layer. This is because, as can be seen by comparing Figures 4(a) and 6(a), and Figures 5(a) and 7(a), the results are the same whether the air layer is considered or not. However, as can be seen by comparing Figures 4(a) and 5(a), the tendency of amplitude change is similar when the longitudinal wave speed increases and when the thickness decreases. In other words, it is difficult to determine whether the change in amplitude is due to a change in the longitudinal wave speed or a change in thickness. Therefore, it is difficult to accurately calculate thickness and longitudinal wave speed separately using only the amplitude.

Therefore, in the first embodiment, the suitability with the analytical formula is judged taking into account not only the amplitude but also the phase. However, if the phase is also taken into account, the actual measurement will also include the phase change of the air layer. Therefore, suitability cannot be judged appropriately with an analytical formula that does not take the air layer into account. Therefore, as shown in Figures 6 and 7, the air layer is also taken into account in the analytical formula.

As can be seen by comparing Figure 5(b) and Figure 7(b), when the air layer is taken into account, the phase changes with changes in thickness. This is because the distance between the transmitting sensor 2 and the receiving sensor 3 is constant, so that the thickness of the air layer also changes with changes in the thickness of the adhesive 12, and the phase change in the air layer comes into effect. In this way, when an analysis is performed taking the air layer into account, the effect of the thickness on the phase becomes more pronounced. As a result, it becomes possible to accurately calculate the thickness from the phase.

As described above, it can be seen from Figures 4 to 7 that it is possible to simultaneously calculate thickness and longitudinal wave sound velocity by taking into account the air layer in the analytical formula and taking into account the phase change in the air layer, and then determining the compatibility between the measured values and the analytical formula in terms of both amplitude and phase.

(Experiment 2)
The transmitted waves of the laminate 14 were simulated by the finite element method, and the thickness of the adhesive 12 and the longitudinal wave sound velocity were calculated from the simulation by the method of the first embodiment (Example 1). Various physical properties of the laminate 14 are shown in Table 1.

Three types of adhesive 12 (adhesives A, B, and C) with different thicknesses and longitudinal wave sound velocities were used. For comparison, an analytical formula that does not take into account the air layer was used, and the thickness and longitudinal wave sound velocity of adhesive 12 were calculated when the compatibility of the measured values and the analytical formula was judged by RMSE using only the amplitude (Comparative Example 1).

In the finite element method simulation, a waveform actually sampled from an airborne ultrasonic sensor with a central wavelength of 330 kHz was used as the ultrasonic signal to be irradiated to the target object 10. The distance between the transmitting sensor 2 and the receiving sensor 3 was 30 mm, the distance from the transmitting sensor 2 to the first adherend 11 was 14 mm, the sound speed of air was 340 m/s, and the acoustic impedance was 408 kg/(s· ^m2 ). The reference test piece was an Al plate with a thickness of 1 mm.

Figure 8 is a graph showing the time waveform of the transmitted wave received by the receiving sensor 3. This time waveform was obtained by finite element method simulation. Figures 9 and 10 show the frequency spectrum of the amplitude and phase obtained by Fourier transforming this time waveform. Here, the amplitude and phase are shown as relative values based on the amplitude and phase of a reference test piece. Note that the relative value is the ratio to the amplitude of the reference test piece for the amplitude, and the difference from the phase of the reference test piece for the phase.

The amplitude and phase at frequencies between 320 and 350 kHz, where strong amplitudes were obtained in the frequency spectrum of Figure 9, were used to evaluate the compatibility with the analytical formula by RMSE. 50 equally spaced frequency points were used between 320 and 350 kHz. The thickness and longitudinal wave velocity of the analytical formula were determined by scanning the thickness range of 0 to 500 μm at 1 μm intervals, and the longitudinal wave velocity was calculated from Young's modulus using formula (7). The Young's modulus was changed in increments of 0.01 GPa in the range of 0.5 to 4.5 GPa, and scanning was performed in the range of 730 to 2308 m/s. The longitudinal wave velocity may be directly changed and scanned instead of being calculated from formula (7).

The calculated thickness and longitudinal wave velocity are shown in Table 2.

As shown in Table 2, the calculation result in Comparative Example 1 was significantly different from the correct answer, whereas the calculation result in Example 1 was close to the correct answer. From this result, it was found that by using an analytical formula that takes into account the air layer and determining the compatibility with the analytical formula using both the amplitude and phase, it is possible to measure the thickness of the adhesive 12 and the longitudinal wave sound velocity simultaneously with high accuracy.

The present invention can be used, for example, to measure the thickness and longitudinal wave sound velocity of an adhesive and detect uncured or poor adhesion of the adhesive.

1: Transmitting/receiving source 2: Transmitting sensor 3: Receiving sensor 4: Fourier transform section 5: Analysis section

Claims (7)

A measuring device for simultaneously measuring the thickness and longitudinal wave velocity of an object, comprising:
A transmitter that irradiates the target with ultrasonic waves;
A receiving unit that receives ultrasonic waves, which are transmitted waves or reflected waves from the object, as electrical signals of a time waveform;
A converter for converting the electrical signal into an amplitude and phase frequency spectrum;
an analysis unit that calculates an amplitude and phase frequency spectrum when the thickness and longitudinal wave speed of the object are set to a predetermined value by an analytical formula, repeatedly determines the compatibility between the amplitude and phase frequency spectrum by the conversion unit and the amplitude and phase frequency spectrum by the analytical formula by changing the thickness and longitudinal wave speed of the object used in the analytical formula, and calculates the thickness and longitudinal wave speed of the object used in the analytical formula as a solution when the amplitude and phase frequency spectrum by the conversion unit and the amplitude and phase frequency spectrum by the analysis are most compatible;
having
The analytical formula is a formula that takes into account a medium existing between the transmitting unit and the target object and between the target object and the receiving unit, and takes into account a phase change of the ultrasonic wave due to the medium.
A measuring device characterized by: The measurement device according to claim 1, characterized in that the suitability is determined by RMSE, maximum likelihood estimation, or machine learning. The measuring device according to claim 1 or 2, characterized in that the medium is air. The measuring device according to any one of claims 1 to 3, characterized in that the receiving unit receives a transmitted wave from the object. 5. The measurement device according to claim 1, wherein the analytical expression is an expression calculated using a distributed constant circuit model. The measuring device according to any one of claims 1 to 5, characterized in that the object is one layer of a laminate composed of multiple layers. A method for simultaneously measuring a thickness and a longitudinal wave velocity of an object, comprising the steps of:
A transmitting unit irradiates the target with ultrasonic waves;
The ultrasonic wave, which is a transmitted wave or a reflected wave from the object, is received by a receiving unit as an electrical signal having a time waveform;
converting said electrical signal into an amplitude and phase frequency spectrum;
The frequency spectrum of the amplitude and phase when the thickness and longitudinal wave speed of the object are set to predetermined values is calculated by an analytical formula, and the compatibility between the frequency spectrum of the amplitude and phase converted from the electrical signal and the frequency spectrum of the amplitude and phase obtained by the analytical formula is repeatedly determined by changing the thickness of the object and the longitudinal wave speed used in the analytical formula, and when the frequency spectrum of the amplitude and phase converted from the electrical signal and the frequency spectrum of the amplitude and phase obtained by the analysis are most compatible, the thickness of the object and the longitudinal wave speed used in the analytical formula are calculated as a solution,
The analytical formula is a formula that takes into account a medium existing between the transmitting unit and the target object and between the target object and the receiving unit, and takes into account a phase change of the ultrasonic wave due to the medium.
A measuring method comprising: