Measuring device and measuring method

Abstract

To provide a measuring device capable of simultaneously and accurately measuring the thickness and longitudinal wave sound velocity of an object.SOLUTION: In a transmitting sensor 2, a transmission signal is converted into ultrasound and the ultrasound is emitted from the transmitting sensor 2 to a laminate 14. The ultrasound after passing through the laminate 14 is received by a receiving sensor 3 as a time waveform, and in a Fourier transform unit 4, the ultrasound is converted into a frequency spectrum of amplitude and phase. Next, in an analysis unit 5, the compatibility between the measured frequency spectrum of amplitude and phase and the frequency spectrum of amplitude and phase obtained from the analytical expression is determined. When the best compatibility is achieved, the thickness and longitudinal wave sound velocity of a target object 10 used in the analytical expression are calculated as a solution. The analytical expression takes into account a medium present from the transmitting sensor 2 and receiving sensor 3 to the laminate 14, and considers a phase change of the ultrasound due to the medium.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a measuring device and a measuring method for simultaneously measuring the thickness and longitudinal wave sound velocity of an object using ultrasonic waves. [Background technology]

[0002] Techniques for simultaneously measuring the thickness and sound speed of an object include Patent Document 1 and Non-Patent Documents 1 and 2.

[0003] Patent Document 1 describes a method of calculating the sound speed from the interference undulations caused by the elastic waves inside a transparent thin film by making ultrashort pulse coherent light interfere with the thin film. It also describes a method of calculating the thickness of the thin film from the obtained sound speed and the propagation time of the elastic waves inside the thin film.

[0004] 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.

[0005] Non-Patent Document 2 describes a method in which ultrasonic waves are irradiated onto a thin film on a substrate, the composite wave of reflected waves from the front and back surfaces of the thin film is measured, and the thickness and sound speed of the thin film are calculated based on the frequency spectrum of the amplitude. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-346309 [Non-patent literature]

[0007] [Non-Patent Document 1] Graciet, C., Hosten, B., Proceedings of IEEE Ultrasonics Symposium(1994), pp.1219-1223 [Non-Patent Document 2] Zhao, Y., Lin, L., Li, MK, NDT&E International, Vol.43, No.7(2010), pp.579-585 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the method of Patent Document 1 has a problem in that it cannot be applied to opaque bodies because it requires interference of laser light within the target object.

[0009] Furthermore, in Non-Patent Document 1, it is necessary to measure the waves reflected from the front surface and the back surface separately, and this cannot be applied when the target object is thin.

[0010] In Non-Patent Document 2, it is not necessary to separate the reflected waves from the front surface and the back surface, but it is necessary to separate the reflected waves from the substrate. Therefore, it is difficult to apply this method to thin substrates. In addition, since both the thickness and the 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 calculate the thickness and the longitudinal wave sound velocity simultaneously with high accuracy. Therefore, the method in Non-Patent Document 2 could only be applied to the water immersion ultrasonic method and the contact ultrasonic method.

[0011] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a measuring device and a measuring method capable of simultaneously measuring the thickness and longitudinal wave velocity of an object with high accuracy. [Means for solving the problem]

[0012] 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 ultrasonic waves onto the object; a receiving unit that receives ultrasonic waves, which are transmitted waves or reflected waves from the object, as an electrical signal of a time waveform; a converting unit that converts the electrical signal into an amplitude and phase frequency spectrum; 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 between 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 analytical formula by changing the thickness of the object and the longitudinal wave sound velocity used in the analytical formula, and calculates the thickness and longitudinal wave sound velocity of the object 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, wherein the analytical formula is a formula that takes into account the medium existing from the transmitting unit to the object and from the object to the receiving unit, and takes into account the phase change of the ultrasonic waves caused by the medium.

[0013] The present invention also provides a method for simultaneously measuring the thickness and longitudinal wave sound velocity of an object, comprising: irradiating the object with ultrasonic waves from a transmitting unit; receiving the ultrasonic waves, which are transmitted waves or reflected waves from the object, as electrical signals of a time waveform at a receiving unit; converting the electrical signals into frequency spectra of amplitude and phase; and calculating the frequency spectra of amplitude and phase when the thickness and longitudinal wave sound velocity of the object are set to predetermined values ​​by an analytical formula; Converted from the electrical signal repeatedly determining the compatibility of the amplitude and phase frequency spectrum with the amplitude and phase frequency spectrum obtained by the analytical formula by varying the thickness of the object and the longitudinal wave velocity used in the analytical formula; Converted from the electrical signal The measurement method is characterized in that the thickness of the object and the longitudinal wave sound velocity used in the analytical formula are calculated as a solution when the frequency spectrum of the amplitude and phase and the frequency spectrum of the amplitude and phase obtained by analysis are most compatible, and the analytical formula is a formula that takes into account the medium existing from the transmitting unit to the object and from the object to the receiving unit, and takes into account the phase change of the ultrasound due to the medium.

[0014] In the present invention, the fitness can be determined by RMSE, maximum likelihood estimation, or machine learning.

[0015] In the present invention, the medium may be air.

[0016] In the present invention, the receiving section may receive a transmitted wave from an object.

[0017] In the present invention, the analytical formula may be a formula calculated using a distributed constant circuit model.

[0018] In the present invention, the target object may be one layer of a laminate composed of multiple layers. Effect of the Invention

[0019] According to the present invention, the thickness and longitudinal wave velocity of an object can be measured simultaneously with high accuracy. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing the configuration of a measurement device according to a first embodiment. [Diagram 2] FIG. 2 is a flowchart showing a measurement method according to the first embodiment. [Diagram 3] FIG. 2 is a diagram showing a distributed constant circuit model between a transmitting sensor 2 and a receiving sensor 3. [Figure 4] A graph showing the relationship between longitudinal wave speed and amplitude and phase. [Diagram 5] Graph showing the relationship between thickness and amplitude and phase. [Figure 6] A graph showing the relationship between longitudinal wave speed and amplitude and phase. [Figure 7] Graph showing the relationship between thickness and amplitude and phase. [Figure 8] 1 is a graph showing the time waveform of a transmitted wave. [Figure 9] Graph showing the frequency spectrum of the amplitude of the transmitted wave. [Figure 10]Graph showing the frequency spectrum of the phase of a transmitted wave. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] (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.

[0022] The object 10 may be a single layer material, or may be one layer of a material consisting of multiple layers. In the first embodiment, even a thin material in which the reflected wave from the front side and the reflected wave from the back side cannot be separated can be measured. For example, in a structure in which two thin materials are bonded with a thin adhesive, the thickness of the adhesive and the longitudinal wave sound velocity can be measured simultaneously. FIG. 1 shows a three-layer laminate 14 of a first adherend 11, an adhesive 12, and a second adherend 13, in which the adhesive 12 is the object 10.

[0023] 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.

[0024] The transmitting sensor 2 is connected to the transmission / reception source 1. The transmitting sensor 2 is a device that converts a transmission signal (electrical signal) from the transmission / reception 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 object 10. Therefore, low-cost sensors can be used for the transmitting sensor 2 and the receiving sensor 3.

[0025] 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 electric signal (time waveform). The converted electric signal is input to the transmission / reception source 1. Note that in the first embodiment, the transmitted wave of the laminate 14 is received, but it is also possible to receive a reflected wave from the laminate 14. However, the reflected wave from the laminate 14 has a stronger intensity than the transmitted wave, and care must be taken to ensure that the reception intensity at the receiving sensor 3 does not become saturated.

[0026] The transmitting sensor 2 and the receiving sensor 3 are disposed facing each other with a gap therebetween. The laminate 14 is disposed between the transmitting sensor 2 and the receiving sensor 3 so that the ultrasonic wave from the transmitting sensor 2 is incident perpendicularly thereto.

[0027] 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 the result. The time waveform may 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 by a detector, etc. In that case, the input signal is preferably a continuous wave.

[0028] 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. A specific calculation method will be described later.

[0029] In the first embodiment, there is air between the transmitting sensor 2 and the receiving sensor 3 and the target object, and measurement is performed using an airborne ultrasonic method, but the medium is not limited to air and may be any medium, such as water.

[0030] 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 the 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.

[0031] (Measurement method) Next, a method for measuring the thickness and longitudinal wave speed of the object 10 using the measurement device of the first embodiment will be described.

[0032] First, a transmission signal is sent from the transmission / reception source 1 to the transmission sensor 2, where the transmission signal 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 further converted into a frequency spectrum of amplitude and phase by the Fourier transform unit 4. The time when the transmission signal is transmitted by the transmission / reception source 1 is set as the origin. This can be determined, for example, by issuing a trigger signal simultaneously with transmission.

[0033] Next, the thickness and longitudinal wave sound velocity of the object 10 are simultaneously calculated from the frequency spectrum of the amplitude and phase in the analysis unit 5. The details will be described with reference to the flow chart of FIG.

[0034] First, the frequency spectrum of the amplitude and phase is converted into a complex number as shown in the following formula (1) (step S1 in FIG. 2). In formula (1), V m (f) is the complex measurement signal at frequency f, A m (f) is the measured amplitude at frequency f, θ m (f) is a measurement of the phase at frequency f, and j is the imaginary unit.

[0035]

number

[0036] Next, V m (f) is the measured signal V m0 Divide by (f) to get the specific complex transmittance Tr' m (f) is calculated (Step S2 in FIG. 2). The reference test piece is preferably a flat plate made of a material with known thickness, longitudinal wave velocity, and density, and with low attenuation.

[0037] Next, the complex permeability Tr of the laminate 14 at a certain thickness and longitudinal wave velocity is c (f) is analytically calculated (step S3 in FIG. 2). The details of the analytical model will be described later, but it is a model that takes into account the air layer between the transmitting sensor 2 and the receiving sensor 3 and the target 10. 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 analytic value of the phase at frequency f, and j is the imaginary unit.

[0038]

number

[0039] Next, Tr c (f) is the complex permeability Tr of the reference test piece, which was analytically obtained in advance. c0 Divide by (f) to get the specific complex transmittance Tr' c (f) is calculated (step S4 in FIG. 2).

[0040] In addition, V m (f),Tr c The reason why (f) is converted to a ratio to the standard test piece is as follows. The measurement signal is equivalent to the product of the transmission signal and the complex transmittance, and the measurement signal and the complex transmittance have different units and scales. m (f) and Tr c (f) is not enough to compare the two. m (f) and Tr c By making (f) a ratio to a reference test piece, the data is made dimensionless and the scale is adjusted, allowing the two to be compared.

[0041] Next, Tr' m (f) and Tr' c The RMSE of (f) is calculated by the following formula (3) (step S5 in FIG. 2).

[0042]

number

[0043] In formula (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.

[0044] 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 FIG. 2).

[0045] Next, Tr' with the smallest RMSE c The thickness and longitudinal wave sound velocity used in (f) are output as the thickness and longitudinal wave sound 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 sound velocity.

[0046] These steps S3 to S6 are, in other words, Tr' m (f) and Tr' c The degree of fit of (f) is evaluated by RMSE, and the combination of thickness and longitudinal wave velocity is changed in a brute-force manner to obtain the best fit Tr'. c (f) is obtained, and its Tr' c The solution is the combination of thickness and longitudinal wave velocity used in (f). However, Tr' m (f) and Tr' c The index of goodness of fit in (f) is not limited to RMSE, and the method of selecting the best fit is not limited to the above. For example, the best fit Tr' can be selected by maximum likelihood estimation or machine learning. c (f) may also be sought.

[0047] (About the analytical formula) Next, the complex transmittance Tr c(f) and Tr c0 The analytical formula used to calculate (f) will now be explained.

[0048] Complex transmittance Tr c (f) and Tr c0 (f) is calculated by an analytical formula derived based on a distributed constant circuit model. A distributed constant circuit model is a model that expresses the relationship between the input and output signals of a circuit element using an equation called S-parameters, which express the reflection, transmission, and propagation characteristics of the circuit element. The matrix S, which is an S-parameter, is given by the following equation (4).

[0049]

number

[0050] 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, expressed by a distributed constant circuit model. As shown in FIG. 3, the S parameters are as follows: the air layer between the transmitting sensor 2 and the laminate 14 is S1, the interface between the air layer and the first adherend 11 is S2, 12 , the first adherend 11 is S2, and the interface between the first adherend 11 and the adhesive 12 is S 23 , the adhesive 12 is S3, and the interface between the adhesive 12 and the second adherend 13 is S 34 , the second adherend 13 is S4, and the interface between the second adherend 13 and the air layer is S 45 , the air gap between the second adherend 13 and the receiving sensor 3 is S5, and S1, S 12 , S2, S 23 , S3, S 34 , S4, S 45 , S5 in this order.

[0051] The S parameters of each layer and interface are expressed by the following equations (5) and (6).

[0052]

number

number

[0053] In formula (5), c n is the longitudinal wave velocity of the ultrasonic wave in the nth layer, t n is the thickness of the nth layer, where c n is expressed by the following equation (7).

[0054]

number

[0055] In formula (7), E n is the Young's modulus of the nth layer, ρ n is the density of the nth layer, ν n is the Poisson's ratio of the nth layer. As shown in equation (7), if the density and Poisson's ratio of the material are known, Young's modulus can be calculated from the longitudinal wave velocity.

[0056] In addition, in equation (6), Γ (n+1) n indicates the reflection coefficient when ultrasonic waves propagate from the nth layer to the (n+1)th layer, and Tr (n+1) n indicates the reflectance when an ultrasonic wave propagates from the nth layer to the (n+1)th layer.

[0057] Gamma (n+1) n ,Tr (n+1) n is expressed by the following equations (8) and (9).

[0058]

number

number

[0059] In equations (8) and (9), Z n is the acoustic impedance of the nth layer and is expressed by the following equation (10).

[0060]

number

[0061] By converting the S-parameters to T-parameters, the cascade connection can be expressed simply by matrix multiplication. The conversion from S-parameters to T-parameters is expressed by equation (11). In addition, the overall T-parameter (T all ) is expressed by equation (12).

[0062]

number

number

[0063] In equation (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.

[0064] The T parameter calculated using equation (12) all Converting it back into S-parameters, we get the overall S-parameters S from transmitting sensor 2 to receiving sensor 3. all is calculated. T all From S all The conversion to is expressed by equation (13).

[0065]

number

[0066] As can be seen by comparing with equation (6), S all Ingredient S all 21 is the complex transmittance from the transmitting sensor 2 to the receiving sensor 3, and Tr c This corresponds to (f). In this way, the Tr c The analytical expression for (f) is obtained. all Ingredient S all 11 corresponds to the complex reflectance.

[0067] The Tr calculated as above c The analytical formula (f) takes into account the relationship between the amplitude and phase of the reflected wave and the transmitted wave at each interface. In other words, it takes into account how the reflected wave and the transmitted wave overlap. 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.

[0068] In addition, as shown 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, and the phase change of the ultrasonic wave in the air layers is taken into account. Therefore, the thickness of the object is expressed by the complex transmittance Tr c (f) is strongly reflected in the phase of Tr' m (f) and Tr' c It will also be possible to more appropriately evaluate the suitability of (f).

[0069] The analytical formula does not necessarily have to be based on a distributed constant circuit model, and any formula may 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 10, and the phase change of the ultrasonic wave in the air layer. For example, a model may be used that analyzes the amplitude and phase of the reflected wave and the 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.

[0070] As described above, in the first embodiment, not only the amplitude of the ultrasonic wave but also the phase is measured and used, and the analysis is performed taking into consideration the phase change that occurs when the ultrasonic wave propagates 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.

[0071] In addition, in the first embodiment, the thickness and longitudinal wave sound velocity can be obtained with high accuracy even at low frequencies, so that it can also be used in a non-contact airborne ultrasonic method. In addition, the thickness and longitudinal wave sound velocity can be measured simultaneously even for a thin layer 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 a contact type or water immersion type, 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.

[0072] Next, various experimental results relating to the first embodiment will be described.

[0073] (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, Figs. 6 and 7 show the results of the analysis with the air layer in mind, and the amplitude and phase of the complex transmittance are calculated. Figs. 4(a) and 6(a) show the relationship between the longitudinal wave sound velocity and the amplitude, and Figs. 4(b) and 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. Figs. 5(a) and 7(a) show the relationship between the thickness and the amplitude, and Figs. 5(b) and 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. Also, in Figs. 4 to 7, the first adherend 11 was an Al plate with a thickness of 1 mm, the second adherend 13 was a steel plate with a thickness of 0.8 mm, and the density of the adhesive 12 was 1264 kg / m 3 , and Poisson's ratio was 0.3. The frequency of the ultrasonic waves was 330 kHz. In Figs. 6 and 7, the distance between the transmitting sensor 2 and the receiving sensor 3 was 30 mm, and the distance from the transmitting sensor 2 to the target object 10 (the distance 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 m 2 ) was decided.

[0074] In the conventional method, in which thickness and longitudinal wave velocity were measured by considering only the amplitude, it was not necessary to consider the air layer. This is because, as can be seen by comparing Figure 4(a) with Figure 6(a) and Figure 5(a) with Figure 7(a), the results are the same whether the air layer is considered or not. However, as can be seen by comparing Figure 4(a) with Figure 5(a), the tendency of the amplitude change is similar when the longitudinal wave velocity increases and when the thickness decreases. In other words, it is difficult to determine whether the change in amplitude is due to the change in the longitudinal wave velocity or the change in thickness. Therefore, it is difficult to accurately calculate the thickness and longitudinal wave velocity separately by the amplitude alone.

[0075] Therefore, in the first embodiment, the suitability with the analytical formula is judged by considering not only the amplitude but also the phase. However, if the phase is also taken into consideration, the actual measurement also includes the phase change of the air layer. Therefore, the suitability cannot be judged appropriately with an analytical formula that does not consider the air layer. Therefore, the air layer is also taken into consideration in the analytical formula as shown in Figs. 6 and 7.

[0076] 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 becomes more pronounced on the phase. As a result, it becomes possible to accurately calculate the thickness from the phase.

[0077] 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 for both amplitude and phase.

[0078] (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 therefrom by the method of the first embodiment (Example 1). Various physical properties of the laminate 14 are shown in Table 1.

[0079] [Table 1]

[0080] 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 consider the air layer was used, and the thickness and longitudinal wave sound velocity of the adhesive 12 were calculated for a case in which the compatibility between the measured value and the analytical formula was determined by RMSE using only the amplitude (Comparative Example 1).

[0081] 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 in air was 340 m / s, and the acoustic impedance was 408 kg / (s m 2 The standard test piece was an aluminum plate with a thickness of 1 mm.

[0082] 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. The relative values ​​are 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.

[0083] The conformity with the analytical formula was evaluated by RMSE using the amplitude and phase at frequencies of 320 to 350 kHz, where strong amplitudes were obtained in the frequency spectrum of Figure 9. 50 equally spaced frequency points were set between 320 and 350 kHz. The thickness and longitudinal wave velocity of the analytical formula were obtained by scanning the thickness range of 0 to 500 μm at 1 μm intervals, and the longitudinal wave velocity was obtained 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 obtained from formula (7).

[0084] The calculated thickness and longitudinal wave velocity are shown in Table 2.

[0085] [Table 2]

[0086] As shown in Table 2, the calculation result in Comparative Example 1 was significantly different from the correct answer, whereas the calculation result was close to the correct answer in Example 1. From this result, it was found that by using an analytical formula that takes the air layer into account and determining the compatibility with the analytical formula using both the amplitude and phase, it is possible to simultaneously measure the thickness of the adhesive 12 and the longitudinal wave sound velocity with high accuracy. [Industrial Applicability]

[0087] The present invention can be used, for example, to measure the thickness and longitudinal wave sound velocity of an adhesive and detect uncured adhesives and adhesive failures. [Explanation of symbols]

[0088] 1: Transmitting / receiving source 2: Transmitting sensor 3: Receiving sensor 4: Fourier transform section 5: Analysis section

Claims

1. 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, by an analytical formula, a frequency spectrum of amplitude and phase when the thickness and longitudinal wave speed of the object are set to a predetermined value, repeatedly determines the compatibility of the frequency spectrum of amplitude and phase by the conversion unit with the frequency spectrum of amplitude and phase by the analytical formula by changing the thickness of the object and the longitudinal wave speed used in the analytical formula, and calculates, as a solution, the thickness of the object and the longitudinal wave speed used in the analytical formula when the frequency spectrum of amplitude and phase by the conversion unit and the frequency spectrum of amplitude and phase by 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:

2. The measurement device according to claim 1 , wherein the suitability is determined by RMSE, maximum likelihood estimation, or machine learning.

3. 3. The measuring device according to claim 1, wherein the medium is air.

4. The measuring device according to claim 1 , wherein the receiving section receives a transmitted wave from the object.

5. 5. The measurement device according to claim 1, wherein the analytical formula is calculated using a distributed constant circuit model.

6. 6. The measuring device according to claim 1, wherein the object is one layer of a laminated body made up of a plurality of layers.

7. 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:

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