JP2006084454A - Method for measuring original waveform of elastic wave and apparatus for measuring original waveform of elastic wave - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for measuring original waveform of elastic wave capable of accurately measuring and analyzing the original waveform of a minute elastic wave. <P>SOLUTION: A reference object is collided to a predetermined position of a measuring object in a condition such that a minimum point of frequency area of power spectrum of the original waveform of a reference elastic wave generated by this collision is located in a desired frequency, and a response function of a propagation system is determined by use of the original waveform of the reference elastic wave generated by the collision and a measured waveform of the reference elastic wave obtained by measuring the original waveform of the reference elastic wave through the propagation system. The original waveform of a minute elastic wave generated by applying a minute impact force to the predetermined position of the measuring object is determined by use of a measured waveform of the minute elastic wave obtained by measuring the original waveform of the minute elastic wave through the propagation system and the response function. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an original waveform measurement method for measuring an original waveform of a minute elastic wave with high accuracy, and in particular, an elastic wave for quantitatively measuring an original waveform of an elastic wave due to a foaming phenomenon in an inkjet head chip. The present invention relates to an original waveform measuring method and an elastic wave original waveform measuring apparatus.

  In acoustic emission (hereinafter referred to as “AE”), the strain energy stored locally in an object is released instantly due to discontinuous phenomena such as microcracking and growth in the material. It is a phenomenon. Accompanying this AE, elastic waves called AE waves are generated in the material. Since the state of the measurement object can be known by measuring and analyzing this AE wave, the AE wave is used for various purposes such as non-destructive inspection of materials.

  In general, an AE wave is an elastic wave having a high frequency, and an AE sensor has been conventionally used to detect such a high frequency elastic wave.

  In some cases, the AE sensor is attached not directly to the measurement object but via the propagation medium. In this case, the waveform (detection waveform) detected by the AE sensor is affected by the frequency characteristics of the propagation medium. Also, since the AE sensor itself has a certain frequency characteristic, the detection waveform of the AE sensor is also affected by the frequency characteristic of the AE sensor itself. Further, the frequency characteristics are also affected between the sensor and the measuring device such as an oscilloscope. As a result, the measurement waveform measured by a measurement device such as an oscilloscope is completely different from the waveform (original waveform) at the generation source.

  In order to satisfactorily evaluate the material, it is preferable to obtain an original waveform of an elastic wave generated at a predetermined position of the measurement object by measurement. For this purpose, the frequency characteristic (response function) of the entire propagation system that affects the frequency characteristic of the elastic wave, such as the measurement object, propagation medium, AE sensor, measuring device, etc., is detected quantitatively before the elastic wave is detected. An analysis method is adopted in which the original waveform is calculated by removing the influence of the propagation system from the measurement waveform by deconvolution of the measurement waveform using this response function. This is called “original waveform analysis”.

Conventionally, release of a load when a pencil core or a glass capillary tube is crushed has been used as a reference sound source used for obtaining a response function. However, in this method, since the load released by each pencil lead and glass capillary tube varies, there is a problem in reproducibility and quantification. Therefore, the impact force caused by the collision of a free-falling steel ball is used as a reference sound source. Have been reported (for example, see Non-Patent Document 1). Since the impact force caused by the free-fall collision of a steel ball as in Non-Patent Document 1 has good reproducibility, quantitative waveform analysis can be performed by using it as a reference sound source.
ANALYSIS OF BUBBLE PRESURE IN JET PRINTING TECHNOLOGY, K.K. Tsuchii et. al. , Japan Hardcopy, P235-236, 1993.

  If a reference sound source using a steel ball as shown in Non-Patent Document 1 is used, a quantitative original waveform analysis is possible, but the one shown therein has a high noise level as a whole, and S / S at 270 KHz. Noise with an N ratio of about 4.7 can be seen. For this reason, the configuration shown in Non-Patent Document 1 cannot obtain a highly accurate response function in a wide frequency band that can be used for measuring a micro impact force on the order of microseconds. This is probably because the frequency band of the reference sound source is narrow and covers only up to about 270 KHz.

  Further, the reference sound source disclosed in Non-Patent Document 1 has a problem based on the power spectrum of impact force generated when an object having a spherical collision surface collides. FIG. 28 is a graph showing a power spectrum of impact force generated when an object having a spherical impact surface collides. Referring to FIG. 28, in the collision of an object whose collision surface is a spherical surface, there exists a minimum point (hereinafter referred to as “node”) at a frequency at which the intensity of impact force becomes a minimum near zero. In this “section”, since the ratio of noise to the original waveform in the measurement wave of the reference sound source is high, the noise greatly affects the calculation of the response function. Therefore, the error of the response function becomes large near the node, and the original waveform analysis cannot be performed with sufficient accuracy.

  The object of the present invention is to adjust the above-mentioned nodes to a desired position so that an accurate response function can be obtained in a wide frequency band, which can be used for measuring a micro impact force on the order of microseconds. Thus, it is an object to provide a method and an apparatus for measuring an original waveform of a minute elastic wave capable of reducing the influence of noise due to the influence of a node and performing an original waveform analysis with high accuracy in a desired frequency band.

  The present invention relates to a method for measuring an original waveform of a minute elastic wave, and a reference elastic wave obtained by measuring an original waveform of a reference elastic wave generated by colliding a reference object with a predetermined position of an object to be measured through a propagation system. A step of obtaining a measurement waveform and a measurement waveform of a minute elastic wave obtained by measuring an original waveform of a minute elastic wave generated by applying a minute impact force to the predetermined position of the measurement object through the propagation system. Using the original waveform of the reference elastic wave and the measurement waveform of the reference elastic wave to obtain a response function of the propagation system, the measurement waveform of the minute elastic wave, and the response function, Obtaining the original waveform of the minute elastic wave, and the reference object is moved to the predetermined position under the condition that the minimum point in the frequency region of the power spectrum of the original waveform of the reference elastic wave is located at a frequency of 650 KHz or more. And wherein the impinging on.

  An apparatus for measuring an original waveform of an elastic wave having a propagation system including a measurement object and a measurement unit that measures an elastic wave generated at a predetermined position of the measurement object, The minimum point in the frequency region of the power spectrum of the original waveform of the reference elastic wave generated when the reference object collides with the predetermined position is located at the predetermined position of the measurement object so that the minimum point is located at a frequency of 650 KHz or higher. The present invention relates to an apparatus for measuring an original waveform of a minute elastic wave, comprising means for generating an original waveform of the reference elastic wave by colliding the reference object.

  According to the present invention, the position of the minimum point (node) in the frequency domain of the reference elastic wave used for calculating the response function of the propagation system by colliding the reference object serving as the reference sound source with the propagation medium under a predetermined collision condition. By selecting a good value, the influence of the clause is reduced, and the reproducibility and quantification of the reference sound source are good, so the effect of noise is reduced in the desired frequency band wider than before and the response function is highly accurate. And the original waveform can be calculated with high accuracy using a response function with high accuracy.

  FIG. 1 is a schematic diagram showing a configuration of a measurement apparatus system that applies a reference sound source to a measurement object in order to obtain an original waveform of a minute impact force according to the present invention. As the reference sound source, for example, an impact when the zirconia ball 9 as a reference object is dropped at a predetermined position is used. As a minute impact force for performing the original waveform analysis, for example, a cavitation force due to a foaming phenomenon that occurs on a heater of a head for an ink jet printer can be cited. Cavitation is a force generated when bubbles are generated in a liquid by applying thermal energy to the liquid with a heater or the like, and the bubbles disappear (hereinafter referred to as “defoaming”). Here, an inkjet head chip 7 which is a chip provided with a heater (not shown) is used as an object to be measured, and an original waveform of an elastic wave (AE wave) of a minute impact force due to a foaming phenomenon that occurs on the heater of the head chip is measured. An example of performing with high accuracy is shown.

  The measuring device system includes an AE sensor 1 (for example, M6W manufactured by Fuji Ceramics Co., Ltd.), a propagation medium 2, an antireflection member 3, a preamplifier 4, a discriminator 5, and a digital oscilloscope 6 that are excellent in detecting high-frequency elastic waves. And a reference object dropping device 8.

  The reference object dropping device 8 is a device for dropping the reference object at a predetermined position of the measurement object on the propagation medium, and includes tweezers on the Z-axis stage in the vertical direction on the measurement object.

  A propagation system that influences the elastic wave in the path from the detection of the elastic force of the reference sound source or the impact force caused by the foaming phenomenon by the AE sensor to the oscilloscope 6 is called a propagation system. For example, the inkjet head chip 7, the propagation medium 2, and the AE sensor 1, as well as the silicone adhesive that bonds the AE sensor 1 to the propagation medium 2, the preamplifier 4, the discriminator 5, and the like are also included in the propagation system.

  The propagation medium 2 is a medium that transmits elastic waves generated by the ink jet head chip 7 to the AE sensor 1. Since the substrate of the inkjet head chip 7 is a silicon wafer, in order to make the acoustic impedance of the propagation medium 2 and the inkjet head chip 7 equal, a single crystal silicon ingot that propagates an elastic wave is used as the material of the propagation medium 2. . Further, by using a single crystal member having no crystal grain boundary, attenuation of high-frequency elastic waves is reduced, and original waveform analysis can be performed satisfactorily. Since the head chip that is the object to be measured is small, the measurement was performed using the head chip on the medium. However, if the measurement is possible without the medium, the medium may not be used. .

  The antireflection member 3 is made of butyl rubber and is provided on the end surface of the propagation medium 2. The antireflection member 3 prevents reflection of elastic waves at the end face of the propagation medium 2.

  The reference elastic wave generated when the zirconia ball 9 as the reference object is dropped from the reference object dropping device 8 and collided with a predetermined position of the measurement object is detected by the AE sensor 1, and the AE sensor 1 is detected by the preamplifier 4. Amplifies the signal detected in step 1. The discriminator 5 includes a main amplifier (not shown) and a filter (not shown). The signal amplified by the preamplifier 4 is further amplified by the main amplifier and filtered by the filter. The digital oscilloscope 6 measures the measurement waveform of the signal that has passed through the discriminator 5. Here, as an example, AE-912 manufactured by NF Circuit Design Block, Inc. is used as a preamplifier, AE9922 manufactured by NF Circuit Design Block, Inc. is used as a discriminator, and DL7200 manufactured by Yokogawa Electric is used as a digital oscilloscope.

  A procedure for obtaining the response function of the propagation system using the measurement apparatus system shown in FIG. 1 will be described.

  FIG. 27 is a flowchart showing an outline of a general flow of original waveform analysis. Referring to FIG. 27, a theoretical value P (t) that is an original waveform of a (time profile) of a reference elastic wave generated when a reference sound source is applied to a predetermined position of a measurement object is obtained in advance by calculation or measurement. ing. A frequency profile obtained by performing a Fourier transform on P (t) using FFT (Fast Fourier Transform) is P (ω).

  First, a reference elastic wave is generated using a reference sound source, a detection waveform is detected by an AE sensor through a propagation medium, and a measurement waveform V (t) of the reference elastic wave obtained by an oscilloscope is converted into an Fourier by FFT. Conversion is performed to calculate V (ω) (step 901). Next, according to Equation (1), V (ω) is divided by P (ω) to obtain a response function G (ω) that is a frequency characteristic of the propagation system (step 902).

  Next, an elastic wave is generated by applying a minute impact force at the same position as the position where the reference sound source of the measurement object is added, and a measurement waveform V ′ (t) of the minute elastic wave is measured through the propagation system. To do. Then, V ′ (t) is Fourier transformed by FFT to calculate V ′ (ω) (step 903). Here, FIG. 3 shows a configuration of a measuring apparatus system for measuring an elastic wave due to a foaming phenomenon of the head chip, which is a minute impact force. Referring to FIG. 3, the reference object dropping device 8 is removed from the state of FIG. 1, and the foam driver 10 is connected to the inkjet head chip 7 that is a measurement object. Ink 11 is dropped on the inkjet head chip 7 so as to sufficiently cover the heater. The foam driver 10 is a drive circuit for driving the ink jet head chip 7 to generate a foaming phenomenon with a minute impact force. First, the foam driver 10 is driven to generate a foaming phenomenon on the heater of the inkjet head chip 7. The elastic wave generated by the impact force is measured by the digital oscilloscope 6 through the propagation system. This is an elastic wave measurement waveform V ′ (t), and V ′ (ω) is a result of Fourier transform of the V ′ (t).

  Next, by dividing the measurement waveform V ′ (ω) of the elastic wave by the response function G (ω) obtained by the above method according to the equation (2), the elastic wave of the foaming phenomenon which is a minute impact force is obtained. An original waveform P ′ (ω) is obtained.

Finally, by performing inverse Fourier transform on this P ′ (ω), the original waveform P ′ (t) in the time domain due to the minute impact force caused by the foaming phenomenon can be obtained quantitatively. (Step 904)
As a result, for example, it is possible to accurately calculate how the impact force due to the foaming phenomenon is applied to the cavitation film of the head chip as compared with the conventional case. Although an example in which the calculation of the original waveform analysis is performed in the frequency domain is shown here, this calculation is not limited to the frequency domain. Since the frequency domain and the time domain are mathematically equivalent through Fourier transformation, the original waveform analysis can also be performed by performing deconvolution integration in the time domain.

[First Embodiment]
First, in FIG. 1, a zirconia ball having a diameter of 0.5 mm is used as a zirconia ball 9 as a reference object, and the head chip 7 as a measurement object is freely dropped from a height of 97.0 mm in a first embodiment. An example is shown. In this embodiment, the zirconia ball is used for a ball mill, but more preferably a bearing ball may be used as a reference object.

  The procedure for obtaining the response function is basically the same as that shown in FIG. It is assumed that the theoretical value P (t) of the original waveform of the reference elastic wave by the reference sound source is obtained in advance by calculation. This P (t) is Fourier transformed to calculate P (ω).

  A zirconia ball 9 which is a reference object is freely dropped from a reference object dropping device 8 and is made to collide with a predetermined position of a head chip which is a measurement object. A reference elastic wave generated at this time is detected by the AE sensor 1, and a propagation system The measurement waveform V (t) of the reference elastic wave is measured by the digital oscilloscope 6 through V, and V (ω) is calculated by Fourier transforming the measurement waveform V (t) of the reference elastic wave.

  Next, by dividing V (ω), which is the measurement waveform of the reference elastic wave of the reference sound source, by the original waveform P (ω) of the reference sound wave of the reference sound source, which is a theoretical value, according to Equation (1), AE A response function G (ω) of the propagation system in the entire frequency band sensed by the sensor is obtained.

  The foaming driver 10 is driven to generate a foaming phenomenon on the heater of the inkjet head chip 7, and an elastic wave due to the foaming phenomenon measured by the digital oscilloscope 6 is used as an elastic wave measurement waveform V ′ (t). (T) is Fourier transformed to obtain V ′ (ω).

  Finally, by dividing the measurement waveform V ′ (ω) of the elastic wave by the above-mentioned response function G (ω) according to the equation (2), the original frequency domain of the elastic wave due to the foaming phenomenon which is a minute impact force is obtained. The waveform P ′ (ω) is obtained, and by performing inverse Fourier transform on the P ′ (ω), the original waveform P ′ (t) in the time domain due to the minute impact force caused by the foaming phenomenon is quantitatively obtained, and this is shown in FIG. As shown in FIG.

  Here, as a comparative example, FIG. 4 shows a foaming phenomenon in a case where a reference sound source obtained by freely dropping a conventional steel ball for ball bearing having a diameter of 0.8 mm from a height of 97.0 mm is used. The original waveform of the elastic wave of minute impact force is shown.

  4 and 5, the original waveform of the elastic wave having a minute impact force due to the foaming phenomenon is a portion surrounded by an ellipse, and the other portion is a noise component. Referring to FIG. 4, which is a conventional method, when an impact force with an impact time width of several μs and an impact strength of about 0.05 N is measured, noise having an intensity substantially equal to the impact force appears as a whole. It can be said that the measurement accuracy is very bad. On the other hand, referring to FIG. 5 which is the present embodiment, it can be seen that noise is reduced as a whole compared to FIG.

  In addition, when a conventional steel ball for a ball bearing with a diameter of 0.8 mm is used, the power spectrum of the original waveform of the reference elastic wave obtained by calculation is the frequency at which the first minimum point (node) is Whereas it is about 650 KHz, the first minimum point (node) of the power spectrum of the original waveform of the reference elastic wave obtained by calculation when using the zirconia ball for a ball mill having a diameter of 0.5 mm of this embodiment is As shown in FIG. 2, the frequency was about 950 KHz. That is, since the frequency component of the minute force that is applied for a short time extends to a high frequency, it is necessary to obtain a response function in a wide frequency band. For this purpose, as in the present embodiment, the position of the first local minimum point (node) of the power spectrum is appropriately selected so as to be in the high frequency region. Even in a high frequency band that could not be used as a response function, a quantitative response function can be obtained, and the accuracy of the original elastic wave analysis by a minute force is improved.

[Second Embodiment]
In the original waveform analysis, if the collision speed of the reference object is changed, the minimum point of the power spectrum of the reference elastic wave of the reference sound source can be changed.

  Therefore, the second embodiment is good by making the speed at which the zirconia ball 9 as the reference object collides with the inkjet head chip 7 faster than the first embodiment so that the minimum point is in the high frequency region. An example of expanding the frequency band in which the original waveform analysis can be performed with high accuracy is shown.

  In the first embodiment, the collision speed of 1.4 m / s was obtained by allowing the zirconia ball 9 to freely drop from a height of 97.0 mm. On the other hand, in the second embodiment, the collision speed is twice that of the first embodiment.

  In order to double the collision speed in free fall, the drop height needs to be quadrupled, which is not easy considering the mechanism of the reference object dropping device 8 and the indoor environment. Further, if the height of free fall is increased, the effect of air resistance and the like increases, and the error between the collision speed obtained by calculation and the actual collision speed increases. Furthermore, in the original waveform analysis of elastic waves, it is preferable to collide the reference object from the direction perpendicular to the collision surface of the object to be measured or the propagation medium, but in free fall, the direction of the collision surface is limited to the vertically upward direction. It becomes.

  Therefore, in the second embodiment, instead of the reference object dropping device 8 in FIG. 1, a reference object launching device that can launch a reference object in an arbitrary direction at an arbitrary speed is used. The reference object launching apparatus of the present embodiment forcibly applies an initial velocity with a force such as a spring, compressed air, a magnetic field, and an electric field, and fires the reference object. If this is used, the normal of the collision surface can be arbitrarily selected, and the configuration of the measurement apparatus system and the degree of freedom of the measurement object are increased. It is also possible to change the collision speed, for example, by selecting a spring constant.

  FIG. 6 is a graph showing the power spectrum of the original waveform of the elastic wave of the reference sound source when the collision speed is 1.4 m / s. FIG. 7 is a graph showing the power spectrum of the original waveform of the elastic wave of the reference sound source when the collision speed is 2.8 m / s. The collision speed of 1.4 m / s corresponds to free fall from a height of about 100 mm, and the collision speed of 2.8 m / s corresponds to free fall from a height of about 400 mm. The mass of the zirconia balls in FIGS. 6 and 7 is 0.4 g.

  In FIG. 6, the first minimum point (node) is about 1.1 MHz, whereas in FIG. 7, the first minimum point is close to 1.4 MHz. From this, it can be seen that increasing the collision speed is very effective in expanding the frequency band.

  According to the present embodiment, the collision condition is appropriately selected by selecting the speed at which the zirconia ball 9 that is the reference sound source collides with a predetermined position of the measurement object, thereby being used for highly accurate original waveform analysis. It becomes possible to easily select the frequency band, and by obtaining the response function in the same manner as in the first embodiment, it is possible to analyze the original waveform of the minute elastic wave with high accuracy.

[Third Embodiment]
The third embodiment is an example in which parameters of a collision condition that enable selection of a frequency band are generalized in calculating a response function of a propagation system using a reference object. The configuration of the measuring apparatus system is the same as that of the first or second embodiment.

  To widen the waveform in the frequency domain, it is only necessary to narrow the waveform in the time domain, that is, in the frequency band that is the frequency domain up to the first node of the power spectrum of the reference sound source, the reference object collides with the propagation medium. If the time (hereinafter referred to as “collision time”) is shortened, the time will increase. The collision time t of the reference object to the propagation medium can be expressed by Equation (3).

Here, C is a proportionality constant. E ₁ is the Young's modulus of the propagation medium 2 made of silicon ingot, and E ₂ is the Young's modulus of the zirconia ball 9. υ ₁ is the Poisson ratio of the propagation medium 2, and υ ₂ is the Poisson ratio of the zirconia ball 9. m ₂ is the mass of the zirconia ball. v is the collision speed. R ₂ is the radius of the zirconia ball.

  As can be seen from Equation (3), the collision time can be shortened by reducing the mass m.

  FIG. 8 is a diagram showing the shape of a reference object with a reduced mass. FIG. 9 is a diagram showing the shape of a reference object with a further reduced mass.

  The reference object 91 in FIG. 8 has a shape obtained by removing the upper half (removed portion 91B in the drawing) from the reference object 9 of the first embodiment. Thereby, the mass m is reduced. Further, the reference object 92 in FIG. 9 has a shape obtained by removing the upper half and the central portion (removal portion 92B in the drawing) from the reference object 9 of the first embodiment. According to this, the mass m is further reduced.

  Since the materials of the reference objects 91 and 92 are both the same zirconia as in the first embodiment, the Young's modulus and Poisson's ratio are not changed. Further, the radii of curvature of the collision surfaces 91A and 92A of the zirconia balls 91 and 92 are the same as those in the first embodiment. The hatched portions in FIGS. 8 and 9 indicate portions that are displaced at the time of collision. The removal portions 91B and 92B should be within a range that does not affect the displacement of the collision surfaces 91A and 92A.

The reference objects 91 and 92 have a small mass m without changing the Young's modulus E ₂ , Poisson's ratio υ ₂ , and the radius of curvature R ₂ of the collision surface. Thereby, the collision time t shown by Formula (3) can be shortened, As a result, a highly accurate response function can be obtained in a wide frequency band.

  In the present embodiment, the reference object launching device that can launch the reference object at an arbitrary speed and direction is used. However, the reference object dropping device 8 may be used as in the first embodiment. In that case, since the reference objects 91 and 92 collide with the propagation medium 2 by free fall as in the first embodiment, the collision speed is changed by the drop height.

  Further, since the reference objects 91 and 92 are not spheres, when the reference objects 91 and 92 collide with the propagation medium 2 due to free fall, they do not necessarily collide with the collision surfaces 91A and 92B. However, when colliding with the propagation medium 2 at a portion other than the collision surfaces 91A and 92A, the rebound behavior and measurement waveform are different from those when colliding with the collision surfaces 91A and 92B. can do.

  On the other hand, if the reference object launching device that determines the collision speed by the force of a spring or the like is used, the reference objects 91 and 92 can be made to collide with the propagation medium 2 from a short distance, and therefore it is relatively easy to make the collision on the collision surface. is there.

As described above, the power spectrum of the original waveform of the reference elastic wave shown in FIG. 6 is a graph measured using a zirconia ball 9 having a mass of 0.4 g. FIG. 10 is a graph showing the power spectrum of the original waveform of the reference elastic wave of the reference sound source when a reference object having a mass of 0.2 g is used according to this embodiment. The reference object of FIG. 6 and the reference object of FIG. 10 are different in mass m, but have the same Young's modulus E _2, Poisson's ratio υ ₂ , and the radius of curvature R ₂ of the collision surface.

  Comparing FIG. 6 and FIG. 10, in FIG. 6, the first minimum point (node) is about 1.1 MHz, whereas in FIG. 10, the first minimum point is close to 1.6 MHz, and the frequency band of the reference sound source Is expanding. Therefore, according to the present embodiment, a highly accurate response function can be obtained in a wide frequency band.

  According to the present embodiment, the frequency of the node is theoretically selected using the collision speed of the reference object such as the zirconia ball 9, the Young's modulus of the reference object itself, the Poisson's ratio, the mass, or the radius of curvature of the collision surface as parameters. Therefore, it is possible to easily and reliably obtain a response function using a plurality of results obtained under different collision conditions.

  In addition, by using a reference object with a shape that removes a part of the sphere other than the collision surface, the mass can be changed without changing the material of the reference object or the radius of curvature of the collision surface. The degree of freedom in selecting conditions can be further improved.

[Fourth Embodiment]
In the fourth embodiment, in calculating the response function of the propagation system using the reference object, the reference object is collided with the propagation medium a plurality of times, and the response function is calculated by averaging.

  In addition, at that time, by changing the height of the free fall of the reference object, the collision speed is changed and the collision is performed multiple times, and further, the measurement at each height is performed multiple times and the response function is obtained by averaging. calculate. As a result, since the response function is calculated using the results of multiple measurements, variations in the calculation result due to various factors such as the collision position can be reduced, and highly accurate original waveform analysis can be performed. . In addition, since the values obtained by multiple collision conditions with different positions of the local minimum points are used, the effect of the local minimum points in the values determined by each collision condition is offset and high frequency noise due to the local minimum point is reduced. A response function can be obtained.

  In the present embodiment, the configuration of the measurement apparatus system for obtaining the response function is the same as that of the first embodiment shown in FIG. Further, the configuration of the measuring apparatus system for measuring a measurement wave of a minute impact force is the same as that of the first embodiment shown in FIG. Further, the zirconia balls 9 and the ink jet head chip 7 are the same as those in the first embodiment.

  A procedure for obtaining the response function of the propagation system in the present embodiment will be described.

  First, the zirconia ball 9 is caused to freely fall and collide with a predetermined position of the measurement object on the propagation medium using the reference object dropping device 8. And this free fall is performed several times by changing the collision speed by changing the drop height. Moreover, it measured several times in each height, and used the averaged value.

Here, as shown in Table 1, the reference object was free-falled in a total of five patterns of conditions 1 to 5 with different collision velocities. The response functions G ₁ (ω) to G ₅ (ω) of the propagation system were obtained according to Equation (4).

Then, the obtained five response functions G ₁ (ω) to G ₅ (ω) are averaged according to Equation (5). The response function G _ave (ω) obtained by averaging is hereinafter referred to as “averaged response function”.

FIG. 11 is a graph showing the power spectrum of the response function G ₅ (ω) obtained under condition 5. FIG. 12 is a graph showing the power spectrum of the averaged response function G _ave (ω) obtained by averaging the conditions 1 to 5.

Referring to FIG. 11, the response function G ₅ (ω) has a plurality of steep peaks. There is a minimum point (node) in the original waveform P ₅ (ω) resulting from the collision of a reference object with a spherical collision surface, and as a result, a peak appears in the frequency of the node in the response function. This is because the influence of noise is large at the node frequency, and the response function cannot be obtained accurately. Therefore, this peak does not show the original response function, but is due to noise.

According to the above equation (3), the collision time t varies with the collision speed v. Further, the frequency of the minimum point in the power spectrum varies depending on the collision time t. Therefore, the power spectra of conditions 1 to 5 have local minimum points at different frequencies. Therefore, by averaging the response functions G ₁ (ω) to G ₅ (ω) obtained according to each condition, as shown in FIG. 12, the influence of the nodes can be reduced and the peak can be removed. As a result, the accuracy of calculating the response function can be increased.

  Comparing FIG. 11 and FIG. 12, the peak due to nodal influence found in the power spectrum of the response function is reduced to about 1/3 by averaging.

In this embodiment, a procedure for measuring a measurement waveform of a minute impact force and obtaining an original waveform from the measurement waveform is the same as the procedure in the first embodiment. A foaming phenomenon is generated on the heater of the inkjet head chip 7 by the foaming driver 10, and an elastic wave due to the impact force is measured by the oscilloscope 6 through the propagation system. Then, the measurement waveform V ′ (t) measured by the oscilloscope 6 is converted into V ′ (ω) in the frequency domain by Fourier transform, and after being divided by the average response function G _ave (ω) according to Equation (6), the inverse is performed. The original waveform P ′ (t) of a minute impact force can be obtained by performing Fourier transform.

FIG. 13 is a graph showing the original waveform of the impact force due to the foaming phenomenon, obtained using the response function G ₅ (ω) calculated from only condition 5. FIG. 14 is a graph showing the original waveform of the impact force due to the foaming phenomenon, obtained using the averaged response function G _ave (ω) calculated from Conditions 1 to 5.

  It can be seen from FIG. 13 and FIG. 14 that a short time impact force due to the foaming phenomenon is measured. However, compared to FIG. 13, the influence of noise is reduced in FIG. 14, and the original waveform is measured more accurately.

  When the portion surrounded by the solid line in FIG. 13 is viewed, high-frequency noise on the order of MHz appears. The high-frequency noise of the MHz order is a node effect, but the high-frequency noise of the MHz order does not appear in the portion surrounded by the solid line in FIG. From this, it can be seen that the influence of the node is reduced by using the averaged response function. That is, according to the present embodiment, the values obtained by a plurality of reference sound sources having different node positions are averaged, so that the influence of the nodes in the values obtained by the respective reference sound sources is canceled out, and the high frequency noise due to the effect of the nodes is canceled out. An averaged response function with reduced can be obtained.

  Comparing the portions surrounded by solid lines in FIGS. 13 and 14, FIG. 14 shows a flatter waveform. Since the portion surrounded by the solid line is a point before the occurrence of the foaming phenomenon, if it is (ideally), it should be a completely flat waveform. From this, it can be seen that the influence of noise is reduced by using the averaged response function.

  According to the present embodiment, since the results of calculation of the response function for a plurality of times are averaged, variations in the calculation results due to various factors such as the collision position can be reduced by averaging, and a highly accurate original waveform analysis It can be performed. This effect can be obtained not only by averaging the calculation results of a plurality of different collision conditions as in the present embodiment, but also by averaging the calculation results of the same collision conditions.

[Fifth Embodiment]
The parameter for changing the frequency of the node existing in the original waveform of the impact force due to the collision of the reference object having a spherical collision surface is not limited to the collision speed shown in the second embodiment. In the third embodiment, the Young's modulus, Poisson's ratio, mass, and radius of curvature of the collision surface shown in Expression (3) can also be used as parameters for changing the frequency of the node. Further, the density of the reference object itself can also be used as a parameter for appropriately changing the node frequency.

FIG. 15 shows an object in which the collision surface is a spherical surface under a collision condition in which the Young's modulus is 3 × 10 ¹¹ N / m ² , the density is 3000 kg / m ³ , the radius of curvature is 0.5 mm, and the collision speed is 1.0 m / s. It is a graph which shows the power spectrum of the impact force by a collision. Referring to FIG. 15, the frequency of the first node is about 1.5 MHz. Hereinafter, the change of the power spectrum when each parameter is changed will be considered with reference to the graph shown in FIG.

FIG. 16 is a graph showing a power spectrum when the collision speed is 0.5 m / s. Referring to FIG. 16, the frequency of the first node has changed to about 1.3 MHz. FIG. 17 is a graph showing a power spectrum when the Young's modulus is 2 × 10 ¹¹ N / m ² . Referring to FIG. 17, the frequency of the first node has changed to about 1.4 MHz. FIG. 18 is a graph showing a power spectrum when the density is 8000 kg / m ³ . Referring to FIG. 18, the frequency of the first node has changed to about 1.0 MHz. FIG. 19 is a graph showing a power spectrum when the radius of curvature is 1.0 mm. Referring to FIG. 19, the frequency of the first node has changed to about 0.7 MHz.

  From the comparison of FIGS. 15 to 19, it can be seen that the frequency of the node changes by changing each of these parameters. Accordingly, when obtaining the averaged response function shown in the fourth embodiment, a plurality of response functions obtained by changing these parameters can be used.

  As described above, by changing each parameter of the reference object, the reference object is made to collide with the measurement object so that the first node comes in the conventional high frequency region of 650 KHz or higher as described in each embodiment. Therefore, it becomes possible to accurately measure the original wave of a minute elastic wave.

[Sixth Embodiment]
In the sixth embodiment, in calculating the response function of the propagation system using the reference object, as in the fourth embodiment, the reference object is caused to collide with the propagation medium a plurality of times under different collision conditions, and the response function is obtained by averaging. Is calculated. Here, by using a plurality of reference sound source balls made of different materials as the reference object, the collision condition is changed depending on the material. Also in the present embodiment, preferably, the collision condition is set such that the minimum point in the frequency region of the power spectrum of the original waveform of the reference elastic wave is located at a frequency of 650 KHz or higher.

  Since the measurement apparatus system shown in FIG. 1 does not consider ink state changes (for example, changes in ink amount or viscosity due to evaporation) in cavitation force measurement, measurement conditions may change. Therefore, a measurement apparatus system that can further improve measurement accuracy and repeatedly generate a stable cavitation force is shown below.

  Through various studies, it has been found that the cavitation force generated on the ink jet head chip varies depending on the amount of liquid (ink amount) on the ink jet head chip. This is presumably because the cavitation force changes depending on the amount of liquid (ink) that flows during the defoaming when bubbles disappear in the foaming phenomenon. That is, in order to obtain a stable cavitation force, it is necessary to maintain a constant amount of ink on the inkjet head chip.

  Specifically, by providing a wall, a top plate, and a spacer on the inkjet head chip, the amount of ink on the inkjet head chip can be kept constant. As a result, the amount of ink flowing during defoaming becomes constant, and a desired cavitation force can be maintained.

  FIG. 20 is a schematic diagram showing a configuration of a measurement apparatus system for obtaining an averaged response function in the sixth embodiment. In this embodiment, an impact when a ceramic ball 93 made of various materials is freely dropped to a predetermined position (a position where cavitation occurs) is used as a reference sound source. Here, a case where a silicon nitride ball having a diameter of 0.5 mm, a zirconia ball having a diameter of 0.5 mm, and an alumina ball having a diameter of 0.6 mm is used as the ceramic ball 93 will be described. This is performed in order to obtain an averaged response function from a plurality of response functions with different collision conditions. Depending on the material of the reference object, the minimum point in the frequency region of the power spectrum of the original waveform can be set to 650 KHz or more.

  In the present embodiment, a BJ (bubble jet) inkjet head chip 7B having a heater for applying thermal energy to a liquid is used as a measurement object, and an original waveform of an elastic wave of a cavitation force due to a foaming phenomenon occurring thereon is accurately measured. An example is shown. The measuring apparatus system includes an AE sensor 1, a propagation medium 2, an antireflection member 3, a preamplifier 4, a discriminator 5, a digital oscilloscope 6, a reference object dropping device 8, and a cavitation force control device 100.

  The AE sensor 1, the propagation medium 2, the antireflection member 3, the preamplifier 4, the discriminator 5, the digital oscilloscope 6, and the reference object dropping device 8 are the same as those shown in FIG.

  FIG. 21 is a schematic diagram showing a configuration of the cavitation force control device shown in FIG. Referring to FIG. 21, the cavitation force control device 100 includes a wall 101 and a spacer 102.

  The wall 101 surrounds a foaming region corresponding to the heater on the ink jet head chip 7B where bubbles are generated in the liquid, and is adhered to the propagation medium 2 with an epoxy adhesive. The wall 101 can be filled with ink, and a top plate can be provided on the wall 101. However, when obtaining the average response function, the ink is not filled and the top plate is not attached.

  Since the cavitation force generated by the foaming phenomenon on the ink jet head chip 7B is applied to the ink jet head chip 7B, the ink jet head chip 7B, the propagation medium 2, the antireflection member 3, and the AE sensor 1 are used in the measuring apparatus system of FIG. In addition to the silicone adhesive that bonds the AE sensor 1 to the propagation medium 2, the preamplifier 4, and the discriminator 5, a cavitation force control device 100 is also included in the propagation system.

  In addition, since the substrate of the inkjet head chip 7B is a silicon wafer, the acoustic wave of the high frequency is generated by making the acoustic impedance of the propagation medium 2 and the inkjet head chip 7B equal, and by using a single crystal member having no crystal grain boundary. In order to reduce attenuation, a silicon ingot is used as the material of the propagation medium 2 as described above.

  Also in this embodiment, the original waveform analysis is performed according to the general flow shown in FIG.

  A procedure for obtaining an average response function of the entire propagation system will be described.

  First, using the reference object dropping device 8, the ceramic balls 93 made of various materials are allowed to freely fall and collide with the ink jet head chip 7B. In this embodiment, the collision condition is changed depending on the material of the ceramic ball 93, and the drop height is unified to 22.5 mm. Here, condition 1 is silicon nitride, condition 2 is zirconia, and condition 3 is alumina.

Let P ₁ (t) to P ₃ (t) be the original waveforms of the reference sound source in conditions 1 to 3 obtained in advance by calculation. The frequency profiles obtained by Fourier transforming the original waveforms P ₁ (t) to P ₃ (t) are defined as P ₁ (ω) to P ₃ (ω), respectively.

The measurement waveform of the reference sound source in conditions 1 to 3 is V ₁ (t) to V ₃ (t), and V ₁ (ω) is obtained by Fourier transforming the measurement waveforms V ₁ (t) to V ₃ (t). ˜V ₃ (ω).

The response functions G ₁ (ω) to G ₃ (ω) of the propagation system can be obtained according to Equation (7).

Then, the obtained three response functions G ₁ (ω) to G ₃ (ω) are averaged according to Expression (8). An averaging response function G _ave (ω) is obtained by averaging.

  Next, an elastic wave is generated by applying a cavitation force to the inkjet head chip 7B, and a measurement waveform V ′ (t) of a minute elastic wave is measured through a propagation system, and is subjected to Fourier transform to obtain V ′ (ω ) Is calculated.

  FIG. 22 is a schematic diagram showing a configuration of a measuring apparatus system for measuring elastic waves of cavitation force. FIG. 23 is a schematic diagram showing a configuration of a cavitation force control device when a cavitation force is applied.

  Referring to FIG. 22, the reference object dropping device 8 is removed from the state of FIG. 20, and the foam driver 10 is connected to the inkjet head chip 7 </ b> B that is a measurement object. Referring to FIG. 23, ink 104 is filled in the interior surrounded by the wall 101, and a top plate 103 is provided above the ink 104 by being supported by the spacer 102.

  When the reference sound source is applied onto the ink jet head chip 7B, the top plate 103 and the ink 104 are not present as shown in FIG. 21, whereas when the cavitation force is applied, as shown in FIG. In this state, the top plate 103 and the ink 104 are present. Therefore, strictly speaking, the propagation path differs between the former and the latter. However, studies have shown that ink 14 does not have a negligible effect on the propagation path.

  Next, regarding the spacer 103, it is conceivable to use a spacer having a rectangular cross-sectional shape such as a block gauge. However, various studies have revealed that when a rectangular spacer is used, resonance occurs when the top plate 103 is installed, and as a result, it is difficult to measure the original waveform of the cavitation force. In order to reduce the influence on the propagation path, it is preferable to make the contact area between the spacer 102 and the propagation medium 2 as small as possible. In consideration of these points, in this embodiment, a pin gauge having a circular cross-sectional shape is used as the spacer 102 as a suitable example.

  Further, regarding the top plate 103, it is considered that the propagation path does not have a negligible influence if the acoustic impedance is close to air. As a result of various studies, it was possible to reduce the influence of the top plate 103 on the propagation path to a level that can be ignored by using acrylic resin as the material of the top plate. Therefore, in this embodiment, an acrylic plate is used for the top plate 103.

  FIG. 24 is a graph showing a result of measuring an elastic wave due to a cavitation force. The result of 10 times of elastic wave measurement by cavitation force in the configuration of FIGS. 22 and 23 is shown in FIG. 24 (a), and the measurement result of any one of 10 times is shown in FIG. The result of integration (averaging) is shown in (c).

  FIG. 24A shows that almost the same waveform is measured every time in the signal region due to the cavitation force, and in this embodiment, the reproducibility of the cavitation force is very good. Further, comparing the background noises of (b) and (c), it can be seen that only random noise components of the background are reduced by the integration. Note that FIG. 24 shows background noise only in the region before the signal on the inkjet head chip is generated for easy viewing, but this noise actually exists in the entire measurement wave region. To do.

  Here, the diameter of the pin gauge used for the spacer 102 is 1144 μm as an example. In this case, the distance from the surface of the inkjet head chip 7B to the acrylic plate used as the top plate 103 is about 500 μm.

The foaming driver 10 is driven to generate a foaming phenomenon on the heater of the inkjet head chip 7B. At this time, the elastic wave generated by the cavitation force propagates through the entire propagation system and is detected by the AE sensor 1. The elastic wave detected by the AE sensor 1 is measured by the oscilloscope 6 through the propagation system. The measured waveform V ′ (t) is converted into V ′ (ω) in the frequency domain by Fourier, divided by the average response function G _ave (ω) according to the above formula (6), and then subjected to inverse Fourier transform. Thus, the original waveform P ′ (t) of the elastic wave due to the cavitation force can be obtained quantitatively.

  FIG. 25 is a graph showing an original waveform of the foaming phenomenon obtained by the above-described method using the measuring apparatus system of the present embodiment. When FIG. 25 is seen, the impact force and cavitation force at the time of foaming can be confirmed. Referring to FIG. 25, a cavitating force of approximately 0.08 N is required.

  Next, control of the cavitation force by changing the size of the spacer 102 will be described. By controlling the cavitation force, which is a minute impact force, it is preferable because the S / N ratio can be improved by integration and the cavitation resistance of various protective film materials can be easily evaluated. As described above, the cavitation force generated on the ink jet head chip varies depending on the amount of liquid on the ink jet head chip. Therefore, the cavitation force can be controlled by controlling the liquid amount on the ink jet head chip. Specifically, the amount of liquid can be arbitrarily changed by changing the size of the spacer 102 provided inside the wall 101. Thereby, the cavitation force can be changed arbitrarily. Here, the change in cavitation force when the diameter of the pin gauge used as the spacer 102 is changed to 649 μm, 744 μm, 844 μm, 1144 μm, and 1644 μm is observed.

  FIG. 26 is a graph showing a change in cavitation force with respect to the distance from the surface of the inkjet head chip to the top plate. When the spacers 102 (pin gauges) described above are used, the distances from the surface of the inkjet head chip 7B to the top plate 103 are approximately 50 μm, 100 μm, 200 μm, 500 μm, and 1000 μm, respectively. From FIG. 26, it can be seen that the increase or decrease in the ink amount significantly affects the cavitation force.

  As described above, the cavitation force control device of the present embodiment suppresses ink state changes (for example, changes in ink amount and viscosity due to evaporation) in the cavitation force measurement and keeps them in a constant state. Measurement becomes easy and measurement accuracy can be improved. In addition, integration with less error is possible, and measurement accuracy can be improved. In addition, according to the present embodiment, since the same cavitation force can be repeatedly generated, it is easy to evaluate the cavitation resistance of the protective film, which is very useful for the development of the protective film material.

  Furthermore, according to the present embodiment, it is possible to easily extract parameters (such as ink viscosity and the surface energy of the top plate 103) that affect the cavitation force, thereby facilitating optimal design of the heater peripheral portion. .

It is a schematic diagram which shows the structure of the measuring apparatus system for calculating | requiring the response function in 1st Embodiment. It is a graph which shows the power spectrum of the original waveform of a reference | standard sound source. It is a schematic diagram which shows the structure of the measuring apparatus system for measuring the measurement waveform of the micro impact force in this embodiment. It is a graph which shows the original waveform of the micro impact force by the foaming phenomenon calculated | required using the free-fall collision of the conventional ball bearing steel ball bearing of 0.8 mm in diameter as a reference | standard sound source. It is a graph which shows the original waveform of the micro impact force by the foaming phenomenon calculated | required using the zirconia ball | bowl which is a reference | standard object of this embodiment. It is a graph which shows the power spectrum of the original waveform in the case of collision speed 1.4m / s. It is a graph which shows the power spectrum of the original waveform in the case of collision speed 2.8m / s. It is a figure which shows the shape of the reference | standard object which made mass small. It is a figure which shows the shape of the reference | standard object which made mass further smaller. It is a graph which shows the power spectrum of the original waveform of the reference | standard sound source at the time of using the reference | standard object of mass 0.2g. 6 is a graph showing a power spectrum of a response function obtained under condition 5. It is a graph which shows the power spectrum of the averaged response function calculated | required by averaging conditions 1-5. Was determined using the response function G ₅ calculated from only the condition 5 (omega), is a graph showing the original waveform of the impact force due to foaming phenomenon. It is a graph which shows the original waveform of the impact force by a foaming phenomenon calculated | required using the averaged response function calculated from conditions 1-5. Impact due to collision of an object having a spherical impact surface under a collision condition with a Young's modulus of 3 × 10 ¹¹ N / m ² , a density of 3000 kg / m ³ , a radius of curvature of 0.5 mm, and a collision speed of 1.0 m / s It is a graph which shows the power spectrum of force. It is a graph which shows a power spectrum when a collision speed is 0.5 m / s. It is a graph which shows a power spectrum when Young's modulus is 2 * 10 < ¹¹ > N / m < ² >. It is a graph which shows a power spectrum when a density shall be 8000 kg / m < ³ >. It is a graph which shows a power spectrum when a curvature radius is 1.0 mm. It is a schematic diagram which shows the structure of the measuring apparatus system for calculating | requiring the averaged response function in 6th Embodiment. It is a schematic diagram which shows the structure of the cavitation force control apparatus shown in FIG. It is a schematic diagram which shows the structure of the measuring apparatus system for measuring the elastic wave of cavitation force. It is a schematic diagram which shows the structure of the cavitation force control apparatus when applying a cavitation force. It is the graph which measured the elastic wave by the cavitation force in 6th Embodiment. It is a graph which shows the original waveform of the cavitation force in 6th Embodiment. It is a graph which shows the change of the cavitation force with respect to the distance from an inkjet head chip surface to a top plate. It is a flowchart which shows the outline of the flow of a general original waveform analysis. It is a graph which shows the power spectrum of the impact force produced when the object of which a collision surface is spherical.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AE sensor 2 Propagation medium 7 Inkjet head chip 7B Inkjet head chip 8 Reference object dropping device 9 Zirconia ball 91, 92 Reference object 93 Ceramic ball 10 Foaming driver 11, 104 Ink 100 Cavitation force control device 101 Wall 102 Spacer 103 Top plate

Claims (10)

A reference elastic wave measurement waveform obtained by measuring the original waveform of a reference elastic wave generated by colliding a reference object with a predetermined position of the measurement object through a propagation system, and a minute amount at the predetermined position of the measurement object. Obtaining a measurement waveform of a micro elastic wave obtained by measuring an original waveform of a micro elastic wave generated by applying a simple impact force through the propagation system;
Obtaining a response function of the propagation system using an original waveform of the reference elastic wave and a measurement waveform of the reference elastic wave;
Obtaining the original waveform of the minute elastic wave using the measurement waveform of the minute elastic wave and the response function,
The original waveform measurement of a minute elastic wave characterized by causing the reference object to collide with the predetermined position under the condition that the minimum point in the frequency region of the power spectrum of the original waveform of the reference elastic wave is located at a frequency of 650 KHz or higher. Method.   By changing the condition for causing the reference object to collide with the predetermined position, the minimum point of the power spectrum of the original waveform of the reference elastic wave appears at different frequencies, and the plurality of reference elastic waves 2. The microelastic wave according to claim 1, wherein a plurality of the response functions are calculated and averaged from the original waveform of and a measured waveform of the reference elastic wave measured by the plurality of collisions. Original waveform measurement method. The collision surface of the reference object has a spherical surface, and the radius of curvature of the spherical surface, the Young's modulus of the reference object, the density, the mass, the Poisson's ratio, the material, and the reference object collide with the measurement object. The speed at which the reference object collides with the object to be measured, and
By setting at least one of the values to a predetermined value,
The method for measuring an original waveform of a minute elastic wave according to claim 1 or 2, wherein a minimum point in a frequency region of a power spectrum of the original waveform of the reference elastic wave is located at a frequency of 650 KHz or more.   The object to be measured is an inkjet head chip having a heater for applying thermal energy to the liquid, and the minute impact force is generated in the liquid by applying thermal energy from the heater to the liquid on the inkjet chip. The method for measuring an original waveform of a minute elastic wave according to any one of claims 1 to 3, wherein the force is an impact force caused by the wave.   The method for measuring an original waveform of a minute elastic wave according to claim 4, wherein the impact force due to the foaming phenomenon is controlled by controlling the amount of the liquid applied onto the inkjet head chip. An elastic wave original waveform measuring apparatus having a propagation system including a measurement object and a measurement means for measuring an elastic wave generated at a predetermined position of the measurement object,
The measurement object so that the minimum point in the frequency region of the power spectrum of the original waveform of the reference elastic wave generated by colliding the reference object with the predetermined position of the measurement object is located at a frequency of 650 KHz or more. An apparatus for measuring an original waveform of a minute elastic wave, comprising means for generating an original waveform of the reference elastic wave by causing the reference object to collide with the predetermined position. The measurement object is an inkjet head chip having a heater for applying thermal energy to a liquid,
7. The microelasticity according to claim 6, wherein the elastic wave is an elastic wave due to an impact force caused by a foaming phenomenon generated in the liquid by applying thermal energy from the heater to the liquid on the inkjet head chip. Wave original waveform measuring device. A wall surrounding a range including a region where the foaming phenomenon occurs on the inkjet head chip;
A spacer disposed inside the wall;
A top plate disposed on the liquid provided in a range surrounded by the wall and supported by the spacer;
The apparatus for measuring an original waveform of a minute elastic wave according to claim 7, further comprising:   The apparatus of claim 8, wherein the spacer has a circular cross section.   The apparatus for measuring an original waveform of minute elastic waves according to claim 8 or 9, wherein a material of the top plate is an acrylic resin.

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