JP2014139513A - Non-contact acoustic inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid object interior vibration inspection device used for detecting a defect in a concrete structure, that reduces adverse effect caused by vibration-generating acoustic waves incident directly on an optical vibration detection system or noise pollution caused by the vibration-generating acoustic waves on the ambient environment, thereby improving defect detection performance of a non-contact acoustic inspection method or increasing applicable fields.SOLUTION: Acoustic radiation pressure formed by strong ultrasonic waves generates low-frequency vibration-generating force only at a target position, thereby reducing adverse effect caused by vibration-generating acoustic waves on an optical detection system.

Description

  The present invention relates to a vibration inspection apparatus for solids used for detecting internal defects in concrete structures.

  In recent years, deterioration of concrete structures has become a problem, and the diagnosis inside is necessary. Conventionally, various methods using ultrasonic waves have been proposed as diagnostic methods inside the concrete.

  Patent Document 1 discloses a method of discriminating a defective product from a non-defective product by lightly hitting a concrete product with a hammer using an air cylinder and detecting a sound pressure level of a sound wave generated at this time with a sound level meter. Has been.

  Further, in Patent Document 2, an ultrasonic wave is incident on the inside of a concrete structure by dropping a steel ball from a predetermined height onto the surface of the object to be inspected, and the propagating ultrasonic wave is transmitted to the structure. A method for inspecting the presence or absence of cavities in a concrete structure by analyzing the frequency spectrum of the received ultrasonic wave is disclosed.

  However, according to these methods, it is necessary to make a measurement in contact with the inspection object.

  On the other hand, as a non-contact inspection method which does not need to approach, there is a method using ultrasonic waves according to Patent Document 3.

  This method is an inspection method in which an object to be inspected is vibrated with ultrasonic waves from a distance, and vibrations of the vibrated defect portion are optically detected at a distance.

  However, in the ultrasonic vibration according to Patent Document 3, since the frequency of the ultrasonic wave used for vibration is higher than the resonance frequency of the defect portion, it is not possible to excite vibrations of objects having different frequency bands. It becomes difficult.

  In addition, as a non-contact inspection method that does not need to approach, a method according to Non-Patent Document 1 by the inventors is also known.

  This method also includes an inspection method in which a non-inspection object is vibrated from a distance with a sound wave, and vibration of the applied object is optically detected from a distance.

  However, in this method of Non-Patent Document 1, a strong sound wave for excitation is directly incident on the optical detection system and obstructs vibration detection of the object as disturbing vibration. The ability will be greatly reduced.

  Further, in this method of Non-Patent Document 1, a strong audible frequency sound wave for excitation diffuses to the surrounding environment and causes a great noise damage.

  On the other hand, Non-Patent Document 2 discloses basic characteristics of a low-frequency secondary sound formed by nonlinearity of the sound wave propagation medium when a high-frequency ultrasonic wave is transmitted as the primary sound wave.

  Further, Non-Patent Document 3 discloses the sound field distribution characteristic of the secondary sound wave that is formed when the convergent sound wave is the primary sound wave.

  However, such a non-contact acoustic inspection method that transmits ultrasonic waves and uses the formed secondary sound waves is not known.

Japanese Patent Laid-Open No. 7-20097 JP 2000-2692 A JP-A-8-248006

"Study on non-contact acoustic imaging for non-destructive inspection using SLDV and LRAD", Proceedings of the 2012 Acoustical Conference of the Acoustical Society of Japan 1-5-7, March 2012 `` Parametric Acoustic Array '', JASA, pp.535-537, April 1963 "Effect of diffraction on the second harmonic component of convergent ultrasound", Japanese Society of Ultrasonic Medicine, Basic Technology Research Group, 98-3, pp.9-16, Dec.1998

  Accordingly, an object of the present invention is to eliminate various adverse effects caused by the excitation sound wave directly incident on the optical detection system and to improve the defect detection performance in the non-contact acoustic inspection method.

  The present invention forms a strong ultrasonic sound field in a limited space, vibrates a symmetrical object with an acoustic radiation force formed only near the target position by the strong ultrasonic sound field, and This is an inspection method for optically detecting vibration from a distance.

  According to such a configuration in which the symmetrical object is vibrated by the acoustic radiation force formed only in the vicinity of the target position, the intensity of the direct wave directly incident on the optical detection system is reduced, and due to the excitation sound wave applied to the optical detection system Adverse effects are resolved

  Moreover, the local inspection with respect to the limited site | part is also attained from the sound field characteristic of an ultrasonic wave in this invention.

  According to the present invention, noise interference to the surrounding environment is reduced by limiting the area irradiated by ultrasonic waves.

  Furthermore, since the reverberation time is shortened by the square of the frequency, the use of ultrasonic waves is effective in improving the working environment in a closed space such as inspection in a tunnel.

  Further, since the vibration is applied only within the narrow directivity width, the phenomenon that the vibration cannot be generated at the specific incident angle of the vibration ultrasonic wave, which is a problem in the conventional method, does not occur.

  Similarly, since vibration is applied only within a narrow directivity width, a phenomenon incapable of excitation due to interference with the floor reflection component, which is a problem in the conventional method, does not occur.

  Furthermore, since the acoustic radiation force formed by high-intensity ultrasonic waves is given by the energy density of the ultrasonic waves, the frequency characteristic of the acoustic radiation force can be formed up to a direct current component.

  In addition, since the acoustic radiation force generated by high-intensity ultrasonic waves is formed only in the region of the ultrasonic sound field, it can be formed by confining the low-frequency acoustic radiation force to a narrow region. This is particularly effective for low-frequency excitation.

Explanatory drawing showing a conventional example in the non-contact acoustic inspection method Explanatory drawing which shows operation | movement of the prior art example in a non-contact acoustic test method The whole structure by this invention. Example 1 Schematic of ultrasonic transmitter sound field characteristics. Example 1 Explanatory drawing which showed an example of the azimuth | direction sound field characteristic by a concave surface ultrasonic wave transmitter. Example 1 Explanatory drawing which showed an example of the distance direction sound pressure distribution by a concave ultrasonic wave transmitter. Example 1 Explanatory drawing of the waveform and frequency spectrum of the structure which vibrates with single PCW. Example 1 Explanatory drawing of the object defect vibration detection principle of the structure which vibrates by single PCW. Example 1 Explanatory drawing of each part signal shape in the structure which vibrates with single PCW. Example 1 Explanatory drawing of the waveform and frequency spectrum of the structure which vibrates by finite length PCW. (Example 2) Explanatory drawing of the object defect vibration detection principle of the structure which vibrates by finite length PCW. (Example 2) Explanatory drawing of the defect vibration detection principle of the structure which uses the finite length PCW waveform of different frequency. (Example 2) Explanatory drawing of the waveform and frequency spectrum of the structure which vibrates by continuous PCW. (Example 3) Explanatory drawing of the object defect vibration detection principle of the structure which vibrates by continuous PCW. (Example 3) Explanatory drawing of the waveform in the structure which vibrates with a carrier wave suppression double sideband signal. Example 4 Explanatory drawing of the ultrasonic excitation concave surface sound source which converges an ultrasonic wave by concave shape. (Example 5) Explanatory drawing of the ultrasonic excitation concave surface sound source which converges an ultrasonic wave by a time difference. (Example 5) Explanatory drawing of the structure which arrange | positions an optical detection system behind an ultrasonic source. (Example 6)

  The embodiment of the present invention mainly forms a strong ultrasonic sound field in a confined space, and excites a symmetrical object by an acoustic radiation force formed only near the target position by the strong ultrasonic wave. Features.

  FIG. 1 is an explanatory diagram showing problems in a non-contact acoustic inspection method according to a conventional example. In such a conventional example, an excitation low frequency sound wave from an excitation low frequency sound source 1 controlled by a control unit 8 is shown. 2, the object 3 is vibrated, and the vibration state of the defect portion 4 is measured by the measurement light beam 25 emitted from the optical detection system 5 configured by a laser Doppler measurement method or the like. Is determined and output as a determination result 9.

  Here, the direct sound wave component 10 which is a part of the vibration low frequency sound wave 2 generated by the vibration low frequency sound source 1 enters the optical detection system 5 as an unnecessary interference signal, and the object reflected sound wave 11 is a noise disturbance to the environment. Become.

  In particular, since the excitation low-frequency sound source 1 and the optical detection system 5 are arranged close to each other in practice, the direct sound wave component 10 vibrates the optical detection system 5 strongly to detect the target object signal detection sensitivity. Is greatly reduced.

  Moreover, the surrounding structure reflected sound wave 21 by the surrounding structure 20 also enters the optical detection system 5 as an unnecessary interference signal, and the detection sensitivity of the object signal is reduced.

2, in the conventional example is an explanatory view showing the operation of the non-contact acoustic inspection method is repeated at time intervals T ₀ pressurized Fuhiku frequency sound waves s ₀ is short pulse der time length T _1, defect The main component is a low frequency component in the vicinity of the resonance frequency 4.

Due to the excitation by the excitation low-frequency sound wave s _{0 in} FIG. 2, the defect portion 4 vibrates, and this vibration is detected by the optical detection system 5 and becomes the vibration status signal s ₁ in FIG.

The vibration status signal s ₁ is an unnecessary signal s _1A due to the direct sound wave component 10 and vibration of the defective portion 4 present at the position L _2, and exists at the target signal component s _1B to be measured and the position L ₃ . The unnecessary signal component s _1C is generated by the surrounding structure reflected sound wave 22 from the surrounding structure 20.

The unnecessary signal s _1A from the direct sound wave component 10 appears at the sound wave propagation time L ₁ / c with respect to the known distance L ₁ with the sound speed as c, and is a strong component because it is in the vicinity of the excitation low-frequency sound source 1. .

On the other hand, the target signal component s _1B from the defective portion existing at the position L ₂ appears at a time L ₂ / c corresponding to the one-way sound wave propagation time with respect to the distance L ₂ , and since it is far away, the unnecessary signal s _1A Appears backwards.

Further, the surrounding structure reflected sound wave 21 from the surrounding structure 20 existing at the position L ₃ appears strongly as s _{1C at} time 2L ₃ / c from the round-trip sound wave propagation time with respect to the distance L ₃ .

Accordingly, the unnecessary component s _{1C due} to the surrounding structure 20 appears superimposed on the target signal component s _1B as shown by s ₁ in FIG. 2 depending on the situation of the distance L _{3 where} the surrounding structure 20 exists. End up.

In the conventional configuration, the unnecessary signal s _1A is suppressed by the selection signal s ₂ that starts near the appearance time L ₂ / c of the target signal and ends at a time width of approximately T ₃ .

The result of suppressing the unnecessary signal s _1A by the selection signal s ₂ is the signal s ₃ , and the unnecessary signal s _1A by the direct signal 10 is suppressed, but the unnecessary component s _1C by the surrounding structure 20 is the target signal component s _1B and a position which overlaps, becomes inseparable from it is within the selected time selection signal s _2.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments for carrying out the present invention will be described with reference to the drawings. However, the following embodiments do not limit the invention according to each claim, and are described in the embodiments. Not all the combinations of features described are necessarily essential for the solution of the invention.

  The present invention forms a strong ultrasonic sound field in a limited space, vibrates a symmetric object by the acoustic radiation force formed only near the target position, and vibrates the excited object. The basic operation of the present invention will be described with reference to an overall configuration according to the present invention shown in FIG.

  In the overall configuration of FIG. 3, the ultrasonic excitation concave surface sound source 12 is controlled by the ultrasonic control unit 13 and radiates the excitation ultrasonic wave 14.

This, the ultrasonic sound pressure p _H which vibration ultrasound 14 is formed by the non-linear effect of the medium, the acoustic radiation pressure p _L generated on the surface portion of the object 3 located in vibration region 15, the acoustic to vibrate the object 3 by radiation pressure p _L.

The relationship between the ultrasonic sound pressure p _H generated by the vibration ultrasonic wave 14 and the acoustic radiation pressure p _L formed in the vibration region 15 is such that ρ is the density of the medium (in this case, air), and c is the medium. The speed of sound in (in this case air) is

(Equation 1)
p _L = p _H ² / (ρC ² )

This relationship is quadratic, the ultrasonic sound pressure p _H is reduced due to vibration ultrasound 14, the acoustic radiation pressure p _L formed in vibration region 15 decay rapidly, is virtually eliminated.

To illustrate, p _H: 3000 Pa (Pascal: Newtons / ^{m 2)} in the _{p L: 100Pa (134dB-SPL} ), p H: p L in 300 Pa: decreases the 1Pa (94dB-SPL), further, p _H: in _{30Pa p L: 0.01Pa (54dB-} SPL) next, p _H is excitation of the object 3 according to the following ultrasonic 30Pa by acoustic radiation pressure p _L becomes virtually impossible.

Accordingly, vibration due to acoustic radiation force according to the present invention, ultrasonic sound pressure p _H is by using a more powerful ultrasound 30 Pa, is the first time realized favorably.

  In the present invention, the vibration state of the defect portion 4 vibrated by the acoustic radiation force is detected by the measurement light beam 25 by the optical detection system 5, the presence or absence of the defect 6 is determined by the processing portion 7, and the determination result 9 is output. To do.

The ultrasonic sound source used in the embodiment of FIG. 3 is an ultrasonic excitation concave sound source 12, and the concave ultrasonic transmitter sound field characteristic is as shown in FIG. 4a), as well known, and the curvature radius of the concave surface. Converge at a focal length F corresponding to.

Here, when the wavelength of the ultrasonic wave is λ and the aperture of the transmitter is Dc, the azimuthal sound field distribution at the focal length F is the azimuth beam width d _C determined by the diffraction limit angle λ / Dc (≈λF / D _C) to become.

In this manner, since only the narrow azimuth direction beam width d _C is vibrated, it is possible to locally inspect the object.

In addition, since the vibration is performed only within the narrow directivity width d _C as described above, the vibration impossible angle at the incident angle of the vibration ultrasonic wave 14 due to the phase of the vibration force being reversed in the target object is It will not occur.

An example of such an azimuthal sound field characteristic by a concave ultrasonic wave transmitter is shown in FIG. 5 when an ultrasonic wave having a wavelength of 8 mm is transmitted by a wave transmitter having a diameter of 30 cm and a focal length of 1 m. It will form the azimuth beamwidth d _C only high ultrasonic sound pressure p _H of 6 cm.

5, the dashed line is an ultrasonic sound pressure p _H, solid line is the acoustic radiation pressure p _L (relative value to the maximum value either).

Further, the length W _C of the convergence region formed near the focal point of the concave ultrasonic wave transmitter is given by W _C ≈d _C ² / λ by the azimuth beam width d _{C at the} focal point. It is also known that in the distance, the ultrasonic beam diffuses rapidly and the intensity decreases.

As described above, since the ultrasonic beam diffuses rapidly and decreases in intensity far from the convergence region, noise interference with respect to the surrounding environment other than the convergence region is greatly reduced.

An example of the on-axis sound pressure distribution by such a concave ultrasonic wave transmitter is shown in FIG. 6 when an ultrasonic wave with a wavelength of 8 mm is transmitted by a wave transmitter having a diameter of 30 cm and a focal length of 1 m. It will form the focal region W _{C 'only} in high ultrasonic sound pressure p _H of 6 cm.

6, a broken line is an ultrasonic sound pressure p _H, solid line is the acoustic radiation pressure p _L (relative value to the maximum value either).

Here, the acoustic radiation pressure p _L to contribute to the actual vibration is proportional to the square of the ultrasonic sound pressure p _H, the focal region W _C next to FIG. 6 as assessed by p _L, narrower about 5cm It is shown that the driving force is limited to the area.

Thus, vibration region 15 is formed by a concave ultrasonic wave transmitter, since it is confined to the vicinity of the focal region W _C, in the configuration shown in FIG. 3, the direct ultrasound in the vicinity of the optical detection system 5 The component 16 is weak, and the direct ultrasonic component 16 has a slight interference with the optical detection system 5, so that the processing unit 7 can accurately determine a defect.

Although acoustic radiation pressure p _L and the ultrasonic sound pressure p _H is reflected by both the object, these objects reflection components shown in 24 of FIG. 3 are all spherically diffuse because it is emitted from the minute area, Since it attenuates rapidly in inverse proportion to the square of the distance from the irradiation target position, the adverse effect of the object reflection component on the surrounding environment is also small.

The ultrasonic sound source illustrated in FIG. 3 may be configured as an ultrasonic excitation flat sound source 23, and the flat sound source sound field characteristic is schematically shown in FIG. 4b) as is well known.

Also in the flat sound source 23, as shown in FIG. 4b), the sound source diameter is within the short-distance sound field distance W _F ≈D _F ² / λ, where λ is the wavelength of the ultrasonic wave and _DF is the diameter of the transmitter. Sound pressure can be formed only in a limited space equivalent to _DF .

Here if the ultrasonic wavelength lambda and 1 cm (about ultrasonic frequency 30 kHz), when the diameter _{D F} of the plane sound source 23 and 30 cm, near field distance ^{_{W F (≒ D F 2 /}} λ) is 900 cm ( 9m), and it is possible to form an irradiation area limited to a columnar shape with a diameter of 30 cm by the planar sound source 23 by a distance of 9 m.

In the present embodiment, the vibration ultrasound 14 of waveform used in the construction of FIG. 3, shown in FIG. 7a), and a single PCW waveform _{s SA} is the most basic waveform, a single PCW waveform _{s SA} the frequency spectrum shown in _{S SA} of FIG. 7b).

The square of the vibration ultrasonic waveform s _SA is, since the acoustic radiation pressure p _L formed in vibration region 15, the acoustic radiation pressure p _L is a s _SB in Fig 7a).

Since this acoustic radiation pressure s _SB is represented by the sum of two waveforms s _SC and s _SD shown in FIG. 7a), the frequency spectrum S _SB of the acoustic radiation pressure s _SB becomes FIG. a high-frequency component spectrum _{S SC} having a sonic waveform _{s SA} of the center frequency _(f 0) 2 times the center frequency (2f _0), will have a low-frequency component spectrum _{S SD} also having DC component.

Thus, the low-frequency component spectrum S _SD acoustic radiation pressure s _SB is vibration from being formed by the square of the ultrasonic waveform s _SA, similar waveform to the envelope shape of the vibration ultrasonic waveform s _SA , and the by selecting the envelope shape of the vibration ultrasonic waveform s _SA, may be similar to the low-frequency component spectrum S _SD shape resonance frequency characteristic of the defect.

Here, the frequency spectrum _{S SB} acoustic radiation pressure _{s SB} is as shown in FIG. 8a), when the _{S F} indicating a resonance spectrum of an object defect in FIG. 8b), the low-frequency component spectrum _{S SD} in FIG. 8a) during, since it contains a frequency component of S _F, acoustic radiation pressure s _SB result of the object vibration by, so that the vibration of the object defects and S _SRF in Figure 8c) the frequency spectrum is excited.

In this embodiment, the vibration of the object defect whose frequency spectrum becomes S _{SRF in} FIG. 8c) is optically detected as a time waveform s _SRF .

Here, if the duration length of the defect vibration waveform s _SRF and T _2, the bandwidth of the object defect resonance spectrum S _F is 1 / T _2, and this duration length T ₂ are, detailed studies of the inventors Therefore, it has been found that it is approximately 10 ms for a normal concrete internal defect.

  In this way, in the configuration in which the excitation force is generated by the acoustic radiation force of the ultrasonic wave, a low-frequency excitation force is formed regardless of the ultrasonic frequency, so the ultrasonic wave is generated regardless of the vibration frequency of the target defect. The frequency can be selected, and by setting the frequency to be higher than the audible frequency (16 kHz or higher), it is possible to reduce noise disturbance to surrounding residents.

Hereinafter, according to this embodiment, the vibration frequency sound waves _{s SA (s SA1, s SA2} , s SA3 -) in a configuration to be described each part of the signal shape by FIG.

In the operation of FIG. 9, the excitation high-frequency sound wave s _SA is a single PCW high-frequency signal having a time length T _{1 that} repeats at a time interval T ₀ , and a low-frequency component near the resonance frequency of the defect portion 4 due to a non-linear effect. Form.

It vibrated objects by vibrating frequency sound waves s _SA in FIG. 9, by measuring the optical detection system 5 the vibrations of the object, the vibration condition signal s _SR of the object shown in FIG. 9 is obtained.

This, the oscillating condition signal s _SR object, and unwanted signal s _SRD by unwanted feedthrough ultrasonic component 16, which has the desired signal component s _SRF as measured from the defective portion at the position L _2.

On the other hand, the surrounding structure 20 at the position L _3, since the irradiation region outside the excitation ultrasound, surrounding structures reflected ultrasound 21 is a reflected wave from the surrounding structure 20 is not generated, the vibration situation and thus not included in the signal s _SR.

In the present invention, the target signal component is selectively selected by the selection signal s _G starting from the vibration state signal s _{SR in the} vicinity of the target signal appearance time L ₂ / c and having a time width of approximately T ₃ (> T ₂ ). Extraction is made into a selective extraction signal s _SRG .

The unnecessary signal s _SRD due to the direct ultrasonic component 16 is suppressed by the selection signal s _G , and since the surrounding structure reflected ultrasonic wave 21 does not exist because it is outside the irradiation area of the excitation ultrasonic wave, the selective extraction signal The s _SRG includes only the signal component s _SRF due to the target defect of interest.

As described above, since the selective extraction signal s _SRG includes only the signal component s _SRF due to the target defect of interest, the configuration of this embodiment enables highly accurate defect detection that is not affected by unnecessary signals. .

Here, as a second embodiment, the operation of a configuration using the finite-length PCW waveform shown in FIG. 10 a) as the excitation ultrasonic waveform s _MA as the excitation ultrasonic wave 14 in the configuration of FIG. 3 will be described. To do.

The square of the vibration ultrasonic waveform s _MA is, since the acoustic radiation pressure p _L formed in vibration region 15, the acoustic radiation pressure p _L is a s _MB in Figure 10a).

Since this acoustic radiation pressure s _MB is the sum of the waveforms s _MC and s _{MD of} FIG. 10a), the frequency spectrum S _MB of the acoustic radiation pressure s _MB is a high-frequency component spectrum having a double center frequency, and A low frequency component spectrum _SMD .

Here, the component that contributes to the driving of the object is the low-frequency component spectrum _SMD , and the low-frequency component spectrum _SMD has a center frequency of 1 / T _{4 as} shown in FIG. It is limited to 1 / T _5.

Here, since the bandwidth of the low frequency component spectrum _SMD is limited to 1 / T ₅ , the signal strength is increased for the signal component in this band.

Such acoustic radiation pressure s _MB, when vibrated objects defect having a resonance spectrum S _F in FIG. 11b), the object by the low-frequency component spectrum S _MD is vibrated, the frequency spectrum S shown in FIG. 11c) _It vibrates as _MRF and is detected optically.

Here, the low-frequency component spectrum _{S MD} by acoustic radiation pressure _{s MB} is a diagram 11a), a resonance spectrum _{S F} of the object defect, because they contain strong in the low-frequency component spectrum _{S MD,} acoustic radiation pressure _{s MB} results of the object vibration by, so that the vibration of the object defects and S _MRF in Figure 11c) the frequency spectrum is strongly excited.

Also in this embodiment, the vibration of the object defect whose frequency spectrum is S _MRF in FIG. 11c) is optically detected as the time waveform s _MRF .

Here, the center frequency of the resonant spectrum S _F in FIG. 11b) is unknown, if the position of the low-frequency component S _MD and position of the resonance spectrum S _F do not coincide, since the object is not vibrated, Object defects are not detected.

Even in such a case, the frequency spectrum of each transmission pulse is shown in FIG. 12b) by sequentially connecting and using finite-length PCW waveforms whose center frequency sequentially changes as shown in s _MTD in FIG. 12a). for superimposing each other as _{S MTD2, S MTD3, S NTD4} , unknown resonance spectrum _{S F,} the oversight not detectable as a frequency spectrum _{S MTRF} shown in FIG. 12b) (in this figure, the _{T 5} constant indicating And N is a natural number and T ₅ = NT ₄ ).

As shown in FIG. 12, in the configuration in which the center frequency of the acoustic radiation pressure is sequentially changed with time, the frequency range of interest is set to the acoustic radiation pressure by using frequency selection means (filter) for the selective extraction signal s _SRG . A configuration that can be changed in response to changes in the center frequency is possible.

Specifically, in FIG. 12, at time T _MTD2 , only the frequency component of the frequency spectrum S _MTD2 is passed by the frequency selection means, and at time T _MTD3 , only the frequency component of the frequency spectrum S _MTD3 is passed. Similarly, at time T _MTD4 , only the frequency component of frequency spectrum S _MTD4 is passed.

  In this way, by configuring the frequency range of interest to change in response to the change in the center frequency of the acoustic radiation pressure, it becomes possible to effectively eliminate mixing of unnecessary signals due to front and rear excitation, Detection accuracy is improved.

Here, as a third embodiment, the operation will be described for a configuration in which the continuous PCW waveform shown in FIG. 13A) is used as the excitation ultrasonic waveform s _IA as the excitation ultrasonic wave 14 in the configuration of FIG. .

Since the square of the excitation ultrasonic waveform s _IA becomes the acoustic radiation pressure p _L formed in the excitation region 15, the waveform of the acoustic radiation pressure p _L becomes s _{IB in} FIG. 13a).

Since this waveform s _IB is the sum of s _IC and s _ID in FIG. 13 a), the frequency spectrum S _IB of the waveform s _IB of the acoustic radiation pressure p _L is a high-frequency component spectrum having a double center frequency. , it will have a low-frequency component spectrum S _ID.

Here, the component contributing to the driving of the object is the low frequency component spectrum S _ID , and the low frequency component spectrum S _ID becomes a line spectrum of frequency 1 / T ₄ as shown in FIG. Signal strength is highest.

By varying the repetition period _{T 4} in such a waveform _{s IA,} varying the frequency of the low frequency component _{s ID} (frequency sweep width Bs), an object having a resonant spectrum _{S F} in FIG. 14b) This _{s ID} When a defect vibrated, object defects by S _ID of the frequency that matches the unknown S _F is vibrated, ultimately, the vibration signal according to the frequency spectrum S _IRF shown in FIG. 14c) is obtained, the object defects Will be detected optically.

As a fourth embodiment, a carrier-suppressed double sideband signal (DSB-SC wave) shown in FIG. 15 is formed by two types of finite-length sinusoidal waves as the excitation ultrasonic wave 14 in the configuration of FIG. ) A configuration using _sWA will be described.

The square of the vibration ultrasonic waveform s _WA is, since the acoustic radiation pressure p _L formed in vibration region 15, the acoustic radiation pressure p _L is a s _WB in FIG.

This acoustic radiation pressure s _WB is decomposed into a high frequency component waveform s _WC and a low frequency component waveform s _WD in FIG. 15, and this low frequency component waveform s _WD is a waveform similar to s _MD in FIG. 10a). Because of the shape of the sine wave, there is no harmonic component and excitation with less unnecessary signals is possible.

Therefore, the accuracy of defect detection is improved by the configuration using this carrier-suppressed double-sideband signal _sWA .

  Here, in the frequency modulation wave (FM wave), if the modulation index (modulation index: carrier frequency deviation amount / modulation signal frequency) is 2.40483 which is the first zero point of the zero-order Bessel function, the frequency modulation wave The carrier wave component disappears and only the double sideband signal is obtained.

Thus, the modulation index by the frequency-modulated wave to the 2.40483, narrow the band driving the ultrasonic vibrator of the single resonance characteristic, that the ultrasound 14 vibrating by double sideband suppressed carrier signal s _WA is radiated Become.

  As described above, the excitation ultrasonic waveform used as the excitation ultrasonic wave 14 can be variously selected and is not limited to the present embodiment.

  Here, a configuration example of the ultrasonic excitation concave sound source 12 in the configuration of FIG. 3 will be described with reference to FIGS. 16 and 17.

  In the configuration example of FIG. 16, a number of micro ultrasonic transducers 17 are arranged in a concave shape 18, and a concave wavefront 19 is sent out by applying a common drive signal, and the ultrasonic waves are converged at the focal position F. Can be made.

  In the configuration example shown in FIG. 17, the micro ultrasonic transducers 17 are arranged on a plane, and the concentric elements 17 are connected in common by the partial wiring 26.

  An individual signal 29 generated by giving a common drive signal 28 to the partial wiring 26 by providing a concave time difference by a tapped delay line 27 is applied.

  By the individual driving of the partial wiring 26 by this individual signal 29 having a time difference, similarly, the concave wavefront 19 can be sent out and the ultrasonic wave can be converged to the focal position F.

  The configuration of the ultrasonic excitation concave surface sound source 12 is not limited to the configuration described in the present embodiment, and a sound source configured by a single large planar element or a convex surface shape allows a relatively wide area. It is obvious that various changes can be made for the purpose of achieving the function, such as a sound source that irradiates the excitation ultrasonic wave 14.

  Here, as Example 6, the configuration of the ultrasonic excitation concave sound source 12 and the optical detection system 5 in the configuration of FIG. 3 will be described with reference to FIG.

  Here, in the configuration of FIG. 18, a passage hole 30 for the measurement light beam 25 is formed in the center of the ultrasonic vibration concave surface sound source 12, and the optical detection system 5 is arranged behind the ultrasonic vibration concave surface sound source 12. To do.

  Here, when the measurement light beam 25 is arranged on the central axis 31, the measurement light beam 25 always passes through the vibration region 15.

  According to such a configuration of FIG. 18, the distance to the object can be measured by the measurement light beam 25 on the central axis 31 of the ultrasonic excitation concave surface sound source 12, and this optical distance measurement result is obtained. Accordingly, by setting the concave time difference to be given to the tapped delay line 27, the focal position of the ultrasonic excitation concave surface sound source 12 can be matched with the target surface position.

  Further, by arranging the optical detection system 5 behind the ultrasonic excitation concave surface sound source 12 in this way, the optical detection system 5 is not subjected to the disturbing vibration of the concave wave surface 19, and high-precision measurement is performed. Is possible.

  According to the present invention, since the excitation ultrasonic wave 14 is formed only in the limited space, the interference signal to the optical detection system is reduced, so that the measurement time is shortened and the minute defect can be detected. Become.

  Similarly, since the excitation ultrasonic wave 14 is formed only in a limited space, radiation noise to residents or the surrounding environment in a residential area or the like is also reduced.

  In addition, since the vibration ultrasonic wave 14 is formed only in a limited space, the formation of an uninspectable region due to interference with the floor reflection component, which is a problem in the conventional method, is also eliminated.

  Furthermore, since only a small area is vibrated, a detailed inspection for a limited part such as a local inspection for a small defect can be performed.

In addition, since only a small area is vibrated, the non-vibration phenomenon that occurs when a vibrating ultrasonic wave is incident at a specific angle does not occur. Area defects can be detected from a distance without being overlooked.

  In addition, due to the characteristics of excitation by acoustic radiation pressure in the present invention, ultra-low frequency excitation up to direct current is possible, and it is possible to detect defects that vibrate at low frequencies, such as large peeling defects where the resonance frequency is low It becomes.

The maximum usable frequency in the excitation ultrasonic wave 14 in the present invention is limited because the propagation attenuation of the ultrasonic wave in the air rapidly increases with the frequency. Usually, the center frequency f ₀ in the excitation ultrasonic wave 14 is set to 500 kHz or less. Is desirable.

1 Exciting Low Frequency Sound Source 2 Exciting Low Frequency Sound 3 Object 4 Defect 5
Optical detection system 6 Defect 7 Processing unit 8 Control unit 9 Determination result 10 Direct sound wave component 11 Object reflected sound wave 12 Ultrasonic excitation concave surface sound source 13 Ultrasonic control unit 14 Excitation ultrasonic wave 15
Excitation area 16 Direct ultrasonic component 17 Micro ultrasonic transducer 18 Concave shape 19 Concave ultrasonic wave front 20 Surrounding structure 21 Reflecting sound of surrounding structure 22 Reflecting ultrasonic wave of surrounding structure 23 Ultrasonic excitation plane sound source 24 Target object Reflective component 25 Measurement beam 26 Partial wiring 27 Delay line with tap 28 Common drive signal 29 Individual signal 30 Passing hole 31 Central axis

Claims (8)

  A transmission configuration for transmitting ultrasonic waves to an object, an optical measurement configuration for optically measuring the movement state of the object, arranged near the transmission configuration, and processing the optical measurement results to obtain inspection results In an apparatus having a processing configuration for outputting, the ultrasonic wave has a strength that forms a sufficient acoustic radiation pressure, and the amplitude of the ultrasonic wave is changed with time so that the acoustic radiation pressure has a low frequency component. A non-contact acoustic inspection apparatus characterized by comprising. The non-contact acoustic inspection apparatus according to claim 1, wherein the transmission structure according to claim 1 is a structure for transmitting a convergent ultrasonic wave. The non-contact acoustic inspection apparatus according to claim 1, wherein the transmission configuration according to claim 1 is a configuration in which an ultrasonic signal having a finite time length is transmitted and a specific time portion of an optical measurement result is selected and used. . The transmission configuration according to claim 1 is configured such that the frequency of the acoustic radiation pressure changes with time, and has a frequency selection means for extracting only the frequency component of the received signal corresponding to the change in the frequency. A non-contact acoustic inspection apparatus. The non-contact acoustic inspection apparatus, wherein the frequency of the ultrasonic wave according to claim 1 is a high frequency equal to or higher than an audible frequency. The non-contact acoustic inspection apparatus according to claim 1, wherein the transmission structure according to claim 1 is a structure in which a large number of small ultrasonic transmitters are arranged in a concave shape. The non-contact acoustic inspection apparatus according to claim 1, wherein the transmission configuration according to claim 1 is a configuration in which a large number of small ultrasonic transmitters are arranged in a planar shape and are commonly connected concentrically. The non-contact acoustic inspection apparatus according to claim 1, wherein the optical measurement configuration is configured to measure along a central axis of the transmission configuration. .

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