Detection Of Ultrasonic Waves Research Articles

104 SH波型電磁超音波センサによる高調波検出の基礎検討(セッション1 センサ技術・信号処理)

The nonlinearity of a solid material is very small compared with that of a liquid medium, and a liquid medium with a high nonlinear efficiency had to be used as a coupling medium. We then attempted to apply an electromagnetic acoustic transducer (EMAT), which does not require a coupling medium. Especially, we studied the conditions under which the EMAT could a Shear Horizontal (SH) -plate wave. Although we observed an increase in the higher frequency components when a SH-plate wave was parallel injected into a V-shaped slit, althogh this was not observed when a Lamb wave was injected at he same condition. This phenomenon indicates that the nonlinear ultrasonic wave detection method by SH-plate wave or a Lamb wave can also provide information on the direction of a crack.

Leaky Rayleigh and Scholte waves at the fluid–solid interface subjected to transient point loading

The analysis of acoustic waves generated by a transient normal point load applied on a fluid–solid interface is presented. The closed-form exact solution of the wave motion is obtained by using integral transform techniques. The obtained analytical solution provides necessary theoretical background for optimization of fluid-coupled ultrasonic and acoustic wave detection in experiments. Numerical simulation (elastodynamic finite integration technique) is performed to verify the obtained analytical solution. Detailed descriptions of leaky Rayleigh and Scholte wave solutions are presented. A simplified solution to isolate the contributions of leaky Rayleigh and Scholte waves generated by a transient point load is proposed, and closed-form formulations for displacement and stress components are then presented. The simplified solution is compared to the exact solution for two configurations: water/concrete and air/concrete. The excitation effectiveness of leaky Rayleigh waves for the air/concrete configuration is studied, which has practical significance to air-coupled sensing in civil engineering structures.

Surface-bonded fiber optic Sagnac sensors for ultrasound detection

This paper describes a fiber optic sensor suitable for remote sensing and multi-point detection of ultrasound. This ultrasound sensor is based on the surface-bonded fiber optic Sagnac interferometer with the output fringe visibility of 1; it consists of a laser source, an ordinary single mode fiber delay line, a fiber coupler, a phase modulator and polarization controllers. For the validation of the sensor, surface acoustic waves and Lamb waves are excited by illuminating a steel specimen with an array of Q-switched Nd:YAG laser-generated line sources and the measurement of laser-generated ultrasonic waves are performed on the specimen surface using the surface-mounting fiber optic Sagnac sensor. The surface-bonded fiber optic sensor developed in this study has a simple configuration for detection of ultrasonic waves. Effectiveness of surface-bonded fiber optic Sagnac sensors for remote sensing of ultrasound and in situ monitoring of structures is investigated. The capability of multi-point detection of ultrasound by this Sagnac sensor is also discussed.

Photoacoustic imaging of blood vessels with a double-ring sensor featuring a narrow angular aperture

A photoacoustic double-ring sensor, featuring a narrow angular aperture, is developed for laser-induced photoacoustic imaging of blood vessels. An integrated optical fiber enables reflection-mode detection of ultrasonic waves. By using the cross-correlation between the signals detected by the two rings, the angular aperture of the sensor is reduced by a factor of 1.9, from 1.5 to 0.8 deg. Consequently, photoacoustic images could be obtained in a manner analogous to the ultrasound B-scan mode. Next, the cross section of artificial blood vessels is visualized by reconstruction of the absorbed energy distribution. Finally, in vivo imaging and the subsequent reconstruction of the absorbed energy distribution is demonstrated for superficial blood vessels in the human wrist.

532 ガイド波用電磁超音波センサによる非線形超音波検出法の検討(OS 非破壊評価とモニタリング(1))

532 ガイド波用電磁超音波センサによる非線形超音波検出法の検討(OS 非破壊評価とモニタリング(1))

P1-31 Harmonic ultrasonic wave detection by EMAT for a guided wave

P1-31 Harmonic ultrasonic wave detection by EMAT for a guided wave

Transmission and Detection of Light Diffraction Signal by Low-Frequency Ultrasonic Wave

Measurement of low-frequency ultrasonic waves in water was examined by the light diffraction effect of a visible laser beam. This laser beam was much narrower than the ultrasonic wavelength. Characteristics of detected signals agreed well with the theoretical prediction based on Fraunhofer diffraction. As shown in the results, light diffraction waves transmitted through a polarization-maintaining fiber could be detected correctly. The results enable us to construct a novel optical fiber sensor which will be used for the detection of low-frequency ultrasonic waves as well as the transmission of light diffraction signals.

Response of a fiber Bragg grating ultrasonic sensor

A fiber Bragg grating (FBG) sensor for detection of ultrasonic waves in liquids and solid structures is investigated. The sensor contains a fiber probe with a FBG, a tunable narrowband laser source, and a photodetector. When ultrasonic waves impinge on the fiber probe, the pitch of the grating is modulated through the elasto-optic effect. The corresponding changes in reflectivity of the grating are detected by a photodetector. The sensitivity of the sensor and its frequency and directional response in the 0.5 to 3.0 MHz range are measured. Some anomalous features of the FBG ultrasound sensor response are noted. It is shown that these features result from a combination of the sensor's response to the direct ultrasonic waves propagating through the medium and the signal generated by axially guided ultrasonic waves propagating through the fiber probe.

Noncontact detection of ultrasonic waves using fiber optic Sagnac interferometer

This paper describes a fiber optic sensor suitable for noncontact detection of ultrasonic waves. This sensor is based on the fiber optic Sagnac interferometer, which has a path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. Ultrasonic oscillations produced by conventional ultrasonic piezoelectric transducers were successfully detected, and the performance of this interferometer was investigated by a power spectrum analysis of the output signal. Based on the validation of the fiber optic Sagnac interferometer, noncontact detection of laser-generated surface waves was performed. The configured Sagnac interferometer is very effective for the detection of small displacement with high frequency, such as ultrasonic waves used in conventional nondestructive testing (NDT).

Evaluation of the coating–substrate adhesion by laser-ultrasonics: Modeling and experiments

The aim of the present study is to investigate a laser-ultrasonic method to determine the oxide-coating’s adhesion strength on a metallic substrate. In order to demonstrate this method a completely contactless system is used, combining laser generation and detection of ultrasonic waves. A nanosecond pulsed Nd:YAG laser is used to irradiate the transparent oxide coatings, while the normal displacement of the rear surface of the metallic substrate is detected at the epicenter by a laser heterodyne interferometer. Increasing the laser beam energy, the generated acoustic wave forms are correlated with the thermoelastic regime, the fracture of the coating–substrate interface, and finally the expulsion of the coating. The generation of ultrasonic signals in the thermoelastic regime is described by a two-dimensional model suitable to calculate the in- and out-of-plane components of the mechanical displacement versus time. The values of the so-called practical adhesion found are in agreement with those obtained by classic contact techniques (tensile adhesion test, indentation, bending test). This work demonstrates the suitability of this quantitative and contactless test to evaluate the coating–substrate adhesion.

Non-contact detection of laser-generated surface acoustic waves using fiber optic Sagnac interferometer

A high powered Q-switched Nd:YAG laser was used to excite the surface waves, and an optical fiber sensor was used to detect the out-of-plane displacements due to the propagating waves. This sensor is based on the fiber optic Sagnac interferometer, which has the path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence in an optical path using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. The performance of the fiber optic Sagnac interferometer was investigated, and laser-generated surface wave signals were detected using this fiber optic sensor. The developed fiber optic sensor configured in this study is very simple and is effective for non-contact detection of ultrasonic waves.

An optodynamic determination of the depth of laser-drilled holes by the simultaneous detection of ultrasonic waves in the air and in the workpiece

A sufficiently powerful pulsed-laser beam can be used to `drill' a hole in a stainless-steel workpiece. Here we present a real-time method for determining the depth of such a hole produced by multi-pulse laser drilling with a Q-switched Nd:YAG laser. The developed experimental setup allowed us to detect the laser-induced ultrasonic waves in the surrounding air and in the workpiece simultaneously by means of a probe-beam-deflection method and a piezoelectric transducer. Our optodynamic approach involved an analysis of these ultrasonic waves in order to determine the depth of the hole at any stage of the process. The increasing depth of the hole and its maximum extent were estimated from changes in the propagation time of the ultrasonic waves traveling from the bottom of the hole to both detectors. Measurements of the maximum hole depth were compared with the predictions of a theoretical model and they were found to be in a good agreement.

Noncontact Acoustical Techniques for Nondestructive Characterization of Materials and Structures

The Johns Hopkins University Center for Nondestructive Evaluation (CNDE) is an interdisciplinary cooperative center between the university, government, and industrial organizations dedicated to the development of more accurate and innovative methods for the nondestructive evaluation of materials and to the education of talented students. This paper will describe several innovative noncontact nondestructive materials characterization methods developed in the CNDE. Lasers, optical interferometers, electro-magnetic transducers, and air(gas)-coupled systems are used for noncontact generation and detection of ultrasonic waves to inspect art paintings, metals, wood, and composites. Optical detection of acoustic emission signals permits detection of surface displacements caused by acoustic emission events without any modification of the detected waveforms or frequency spectra.

Non-contact Detection of Ultrasonic Waves Using Fiber Optic Sagnac Interferometer

This paper describes a fiber optic sensor suitable for non-contact detection of ultrasonic waves. This sensor is based on a fiber optic Sagnac interferometer. Quadrature phase bias between two interfering laser beams in Sagnac loop is introduced by a polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output versus phase bias. This method eliminates a digital signal processing for detection of ultrasonic waves using Sagnac interferometer. Interference intensity is affected by the frequency of ultrasonic waves and the time delay of Sagnac loop. Collimator is attached to the end of the probing fiber to focus the light beam onto the specimen surface and to collect the reflected light back into the fiber probe. Ultrasonic waves produced by conventional ultrasonic transducers are detected. This fiber optic sensor based on Sagnac interferometer is very effective for detection of small displacement with high frequency such as ultrasonic waves used in conventional non-destructive testing.

Transmission and Detection of Ultrasonic Wave by Electromagnetic Acoustic Transducers. Effects of a Flaw in a Specimen.

Transmission and Detection of Ultrasonic Wave by Electromagnetic Acoustic Transducers. Effects of a Flaw in a Specimen.

レーザー励起広帯域表面波を用いた微小き裂サイジング手法

A new method to estimate crack depth based on laser-induced surface acoustic wave (SAW) is proposed. Laser ultrasonic technique that uses laser beams for generation and detection of ultrasonic waves allows remote and non-contacting inspection. Moreover, since laser-induced SAW has a wide frequency band, it also offers crack-depth measurement using a frequency analysis. To confirm the performance, some feasibility tests using artificial slits were performed. Simulated surface cracks were machined on the type 304 stainless steel plates; each of them had a width of about 100μm and a depth of from 0.2mm to 1.5mm. The location and the depth of the slits were estimated from the detected waves by both the pulse-echo measurement and a frequency analysis. Results of the frequency analysis show that a surface slit behaves as the low pass filter to the laser-induced SAW and the step response time of the transfer function has linear relationship with the slit-depth. Consequently, it is possible to detect small cracking having 0.2mm depth and good agreement can be achieved between measured and nominal depths.

Directional detection of laser-generated ultrasound with an adaptive two-wave mixing photorefractive configuration

We report directional detection of laser-generated ultrasonic waves in real as-processed objects using holographic adaptive configuration. The scheme is based on two-wave mixing in the photorefractive crystal where holographic recording occurs through the drift mechanism. Directional detecting properties are achieved by projecting the object surface irradiated by a broad probe beam onto the photorefractive sample plane. An additional slit aperture, whose orientation determines the direction of the maximal detection sensitivity, is put behind the sample into the reference wave. Its overall output intensity is measured by a single integrating photodiode. Experimental results for the scheme using Bi 12SiO 20 and operating at λ=532 nm are presented to demonstrate the idea of the proposed technique.

Sagnac-type fiber-optic array sensor for detection of bulk ultrasonic waves

In this paper, we describe a fiber optic array sensor suitable for detection of bulk ultrasonic waves. This sensor is based on an intrinsic fiber optic Sagnac interferometer. The fiber array is formed by multiple folding of a continuous length of an optical fiber into flat coils. Depending on the orientation of the fiber array with respect to the ultrasonic wave, the proposed sensor can act as a conventional in-phase detector or as a narrowband detector. In the narrowband mode, the center frequency of detection can be tuned by adjusting the spacing of the fiber array elements to be equal to the ultrasonic wavelength of interest. This feature distinguishes this array sensor from conventional hydrophones in which a receiver is typically much smaller than the acoustical wavelength. It is shown that the array sensor provides an enhanced signal-to-noise ratio (SNR) compared with a single element detection scheme. Results are presented for detection of ultrasonic waves in water arising from both piezoelectric and laser ultrasonic sources. Potential areas of application of this sensor include process monitoring, smart structures, bio-medical ultrasound, and chemical sensing.

Elastographic imaging

Elastographic imaging

Detection of laser excited surface acoustic waves by infrared radiation

Remote detection of ultrasonic waves is shown experimentally by measuring the infrared (IR) radiation accompanying the adiabatic propagation of surface waves. The Rayleigh waves were excited by a pulsed Nd:yttrium–aluminum–garnet laser on the surface of a steel sample at temperatures up to 700 °C. The observed time-of-flight data of the Rayleigh waves correspond to values obtained by optical interferometry and the measured signal-to-noise ratio of ≈0.1 agrees with the estimated value using an IR detector with a sensitivity of D*=1.7×109 mm √Hz/W. Further improvements of IR detection may lead to a viable tool for laser ultrasonics.