Tone-burst Wave Research Articles

Nonlinear Ultrasonic C-Scan Imaging for Contact-Type Defects in Diffusion-Bonded Joints-A Case Study.

Diffusion bonding technology is widely used in the connection of precision components, yet accurately and reliably detecting contact-type defects on the bond interface still remains a significant problem. Nonlinear ultrasonic methods have been proven to be sensitive to contact-type defects; however, the use of continuous wave or tone burst wave excitation limits its wider application. In this paper, dual-probe nonlinear ultrasonic testing with pulse wave excitation is proposed to detect contact-type defects in diffusion-bonded joints. A titanium alloy diffusion-bonded specimen with artificial defects was fabricated, and the corresponding detection device was designed based on the existing ultrasonic C-scan testing system. A C-scan imaging program based on nonlinear parameters was developed by extracting the fundamental and second harmonic waves of the reflection echo on the bond interface. The results demonstrated that the proposed detection scheme can obtain the nonlinear parameters of diffusion-bonded interfaces, and the nonlinear ultrasonic C-scan image of the bond interface is also obtained. The nonlinear parameter in the contact-type defects areas calculated from the bond interface echo is about 10 times (20 dB) higher than that in macro defects areas, whose gap is about 10 μm. The results indicate that the nonlinear ultrasonic methods seem to be more sensitive to contact-type defects and have a great potential to complement the insufficient detection capability of linear ultrasound for diffusion-bonded joints.

A novel pulse-echo piezoelectric transducer for detecting quasi-static component induced by an ultrasonic longitudinal wave

For effectively detecting the quasi-static component (QSC) of an ultrasonic longitudinal wave, which is closely related to the elastic nonlinearity of material, we proposed a novel pulse-echo piezoelectric transducer consisting of a high-frequency piezoelectric wafer, a frequency selective isolation layer, a low-frequency piezoelectric wafer, and an acoustic backing. The high-frequency wafer generates the primary longitudinal wave (PLW) tone burst, while the high- and low-frequency wafers receive the pulse echo containing both the PLW component and QSC, respectively. We analyze the pulse-echo formation of the high-frequency PLW tone burst in a specimen, and conduct numerical simulations and experiments to validate the effectiveness of the proposed transducer. The results demonstrate that the low-frequency receiver is more efficient at detecting the QSC, even though the high-frequency wafer can also receive the echo of the QSC pulse. Specifically, the QSC pulse can still be detected by the low-frequency receiver when the high-frequency PLW tone burst is completely attenuated. The novel pulse-echo transducer proposed in this paper expands the design perspectives for transducers used in ultrasonic non-destructive testing.

The Acoustic Emission Source Localization in the Pipeline Network with consideration of Radial Position of Defect

Pipeline as one important mode of transportation, its safety is a very critical public concern. the acoustic emission (AE) played a very important role in pipeline safety inspection and monitoring due to its Many advantages. Moreover, AE is capable of localizing the defects in complex geometry in a real time, which is one of the most significant merits of this technique. For the localization algorithm, the 1D or 2D localization is most commonly used in AE measurement. The pipeline has been simplified as “axial line” without consideration of radial direction; however, in large-diameter pipelines, if the radial or circumferential direction across the certain position was ignored, it can cause the negative impact on the accuracy of the AE localization of pipeline defects. Therefore, this study explores the influence of radial position of the defects associated with the pipeline diameter on AE localization. Six typical pipe schedules were selected and modelled by COMSOL Multiphysics5.5 software. the tone burst wave and pencil lead break was used as the artificial AE source. The numerical model has been validated experimentally. By parametric study, it has been concluded that with the increase of diameter, the wave propagation path cannot be simply considered as the straight line anymore. Otherwise, the error of the localization will increase. Therefore, it is necessary to consider the influence of the radial position and real path of wave propagation for the precise localization of the defects in the large diameter-pipeline.

Experimental observation of static component generation by Lamb wave propagation in an elastic plate

The experimental observation of acoustic radiation induced static component (SC) generation by Lamb wave propagation in an elastic plate is first reported. An experimental approach to directly detect the generated SC of primary Lamb wave propagation in an elastic plate is proposed, where a low-frequency wedge transducer is used to detect the SC pulse generated by primary Lamb wave tone-burst that is excited by a high-frequency wedge transducer. The basic requirements are that the group velocity of primary Lamb wave needs to be equal to that of the s0 mode at zero frequency (i.e., the SC), and that the central frequency of the low-frequency wedge transducer needs to be near the center of the main lobe frequency range of the generated SC pulse. For this purpose, the S4 mode whose group velocity is equal to that of the generated SC is selected as the primary Lamb wave, and then the specific mode pair S4-s0 is focused and analyzed. Accompanying propagation of the S4 mode tone-burst, the generated SC pulse detected with the low-frequency wedge transducer is clearly observed. Through respectively measuring the amplitudes of the S4 mode and the generated SC for different spatial separation between the transmitting and receiving wedge transducers, the quantitative relationship of the relative nonlinear acoustic parameter with propagation distance is obtained. The experimental results show that the proposed approach can be used to directly detect the generated SC of Lamb wave propagation, and that the said SC does have a cumulative growth effect with propagation distance.

Noncontact manipulation of particles in air by switching pulse drive of ultrasonic speakers arrayed on a semicylinder

Noncontact micromanipulation techniques are necessary for micromachine technology, biotechnology, materials processing, and so on. By using a bolted Langevin transducer and a reflector, one can trap small objects in air at nodes of sound pressure in a standing wave field, but such a technique requires high-voltage drive and careful tuning to achieve resonance. In this study, a large number of small ultrasonic speakers were placed on the inner surface of a semicylinder to form a strong sound field in the focus line. We showed that the pressure node can be moved, and thus the small object, along the focus line simply by switching the driving ultrasonic speakers without using complex electronics. We also showed that the object can be trapped and manipulated even at a duty ratio of 50% in tone burst waves. The above results are discussed by showing the experimental and calculated sound pressure distributions.

Modeling and simulation of static component generation of Lamb wave propagation in a layered plate

Modeling of the acoustic-radiation-induced static component (SC) generation of primary Lamb wave tone burst propagating in a layered plate is conducted. Accompanying the propagation of primary Lamb wave tone burst, there are the finite-duration SC bulk driving force in the interior of the layered plate, and the finite-duration SC traction stress on each surface/interface. According to the modal analysis approach for waveguide excitation, the function of the finite-duration SC bulk driving force and traction stress is to generate the finite-duration SC of primary Lamb wave tone burst. Compared with the second harmonic (SH) generation of Lamb wave propagation in a layered plate, the phase velocity matching is no longer required for the generation of the SC with a cumulative growth effect. Based on modeling of the finite-duration SC generation, it is found that the integrated amplitude of the finite-duration SC generated by propagation of the primary Lamb wave tone burst does grow with propagation distance. Meanwhile, the numerical analyses and the finite element (FE) simulations are conducted to investigate the effect of the said SC generation. It is found that, although the interfacial layer of the layered plate considered is quite thin compared with the upper and lower layers, the numerical analyses indicate that the influence of the interfacial property on the cumulative growth effect of the SC of primary Lamb wave is significant. Furthermore, the FE simulations demonstrate that the cumulative SC of primary Lamb wave tone burst will exhibit a monotonic and sensitive response to the degree of interfacial degradation. This investigation provides an physical insight not previously available into the process of the SC generation of Lamb wave propagation in a layered plate.

Mode-mixing-induced second harmonic A0 mode Lamb wave for local incipient damage inspection

This paper reports the discovery of a special type of second harmonic A0 mode Lamb wave, which is generated through the mixing of primary S0 and A0 mode Lamb waves in a PZT-activated weakly nonlinear plate. Owing to the different propagating velocities of the S0 and A0 waves and the finite duration of their corresponding tone-burst wave packets, wave mixing takes place within a confined area which can be precisely controlled by tuning the wave excitation durations. When local incipient damage falls into the mixing zone, this second harmonic A0 mode wave provides higher damage detectability than the commonly used second harmonic S0 mode wave resulting from the global material nonlinearity. Moreover, through a tactic tuning of the mixing zone size, damage detection can be carried out zone by zone along the transmitter–receiver path to achieve damage localization. Finite element (FE) simulations are first carried out to ascertain the theoretically predicted phenomenon and the underlying generation mechanism of the second harmonic A0 mode Lamb waves. Capitalizing on its mode mixing feature between the primary A0 and S0 mode Lamb waves, a dedicated damage localization strategy alongside the corresponding algorithm is then proposed. Experiments are finally carried out with a dedicatedly designed inspection system with mitigated non-damage-related nonlinear interference. Both FE and experimental results demonstrate the appealing characteristics and the potential of the second harmonic A0 mode Lamb waves for local incipient damage detection and localization.

Adaptive signal decomposition and dispersion removal based on the matching pursuit algorithm using dispersion-based dictionary for enhancing damage imaging

This paper aims to develop a method for high-resolution damage imaging for a sparsely distributed sensor network on a plate-like structure. Techniques for dispersion removal and signal decomposition are indispensable to accurate damage localization. By combining the dispersion-removed wave packets with the damage-imaging algorithm, a point-like damage can be precisely localized. In this article, a matching pursuit algorithm was utilized to decompose overlapping wave packets and then recompress the dispersion. The matching pursuit dictionary was constructed based on an asymptotic solution of the dispersion relation for Lamb waves in toneburst wave packets. The dispersion-based Hanning-window dictionary provided the parametric information for the extracted wave packets, such as propagation time-delay, dispersion extent, and phase. The parameters were leveraged for the dispersion-removal algorithm. Results of the simulation indicate that the proposed algorithm is capable of recompressing multiple dispersive wave packets with the different modes. Finally, the proposed approach was validated by the results of the experiment using a sparse array of piezoelectric wafers on an aluminum plate. Extracting the parameters of individual wave packets and removing the dispersion through matching pursuit, the algorithm for minimum-variance imaging produced a high-quality image with a fine spatial resolution. The image artifacts were significantly suppressed, and the accuracy was improved by 62.1% compared to conventional minimum-variance imaging.

Synthetic aperture imaging of contact acoustic nonlinearity to visualize the closing interfaces using tone-burst ultrasonic waves

Abstract Contact acoustic nonlinearity (CAN) effect was visualized by synthetic aperture focusing technique (SAFT) via a signal-processing method for acoustic nonlinearity imaging. The proposed signal-processing technique, named Synthetic Aperture Imaging of Acoustic Nonlinearity (SAIAN), allows the SAFT to visualize CAN that is difficult to be visualized by linear ultrasonic imaging. Using the SAIAN algorithm, the fundamental and second-order harmonic frequency components are extracted from the tone-burst wave signal and then these component signals are transformed into pulse-like signals. From the pulse-like signals, the CAN parameter signals can be obtained in the form of pulses, which allows CAN to be visualized by SAFT. In order to verify the effectiveness of the SAIAN, the nonlinear ultrasonic measurements using tone-burst waves were conducted to visualize closing interfaces. As a result, CAN effect appeared at partially closed part of a contacting interface in the images of the CAN signals converted by the SAIAN; on the contrary, the CAN feature was not shown in linear ultrasonic images based on the fundamental frequency component. These results support that the SAIAN is a useful signal processing for acoustic nonlinearity visualization that improves the probability of detection of closing interfaces and the accuracy in crack sizing.

High speed non-contact acoustic inspection method using long distance acoustic irradiation-induced vibration

The non-contact acoustic inspection method using air-borne sound can detect the cavity defect and crack of inside concrete near the surface. As a feature of this technique, focusing on the physical phenomenon of flexural vibration of defects, we succeed in improving energy efficiency to vibrate the defect effectively. It is possible to measure all day using a small dynamo. Moreover, using a low-output laser Doppler vibrometer (LDV), high signal to noise (S/N) ratio is achieved by our proposed broadband “Tone Burst Wave” and “Time & Frequency-gate (T-F gate).” Therefore, although a possible distance from a sound source and a LDV to target is dependent on output power of acoustic radiation, it was already confirmed that a measurement of long distance over 30 m away is possible under the condition that a target is excited efficiently. In order to shorten measurement time, we propose the “Multi Tone Burst wave” that fully utilized the principle of T-F gate. After many experiments using a concrete test objects and some experiments of real concrete structures (bridge, etc.), we confirmed the validity of high-speed measurement technique of the “Multi-Tone Burst wave.”

Generation of narrowband elastic waves with a fiber laser and its application to the imaging of defects in a plate

Pulsed laser equipment can be used to generate elastic waves through the instantaneous reaction of thermal expansion or ablation of the material; however, we cannot control the waveform generated by the laser in the same manner that we can when piezoelectric transducers are used as exciters. This study investigates the generation of narrowband tone-burst waves using a fiber laser of the type that is widely used in laser beam machining. Fiber lasers can emit laser pulses with a high repetition rate on the order of MHz, and the laser pulses can be modulated to a burst train by external signals. As a consequence of the burst laser emission, a narrowband tone-burst elastic wave is generated. We experimentally confirmed that the elastic waves agreed well with the modulation signals in time domain waveforms and their frequency spectra, and that waveforms can be controlled by the generation technique. We also apply the generation technique to defect imaging with a scanning laser source. In the experiments, with small laser emission energy, we were not able to obtain defect images from the signal amplitude due to low signal-to-noise ratio, whereas using frequency spectrum peaks of the tone-burst signals gave clear defect images, which indicates that the signal-to-noise ratio is improved in the frequency domain by using this technique for the generation of narrowband elastic waves. Moreover, even for defect imaging at a single receiving point, defect images were enhanced by taking an average of distributions of frequency spectrum peaks at different frequencies.

High-speed non-contact defect imaging for a plate-like structure

Images of defects in a plate-like structure can be obtained from amplitude distributions measured using the scanning laser source technique. This paper discusses high-speed non-contact imaging for defects in a plate. Fundamental experiments conducted using a contact piezoelectric transducer as a receiving device revealed the effect of the generated wave shape and measurement speed on the defect images. Generating tone-burst waves consisting of multiple frequency components and averaging the images obtained in multiple frequency bands (frequency image averaging, FIA) gave clearer defect images in which noisy effects due to low signal-to-noise ratio and spurious images due to multiple reflections in high-speed imaging were reduced. Moreover, FIA was shown to be effective for high-speed non-contact imaging using a laser Doppler vibrometer.

Generation of cumulative second-harmonic ultrasonic guided waves with group velocity mismatching: Numerical analysis and experimental validation

The generation of second-harmonic Lamb waves in a homogeneous, isotropic, stress-free elastic plate is analytically and experimentally investigated. The numerical analyses show that whether the matching condition of the group velocity is satisfied or not, the integrated amplitude of a second-harmonic Lamb wave accumulates with the propagation distance when both the finite duration of the primary Lamb wave tone burst and the phase velocity matching are given. The theoretical analyses are validated by experimental measurements of an aluminium plate. Our conclusions are different from those of the previous works that reported that the group velocity matching is required for the generation of the cumulative second-harmonic Lamb waves with the finite duration of tone bursts.

Study on the measurement speed and signal to noise ratio of multi tone burst wave for high speed non-contact acoustic inspection method

The non-contact acoustic inspection method using an air-borne sound can detect the cavity defect and crack near the measurement surface by using flexural resonance. By this method which uses the conventional single tone burst wave, since only one frequency was used for one sound wave emission, the length of measurement time had become a problem. Therefore, the multi-tone burst wave was devised for high speed improvement. However, measurement time and signal to noise (S/N) ratio change with the parameters in which a multi-tone burst wave is contained at the time of one sound wave emission, such as the number of frequency, the arranging method, pulse length, and the average number of times. Therefore, the experiment using the concrete test object having the styrofoam which imitated the cavity defect was conducted and a multi-tone burst wave was used, it was investigated how the measurement time and the S/N ratio of this method would change. From the experimental result, it became clear that the improvement in the measurement speed of several or more times was realizable maintaining a comparable S/N ratio as compared with the conventional single tone burst wave.

High speed non-contact acoustic inspection method using multi tone burst wave

The non-contact acoustic inspection method using an air-borne sound can detect the cavity defect and crack near the measurement surface by using flexural resonance. By this method using a single tone burst wave, the length of the measurement time of a two-dimensional scan was a practical problem. This is because only one frequency was used for one sound wave emission so that a high signal to noise (S/N) ratio could be obtained with the laser Doppler vibrometer (LDV) of a weak laser power (e.g., He-Ne 1mW). However, two or more frequency can be used at the time of one sound wave emission (multi tone burst wave) by taking into consideration the difference of the propagation velocity of a sound wave and laser light. That is, it becomes possible to perform high-speed measurement as compared with the conventional method, using effectively the time & frequency gate for raising a S/N ratio by terminating measurement before the reflective sound wave reaches a laser head from the measurement surface. The experiment using a concrete test object was carried out and the validity of this multi tone burst wave as high-speed measurement was confirmed from the experimental result.

Change of Cognition Effects by Impact of the Transcranial Magnetic Stimulation

The purpose of this paper is to investigate the effects of sub- or supra-threshold low-frequency repetitive transcranial magnetic stimulation (rTMS) on cognitive function. The magnetic stimulation was delivered at 1 Hz to the left supramarginal gyrus, which is considered to be the area of origin of the P300 event-related potential component. The intensity of magnetic stimulation was 80% or 120% of motor threshold, and 100 magnetic pulses were applied. The auditory oddball task, consisting of tone burst waves, was used to elicit P300 before and shortly after magnetic stimulation. We found that P300 latency depended on the intensity of the 1 Hz magnetic stimulation. With subthreshold rTMS, P300 latency was significantly shortened compared with before magnetic stimulation by around 10 ms (Cz: p<;0.05) on average. With the suprathreshold rTMS, the latency was significantly delayed compared with before magnetic stimulation by around 10 ms (Cz: p<; 0.01) on average. The facilitation of cortical excitability by rTMS may induce the shortening of P300 latency, whereas the inhibition of cortical excitability may induce its delay. Thus, P300 latency can be altered by both sub- and supra-threshold low-frequency magnetic stimulation.

Study on detectable size and depth of defects in noncontact acoustic inspection method

We study a noncontact inspection method for large-scale structures such as tunnels and bridges. This method involves the use of a high-powered sound source and a scanning laser Doppler vibrometer (SLDV). In our previous study, we proposed a tone burst wave method to improve the signal-to-noise ratio (SNR) of the measured result. Using this method, a defect that was difficult to detect using our previous method was detected. In this study, we examined the detectable size and depth of the defect by using a model wall with circular defects. The distance between the sound source and the concrete test piece was 5 m, and the output sound pressure was about 100 dB near the surface of the concrete test piece. As the transmitted wave, tone burst waves with different center frequencies from 500 to 7000 Hz were used. A conventional investigation by the hammer method was also simultaneously carried out for comparison and almost identical performance was confirmed. From the experimental result, we confirmed that the bending resonance frequency detected was proportional to the depth of the circular defect, and was in inverse proportion to the plane size (area) coincident to the analytical result for a circular plate. We also found that the vibration energy of the defect shows a strong dependency on its depth. Therefore, the possibility of defect depth estimation using the resonance frequency and the vibration energy ratio is expected. In the future, a practical investigation system that will replace the hammer method might be developed.

Visualization of temperature elevation due to focused ultrasound generated by tone burst wave

The temperature elevation effect due to burst wave ultrasound was investigated experimentally. To observe the temperature distribution when focused ultrasound is radiated onto an acoustic dissipative medium of gelatin, a thermochromic film was used to perform a temperature visualization method. The discolored area on the thermochromic film caused by the ultrasound increased with different speeds depending on the duty cycle of the tone burst signal. Using the image process, the high-temperature region, the discolored region, caused by the focused ultrasound was measured. It is confirmed experimentally that the high-temperature area can be controlled by adjusting the duty cycle of the burst signal.

One-dimensional time-domain finite-element modelling of nonlinear wave propagation for non-destructive evaluation

This one-dimensional time-domain finite-element model achieves accurate quantitative modelling of ultrasonic wave propagation in multi-layered structures. First, a sinusoidal wave toneburst is sent into a single layer of material exhibiting inherent material nonlinearity characterised by the nonlinear parameter β and thick enough for the toneburst received in through transmission to be resolved. The signal processing protocol that yields the theoretically correct quantitative value of β involves measuring the received toneburst for several propagation distances as well as the use of scaling factors taking into account the fast Fourier transform implementation, input signal windowing and material damping. Using that model configuration, model parameters (element size, time step, frequency step, input pressure, etc.) are then optimised and chosen quantitatively to generate accurate results. Finally, these model parameters are used for cases of interest where the configuration is not such that the exact β value can be obtained – e.g. thinner sample, pulse-echo etc. but where confidence in the results remains. This quantitative model that can be used for multi-layered structures provides a tangible resource useful to NDE engineers: a new prediction tool expected to enable them to choose the experimental set-up, driving frequency and post-processing method that would optimise kissing bond detection capability.

Effect of pulse repetition frequency and scan step size on the dimensions of the lesions formed in agar by HIFU histotripsy

Histotripsy uses high-intensity focused ultrasound pulses at low duty cycle to generate energetic bubble clouds inside tissue to fractionate a region. As a potential tumor treatment modality, this cavitation-based non-invasive technique has the advantages of easy monitoring and sharp borders. Aiming at therapy efficiency, we experimentally investigated the effects of pulse repetition frequency (PRF) and lateral scan step size on the dimensions of lesions formed through HIFU histotripsy in agar mimicking tissue in terms of mechanical (not acoustical) properties. The single-element spherically focused source (1.1MHz, 6.34cm focal length, f/1) was excited to reach the peak compressional and rarefactional pressures of ∼102 and 17MPa, respectively. A targeted rectangular block of 4.5mm wide (lateral) and 6mm deep (axial) was scanned in a raster pattern with a constant axial step size of 3mm. The lateral step size was varied between 375, 750, 1500, 2250 and 4500μm. Pulses at each treatment location consisted of 5000 20-cycle sine wave tone bursts with the PRF of 167, 333 or 1000Hz. Results suggested that the bubble activity region could extend beyond the −3dB region and that refining the lateral scan mesh and/or increasing PRF enlarged the lesion extent. The 1500μm–333Hz and the 1500μm–1kHz conditions were in a more favorable position to be viewed as optimal with regard to lesion volume generation rate, bubble activity region width, and the potential for thermal damage.