Surface Acoustic Wave Signal Research Articles

Single-shot analytical assay based on graphene-oxide-modified surface acoustic wave biosensor for detection of single-nucleotide polymorphisms.

The combination of a surface acoustic wave (SAW) biosensor with graphene oxide (GO) provides a promising perspective for detecting DNA mutation. The GO-modified SAW biosensor was prepared by conjugating GO onto the SAW chip surface via electrostatic interaction. Afterward, the probe was immobilized on the GO surface, and detection of DNA mutation was realized by hybridization. The hybridization with a variety of targets would yield different mass and conformational changes on the chip surface, causing the different SAW signals in real time. A total of 137 clinical samples were detected by a single-shot analytical assay based on GO-modified SAW biosensor and direct sequencing in parallel. The diagnostic performance (both sensitivity and specificity) of the assay was evaluated with the direct sequencing as a reference testing method. The phase-shift value of three genotypes in 137 clinical samples was significantly different (p < 0.001). Furthermore, testing of diagnostic performance yielded diagnostic sensitivity and specificity of 100% and 88.6% for identifying CT and CC genotype, 98.0% and 96.2% for identifying CT and TT genotype, respectively. The single-shot analytical assay based on the GO-modified SAW biosensor could be exploited as a potential useful tool to identify CYP2D6*10 polymorphisms in clinical practice of personalized medicine.

Impact of humidity on surface acoustic wave propagation in vanadium pentoxide xerogel–lithium niobate structure

The impact of ambient humidity on surface acoustic wave (SAW) propagation in the structure consisting of vanadium pentoxide xerogel (V2O5∙nH2O) layer deposited on a piezoelectric lithium niobate (LiNbO3) substrate has been studied. Thin V2O5∙nH2O layers were synthesized using sol–gel method and employed as humidity sensing materials. Freshly prepared layer drastically reduced the transmitted SAW signal, which later increased with time reaching saturation after more than 120 h at the level well below the free-surface value. The experimental observations of SAW behaviour were discussed and found related to the variations in resistance and dielectric permittivity of the V2O5∙nH2O.

High frequency microfluidic performance of LiNbO3 and ZnO surface acoustic wave devices

Rayleigh surface acoustic wave (SAW) devices based on 128° YX LiNbO3 and ZnO/Si substrates with different resonant frequencies from ∼62 MHz to ∼275 MHz were fabricated and characterized. Effects of SAW frequency and power on microfluidic performance (including streaming, pumping, and jetting) were investigated. SAW excitation frequency influenced the SAW attenuation length and hence the acoustic energy absorbed by the liquid. At higher frequencies (e.g., above 100 MHz), the SAW dissipated into liquid decays more rapidly with much shorter decay lengths. Increasing the radio frequency (RF) frequencies of the devices resulted in an increased power threshold for streaming, pumping, and especially jetting, which is attributed to an increased absorption rate of acoustic wave energy. ZnO SAW devices could achieve similar streaming, pumping, and jetting effects as well as frequency effect, although the SAW signals are relatively weaker.

Experimental and numerical studies for nondestructive evaluation of human enamel using laser ultrasonic technique

In this paper, a nondestructive laser ultrasonic technique is used to generate and detect broadband surface acoustic waves (SAWs) on human teeth with different demineralization treatment. A scanning laser line-source technique is used to generate a series of SAW signals for obtaining the dispersion spectrum through a two-dimensional fast Fourier translation method. The experimental dispersion curves of SAWs are studied for evaluating the elastic properties of the sound tooth and carious tooth. The propagation and dispersion of SAWs in human teeth are also been studied using the finite element method. Results from numerical simulation and experiment are compared and discussed, and the elastic properties of teeth with different conditions are evaluated by combining the simulation and experimental results.

Nondestructive determination of interfacial adhesion property of low-k/Si by the surface acoustic waves

Nondestructive surface acoustic wave (SAW) technique promoted for interfacial adhesion investigation is employed to study the adhesion properties of both the porous and the dense low dielectric constant (low-k) films deposited on the silicon substrate. Spring boundary model is employed by introducing the parameters of distributed shear and normal spring constant per unit area (KT and KN) between the film and the substrate to take the adhesion property into account to calculate the theoretical SAW dispersion curves. Broadband SAW signals are generated by short pulse ultraviolet laser source and detected by a piezoelectric transducer. Interfacial adhesion properties of the low-k samples can be obtained by fitting the experimental dispersion curve with the theoretical ones. The smooth experimental dispersion curves with maximum frequency up to 150 and 200MHz are achieved for the porous and dense low-k samples, respectively. The determination result indicates that the adhesion property of dense low-k film is much better than that of the porous low-k sample used in this study. The determined adhesion result by SAW exhibits the same trend with the test of the nanoscratch.

Frequency dependence of laser ultrasonic SAW phase velocities measurements

Advances in the field of laser ultrasonics have opened up new possibilities in applications in many areas. This paper verifies the relationship between phase velocities of different materials, including hard solid and soft solid, and the frequency range of SAW signal. We propose a novel approach that utilizes a low coherence interferometer to detect the laser-induced surface acoustic waves (SAWs). A Nd:YAG focused laser line-source is applied to steel, iron, plastic plates and a 3.5% agar–agar phantom. The generated SAW signals are detected by a time domain low coherence interferometry system. SAW phase velocity dispersion curves were calculated, from which the elasticity of the specimens was evaluated. The relationship between frequency content and phase velocities was analyzed. We show that the experimental results agreed well with those of the theoretical expectations.

Numerical simulation and experimental study on surface acoustic waves interacting with cracks heated by scanning heating laser source

The influence on surface acoustic waves (SAWs) propagate through the micro-crack with partial closure is presented in this paper. Heating brought by laser irradiation causes the thermal expansion of the sample, which leads to partial closure of the micro-crack. The partial closure of crack impacts the transmission efficiency of acoustic pulses strongly. Detected SAWs signals are different when heating laser irradiates different regions, when the middle region of the crack is heated, the amplitude of SAWs signals reach the maximum value. Based on this, the experimental system for detecting micro-crack is set up. The crack can be detected effectively by scanning the laser heating source. The finite element method is applied to simulate the temperature rise and relative displacement of crack edges caused by laser irradiation. The relative displacement change with different location of heating laser source is also calculated. The results of numerical simulation and experiment coincide with each other.

Quantitative elastography provided by surface acoustic waves measured by phase-sensitive optical coherence tomography

We report on a quantitative elastography technique achieved by combining phase-sensitive optical coherence tomography (PhS-OCT) with the surface acoustic wave (SAW) method. Different from traditional optical coherence elastography, the elastography is achieved by impulse-stimulated SAW, rather than by shear waves. PhS-OCT serves not only as a detector to measure SAW signals but also as a means to provide a cross-sectional image of the sample. The experimental results indicate that the combination of PhS-OCT with SAW is feasible to provide quantitative elastography of heterogeneous tissue samples.

Emission and detection of surface acoustic waves by AlGaN/GaN high electron mobility transistors

Using integrated interdigital transducers (IDTs), we demonstrate the emission of surface acoustic waves (SAWs) by AlGaN/GaN high electron mobility transistors (HEMTs) under certain bias conditions through dynamic screening of the HEMTs vertical field by modulation of its two-dimensional electron gas. We show that a strong SAW signal can be detected if the IDT geometry replicates the HEMT electrode geometry at which RF bias is applied. In addition to characterizing SAW emission during both gate-source and drain-source modulation, we demonstrate SAW detection by HEMTs. Integrated HEMT-IDT structures could enable real-time evaluation of epitaxial degradation as well as high-speed, amplified detection of SAWs.

Young’s Modulus Detection for Ultra-Thin Film by LSAWs Technique with Wavelet and FIR Filter De-Noising

Laser-generated surface acoustic waves (LSAWs) technique is a feasible method to determine the Young’s modulus of thin films. The raw surface acoustic wave (SAW) signals detected from the experimental system are often contaminated by external noises. A novel de-noising method is proposed in this paper with wavelet and FIR filter. The wavelet threshold de-noising is essential to reduce the high frequency noise components in the raw SAW signals, while FIR filter can remove the useless low frequency noises. The useful bandwidth of the detected signal ranges from 50 to 190 MHz. Young’s modulus of the detected samples can be obtained by matching the experimental dispersive curves with the theoretical calculated ones via an improved least square fitting method. The Young’s moduli of four low dielectric constant (low-k) samples detected in the measurement are 7.1, 6.8, 1.1 and 1.0 GPa, respectively.

Elastic properties of soft tissue-mimicking phantoms assessed by combined use of laser ultrasonics and low coherence interferometry

Advances in the field of laser ultrasonics have opened up new possibilities in medical applications. This paper evaluates this technique as a method that would allow for rapid characterization of the elastic properties of soft biological tissue. In doing so, we propose a novel approach that utilizes a low coherence interferometer to detect the laser-induced surface acoustic waves (SAW) from the tissue-mimicking phantoms. A Nd:YAG focused laser line-source is applied to one- and two-layer tissue-mimicking agar-agar phantoms, and the generated SAW signals are detected by a time domain low coherence interferometry system. SAW phase velocity dispersion curves are calculated, from which the elasticity of the specimens is evaluated. We show that the experimental results agree well with those of the theoretical expectations. This study is the first report that a laser-generated SAW phase velocity dispersion technique is applied to soft materials. This technique may open a way for laser ultrasonics to detect the mechanical properties of soft tissues, such as skin.

The experimental study of fatigue crack detection using scanning laser point source technique

For the purpose of better understanding the interaction of Rayleigh wave and the fatigue crack in a metallic sample, a set of experimental setups is built, based on the scanning laser source (SLS) technique, utilizing a point source to take place of the line source to generate surface acoustic waves (SAWs), and an interferometer is to detect the SAWs signal. The information of the crack (such as position and length) can be obtained by utilizing a two-dimensional scan of the material surface. This paper focuses on the detection of visible and invisible fatigue crack by using this point-source-based scanning laser source technique, and comparing the results with those of conventional pitch-catch technique. The result shows that with two-dimensional scanning, and analyzing the amplitude of the generated SAWs, not only the visible fatigue can be identified, but also the invisible fatigue crack can be discriminated. As a result, the sensitivity of the scanning point laser source technique is higher than the conventional pitch-catch technique.

Numerical Study on Depth Gauging of Surface Breaking Defects Using Laser-Generated Surface Acoustic Waves

Laser-generated surface acoustic waves scattering from surface cracks of various depths and widths have been calculated by the finite element method, where a surface notch is introduced to represent a fatigue crack for the convenience of modeling. The bipolar Rayleigh waves have been captured clearly using this model, as the laser line source close to the surface crack. In addition, the numerical results demonstrate that there exist clear oscillation signals following the reflected Rayleigh waves, the temporal cycles of which are found to be dependent on only notch depth, the arrival time of which is related mainly to the width of the notch. Therefore, a new crack evaluation method based on the temporal characteristics of surface acoustic wave signals has been proposed and discussed in this paper, which is helpful for measuring the depth of surface cracks accurately.

Influence of intermediate hydrogel layer and amount of binding sites on the signal response of surface acoustic wave biosensors

Surface acoustic wave (SAW) devices based on horizontally polarized surface shear waves allow direct and label-free detection of biomolecules in real time. Binding reactions on SAW sensor surfaces are detected by determining changes in surface wave velocity caused mainly by mass loading or viscoelasticity changes in the sensing layer. In many cases, analyte-specific capture molecules or ligands are covalently bound on the sensor surface via an intermediate hydrogel layer. It is a fact that the SAW signal response strongly depends on the nature of the hydrogel matrix due to different relative changes of its acousto-mechanical parameters such as density and viscoelasticity. We studied the effect of different hydrogels in two affinity assays. One assay used a low amount of immobilized capture molecules, the other a high amount of immobilized ligands as binding sites in the sensing layer. Significant variations of the SAW signal response were observed. However, performing the assay with immobilized capture molecules resulted in decreasing signal height with increasing molar mass of the hydrogel whereas a reverse signal behavior was obtained performing the assay with immobilized ligands. This means that each affinity system requires its specific hydrogel matrix to obtain maximal signal response.

The Focused Beam Forming with a Monolithic 2D Phased Array

A new type of the monolithic acoustic scanner based on a near-surface quasicomposite two-dimensional array, implemented in the solid elastic substrate was proposed. It provides a simple means of focusing and scanning a beam of acoustic waves, radiated into the depth of the elastic solid substrate. A chirped surface acoustic wave is converted into a focused bulk wave by scattering from an array composed of a 2D periodic system of regions with varying material parameters, located at the surface of a surface acoustic waves substrate. In the paper, a simple numerical simulation model is presented to analyse the in∞uences of the dynamical and geometrical parameters of the surface structure, as well as the in∞uences of incident surface acoustic waves signal proflle on the focal distribution.

Surface Acoustic Waves in Reverse-Biased AlGaN/GaN Heterostructures

Properties of surface acoustic waves (SAWs) in reverse-biased AlGaN/GaN heterostructures on (0001) sapphire substrates were studied by examining the characteristics of SAW filters composed of interdigital Schottky and ohmic contacts. The fundamental and higher frequency SAW signals in measured -parameters were attributed to Rayleigh and Sezawa modes, respectively. The onsets of the SAW signals, which were close to the threshold voltage of HEMTs in the vicinities of the respective filters, changed in response to the spatial variation of the threshold voltage. The onset of Sezawa mode was deeper than that of Rayleigh mode, and the difference in onset was larger for longer SAW wavelengths. These results are possibly explained by the change of the input capacitance of interdigital transducers due to the reverse-bias voltages or by the difference in the distribution of SAW energy between the two modes.

Effect of photoacoustic generation mechanisms on transient grating measurements of thin films on silicon

Laser induced transient gratings technique is widely used for non-contact measurements of surface acoustic waves (SAWs). One major application of such measurements is characterization of thin films used in microelectronics. A peculiar phenomenon has been observed in transient gratings measurements of thin films on a silicon substrate: if the film is transparent, there is a systematic discrepancy between the measured and expected SAW velocity values that cannot be accounted for by instrumental errors. However, as soon as the sample is coated by an opaque metal film, the discrepancy disappears. In this presentation, we will show that the origin of the effect is in the competition of thermal and electronic mechanisms of the optical generation of sound in silicon. We will also describe another effect of the same origin observed on very thin semi-transparent metal films: at a certain film thickness, the SAW signal vanishes as the thermal expansion of the film and the contraction of silicon caused by photoexcited carriers cancel each other.

Influence of intermediate aminodextran layers on the signal response of surface acoustic wave biosensors

Surface acoustic wave (SAW) devices based on horizontally polarized surface shear waves enable direct and label-free detection of proteins in real time. Binding reactions on the sensor surface are detected by determining changes in surface wave velocity caused mainly by mass adsorption or change of viscoelasticity in the sensing layer. Intermediate hydrogel layers have been proven to be useful to immobilize capture molecules or ligands corresponding to the analyte. However, the SAW signal response strongly depends on the morphology of the hydrogel due to different relative changes of its acoustomechanical parameters such as viscoelasticity and density. In this work five aminodextrans (AMD) and one diamino polyethylene glycol (DA-PEG) were used as intermediate hydrogel layers. Sensors with immobilized streptavidin and samples containing biotinylated bovine serum albumin were used to exemplify affinity assays based on immobilized capture molecules for protein detection. The effects of the three-dimensional AMDs and the two-dimensional (2D) DA-PEG on the SAW signal response were investigated. The signal height decreased with increasing molar mass and increasing amount of immobilized AMD. Consequently, thin hydrogel layers are ideal to obtain optimum signal responses in this type of assay, whereas it is not necessarily a 2D hydrogel that gives the best results.

激光冲击硬化材料中的声表面波

Laser shock peening is a well-known method for extending the fatigue life of metal components by introducing near-surface compressive residual stress. The surface acoustic waves (SAWs) are dispersive when the near-surface properties of materials are changed. So the near-surface properties (such as the thickness of hardened layers, elastic properties, residual stresses, etc.) can be analyzed by the phase velocity dispersion. To study the propagation of SAWs in metal samples after peening, a more reasonable experimental method of broadband excitation and reception is introduced. The ultrasonic signals are excited by laser and received by polyvinylindene fluoride (PVDF) transducer. The SAW signals in aluminum alloy materials with different impact times by laser shock peening are detected. Signal spectrum and phase velocity dispersion curves of SAWs are analyzed. Moreover, reasons for dispersion are discussed.

SAW Filters Composed of Interdigital Schottky and Ohmic Contacts on AlGaN/GaN Heterostructures

We proposed surface acoustic wave (SAW) filters composed of interdigital Schottky and ohmic contacts on AlGaN/GaN heterostructures. The contribution of the SAWs appeared in the radio frequency characteristics of the filters when the Schottky contacts were reverse biased. Onsets of the SAW signals and the threshold voltage of simultaneously fabricated high-electron mobility transistors were found to almost agree with one another. We also obtained an isolation of >40 dB. These results suggest that SAW-based functional devices are likely to be realized using AlGaN/GaN heterostructures with interdigital Schottky and ohmic contacts