Surface Acoustic Wave Measurements Research Articles

Detection of Water Surface Acoustic Waves Using Sinusoidal Phase Modulation Interferometer and Prenormalized PGC-Arctan Algorithm

A sinusoidal phase modulation laser interferometer is proposed to detect water surface acoustic waves excited by underwater acoustic radiation, and an improved PGC-Arctan demodulation algorithm that combines prenormalization and Lissajous ellipse fitting is proposed to demodulate detection signals. In this paper, the effects of phase modulation depth, carrier phase delay, and interference signal visibility on the Lissajous figure formed by quadrature interference components are analyzed. The demodulation algorithm first uses the amplitudes of multiple Fourier spectral components of an interference signal to calculate the phase modulation depth C, and calculation of the carrier phase delay Vc is achieved through the introduction of a quadrature carrier signal. Then, certain coefficients regarding C and Vc are constructed for prenormalization of the two quadrature interference signal components to eliminate the local nonuniform widening phenomenon of Lissajous ellipse. Next, the outer and the inner contours are extracted from a uniformly widened Lissajous ellipse resulting from light intensity disturbance, and the axial ratio of the ellipse is obtained, which is used to correct the ratio of the quadrature interference signal to eliminate the effect of filter gain coefficients. At last, through the combination of an Arctan algorithm and a phase-unwrapping algorithm, high-precision demodulation of the interference signal is realized. A sinusoidal phase modulation interferometer was set up to detect water surface acoustic waves, and a series of detection experiments were carried out. The experiment results show that the detection method and demodulation algorithm described in this paper can accurately realize the measurement of weak water surface acoustic waves. The proposed algorithm shows less distortion in demodulation results, and its signal-to-noise distortion ratio is less than 20 dB at 500 Hz, which is significantly better than traditional algorithms. The experimental results demonstrate the effectiveness and accuracy of water surface acoustic wave detection using sinusoidal phase modulation interferometer.

Characteristics of TiN Thin Films Deposited by Substrate Temperature Variables Using Scanning Acoustic Microscopy

In this study, TiN thin films fabricated based on the substrate temperature process parameters of a DC magnetron sputtering device and their characteristics are analyzed. TiN thin films are deposited on Si wafer (100) substrates by setting the substrate temperatures to ambient temperature, 100, 200, and 300 °C. The residual stress measurement using the XRD method, adhesion characteristic analysis performed using a nanoscratch test to measure the critical load of the nanoindentation device, and leaky surface acoustic wave (LSAW) measurement were conducted using the V(z) technique of the ultrasonic microscope; the correlations between each measurement were analyzed. The residual stress of the TiN thin film was relieved by up to approximately 48% and adhesion properties enhanced by approximately 10% with an increase in the substrate temperature. In addition, the velocity of the LSAW presented a tendency to increase by up to approximately 5%. The residual stress and velocity of the LSAW were found to be inversely proportional, while the critical load and velocity of the LSAW were directly proportional.

Laser-based ultrasound interrogation of surface and sub-surface features in advanced manufacturing materials

Structures formed by advanced manufacturing methods increasingly require nondestructive characterization to enable efficient fabrication and to ensure performance targets are met. This is especially important for aerospace, military, and high precision applications. Surface acoustic waves (SAW) generated by laser-based ultrasound can detect surface and sub-surface defects relevant for a broad range of advanced manufacturing processes, including laser powder bed fusion (LPBF). In particular, an all-optical SAW generation and detection configuration can effectively interrogate laser melt lines. Here we report on scattered acoustic energy from melt lines, voids, and surface features. Sub-surface voids are also characterized using X-ray Computed Tomography (CT). High resolution CT results are presented and compared with SAW measurements. Finite difference simulations inform experimental measurements and analysis.

Optical polarimetric measurement of surface acoustic waves

A surface acoustic wave (SAW) is utilized in diverse fields ranging from physics, engineering, to biology for transducing, sensing, and processing various signals. Optical measurement of the SAW provides valuable information since the amplitude and the phase of the displacement field can be measured locally with the resolution limited by the spot size of the optical beam. So far, optical measurement techniques rely on modulation of the optical path, phase, or diffraction associated with SAWs. Here, we demonstrate that SAWs can be measured with an optical polarimeter. We show that the slope of the periodically tilting surface due to the coherently driven SAW is translated into the angle of polarization rotation, which can be straightforwardly calibrated when polarimeters work in the shot-noise-limited regime. The polarimetric measurement of SAWs is, thus, beneficial for quantitative studies of SAW-based technologies.

Nondestructive Evaluation of Electroplating-Induced Hydrogen Embrittlement in Cadmium-Coated High-Strength Steel Using Ultrasonic Surface Waves

Development of a nondestructive evaluation (NDE) method to detect nascent hydrogen embrittlement (HE) in electroplated high-strength steel parts is becoming important for the aerospace industry. This research investigates the feasibility of surface acoustic waves (SAWs) measurements to distinguish between cadmium (Cd) plated SAE 4340 steel samples with low and high HE susceptibilities. SAWs were generated with a 10 MHz piezoelectric transducer and detected by line scans via a laser Doppler vibrometer setup. Using signal processing algorithms in MATLAB, SAW velocities as well as attenuation coefficients were estimated. Depth profiles of steel hardness near coatings were also evaluated using Vickers microindentation tests. Average steel hardness in not-baked samples was slightly increased. Cd coatings were characterized by laser and optical microscopy methods. Small variations found in thickness and surface roughness of the Cd coatings among the samples did not significantly affect the NDE results. On average, samples in the not-baked condition (high HE risk) exhibited lower SAW attenuation coefficients compared to immediately baked and late-baked conditions (low HE risk). However, it was not possible to distinguish between the manufacturing conditions of individual samples due to overlaps in attenuation measurement results. SAW velocities as estimated by the cross-correlation method were found to be not sensitive to manufacturing conditions.

Effect of Liquid Crystalline Host on Structural Changes in Magnetosomes Based Ferronematics.

The effect of the liquid crystalline host on structural changes in magnetosomes based on ferronematics is studied using the surface acoustic wave (SAW) technique supported by some capacitance and light transmission measurements. The measurement of the attenuation response of SAW propagating along the interface between LC and the piezoelectric substrate is used to study processes of structural changes under magnetic field. The magnetosome nanoparticles of the same volume concentration were added to three different nematic LCs, 5CB, 6CB, and E7. Unlike to undoped LCs, the different responses of SAW attenuation under the influence of magnetic and electric fields in LCs doped with magnetosomes were observed due to characteristic structural changes. The decrease of the threshold field for doped LCs as compared with pure LCs and slight effects on structural changes were registered. The threshold magnetic fields of LCs and composites were determined from capacitance measurements, and the slight shift to lower values was registered for doped LCs. The shift of nematic-isotropic transition was registered from dependencies of SAW attenuation on temperature. The acoustic anisotropy measurement approved the previous supposition about the role of bulk viscosity in used SAW measurements. In addition, capacitance and light transmition investigations supported SAW results and pointed out conclusions about their magnetic field behavior. Obtained results are discussed and confronted with previous ones and coincide well with those observed using acoustic, optical, or dielectric techniques.

Lateral resolution limit of laser Doppler vibrometer microscopes for the measurement of surface acoustic waves

The lateral or transverse resolution of single-point interferometers for vibration measurement is especially critical for microelectromechanical systems (MEMS) vibrating up to the gigahertz range. In this regime, the acoustic wavelengths are typically in the range of the size of the laser focus. Thus, a successful vibration measurement requires distinct knowledge about the lateral resolution limit and its dependencies with instrumentation parameters. In this paper, we derive an analytic approximation formula, which allows for estimation of the systematic measurement deviation of the vibration amplitude and, thus, a definition of the lateral resolution limit of single-point interferometers for vibration measurement. Further, a compensation and an optimum numerical aperture are proposed the reduce the measurement deviation. For this, the model includes a laser-interferometer microscope of Mach-Zehnder type with Gaussian laser beams considering the Gouy effect and wavefront curvature. As a measurement scenario, an unidirectional surface acoustic wave (SAW) is regarded. The theoretic findings have been validated in the experiment with a representative vibration measurement on a SAW filter at 433,{mathrm {MHz}} with our heterodyne laser-Doppler interferometer with offset-locked semiconductor lasers. The provided formulas help instrument designers and users to choose suitable instrument parameters, especially the numerical aperture of the utilized microscope objective.

Langasite as Piezoelectric Substrate for Sensors in Harsh Environments: Investigation of Surface Degradation under High-Temperature Air Atmosphere.

Langasite crystals (LGS) are known for their exceptional piezoelectric properties at high temperatures up to 1000 °C and more. In this respect, many studies have been conducted in order to achieve surface acoustic wave (SAW) sensors based on LGS crystals dedicated to high-temperature operations. Operating temperatures of more than 1000 °C and 600 °C for wired and wireless sensors, respectively, have been reached. These outstanding performances have been obtained under an air atmosphere since LGS crystals are not stable in high-temperature conditions under a low-oxygen atmosphere due to their oxide nature. However, if the stability of bulk LGS crystals under a high-temperature air atmosphere is well established, the surface deterioration under such conditions has been hardly investigated, as most of the papers dedicated to LGS-based SAW sensors are essentially focused on the development of thin film electrodes that are able to withstand very elevated temperatures to be combined with LGS crystals. Yet, any surface modification of the substrate can dramatically change the performance of SAW sensors. Consequently, the aim of this paper is to study the stability of the LGS surface under a high-temperature air environment. To do so, LGS substrates have been annealed in an air atmosphere at temperatures between 800 and 1200 °C and for durations between one week and one month. The morphology, microstructure, and chemical composition of the LGS surface was examined before and after annealing treatments by numerous and complementary methods, while the surface acoustic properties have been probed by SAW measurements. These investigations reveal that depending on both the temperature and the annealing duration, many defects with a corolla-like shape appear at the surface of LGS crystals in high-temperature prolonged exposure in an air atmosphere. These defects are related to the formation of a new phase, likely an oxiapatite ternary compound, the chemical formula of which is La14GaxSi9−xO39−x/2. These defects are located on the surface and penetrate into the depth of the sample by no more than 1–2 microns. However, SAW measurements show that the surface acoustic properties are modified by the high-temperature exposure at a larger deepness of at least several tens of microns. These perturbations of the LGS surface acoustic properties could induce, in the case of LGS-based SAW sensors operating in the 434 MHz ISM band, temperature measurement errors around 10 °C.

Research on Temperature Monitoring Method and System Design for Key High Voltage Equipment of Wind Farm

This paper focuses on the temperature detection of high-voltage equipment in wind power plant, puts forward the surface acoustic wave measurement method, and deeply studies the design process of surface acoustic wave sensor device and the design scheme of monitoring system. In different process materials of piezoelectric substrate and antenna design mode, there will be great differences in the transmission efficiency and anti-interference ability of surface acoustic wave. Therefore, the influence of surface acoustic wave on the performance of surface acoustic wave sensor device is possible Testing and setting the surface measurement parameters can improve the measurement performance. In the aspect of detection system, the typical key temperature monitoring equipment of high voltage switch cabinet in wind farm is selected to form a practical deployment scheme, which realizes the integrated functions of automatic temperature measurement, parameter optimization and adjustment, alarm and so on. The research and design method in this paper has great practical application value in the operation and control of new energy system.

Love wave transference in piezomagnetic layered structure guided by an imperfect interface

The problem presents an analytical study of the wave transference in piezo-composite layer lying over an elastic substrate. The interface of the geometry is assumed to be imperfect. The imperfection is characterized by Linear Spring Model. Dynamics of the media taken are framed in form of direct Sturm–Liouville problem. Dispersion relations are found for both magnetically open and magnetically short case. Velocity profile of Love wave has been delineated through graphs for different affecting parameters (i.e., imperfection at the interface, layer thickness and heterogeneity in the substrate). It has been shown that the increase in these parameters increases the phase velocity of the Love wave. Further, layer thickness is noted to have a less effect on the velocity profile of the wave as compared to heterogeneity in the substrate. Moreover, a comparative study has been shown between the aforementioned cases with the variation in imperfect parameter. The velocity in open case is found to be higher than that of short case. The obtained results may provide guidance towards optimization of Surface Acoustic Wave devices and measurement of imperfections.

Super-resolution measurement method for passive wireless resonant surface acoustic wave sensor

PurposeThis study aims to use resonant surface acoustic wave (SAW) sensors, which have advantages in the harsh application environments, to measure different physical parameters such as temperature, pressure and force. For SAW sensors, the locality in measurement resolution by the effective time is poor, it cannot give the detailed results of SAW echoes.Design/methodology/approachTo promote the application of SAW sensor, this paper proposes a convex program-based super-resolution measurement method to recover the missing spectral line and enhance frequency resolution.FindingsThe proposed method reduces the reliance on effective time and improves the measurement resolution of SAW sensors. The performance was validated by experiments.Originality/valueThe limited resolution capability restricts the benefit of SAW technology in harsh environments. The proposed method shed light on SAW measurement resolution increase, exploiting its full potential and leading to commercial applications.

Nanoscale thermal transport and elastic properties of lithiated amorphous Si thin films

Silicon is the heart of modern electronics and due to it is high theoretical storage capacity it also attracted much attention as a possible anode material for the next generation Li-ion batteries. Heat conduction is one of the major properties in the development of Li-ion batteries for energy conversion systems and it is of paramount importance to have comprehensive understanding of heat dissipation on the scale of electrochemical storage device. In this work we report ex-situ study of nanoscale thermal transport and elastic properties of lithiated amorphous Si (a-Si) anode films using picosecond time-domain thermoreflectance (TDTR). Radio frequency (rf) magnetron sputtering was used to deposit a ∼330 nm thick a-Si films on glass substrate. Near-surface nanoscale thermal transport measurements show 40% increase in thermal conductivity of a-Si upon electrochemical lithiation reaching up to 2.2 W m-1K−1. This sizeable increase might be due to Li+ ion-mediated heat conduction during lithiation process. The standard deviation of measured thermal conductivity was slightly higher likely due to inhomogeneous lateral and cross-plane Li+ ions distribution in the sub-surface film region. Nanosecond laser pulsed induced surface acoustic waves (SAWs) measurements showed the decrease in Young’s modulus after lithiation on nanometre scale, which is attributed to volumetric expansion of Si upon Li+ ions insertion.

Holographic measurement of surface acoustic wave parameters in crystals

The theoretical basis of a specialized technique for applying digital holographic interferometry to measure the parameters of surface acoustic waves is presented, a measuring system for visualization and quantitative analysis of the parameters of ultralow-amplitude high-frequency oscillations arising in electronic devices using surface acoustic waves is developed, and experimental results of the study of surface acoustic waves in crystals of lithium niobate are obtained. In this case, to ensure the possibility of recording precision double-exposure interferograms of high-frequency surface acoustic waves, a picosecond pulsed laser with two-stage frequency multiplication was used as a radiation source, and to increase the spatial resolution of the system with the possibility of observing a wide field of view, an adjustable optical zoom of the incoming image was applied to the matrix input (based on charge-coupled devices) of the recording camera and digital zoom was used for obtained interferogram. We achieved the measuring sensitivity of the surface acoustic waves amplitude and spatial-temporal resolution allowing visualization and measurement of surface acoustic waves with amplitudes of the order of 1 nm and frequencies of the order of 10 MHz, which is far beyond the capabilities of standard methods of holographic interferometry.

Surface acoustic wave pressure sensor and its matched antenna design

Interdigital transducer and signal transmission in surface acoustic wave pressure sensor design is one of the difficulties in sensor design. The transmission antenna is an important design indicator to determine the wireless function of the sensor. In this paper, we simulated the design of the interdigital transducer of surface acoustic wave pressure sensor through COMSOL and analyzed the relationship between the eigenfrequency of the single-pair interdigital model and the interdigital electrode. Then, we obtained the design of the interdigital electrode with error of 0.01 MHz. We also simulated the size, bandwidth, impedance matching, and other parameters of antenna through high frequency structure simulator, and a matching dipole transmission antenna was designed and miniaturized. When the bandwidth is satisfied, the control matching impedance error is within [Formula: see text], and it is verified that the antenna satisfies the signal transmission requirement of the surface acoustic wave pressure sensor. This design provides a more comprehensive approach to the design of interdigital transducers and signal transmission for the field of surface acoustic wave measurement pressure.

AlN/GaN/Sapphire heterostructure for high-temperature packageless acoustic wave devices

Surface acoustic waves (SAW) technology is very promising to achieve wireless sensors able to operate in high temperature environments up to possibly 1000 °C. However, there is currently a bottleneck related to the packaging of such sensors. The current high-temperature packaging solutions can withstand 600 °C at most. This limitation could be overtaken by the development of packageless devices, based on the waveguiding layer acoustic waves (WLAW) principle. In such devices, the acoustic wave is confined inside an inner layer and is then isolated from undesired surface perturbations like dust deposition.In this paper, we investigate the performance of an AlN/IDT/GaN/Sapphire WLAW device used as a temperature sensor able to operate up to 500 °C. After validating a room-temperature GaN material constant set with basic SAW measurements performed on IDT/GaN/Sapphire structure, the AlN/IDT/GaN/Sapphire device is simulated to determine the optimal relative thicknesses of AlN and GaN films in order to obtain a good wave confinement. Based on these calculations, an experimental WLAW device is performed and electrically characterized. The full wave confinement is experimentally confirmed by the lamination of an acoustic absorber on top of the device: no change in the scattering parameters was observed. The WLAW device is then electrically characterized between the ambient temperature and 500 °C. A temperature coefficient of frequency (TCF) value of −34.6 ppm/°C is obtained, demonstrating the potential of the WLAW AlN/IDT/GaN/Sapphire structure as a packageless temperature sensor. Finally, the theoretical TCF of the AlN/IDT/GaN/Sapphire structure was numerically calculated by changing the material constants of AlN, GaN and Sapphire according to the temperature coefficients available in the literature. The theoretical and experimental data were found in good accordance.

Local activation of surface and hybrid acoustic waves in optical microwires.

Elastic vibrations in subwavelength structures have gained importance recently in fundamental light-matter studies and various optoacoustic applications. Existing techniques have revealed the presence of distinct acoustic resonances inside silica microwires yet remain unable to individually localize them. Here, we locally activate distinct classes of acoustic resonances inside a tapered fiber using a phase-correlation distributed Brillouin method. Experimental results verify the presence of surface and hybrid acoustic waves at distinct fiber locations and demonstrate, to the best of our knowledge, the first distributed surface acoustic wave measurement. This technique is important for understanding properties of optoacoustic interactions and enabling designs of novel optomechanical devices.

Measurement of surface acoustic wave resonances in ferroelectric domains by microwave microscopy

Surface Acoustic Wave (SAW) resonances were imaged within a closed domain in the ferroelectric LiTaO3 via scanning Microwave Impedance Microscopy (MIM). The MIM probe is used for both SAW generation and measurement, allowing the contact-less measurement within a mesoscopic structure. Measurements taken over a range of microwave frequencies are consistent with a constant acoustic velocity, demonstrating the acoustic nature of the measurement.

Measurement of surface acoustic waves in high-frequency ultrasound: Preliminary results.

Skin lesions change elastic properties near the surface. In the last decades, several non-invasive elastography techniques have been developed for detecting the mechanical properties of tissue. In particular, harmonic elastography is characterized for inducing shear wave propagation by an external vibrator in order to estimate shear modulus. However, near the boundary region, propagation is governed by surface acoustic waves (SAW). This paper combines crawling waves elastography with a high-frequency ultrasound (HFUS) system for the estimation of the SAW-to-shear compensation factor when ultrasound (US) gel is used as coupling interface. Experiments explore the SAWspeed in a homogeneous phantom with a solid-water interface in order to corroborate theoretical findings. Subsequently, experiments in a solid-US gel interface are conducted in order to find the correct compensation factor. Preliminary results suggest that SAW propagation can be detected using HFUS, and shear velocity maps can be generated by applying the estimated empirical correction factor. This study will potentially avoid the underestimation of shear modulus when using SAW-based HFUS elastography which is promising for the better diagnosis of skin diseases.

Charge metastability and hysteresis in the quantum Hall regime

We report simultaneous quasi-dc magnetotransport and high frequency surface acoustic wave measurements on bilayer two-dimensional electron systems in GaAs. Near strong integer quantized Hall states a strong magnetic field sweep hysteresis in the velocity of the acoustic waves is observed at low temperatures. This hysteresis indicates the presence of a metastable state with anomalously high conductivity in the interior of the sample. This non-equilibrium state is not revealed by conventional low frequency transport measurements which are dominated by dissipationless transport at the edge of the 2D system. We find that a field-cooling technique allows the equilibrium charge configuration within the interior of the sample to be established. A simple model for this behavior is discussed.

Assessment of Thermal Aging of Aluminum Alloy by Acoustic Nonlinearity Measurement of Surface Acoustic Waves

ABSTRACTAcoustic nonlinearity measurements via contact and noncontact generations of surface acoustic waves (SAWs) were performed in order to characterize the thermal aging of aluminum alloy. The experiments were conducted on aluminum alloy samples (Al6061-T6) that were heat-treated at 220°C for different times (0 min, 20 min, 40 min, 1 h, 2 h, 10 h, 100 h, 1,000 h) and thus had the different levels of thermal aging. The acoustic nonlinearity of the specimens in two types of SAWs was observed according to the thermal aging. The fractional changes in the acoustic nonlinearity exhibited similar trends in both contact and noncontact SAWs, showing that the acoustic nonlinearity measurement via SAWs is independent of the SAW-excitation method. Furthermore, the fractional changes agreed well with the variation in the yield strength, which was a minimum when the acoustic nonlinearity reached its first peak. Then, the acoustic nonlinearity drastically dropped while the yield strength increased to its highest value. Thus, the variation in the acoustic nonlinearity can be perceived as an indicator of the aging level. These results demonstrate the potential feasibility of acoustic nonlinearity measurements via SAWs for the nondestructive evaluation of material degradations.