Surface Acoustic Wave Velocity Research Articles

Single-Ended Surface Acoustic Wave Pressure Resonators

Abstract Surface acoustic wave (SAW) sensors exhibit advantageous attributes for pressure detection, including compact dimensions, cost-effectiveness, facile integration, elevated sensitivity, and a high quality factor (Q value). In this study, the single-ended resonant configuration of SAW pressure sensing element based on ST-X cut quartz was simulated and fabricated. The influence of the interdigitated transducer (IDT) and applied pressure on the resonance frequency of SAW were simulated and analyzed. The designed phase velocity (3159.344 m/s) without IDT is closest to the theoretical phase velocity (3158 m/s) of SAW propagation in the substrate, and the relative error is about 0.043%. The designed phase velocity of SAW dropped to 3149.198 m/s due to the loading of the IDT mass. With an increase in applied pressure from 0 to 350 kPa, the resonance frequency of the SAW decreases from 157.05 to 154.02 MHz, yielding a maximum linear pressure sensitivity of approximately 8.6 kHz/kPa. The measured center frequencies of the fabricated single-ended SAW devices are predominantly clustered around 157 MHz, exhibiting a deviation of 0.46 MHz from the simulated results. The present work establishes a foundation for subsequent experimental investigations into pressure sensing.

Application of Graphene in Acoustoelectronics.

An interdigital transducer structure was fabricated from multilayer graphene on the surface of the YZ-cut of a LiNbO3 ferroelectric crystal. The multilayer graphene was prepared by CVD method and transferred onto the surface of the LiNbO3 substrate. The properties of the multilayer graphene film were studied by Raman spectroscopy. A multilayer graphene (MLG) interdigital transducer (IDT) structure for surface acoustic wave (SAW) excitation with a wavelength of Λ=60 μm was fabricated on the surface of the LiNbO3 crystal using electron beam lithography (EBL) and plasma chemical etching. The amplitude-frequency response of the SAW delay time line was measured. The process of SAW excitation by graphene IDT was visualized by scanning electron microscopy. It was demonstrated that the increase in the SAW velocity using graphene was related to the minimization of the IDT mass.

ELECTROMECHANICAL PROGRAMMER FOR ACOUSTOELECTRONIC SENSORS OF PHYSICAL QUANTITIES

An electromechanical programmer is described, intended for programming an acoustoelectronic angular displacement meter, constructed on the basis of the effect of dependence of the phase velocity of surface acoustic waves on the direction of propagation relative to the crystallographic axis of a piezoelectric sound conductor.

Modeling acoustic characteristics of artificial bone alloys for medical and surgical use under thermodynamic conditions

The study examines the impact of porosity on mechanical, acoustic, and behavioral properties of (Ti-6Al-4 V alloy) alloys, which are manufactured to mimic human bones. It investigates how porosity, controlled through factors like pressure, particle size, and temperature during sintering, affects properties such as modulus of elasticity, surface acoustic wave (SAW) velocities, hardness coefficients, and acoustic resistance.The findings suggest that different levels of porosity at varying sintering temperatures significantly alter the dynamic elastic modulus of the alloys. Specifically, increasing porosity values seem to correlate with a decrease in elastic constants, elastic modulus values, and surface acoustic wave types. This phenomenon may be attributed to the transitional crystalline structure phases of Ti6Al4V alloy and the manufacturing process.Remarkably, the study concludes that these (Ti-6Al-4 V alloy) alloys exhibit superior porosity, mechanical, and acoustic qualities compared to various types of human bone, including cortical, trabecular, and cancellous bone.

Generation of GHz surface acoustic waves in (Sc,Al)N thin films grown on free-standing polycrystalline diamond wafers by plasma-assisted molecular beam epitaxy

Abstract Telecommunication of the next generation demands filters that can operate in the 10 GHz range with sufficient bandwidths. For surface-acoustic-wave (SAW) devices this prerequisite translates into high sound velocities and high piezoelectric couplings. Wurtzite AlN on diamond, which exploits the strong piezoelectricity of AlN with the very high SAW velocity of diamond, has been considered a promising platform. A significant boost (up to a factor of 4) of the piezoelectric response can be obtained by alloying AlN with Sc. Here, the main challenge lies in the synthesis of highly-oriented thin (Sc,Al)N films on diamond. In this work, we aim at establishing a platform for SAW devices using plasma-assisted molecular beam epitaxy for the deposition of Sc0.2Al0.8N on diamond. We investigate the structural properties related to SAW generation gearing towards applications at high frequencies. To this end, we prepare (Sc,Al)N thin films using plasma-assisted MBE on polished polycrystalline diamond wafers and demonstrate the efficient generation of SAW modes with frequencies up to 8 GHz. Systematic studies of the dependence of the SAW velocity and electromechanical coupling coefficient on the Sc0.2Al0.8N film thickness is presented for various SAW modes. Our result demonstrates the potential of this material combination for future application that requires large bandwidth in the ultra-high frequency range.

Design and Characterization of SAW-Based Wireless and Passive Temperature Sensing System

Abstract The Surface Acoustic Wave (SAW) temperature sensor has received significant attention due to its wirelessly-powered, battery-free, and chipless capabilities. This paper proposes a wireless sensing system comprising a one-port SAW resonator, antennas, and transceiver circuit. The SAW resonator utilized in this system was based on Aluminum Nitride (AlN) thin film, which exhibits high SAW velocity and excellent piezoelectric properties. To completely investigate the performance of the SAW resonator, simulation and experiments were conducted. Upon connecting the SAW sensor to the temperature sensing system via the antenna, the reflection peak of the SAW resonator was clearly observed in the spectrum of the return signal. Additionally, during the temperature tests, the response frequency displayed almost linear behavior as the temperature increased from 30°C to 150°C. The fitted temperature coefficient of frequency (TCF) was 30.68ppm/°C, indicating that the wireless temperature sensing system has high temperature sensitivity.

Evaluation of surface corrosion damage in thin plates by Zero-Group Velocity Lamb waves based on PVDF comb transducers

This paper introduces a novel method for assessing surface corrosion damage in thin plates by leveraging the high sensitivity of Zero-Group Velocity (ZGV) Lamb waves and the versatility of polyvinylidene fluoride (PVDF) comb transducers. Theoretical analyses of ZGV Lamb wave modes and their differentiation from thickness vibration modes were conducted. The functionality and utility of the PVDF comb transducer tailored for the specific S1-ZGV mode were assessed. Experimental findings demonstrate that the PVDF comb transducer efficiently excites and captures the S1-ZGV mode, enabling effective assessment of surface corrosion damage in thin aluminum plates. Compared to the variations in wave velocity of surface acoustic waves (SAW) and the S1-ZGV frequency, the spectral amplitude at the initial S1-ZGV frequency exhibits a monotonically decreasing trend with increasing corrosion levels, proving to be more sensitive and reliable for evaluating surface corrosion damage. This research offers theoretical underpinnings and experimental validation for damage assessment using ZGV Lamb waves with the PVDF comb transducer, showcasing significant potential for practical engineering applications.

Microstructural and material property changes in severely deformed Eurofer-97

Severe plastic deformation changes the microstructure and properties of steels, which may be favourable for their use in structural components of nuclear reactors. In this study, high-pressure torsion (HPT) was used to refine the grain structure of Eurofer-97, a ferritic/martensitic steel. Electron microscopy and X-ray diffraction were used to characterise the microstructural changes. Following HPT at room temperature to a maximum shear strain of 230, the average grain size reduced by a factor of ∼30, with a marked increase in high-angle grain boundaries. Dislocation density also increased by more than one order of magnitude. The thermal stability of the deformed material was investigated via in-situ annealing during synchrotron X-ray diffraction. This revealed substantial recovery between 450 K – 800 K. Irradiation with 20 MeV Fe-ions to ∼0.1 dpa caused a 20% reduction in dislocation density compared to the as-deformed material. However, HPT deformation prior to irradiation only had a minor effect in mitigating the irradiation-induced reductions in thermal diffusivity and surface acoustic wave velocity of the material. Microstructural and material property changes are dominated by deformation compared to irradiation. In light of this, the benefits of using HPT to improve the irradiation resistance of Eurofer-97 are limited. These results provide a multi-faceted view of the changes in ferritic/martensitic steels due to severe plastic deformation, and how these changes can be used to alter material properties.

Probing phonon focusing, thermomechanical behavior, and moiré patterns in van der Waals architectures using surface acoustic waves

Surface acoustic waves (SAWs) propagate along solid-air, solid-liquid, and solid-solid interfaces. Their characteristics depend on the elastic properties of the solid. Combining transmission electron microscopy (TEM) experiments with molecular dynamics (MD) simulations, we probe atomic environments around intrinsic defects that generate SAWs in vertically stacked two-dimensional (2D) bilayers of MoS2. Our joint experimental-simulation study provides insights into SAW-induced structural and dynamical changes and thermomechanical responses of MoS2 bilayers. Using MD simulations, we compute mechanical properties from the SAW velocity and thermal conductivity from thermal diffusion of SAWs. The results for Young’s modulus and thermal conductivity of an MoS2 monolayer are in good agreement with experiments. The presence of defects, such as nanopores which generate SAWs, reduces the thermal conductivity of 2D-MoS2 by an order of magnitude. We also observe dramatic changes in moiré patterns, phonon focusing, and cuspidal structures on 2D-MoS2 layers.

Metamaterial control of the surface acoustic wave streaming jet

The phenomenon of surface acoustic wave (SAW) streaming, where a streaming jet is created, occurs when an SAW propagating on the surface of a solid interacts with water, and underpins the increasingly important area of SAW microfluidics. A key characteristic of the streaming jet is the Rayleigh angle, i.e. the angle at which the jet is formed relative to the surface normal of the solid, which is determined by the ratio of the velocity of the acoustic wave in the fluid and in the solid. Although the ability to dynamically tune this angle would offer a novel tool for microfluidic control, the SAW velocity is normally fixed by the characteristics of the solid and liquid material properties. In this paper we show, using finite element method modelling, that changing the SAW Rayleigh wave phase velocity by patterning a metamaterial array, consisting of square annular holes, onto the surface of an SAW device can change the acoustic streaming Rayleigh angle by approximately a factor of two, in good agreement with calculations based on the change in velocity.

Remote measurement of material elastic property at elevated temperature with grating laser ultrasonic testing

ABSTRACT As a pivotal elastic property, elastic modulus plays a crucial role in characterising the mechanical performance of materials. To achieve the convenient and remote measurement of the elastic modulus of materials at elevated temperatures, a method based on diffracted grating laser-induced narrowband surface acoustic waves (SAW) is proposed. The design scheme of the diffraction grating is disclosed, and a CCD camera is deployed to confirm the generated grating pattern and determine the actual grating period. Delving into the viability of an effortless and reliable procedure for calculating elastic modulus is discussed. The elastic modulus determined by the SAW does not depend on the exact Poisson’s ratio, which can be calculated from the SAW velocity with a given, less precise value for Poisson’s ratio. Experimental results of the three metals are in line with the reference values, and the elastic modulus at elevated temperature is successfully measured remotely, thereby verifying the feasibility of the proposed method.

Growth of ferroelectric lithium niobate-tantalate LiNb(1-x)TaxO3 crystals

Congruent and stoichiometric ferroelectric lithium niobate-tantalate crystals LiNb(1-x)TaxO3 of different compositions were grown by the Czochralski method. The stoichiometric crystals were grown using the top seeded solution growth method using LiWO4, which increases the Li content in the melt and in the grown crystal. Also, the use of a solvent can significantly reduce the temperature of the melt. The composition of the crystals was studied by inductively coupled plasma mass spectrometry using laser ablation, which allow studying the change in the composition of the grown crystals along the length and diameter. It is demonstrated that the content of Ta in the crystals exceeds the content of Ta in the initial charge, i.e., in the process of crystal growth, the melt becomes depleted in Ta. It is shown that the Ta content decreases along the crystal length due to the decrease in the Ta content in the melt. In the LiNb0.88Ta0.12O3 crystals, the piezoelectric moduli d22 and d33, and the velocities of bulk and surface acoustic waves were measured. The values of piezoelectric moduli and acoustic wave velocities are shown to occupy an intermediate position between LiNbO3 and LiTaO3 crystals.

Asynchronous STW resonators with the high quality factor and reduced sizes

Surface transverse waves (STW) on quartz have the high propagation velocity, which is higher by 60% than velocity of the Rayleigh surface acoustic waves (SAW), high temperature stability comparable with temperature stability of SAW on quartz. Those advantages allow successfully use STW in the high frequency resonators. However, a large number of the electrodes 400 in the reflectors is required to ensure the high quality factor of the resonators. This leads to increase the resonators sizes, especially on the frequencies < 1000 MHz. The 500-1000 MHz STW resonators with high quality factor on 36°YX90° cut quartz and reduced size were presented. Use of the asynchronous topology, constructional, topological and technological optimization with a computer simulation on the base of a equivalent circuit model allowed obtain in the frequency range of 500-1000 MHz the high quality factor of 8600-9500, reduced sizes of the topology in comparison with the known prototypes and place the resonators in the 3×3×1.2 mm and 5×5×1.8 mm SMD packages. The developed STW resonators with high quality factor and reduced sizes will be widely used in the miniature low noise oscillators.

The generation of large-amplitude surface acoustic waves induced by a moving laser source

This letter focuses on the non-contact generation of surface acoustic waves by using a continuous wave laser moving along the sample surface. The desired large-amplitude surface acoustic waves can be generated efficiently if the laser moving speed matches the Rayleigh value, which is a typical characteristic of the continuous laser moving excitation method. The different amplitudes of surface acoustic waves were generated at different laser moving speeds, and the largest amplitude occurred when the laser moving speed approached the surface acoustic wave velocity of the material. Subsequently, the influence of laser moving distance on the wave’s amplitude under Rayleigh resonance conditions was investigated. The surface acoustic waves’ amplitude grew linearly with the laser’s moving distance in the elastic range. In brief, this paper provides a novel method to excite large amplitude surface acoustic waves by simply changing the moving speed and moving distance of the light.

Improved Crystallinity of Annealed 0002 AlN Films on Sapphire Substrate

AlN is a piezoelectric material used in telecommunication applications due to its high surface acoustic wave (SAW) velocity, stability, and mechanical strength. Its performance is linked to film quality, and one method to achieve high-quality films goes through the process of annealing. Consequently, c-orientated AlN film with a thickness of 1.1 μm deposited on sapphire was annealed at temperatures of 1100 °C and 1150 °C in a N2 controlled atmosphere. This was compared to annealing at 1100 °C, 1450 °C, and 1700 °C with N2 flow in an open atmosphere environment. Sample rotation studies revealed a significant impact on the ⍵-2θ X-ray rocking curve. A slight variation in the film crystallinity across the wafer was observed. After the annealing, it was found that the lattice parameter c was increased by up to 2%, whereas the screw dislocation density dropped from 3.31 × 1010 to 0.478 × 1010 cm-2, and the full width at half maximum (FWHM) of reflection (0002) was reduced from 1.16° to 0.41° at 1450 °C. It was shown that annealing in a N2-controlled atmosphere plays a major role in reducing the oxidation of the AlN film, which is important for acoustic wave devices where the electrodes are placed directly on the piezoelectric substrate. The face-to-face arrangement of the samples could further reduce this oxidation effect.

Measurement of temperature dependent shear modulus using frequency dependent SAWs ToF delay in laser-induced temperature gradient

Phase velocity of surface acoustic waves(SAWs) is frequency dependent when propagate on medium with inhomogeneous elasticity over depth. In this work, frequency dependent Time-of-Flight (ToF) variation of SAWs induced by a local and dynamic heating was applied for measurement of temperature dependent shear modulus. Laser-generated broad-band SAWs propagated through the material with elastic properties and density modified by dynamic inhomogeneous temperature field induced by a millisecond laser heating. Sample with spatial dependent material properties introduces phase velocity dispersion in the SAW propagation. As consequence, ToF of SAW becomes frequency dependent. Frequency dependent ToF variation curves at two time instants respected to laser heating were measured by time–frequency analysis together with a differential technique. Free fitted parameters, temperature dependent shear modulus and surface temperature distribution were evaluated by solving the inverse problem by fitting the experimental ToF variation curves into the theoretical ones by means of the differential evolution method. The inversed temperature dependent parameter of shear modulus of Ti–6Al–4V alloy was in good agreement with literature value.

Coexistence of two hole phases in high-quality p−GaAs/AlGaAs in the vicinity of Landau-level filling factors ν=1 and ν=(1/3)

We focused on the transverse AC magnetoconductance of a high-mobility $p$-GaAs/AlGaAs quantum well $(p=1.2\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{cm}}^{\ensuremath{-}2})$ in the vicinity of two values of the Landau-level filling factor $\ensuremath{\nu}$: $\ensuremath{\nu}=1$ (integer quantum Hall effect) and $\ensuremath{\nu}=1/3$ (fractional quantum Hall effect). The complex transverse AC conductance ${\ensuremath{\sigma}}_{xx}^{\mathrm{AC}}(\ensuremath{\omega})$ was found from simultaneous measurements of attenuation and velocity of surface acoustic waves propagating along the interface between a piezoelectric crystal and the two-dimensional hole system under investigation. We analyzed both the real and imaginary parts of the hole conductance and compared the similarities and differences between the results for filling factor 1 and filling factor 1/3. Both to the left and to the right of these values maxima of a specific shape, ``wings,'' arose in the $\ensuremath{\sigma}(\ensuremath{\nu})$ dependences at those two $\ensuremath{\nu}$. Analysis of the results of our acoustic measurements at different temperatures and surface acoustic wave frequencies allowed us to attribute these wings to the formation of collective localized states, namely, the domains of a pinned Wigner crystal, i.e., a Wigner solid. While the Wigner solid has been observed in 2D hole systems previously, we were able to detect it at the highest hole density and, therefore, the lowest hole-hole interaction reported.

Diagnosis of fire damage depth in mortar using nonlinear harmonic method and scanning airborne ultrasound technique

Abstract This paper reports the effectiveness of a new fire depth diagnosis of mortars using airborne ultrasonic source scanning method and non-linear harmonic method(NHM). We propose a model of fire damage mortar in which Young's modulus gradually decreases from the surface layer at high temperature during fire. In addition, based on the model, we also propose to diagnose the depth of fire damage from changes in the propagation velocity of surface acoustic waves. In addition, in order to verify the theory of the proposed method, the propagation speed of surface acoustic waves propagating in the fire damage mortar is simulated by FEM analysis, and the possibility of diagnosing the depth of fire damage is obtained. Finally, we measure the propagation velocity of surface acoustic waves using an experimental sample simulating the fire damage mortar model described above, and obtain results with almost the same tendency as that of FEM analysis.

Influence of top-coat thickness of thermal barrier coating on time–frequency domain and dispersion characteristics of laser-induced surface acoustic wave

Thermal barrier coating is commonly used to insulate the hot end components of aero engine and gas turbine in order to meet extreme high temperature service conditions. The performance of the thermal barrier coating will be significantly impacted by thinning or even spalling during the service process. Given the uniqueness of thermal barrier coating in structure and composition materials, and the fact that laser-induced surface acoustic waves are extremely sensitive to material surface characteristic parameters, laser-induced ultrasonic technology is used to detect the thermal barrier coating in this paper. To characterize the size and defect of thermal barrier coating, the excitation mechanism and propagation law of surface acoustic waves are very crucial. Firstly, the surface acoustic wave propagation law is investigated using spectral analysis and wavelet transform. Then, to study the influence of top-coat thickness on laser-induced surface acoustic wave, the surface acoustic wave velocity dispersion curves of thermal barrier coating with different top-coat thicknesses are extracted using wavelet analysis. The simulative and experimental results indicate that the time–frequency domain and dispersion characteristics of laser-induced surface acoustic wave in multilayered heterostructure are strongly affected by the top-coat thickness. By the establishment of the relationship between phase velocity of laser-induced surface acoustic wave and top-coat thickness, a theoretical basis is provided to characterize the top-coat thickness of multilayered heterostructure.

Impact of Spin-Wave Dispersion on Surface-Acoustic-Wave Velocity

The dependence of the velocity of surface acoustic wave (SAW) as a function of an external applied magnetic field is investigated in a Fe thin film epitaxially grown on a piezoelectric GaAs substrate. The SAW velocity is observed to strongly depend on both the amplitude and direction of the magnetic field. To interpret the experimental data a phenomenological approach to the relative change in SAW velocity is implemented. We find that the experimental velocity variation can be well reproduced provided that the spin wave dispersion is taken into account. The validity of this phenomenological model is attested by the comparison with a quasi-exact magnetoelastic one.