Acoustic Wave Devices Research Articles

The propagation behavior of SH surface wave in a semi-infinite magneto-electro-elastic solid with the periodically gold strips

This article theoretically investigates the propagation of shear horizontal (SH) surface wave in the periodically deposited gold strips separated by vacuum on the magneto-electro-elastic (MEE) substrate. Using field analysis theory based on Bloch-Floquet theorem and electromagnetic open boundary conditions, dispersion equations are derived. The MEE composite is comprised of 80% PZT4 and 20% CoFe2O4. The dispersion, wave mode shape, electric and magnetic potentials are being modelled and computed for the SH wave on the MEE substrate. It is observed that the bandgap occurs at resonance when the wavelength of the SH wave matches with periodicity of the grating. The width of the bandgap can be increased or decreased by increasing the strip height to periodicity ratio. It is found that the gold grating on the surface of MEE substrate can traps the SH wave by slowing down the wave when the wave number is less or equal to wave number at the resonance condition. It is observed that above the resonance condition, SH wave shows supersonic behavior where the phase velocity of SH wave is greater than the surface wave velocity. The trapping and supersonic behavior of SH wave are more pronounced as the strip height to grating periodicity ratio increases. As the strip height to periodicity ratio increases, the wave trapping is enhanced and the leakage of wave energy in the substrate is reduced. The results are relevant to design the surface acoustic wave devices.

An efficient modeling approach for wavelet transform processors using surface acoustic wave devices

Wavelet transform processors (WTPs) using surface acoustic wave devices provide an effective solution to utilize wavelet transform technology in practical applications. This work proposes a novel model of WTPs for predicting their performance characteristics, which might be utilized for single-electrode type and double-electrode type interdigital transducers (IDTs), as there is currently no universal, quick, and accurate simulation technology for WTPs (IDTs). The admittance matrix, transfer function, and insertion loss for both IDTs and WTPs in conjunction with a two-port electrical network are all evaluated by the model. Furthermore, some WTPs samples with a piezoelectric substrate of ST-X quartz and IDTs of Al thin film were fabricated to validate the accuracy of the simulation, with a center frequency and a scale of 60 MHz and 0.215, respectively. A comparison of the simulated and measured results found that the relative error of the frequency is only 0.67%, the maximum relative error of the bandwidth is 5.79% and the relative error of the insertion loss is only 1.24%. The experimental results show that the model is extremely accurate in effective frequency band, and its application will accelerate the design and production of WTPs, promoting the use of WTPs in signal processing systems.

Simulation and Optimization of Surface Acoustic Wave Devices With High Electromechanical Coupling Factor and Zero Temperature Coupling Coefficient by Pattern Piezoelectric Layer

Recently, a more popular patterned surface acoustic wave (SAW) device with better performance was proposed. This structure has a large electromechanical coupling factor. To make surface acoustic wave devices easy to be applied to integrated circuit technology, a multilayer structure based on patterned Al/ZnO/Si is designed by using finite element method (FEM). Firstly, dependence of ZnO piezoelectric material on electromechanical coupling factor is studied systematically. The results show that Al/ZnO/Si structure excites Rayleigh mode and Sezawa mode with high electromechanical coupling factor. The patterning of piezoelectric materials could be achieved by etching. The electromechanical coupling factor of Rayleigh mode is as high as 7.98%, and the electromechanical coupling factor of Sezawa mode is up to 9.68%. As we all know, temperature will affect the characteristics of SAW devices. Therefore, the temperature characteristics based on this structure are systematically studied. To achieve zero temperature coupling coefficient, SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is used as an intercalation layer for temperature compensation. The structure of Rayleigh mode and Sezawa mode with the thinner SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer is easier to achieve zero temperature coupling coefficient than that of conventional structure. Meanwhile, the electromechanical coupling factor of Sezawa mode based on patterned Al/ZnO/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si structure does not change significantly with the increase of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness, with the maximum value of 10.78%, and the minimum value of 10.62%, which is 1.1% larger than that of structure without SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Aerosol jet printing of piezoelectric surface acoustic wave thermometer

Surface acoustic wave (SAW) devices are a subclass of micro-electromechanical systems (MEMS) that generate an acoustic emission when electrically stimulated. These transducers also work as detectors, converting surface strain into readable electrical signals. Physical properties of the generated SAW are material dependent and influenced by external factors like temperature. By monitoring temperature-dependent scattering parameters a SAW device can function as a thermometer to elucidate substrate temperature. Traditional fabrication of SAW sensors requires labor- and cost- intensive subtractive processes that produce large volumes of hazardous waste. This study utilizes an innovative aerosol jet printer to directly write consistent, high-resolution, silver comb electrodes onto a Y-cut LiNbO3 substrate. The printed, two-port, 20 MHz SAW sensor exhibited excellent linearity and repeatability while being verified as a thermometer from 25 to 200 ∘C. Sensitivities of the printed SAW thermometer are -96.9times 1{0{}^{-6}}^{circ }C−1 and -92.0times 1{0{}^{-6}}^{circ }C−1 when operating in pulse-echo mode and pulse-receiver mode, respectively. These results highlight a repeatable path to the additive fabrication of compact high-frequency SAW thermometers.

Integrated transparent surface acoustic wave technology for active de-fogging and icing protection on glass

There have been great concerns on poor visibility and hazardous issues due to fogging and ice/frost formation on glass surfaces of windshields, windows of vehicles/airplanes, and solar panels. Existing methods for their monitoring and removal include those active ones (such as using resistance heating) or passive ones (such as using surface icephobic treatments), which are not always applicable, effective or reliable. In this study, we proposed a novel strategy by implementing transparent thin film surface acoustic wave (SAW) devices by directly coating ZnO films onto glass substrate and studied their de-fogging, active anti-icing and de-icing mechanisms using the SAW technology. Effects of powers and wavelengths of SAW devices were investigated and influences of acousto-heating and surface hydrophobic treatments were evaluated. Results showed that de-fogging time was dramatically decreased with the increase of SAW powers when the thin film-based SAW devices were exposed to humid air flow for different durations. The icing accretion was significantly delayed under the applied SAW agitation, and SAW application has also effectively promoted de-icing on glass substrate, due to the interfacial nanoscale vibration and localized heating effect.

Linear spring model to analyse the effect of interfacial imperfection on the propagation and attenuation of Love-type waves in viscoelastic-FGPM bedded structure

This article is dedicated to analyse the propagation and attenuation behaviour of Love-type waves in an imperfectly bonded viscoelastic-functionally graded piezoelectric material (FGPM) layered structure. The linear spring model is adopted to portray the interfacial imperfection. The wave solutions in the FGPM substrate are approximated using Wentzel–Kramers–Brillouin (WKB) approximation technique. Dispersion relation is obtained and found to be complex in nature, when traction-free and electrically short conditions are taken into account. Numerical example and computations have been presented to analyse the dispersion equation. The pronounced effects of different parameters such as gradient coefficients, layer’s width, interfacial imperfection, and dissipation factor on the phase velocity, as well as attenuation coefficient of the Love-type wave have been illustrated graphically. Obtained results may be used to achieve better performance of surface acoustic wave (SAW) devices and Love-wave sensors.

Surface acoustic wave resonators on thin film piezoelectric substrates in the quantum regime

Lithium niobate (LNO) is a well established material for surface acoustic wave (SAW) devices including resonators, delay lines and filters. Recently, multi-layer substrates based on LNO thin films have become commercially available. Here, we present a systematic low-temperature study of the performance of SAW devices fabricated on LNO-on-insulator and LNO-on-Silicon substrates and compare them to bulk LNO devices. Our study aims at assessing the performance of these substrates for quantum acoustics, i.e. the integration with superconducting circuits operating in the quantum regime. To this end, we design SAW resonators with a target frequency of and perform experiments at millikelvin temperatures and microwave power levels corresponding to single photons or phonons. The devices are investigated regarding their internal quality factors as a function of the excitation power and temperature, which allows us to characterize and quantify losses and identify the dominating loss mechanism. For the measured devices, fitting the experimental data shows that the quality factors are limited by the coupling of the resonator to a bath of two-level-systems. Our results suggest that SAW devices on thin film LNO on silicon have comparable performance to devices on bulk LNO and are viable for use in SAW-based quantum acoustic devices.

Super-High-Frequency Low-Loss Sezawa Mode SAW Devices in a GaN/SiC Platform.

This paper presents a comprehensive study of the performance of Sezawa surface acoustic wave (SAW) devices in SweGaN QuanFINE® ultrathin GaN/SiC platform, reaching frequencies above 14 GHz for the first time. Sezawa mode frequency scaling is achieved due to the elimination of the thick buffer layer typically present in epitaxial GaN technology. Finite element analysis (FEA) is first performed to find the range of frequencies over which the Sezawa mode is supported in the grown structure. Transmission lines and resonance cavities driven with Interdigital Transducers (IDTs) are designed, fabricated, and characterized. Modified Mason circuit models are developed for each class of devices to extract critical performance metrics. We observe a strong correlation between measured and simulated dispersion of the phase velocity (vp) and piezoelectric coupling coefficient (k2). Maximum k2 of 0.61% and frequency-quality factor product (f.Qm) of 6×1012 s-1 are achieved for Sezawa resonators at 11 GHz, with a minimum propagation loss of 0.26 dB/λ for the two-port devices. Sezawa modes are observed at frequencies spanning up to 14.3 GHz, achieving a record high in GaN microelectromechanical systems (MEMS) to the best of the authors' knowledge.

Fabrication and characterization of hybrid bulk and surface acoustic wave resonators with Ag/patterned-AlN/Mo/diamond/Si layered structure

Hybrid bulk acoustic wave and surface acoustic wave (BAW/SAW) devices attract extensive interests due to their high electromechanical coupling coefficient and quality factor. In this study, longitudinal BAW coupled SAW resonators with piezoelectric AlN inter-digital transducers (IDT) were simulated and fabricated on diamond substrates to increase the working frequency as well. The simulated figure of merit value is 104, 123 % improved comparing with the corresponding metal IDT of 46.5. The frequency response spectrum of single port reflection (S11) shows dominant harmonic resonance at 913 MHz with electromechanical coupling coefficient of 2.16 % and quality factor of 913. These results indicate mutual transductions between BAW and SAW occur with sufficient efficiency in hybrid structures, which is analyzed and interpreted by equivalent acoustic impedance theory.

A Passive Wireless Sensing Method Based on Magnetic Resonance Coupling and Bulk Acoustic Wave Device

In this article, we propose a passive wireless strain sensing system with magnetic resonance coupling and bulk acoustic wave (BAW) strain sensor to evaluate the structural safety of megastructures. The BAW sensor provides a high quality factor, and the magnetic resonance coupling enhances the transmitter’s gain at the system’s operational frequency. The experimental and analytical methods are investigated to characterize the effect of different parameters on this system. The results show that the sensing system can detect the resonant frequency of the receiver when the coupling coefficient is less than 0.01. Experimental demonstrations show that a prototype sensing system had a strain measurement range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500\,\mu \varepsilon $ </tex-math></inline-formula> and a resolution of 4 Hz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> when the separation distance between coils was 10 cm. Compared with conventional passive wireless sensing systems, the change of coupling coefficient has little effect on the resonant frequency of the receiver. We envision that this system has the potential to realize noncontact strain measurement, while the measurement device is in an unsteady movement mode. In the future, this sensing system can be integrated into an unmanned aerial vehicle (UAV) to measure the strain in megastructures.

A Novel Modeling Approach for Wavelet Reconstruction Processors Using Surface Acoustic Wave Devices

Wavelet reconstruction processors (WRPs) using surface acoustic wave (SAW) devices are a simple and efficient implementation of inverse wavelet transform technology in practical industrial applications. To assure the accuracy of the device fabrication, this article proposed a new model of WRPs based on the channel division approach and the two-port electrical network after investigating the Delta-Function Model (DFM) of interdigital transducers (IDTs), which can easily analyze the bandwidth, the admittance matrix, transfer function and insertion loss for an IDTs and a WRPs. Furthermore, to validate the simulation effect, some samples of WRPs were successfully manufactured with ST-X quartz as the piezoelectric substrate and Al thin film as the IDTs material, the center frequency and the scale are 49.0 MHz and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2^{-{2}}$ </tex-math></inline-formula> , respectively. A comparison of the experimental and simulation results reveals that the model possesses high accuracy with the relative error operating frequency of 0.204%, the relative error in insertion loss less than 1.17% at the operating frequency. This work provides an effective model for WRPs with higher precision, low consumption, high operation speed, making it possible for the acceleration of the development process of the WRPs for large-scale application and commercial promotion.

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.

Single-crystalline AlN/sapphire and composite electrode based ultra-high temperature surface acoustic wave devices

Single crystalline AlN material is very attractive for the development of high temperature electronic devices owing to its high temperature resistance. However, at ultrahigh temperatures, AlN film still will be oxidized and metal electrodes used for the devices will aggregate and vaporize. The deterioration of the material and metal electrodes eventually fails the AlN-based devices. Here, we report a single crystalline AlN film-based ultrahigh temperature surface acoustic wave (SAW) device. By using a thin alumina (Al2O3) protection layer on surface, oxidation of the AlN piezoelectric film was effectively inhibited at high temperatures. A composite electrode based on multilayer structure of Pt-Rh and Al2O3 was designed and fabricated, with the Al2O3 layer as the diffusion barrier layers to suppressed inter-diffusion, agglomeration and vaporization of the metals. The results showed that the developed AlN SAW devices can withstand high temperatures, and work well at temperatures up to 1400 °C.

Experimental investigation on microfluidic devices for particle separation using standing surface acoustic waves

In this work, we designed and experimentally tested a microfluidic device for particle separation by using standing surface acoustic waves (SSAW). Emphasis is being placed on an effective microfluidic device being capable of continuous separation of particles in a microchannel design on its size. For this, we developed a miniaturized (e.g., lab-on-a-chip) system for biological and chemical analyses. For demonstration, we experimentally demonstrated that separation of dissimilarly-sized polystyrene particles suspended in water medium was successfully achieved. Numerical simulations were conducted by using COMOSL Multiphysics 5.0 to investigate the effects of sheath layer thickness and particle size on separation efficiency of the microfluidic device. The present numerical and experimental findings were then applied to propose an improved design and fabrication process of Standing surface acoustic waves devices, which has great potential for biological applications.

Methods of Solving Passband Ripples and Sidelobes for Wavelet Transform Processor Using Surface Acoustic Wave Device

This article proposes an approach using surface acoustic wave (SAW) device to decrease passband ripples and sidelobes as two key problems of wavelet transform processors (WTPs). The passband ripples are primarily generated through electrode reflections and transducer end-effects. The proposed method uses unbalanced split-electrode interdigital transducers (IDTs) to prevent electrode reflections. The problem of transducer end-effects is alleviated by attaching SAW absorbers to both ends of the substrate edge, which can effectively absorb the spurious SAW arriving at the edges of the piezoelectric substrate. Moreover, because the radiation energy of bulk acoustic wave (BAW) has a sidelobe distribution, the greater sidelobes are predominantly caused by the BAW radiation. This problem is alleviated by engraving bidirectional slots on the substrate at the back of the WTPs of the unbalanced split-electrode IDTs to suppress the BAW radiation. The experimental results demonstrate that the passband ripples and sidelobes of the WTPs decrease to 0.72 and 6.58 dB, respectively.

Durability of TiAl based surface acoustic wave devices for sensing at intermediate high temperatures

TiAl based surface acoustic wave (SAW) devices, which offer a promising cheap and easy to handle wireless sensor solution for intermediate high temperatures up to 600 °C, were prepared and investigated with respect to their durability. To obtain the devices, Ti/Al multilayers were deposited on high-temperature stable piezoelectric catangasite (CTGS) substrates and structured as electrodes via the lift-off technique. AlNO cover layers and barrier layers at the substrate site served as an oxidation protection. The devices were characterized regarding their electrical behavior by ex-situ measurements of their frequency characteristics after heat treatments up to 600 °C in air. In addition, long-term in situ measurements up to 570 °C were performed to analyze a possible drift of the resonant frequency in dependence on the temperature and time. Scanning electron microscopy of the surfaces of the devices and scanning transmission electron microscopy of cross sections of TiAl interdigital transducer electrode fingers and the contact pads were conducted to check the morphology of the electrode metallization and to reveal if degradation or oxidation processes occurred during the heat treatments.The results demonstrated a sufficient high-temperature stability of the TiAl based devices after a first conditioning of system. A linear dependence of the resonant frequency on the temperature of about −37 ppm/K was observed. In summary, the suitability of TiAl based SAW sensors for long-term application at intermediate temperatures was proven.

Perturbation analysis of second-order nonlinearity and its effectiveness for radiofrequency bulk acoustic wave devices

Suppression of nonlinear signal generation in radiofrequency (RF) surface and bulk acoustic wave devices is one of the most important subjects for the RF front-end modules of recent cellular handsets. In particular, issues with second-order nonlinear products of bulk acoustic waves are well known. In this work, we succeeded in extracting the dominant parameters for second-order nonlinear analysis proposed by Hashimoto et al. [Joint Conf. European Frequency and Time Forum and IEEE Freq. Cont. Symp., 2017, p. 538] and verified that it is applicable in a wide frequency range and also effective for film bulk acoustic resonator (FBAR) device design. Combining the extracted nonlinear coefficients on the perturbation analysis by driving near the fundamental frequency (f0) and half resonant frequency (1/2f0) of the FBAR could reproduce second-order nonlinear characteristics in a wide frequency range. It was also confirmed that the proposed simulations are in good agreement with measurement results for various types of resonators and FBAR filters.

Surface Effects on the Frequency Dispersion of Flexural Waves in Timoshenko Nanobeams

The surface effects play an important role in nanobeams. Based on a recently developed theory of surface elastodynamics, a model of the flexural wave propagation in Timoshenko nanobeams is established, in which the surface effects characterized by surface energy and surface inertia are introduced. It is found that when the size of a beam is comparable with nanometers, the surface energy effect would enhance the wave speed, while the surface inertial one would reduce it. An interesting phenomenon discovered is that with an increasing wave frequency, the dominant role transits from the surface energy effect to the surface inertial effect. The two kinds of surface effects exhibit a frequency-dependent competitive mechanism. In contrast to the macroscopic beams, due to the surface effects, the frequency dispersion of flexural waves in nanobeams becomes size-dependent. Furthermore, a comparison of the Timoshenko nanobeam and the Euler one indicates that the shear deformation effect and rotary inertial one cannot be neglected for a large wave number, which would prominently decrease the wave speed. Besides, when the size of the beam is large enough, the surface effects can be neglected and the present results can degenerate to the classical Timoshenko ones. The present results should be helpful not only for deep understanding of the dispersive mechanism of flexural waves in nanobeams, but also for optimal design of nanobeam-based acoustic wave devices.

A droplet-based micropillar-enhanced acoustic wave (μPAW) device for viscosity measurement

Viscosity monitoring has recently received significant attention in various fields such as pharmacy, oil industry, food industry, and medical diagnostics. Given that the commercially available viscometers usually require a large sample volume to conduct accurate measurement, there is an urgent need to develop a viscometer that can consume the least sample while maintaining high accuracy. Despite of being simple, rapid, and cost-effective, quartz crystal microbalance (QCM) based viscometers are low in sensitivity and not able to measure viscosity directly. This work focuses on the development of a novel micropillar-enhanced QCM viscosity measurement device which relies on the coupled vibration between micropillars and quartz substrate (QCM-P) to achieve an ultra-sensitive viscosity measurement of a sample droplet. A hybrid model by integrating an equivalent circuit and numerical simulation approach was established to understand the working principle of the QCM-P device and evaluate the viscosity value. The experimental results and analysis demonstrate that the micropillar-enhanced acoustic wave (μPAW) devices such as QCM-P viscometer is a promising device for droplet-based viscosity measurement.

A Holistic Solution to Icing by Acoustic Waves: De‐Icing, Active Anti‐Icing, Sensing with Piezoelectric Crystals, and Synergy with Thin Film Passive Anti‐Icing Solutions

AbstractIcing has become a hot topic both in academia and in the industry given its implications in transport, wind turbines, photovoltaics, and telecommunications. Recently proposed de‐icing solutions involving the propagation of acoustic waves (AWs) at suitable substrates may open the path for a sustainable alternative to standard de‐icing or anti‐icing procedures. Herein, the fundamental interactions are unraveled that contribute to the de‐icing and/or hinder the icing on AW‐activated substrates. The response toward icing of a reliable model system consisting of a piezoelectric plate activated by extended electrodes is characterized at a laboratory scale and in an icing wind tunnel under realistic conditions. Experiments show that surface modification with anti‐icing functionalities provides a synergistic response when activated with AWs. A thoughtful analysis of the resonance frequency dependence on experimental variables such as temperature, ice formation, or wind velocity demonstrates the application of AW devices for real‐time monitoring of icing processes.