Acoustic Wave Applications Research Articles

Comprehensive characterization of ZnO thin films for surface acoustic wave applications

This paper presents a comprehensive characterization of a very smooth, c-axis oriented, highly piezoelectric and electrically resistive 2.5 µm-thick ZnO thin film deposited by a radio frequency (RF) magnetron sputtering system on SiO2/Si substrate. Thin film properties such as surface roughness, crystallography, stoichiometry, and electrical resistivity are measured. Two-port surface acoustic wave (SAW) devices with bidirectional interdigital transducer (IDT) periods of 16 µm, 20 µm and 24 µm are fabricated on top of the ZnO thin film. A detailed finite element analysis (FEA) of the thin film is elaborated by varying ZnO thickness and IDT configuration. FEA results shows that acoustic wave velocities and resonance frequencies of the SAW devices are decreasing together with increasing ZnO thickness. Frequency response of the fabricated SAW devices are measured with a vector network analyzer (VNA) and compared to FEA results. First two wave modes, namely the Rayleigh and Sezawa waves, of the fabricated SAW devices on the ZnO thin films are interrogated. Resonance frequencies of the SAW devices with wavelengths of 16 µm, 20 µm, and 24 µm are measured as 204.8 MHz, 176.3 MHz, and 155.3 MHz for the Rayleigh mode, 335.9 MHz, 275.3 MHz, and 235.1 MHz for the Sezawa mode, respectively. In addition, omnidirectional wave propagation of ZnO thin film is shown with 45° rotated IDTs. Overall, experimental results are in good agreement with simulation results, demonstrating ZnO thin film fabrication is successfully carried out, and FEA is an appropriate method for modeling SAW devices on thin films.

Fabrication and performance of a self-powered damage-detection aggregate for asphalt pavement

The use of wireless sensors to monitor concealed damage to asphalt pavement has become an important research topic. The main obstacle to wireless sensor applications is the protection of sustainable power supplies. For this study, the self-powered damage-detection aggregate (SPA) was fabricated by encapsulating the piezoelectric vibrator with epoxy resin, prepared by compositing the piezoelectric ceramics (PZT) and polyvinylidene fluoride. The optimal PZT content in the piezoelectric vibrator was recommended as 60% according to the test results. The sensing and driving characteristics, sensitivity, and mechanical strength of the SPAs were studied, and the best SPA is recommended. The compressive strength of the SPA was 16 MPa at a temperature of 160 °C, which is far greater than the average tire pressure of 0.5 MPa to 1.3 MPa on pavement. During laboratory testing, a voltage of 75.0 V and an energy of 4.31 μJ was harvested when an SPA was embedded in an asphalt mixture slab. The coefficient of the acoustic wave attenuation, obtained from the SPA, decreased as the crack width in an asphalt pavement increased. We proved that the application of acoustic waves excited by the SPA to monitor concealed cracks of asphalt pavement is feasible.

Attenuation of acoustic wave excited by piezoelectric aggregate in asphalt pavement and its application to monitor concealed cracks

Abstract The use of sensors to monitor concealed cracks in asphalt pavement has become a research topic of interest. In this paper, piezoelectric aggregates (PAs) were embedded into an asphalt pavement. One was used as an actuator for transmitting a signal, and the other as a sensor for receiving the signal. The coefficient of acoustic wave attenuation a, referring to the amplitude ratio of the excitation signal to receiving signal, decreases as crack width in an asphalt pavement increases, indicating that the application of acoustic waves excited by PA to monitor concealed cracks of asphalt pavement is feasible. The driving frequency imposes obvious influence on the a, which is at its maximum when the driving frequency is 500 Hz. The value of a decreases as asphalt viscosity, nominal maximum particle size and air voids increase, and as asphalt content decreases. Temperature and moisture have obvious influences on wave attenuation, and the value of a increases as temperature and moisture increase. A more universal indicator–average absolute deviation (AAD) was proposed, which is independent of the asphalt mixture properties and grows linearly with the crack width in an asphalt pavement. In practical engineering, the pavement concealed cracks can be monitored by the acoustic saves excited by PA and be calculated by ADD. This study provides a reference for the development and application of intelligent monitoring of concealed damage in asphalt pavements.

Registration of high-frequency waves on the surface by the interference methods

Capillary waves are frequently used to measure the surface tension of liquids. However, this approach has not found wide application in the manufacture of modern commercial tensiometers because of the limitations imposed by capillary wave excitation techniques and the labor input associated with its practical implementation. In this paper we introduce a modified version of the capillary wave method which allows one to avoid the existing limitations and disadvantages. The distinguishing features of the proposed technique are as follows: acoustic wave generation and application of an interferometry technique for 3D surface profile reconstruction. A dynamic speaker with controlled vibration frequency and amplitude is used to produce acoustic vibrations. Application of a conventional Fizeau interferometer and the spatial phase shifting method makes it possible to perform surface form measurements with a high accuracy. For calculating wavelengths and the damping co-efficient, the surface profile is fitted with a decaying cylindrical wave equation. The accuracy of surface tension measurement by the modified capillary wave technique is 0.3 %. Owing to the non-contact way of wave generation and the small amounts of the examined fluid, the proposed method can be used in different studies.

Application of acoustic waves to estimate mechanical and electrical parameters of ceramic materials obtained by sintering

Abstract The paper proposes an algorithm for estimating the physical parameters of piezoceramic materials obtained by the sintering technology. The task of analyzing the state of such materials is a modern actual material science problem. The efficiency of application of methods of acoustic microscopic flaw detection for the analysis of the structure of roller materials, determination of their density and porosity, optimization of annealing temperatures is demonstrated. It is shown that the measurement of a number of acoustic characteristics of piezoceramics allows us to determine the values of its electrical characteristics. To obtain the extreme values of the parameters, the methods of solving optimization problems are applied.

Analytical study of (3 + 1)-dimensional fractional ultralow-frequency dust acoustic waves in a dual-temperature plasma

Ultralow-frequency dust acoustic waves in plasma are an important branch of study in plasma physics. Due to the important application of dust acoustic waves in the space environment, industrial pro...

Acoustic surface waves on three-dimensional groove gratings with sub-wavelength thickness

Spoof surface acoustic waves (SSAWs) can be tightly confined at the subwavelength scale by groove gratings and propagate along the surface with low loss in a broad bandwidth. Here, we put forward a three-dimensional SSAW waveguide with a compact cross section perpendicular to the propagation direction. By introducing an additional transition part for mode conversion, the proposed SSAW waveguide can guide surface modes in a wide frequency range under the excitation of a point source. Both numerical and experimental results confirm the validity of the proposed design, thus offering attractive prospects for acoustic surface wave applications.

Driving useful morphological changes in magnetic nanoparticle structures through the application of acoustic waves and magnetic fields

The growing interest in acoustic manipulation of particles in micro to nanofluidics using surface acoustic waves, together with the many applications of magnetic nanoparticles—whether individual or in arrays—underpins our discovery of how these forces can be used to rapidly, easily, and irreversibly form 1D chains and 2D films. These films and chains are difficult to produce by other methods yet offer many advantages over suspensions of individual nanoparticles by making use of the scale of the structures formed, 10−9 to 10−5 m, and by taking a balance of the relevant external and interparticle forces, the underlying mechanisms responsible for the phenomena become apparent. For loosely connected 1D chains, the magnetic field alone is sufficient, though applying an acoustic field drives a topology change to interconnected loops of ∼10–100 particles. Increasing the acoustic field intensity drives a transition from these looped structures to dense 2D arrays via interparticle Bjerknes forces. Inter-particle drainage of the surrounding fluid leaves these structures intact after removal of the externally applied forces. The self-evident morphology transitions depend solely upon the relative amplitudes of the Brownian, Bjerknes, and magnetic forces.

Acoustic waves effect on the generation of nitrogen oxides by corona discharge in air

We studied the interaction of acoustic waves with negative corona discharge in air at atmospheric pressure. The application of acoustic waves on the discharge causes a mixing of ambient air with the gas between the electrodes, which results in cooling of the gas in the inter-electrode gap. As a rough indirect indicator of the discharge cooling, we used a concentration of nitrogen oxides generated by the discharge. We chose these oxides because they exhibit antibacterial properties. We showed that for a particular discharge power with increasing amplitudes of acoustic displacements, the concentration of generated nitrogen mono/dioxide decreases, and that this decrease could be attributed mainly to the temperature. We also found that application of acoustic waves on the discharge for a particular power substantially decreases transient spark frequency, increases the magnitude of the streamer onset voltage, and increases the difference between the streamer and spark onset voltage.

Low frequency acoustic and ultrasound waves to characterise layered media

Poor penetration and excessive absorption of high frequencies limit spectroscopic approaches using fast rise pulses for inspecting many engineered structures. So, this study focused on the alternative application of low frequency acoustic and ultrasound waves for the characterisation of challenging structures in airborne and waterborne environments. A simple, transfer matrix model approach was developed for the simulation of 1D sound propagation through layered media that comprise many engineered structures. This model was used to test the feasibility of using sound waves for non-destructive characterisation of an articulated lorry transported trailer and offshore foundation infrastructure. The targets were not in contact with the sound sensors and incorporated highly attenuating layers with acoustic contrasts to the surrounding medium that result in over 90% reflection of incident wave pressure. In both cases, resonances controlled by the thicknesses and interval velocities of component layers modulated sound reflection from, and transmission through the whole structure. These effects were observed as local maxima and minima in the spectra of the transmission and reflection coefficients. These spectral coefficients also determined the modulation to the temporal envelope of a linear frequency modulated pulse used to insonify the targets. In the acoustic study, which comprised only theoretical modelling, discrimination of differing cargo widths and between solid versus empty cargo trailers was possible using the transmission coefficient. In the ultrasound study, which comprised theoretical modelling and experimental testing, discrimination of differing steel and concrete substructure thicknesses and also of gaps between them was possible using the reflection coefficient. The model outcomes indicated while an acoustic system would require around 90–100 dB of dynamic range, an ultrasound system would only require around 40 dB to be effective.

Модификация метода капиллярных волн

Capillary waves are frequently used to measure the surface tension of liquids. However, this approach has not found wide application in the manufacture of modern commercial tensiometers because of the limitations imposed by capillary wave excitation techniques and the labor input associated with its practical implementation. In this paper we introduce a modified version of the capillary wave method which allows one to avoid the existing limitations and disadvantages. The distinguishing features of the proposed technique are as follows: acoustic wave generation and application of an interferometry technique for 3D surface profile reconstruction. A dynamic speaker with controlled vibration frequency and amplitude is used to produce acoustic vibrations, which are transferred via waveguides and create the local source of pressure oscillations on the fluid surface. Application of a conventional Fizeau interferometer and the spatial phase shifting method makes it possible to perform surface form measurements with an accuracy of 5 nm. For calculating wavelengths and the damping coefficient, the surface profile is fitted with a decaying cylindrical wave equation. The accuracy of surface tension measurement by the modified capillary wave technique is 0.3 % , and the measured values coincide with the known values of these parameters determined using other measuring instruments. Owing to the non-contact way of wave generation and the small amounts of the examined fluid, the proposed method can be used in biological, magnetic fluids studies and rheological investigations in physical chemistry.

Enhanced SAW characteristics of a-plane AlN epitaxial films using ZnO buffer layer

High-quality a-plane AlN epitaxial films were successfully deposited on r-plane sapphire using a thin ZnO buffer layer for surface acoustic wave (SAW) applications. Structural properties of AlN epitaxial films on different thicknesses of ZnO buffer and the related SAW characteristics were investigated systematically. The results demonstrate that AlN films were epitaxially grown on ZnO buffered-substrate with orientation relationship of $$(11\overline {2} 0){\text{ }}[10\overline {1} 0]$$ AlN// $$(11\overline {2} 0){\text{ }}[10\overline {1} 0]$$ ZnO// $$(01\overline {1} 2){\text{ }}[\overline {2} 110]$$ Al2O3. A thin ZnO buffer layer with moderate thickness significantly facilitated the crystal quality of a-plane AlN films, and in turn enhanced the SAW characteristics. High frequency SAW devices with a center frequency of ~ 1500 MHz corresponding to a high phase velocity of 6000 m/s were achieved on the obtained AlN films. The as-grown a-plane AlN epitaxial films with 40 nm optimized ZnO buffer exhibit high crystal quality with a FWHM value of the rocking curve of 0.76° and good performance of SAW devices with low insertion loss and large out-of-band rejection. This work offers an effective approach to achieve high-quality a-plane AlN epitaxial films on sapphire substrates for the AlN-based SAW devices applications.

Exploration of acoustic spiral waves in an underwater environment

The work to be presented is regarding a research project to investigate the viability and possible application of spiral or helical acoustic waves for use in underwater environments. The investigation encompasses studies into the properties and generation of spiral or helical acoustic waves. Spiral waves can be generated by precisely controlling the phase of the wave, which could have different physical properties due to what is known as “topological charge.” This topological charge could be adjusted in some advantageous way, depending upon the desired application. In addition, reception of spiral or helical waves was investigated. The goal of the research is a proof of concept and presentation of the results of generation and reception of spiral acoustic waves. Spiral waves have been investigated for acoustic navigation and may lend itself well for use in other applications.

Comparison between Ir, Ir0.85Rh0.15 and Ir0.7Rh0.3 thin films as electrodes for surface acoustic waves applications above 800 °C in air atmosphere

In this paper, we investigate the suitability of Ir, Ir0.85Rh0.15 and Ir0.7Rh0.3 thin films as electrodes for surface acoustic waves (SAW devices) applications taking place above 800°C in air atmosphere. As expected, all films oxidize from 800°C in IrO2 or IrxRh1-xO2 phase. The electrical properties of the latter remain compatible with the design of SAW devices, with a specific electrical resistance of 151 and 100μΩ·cm for x=0.7 and x=0.85 respectively. Moreover, we observe that the IrxRh1-xO2 phase is much more stable regarding sublimation effect than the IrO2 phase, highlighting the interest of alloying Ir with Rh for high-temperature applications. SAW devices based on langasite substrate and Ir0.85Rh0.15 electrodes show a very good stability for at least several days at 800°C in air. In the case of Ir0.7Rh0.3 electrodes, this stability is extended to temperatures up to 900°C.

Quality-enhanced AlN epitaxial films grown on c-sapphire using ZnO buffer layer for SAW applications

AlN epitaxial films with a thin ZnO buffer layer were successfully deposited on c-sapphire by DC magnetron sputtering for surface acoustic wave (SAW) applications. The effect of ZnO buffer layer thickness on structural properties of AlN epitaxial films and the related SAW properties were investigated systematically. The results revealed that a thin ZnO buffer layer can significantly enhance the crystalline quality of AlN films and release the strain in AlN films. The AlN films were epitaxially grown on ZnO buffered-substrate with orientation relationship of (0001)[101¯0]AlN//(0001)[101¯0]ZnO//(0001)[2¯110]Al2O3. High frequency SAW devices with a center frequency of 1.4GHz, a phase velocity of 5600m/s were achieved on the obtained AlN films. The optimum ZnO buffer layer thickness was found to be 10nm, resulting in high-quality epitaxial AlN films with a FWHM value of the rocking curve of 0.84°, nearly zero stress and low insertion loss of SAW devices. This work offers an effective approach to achieve high-quality AlN epitaxial films on sapphire substrates for the applications of AlN-based SAW devices.

In Memoriam: Professor Eugeniusz Jan DANICKI

Professor Eugeniusz Danicki, a distinguished academic teacher, outstanding specialist in the theory and application of acoustic waves and electronics, passed away on 11 September, 2016.

Effects of simultaneous acoustic and electric fields on removal of fine particles emitted from coal combustion

Traditional electrostatic precipitation has a relatively low collection efficiency of fine particles emitted from coal combustion due to insufficient particle charging. This paper establishes an experimental system combining travelling sound waves with wire-duct electrostatic precipitation in order to measure the separated and simultaneous effects of an electric and acoustic field on fine particle penetration efficiency. The ranges of the main physical parameters are as follows: discharge voltage, V=8–12kV; acoustic frequency, ƒ=800–2400Hz; sound pressure level (SPL), SPL=130–148dB; residence time, t=2–6s; initial fine particle concentration, N0=6.5×105–4.99×106/cm3. The application of acoustic waves in an electric field is proven as an advisable method to remove fine particles with the lowest total penetration efficiency of 4.4%. Although the sound does not change the current–voltage curves of negative corona, it can distort the motion trajectory of the particles leading to a positive result for fine particle removal. The effectiveness of sound on the improvement of fine particle removal diminishes as the voltage increases. For a given discharge voltage, there exists an optimal frequency and SPL. The optimal frequency slightly increases, while the optimal SPL decreases as the applied voltage increases. The influence of residence time and initial fine particle concentration in combined fields are also studied.

AlN films deposited by dc magnetron sputtering and high power impulse magnetron sputtering for SAW applications

In this work, aluminium nitride (AlN) films were deposited on silicon substrates buffered by an epitaxial AlN thin film for surface acoustic wave (SAW) applications. The films were deposited by dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) deposition techniques. The structural properties of AlN films were investigated using x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy and atomic force microscopy. In both cases of films deposited by dcMS and HiPIMS, the XRD results showed that the obtained films are oriented, with full width at half maximum rocking curves of around 1°. Raman spectroscopy revealed higher residual stress relaxation in the AlN epilayers grown by HiPIMS compared to AlN grown by dcMS, highlighted by a blue shift in the E2(high) Raman mode. The SAW measurements indicated an insertion loss of AlN-SAW devices of about 53 and 35 dB for the AlN films deposited by dcMS and HiPIMS respectively. The relation between the structural properties of AlN and the characteristics of AlN-SAW devices were correlated and discussed.

AlN, ZnO thin films and AlN/ZnO or ZnO/AlN multilayer structures deposited by PLD for surface acoustic wave applications

(0002)‐oriented AlN and ZnO thin films are deposited on C‐sapphire substrates by pulsed laser deposition at 700 °C. Multilayered structures AlN/ZnO and ZnO/AlN are also grown on C‐sapphire and investigated by X‐ray diffraction, scanning electron microscopy and transmission measurements. Ellipsometry analysis is employed to investigate the stack of layers and the optical properties of thin films. This non‐destructive analysis identified an intermediate layer between AlN and ZnO thin films for AlN/ZnO multilayer which didn't change the crystalline structure or piezoelectric properties of the multilayer. Surface acoustic wave velocities are respectively 5060 m s−1 for AlN and 5350 m s−1 for ZnO. In fact, investigations of surface acoustic wave (SAW) devices revealed a similar resonant frequency for both multilayers and in agreement with those measured for ZnO or AlN thin films.

Monolithic phononic crystals with a surface acoustic band gap from surface phonon-polariton coupling.

We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z-cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics.