Surface Transverse Wave Research Articles

Theoretical validation on the existence of two transverse surface waves in piezoelectric/elastic layered structures

In this paper, we analytically study the dispersion behavior of transverse surface waves in a piezoelectric coupled solid consisting of a transversely isotropic piezoelectric ceramic layer and an isotropic metal or dielectric substrate. This study is a revisit to the stiffened Love wave propagation done previously. Closed-form dispersion equations are obtained in a very simple mathematical form for both electrically open and shorted cases. From the viewpoint of physical situation, two transverse surface waves (i.e., the stiffened Love wave and the FDLW-type wave) are separately found in a PZT-4/steel system and a PZT-4/zinc system. All the observed dispersion curves are theoretically validated through the discussion on the limit values of phase velocity using the obtained dispersion equations. Those validation and discussion give rise to a deeper understanding on the existence of transverse surface waves in such piezoelectric coupled structures. The results can be used as a benchmark for the study of the wave propagation in the piezoelectric coupled structures and are significant in the design of wave propagation in the piezoelectric coupled structures as well.

Dispersion characteristics of transverse surface waves in piezoelectric coupled solid media with hard metal interlayer

The propagation of transverse surface waves in a piezoelectric layer/metal substrate system with one or multiple hard metal interlayer(s) is investigated analytically. The general dispersion equations for the existence of the waves are obtained in a simple mathematic form for class 6 mm piezoelectric materials. The presence of a hard metal interlayer can not only get rid of the undesired mode appearing in the case without an interlayer but shorten the existence range of the phase velocity within which a nonleaky but dispersive mode exists. The effects of the hard interlayer on the phase velocity can be used to manipulate the behavior of the waves and has implications in acoustic wave devices.

Friction Drag Variation via Spanwise Transversal Surface Waves

The introduction of spanwise velocity is a promising technique to effect the near-wall turbulent flow field to influence friction drag. However, the essential physical mechanism which significantly reduces friction drag has not been understood, yet. It is the objective of this numerical study to improve the fundamental knowledge on the drag reduction mechanism. The investigation is based on spanwise traveling transversal surface waves which are applied to modify the near-wall flow field and to influence friction drag. Two actuation configurations are analyzed in detail. Compared with an unactuated flat plate boundary layer simulation the first wave setup, which represents a low frequency wave at an amplitude larger than the viscous sublayer, leads to a reduced wall-shear stress resulting in friction drag reduction of up to 9%. The second wave setup, which possesses a higher frequency and an amplitude in the range of the viscous sublayer, yields an increase of friction drag of about 8%. Unlike previous investigations which focus on excitation setups to lower friction drag, the comparison of the two wave setups in this study allows to identify the effects which on the one hand, lead to drag reduction and on the other hand, result in drag increase. That is, due to the pronounced differences the major effects determining the friction distribution are more evident. The two key features for drag reduction are the damping of the wall-normal vorticity fluctuations above the entire surface and the decrease of turbulence production. Furthermore, the effect of rearranging streamwise vorticity, which has been stated to be responsible for drag reduction, is found to occur at increasing and decreasing drag, i.e., it is not the effect that lowers the friction drag.

Investigations of several langasite cuts by high temperature in situ characterizations of surface acoustic waves delay lines

In this paper, we investigate the thermal frequency behavior of the surface acoustic waves (0°, 138.5°, 26.7°), (0°, 22°, 31°) and surface transverse waves (STW) (0°, 22°, 90°) langasite (LGS) cuts by RF characterization means performed on delay lines up to 900°C. Above 700°C, results are altered by degradation phenomena of the Pt electrodes. We observed a strong impact of the operating frequency on the thermal frequency shifting of devices. Around the 434 MHz-ISM band, the (0°, 22°, 90°) STW cut offers similar thermal behavior as the one of the wellknown (0°,138.5°, 26.7°) Rayleigh cut. Moreover, associated to the (0°, 22°, 31°) cut, the STW one could allow for differential measurements on one unique substrate.

Method for nondestructive testing of the film coating behavior of surface acoustic wave (SAW) sensors

This paper presents a practical non-destructive method for studying the film coating behavior of SAW devices by using a water soluble dielectric film (manitol) deposited on the SAW device surface by resistive evaporation. After measuring the electrical parameters of the film coated SAW device, the film can easily be removed from its surface by water rinsing without causing any damage to it. The SAW device can then be used over and over again in a large number of film depositions. The method was tested on a 1 GHz surface transverse wave (STW) resonator coated with manitol of varying thickness. After each coating and evaluation, the STW device was successfully recovered without significant performance degradation. Data is presented on the electrical changes of the STW device as a result of depositing manitol coatings of various thicknesses.

A novel type of transverse surface wave propagating in a layered structure consisting of a piezoelectric layer attached to an elastic half-space

The existence and propagation of transverse surface waves in piezoelectric coupled solids is investigated, in which perfect bonding between a metal/dielectric substrate and a piezoelectric layer of finite-thickness is assumed. Dispersion equations relating phase velocity to material constants for the existence of various modes are obtained in a simple mathematical form for a piezoelectric material of class 6 mm. It is discovered and proved by numerical examples in this paper that a novel Bleustein–Gulyaev (B–G) type of transverse surface wave can exist in such piezoelectric coupled solid media when the bulk-shear-wave velocity in the substrate is less than that in the piezoelectric layer but greater than the corresponding B–G wave velocity in the same piezoelectric material with an electroded surface. Such a wave does not exist in such layered structures in the absence of piezoelectricity. The mode shapes for displacement and electric potential in the piezoelectric layer are obtained and discussed theoretically. The study extends the regime of transverse surface waves and may lead to potential applications to surface acoustic wave devices.

Transverse Surface Waves in a Functionally Graded Substrate Carrying a 6mm Piezoelectric Material Layer

The propagation of transverse surface waves in a functionally graded material carrying a piezoelectric layer is investigated analytically. The material properties in the substrate change gradually with the depth coordinate. We here assume that all material properties of the substrate have the same exponential function distribution along the depth direction. The dispersion equations relating phase velocity to the material gradient in the substrate for the existence of the waves are obtained in a simple mathematic form for class 6mm piezoelectric materials. It is demonstrated that the material gradient in the elastic substrate significantly affects the phase velocity and cut-off frequency of long waves but has only negligible effects on short waves. The effects of the material gradient on the penetration depth and electromechanical coupling factor, which are two parameters of practical interest, are also calculated and plotted. The significant influence of the material gradient on the wave propagation behavior provides a potential factor for designing acoustic wave devices.

Drag reduction by spanwise transversal surface waves

A numerical simulation of a spatially evolving turbulent boundary layer impacted by a spanwise traveling transversal sinusoidal wall oscillation is performed. Compared to boundary layer flow over a non-oscillating surface, i.e a standard flat plate boundary layer, a reduction of friction drag of more than 6% is found. A detailed discussion of the near-wall flow reveals similar effects as observed by other excitation methods, such as additionally implemented volume forces or longitudinal sinusoidal wall oscillation. Secondary flow structures induced by the moving wall and a controlled formation of streamwise vorticity close to the wall are identified. The wall-normal vorticity fluctuations are found to be damped such that streak instability and formation of new streaks are reduced yielding an evidently decreased friction drag.

Effects of material gradient on transverse surface waves in piezoelectric coupled solid media

An analytical study on transverse surface waves propagating in a functionally graded material carrying a piezoelectric layer is carried out by Wentzel–Kramers–Brillouin technique. Dispersion relations for the existence of the waves are obtained for material gradient of arbitrary functions and the effects of material gradient on wave propagation are quantified. Numerical examples show the presence of material gradient significantly affects long waves but has only negligible effects on short waves. Depending on whether the surface wave velocity is smaller or greater than the bulk-shear-wave velocity in the piezoelectric layer, two different types of dispersion behavior are discussed.

Surface Generated Acoustic Wave Biosensors for the Detection of Pathogens: A Review

This review presents a deep insight into the Surface Generated Acoustic Wave (SGAW) technology for biosensing applications, based on more than 40 years of technological and scientific developments. In the last 20 years, SGAWs have been attracting the attention of the biochemical scientific community, due to the fact that some of these devices - Shear Horizontal Surface Acoustic Wave (SH-SAW), Surface Transverse Wave (STW), Love Wave (LW), Flexural Plate Wave (FPW), Shear Horizontal Acoustic Plate Mode (SH-APM) and Layered Guided Acoustic Plate Mode (LG-APM) - have demonstrated a high sensitivity in the detection of biorelevant molecules in liquid media. In addition, complementary efforts to improve the sensing films have been done during these years. All these developments have been made with the aim of achieving, in a future, a highly sensitive, low cost, small size, multi-channel, portable, reliable and commercially established SGAW biosensor. A setup with these features could significantly contribute to future developments in the health, food and environmental industries. The second purpose of this work is to describe the state-of-the-art of SGAW biosensors for the detection of pathogens, being this topic an issue of extremely importance for the human health. Finally, the review discuses the commercial availability, trends and future challenges of the SGAW biosensors for such applications.

Surface Generated Acoustic Wave Biosensors for the Detection of Pathogens: A Review

This review presents a deep insight into the Surface Generated Acoustic Wave (SGAW) technology for biosensing applications, based on more than 40 years of technological and scientific developments. In the last 20 years, SGAWs have been attracting the attention of the biochemical scientific community, due to the fact that some of these devices - Shear Horizontal Surface Acoustic Wave (SH-SAW), Surface Transverse Wave (STW), Love Wave (LW), Flexural Plate Wave (FPW), Shear Horizontal Acoustic Plate Mode (SH-APM) and Layered Guided Acoustic Plate Mode (LG-APM) - have demonstrated a high sensitivity in the detection of biorelevant molecules in liquid media. In addition, complementary efforts to improve the sensing films have been done during these years. All these developments have been made with the aim of achieving, in a future, a highly sensitive, low cost, small size, multi-channel, portable, reliable and commercially established SGAW biosensor. A setup with these features could significantly contribute to future developments in the health, food and environmental industries. The second purpose of this work is to describe the state-of-the-art of SGAW biosensors for the detection of pathogens, being this topic an issue of extremely importance for the human health. Finally, the review discuses the commercial availability, trends and future challenges of the SGAW biosensors for such applications.

Transverse surface waves in a piezoelectric material carrying a gradient metal layer of finite thickness

The existence and propagation behavior of transverse surface waves in a layered structure concerning a piezoelectric substrate and a gradient metal layer are theoretically investigated in this paper. The Wentzel–Kramers–Brillouin (WKB) method is applied to obtain the analytical solutions in the gradient metal layer. The dispersion equation for transverse surface waves in such structure is obtained in a quite simple mathematical form, where the material gradient of the metal layer assumes arbitrary functions. Effects of material gradient on three types of dispersion behavior are discussed in detail based on a proper classification. Numerical results show that the material gradient in the metal layer evidently affects the fundamental mode shape of the transverse surface waves but has negligible effects on the higher order modes.

Waves in Linear Elastic Media with Microrotations, Part 1: Isotropic Full Cosserat Model

In this article, we consider a problem of the surface elastic wave propagation within the framework of the isotropic Cosserat continuum. The medium deformation in this model is described not only by the displacement vector but also by a kinematically independent rotation vector. We discuss the general solution of equations of motion. This solution describes the following wave types: longitudinal and transverse bulk waves, Rayleigh wave, surface transverse wave in a half-space as well as Lamb wave and transverse wave in a thin layer. Within the framework of Cosserat continuum, both the Rayleigh and surface transverse waves in a half-space are dispersive. The transverse wave in a thin layer and the surface transverse wave in a half-space do not have any analogies in the classical elasticity theory.

STW resonator with organo-functionalized metallic nanoparticle film for vapor sensing

A 1 GHz surface transverse wave resonator on 36 degrees Y-cut quartz plate coated with organothiol-functionalized gold nanoparticle film has been studied as a chemical gas sensor. Considerable sensitivity of the resonant frequency to vapors of ethanol, methanol, chloroform, and acetic acid has been found. Owing to the high short-term stability of the oscillator built, the detection limit is in the low ppm range. The results qualitatively confirm previous results on the same film type obtained by conductivity measurements. In the present case, the conductivity effect resulting from variable separation of nanoparticles is accompanied with surface-attached mass of the absorbed gas. The film matrix exhibits considerable capacity to absorb large amounts of molecules at high gas concentrations.

Effect of initial stresses on dispersion relation of transverse waves in a piezoelectric layered cylinder

Effect of initial stresses on dispersion relation for transverse surface waves circulating around a piezoelectric cylinder covered with perfectly conducting layers is investigated. Two overlay materials are considered: Gold and Aluminum. The piezoelectric substrate is considered to have the symmetry of a hexagonal crystal, and the layer is perfectly conducting. The dispersion equation has been given in the form of determinant involving Bessel functions. The roots of the dispersion equation give the values of the characteristic circular frequency parameters of the first three modes for various geometries. These roots are numerically calculated by “Bisection method iterations technique” and presented graphically for various thickness of the overlayer and for different values of the initial stress. The effects of the initial stress on the natural frequencies are illustrated on the figures. It is found that both the thickness of the overlayer and the initial stress have a substantial effect on the dispersion behavior. The results obtained in this paper may not only help us get insight into the electro-mechanical coupling behavior of the piezoelectric composites cylinders, but can also offer theoretical basis and meaningful suggestions for the design of piezoelectric probes and electro-acoustic devices in the nondestructive evaluation technology. Finally, the results are compared graphically when the overlay is Gold or Aluminum with some special cases which do not have initial stresses and electric field.

Transverse surface waves in a 6 mm piezoelectric material carrying a prestressed metal layer of finite thickness

The propagation of transverse surface waves in a piezoelectric material carrying a prestressed metal layer of finite thickness is investigated analytically. The dispersion equation is solved in closed form for class 6 mm piezoelectric materials and the conditions for the existence of various wave modes are obtained. Numerical examples are presented for an aluminum, gold, or zinc layer on a PZT-4 ceramic substrate. The presence of initial stress can extend or shorten the range of phase velocity within which a nonleaky but dispersive mode exists. The dependence of phase velocity on initial stress opens a new window for designing acoustic wave devices.

The radiation power of elastic waves excited in a solid half-space by a subsurface time-harmonic source

The method of Fourier transforms is used to solve the problem of excitation of longitudinal, transverse, and Rayleigh surface waves by a time-harmonic point source placed in a homogeneous isotropic, perfectly elastic half-space and acting along the normal surface. Expressions for the time-average radiation powers of the aforementioned waves are obtained by the method of radiation reaction without using any approximations. The distribution of radiation power over different types of waves depending on their velocities and the source’s depth is investigated in detail.

Transverse surface waves in a functionally graded piezoelectric substrate coated with a finite-thickness metal waveguide layer

An analytical study on transverse surface waves propagating in a functionally graded piezoelectric substrate carrying a metal layer of finite thickness was carried out. Dispersion relations for the existence of the waves were obtained and the effects of material gradient on wave propagation were quantified. Numerical examples show that the presence of the material gradient affects significantly the fundamental mode but has only negligible effects on the higher order modes. Depending on whether the surface wave velocity is smaller or greater than the bulk shear wave velocity in the metal layer, three different types of the dispersion behavior are discussed.

A mixed finite element/boundary element approach to simulate complex guided elastic wave periodic transducers

The development of new surface acoustic wave devices exhibiting complicated electrode patterns or layered excitation transducers has been favored by an intense innovative activity in this area. For instance, devices exhibiting interdigital transducers covered by piezoelectric or dielectric layers have been fabricated and tested, but the design of such structures requires simulation tools capable to accurately take into account the actual shape of the wave guide elements. A modeling approach able to address complicated surface acoustic wave periodic structures (defined in the saggital plane) exhibiting any geometry then has been developed and implemented. It is based on the combination of a finite element analysis and a boundary element method. A first validation of the computation is reported by comparison with standard surface wave devices. Surface transverse wave resonators covered by amorphous silica have been built and consequently used for theory/experiment assessment. Also the case of recessed electrodes has been considered. The proposed model offers large opportunities for modeling any two-dimensional periodic elastic wave guide.

Transverse surface waves in an FGM layered structure

The existence and propagation behavior of Love waves in a functionally graded material (FGM) layered structure are theoretically investigated in this paper based on the three-dimensional equations of linear electricity. The Wentzel–Kramers–Brillouin (WKB) method is applied to obtain the analytical solutions in the FGM layer. The dispersion equation for a Love surface wave in this kind of structure is obtained in a simple mathematical form, where the material property variation of the FGM layer is arbitrary. First, the solution is used to study the effect of the gradient coefficients on the dispersion curves and the phase velocities of Love waves. Then, the influence of gradient coefficients on the stress and displacement fields is discussed in detail. The reported results are important in the design of surface acoustic wave (SAW) devices with high performance.