Shear Horizontal Acoustic Plate Mode Research Articles

Scattering matrix approach to SHAPM delay line with long interdigital transducers on BT-cut quartz

Transfer function of a shear horizontal acoustic plate mode (SHAPM) delay line with long interdigital transducers (IDTs) was derived using the scattering matrix method. Analytical expressions for the admittance, scattering coefficients, and reflection coefficient of the periodic electrodes of the IDT, derived previously for SAWs, were used for numerical calculations. By matching the measured and calculated amplitude responses, the velocity, electromechanical coupling coefficient, and reflection coefficient of an aluminum electrode on BT-cut quartz were determined. It was shown that for a sufficiently thick aluminum layer, a reasonable insertion loss could be achieved in spite of a very small electromechanical coupling coefficient.

Properties of shear horizontal acoustic plate modes in BT-Cut quartz

Properties of shear horizontal acoustic plate modes (SHAPMs) in BT-cut quartz were calculated and measured. A delay line with a long interdigital transducer, deposited on -50.5°YX90°-oriented quartz plate, was used for the measurements. For one of the SHAPMs, at a frequency of about 100.4 MHz, insertion loss, turnover temperature, and quadratic temperature coefficient of frequency of about 10 dB, 15°C, and -30 ppb/(°C)(2) in air, respectively, were obtained. Using water and glycerin solutions, insertion loss changes against dynamic viscosity were measured for this mode. In a viscosity range from about 1 mPa·s to 1000 mPa·s, an insertion loss change of about 14 dB was obtained.

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.

Generalized concept of shear horizontal acoustic plate mode and Love wave sensors

An approach to mass and liquid sensitivity for both the phase velocity and insertion loss ofshear mode acoustic wave sensors based on the dispersion equations for layered systems isoutlined. The approach is sufficiently general to allow for viscoelastic guiding layers. Anequation for the phase velocity and insertion loss sensitivities is given which depends on theslope of the complex phase velocity dispersion curves. This equation contains the equivalentof the Sauerbrey and Kanazawa equations for loading of a quartz crystal microbalance byrigid mass and Newtonian liquids, respectively, and also describes surface loading byviscoelastic layers. The theoretical approach can be applied to a four-layer system, withany of the four layers being viscoelastic, so that mass deposition from a liquidcan also be modelled. The theoretical dispersion equation based approach tolayer-guided shear horizontal acoustic wave modes on finite substrates presented inthis work provides a unified view of Love wave and shear horizontal acousticplate mode (SH-APM) devices, which have been generally regarded as distinctin sensor research. It is argued that SH-APMs with guiding layers possessingshear acoustic speeds lower than that of the substrate and Love waves are twobranches of solution of the same dispersion equation. The layer guided SH-APMshave a phase velocity higher than that of the substrate and the Love waves aphase velocity lower than that of the substrate. Higher-order Love wave modes arecontinuations of the layer-guided SH-APMs. The generalized concept of SH-APMs andLove waves provides a basis for understanding the change in sensitivity withhigher-frequency operation and the relationship between multiple modes in Love wavesensors. It also explains why a relatively thick layer of a high-loss polymer canbe used as a waveguide layer and so extends the range of materials that can beconsidered experimentally. Moreover, it is predicted that a new type of sensor,a layer-guided SH-APM sensor, can be constructed in a manner analogous toa Love wave device. The sensitivity of such a device is predicted to approachthat of a Love wave sensor whilst retaining the advantage of the SH-APM ofusing the face opposite the one possessing the transducers as the sensing surface.

Theoretical mass, liquid, and polymer sensitivity of acoustic wave sensors with viscoelastic guiding layers

The theoretical sensitivity of Love wave and layer-guided shear horizontal acoustic plate mode (SH-APM) sensors for viscoelastic guiding layers and general loading by viscoelastic materials is developed. A dispersion equation previously derived for a system of three rigidly coupled elastic mass layers is modified so that the second and third layers can be viscoelastic. The inclusion of viscoelasticity into the second, wave guiding layer, introduces a damping term, in addition to a phase velocity shift, into the response of the acoustic wave system. Both the waveguiding layer and the third, perturbing layer, are modeled using a Maxwell model of viscoelasticity. The model therefore includes the limits of loading of both nonguided shear horizontal surface acoustic wave and acoustic plate mode (APM) sensors, in addition to Love wave and layer-guided SH-APM sensors, by rigidly coupled elastic mass and by Newtonian liquids. The three-layer model is extended to include a viscoelastic fourth layer of arbitrary thickness and so enable mass deposition onto an immersed Love wave or layer-guided SH-APM sensor to be described. A relationship between the change in the complex velocity and the slope of the complex dispersion curve is derived and the similarity to the mass and liquid sensor response of quartz crystal microbalances is discussed. Numerical calculations are presented for the case of a Love wave device in vacuum with a viscoelastic waveguiding layer. It is shown that, while a particular polymer relaxation time may be chosen such that the effect of viscoelasticity on the real part of the phase speed is relatively small, it may nonetheless induce a large insertion loss. The potential or the use of insertion loss as a sensor parameter is discussed.

Theoretical mass sensitivity of Love wave and layer guided acoustic plate mode sensors

A model for the mass sensitivity of Love wave and layer guided shear horizontal acoustic plate mode (SH–APM) sensors is developed by considering the propagation of shear horizontally polarized acoustic waves in a three layer system. A dispersion equation is derived for this three layer system and this is shown to contain the dispersion equation for the two layer system of the substrate and the guiding layer plus a term involving the third layer, which is regarded as a perturbing mass layer. This equation is valid for an arbitrary thickness perturbing mass layer. The perturbation, Δν, of the wave speed for the two-layer system by a thin third layer of density, ρp and thickness Δh is shown to be equal to the mass per unit area multiplied by a function dependent only on the properties of the substrate and the guiding layer, and the operating frequency of the sensor. The independence of the function from the properties of the third layer means that the mass sensitivity of the bare, two-layer, sensor operated about any thickness of the guiding layer can be deduced from the slope of the numerically or experimentally determined dispersion curve. Formulas are also derived for a Love wave on an infinite thickness substrate describing the change in mass sensitivity due to a change in frequency. The consequences of the various formulas for mass sensing applications are illustrated using numerical calculations with parameters describing a (rigid) poly(methylmethacrylate) wave-guiding layer on a finite thickness quartz substrate. These calculations demonstrate that a layer-guided SH–APM can have a mass sensitivity comparable to, or higher, than that of Love waves propagating on the same substrate. The increase in mass sensitivity of the layer guided SH–APMs over previously studied SH–APM sensors is of significance, particularly for liquid sensing applications. The relevance of the dispersion curve to experiments using higher frequencies or frequency hopping and to experiments using thick guiding layers is discussed.

Microacoustic Sensors for Liquid Monitoring

In recent years, much effort has been expended to developing miniaturized, reliable sensors for measuring physical and chemical liquid properties. Microacoustic devices may be employed to determinate physical quantities perturbing the propagation conditions of the acoustic wave, even in liquid environments. For liquid sensors, acoustic modes with shear polarization are often used in order to avoid radiation losses. Examples are shear bulk modes, surface skimming bulk waves, shear-horizontal acoustic plate modes, and Love modes. Furthermore, modes with sagittal polarization may be applied if their phase velocity is sufficiently lower than the sound velocity in the adjacent liquid. General interactions between acoustic waves and liquids are viscous coupling, acoustoelectric effects, and mass loading. The resulting changes in device frequency and attenuation may be utilized for sensing purposes. The general advantages of microacoustic sensors are high sensitivity, simple fabrication, and quasidigital frequency readout. Hence, a wide variety of devices based on different modes for very different applications has been discussed in the relevant literature. The aim of this review is to provide a systematic overview of microacoustic sensors particularlay suited for operation in liquids. First, we provide a brief introduction to surface acoustic wave devices and the underlying physics, basic microacoustic structures, and general measurement techniques. A description of the mechanisms of interaction between liquids and acoustic waves is then followed by a comprehensive survey covering the different types of microacoustic liquid sensors, with emphasis on the mode-specific device properties. Thereafter, aspects of material selection and device fabrication are summarized. Lastly, an overview is given indicating where microacoustic liquid sensors have already been put into practice and where their application may be expected in the near future.

Mass sensitivity of SH-APM sensors: potentialities for organophosphorous vapors detection

Using the mathematical software MapleV, a model was previously developed to determine the mass sensitivity of Shear Horizontal Acoustic Plate Mode (SH-APM) sensors. The theoretical approach and results obtained are briefly recalled in this paper. They led to the realization of test devices. To validate the model in the case of a mass loading effect, SH-APM devices were tested in gas medium and allowed the detection of organophosphorous vapors.

Analysis of the coupling between shear horizontal plate waves and liquids: Application to the measurement of the shear rigidity modulus of glycerol solutions

This article presents an acoustic wave viscometer based on the shear horizontal acoustic plate mode excited by interdigital transducers on a ST-cut quartz substrate. A theoretical model, which is an extension of the plate effective permittivity function taking into account the presence of liquids, is developed in order to predict the phase and attenuation variations versus the viscosity of liquid. These results are discussed and compared to those of models from the literature such as variational or perturbation methods. The measured results for aqueous solutions of glycerol show linear dependence between the phase and attenuation variations and the square root of liquid viscosity, and are consistent with the theoretical results. The device can be used for viscosity measurements up to 1000 mPa s. For higher viscosities, the viscoelastic behavior of the solution appears and the shear rigidity modulus must be taken into account. The value of μ∞=2.5×109 N m2 has been obtained for glycerol by fitting the theoretical curves to the experimental points.

The multi-layered effective permittivity function applied to the mass loading and viscous coupling in shear horizontal-acoustic plate modes

It is now well known that acoustic plate wave devices are very promising as gravimetric sensors in liquid phase as well as liquid properties sensors. Here, a model based on the effective permittivity function is developed to take into account the multi-layered configuration of these devices operating in liquid phase. Indeed, for gravimetric applications, a three-layered configuration is implemented: the piezoelectric plate, the elastic solid film and the semi-infinite liquid medium. The predictions of the model for an increasing solid film thickness are compared with experimental measurements obtained by electrodeposition. For the determination of liquid properties, a two-layered configuration is appropriate: the piezoelectric plate loaded by the liquid medium. Here, particular attention is paid to the effect of the density and the viscosity of the liquid medium on the device response. The theoretical results are compared with measurements performed with aqueous glycerol solutions, whose density and viscosity increase with concentration of glycerol. For high concentrations, the Maxwellian behavior of the aqueous glycerol solutions allows to determine the shear rigidity modulus of glycerol.

Study of the mass sensitivity of SH-APM sensors with Maple V

Shear horizontal acoustic plate mode (SH-APM) devices offer interesting possibilities to probe liquid or polymer physico-chemical properties. As many parameters can influence their sensitivity, our research on these sensors involves modelling. This was based on the `partial waves' method, and was carried out with the mathematical software Maple V. In this paper, we study the mass sensitivity of SH-APModes, in the case of a quartz plate covered by a copper phthalocyanine (CuPC) layer. The influence of multiple parameters on the sensor sensitivity was evaluated: sensitive coating nature and thickness, quartz plate thickness and crystallographic cut, transducer electrode periodicity and mode order. The results of modelling are compared to available experimental results (mainly the influence of an isotropic layer); and also to the mass sensitivity of SAW devices.

Electrochemical piezoelectric sensors for trace ionic contaminants

Industrial processes, such as fossil fuel combustion and nuclear materials processing, have resulted in heavy metal contamination of soils and potentially of the surrounding groundwater. In particular, mercury contamination of groundwater is a serious threat to the ecosystem, cumulating in serious health problems for humans as well as wildlife. Monitoring of mercury contamination in groundwater requires a method of long-term verification. Sensors with lifetimes of months to years of operation without operator intervention are required. One sensor geometry, which is capable of detecting relevant concentrations of aqueous ionic contaminants, such as mercury, while withstanding typical environmental conditions, is the shear horizontal acoustic plate mode (SHAPM) sensor. This sensor protects the electronics from the potentially corrosive aqueous fluid environment while providing a significant interaction with the fluid. Gold films are employed to accumulate the mercury via surface amalgamation. The added mass is measured as a change in the resonant frequency of the piezoelectric sensing element. Electrochemical techniques are employed to impart reversibility and to accelerate response kinetics. Results indicate a sensitivity of approximately 2.4 ng/mL, which approaches the 2.0 ng/mL limit imposed by the Safe Drinking Water Act (SDWA).

Mass sensitivity of acoustic plate mode in liquids

In this paper, the concept of electrical effective permittivity function is used to calculate the eigen-frequencies and the particle displacements of piezoelectric acoustic plate modes (APM). These results allowed us to determine the mass sensitivities of the first order vibration modes using a first order perturbation theory. Theoretical results are discussed and compared to those of a variational method and isotropic two-layer composite analysis in the case of a shear horizontal APM sensor on a singly rotated cut quartz substrate. Experimental measurements by a copper electrodeposition are carried out and show that the perturbation method leads to a better understanding of the APM behavior.

Using a formal mathematics software for SH-APM sensor modelling

Shear horizontal acoustic plate mode (SH-APM) sensors have been receiving a great deal of attention in biochemical applications for a few years [1–3]. They consist of a quartz plate with two interdigital transducers (IDTs) deposited on one surface, and a sensitive and selective coating layered on the opposite surface along which the wave interferes. The sensor sensitivity to mass loading, the acousto-electric effects, and the influence of viscosity, conductivity and temperature depend strongly on the considered mode and on the geometrical parameters of the delay line. Moreover, the nature and the crystallographic cut of the substrate, the ratio between the plate thickness and the wavelength, and the operating temperature are also important parameters. Systematic experimental studies are all the more difficult to achieve since there are many propagation modes and various detection mechanisms. As a consequence, our research on SH-APM sensors involves modelling devices. The modelling based on a ‘matrix approach’ was carried out with the help of the formal mathematics software MapleV. In this paper are reported the analytical and numerical results obtained with the software, as well as the calculation of the SH-APM phase velocity that can propagate in thin quartz plates of particular crystallographic cuts. These theoretical results are compared with experimental responses.

A shear-horizontal acoustic plate mode (SH-APM) sensor for biological media

Acoustic wave devices are often used as chemical sensors. Those described in the literature are merely based on bulk waves or on surface waves (SAW), also called Rayleigh waves. In this paper we describe another type of device, based on shear-horizontal acoustic plate mode (SH-APM) waves. Experimental results with various modes concerning the influence of the temperature, the viscosity and the concentration of NaCl and tris(hydroxymethyl)aminomethane (Tris) in aqueous solution are presented: they show the better sensitivity of higher-order modes. These results show that this device can be used as a sensor in a biological medium.

Acoustic wave devices to measure gas flow: Comparison between surface acoustic wave (SAW) and shear horizontal acoustic plate mode (SH-APM) oscillators

In recent years there has been growing interest in using acoustic waves for a broad spectrum of physical and chemical sensor applications. In this paper we describe two types of acoustic flow sensors. For both devices, interdigital transducers (IDTs) on a piezoelectric substrate have been used to realize delay lines. The substrate is quartz with a SAW (SH-APM) propagation direction along (normal to) the crystallographic X axis. The delay line, mounted in an oscillator configuration and heated at a constant power with a screen-printed resistor, is placed in the path of the flowing fluid. Cooling caused by fluid motion induces a change in the oscillator frequency. The sensitivity of the two configurations (SAW and SH-APM) to flow rate at various heating power levels is presented and discussed. Taking into account simplified assumptions, we obtain an evaluation of the different heat-loss sources (thermal conduction, natural and forced convections). The interest of the SH-APM oscillator in terms of sensitivity and response time is demonstrated. This is all the more interesting as SH-APM devices are able to work in a liquid environment.

Shear Horizontal Acoustic Plate Mode Viscosity Sensor

Mode analysis of a LiTaO3 (LTO) plate has been carried out numerically, and an interference-free shear horizontal acoustic plate mode (SH-APM) suitable for measuring the liquid viscosity was found. A viscosity sensor having a liquid container on the side opposite to interdigital transducers (IDTs) was fabricated on X-cut 148° Y-prop LTO. Satisfactory agreement was obtained between the calculated frequency spectrum and the experimental one. A loading test was carried out for a series of Newtonian liquids, which showed good agreement with the perturbation theory.

Acoustic love-wave sensor for K + concentration in H 2O solutions

An acoustic delay-line sensor for the detection of K + ion concentrations in water solutions is described. It uses shear horizontal (SH) acoustic plate modes propagating in plates in order to minimize acoustic energy loss in the liquid. The device consists of a quartz plate with one of the free surfaces covered with a thin membrane that selectively sorbs K ions. The membrane consists of a mixture of polyvinylchloride (PVC), dibutylsebacate, tetrahydrofuran and valinomycin, which is a well-known ligand for K +. SH waves are generated and detected by interdigital transducers located on the opposite surface of the plate. The advantage of this arrangement is that electroacoustic transducers are separated from the liquid environment under test. The operation of the device is based on the changes produced by the K ions captured by the membrane on the phase velocity of the acoustic waves. A differential structure is used with only one line covered by the sensitive membrane in order to compensate common-mode error sources, which are particularly severe for the specific case of devices operating in liquid environments. The time response on K + absorption and desorption, as well as the response versus K + concentration, are reported here.

Monitoring photo-polymerization of thin films using SH acoustic plate mode sensors

Abstract The use of shear-horizontal (SH) acoustic plate mode (APM) devices to monitor the cross-linking of polymer films in real time has been demonstrated. The SH-APM, which is excited and detected in a thinned quartz plate by interdigital transducers patterned on the surface, has displacement in the plane of the surface and normal to the direction of mode propagation. Because APM propagation velocity is affected by the shear stiffness (but not the bulk modulus) of a thin film in contact with the device surface, the APM acts as a sensitive probe of this film property. Using an APM sensor, the changes in shear modulus which accompany the photocross-linking of a negative photoresist polymer film were monitored as a function of time and of the wavelength of the cross-linking radiation.