Ultrasonic linear motor using surface acoustic waves

The first success in the operation of an ultrasonic linear motor at HF band driving frequency using the Rayleigh wave is described. The substrate material is a 127.8° Y-cut LiNbO₃ wafer whose diameter is three inches. Four interdigital transducers (IDT's) are arranged to excite x- and y-propagation waves in both directions. The dimensions of the IDT are 25 mm aperture size, 400 μm pitch, 100 μm strip width, and 10 pairs. The operation area is about 25 mm square, The driving frequency is about 9.6 MHz in the x direction and about 9.1 MHz in the y direction. The most important point of the success is the shape of the contact surface and slider materials. For the contact materials, small balls about 1 mm in diameter are introduced to obtain sufficient contact pressure around 100 MPa. The use of ruby balls, steel balls, and tungsten carbide balls is investigated. Each slider has three balls to enable stable contact at three points. The maximum transfer speed is about 20 cm/s. The transfer speed is controllable by changing the driving voltage     

Kapitza conductance model using loaded acoustic surface waves

An investigation is presented of the heat transfer between liquid helium and solids associated with surface impurities or faults. The solid is described as a linear chain which is terminated by a matched dissipating element, formed by an impurity, which excites loaded acoustic surface waves (loaded Rayleigh waves). Using established theoretical and experimental results on the behavior of acoustic surface waves on a solid-to-helium interface, a heat transfer coefficient is calculated. Suggestions are made on the interpretation of some outstanding problems in Kapitza work in the light of the present model.Supported by the SRC in the form of research grants.     

Investigation of cocaine plumes using surface acoustic wave immunoassay sensors

Vapor sensors, aka electronic noses, are becoming an increasingly popular analytical tool for detection and identification of small molecules in the gas phase. In this paper, we present the results of a series of experiments demonstrating real-time vapor phase detection of cocaine molecules. A distinctive response or signature was observed under laboratory conditions in which the cocaine vapors were presented using an INEL vapor generator and under "field" conditions facilitated by the Georgia Bureau of Investigation (GBI) Crime Lab. For these experiments, the sensor component was a two-port resonator on ST-X quartz with a center frequency of approximately 250 MHz. On this cut of quartz, a temperature-compensated surface acoustic wave is generated via an interdigital transducer. Antibenzoylecgonine (anti-BZE) antibodies are attached to the electrodes on the device surface via a protein-A cross linker. We observed a large transient frequency shift accompanied by baseline shift with the anti-BZE coated sensor. After repeated experiments and the use of numerous controls, we believe that we have achieved real time molecular recognition of cocaine molecules.     

Modeling of surface acoustic wave strain sensors using coupling-of-modes analysis

SAW devices may be configured as strain sensors, providing passive, wireless strain measurement in demanding conditions. A key consideration is the modeling of the sensors, enabling different device designs to be considered. This paper presents a simulation scheme using coupling-of-modes (COM) analysis which allows both the frequency response of a SAW strain sensor and its bias sensitivity to be evaluated. Example applications are presented to demonstrate the use of the model.     

Controlling the properties of surface acoustic waves using graphene

Surface acoustic waves (SAWs) are elastic waves that propagate on the surface of a solid, much like waves on the ocean, with SAW devices used widely in communication and sensing. The ability to dynamically control the properties of SAWs would allow the creation of devices with improved performance or new functionality. However, so far it has proved extremely difficult to develop a practical way of achieving this control. In this paper we demonstrate voltage control of SAWs in a hybrid graphene-lithium niobate device. The velocity shift of the SAWs was measured as the conductivity of the graphene was modulated using an ion-gel gate, with a 0.1% velocity shift achieved for a bias of approximately 1 V. This velocity shift is comparable to that previously achieved in much more complicated hybrid semiconductor devices, and optimization of this approach could therefore lead to a practical, cost-effective voltage-controlled velocity shifter. In addition, the piezoelectric fields associated with the SAW can also be used to trap and transport the charge carriers within the graphene. Uniquely to graphene, we show that the acoustoelectric current in the same device can be reversed, and switched off, using the gate voltage.

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Thin-film characterization using a scanning laser acoustic microscope with surface acoustic waves

The use of surface acoustic waves in a scanning laser acoustic microscope for the characterization of the mechanical or acoustic properties of thin films deposited on piezoelectric substrates is demonstrated. Quantitative measurements of mass loading effects of 5000-A-thick tungsten films deposited on lithium niobate substrates were obtained using 100-MHz surface acoustic waves. No information about the tungsten film could be obtained using 100-MHz compressional waves. Methods of generating surface waves on nonpiezoelectric materials so that this technique could be used on arbitrary substrates are discussed.     

Molecular recognition for electronic noses using surface acoustic wave immunoassay sensors

In this paper, we present the results of a series of experiments on vapor phase surface acoustic wave (SAW) sensors using a layer of antibodies as the chemically sensitive film. For these experiments, the sensor component was a ST-quartz resonator with a center frequency of approximately 250 MHz. Anti-FITC antibodies were attached to the electrodes on the device surface via a protein-A crosslinker. SAW resonator devices with various coatings were mounted in TO-8 packages, inserted into a sensor head module and subjected to various fluorescent analyte gases. Numerous controls were performed including the use of coated and uncoated devices along with devices coated with antibodies which were not specific for the target analyte. The SAW immunosensor response was monitored and a baseline frequency shift was observed when the analyte being presented was the antigen for the immobilized antibody. To provide an independent measure of antibody/antigen binding, the devices were removed from the sensor head, washed with a buffer solution to remove any unbound analyte, and then inspected using a confocal laser scanning microscope (CLSM). Since all the analytes being used in these experiments were fluorescent, this afforded us the opportunity to visualize the attachment of the analyte to the antibody film. Given the high resolution of the CLSM, we were able to identify the location of the attachment of the fluorescent analytes relative to the 1.5 /spl mu/m wide electrodes of the SAW device. We believe that these experiments demonstrate that we have achieved real time molecular recognition of these small molecules in the vapor phase.     

Vapor phase detection of a narcotic using surface acoustic wave immunoassay sensors

Currently, the narcotic sniffing dog remains the most accurate, reliable, and widely used sensing technology in the war on drugs. However, recent studies done at the Institute for Biological Detection Systems at Auburn University, Auburn, AL, have shown that in the presence of extraneous odors (nontarget odors), these animals show a higher propensity for so-called false alarms. For this reason, there have been an increasing demand for a portable, highly specific vapor-sensing device capable of distinguishing a target vapor signature in a complex odor. In this paper, we present the results of a series of experiments demonstrating real-time vapor phase detection of cocaine molecules. A distinctive response or signature was observed under laboratory conditions, where the cocaine vapors were presented using an INEL vapor generator and under "field" conditions facilitated by the Georgia Bureau of Investigation Crime Lab. For these experiments, the sensor component was an ST-X quartz resonator with a center frequency of approximately 250-MHz. Anti-benzoylecgonine (anti-BZE) antibodies are attached to the electrodes on the device surface via a protein-A cross linker. We observed a large transient frequency shift accompanied by baseline shift with the anti-BZE coated sensor. After repeated experiments and the use of numerous controls, we believe that we have achieved real-time molecular recognition of cocaine molecules.     

Scanning displacement sensors with surface acoustic wave modulation

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 3–4, October, 1990.     

Reflective acousto-optic modulation with surface acoustic waves

A reflective optical modulator based on acousto-optic modulation of light by a mirror corrugated with surface acoustic waves is presented. Modulation of optical amplitude, frequency, and phase is demonstrated at visible (633- and 488-nm) and deep UV (244-nm) wavelengths. The reflective modulator has eight channels and achieves a maximum first-order diffraction efficiency of 6.0%.     

Propagation of surface acoustic waves inn-type GaAs films

The effect of nonparabolicity on the amplification of surface acoustic waves in n-type GaAs films is investigated quantum mechanically in the GHz frequency region. Numerical results show that the amplification coefficient for the nonparabolic band structure is enhanced due to the nonlinear nature of the energy band in semiconductors. Moreover, the amplification coefficients in semiconductors depend on the temperature, the electronic screening effect, the frequency of sound waves, the applied electric field, and the thickness of the semiconductor film.Partially supported by National Science Council of the Republic of China.     

Review of shear surface acoustic waves in solids

General considerations about physical reasons for the existence of surface acoustic waves and, in particular, shear surface acoustic waves in solids are presented. The results of calculations for various types of shear surface acoustic waves are described, and corresponding physical explanations are given.     

Stress-sensitivity mapping for surface acoustic waves on quartz

A model is presented, relating the velocity shifts of surface acoustic waves (SAW) to the six tensor components of quasistatic stresses. Stress sensitivity is then defined through six independent coefficients, whatever the origin of the stress (direct external forces, thermoelastic stresses) might be. These coefficients, depending on crystal anisotropy, are computed for different cut angles and propagation directions of quartz crystal, and represented as a contour-line mapping. The determination of SAW quartz cuts compensated for both planar isotropic stresses and first-order temperature effects make it possible to define a family of quartz cuts with potentially low stress and temperature sensitivities for oscillator applications.     

Nonlinear surface acoustic waves on an isotropic solid

A systematic derivation of the approximate coupled amplitude equations governing the propagation of a quasi-monochromatic Rayleigh surface wave on an isotropic solid is presented, starting from the non-linear governing differential equations and the non-linear free-surface boundary conditions, using the method of mulitple scales. An explicit solution of these equations for a signalling problem is obtained in terms of hyperbolic functions. In the case of monochromatic excitation, it is shown that the second harmonic amplitude grows initially at the expense of the fundamental and that the amplitudes of the fundamental and second harmonic remain bounded for all time.     

Temperature-sensitive cuts for surface acoustic waves in quartz

Temperature is the main parameter that affects the stability of surface acoustic wave (SAW) devices such as the external and internal stress. The temperature sensitivity of the frequency as a function of quartz crystal anisotropy is presented by a perturbation equation because of a temperature change. The analytical result shows which cut is suitable for high temperature sensitivity of the quartz and which cut is associated with low temperature sensitivity. The theoretical sensitivity values are compared with experimental results. Both the experimental and theoretical results are in good agreement.     

Elastic effects of polymer coatings on surface acoustic waves

Surface acoustic wave (SAW) devices are presently receiving careful scrutiny for applications in chemical sensing as well as in polymer characterization. Gas monitors based on SAW sensors have the potential for miniaturization and high sensitivity to a wide variety of substances. Polymer characterization is applicable to such diverse fields as protective coating design and decontamination of polymers. To better understand the physical mechanisms behind SAW response, the effects of the elastic properties in comparison to the mass loading of polymer coatings on SAW substrates were investigated. A theoretical basis for the effects of vapor-induced swelling or of thermal expansion was established. Compressive tension and its effect on SAW frequencies were found to be simple to describe, if there is no film slippage or polymer flow. The response of quartz substrate SAW crystals coated with polycarbonate and polyimide (glassy polymers) upon exposure to toluene and methanol was measured. Practical problems as to film uniformity, thickness measurement, and environmental control necessary in such measurements are described. Contrary to recent reports in the literature, no significant elastic tightening effect was observed with these vapor/polymer pairs.     

Nonlinear reflection of surface acoustic waves from contact lines

We present the results of an experimental investigation of nonlinear processes accompanying the interaction of surface acoustic waves (SAWs) with real cracking defects and contact lines. The dynamic characteristics of the nonlinear reflection of higher harmonics are presented. It is shown that the third harmonic generation has a pronounced threshold character, the dynamic characteristics exhibit hysteresis, and the efficiency of nonlinear response depends on the duration of SAW action on the defect. The results lead to a conclusion that the nonlinear reflection of SAWs from a contact line provides an adequate model of reflection from a real cracking defect.     

Scanning tomographic acoustic microscopy using shear waves

We propose to use shear waves instead of longitudinal waves in a novel scanning tomographic acoustic microscope (STAM) in which the specimens are solid. When a specimen with a shear modulus is immersed in the microscope's water bath, mode conversion takes place at the water-solid interface. The shear wave energy is detectable and can be used for image reconstruction. Although wave transmission in most solid specimens is limited to about 20 degrees for longitudinal waves, it is about twice that for shear waves. Also, velocities of shear waves are lower than those of longitudinal waves and hence the wavelengths at the same frequency are smaller. For these and other reasons we can expect that for many specimens the resolution of a shear-wave STAM to be substantially better than that of a longitudinal-wave STAM. We use computer simulation in order to compare the operation of a shear-wave STAM with that of the conventional longitudinal-wave STAM. We have simulated tomographic reconstruction for each. The corresponding critical angles of incidence are computed and tomographic reconstructions of a particular solid specimen is obtained by using the back-and-forth propagation algorithm (BFP). Our simulation results show that shear-wave STAM has better resolution than longitudinal-wave STAM.     

A uniform asymptotic solution for nonlinear surface acoustic waves

A complete investigation of the coupled amplitude theory of nonlinear surface acoustic waves on an isotropic elastic solid, which avoids the limitations encountered in previous theories, is given here. A complete, uniformly valid solution in the interior of the medium is derived. Perspective drawings to study asymptotically the growth-decay cycles the displacement and the velocity profiles, have also been done.