Shear Horizontal Surface Acoustic Wave Research Articles

Rayleigh SAW-Assisted SH-SAW Immunosensor on X-Cut 148-Y LiTaO3.

In this paper, we describe a shear horizontal surface acoustic wave (SH-SAW) immunosensor that utilizes induce agitation by a Rayleigh SAW (R-SAW) on an X-cut 148-Y LiTaO3 substrate. On this substrate, SH-SAWs and R-SAWs with different frequencies can be effectively generated at an interdigital transducer (IDT). First, to consider the power flow angles of SH-SAWs and R-SAWs on this substrate, the 360-MHz delay lines with six different tilt angles were designed and fabricated. From the experiments, an optimal power flow angle of 9° for the SH-SAW on this substrate is obtained. Second, in order to consider the immunoreactions of the SH-SAW immunosensors, a delay line with a tilt angle of 9° was designed and fabricated on this substrate. The delay line, which can generate two SAWs, namely, a 100-MHz SH-SAW and an 88.8-MHz R-SAW, has a propagation area covered with antigens of human serum albumin between transmitting and receiving IDTs. The immunoreactions caused by antigen-antibody binding events on the surface of the delay line were investigated on the basis of the velocity changes of the SH-SAWs for sensing with and without the assistance of an R-SAW. As a result, it was confirmed that the SH-SAW velocity changes due to antigen-antibody reactions can be markedly increased by the assistance of R-SAW agitation.

Real-time monitoring of methanol concentration using a shear horizontal surface acoustic wave sensor for direct methanol fuel cell without reference liquid measurement

In recent years, there has been an increasing demand for sensors that continuously measure liquid concentrations and detect abnormalities in liquid environments. In this study, a shear horizontal surface acoustic wave (SH-SAW) sensor is applied for the continuous monitoring of liquid concentrations. As the SH-SAW sensor functions using the relative measurement method, it normally needs a reference at each measurement. However, if the sensor is installed in a liquid flow cell, it is difficult to measure a reference liquid. Therefore, it is important to establish an estimation method for liquid concentrations using the SH-SAW sensor without requiring a reference measurement. In this study, the SH-SAW sensor is installed in a direct methanol fuel cell to monitor the methanol concentration. The estimated concentration is compared with a conventional density meter. Moreover, the effect of formic acid is examined. When the fuel temperature is higher than 70 °C, it is necessary to consider the influence of liquid conductivity. Here, an estimation method for these cases is also proposed.

Estimation of liquid properties by inverse problem analysis based on shear horizontal surface acoustic wave sensor responses

A shear horizontal surface acoustic wave (SH-SAW) sensor can detect liquid properties, such as viscosity, density, permittivity, and conductivity. The advantage of using the SH-SAW sensors is the simultaneous detection of the mechanical and electrical properties of liquids. In this paper, we proposed a method of estimating the density and viscosity of liquids based on the inverse problem analysis. Glycerol or ethanol aqueous solutions were measured. The estimated and literature values were compared. For glycerol aqueous solutions, when the concentration is low, those values agree well. However, when the concentration is high, those values did not agree because the bulk modulus of glycerin solutions cannot be assumed as constant. On the other hand, as the bulk modulus of ethanol aqueous solutions can be assumed to be the same as that of water, the deviations between those values were small. Therefore, the proposed method is effective when the bulk modulus is assumed as constant.

Temperature dependence of immunoreactions using shear horizontal surface acoustic wave immunosensors

In this paper, the temperature dependence of immunoreactions, which are antibody–antigen reactions, on a shear horizontal surface acoustic wave (SH-SAW) immunosensor is described. The immunosensor is based on a reflection-type delay line on a 36° Y-cut 90° X-propagation quartz substrate, where the delay line is composed of a floating electrode unidirectional transducer (FEUDT), a grating reflector, and a sensing area between them. In order to evaluate the temperature dependence of immunoreactions, human serum albumin (HSA) antigen–antibody reactions are investigated. The SH-SAW immunosensor chip is placed in a thermostatic chamber and the changes in the SH-SAW velocity resulting from the immunoreactions are measured at different temperatures. As a result, it is observed that the HSA immunoreactions are influenced by the ambient temperature and that higher temperatures provide more active reactions. In order to analyze the immunoreactions, an analytical approach using an exponential fitting method for changes in SH-SAW velocity is employed.

Investigation of interaction of shear horizontal surface acoustic wave with controlled electroinduced domain structure

In recent years, there has been great interest in developing different kinds of phononic crystals (PCs) with advanced ultrasound properties. In this study, we examined the possibility of creating a periodic domain structure controlled by an external electric field. The electric field was induced using crossed electrodes on the surface of a LiTaO3 single crystal. We investigated the domain formation process, in which the external electric field was smaller than the coercive electric field, and spontaneous polarization is not inverted. We proposed a new type of surface acoustic wave device and studied the parameters of interaction of a low-velocity shear horizontal acoustic wave with an electroinduced domain structure. This new kind of acoustic device allows the study of various ultrasound effects and the development of advanced controllable acoustoelectronic devices.

Influence of coupling with shear horizontal surface acoustic wave on lateral propagation of Rayleigh surface acoustic wave on 128°YX-LiNbO3

In this paper, we investigate the impact of the coupling with shear horizontal (SH) surface acoustic wave (SAW) on the propagation of Rayleigh SAW in periodic grating structures on 128°YX-LiNbO3. First, the frequency dispersion behavior with longitudinal and lateral wavenumbers of Rayleigh SAW is calculated using the finite element method (FEM) software COMSOL. It is shown that the coupling causes (1) the satellite stopband and (2) variation of the anisotropy factor. It is also shown these phenomena remain even when the electromechanical coupling factor of SH SAW is zero. Then, the extended thin plate model which can take coupling between two SAWs into account, is applied to simulate the result of FEM. Good agreement between these results indicated that the mechanical coupling is responsible for these two phenomena. Finally, including electrical excitation and detection, the model is applied to the infinitely long interdigital transducer (IDT) structure and the calculated result is compared with that obtained by the three-dimensional FEM. The excellent agreement of both results confirms the effectiveness of the extended thin plate model.

Extra two new piezoelectromagnetic SH-SAWs with dramatic dependence on small electromagnetic constant

It is expected that this theoretical report finalizes the research regarding to the shear-horizontal surface acoustic wave (SH-SAW) propagation along the suitable surface of the transversely isotropic (6mm) piezoelectromagnetics. This report examines extra two new SH-SAWs, the existence of which dramatically depends on the small electromagnetic constant that is responsible for the magnetoelectric effect. This study also provides some comparison with the previously obtained theoretical results and the phenomenon called the Goldstone excitation. The obtained results can be useful for educational purposes, creation of novel technical devices based on the magnetoelectric effect that can find applications in spintronics, further theoretical treatments of the SH-wave propagation in plates, nondestructive testing and evaluation of apt surfaces and plates, etc.

Modeling and Analysis of Lateral Propagation of Surface Acoustic Waves Including Coupling Between Different Waves.

This paper discusses lateral propagation of surface acoustic waves (SAWs) in periodic grating structures when two types of SAWs exist simultaneously and are coupled. The thin plate model proposed by the authors is extended to include the coupling between two different SAW modes. First, lateral SAW propagation in an infinitely long periodic grating is modeled and discussed. Then, the model is applied to the Al-grating/42° YX-LiTaO3 (42-LT) substrate structure, and it is shown that the slowness curve shape changes from concave to convex with the Al grating thickness. The transverse responses are also analyzed on an infinitely long interdigital transducer on the structure, and good agreement is achieved between the present and the finite-element method analyses. Finally, SAW resonators are fabricated on the Cu grating/42-LT substrate structure, and it is experimentally verified that the slowness curve shape of the shear horizontal SAW changes with the Cu thickness.

Suppression of Rayleigh wave spurious signal in ultra-wideband surface acoustic wave devices employing 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystals

The propagation characteristics of surface acoustic waves (SAWs) on rotated Y-cut X-propagating 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3(PMN-33%PT) substrate are theoretically analyzed. It is shown that besides the existence of a shear horizontal (SH) SAW with ultrahigh electromechanical coupling factor K2, a Rayleigh SAW also exists causing strong spurious response. The calculated results showed that the spurious Rayleigh SAW can be sufficiently suppressed by properly selecting electrode and its thickness with optimized rotating angle while maintaining large K2 of SH SAW. The fractional -3 dB bandwidth of 47% is achievable for the ladder type filter constructed by Au IDT/48oYX-PMN-33%PT resonators.

Vertical jetting induced by shear horizontal leaky surface acoustic wave on 36° Y-X LiTaO3

Shear horizontal surface acoustic waves (SH-SAWs) have been regarded as good candidates for liquid sensing applications but are inefficient in fluid manipulation due to a minimal fluid coupling between the fluid and acoustic waves. However, in this letter, a vertical jetting function was realized using the SH-SAW generated from a 36° Y-X LiTaO3 SAW device. The jetting of the droplet induced by the SH-SAWs was observed nearly along the vertical direction, and the aspect ratio of the liquid beam is proportional to the applied power before breaking up, which is dramatically different from those generated from the conventional Rayleigh SAWs. By conducting theoretical simulation and experimental investigation on the SH-SAWs systematically, we concluded that the wave/energy pressure dissipated into the sessile droplets causes this vertical ejection on the device surface.

Rapid cell separation with minimal manipulation for autologous cell therapies

The ability to isolate specific, viable cell populations from mixed ensembles with minimal manipulation and within intra-operative time would provide significant advantages for autologous, cell-based therapies in regenerative medicine. Current cell-enrichment technologies are either slow, lack specificity and/or require labelling. Thus a rapid, label-free separation technology that does not affect cell functionality, viability or phenotype is highly desirable. Here, we demonstrate separation of viable from non-viable human stromal cells using remote dielectrophoresis, in which an electric field is coupled into a microfluidic channel using shear-horizontal surface acoustic waves, producing an array of virtual electrodes within the channel. This allows high-throughput dielectrophoretic cell separation in high conductivity, physiological-like fluids, overcoming the limitations of conventional dielectrophoresis. We demonstrate viable/non-viable separation efficacy of >98% in pre-purified mesenchymal stromal cells, extracted from human dental pulp, with no adverse effects on cell viability, or on their subsequent osteogenic capabilities.

Full-Wave Analysis of Ultrahigh Electromechanical Coupling Surface Acoustic Wave Propagating Properties in a Relaxor Based Ferroelectric Single Crystal/Cubic Silicon Carbide Layered Structure

This paper describes a full-wave analysis of ultrahigh electromechanical coupling surface acoustic wave (SAW) of Y-cut X propagating Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (YX-PIMNT) single crystals on a cubic silicon carbide (3C-SiC) substrate. There are several eigenmodes including shear horizontal (SH) and Rayleigh SAWs. Based on the finite-element method (FEM), the phase velocity (vp) and coupling factor (K2) of SAWs varying with the top electrode thickness, thickness, and Euler angle (θ) of the YX-PIMNT substrate have been investigated. K2 of SH SAW can reach an extremely high value of 75.9%. The proper control of structural parameters can suppress unwanted responses caused by other modes without deteriorating the coupling factor. The large K2 value of SH SAW and suppression of unwanted responses have highly promising applications in developing ultrawideband and tunable SAW filters. Finally, the performance of 3C-SiC and 6H-SiC as substrates was investigated, and 3C-SiC was identified as a more attractive substrate candidate than 6H-SiC.

Highly Sensitive Escherichia coli Shear Horizontal Surface Acoustic Wave Biosensor with Silicon Dioxide Nanostructures

In this study, a shear horizontal surface acoustic wave (SHSAW) was used for Escherichia coli (E. coli) detection. E. coli O157:H7 serotype, a dangerous strain among 225 E. coli unique serotypes was chosen as test sample. A few cells of this bacterium are able to cause young children to be most vulnerable to serious complications. Presence of higher than 1 cfu E. coli O157:H7 in 25 g of food has been considered as a dangerous level. The SHSAW biosensor was fabricated on 640 YX LiNbO3 substrate. Five different interdigital transducers (IDT) parameters (Fig. 1(a)-1(e)) SHSAW were fabricated to compare the mass loading sensitivity before advancing to the bio sensing application: four of them were 32 μm pitch size (with the average of synchronous frequency, f0 = 144.303 MHz) and one was 12 μm pitch size (with f0 = 384.948 MHz). All of the four 32 μm pitch sizes were with different combination of delay line length (3.904 mm and 7.296 mm) and aperture size (1.376 mm and 2.464 mm). As for the 12 μm pitch size device, it was with 2.1 mm delay line length and 0.72 mm aperture size. Eventually, 12 μm pitch size device was selected for oligonucleotides detection and its mass loading sensitivity was 1558.04 MHz/ (mg/mm2), 4.8-fold higher than the most sensitivity one in 32 μm pitch size).Its sensitivity was enhanced by depositing 130 nm thin layer of SiO2 nanostructures with particle size less than 70 nm (Fig. 1(f)-1(g)). The nanostructures act both as a waveguide as well as the surface physical modification of the sensor prior to biomolecule immobilization. For this work, a specific DNA sequence from E. coli O157:H7 having 22 mers as an amine-terminated probe ssDNA was immobilized on the thin film sensing area through chemical functionalization [(CHO-(CH2)3-CHO) and (APTES; NH2-(CH2)3-Si(OC2H5)3]. The high-performance of sensor was shown with the oligonucleotide target and attained the sensitivity of 0.6439 nM/ 0.1 kHz and detection limit was down to 1.8 femtomolar (1.8 x 10-15 M). Further evidence was provided by specificity analysis using single mismatched and complementary oligonucleotide sequences.

Highly Sensitive SH-SAW Resonator with SiO2 trenches for Biosensing Application

The paper presents three dimensional finite element simulation of a sensitive shear-horizontal surface acoustic wave device for biosensing application. The resonator consisting of 36°-YX LiTaO3 substrate with SiO2 trenches generates a shear-horizontal standing wave. Eigenmode study and frequency response are used to calculate displacements, admittance and electromechanical coupling coefficient of the device. For a given mode, the coupling coefficient of the device increases with trench height to a maximum of about 7% and then starts to decrease till next higher order mode becomes dominant. The trenches not only serve as guiding layer to keep the energy of the wave at the surface but also cause coupled resonance leading to increase in resonance frequency and average stress at the contact area between trench and substrate. Mass loading of resonator is simulated by applying the equivalent surface mass density of double stranded DNA of length 50 base pairs uniformly over the surface area of trenches. Close to the resonant height of trenches, mass loading causes a large frequency shift making the device a highly sensitive biosensing platform.

Investigation of Polymer-Plasticizer Blends as SH-SAW Sensor Coatings for Detection of Benzene in Water with High Sensitivity and Long-Term Stability.

We report the first-ever direct detection of benzene in water at concentrations below 100 ppb (parts per billion) using acoustic wave (specifically, shear-horizontal surface acoustic wave, SH-SAW) sensors with plasticized polymer coatings. Two polymers and two plasticizers were studied as materials for sensor coatings. For each polymer-plasticizer combination, the influence of the mixing ratio of the blend on the sensitivity to benzene was measured and compared to commercially available polymers that were used for BTEX (benzene, toluene, ethylbenzene, and xylene) detection in previous work. After optimizing the coating parameters, the highest sensitivity and lowest detection limit for benzene were found for a 1.25 μm thick sensor coating of 17.5%-by-weight diisooctyl azelate-polystyrene on the tested acoustic wave device. The calculated detection limit was 45 ppb, with actual sensor responses to concentrations down to 65 ppb measured directly. Among the sensor coatings that showed good sensitivity to benzene, the best long-term stability was found for a 1.0 μm thick coating of 23% diisononyl cyclohexane-1,2-dicarboxylate-polystyrene, which was studied here because it is known to show no detectable leaching in water. The present work demonstrates that, by varying type of plasticizer, mixing ratio, and coating thickness, the mechanical and chemical properties of the coatings can be conveniently tailored to maximize analyte sorption and partial chemical selectivity for a given class of analytes as well as to minimize acoustic-wave attenuation in contact with an aqueous phase at the operating frequency of the sensor device.

Highly sensitive Escherichia coli shear horizontal surface acoustic wave biosensor with silicon dioxide nanostructures

Surface acoustic wave mediated transductions have been widely used in the sensors and actuators applications. In this study, a shear horizontal surface acoustic wave (SHSAW) was used for the detection of food pathogenic Escherichia coli O157:H7 (E.coli O157:H7), a dangerous strain among 225 E. coli unique serotypes. A few cells of this bacterium are able to cause young children to be most vulnerable to serious complications. Presence of higher than 1cfu E.coli O157:H7 in 25g of food has been considered as a dangerous level. The SHSAW biosensor was fabricated on 64° YX LiNbO3 substrate. Its sensitivity was enhanced by depositing 130.5nm thin layer of SiO2 nanostructures with particle size lesser than 70nm. The nanostructures act both as a waveguide as well as a physical surface modification of the sensor prior to biomolecular immobilization. A specific DNA sequence from E. coli O157:H7 having 22 mers as an amine-terminated probe ssDNA was immobilized on the thin film sensing area through chemical functionalization [(CHO-(CH2)3-CHO) and APTES; NH2-(CH2)3-Si(OC2H5)3]. The high-performance of sensor was shown with the specific oligonucleotide target and attained the sensitivity of 0.6439nM/0.1kHz and detection limit was down to 1.8femto-molar (1.8×10−15M). Further evidence was provided by specificity analysis using single mismatched and complementary oligonucleotide sequences.

Shear-horizontal surface acoustic wave characteristics of a (110) ZnO/SiO2/Si multilayer structure

Shear-horizontal (SH) surface acoustic wave (SAW) propagation characteristics in IDT/(110)ZnO/SiO2/Si multilayered structure were theoretically investigated using 3-dimensions (3D) finite element analysis (FEA). X-ray diffraction result shows that the prepared ZnO films have preferred (110) orientation with its c-axis parallel to the substrate. 3D FEA results and the out of plane vibration experiment confirmed that SH-SAW was successfully excited in the multilayered structure. The phase velocities Vp, electromechanical coupling coefficients K2, and temperature coefficient of frequency (TCF) dispersion properties of mode 0 were studied considering various thicknesses of ZnO and SiO2 thin films, which were verified by experiments. SiO2 film with a positive TCF not only compensate the negative TCF of the (110) ZnO but also enhance the K2. A large K2 of 3.37 and nearly zero TCF of −0.1 ppm/°C was achieved in SH-SAW device based on IDT/(110)ZnO(2 μm)/SiO2(1 μm)/Si multilayer structure, which is promising for high sensitive and temperature stable bio-sensing application.

Determining biosensing modes in SH-SAW device using 3D finite element analysis

Surface acoustic wave (SAW) sensors are electromechanical devices that exploit the piezoelectric effect to induce elastic (acoustic) waves which are sensitive to small perturbations: for example specific binding and recognition of disease biomarkers. Shear horizontal surface acoustic waves (SH-SAWs) are particularly suited to biosample analysis as the wave is not completely radiated and lost into the liquid medium (e.g., blood, saliva) as is the case, for example, in a device implementing Rayleigh waves. Here, using 3D finite element analysis (FEA) the nature of waves launched on a particular quartz device is investigated with respect to the cut of the quartz, the addition of gold guiding layers, and the addition of other linear elastic materials of contrasting acoustic properties. It is demonstrated that 3D FEA analysis showing the device's frequency shift with added guiding layer height reveals a proportional relationship in agreement with the Sauerbrey equation from perturbation theory. It is directly shown, given certain device parameters and a gold guiding layer, that shear horizontally polarized waves are launched on the surface with a dominant mode frequency around 250MHz. This would be an appropriate biosensing mode in Point of Care (POC) testing for the particular properties of certain disease biomarkers delivered via a liquid medium.

Enlarged phase velocities of ultra-wideband surface acoustic wave devices with relaxor based ferroelectric single crystal/diamond layered structure

The surface acoustic wave (SAW) characteristics of Y-cut X propagating Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (YX-PIMNT) single crystals on a diamond substrate have been theoretically calculated. The simulated results show that the phase velocity of the shear horizontal (SH) SAW may be greatly enhanced from the 1350m/s to 3350m/s by reducing the thickness of the PIMNT from 0.5λ to 0.05λ, with a corresponding decrease in the electromechanical coupling factor (K2) from 73.6% to 19.6%. The dispersion curves of phase velocity and K2 as a function of PIMNT thickness are given for the proposed layered structure. Besides the SH SAW, there are also higher order modes that would cause unwanted responses in the pass-band of wideband SAW filters. These were suppressed by properly controlling structural parameters including top electrode thickness, thickness and Euler angle (θ) of PIMNT substrate. The calculated results demonstrate the effectiveness of this approach to enlarge the phase velocity of the SH SAW without dramatically sacrificing its K2, which makes relaxor based ferroelectric single crystals promising for realizing ultra-wideband SAW devices working in ~GHz range.

Rayleigh and Wood anomalies in the diffraction of acoustic waves from the periodically corrugated surface of an elastic medium

By the use of the Rayleigh method we have calculated the angular dependence of the reflectivity and the efficiencies of several other diffracted orders when the periodically corrugated surface of an isotropic elastic medium is illuminated by a volume acoustic wave of shear horizontal polarization. These dependencies display the signatures of Rayleigh and Wood anomalies, usually associated with the diffraction of light from a metallic grating. The Rayleigh anomalies occur at angles of incidence at which a diffracted order appears or disappears; the Wood anomalies here are caused by the excitation of the shear horizontal surface acoustic waves supported by the periodically corrugated surface of an isotropic elastic medium. The dispersion curves of these waves in both the nonradiative and radiative regions of the frequency-wavenumber plane are calculated, and used in predicting the angles of incidence at which the Wood anomalies are expected to occur.