Input Interdigital Transducers Research Articles

Temperature Compensation of SAW Winding Tension Sensor Based on PSO-LSSVM Algorithm.

In this paper, a SAW winding tension sensor is designed and data fusion technology is used to improve its measurement accuracy. To design a high-measurement precision SAW winding tension sensor, the unbalanced split-electrode interdigital transducers (IDTs) were used to design the input IDTs and output IDTs, and the electrode-overlap envelope was adopted to design the input IDT. To improve the measurement accuracy of the sensor, the particle swarm optimization-least squares support vector machine (PSO-LSSVM) algorithm was used to compensate for the temperature error. After temperature compensation, the sensitivity temperature coefficient αs of the SAW winding tension sensor was decreased by an order of magnitude, thus significantly improving its measurement accuracy. Finally, the error with actually applied tension was calculated, the same in the LSSVM and PSO-LSSVM. By multiple comparisons of the same sample data set overall, as well as the local accuracy of the forecasted results, which is 5.95%, it is easy to confirm that the output error predicted by the PSO-LSSVM model is 0.50%, much smaller relative to the LSSVM's 1.42%. As a result, a new way for performing data analysis of the SAW winding tension sensor is provided.

A Piezoelectric Flexural Plate Wave (FPW) Bio-MEMS Sensor with Improved Molecular Mass Detection for Point-of-Care Diagnostics

Abstract A piezoelectric FPW-sensor has been developed for a point of care device in this work. The Bio- MEMS FPW-sensor consists of an electrode configuration termed as an interdigital transducer (IDT) placed on a membrane. An input IDT excites and an output IDT detects the propagating acoustic waves through a PZT layer. Design optimizations and fabrication improvements of the FPW-sensor led to significantly reduced attenuation of the wave signal and the damping of the propagating waves between the IDTs. The working principle of mass loading is shown using different low-viscous liquids. A densitydependent sensitivity of -0.39 MHz/g/cm³ was evaluated. After the membrane was functionalized, the Bio-MEMS FPW-sensor was used to measure a specific chemokine in complex solution. By design improvements, the resolution was significantly increased from 0.7 Hz/nM to 14 Hz/nM.

Analysis on scattering characteristics of Love-type wave due to surface irregularity in a piezoelectric structure.

Surface irregularity in piezoelectric sensors causes scattering of Love-type waves, which may lead to significant signal insertion loss. Also, as the reflected wave field in the piezoelectric sensor is increased due to surface irregularity, the input interdigital transducer (IDT) can be damaged. The present analysis confers the characteristics of Love-type waves scattered through surface irregularity in piezoelectric composite structures with different shaped surface irregularity, e.g., rectangular shaped, parabolic shaped, and triangular notch shaped. The expressions of phase and group velocities of scattered Love-type waves are derived for electrically open and short conditions. Also, expressions of mechanical displacement and electrical potential function due to incident and scattered Love-type waves are deduced for both electrical conditions. It is reported from the analysis that the increase in vertical irregularity parameter causes stronger reflected wave fields. Also, with the increase in piezoelectricity of the superficial layer, signal insertion loss and strength of reflected wave field diminish.

Nano- and submicro-sized three-dimensional shape measuring system using a SAW-based capacitance sensor

SAW-based capacitance sensors were developed by measuring the changes in the voltage ratio between an output inter-digital transducer (IDT) and an input IDT, induced by the variation in the capacitance between hemi-spherical conductive tips with diameters on the order of micrometers. We derived the transfer and sensitivity functions, which describes the ratio of the variation in the output voltage to the variation in the input voltage with a 2-port network model of a SAW based on Mason’s equivalent electro-acoustic circuit and analytical model for the apex capacitance. We then conducted an experiment to verify and measure the transfer function and the 3-D shape. The system was found to have an average resolution of approximately 10 nanometers. We also used the constructed system to measure nano- and submicro-sized 3-D shapes, and verified that the measurement results were accurate.

Research on two-port network of wavelet transform processor using surface acoustic wavelet devices and its application

The goal of this research is to study two-port network of wavelet transform processor (WTP) using surface acoustic wave (SAW) devices and its application. The motive was prompted by the inconvenience of the long research and design cycle and the huge research funding involved with traditional method in this field, which were caused by the lack of the simulation and emulation method of WTP using SAW devices. For this reason, we introduce the two-port network analysis tool, which has been widely used in the design and analysis of SAW devices with uniform interdigital transducers (IDTs). Because the admittance parameters calculation formula of the two-port network can only be used for the SAW devices with uniform IDTs, this analysis tool cannot be directly applied into the design and analysis of the processor using SAW devices, whose input interdigital transducer (IDT) is apodized weighting. Therefore, in this paper, we propose the channel segmentation method, which can convert the WTP using SAW devices into parallel channels, and also provide with the calculation formula of the number of channels, the number of finger pairs and the static capacitance of an interdigital period in each parallel channel firstly. From the parameters given above, we can calculate the admittance parameters of the two port network for each channel, so that we can obtain the admittance parameter of the two-port network of the WTP using SAW devices on the basis of the simplification rule of parallel two-port network. Through this analysis tool, not only can we get the impulse response function of the WTP using SAW devices but we can also get the matching circuit of it. Large numbers of studies show that the parameters of the two-port network obtained by this paper are consistent with those measured by network analyzer E5061A, and the impulse response function obtained by the two-port network analysis tool is also consistent with that measured by network analyzer E5061A, which can meet the accuracy requirements of the analysis of the WTP using SAW devices. Therefore the two-port network analysis tool discussed in this paper has comparatively higher theoretical and practical value.

Electrode-width-weighted wavelet transform processor using SAW devices

PurposeWhen designing the electrode widths of the electrode-width-weighted (EWW) input interdigital transducers (IDTs) according to the envelope amplitudes of the wavelet function, the EWW wavelet transform processor (WTP) using surface acoustic wave (SAW) devices can be fabricated. The electrode widths have influence on the frequency characteristic of the EWW WTP using SAW devices. The purpose of this research is to solve the influence of the electrode width accuracy on the frequency characteristic of the EWW WTP using SAW devices.Design/methodology/approachIn order to solve the influence of the electrode width accuracy on the frequency characteristics of the EWW WTP using SAW devices, the function between the electrode widths and the −3 dB bandwidth is derived. That the −3 dB bandwidth varies as the electrode widths is known according to this function so that the exposure time and the etching are presented as the two key problems.FindingsSolutions to these problems are achieved in this study. As long as there is accurate exposure time, the precision IDTs (i.e. the precision electrode widths) will be obtained. The accuracy of the exposure time for the EWW WTP using SAW devices is ±1 per cent. Because the dry etching is a type of etching technology in gas medium, it can etch nanometer lines, even more fine lines, so that the dry etching is used in EWW WTP using SAW devices.Originality/valueResearch highlights solving the influence of the electrode width accuracy on the frequency characteristic for the EWW WTP using SAW devices; deriving the function between the electrode widths and the −3 dB bandwidth (it is known from this function that the −3 dB bandwidth varies as the electrode widths); and presenting the exposure time and the etching as two key problems.

A novel electrode‐area‐weighted method of implementing wavelet transform processor with surface acoustic wave device

SummaryThe objective of this research was to investigate the possibility of a novel electrode‐area‐weighted (EAW) method of implementing wavelet transform processor (WTP) with surface acoustic wave (SAW) device. The motivation for this work was prompted by a diffraction problem of the WTP using SAW device. In this paper, we propose a novel EAW method in order to solve the diffraction problem. When the electrode areas of the EAW wavelet interdigital transducer (IDT) (i.e. the input IDT) are designed according to the envelope areas of the wavelet function, the impulse‐response function of the EAW wavelet IDT is equal to the wavelet function, so that the novel EAW WTP using SAW device can be fabricated. In this study, we also present the diffraction problem, the substrate material, and the electrode number of the output IDT as three key problems, and the solutions to the three key problems are implemented. Copyright © 2016 John Wiley & Sons, Ltd.

Implementing wavelet inverse-transform processor with surface acoustic wave device

The objective of this research was to investigate the implementation schemes of the wavelet inverse-transform processor using surface acoustic wave (SAW) device, the length function of defining the electrodes, and the possibility of solving the load resistance and the internal resistance for the wavelet inverse-transform processor using SAW device.In this paper, we investigate the implementation schemes of the wavelet inverse-transform processor using SAW device. In the implementation scheme that the input interdigital transducer (IDT) and output IDT stand in a line, because the electrode-overlap envelope of the input IDT is identical with the one of the output IDT (i.e. the two transducers are identical), the product of the input IDT’s frequency response and the output IDT’s frequency response can be implemented, so that the wavelet inverse-transform processor can be fabricated. X-1120Y LiTaO3 is used as a substrate material to fabricate the wavelet inverse-transform processor. The size of the wavelet inverse-transform processor using this implementation scheme is small, so its cost is low.First, according to the envelope function of the wavelet function, the length function of the electrodes is defined, then, the lengths of the electrodes can be calculated from the length function of the electrodes, finally, the input IDT and output IDT can be designed according to the lengths and widths for the electrodes.In this paper, we also present the load resistance and the internal resistance as the two problems of the wavelet inverse-transform processor using SAW devices. The solutions to these problems are achieved in this study. When the amplifiers are subjected to the input end and output end for the wavelet inverse-transform processor, they can eliminate the influence of the load resistance and the internal resistance on the output voltage of the wavelet inverse-transform processor using SAW device.

Frequency Response Optimization of Saw Filter using Canonical Genetic Algorithm

An optimization program is employed to design the inter-digital transducer (IDT) structure of the surface acoustic wave (SAW) transducer to aim at improvement in the transducer characteristics and to improve the frequency response of SAW filter. In this paper, Genetic algorithm is used to optimize the response of a SAW filter. Then, the comparison of the response of SAW filter is done by using GA and without GA. The goal of optimization is to find best value for each variable in order to achieve minima or maxima of an objective function within the given constraints. In present study, three design variables of SAW filter i.e. number of finger pairs in input IDT (Np1), number of finger pairs in `output IDT (Np2), center to center distance between two electrodes in a finger pair (d), are optimized. After getting the optimized parameters of SAW filter, the frequency response of bandpass SAW filter is obtained, which is better as compared to the frequency response of SAW filter getting from other methods in terms of bandwidth and ripples amplitude.

Enhancement of acoustic streaming induced flow on a focused surface acoustic wave device: Implications for biosensing and microfluidics

Fluid motion induced on the surface of 100 MHz focused surface acoustic wave (F-SAW) devices with concentric interdigital transducers (IDTs) based on Y-cut Z-propagating LiNbO3 substrate was investigated using three-dimensional bidirectionally coupled finite element fluid-structure interaction models. Acoustic streaming velocity fields and induced forces for the F-SAW device are compared with those for a SAW device with uniform IDTs (conventional SAW). Both, qualitative and quantitative differences in the simulation derived functional parameters, such as device displacements amplitudes, fluid velocity, and streaming forces, are observed between the F-SAW and conventional SAW device. While the conventional SAW shows maximum fluid recirculation near input IDTs, the region of maximum recirculation is concentrated near the focal point of the F-SAW device. Our simulation results also indicate acoustic energy focusing by the F-SAW device leading to maximized device surface displacements, fluid velocity, and streaming forces near the focal point located in the center of the delay path, in contrast to the conventional SAW exhibiting maximized values of these parameters near the input IDTs. Significant enhancement in acoustic streaming is observed in the F-SAW device when compared to the conventional ones; the increase in streaming velocities was computed to be 352% and 216% for tangential velocities in propagation and transverse directions, respectively, and 353% for the normal velocity. Consequently, the induced streaming force for F-SAW is 480% larger than that for conventional SAW. In biosensing applications, this allows for the removal of smaller submicron sized particles by F-SAW which are otherwise difficult to remove using the conventional SAW. The F-SAW presents an order of magnitude reduction in the smallest removable particle size compared to the conventional device. Our results indicate that the acoustic energy focusing and streaming enhancement brought about by the F-SAW device manifests itself as enhanced biofouling removal efficiency of F-SAW throughout the device delay path compared to the conventional device, thereby providing enhanced device sensitivity, selectivity, and reusability. Furthermore, contrary to the conventional SAW in which the smallest particle is removable near the input IDTs, the F-SAW device removes the smallest particle near the device focal point. The results of this work are shown to have significant implications in typical biosensing and microfluidic applications. In a broader context, the results of the present study demonstrate a technique of enhancing streaming induced flows, which is of great importance to contemporary problems involving microfluidic and sensing applications of piezoelectric devices.

Ultrasound radiation device into a material

When input electric signals E i (i=1, 2, . . . n) with frequencies f i (i=1, 2, . . . , n), respectively, are applied to an input interdigital transducer, elastic waves are excited in a piezoelectric substrate. Leaky components of the elastic waves are radiated into a material in the form of longitudinal waves, which are reflected at a bottom boundary-surface of the material. One of reflected longitudinal waves are detected at an output interdigital transducer as a delayed output signal with one of the frequencies f i . When the delayed output signal is applied to at least one interdigital transducer for radiation, an elastic wave is excited in the piezoelectric substrate. A leaky component of the elastic wave is radiated into the material in the form of a longitudinal wave, which is reflected at the bottom boundary-surface and re-reflected at a top boundary-surface of the material, and thus a continuous reflection occurs.

Integrated nitride-based acoustic wave devices and methods of fabricating integrated nitride-based acoustic wave devices

A monolithic electronic device includes a substrate, a semi-insulating, piezoelectric Group III-nitride epitaxial layer formed on the substrate, a pair of input and output interdigital transducers forming a surface acoustic wave device on the epitaxial layer and at least one electronic device (such as a HEMT, MESFET, JFET, MOSFET, photodiode, LED or the like) formed on the substrate. Isolation means are disclosed to electrically and acoustically isolate the electronic device from the SAW device and vice versa. In some embodiments, a trench is formed between the SAW device and the electronic device. Ion implantation is also disclosed to form a semi-insulating Group III-nitride epitaxial layer on which the SAW device may be fabricated. Absorbing and/or reflecting elements adjacent the interdigital transducers reduce unwanted reflections that may interfere with the operation of the SAW device.

Active SAW devices on 2DEG heterostructures

Active surface acoustic wave filters with voltage-controlled insertion losses have been achieved using AlGaN/GaN 2DEG heterostuctures as piezoelectric substrates. Transfer control is performed by moderate DC voltages between the fingers in either or both input and output interdigital transducers. These filters can be integrated into future MMIC circuits based on AlGaN/GaN high electron mobility transistors.

Design of withdrawal-weighted SAW filters.

This paper presents a new design algorithm for a withdrawal-weighted surface acoustic wave (SAW) transversal filter. The proposed algorithm is based on the effective transmission loss theory and a delta function model of a SAW transversal filter. The design process consists of three steps, which eventually determine eight geometrical design parameters for the filter in order to satisfy given performance specifications. First, the number of fingers in the input and output interdigital transducers (IDTs), plus their geometrical sizes is determined using the insertion loss specification. Second, the number and positions of the polarity reverses in the output IDT are determined using the bandwidth and ripple specifications. Third, the number and position for withdrawing and switching specific fingers in the output IDT and attached electrode area are determined to achieve the desired sidelobe level. The efficiency of the technique is illustrated using a sample design of an IF filter consisting of a uniform input IDT and withdrawal-weighted output IDT. The proposed algorithm is distinct from conventional techniques in that it can optimize the structural geometry of a withdrawal-weighted SAW filter in a direct manner by considering all the performance specifications simultaneously.

Ultrasound-signal radiating device

An ultrasound-signal radiating device comprises a piezoelectric substrate, a first input interdigital transducer, a second input interdigital transducer, an output interdigital transducer, a cap, an amplifier, and a modulator with an input terminal. All the interdigital transducers are formed on one end surface of the piezoelectric substrate. The cap is mounted on a surface part of the other end surface of the piezoelectric substrate. If an input electric signal is applied to the first input interdigital transducer, a non-leaky elastic wave is excited in the piezoelectric substrate owing to the existence of the cap. The non-leaky elastic wave is detected at the output interdigital transducer as a delayed electric signal, which is amplified via the amplifier. A signal part of an amplified electric signal is fed back to the first input interdigital transducer, again. A remaining signal part, as a carrier signal, of the amplified electric signal is transmitted to the modulator, where an amplitude of the carrier signal is modulated according to an input message-signal applied from the input terminal. Thus, an AM signal is generated, and then, applied to the second input interdigital transducer. In this time, a leaky elastic wave is excited in the piezoelectric substrate, and radiated effectively in the form of a longitudinal wave into a liquid kept in contact with a remaining surface part of the other end surface of the piezoelectric substrate.

Optimization of the frequency characteristics in saw filter design

The transmission characteristics of surface acoustic wave (SAW) filters is considered. In the process of the design, the bandpass characteristics is requested to meet a specification in the process of the design. The apodization in the input interdigital transducer (IDT) is adopted to achieve the desired characteristics of the frequency bandwidth and the attenuation of the passband for the central frequency given. In the present paper, optimization procedures are discussed and some demonstrations are presented. The frequency characteristics of a SAW filter is characterized by the delta function modelling. The apodization is made by varying the length of each electrode with the input IDT. The objective function is defined as the error norm between the required frequency characteristics and the calculated one for the assumed length of each electrode. The calculation is repeated to minimize the objective function. Three optimization methods, the Least-Mean-Square (LMS) method, the Davidon-Fletcher-Powell (DFP) method and the genetic algorithm (GA) are examined for this purpose. The paper demonstrates the capability and efficiency of the above three approaches for the SAW filter design with a couple of worked examples.

Design of SAW expander and compressor on LiTaO/sub 3/ for a TCDMA spread spectrum system

We report on the design and performance of surface-acoustic wave (SAW) minimum shift keying (MSK) tapped delay lines using pseudonoise code sequences with a length of 128 chips. As a substrate, X112/spl deg/rotY-LiTaO/sub 3/ has been used due to the system requirements of a given CDMA/TDMA (TCDMA) radio communication system. System IF frequency, bandwidth of the major lobe, and integration time of the SAW devices were, respectively, 360 MHz, 63.5 MHz, and 3 /spl mu/s. We used SAW tapped delay lines employing nonweighted as well as cosine-weighted input interdigital transducers incorporating split-fingers. We designed both expander as well as compressor filters attaining very similar experimental results. We found insertion loss values down to 16 dB and amplitude ripples of less than 2 dB. The close-in selectivity was 28 dB.

Longitudinal-mode leaky SAW resonator filters on 64/spl deg/ Y-X lithium niobate

Y-parameter modeling is applied to obtain the frequency response of a first/third dual-mode longitudinally-coupled leaky-SAW (LSAW) resonator-filter on 64/spl deg/C Y-X LiNbO/sub 3/. Conventional driving-point and transfer admittance relationships for SAW filters are modified to incorporate the effects of LSAW reflection and bulk-wave scattering in the interdigital transducers and are expanded to include reflection gratings with shorted-metal strips. As inferred from experiment, the grating parameters incorporate a phase-shift term to relate the anomalous dispersion of shorted gratings, as well as a modified phase-slope parameter between input and output interdigital transducers (IDT's). Good agreement is obtained with experimental results published for 836.5 MHz two- and four-pole structures in the maximum-bandwidth configuration. >

SAW filters with high stopband rejection based on a cascade connection of selective elements

To achieve a high stopband rejection in surface acoustic wave (SAW) filters a construction that includes a cascade of some elements (interdigital transducers (IDT) and multistrip couplers (MSC)) is used. In this case each element has to maintain a comparatively low frequency selectivity, and this permits a simple model and a high-speed calculation process to be employed for its design. The proposed constructions have an apodized transducer with a metal coating instead of a passive electrode region as the input IDT and broadband withdrawal weighted unapodized transducer as the output IDT. One or two group-type multistrip couplers (MSC) provide an additional frequency selectivity. The original synthesis algorithms have been developed for design of IDT and MSC structure. >

Microwave saw monochromator

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