Single-phase Unidirectional Transducers Research Articles

Design and implementation of high data capacity RFID tag using eight-phase encoding

Enhancing the data capacity of surface acoustic wave (SAW) radio frequency identification (RFID) tags using the combination of time position and phase encoding with fewer number of reflectors is investigated in this work. Simulation and fabrication of SAW RFID tags are performed using COMSOL Multiphysics and standard photolithography process. Lithium Tantalite (LiTaO3) is used as a substrate and Aluminium metal electrodes are used to realise the interdigital transducer (IDT) electrodes. The data capacity enhancement is tested using a SAW RFID tag consisting of a single-phase unidirectional transducer (SPUDT) transducer and four code reflectors. By designing the width of SPUDT electrodes and floating electrodes and proper positioning of reflectors, eight phases (i.e. 0°, −45°, −90°, −135°, −180°, −225°, −270° and −315°) are detected which correspond to 3 bits of data per reflector. These eight phases would result to have one more data bit per reflector. Therefore, eight phase states along with four time positions lead to 32 different states (i.e. 5 bits of data per reflector). To facilitate the realisation of our idea, the fabrication process has been performed at 250 MHz; however, it can easily be implemented at higher frequencies (i.e. GHz range).

Study of low insertion loss and miniaturization wavelet transform and inverse transform processor using SAW devices

In this paper, we propose a low insertion loss and miniaturization wavelet transform and inverse transform processor using surface acoustic wave (SAW) devices. The new SAW wavelet transform devices (WTDs) use the structure with two electrode-widths-controlled (EWC) single phase unidirectional transducers (SPUDT–SPUDT). This structure consists of the input withdrawal weighting interdigital transducer (IDT) and the output overlap weighting IDT. Three experimental devices for different scales 2−1, 2−2, and 2−3 are designed and measured. The minimum insertion loss of the three devices reaches 5.49dB, 4.81dB, and 5.38dB respectively which are lower than the early results. Both the electrode width and the number of electrode pairs are reduced, thus making the three devices much smaller than the early devices. Therefore, the method described in this paper is suitable for implementing an arbitrary multi-scale low insertion loss and miniaturization wavelet transform and inverse transform processor using SAW devices.

A solution to reducing insertion loss and achieving high sidelobe rejection for wavelet transform and reconstruction processor using SAW devices

An arbitrary wavelet transform and reconstruction processor is composed of multiple single-scale wavelet transform devices (SSWTDs) with different scales. For improving the performance of the processor using surface acoustic wave (SAW) devices, this research investigates how to reduce the insertion loss (IL) and achieve a high sidelobe rejection. To reduce the triple transit echo (TTE) and to achieve a high signal–noise ratio (SNR), the structure of the SSWTD consists of two electrode-widths-controlled (EWC) single phase unidirectional transducers (SPUDTs). In the propagation process of the SAW, the unidirectional characteristic of the new structure reduces the bidirectional loss of the entire device. In addition, to enlarge the fractional bandwidth and the sidelobe rejection, the internal structure of the SSWTD uses an input apodized transducer according to the envelope of the Morlet wavelet function as well as an output withdrawal weighting transducer.In this paper, we present a SSWTD for scale 2−2 as an example to illustrate the design method and experimental results. The new device is fabricated on 128° rotated YX-cut lithium niobate (Y128°X–LiNbO3) with the electromechanical coupling coefficient k2=5.5% and the SAW velocity 3992m/s. We get the experimental frequency response with the center frequency 68.14MHz, the minimum IL −9.96dB, the fractional bandwidth 3.3%, the maximum passband ripples 0.4dB and the sidelobe rejection greater than 40dB. The proposed method and structure can be extended to an arbitrary SSWTD. The experimental results confirm that the performance of the wavelet transform and reconstruction processor can be improved by the proposed solution.

Study of a Low Insertion Loss SAW Filter with SPUDT Structure Using YZ-LiNbO<sub>3</sub>

To meet the demand for low insertion loss, we have studied a SAW filter with single phase unidirectional transducer (SPUDT) structure using piezoelectric materials YZ-LiNbO3. This article shows the simulation results of the SAW filter using Matlab software with the SAW velocity 3488m/s and electromechanical coupling constant 0.048. The theoretical center frequency is 72MHz and the 3dB bandwidth is 2.9MHz. The total frequency response of the entire SAW device is the product of the frequency response of the input transducer and the output transducer. It can be seen from the simulation results that the magnitude response and the linear phase response of interdigital transducer are consistent with the theoretical values and the minimum insertion loss reaches 5.43dB. So the low insertion loss SAW filter with SPUDT structure using YZ-LiNbO3 adapts the requirements of the radar, communications and other electronic systems.

Miniaturized Lab‐on‐a‐Disc (miniLOAD)

A miniaturized centrifugal microfluidic platform for lab-on-a-chip applications is presented. Unlike its macroscopic Lab-on-a-CD counterpart, the miniature Lab-on-a-Disc (miniLOAD) device does not require moving parts to drive rotation of the disc, is inexpensive, disposable, and significantly smaller, comprising a 10-mm-diameter SU-8 disc fabricated through two-step photolithography. The disc is driven to rotate using surface acoustic wave irradiation incident upon a fluid coupling layer from a pair of offset, opposing single-phase unidirectional transducers patterned on a lithium niobate substrate. The irradiation causes azimuthally oriented acoustic streaming with sufficient intensity to rotate the disc at several thousand revolutions per minute. In this first proof-of-concept, the capability of the miniLOAD platform to drive capillary-based valving and mixing in microfluidic structures on a disc similar to much larger Lab-on-a-CD devices is shown. In addition, the ability to concentrate aqueous particle suspensions at radial positions in a channel in the disc dependent on the particles' size is demonstrated. To the best of our knowledge, the miniLOAD concept is the first centrifugal microfluidic platform small enough to be self-contained in a handheld device.

Enhanced surface acoustic wave atomization via amplitude modulation

Recent developments in the miniature chip-based microfludic nebulization platform utilizing surface acoustic wave (SAW) atomizer for inhalation therapy offers distinct advantages over other conventional nebulizers. Such efficient hand-held nebulizer system also requires the optimization of the usage of available power systems in the simplest manner. Here, amplitude modulation (AM) is presented as a simple yet effective means of optimizing the power requirement. SAWs are nano meter order amplitude acoustic waves that originate as a result of the application of an alternating current onto a pair of single-phase unidirectional transducers patterned on a piezoelectric substrate. The effect of the AM at modulation frequencies of 500 Hz, 1 kHz, 5 kHz, 10 kHz, 20kHz and 40 kHz sinusoidal signals, on shear-sensitive biomolecules such as plasmid DNA and antibody molecules are shown to be minimal. Energy savings of around 40% can be obtained with more efficient atomization achieved with AM less than 10 kHz. Together with these advantages, AM having little effect of the mean aerosol diameter; particularly important when therapies are to be targeted for the deep lung regions, holds great promise for its use in the SAW nebulizers for non-invasive inhalation therapy. Acknowledgements are dedicated to Asthma Foundation Victoria (Australia).

Development of a New Surface Acoustic Wave Based Gyroscope on a X-112°Y LiTaO3 Substrate

A new micro gyroscope based on the surface acoustic wave (SAW) gyroscopic effect was developed. The SAW gyroscopic effect is investigated by applying the surface effective permittivity method in the regime of small ratios of the rotation velocity and the frequency of the SAW. The theoretical analysis indicates that the larger velocity shift was observed from the rotated X-112°Y LiTaO3 substrate. Then, two SAW delay lines with reverse direction and an operation frequency of 160 MHz are fabricated on a same X-112°Y LiTaO3 chip as the feedback of two SAW oscillators, which act as the sensor element. The single-phase unidirectional transducer (SPUDT) and combed transducers were used to structure the delay lines to improve the frequency stability of the oscillator. The rotation of a piezoelectric medium gives rise to a shift of the propagation velocity of SAW due to the Coriolis force, resulting in the frequency shift of the SAW device, and hence, the evaluation of the sensor performance. Meanwhile, the differential structure was performed to double the sensitivity and compensate for the temperature effects. Using a precise rate table, the performance of the fabricated SAW gyroscope was evaluated experimentally. A sensitivity of 1.332 Hz deg−1 s at angular rates of up to 1,000 deg s−1 and good linearity are observed.

Enhanced sensitivity of a surface acoustic wave gyroscope using a progressive wave

A surface acoustic wave (SAW)-based gyroscope with an 80 MHz central frequency was developed on two different piezoelectric substrates (128° YX LiNbO3 and ST-X quartz). A sensor was developed that contained two SAW oscillators. One oscillator was used as the sensing element and had metallic dots in the cavity between the input and output interdigital transducers (IDTs). The other oscillator was used as a reference element. Two oscillators were formed to extract the Coriolis effect by comparing the oscillation frequencies between these two delay lines, and metallic dots were used to induce a Coriolis force. Three different IDT structures were used to obtain a stable progressive SAW. Coupling of modes modeling was conducted prior to fabrication for determining the optimal device parameters. The device was fabricated and then measured on a rate table in accordance with the results of simulation. When the device was subjected to an angular rotation, the oscillation frequencies of the two oscillators were observed to differ. Depending on the angular velocity, the frequency difference was linearly modulated. The obtained sensitivity was approximately 62.57 Hz deg−1 s−1 at angular rates in the range 0–1000 deg s−1 in the case of the LiNbO3 substrate and single-phase unidirectional transducer and combed electrode structure. The dependence of the device performance on the piezoelectric substrate, IDT structure, and temperatures was also characterized. The developed device has good resistance to mechanical shock and stability to temperature.

Surface Acoustic Wave Sensors of Delay Lines Based on MEMS

A high frequency Surface Acoustic Wave (SAW) filter which is the key point of the SAW sensor is made by MEMS technology. The SAW filter used for sensors needs to have the factors of high frequency, low loss and high quality factor. In order to satisfy the performance of the factors, the SAW delay lines of Electrode Wave Control Single Phase Unidirectional Transducer (EWC/SPUDT) are used in the filter. This transducer can be considered as the networks of connection of some units of IDTs and the loss of device can be effectively reduced. Based on the Coupling of Modes (COM) theory and equivalent circuit modal, the mixed matrix (P matrix) of the transducers can be deduced, and further, the response of the delay lines can be obtained. According to the calculated results, a mask layout is made. Then the SAW delay line is completed and found to agree with the theoretical simulation. Its center frequency is 503 MHz and insertion loss is low enough for use of sensors.

A New Micro-rate Sensor Based on Shear Horizontal Surface Acoustic Wave Gyroscopic Effect

In this paper, we present a new micro-rate sensor based on the shear horizontal surface acoustic wave (SH-SAW) gyroscopic effect. The new SH-SAW propagating along the ST-90°X quartz substrate with heavy metallization exhibits excellent temperature stability, large acoustic velocity, high electromechanical coupling factors, and very small propagation attenuation. The response mechanism of such an SH-SAW micro-rate sensor was established using partial-wave analysis methods. The angular detection sensitivity in the propagation path of SH-SAW was evaluated and the effect of the metal interdigital transducer (IDT) electrode thickness on the sensor performance was also studied, resulting in the realization of the optimized design parameters prior to fabrication. Two SH-SAW delay lines with a reverse direction and an operation of 80 MHz on the same chip are fabricated as the feedback of SAW oscillators. The single-phase unidirectional transducer (SPUDT) was used to structure the delay lines to decrease the insertion loss. The Coriolis force from the external rotation acts on the particles along the SAW propagation path, then a pseudo SAW was induced, and couples with the initial SH-SAW; thus, the SAW velocity was deviated. Meanwhile, the differential oscillation frequency was changed linearly and used to characterize the input angular rate. Then, using the precise rate table, the performance of the fabricated SH-SAW rate sensor was evaluated experimentally. A sensitivity of 1.268 Hz deg-1 s-1 at angular rates of up to 2000 deg s-1, good linearity, and excellent temperature stability are observed.

A new unidirectional transducer using proximity coupling between bidirectional tracks

Usually, directivity is obtained in single-phase unidirectional transducers (SPUDTs) by cascading reflective cells and transduction cells in the same acoustic track. An alternate approach was presented which described a SPUDT using two tracks. The first track had only sources but the second track had sources and reflectors. The directivity was created by proximity coupling of these two tracks. The drawback of the original structure is the low aperture needed to get enough coupling between the tracks. A new device based on a similar approach is presented. The number of tracks is increased to obtain lower impedances and more efficient transduction cells are used. We called this new device the proximity multi-track unidirectional transducer or PMUDT.

A low‐power droplet manipulator employing high‐frequency surface acoustic waves

AbstractA droplet manipulator working with low driving power was developed by using the surface acoustic wave (SAW) technology. The manipulator was driven at a relatively high frequency of 350 MHz to increase the SAW power density. First, a single‐phase unidirectional transducer (SPUDT) was designed. Because of its low insertion loss of 1.5 dB and high directivity of 10 dB, the SPUDT successfully conveyed a 100‐nl water droplet with RF input power of 18 dBm (60 mW). Second, the SPUDT design was extended to a curved transducer to focus and launch the SAW energy into the narrow waveguide. Owing to the increased SAW power density, the required SAW power was reduced to 15 dBm (30 mW) for the 100‐nl droplet manipulation. In addition, fabrication of liquid injectors was discussed for the formation of tiny droplets. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(4): 49–55, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10232

The development of a wireless Love wave biosensor on41° YX LiNbO3

This paper presents a novel wireless Love-wave-based biosensor using apolymethyl methacrylate (PMMA) waveguide and protein A receptor layers on a41° YX LiNbO3 piezoelectric substrate for immunoglobulin G (IgG) detection. A 440 MHz reflective delayline composed of single-phase unidirectional transducers (SPUDTs) and threeshorted grating reflectors was fabricated as the sensor element. A theoreticalmodeling was performed to describe the wave propagation of Love wave devices on a41° YX LiNbO3 piezoelectric substrate with large piezoelectricity. The fabricated devices were wirelesslycharacterized by using the network analyzer as the reader unit. The resultant reflectionpeaks showed large signal/noise ratio, sharp peaks, and few spurious signals. The binding ofthe IgG to the protein A receptor layer induced large phase shifts of the reflection peaksdue to the mass loading effect. Good linearity, reproducibility, and high sensitivity wereobserved in the IgG concentration range 1–65 nM. Unique advantages such as highsensitivity and a simple wireless measurement method over other currently availablebiosensors are also presented.

High-frequency stability oscillator for surface acoustic wave gas sensor

We present a 300 MHz surface acoustic wave (SAW) oscillator for gas sensor application. As the oscillator element, SAW delay lines on an ST-X quartz substrate with low insertion loss and single-mode-selection capability were developed. And they were structured by Electrode Width Control Single Phase Unidirectional Transducer (EWC/SPUDT) configuration and comb transducer. The coupling of modes (COM) model was used to predict device performance prior to fabrication. The measured frequency response S12 showed a good agreement with simulated results; a low insertion loss of less than 9 dB and a linear phase in the 3 dB bandwidth were observed. The experimental results show that the baseline noise of the fabricated oscillators was typically up to ∼0.7×10−7 in a laboratory environment with temperature control. The oscillator was successfully applied to a gas sensor coated with fluoroalcoholpolysiloxane (SXFA) as the sensor material for O-isopropyl methyphosphonofluoridate (GB) detection, and a superior threshold detection limit was obtained (<<0.4 mg/m3).

A Love Wave Reflective Delay Line with Polymer Guiding Layer for Wireless Sensor Application.

This paper presents an optimal design for a Love wave reflective delay line on 41° YX LiNbO3 with a polymer guiding layer for wireless sensor applications. A theoretical model was established to describe the Love wave propagation along the larger piezoelectric substrate with polymer waveguide, and the lossy mechanism from the viscoelastic waveguide was discussed, which results in the optimal guiding layer thickness. Coupling of modes (COM) was used to determine the optimal design parameters of the reflective delay line structured by single phase unidirectional transducers (SPUDTs) and shorted grating reflectors. Using the network analyzer, the fabricated Love wave reflective delay line was characterized, high signal noise ratio (S/N), sharp reflection peaks, and few spurious noise between the peaks were found, and the measured result agrees well with the simulated one. Also, the optimal guiding layer thickness of 1.5∼1.8µm was extracted experimentally, and it is consistent with the theoretical analysis.

Particle concentration and mixing in microdrops driven by focused surface acoustic waves

We report the use of focused surface acoustic waves (SAWs) generated on 128° rotated Y-cut X-propagating lithium niobate (LiNbO3) for enhancing the actuation of fluids and the manipulation of particle suspensions at microscale dimensions. In particular, we demonstrate increased efficiency and speed in carrying out particle concentration/separation and in generating intense micromixing in microliter drops within which acoustic streaming is induced due to the focused SAW beneath the drop. Concentric circular and elliptical single-phase unidirectional transducers (SPUDTs) were used to focus the SAW. We benchmark our results against a straight SPUDT which does not cause focusing of the SAW. Due to the increased wave intensity and asymmetry of the wave, we found both circular and elliptical SPUDTs concentrate particles in under 1 s, which is one order of magnitude faster than the straight SPUDT and several orders of magnitude faster than conventional microscale devices. The concentric circular SPUDT was found to be most effective at a given input power since it generated the largest azimuthal velocity gradient within the fluid to drive particle shear migration. On the other hand, the concentric elliptical SPUDT generated the highest micromixing intensity due to the more narrowly focused SAW radiation that substantially enhances acoustic streaming in the fluid.

Optimal Design of an RSPUDT-Based SAW Filter with Constant Group Delay

This paper describes the application of resonant single-phase unidirectional transducers (RSPUDTs) to the development of low-loss SAW filters with constant group delay in transition bands as well as in the passband. A low-loss SAW filter with constant group delay was designed and fabricated on a 128 degrees YX-LiNbO3 substrate. Experimental results were in good agreement with the design; the group delay deviation of 20 ns was realized over the range of +/-8 MHz at the center frequency of 512 MHz. The minimum insertion loss and -3 dB bandwidth were 4.3 dB and 8.5 MHz, respectively. The application of this technique is also extended to develop high-performance wideband filters employing quasi-slanted interdigital transducers.

One-Port SAW Resonators Using Natural SPUDT Substrates

We discuss the design of one-port surface acoustic wave (SAW) resonators using substrates with a partial or total degree of directivity, that is, the natural single-phase unidirectional transducer (N-SPUDT) effect. A general design method gives a resonance when all three frequencies (the required resonance frequency and the Bragg frequencies) are different. A second method has been derived from the resonance condition for a symmetrical substrate. Two further methods incorporate lamda/4 gaps. The capacitance ratio is presented as a function of the phase of the electrode reflection coefficient. The simulations use data for the N-SPUDT orientation of langasite. The reflection coefficient for Al electrodes has been calculated from finite element modeling (FEM) analysis. The approximate perturbation theory is found to agree well for small film thickness (h/lamda < 2%). The phase of the reflection coefficient is typically 150 degrees, not quite the ideal value of 180 degrees. Measurements on resonators using Al and Cu films are presented.

A novel wireless, passive CO2 sensor incorporating a surface acoustic wave reflective delay line

A 440 MHz wireless and passive surface acoustic wave (SAW) chemical sensor was developed forCO2 detection. The developed SAW gas sensor is composed of single phaseunidirectional transducers (SPUDTs), three shorted grating reflectors, andCO2-sensitivepolymer film on 41° YX LiNbO3 substrate. Coupling of modes (COM) modeling was used to find optimal designparameters. Using the extracted design parameters, the SAW device wasfabricated. Teflon AF 2400 was used as the sensitive film because it provides highCO2 solubility, permeability and selectivity. In wireless device testing using anetwork analyzer, four sharp reflection peaks with high signal-to-noise(S/N) ratio, small signal attenuation, and few spurious peaks were observedin the time domain. The time positions of the reflection peaks werewell matched with the predicted values from the simulation. Infusion ofCO2 into thechamber induced large phase shifts of the reflection peaks. Good linearity and repeatability were observedfor a CO2 concentration of 0–450 ppm. The obtained sensitivity was1.98° ppm−1. Temperature and humidity effects were also investigated during the sensitivity evaluationprocess.

Enhanced sensitivity of SAW gas sensor coated molecularly imprinted polymer incorporating high frequency stability oscillator

This paper presents a 300MHz surface acoustic wave (SAW) gas sensor coated molecularly imprinted polymer incorporating a novel SAW oscillator with high frequency stability. A SAW delay line on ST-X quartz substrate with low insertion loss (less than 12dB) and single mode selection capability was fabricated as the oscillator element. Electrode width control single phase unidirectional transducer (EWC/SPUDT) configuration and comb transducer were used to structure the SAW device to minimize the insertion loss and accomplish the single mode selection, respectively. Prior to fabrication, coupling of modes (COM) simulation was performed to predict device performance. The measured frequency response S12 showed a good agreement with simulated results. The effect of oscillator circuit system temperature shift upon frequency stability of the fabricated oscillator was studied in detail. Typical short-term frequency stability (1h) of ∼0.06ppm (∼20Hz) for the fabricated 300MHz SAW oscillator was observed in a laboratory environment with temperature control. The oscillator was successfully applied to gas sensor coated 10nm molecularly imprinted polymer (MIP) as sensor material for dimethyl-methyl-phosphonate (DMMP), and the MIP was prepared using o-phenylenediamine (o-PD) as a functional monomer, Sarin acid as a molecular template and co-polymerized using cyclic voltammetry (CV). The sensitivity for DMMP concentrations detection in a range of 1–100mg/m3 was evaluated as ∼96Hz/mg/m3, and the threshold detection limit was up to 0.5mg/m3.