Interdigital Transducers Research Articles

Design for SAW Antenna-Plexers with Improved Matching Inductance Circuits.

This study designs antenna-plexers, including a surface acoustic wave (SAW) extractor and an upper- and mid-high band (UHB + MHB) diplexer, for LTE 4G and 5G bands using carrier aggregation. The SAW extractor combines a bandpass filter (BPF) and a band-stop filter (BSF) in a single unit that consists of eight modified Butterworth-van Dyke (mBVD) resonators that resonate in parallel with an inductor and SAW resonators. This BSF behaves as a high-pass filter at frequencies lower than the designed WIFI band and as a capacitor at higher frequencies. The SAW extractor meets product specifications in the frequency range 0.7 to 2.7 GHz. The UHB + MHB diplexer, which is composed of a microwave filter, a SAW filter, and a simple matching inductor, uses frequency response methods to create an RF component for 2.4 GHz + WIFI 6E applications. The design uses a SAW's interdigital transducer (IDT) structure, and the experimental results are in agreement with the simulation results, so the design is feasible.

Material selection in sensor design for additive manufacturing

Surface acoustic sensor technology plays a crucial role in numerous mechatronic systems as it enables the detection of physical interactions with the environment. These sensors, operating at micro scales, can be seamlessly integrated into various industrial applications. To harness their full potential, it is essential to establish a systematic approach for the design and manufacturing of these sensors to meet the demands of cutting-edge applications. This study focuses on creating a finite element analysis-based model, aiming to identify the most suitable Interdigital Transducer (IDT) material for the production of surface acoustic wave sensors using additive manufacturing techniques. By leveraging statistical methods, the research seeks to optimize material selection. The structural design parameters of the chosen material will then be utilized to evaluate the performance of the surface acoustic wave sensor. The study also delves into the prospective applications of this technology in diverse fields, shedding light on its promising future.

High-Performance SAW Resonator with Spurious Mode Suppression Using Hexagonal Weighted Electrode Structure.

Surface acoustic wave resonators are widely applied in electronics, communication, and other engineering fields. However, the spurious modes generally present in resonators can cause deterioration in device performance. Therefore, this paper proposes a hexagonal weighted structure to suppress them. With the construction of a finite element resonator model, the parameters of the interdigital transducer (IDT) and the area of the dummy finger weighting are determined. The spurious waves are confined within the dummy finger area, whereas the main mode is less affected by this structure. To verify the suppression effect of the simulation, resonators with conventional and hexagonal weighted structures are fabricated using the micro-electromechanical systems (MEMS) process. After the S-parameter test of the prepared resonators, the hexagonal weighted resonators achieve a high level of spurious mode suppression. Their properties are superior to those of the conventional structure, with a higher Q value (10,406), a higher minimum return loss (25.7 dB), and a lower ratio of peak sidelobe (19%). This work provides a feasible solution for the design of SAW resonators to suppress spurious modes.

High speed surface acoustic wave and laterally excited bulk wave resonator based on single-crystal non-polar AlN film

One approach to extend the acoustic applications of aluminum nitride (AlN) in the GHz frequency range is to take advantage of the piezoelectric performance and high acoustic velocity (∼11 350 m/s) along the c-axis of this material. In particular, in the case of high-frequency micro-electromechanical systems, it should be possible to simplify the construction of resonators by using a-plane AlN-based structures. In the work described in this Letter, a single-crystalline a-plane AlN layer on an r-plane sapphire substrate is obtained by combining sputtering and high-temperature annealing. Based on this non-polar AlN, a resonator with only planar interdigital transducer electrodes is fabricated. Experiments on this resonator reveal simultaneous excitation of an anisotropic Rayleigh surface acoustic wave (SAW) at 2.38 GHz and a laterally excited bulk acoustic wave (LBAW) at 4.00 GHz. It is found that the Rayleigh SAW exhibits outstanding performance, with a quality factor as high as 2458 and great stability under variations in temperature. The LBAW at 4.00 GHz is excited by pure planar interdigitated electrodes without the need for any cavity or bottom electrode structure, thus demonstrating a promising approach to the construction of high-frequency resonators with a relatively simple structure.

Atomization characteristics of 9.6 MHz directional surface acoustic wave for 1-micron spray system

Surface acoustic wave atomization is also effective for generating microparticles and nanoparticles, because of the small wavelength with the high frequency. In this work, a novel directional surface acoustic wave (SAW) atomizer via a novel 9.6 MHz unidirectional interdigital transducer (U-IDT), a driving interdigital transducer (D-IDT) and a reflector interdigital transducer (R-IDT), is proposed and studied for the 1-micron spray system, such as the pulmonary drug delivery system and high-precision film deposition system. The atomization characteristics of a water drop are evaluated with atomized droplet size, atomizing particle velocity, and atomizing rate. Around 1 µm atomized droplet diameter, 585 mm/s atomizing particle velocity, and 4.2 ml/min atomizing rate are achieved and investigated. Based on the 1-micron atomized droplet diameter and high diffusion velocity, a novel pulmonary drug delivery system with the SAW spray can be excepted as an effective non-intrusive treatment method. It is also suitable for microparticle and nanoparticle spray without the pump and fan systems in the fields of industry, cosmetics, medicine, and medical devices.

Developing a surface acoustic wave-induced microfluidic cell lysis device for point-of-care DNA amplification.

We developed a microchip device using surface acoustic waves (SAW) and sharp-edge glass microparticles to rapidly lyse low-level cell samples. This microchip features a 13-finger pair interdigital transducer (IDT) with a 30-degree focused angle, creating high-intensity acoustic beams converging 6mm away at a 16MHz frequency. Cell lysis is achieved through centrifugal forces acting on Candida albicans cells and glass particles within the focal area. To optimize this SAW-induced streaming, we conducted 42 pilot experiments, varying electrical power, droplet volume, glass particle size, concentration, and lysis time, resulting in optimal conditions: an electrical signal of 2.5W, a 20μL sample volume, glass particle size below 10μm, concentration of 0.2μg, and a 5-min lysis period. We successfully amplified DNA target fragments directly from the lysate, demonstrating an efficient microchip-based cell lysis method. When combined with an isothermal amplification technique, this technology holds promise for rapid point-of-care (POC) applications.

Controlling periodic Fano resonances of quantum acoustic waves with a giant atom coupled to a microwave waveguide

Nanoscale Fano resonances, with applications from telecommunications to ultra-sensitive biosensing, have prompted extensive research. We demonstrate that a superconducting qubit, jointly coupled to microwave waveguides and an inter-digital transducer composite device, can exhibit acoustic Fano resonances. Our analytical framework, leveraging the Taylor series approximation, elucidates the origins of these quantum acoustic resonances with periodic Fano-like interference. By analyzing the analytical Fano parameter, we demonstrate that the Fano resonances and their corresponding Fano widths near the resonance frequency of a giant atom can be precisely controlled and manipulated by adjusting the time delay. Moreover, not just the near-resonant Fano profiles, but the entire periodic Fano resonance features can be precisely modulated from Lorentz, Fano to quasi-Lorentz shapes by tuning the coupling strength of the microwave waveguide. Our analytical framework offers insights into the control and manipulation of periodic Fano resonances in quantum acoustic waves, thereby presenting significant potential for applications such as quantum information processing, sensing, and communication.

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.

Room temperature operating formaldehyde sensor based on n-type ZnO functionalized surface acoustic wave resonator

In this investigation, Surface Acoustic Wave (SAW) formalin gas sensor is explored for low-level formalin gas sensing applications. The formalin gas sensor consists of ST-cut quartz as a base substrate material, interdigitated transducer (IDT) electrodes, reflectors and gas sensing n-ZnO thin film coated on top of the SAW resonator. Nano-structured optimal n-ZnO thin film was deposited as a gas sensing layer. It is noted that the sensor response was not affected by relative humidity and found stable. Formalin gas concentration was established in the controlled process chamber environment. The sensor response was measured at room temperature (25 °C) and relative humidity was 50 % during the experiment. Experimental data shows that return loss peak was shifted towards down side, return loss was better when formalin content (0–8 ppm) was increased in the process chamber. In order to understand, the underlying electrical sensing mechanism, modified Butterworth-Van Dyke (mBVD) equivalent circuit model was developed using Advanced Design System (ADS) software. This model provides the insights about change in electrical behaviour of sensor when it is exposed to relative gas content. The fitted theoretical model follows the experimental data, which indicate the goodness of the mBVD model and curve fitting. The highest frequency down-shift was observed 10.5 kHz due to formalin gas content of 8.0 ppm. Motional arm is mainly influenced by the formalin gas exposure. Motional arm resistance (Rm) and inductance (Lm) was also influenced by the formalin gas content and found to increase by the formalin gas content and mainly accountable for gas sensing behaviour. It is also noted that static arm is not influenced by gas content and only motional arm is accountable for gas sensing behaviour. Highest sensitivity (S) was 1.3125 kHz/ppm and limit of detection (LOD) was 80 ppb. This new kind of formalin sensor is low cost, reliable, robust sensor and highly useful for room temperature operating formalin gas sensor applications.

Design of heterostructure one-port SAW resonator with improved bandwidth using Si and LiNbO3 layer

In this research work, we have designed a heterostructure one-port surface acoustic wave (SAW) resonator. The multi-layer one port SAW resonator is made of a silicon (Si) substrate as base material, 128 ͦ rotated Y-cut X- propagated lithium niobate (LiNbO3) as piezoelectric substrate, and Inter Digital Transducers (IDTs) made of aluminium. This model is designed to operate on a wide frequency of 4–5 GHz with a resonance frequency of 4.74 GHz. Various parameters are taken into consideration during the study and analysis such as high-quality factor, wider bandwidth, better electromechanical coupling coefficient, and a true Figure of merit (FoM). The obtained Quality factor and the electromechanical coupling coefficient (k2) of the designed model are 2700 and 0.18. By using the wide range of frequencies, the bandwidth for the designed model is 1.74 MHz. The obtained results show that the device’s performance of the one port multilayer SAW resonator using the Al/128°YXLiNbO3/Si multi-layered substrate exhibits a commercial application in the 5 G wireless communication system.

Integrated Hybrid Tweezer for Particle Trapping with Combined Optical and Acoustic Forces

We propose an on-chip integrated hybrid tweezer that can simultaneously apply optical and acoustic forces on particles to control their motions. Multiple potential wells can be formed to trap particles, and the acoustic force generated by an interdigital transducer can balance the optical force induced by an optical waveguide. For example, by driving the waveguide with an optical power of 100 mW and the interdigital transducer with a voltage of 1.466 V, the particle with a refractive index of 1.4 and a diameter of 5 μm (similar to yeast cells) can be stably trapped on the waveguide surface, and its trapping position is controllable by changing the optical power or voltage.

HARDWARE AND SOFTWARE COMPLEX FOR CONDUCTOMETRIC MEASUREMENTS WITH HIGH METROLOGICAL RELIABILITY

The article summarizes and supplements the results of the development of methods and tools for improving the reliability of differential measurement of local changes in electrical conductivity in electrolyte solutions using a pair of interdigitated transducers, which are used in conductometric biosensors. The aim of the work is a deeper suppression of the error due to the influence of background changes in a solution when the parameters of a pair of transducers are not completely identical. The essence of the issue, the causes and mechanism of the resulting error, and possible ways to reduce it are considered. The structure and algorithms of operation of a computer biosensor system with an intelligent module of a differential conductometric channel based on an alternating current bridge, with balancing in absolute value and phase of the disequilibrium signal, are described. Methods have been developed for tuning such a bridge to a special quasi- equilibrium state, in which a change in the background electrical conductivity does not change its output informative signal. The results of experimental studies are presented.

Acoustofluidic patterning in glass capillaries using travelling acoustic waves based on thin film flexible platform

Surface acoustic wave (SAW) technology has been widely used to manipulate microparticles and biological species, based on acoustic radiation force (ARF) and drag force induced by acoustic streaming, either by standing SAWs (SSAWs) or travelling SAWs (TSAWs). These acoustofluidic patterning functions can be achieved within a polymer chamber or a glass capillary with various cross-sections positioned along the wave propagating paths. In this paper, we demonstrated that microparticles can be aligned, patterned, and concentrated within both circular and rectangular glass capillaries using TSAWs based on a piezoelectric thin film acoustic wave platform. The glass capillary was placed at different angles along with the interdigital transducer directions. We systematically investigated effects of tilting angles and wave characteristics using numerical simulations in both circular and square shaped capillaries, and the patterning mechanisms were discussed and compared with those agitated under the SSAWs. We then experimentally verified the particle patterns within different glass capillaries using thin film ZnO SAW devices on aluminum (Al) sheets. Results show that the propagating SAWs can generate acoustic pressures and patterns in the fluid due to the diffractive effects, drag forces and ARF, as functions of the SAW device’s resonant frequency and tilting angle. We demonstrated potential applications using this multiplexing, integrated, and flexible thin film-based platform, including patterning particles (1) inside multiple and successively positioned circular tubes; (2) inside a solidified hydrogel in the glass capillary; and (3) by wrapping a flexible ZnO/Al SAW device around the glass capillary.

SAW Filters on LiNbO3/SiC Heterostructure for 5G n77 and n78 Band Applications.

The 5G communication system has experienced a substantial expansion of the spectrum, which poses higher requirements to radio frequency (RF) filters in enhancing their operating frequencies and bandwidths. To this end, this work focused on solving the filtering scheme for challenging 5G n77 and n78 bands and successfully implemented the corresponding spurious-free surface acoustic wave (SAW) filters exploiting large-coupling shear horizontal (SH) modes based on X-cut LiNbO3 (LN)/silicon carbide (SiC) heterostructure. Here, we initially investigated the suppression methods for spurious modes theoretically and experimentally and summarized an effective normalized LN thickness ( [Formula: see text] range of 0.15-0.30 for mitigating Rayleigh modes and higher order modes, as well as tilted interdigital transducers (IDT) by about 24° for eliminating transverse modes. Resonators with wavelengths ( λ) from 0.95 to [Formula: see text] were also fabricated, showing a scalable resonance from 2.48 to 4.21 GHz without any in-band ripple. Two filters completely meeting 5G n77 and n78 full bands were finally constructed, showing center frequencies ( fc) of 3763 and 3560 MHz, 3-dB fractional bandwidths (FBW) of 24.8% and 15.6%, and out-of-band (OoB) rejections of 18.7 and 28.1 dB, respectively. This work reveals that X-LN/SiC heterostructure is a promising underpinning material for SAW filters in 5G commercial applications.

Surface Acoustic Wave (SAW)‐Based Sonoporation of Single‐Adherent‐Cell

Sonoporation refers to the formation of tiny transient pores in cell plasma membranes by using ultrasound to increase the permeability to bioactive materials. Recently, the Sonoporation technique has been widely researched in cell treatment applications, such as gene transfection. However, due to the random distribution of microbubbles, it is challenging to perform controllable and precise localized sonoporation of a target cell. In this work, a device based on the surface acoustic wave is developed to achieve a selective manipulation and cavitation of microbubbles. The device consists of a pair of microbubble positioning slant‐finger interdigital transducers (SFITs) for moving a selected microbubble in a two‐dimensional plane. Meanwhile, another narrow‐frequency‐band SFIT is integrated into the device for local cavitation control of the same microbubble. As a result, a microbubble can be transported orthogonal to and along the acoustic transmission path by continuously adjusting the input frequency and relative phase. Upon reaching the target cell, the selected microbubble can be cavitated without exciting other microbubbles, resulting in local sonoporation. The resolution of phase‐based positioning and frequency‐based transportation are 8.3 and 7.0 µm with 45° and 10 kHz settings, respectively.

On-chip all-electrical determination of the magnetoelastic coupling constant of magnetic heterostructures

We have developed an approach to determine the magnetoelastic coupling constant of magnetic layers in thin film heterostructures. The film is formed on a piezoelectric substrate between two interdigital transducers (IDTs), a platform often used to construct a surface acoustic wave device. With the substrate piezoelectricity, strain is induced into the film by applying a dc voltage to the IDTs. The strain causes changes in the magnetization direction of the magnetic layer, which is probed by measuring changes, if any, in the transverse resistance of the heterostructure. We find that the extracted magnetoelastic coupling constant of the magnetic layer (CoFeB) depends on the film stacking. Such change can be accounted for provided that the elastic properties of the layers that constitute the heterostructures are taken into account. The on-chip all-electrical approach described here provides a versatile means to quantitatively assess the magnetoelastic coupling constant of thin film heterostructures.

High-temperature characterization of interdigitated transducers on gallium arsenide and surface acoustic wave analysis via interdigitated transducer modeling

Interdigitated transducer devices may provide an advantageous platform to study stress-enhanced interfacial phenomena at elevated temperatures, and an appropriate device design requires a thorough understanding of temperature-dependent material properties. In this study, the scattering parameter response for a surface acoustic wave resonator is simulated using a frequency-domain finite element method from 20 to 177 °C. Experimental device measurements are taken for the interdigitated transducer device fabricated on semi-insulating GaAs 100 oriented in the 110 direction, and the results are in good agreement with the simulation. Surface acoustic wave analysis provides the magnitude of bulk stress values and surface displacement over the experimental temperature range produced by a standing surface acoustic wave. The computational analysis combined with experimental verification suggests that such devices, when optimized for the maximum magnitude, can produce strain levels that could influence chemical potential associated with crystalline growth, atomic diffusion, and catalytic reactions. The modeling results demonstrate an interdigitated transducer's potential as an experimental platform to study the impact of strain on temperature-sensitive surface and bulk phenomena in piezoelectric materials.

Aluminum scandium nitride films for piezoelectric transduction into silicon at gigahertz frequencies

Recent advances in the growth of aluminum scandium nitride films on silicon suggest that this material platform could be applied for quantum electromechanical applications. Here, we model, fabricate, and characterize microwave frequency silicon phononic delay lines with transducers formed in an adjacent aluminum scandium nitride layer to evaluate aluminum scandium nitride films, at 32% scandium, on silicon interdigital transducers for piezoelectric transduction into suspended silicon membranes. We achieve an electromechanical coupling coefficient of 2.7% for the extensional symmetric-like Lamb mode supported in the suspended material stack and show how this coupling coefficient could be increased to at least 8.5%, which would further boost transduction efficiency and reduce the device footprint. The one-sided transduction efficiency, which quantifies the efficiency at which the source of microwave photons is converted to microwave phonons in the silicon membrane, is 10% at 5 GHz at room temperature and, as we discuss, there is a path to increase this toward near-unity efficiency based on a combination of modified device design and operation at cryogenic temperatures.

Temperature and strain SAW/BAW sensors on metallic substrates with RFID capability

Surface acoustic wave (SAW) strain sensors require an adhesive—typically a glue—for the mounting on the part under measurement. This comes with strain-transfer, reproducibility and aging issues. In this paper, we propose a novel glue-less solution where the SAW sensor is directly fabricated onto the surface of interest, here a metallic substrate. Here, we study the layered structure ZnO/Ti numerically and experimentally, with ZnO as the piezoelectric layer and titanium as the substrate. In this structure, both bulk acoustic waves and SAW can propagate, and we used both of them to monitor temperature variations up to 300 °C and strain levels up to 1800 μϵ. Moreover, reflective delay line (R-DL) designs were used, to provide the future users with radio frequency identification functionalities. In order to overcome the limitations due to the relatively low electromechanical coupling coefficient of ZnO/Ti, a specific R-DL layout with connected inter-digital transducers was used. The obtained experimental results confirm that the proposed glue-less R-DL structure is a promising solution for the independent evaluation of temperature and strain, with identification.

Velocity and Direction Adjustment of Actuated Droplets Using the Standing Wave Ratio of Surface Acoustic Waves (SAW)

Droplet actuation using surface acoustic wave (SAW) technology has recently been widely employed in “lab-on-a-chip” applications. In this article, SAWs generated by interdigital transducers (IDTs) were used to actuate microdroplets, where their velocity and direction could be adjusted by changing only the excitation phase shift, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> , of the voltage applied to the two IDTs. Specifically, the equation of the vibration of the mixed traveling surface acoustic waves (TSAWs) and standing surface acoustic waves (SSAWs) formed on the substrate surface operating in the exciter–exciter mode has been reported by the authors. An analytical expression for the acoustic standing wave ratio has been derived and given as a function of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> and the spatial phase difference. It can be seen from the expression that the directions of the TSAWs will be opposite to each other, in the range of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> given by (0, π) and (π, 2π), and the component of the TSAWs can be adjusted by changing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> in each direction. Following the theoretical analysis discussed here, two IDTs have been excited to generate a mixture of TSAWs and SSAWs. A series of experiments was carried out to control the velocity and direction of the actuated droplets, by changing only <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> . In addition, an experiment performed to compare the techniques shows that the upper limit of the velocity of the actuated droplets can be significantly increased using the exciter–exciter mode, showing that it has the potential to be an alternative method to the traditional exciter–absorber mode.