Surface Acoustic Wave Substrate Research Articles

Efficient Generation of Plasma‐Activated Aerosols with High Concentrations of Reactive Species via Silicon Dioxide Coated Surface Acoustic Wave Devices

AbstractAn effective method to deliver plasma‐activated water onto contaminated surfaces is with a surface acoustic wave (SAW) nebulizer that can efficiently produce plasma‐activated aerosols. While higher reactive species concentrations in the plasma‐activated aerosols promote more efficient bacterial inactivation and hence reduce the amount of aerosols needed to completely eradicate the bacteria colonies, higher concentrations of reactive species themselves are found to lead to lower nebulization rates due to the increased electrical conductivity of the solution. To circumvent this problem, it is shown that coating the SAW substrate with a thin insulating layer of silicon dioxide (SiO2) can significantly mitigate the nebulization rate reduction. Specifically, when the electrical conductivity increases from 0.25 to 4.0 mS cm−1, the 62% drop in the nebulization rate is observed with the uncoated SAW devices is substantially reduced to 19% simply with the SiO2 coating. This can be attributed to the synergistic effects of increased wettability and the suppression of the electrical body force acting on the liquid film. The concomitant increase in the bacterial colony reduction from 17% to 76% demonstrates this solution to be a facile yet effective way of enhancing the efficiency for spray‐based bacterial inactivation on contaminated surfaces.

Kinetic Modeling and Material Removal Mechanism Analysis of Fixed-Abrasive Polishing for Lithium Tantalite Wafer

As a typical multi-functional soft-brittle material, lithium tantalate (LT) exhibits excellent electro-optical and ferroelectric properties and now has been widely applied in many fields, such as electro-optical modulators, pyroelectric detectors, and surface acoustic wave substrates. Traditional free-abrasive polishing processing of lithium tantalite crystals is generally fraught with poor efficiency for its lower fracture toughness. This study proposed a method of polishing lithium tantalite wafer by means of fixed-abrasive plates. A cutting force model and the relative cutting speed model of the machining mechanism of fixed-abrasive plates were first established, and then the main influencing factors of cutting force and relative cutting speed were analyzed on the basis of the theoretical model. It was found that cutting force is influenced by eccentricity and load, while relative cutting speed is influenced by eccentricity and the fixed-abrasive plates’ rotation speed. Finally, single-factor tests were conducted on these influencing factors, and the comparative analysis between the experimental results and those in the theoretical model shows that they are highly correlated to each other. After 30 min of polishing under the optimized parameters w = 60 rpm, e = 90 mmand applied with variable load, the surface roughness S a of the workpiece can be reduced to 1.234 nm, and the MRR reaches 14.821 μm/h.

Designed Structures of Interdigital Electrodes for Thin Film SAW Devices.

This paper studied the impact of the microstructure of interdigital electrodes on the performance of surface acoustic wave (SAW) resonators and proposed an innovative piston, dummy finger and tilt (PDT) structure, which was then applied to the GLONASS L3 band filters. Through the adoption of 3D finite element simulation (FEM), photolithography, and testing on an incredible high-performance surface acoustic wave (I.H.P. SAW) substrate, it is concluded that the total aperture length is 20T (T is period), resulting in a more optimal resonator performance; changing the width and length of the piston can suppress transverse modes spurious, but it does not enhance impedance ratio; to further improve the quality of the SAW resonator, the proposed PDT structure has been experimentally proven to not only effectively suppress transverse modes spurious but also possess a high impedance ratio. By utilizing a PDT structure within a "T + π" topology circuit, we successfully designed and manufactured a GLONASS L3 band filter with a bandwidth of 8 MHz and an insertion loss of 3.73 dB. The design of these resonators and filters can be applied to the construction of SAW filters in similar frequency bands such as BeiDou B2 band or GPS L2/L5 band.

An Analysis of Edge Chipping in LiTaO3 Wafer Grinding Using a Scratch Test and FEA Simulation

Lithium tantalite (LiTaO3) is a representative multifunctional single-crystal material with electro-optical, acoustic, piezoelectric, pyroelectric, and nonlinear optical properties used as a substrate for surface acoustic wave (SAW) devices. To enhance SAW device performance, thinner LiTaO3 substrates with improved surface roughness are desired. Chemical mechanical polishing (CMP) is employed to achieve the desired surface roughness after grinding. However, the thinning process increases the risk of substrate fracture, especially at the edges, resulting in edge chipping. Edge chipping can lead to complete substrate failure during SAW device fabrication, requiring an effective wafer geometry to prevent it. The study utilizes scratch tests and finite element analysis (FEA) to identify the optimal edge shape (C-cut, trimmed, and thinned) for preventing edge chipping on LiTaO3 wafers. The C-cut edge refers to the rounding of the wafer’s edge, while the trimmed edge refers to the machining of the wafer’s edge to be perpendicular to the wafer surface. As a result of the scratch tests, we observed edge-chipping lengths of 115 and 227 μm on the C-cut and trimmed edges, respectively, while the thinned edge (half C-cut) resulted in complete wafer fracture. In the finite element analysis (FEA), edge-chipping lengths of 80, 120, and 150 μm were obtained on the C-cut, trimmed, and thinned edges (half C-cut), respectively. In conclusion, it has been confirmed that the C-cut, trimmed, and thinned edge shapes are effective in preventing edge chipping. However, considering that the C-cut edge shape becomes thinner through grinding, using the trimmed edge shape appears to be the most effective.

Combination of pulse signal modulation and hydrophilic treatment of a substrate for controlling the thermal distribution in surface acoustic wave atomization

Owing to the temperature limitations of biochemical or biomedical atomization applications, temperature control within a surface acoustic wave (SAW) atomizer is critical. This paper presents a method for controlling the thermal distribution of SAW atomization. This method combines pulse signal modulation and hydrophilic treatment of an SAW substrate. By setting the duty factor to 50 % and contact angle to 30°, the temperature reduces to about 99.3 °C for water and approximately 68.4 °C for a 50 wt% alcohol/water binary mixture during SAW atomization. Therefore, the proposed method effectively controls the thermal distribution during SAW-based atomization. In addition, the particle diameters of the different liquids used for SAW atomization are explored using this method. The results reveal that the general method increases the particle diameters of tiny droplets from 5 μm to 10 μm. Notably, this is within an acceptable range, hence the method has lower effects on the atomization particle diameter.

Fast Extraction of Coupling of Modes Parameters for Surface Acoustic Wave Devices Using Finite Element Method Based Simulation

The finite element method (FEM) has been applied to extract the coupling-of-modes (COM) parameters of surface acoustic wave (SAW) devices for a long time. It always involves calculating the dispersive curves or harmonic admittance, which makes the extraction process and results sophisticated, time-consuming and inaccurate. Therefore, a simple method is proposed to extract all COM parameters of the SAW devices rapidly and accurately in this paper. It is based on the FEM and combines the stationary analysis with modal analysis. We have described in detail the basic principles and procedures of the proposed method, and made a comprehensive comparison between the proposed method and the other two existing methods. We have also examined the proposed method by extracting COM parameters of some common SAW substrate, and compared our extracted results with those reported in the other literatures. Results show that our proposed method holds higher accuracy and more efficiency (~s order) than the others (~h order). Moreover, our extracted COM parameters are in an excellent agreement with those reported in the other literatures.

Simulations of surface acoustic wave interactions on a sessile droplet using a three-dimensional multiphase lattice Boltzmann model.

This study reports the development of a three-dimensional numerical model for acoustic interactions with a microscale sessile droplet under surface acoustic wave (SAW) excitation using the lattice Boltzmann method (LBM). We first validate the model before SAW interactions are added. The results demonstrate good agreement with the analytical results for thermodynamic consistency, Laplace law, static contact angle on a flat surface, and droplet oscillation. We then investigate SAW interactions on the droplet, with resonant frequencies ranging 61.7-250.1 MHz. According to our findings, an increase in wave amplitude elicits an increase in streaming velocity inside the droplet, causing internal mixing, and further increase in wave amplitude leads to pumping and jetting. The boundaries of wave amplitude at various resonant frequencies are predicted for mixing, pumping, and jetting modes. The modeling predictions on the roles of forces (SAW, interfacial tension, inertia, and viscosity) on the dynamics of mixing, pumping, and jetting of a droplet are in good agreement with observations and experimental data. The model is further applied to investigate the effects of SAW substrate surface wettability, viscosity ratio, and interfacial tension on SAW actuation onto the droplet. This work demonstrates the capability of the LBM in the investigation of acoustic wave interactions between SAW and a liquid medium.

(Invited) High-Sensitive Electrochemical Detector with Micro-Stirrer Driven By Surface Acoustic Wave

Micro total analysis system (μTAS), by applying microfabrication technology used in the manufacture of semiconductor integrated circuits, applies chemical processing and biochemical analysis usually conducted using test tubes in a laboratory to microscopic flow paths fabricated on a chip, and it is an ultra compact analytical system.Advantages of μTAS are that it requires only a small amount of sample used for measurement, the space in the groove is narrow, so that the diffusion distance of molecules can be shortened, the reaction time can be shortened, automation of measurement including pretreatment, miniaturization of the equipment, disposable of the equipment, low cost, reduction of manpower and the like can be cited.If μTAS is put into practical use, it is expected that everyone can easily and accurately inspect on site. However, as μTAS uses extremely small samples such as tens of microliters, the issues such as handling difficulty and reproducibility remain. Turning to the electrochemical sensor, electrochemical measurement is effective as a detection method in μTAS because it has advantages such as fast response, inexpensive, easy to miniaturize, and so far, many electrochemical biosensors have been reported. Generally, in the electrochemical measurement, based on the electron transfer between the analyte on the electrode surface and the electrode, the analyte is detected from the current value. In the analysis with a sample volume of several milliliter scale, the agitator is placed in the solution cell and stirring is carried out, whereby the supply to the electrode surface of the measurement analyte is enhanced, whereby high sensitivity can be detected. However, μTAS can not place a stirrer because it uses a small amount of tens of microliters, and it is difficult to stir manually, the diffusion of the detection analyte to the electrode surface becomes rate-limiting, causing a decrease in sensor sensitivity. Therefore, in this research, we focused on an actuator using surface acoustic wave (SAW) in order to solve the problem that sensor sensitivity decreases in electrochemical measurement of a small amount of sample. Surface acoustic waves are vibrations that concentrate and propagate on the surface of an object and can be generated by applying a high frequency potential to the IDT (Inter digital transducer) fabricated on the surface of the piezoelectric substrate. IDT can be easily fabricated by conventional photolithography technology. Since surface acoustic waves can be driven by microscale pattern electrodes fabricated by microfabrication, they are suitable for handling a very small amount of liquid droplets. Many reports have been reported as droplet flow manipulation techniques by using SAW. In the field of biotechnology, application to PCR with enhanced reaction efficiency of trace amounts of samples has been reported. Many researches have also been reported in which SAW is applied as a conversion element of a biosensor. A detection method by label free is proposed by measuring the frequency shift due to adsorption to the sensor surface. In recent years, co-authors reported a technology to place a small amount of 5 μL droplets in the pool and drive them by SAW. They also studied the relation between the power supplied to the IDT and the angular velocity and temperature of stirring the liquid using the SAW driven micro liquid rotor.If we could fuse this SAW technology with electrochemical measurement and stir a small amount of sample, diffusion of the target substance to the electrode surface increased, and we thought that we could solve the problem of sensitivity reduction due to diffusion control. In this research, we propose a novel measurement system which electrochemical detection is carried out by integrating 3 electrode system for electrochemical detection on SAW substrate developed by bicycle, and stirring minute amount of sample by SAW. As a result, it is possible to increase the diffusion rate of the analyte in the small amount sample to the electrode surface, aiming at constructing an electrochemical detection system with high sensitivity and good reproducibility. Figure 1

FEM analysis of piezoelectric film as IDT on the diamond substrate to enhance the quality factor of SAW devices

This paper describes an innovative electro-acoustic coupling structure with a Patterned Piezoelectric film as Inter-Digital Transducer (PP-IDT) on the diamond substrate for Surface Acoustic Wave (SAW) devices of better quality factor and frequency resolution. Theoretical analysis and Finite Element Method (FEM) are employed to investigate the dependence of microwave impedance characters on the thickness of piezoelectric and metal electrode layers. The systematic studies show that the PP-IDT structure can excite the mechanical vibration on the top surface of diamond substrate and derive the SAW. The quality factor increases remarkably in excess to 104 since the SAW is propagating below the diamond surface with little interface loss and transmission loss.

High-Performance SAW Resonator With Simplified LiTaO3/SiO2 Double Layer Structure on Si Substrate.

In response to the increased mobile data traffic, there is a growing need for more low-loss RF band filters with steep frequency characteristics, and high-quality ( Q )-factor and low-temperature coefficient of frequency (TCF) resonators are required to achieve this. We previously reported that for a surface acoustic wave (SAW) resonator on a three-layer structure, which is composed of a thin LiTaO3 (LT) plate whose orientation is 50° rotated YX propagation, SiO2 layer, and AlN layer on a Si substrate, a Q-factor several times higher than that of an SAW resonator on a standard 42° rotated YX propagation LiTaO3 (42YX-LT) substrate could be obtained. In this study, we investigated this layer structure and found that a two-layer structure, in which the AlN layer is removed, achieves a high Q -factor. Numerical analyses using a finite element method showed that the acoustic wave energy can be confined to the surface of the two-layer substrate, and the TCF and electromechanical coupling coefficient ( k2 ) were improved by optimizing the thickness of each layer. We fabricated and evaluated prototype one-port resonators with the two-layer structure and the standard 42YX-LT SAW substrate with resonant frequencies from 0.95 to 3.6 GHz. An improvement of the Q-factor of 3 to 4 times compared with that of the resonator with standard 42YX-LT substrate was observed for the two-layer structure, which means that a reduction of complexity of the layer structure could be obtained without performance loss. The two-layer structure was applied to a 2.4-GHz band Wi-Fi filter to achieve high performances such as low-loss, better steepness, and high attenuation.

An Embedded Surface Acoustic Wave Pressure Sensor for Monitoring Civil Engineering Structures

This paper proposes a novel embedded surface acoustic wave (SAW) pressure sensor for monitoring civil engineering structures. The sensor consists of a pressure cell and a sensing chip in a metal housing. The whole interior of the sensor is filled with silicone oil for pressure transfer. The sensing chip is a SAW die packaged in a seal cavity to monitor the pressure of the silicone oil. Therefore, the external pressure applied to the cell can be detected by this method. In order to optimize the structure, the strain behavior and pressure measurement of the SAW device are analyzed in detail. The positions of the inter-digital transducer and reflectors on the SAW substrate are designed deliberately. The SAW device is fabricated by a lift-off process. The sensor is characterized by a network analyzer. The pressure sensitivity tested is 0.4°/kPa and the nonlinearity is 1.02%. The maximum absolute error is 2.9° in the range of 0–500 kPa.

A highly attenuating and frequency tailorable annular hole phononic crystal for surface acoustic waves

Surface acoustic wave (SAW) devices are widely used for signal processing, sensing and increasingly for lab-on-a-chip applications. Phononic crystals can control the propagation of SAW, analogous to photonic crystals, enabling components such as waveguides and cavities. Here we present an approach for the realisation of robust, tailorable SAW phononic crystals, based on annular holes patterned in a SAW substrate. Using simulations and experiments, we show that this geometry supports local resonances which create highly attenuating phononic bandgaps at frequencies with negligible coupling of SAWs into other modes, even for relatively shallow features. The enormous bandgap attenuation is up to an order-of-magnitude larger than that achieved with a pillar phononic crystal of the same size, enabling effective phononic crystals to be made up of smaller numbers of elements. This work transforms the ability to exploit phononic crystals for developing novel SAW device concepts, mirroring contemporary progress in photonic crystals.

Fast Surface Acoustic Wave-Based Sensors to Investigate the Kinetics of Gas Uptake in Ultra-Microporous Frameworks.

Observation of the kinetics and measurement of the activation energies for gas diffusion in porous materials requires very fast and sensitive sensors. In this work, thin films of metal-organic frameworks (MOFs) with different pore sizes are grown on a surface acoustic wave (SAW) substrate, resulting in very sensitive and specific sensor systems for the detection of various gases at very short time scales. Using specially designed SAW delay lines for the detection, up to 200-nm-wide cubic MOF crystals were grown directly from a solution on the sensitive sensor chip area. One example, MFU-4, exhibits a smallest pore aperture of 2.5 Å and shows a highly sensitive and specific response to CO2, H2, He, NH3, and H2O. It is shown that such a MOF@SAW sensor responds within milliseconds to gas loading and its sensitivity reaches levels as low as 1 ppmv, currently only limited by the gas mixing system. This unique combination of sensitivity and fast response characteristics allows even for real-time investigations of the sorption kinetics during gas uptake and release. As is typical for SAW sensors, the production of the chips is very straightforward and inexpensive and-combined with the unique properties of the MOFs with their tunable pore sizes and adjustable internal surface properties-holds promise for different sensor applications.

A concept of wireless and passive very-high temperature sensor

There is a need for sensors capable operating at temperatures above 1000 °C. We describe an innovative sensor that might achieve this goal. The sensor comprises two main elements: a thermocouple and a surface acoustic wave (SAW) strain sensor. The cold junction of the thermocouple is electrically connected to a highly piezoelectric thin layer, deposited on top of a SAW substrate. In operation, the voltage generated by the temperature gradient between the hot (>1000 °C) and cold junction (<350 °C) generates a strain field in the layer, which is mechanically transmitted to the substrate. This modifies the SAW propagation conditions and therefore the sensors' radiofrequency response. The change depends on the applied voltage and thus on the hot junction temperature. As SAW devices are passive elements that can be remotely interrogated, it becomes possible to infer the hot junction temperature from the radiofrequency response, i.e., to remotely read temperatures above 1000 °C, without embedded electronics. In this paper, we demonstrate the feasibility of this concept, using AlN layers deposited on Y-Z Lithium Niobate (LN). The achieved sensitivity of 80 Hz/V at 400 MHz is constant over a wide voltage range. Numerical simulations were performed to compute the main properties of the demonstrators and suggest optimization strategies. Improvements are expected from the use of stronger piezoelectric layers, such as AlScN or Pb(Ti,Zr)O3 (PZT), which could increase the sensitivity by factors of 3 and 20, as estimated from their transverse piezoelectric coefficients. As a first step in this direction, thin PZT layers have been deposited on Y-Z LN.

Analysis of the thermal and temporal stability of Ta and Ti thin films onto SAW–substrate materials (LiNbO3 and LiTaO3) using AR‐XPS

Modern surface‐acoustic‐wave devices are characterised by their trend to higher frequencies, power densities, and new applications. For this, a shrinking of the dimensions is necessary but hardly possible to achieve with standard Al‐based metallisation because of increased stress‐induced damaging (acoustomigration). In this context additional barrier interlayers between substrates and electrodes are necessary, especially for high‐temperature applications. For this, we present results of a detailed chemical interface analysis of deposited Ta and Ti thin‐film growth onto surface acoustic wave–substrate materials (LiNbO3 and LiTaO3) with respect to their interface layer structure and its temporal and thermal stability in vacuum. The analysis was mainly performed using non‐destructive and surface sensitive angle‐resolved X‐ray photoelectron spectroscopy. Besides a slight oxidation (oxygen adsorption) at the surface of these highly reactive metal thin films all interface sequences are stable up to 24 h. We also report higher thermal stability of Ta thin films up to 600 °C in contrast to Ti thin films (300 °C) because of presumed diffusion of Ti along grain boundaries. Copyright © 2016 John Wiley & Sons, Ltd.

SAW based phononic crystal sensor, technological challenges and solutions

Phononic crystals (PnC) with a specifically designed liquid-filled defect have been recently introduced as a novel sensor platform (Lucklum et al. in Sens Actuators B Chem 171---172:271---277, 2012). Sensors based on this principle feature a band gap covering the typical input span of the measurand as well as a narrow transmission peak within the band gap where the frequency of maximum transmission is governed by the measurand. This approach has been applied for determination of volumetric properties of liquids (Lucklum et al. in Sens Actuators B Chem 171---172:271---277, 2012; Oseev et al. in Sens Actuators B Chem 189:208---212, 2013; Lucklum and Li in Meas Sci Technol 20(12):124014, 2009) and has demonstrated attractive sensitivity. One way to improve sensitivity requires higher probing frequencies in the range of 100 MHz and above. In this range surface acoustic wave (SAW) devices are an established basis for sensors. We have performed first tests towards a PnC microsensors (Lucklum et al. in Towards a SAW based phononic crystal sensor platform. In: 2013 Joint European frequency and time forum and international frequency control symposium (EFTF/IFC), pp 69---72, 2013). The respective feature size of the PnC SAW sensor has dimensions in the range of 10 µm and below. Whereas those dimensions are state of the art for common MEMS materials, etching of holes and cavities in piezoelectric materials that have an aspect ratio diameter/depth is still challenging. In this contribution we describe an improved technological process able to realize considerably deep and uniform holes in a SAW substrate.

Study on grinding of LiTaO3 wafer using effective cooling and electrolyte solution

As a typical multi-functional single crystal material, lithium tantalate (LiTaO3 or LT) exhibits its excellent electro-optical, piezoelectric properties and has now been widely applied into many applications, such as electro-optical modulators, pyroelectric detectors, optical waveguide, piezoelectric transducers and SAW (surface acoustic wave) substrates. LT is known as a very important functional material, however the details of its machinability are not readily available yet. The content in this study is firstly focuses on the physical properties of LT like piezoelectric and pyroelectric effects and their influence on grinding performance. The obtained results are analyzed and discussed to understand its physical properties which have significant influences on their machinability in the grinding process. The crack initiation is possible to be dominated by internal stress which originated from self-polarization of the material itself. Hence, in order to suppress the physical effects induced by polarization during grinding of LT, control the temperature of coolant and increase the electrical conductivity of coolant are purposely tried in this study. The grinding results suggest that control of coolant temperature and use of electrolyte solution can effectively suppress the increasing rate of grinding torque and surface roughness, which in turn enhance the performance of LT wafer grinding. The LT wafers are eventually able to be thinned less than 100μm.

Characterization of an acoustically coupled multilayered microfluidic platform on SAW substrate using mixing phenomena

Optimization of the reusable microfluidic platform on surface acoustic wave (SAW) requires a clear understanding of the various factors that affects the acoustic energy transmission to the fluid in the microchannel. This article reports the characterization and analysis of the reusable SAW microfluidic platform. The acoustic energy transfer through various layers was characterized by the microfluidic mixing phenomenon. During this work, mixing efficiency was considered to evaluate the acoustic energy transmission. The three different parameters taken into consideration are the input voltage, SAW frequency and the coupling layer thickness. The effect of the factors on the output response is examined by conducting experimental studies and developing new analytical models. The acoustic wave was coupled through a liquid layer to a disposable superstrate. The anti-symmetric higher order lamb waves generated on thin glass plate generates compressional waves in the liquid to induce fluid motion. The acoustic energy delivered to the fluid increased as the square of the applied voltage and saturated at 50V. The frequency response demonstrated a higher acoustic energy transmission for the 100MHz compared to the 50MHz, which was validated by numerical studies. Power transmitted through the coupling layer displayed a sinusoidal dependence on the normalized thickness of the layer. Finally, the effect of temperature is also considered to confirm the validity of the developed models.

Wafer–to–wafer transfer process of barium strontium titanate for frequency tuning applications using laser pre-irradiation

This paper describes laser-assisted film transfer technology for barium strontium titanate (BST) deposited on a sapphire substrate. BST is a promising ferroelectric material for varactors, which are required for frequency-tunable RF applications. However, the deposition temperature of BST (600 ~ 700 °C) is too high for surface acoustic wave (SAW) substrates. In this study, BST grown on a sapphire substrate at 650 °C was transferred at low temperature (140 °C) to a borosilicate glass substrate as well as a LiTaO3 substrate. The transferred BST films were characterized as tunable capacitors. A key process in the BST film transfer technology is the laser pre-irradiation of a buffer Pt layer beneath BST from the backside of the sapphire substrate to weaken the BST-to-Pt adhesion. The mechanism of delamination at the BST/Pt interface is discussed using a simple 1D heat transfer model.

RF-Activated Standing Surface Acoustic Wave for On-Chip Particle Manipulation

On-chip flow cytometry provides a powerful tool to characterize cell samples for point-of-care diagnosis. In particular, sample focusing at specific locations along the microchannel is crucial to ensure the accuracy of detection. In this paper, we present a simple strategy of interfacing an RF-activated standing surface acoustic wave (SSAW) substrate with a microfluidic channel, and use this device to study the dynamic process of particle aggregation along the microchannel. Specifically, the SSAW generated by two parallel interdigital transducers induces an acoustic radiation force that propels particles suspended in the liquid toward the pressure nodes whose locations are tunable by judicious choice of the applied SSAW frequency. We also carry out a theoretical analysis that provides an estimation of the time for the particle assembly, which is validated by experimental results. This SSAW transducer can therefore be easily integrated into a microfluidic chip with moderate energy consumption, offering a convenient and effective solution in the development of on-chip flow cytometry.