A novel laser-induced thermoelastic spectroscopy (LITES) system is proposed for the sequential detection of carbon dioxide and aerosols. A quantum cascade laser (QCL) was used as the excitation source, and the second-harmonic wavelength-modulation spectroscopy technique was employed in the sensing system. The laser irradiation position was optimized to maximize the excitation of the in-plane bending vibration mode of the quartz tuning fork-based detector. Optimizing the sensing system's pressure yielded a maximum Q-factor of 20 952 and a resonant frequency of 32 761 Hz at 62.44 torr. Experimental results show that the demodulated signal exhibits a linear relationship with carbon dioxide concentration, saturating at 1297 ppm. Allan deviation was used to analyze the system noise, revealing a detection limit of 133 ppb at an integration time of 64 s, corresponding to a normalized noise-equivalent absorption (NNEA) of 2.91 & times; 10(-9)cm(-1).W . Hz (-1/2 ). Based on the spectral absorption of CO2 and light attenuation by solid aerosols, the designed LITES system enables rapid detection for the sequential monitoring of carbon dioxide concentration and the relative absorption signal of micrometer-sized solid aerosols, with an experimental gas exchange time constant of the sample cell estimated to be 4.8 s based on the cell volume and gas flow rate. The system achieves ultralow noise-equivalent absorption under optimized low-pressure conditions, demonstrating its potential as a platform for advancing dual-parameter spectroscopic sensing.

High-frequency focused ultrasound is widely used in biomedical applications such as high-resolution imaging, neuromodulation, and particle manipulation. However, dynamic tuning of the focal plane in conventional systems often relies on mechanically adjustable components or array-based control with high cost. In this work, an optically transparent, planar compact piezoelectric ultrasonic transducer was designed and fabricated by encoding phase profile corresponding to an ideal converging spherical wave onto a planar aperture, thereby generating focused fields while maintaining compatibility with microscopic imaging platforms. The acoustic field was experimentally characterized in the focal plane at design frequency and in the propagation plane at several excitation frequencies around the design frequency. The focal shift originates from the mismatch between the fabricated phase pattern and the propagation wavenumber at the excitation frequency. An approximate linear relation between focal length and frequency near the design one is derived theoretically, and the finite-range tuning behavior is interpreted using the stationary-phase condition. Both theory and experiment show the focal length varies approximately linearly with excitation frequency near the design frequency. Water-tank measurements agree well with the theoretical prediction, confirming the proposed model. This work provides a simple and cost-effective approach for focal tuning in compact high-frequency ultrasound devices.

This paper presents a high-performance aluminum nitride (AlN) MEMS hydrophone based on an Island Piezopatterned Structure (IPS). By selectively etching the piezoelectric layer to retain isolated active islands, the IPS design reduces the equivalent bending stiffness of the diaphragm and concentrates stress within the sensing region. This significantly enhances charge generation efficiency without introducing non-standard fabrication steps. An 8 & times; 8 sensor array with an effective sensing area of 4 mm & times;4 mm was fabricated on a silicon-on-insulator (SOI) wafer using a standard MEMS process. The device exhibits a resonant frequency of 530.1 kHz and an effective electromechanical coupling coefficient of 2.87%. Integrated with a low-noise preamplifier, the hydrophone demonstrates a flat receiving sensitivity of-174.8 +/- 1.1 dB (re: 1 V/& micro;Pa) within the 20 Hz-10 kHz range. Notably, compared with a conventional clamped boundary structure (CBS) hydrophone fabricated using the identical process, the proposed structure achieves a sensitivity improvement of approximately 6.9 dB. The device also exhibits high linearity (maximum nonlinearity of 0.35%) and excellent horizontal omnidirectionality (deviation < 1 dB). These results confirm that the IPS strategy effectively advances scalar MEMS hydrophones toward higher sensitivity without increasing fabrication complexity. [2026-0011]

Employing photoacoustic spectroscopy to trace gases across varying temperatures in real-world testing environments poses considerable challenges. This study presents a miniaturized resonant photoacoustic cell (MRPAC) based on a MEMS microphone for a temperature-compensated carbon dioxide (CO2) photoacoustic spectroscopy system. The MR-PAC features an ultra-compact volume of 682.3 mu L and maintains stable resonant frequency tracking under varying temperature and CO2 concentration conditions. Detection was performed using 2f-wavelength modulation spectroscopy, achieving a minimum detection limit of 135 ppb at 75 s integration time. A temperature and humidity compensation algorithm was developed based on a Multi-layer Perceptron (MLP) model. Trained on photoacoustic signal, temperature, humidity, and concentration data, this algorithm achieves Mean Squared Error (MSE) of 49.8 ppm2 and R2 of 0.995, demonstrating adequate temperature compensation within the 20-30 degrees C range. Continuous CO2 concentration monitoring over 8 h showed the system's stability, validating its potential for practical, field-deployable applications across a range of temperatures and humidity levels.

A high-efficiency closed-film microheater based on an AlN/Mo composite heterostructure has been developed for a dual-channel microsystem for measuring CO2, integrating photoacoustic and thermoacoustic detection. The microheater can reach a typical temperature of 580 °C in just 12 ms, consuming only 73.1mW of power while effectively limiting thermomechanical stress to below 2.07 GPa. It achieves a modulation depth of 100% at 30.3  Hz, meeting the stringent specifications required for high-sensitivity gas sensing applications. Using this microheater in the photoacoustic–thermoacoustic dual-channel microsystem enables high-precision CO2 measurement in the 0–1% range via differential photoacoustic detection with a detection limit of 6 ppm and a detection resolution of 1.11% across the full concentration range, using the thermoacoustic effect. The normalized noise equivalent absorption coefficient is calculated to be 1.27 × 10-8 cm−1·W·Hz−1/2, and the expanded relative uncertainty is 2.48% (k = 2). This low-cost, compact, and low-power solution offers a fast response time of 8.5  s, making it ideal for portable and practical gas sensing applications.

Miniaturized swimming robots have been widely explored for navigation and precise manipulation in low Reynolds number fluids, showing great potential in biomedical applications. In this work, we propose an asymmetric-pattern Lamb wave resonator (LWR) at an operating frequency of 148 MHz and demonstrate it as a wireless driver for two-dimensional swimming robotics. Experimental results show that the resonator immersed in water could generate strong acoustic streaming with highly directional drag forces even under applied powers of similar to 100 mW. The LWRs are fabricated with standard semiconductor process, leading to convenient design of the operating frequency and device layout. Both the linear motion with a speed of several mm/s and rotation with a speed of more than 100 degrees/s have been realized using a four parallelly connected LWR array as the driver. Therefore, by precisely controlling the movement direction and speed of the robot, flexible two-dimensional swimming has been achieved. This work presents a strategy of microscale acoustofluidic principle for the development of miniaturized two-dimensional swimming robots, inspiring the exploration of tiny robots in minimally invasive surgery and drug delivery domains.[2024-0183]

An integrated microsystem for trace gas detection based on multi-pass radial resonant photoacoustic spectroscopy (MR-PAS) has been proposed. A polished photoacoustic cavity is specifically designed to facilitate incident laser light coupling, enable multi-pass reflection, and resonantly amplify the photoacoustic (PA) pressure. Finite element analysis (FEA) is employed to simulate the acoustic field distribution, frequency response, and ray tracing behavior. Simulation results reveal that the designed cavity achieves 771-fold excitation of the incident laser and amplifies PA pressure by operating in the first-order radial resonant mode. To validate the performance of the MR-PAS, a CO2 detection system is constructed. Experimental results demonstrate that the MR-PAS achieves an impressive minimum detection limit (MDL) of 12.4 ppb with a 274 s integration time, according to the normalized noise-equivalent absorption coefficient of 1.71 x 10(-8) cm(-1)WHz(-1)/(2). The compact photoacoustic cavity (1.1 ml) enables rapid response, with gas replacement and stabilization within similar to 4.4 s at a flow rate of 50 sccm.

The development of digital microfluidics has inspired significant advancements in diverse applications such as virus detection, molecular hybridization, and chemical reactions. The capabilities of digital microfluidics, taking Electrowetting-on-Dielectric (EWOD) for example, are precise handling and detecting targets based on the fundamental manipulations such as transportation, merging, mixing, and splitting of droplets. However, digital microfluidic systems suffer from complex electrode layouts, poor dynamic performance, and low-efficiency droplet manipulation. To address these limitations, we present a digital microfluidic system with enhanced dynamic properties using unidirectional emission surface acoustic waves. Surface acoustic wave device with resonance frequency of 300 MHz has been carefully designed with an acoustic reflector next to one end driving path from the other end, which is demonstrated as long as 600 times the wavelength for droplet transportation. By arranging the SAW array, the system enables precise and high-speed droplet transportation within a large programmed area. A smart platform is developed to automatically program and control droplets with preplanned routes. The SAW droplet manipulation system has shown excellent performance in high speed, ultra-long pathways, and automatic navigation, greatly promoting the acoustic manipulation advancements for biomedical research and chemical engineering.

Acoustic microfluidic separation techniques are suitable for nanoscale particle separation in the biomedical field. However, limited sample throughput and processing speed would make it infeasible to process clinical-scale samples (> 500 million cells). Previous studies have shown that the throughput can be initially improved by designing a bulk acoustic wave (BAW) resonator array. In this work, we optimized the design of a 6x6 BAW array chip to achieve the expansion of the array. In addition, a novel wide bandwidth 36-channel power divider is designed to feed the array based on the stripline principle. The low return-loss power divider realizes a more reasonable power distribution method, and combined with the expanded array BAW chip, it significantly improves the throughput. Experimental results show that the chip achieves efficient separation at 80 mu L/min throughput, which is 2.7x higher than previous results. In addition, size-dependent separation of nanoparticles can be realized based on the difference in capture efficiency.

Acoustic streaming shows great potential in applications such as bubble dynamics, cell aggregation, and nanosized particle isolation in the biomedical and drug industries. As the acoustic shock distance decreases with the increase of incident frequency, the nonlinear propagation effect will play a role in acoustic streaming, e.g., Eckart (bulk) streaming at a few gigahertz. However, the theory of source terms of bulk streaming is still missing at this stage when high-order acoustic harmonics play a role. In this paper, we derive the source term including the contribution of high-order harmonics. The streaming-induced hydrodynamic flow is assumed to be incompressible and no shock wave occurs during the nonlinear acoustic propagation as restricted by the traditional Goldberg number Gamma < 1 or Gamma approximate to 1, which indicates the importance of nonlinearity relative to dissipation. The derived force terms allow evaluating bulk streaming with high-order harmonics at gigahertz and provide an exact expression compared to the existing empirical formulas. Numerical results show that the contribution of higher-order harmonics increases the streaming flow velocity by more than 20%. Our approach clearly demonstrates the errors inherent in the expression introduced by Nyborg which should be avoided in numerical computations as it includes part of the acoustic radiation force that does not lead to acoustic streaming.

The previously reported acoustofluidic tweezers(AFTs) array chip has been demonstrated for rapid enrichment of micro/nanoparticles. However, the chip operates discretely, resulting in limited throughput.This article presents a microfluidic chip fabricated using six layers of bonded polydimethylsiloxane(PDMS). The chip incorporates pneumatic microvalves that enable the switching of two outlets by controlling the pneumatic valves. Furthermore, a comprehensive control system was devised encompassing components such as microscope, microcontroller, computer, signal generator, power amplifier, syringe pump, and air pump. This system facilitates the automation and intelligence of high-throughput submicron/nanoparticle screening.With the aid of the smart microfluidic system, the processing speed of the sample by AFTs can attain the rate of approximately 1-2 mL/h.

This work demonstrates a gas flow rate sensor based on the curvature change of a micro quartz resonator (MQR). We explored the relationship between the resonant frequency shift and gas flow rate theoretically and experimentally. The sensing performance was evaluated by exposing the device to nitrogen gas at different flow rates. Experimental results indicate that the response time is less than 2 s with a sensitivity of 0.16 Hz/(mL·min −l ) in the gas flow ranging from 100 to 800 mL/min. Compared to the conventional gas sensors, our method has many advantages including low temperature drift, rapid response time, and great reproducibility, and provides a multifunctional sensing platform to measure the concentration and flow rate successfully. To the best of our knowledge, this is the first paper about gas flow rate sensing using the mechanical bending effect of an MQR.

This paper verifies that the micro pillar array chip can perform parallel and diverse trapping of particles with theoretical simulation and experiments. Under the excitation of sound source, the vibration of micropillar array excites the local acoustic field, wherein the acoustic streaming and acoustic radiation forces are generated. Micro/nanoscale particles can be effectively trapped under the combined action of these two nonlinear effects. By tuning the vibration mode of the micro pillar, different acoustic streaming modes can be achieved, leading to tunable modes of vortices and particle trapping. It is worth noting that the micro pillar array chip has low working frequency (164 kHz) and simple manufacturing process, which is of great significance to the biomedical applications.

At the single-cell level, cellular parameters, gene expression and cellular function are assayed on an individual but not population-average basis. Essential to observing and analyzing the heterogeneity and behavior of these cells/clusters is the ability to prepare and manipulate individuals. Here, we demonstrate a versatile microsystem, a stereo acoustic streaming tunnel, which is triggered by ultrahigh-frequency bulk acoustic waves and highly confined by a microchannel. We thoroughly analyze the generation and features of stereo acoustic streaming to develop a virtual tunnel for observation, pretreatment and analysis of cells for different single-cell applications. 3D reconstruction, dissociation of clusters, selective trapping/release, in situ analysis and pairing of single cells with barcode gel beads were demonstrated. To further verify the reliability and robustness of this technology in complex biosamples, the separation of circulating tumor cells from undiluted blood based on properties of both physics and immunity was achieved. With the rich selection of handling modes, the platform has the potential to be a full-process microsystem, from pretreatment to analysis, and used in numerous fields, such as in vitro diagnosis, high-throughput single-cell sequencing and drug development.

This study explores the size-effect of silicon-based acoustic micropillar chip for the trapping of particle. Experiments and simulations were carried out in the case of micropillars with different height-diameter ratios. The results show that within a certain range, with the increase of the height-diameter ratio of the micropillars, the particles rotate faster and the particle trajectories are closer to the micropillars, so that trapping ability of the chip is significantly enhanced. At the same time, with the increase of the height-diameter ratio of the micropillar, the acoustic radiation force on the particles increases, resulting in improved trapping under higher streaming velocity. We also characterize the size influence of silicon-micropillar on particle trapping efficiency, which shows great potential in subsequent particle or cell studies, and providing a practical low-cost, low sample consumption and convenient tool for single-cell related studies.

Microrobotics have emerged as a fascinating field with great potential for drug delivery, non-invasive microsurgery, and precise materials assembly. Acoustic devices have been exploited as effective strategies for developing underwater microrobotics. This work presents an integrated wirelessly powered microelectromechanical swimming robot driven by Lamb Wave Resonators (LWRs). Improvements have been made to the structure of LWR driver. The asymmetric distribution of reflectors and leakage hole of the LWR leads to the difference of acoustic wave transmission. Unidirectional drive was realized with the asymmetric acoustic streaming effect. Aided by programming the energy distribution of the LWRs, flexible 2-D motions can be realized, demonstrating an artificial acoustic compartment for tiny swimmers.

This study presents a minimized ultra-centrifugal chip featured with high throughput and precise separation for small nanoparticles (<; 500 nm). A bulk acoustic wave (BAW) resonator array is developed to merge with microfluidics and work as the actuation component. Benefit from the gigahertz frequency, the BAW resonators can efficiently trigger strong vortices to trap micro/nano particles from flowing samples. This chip has been experimentally demonstrated with the ability to efficiently separate nanoparticle as small as 200 nm from the sample flow of 20 μL/min. Furthermore, the trapping efficiency of different particle sizes can be precisely tuned that enables size-dependent separation of nanoparticles. The developed chip realizes the small nanoparticle separation by one on-palm device instead of the on-desk huge and expensive centrifugal instrument, and would contribute to the development of point-of-care biomedical applications.

Acoustofluidics has emerged as a promising method for submicron particle manipulation. However, ultrahigh‐frequency or focused sound waves are usually required to generate sufficient acoustic radiation force or localized streaming vortex for trapping nanoscale objects, which is more challenging in device fabrication. This work presents a novel method using a low‐frequency acoustic field actuated micro‐pillar array (APA) chip to efficiently enable programmable and parallel trapping of nanoparticles. Driven by the acoustic waves, each arrayed vibrating micropillar generates a highly localized acoustic field with enhanced acoustic radiation forces and well‐confined vortex streaming around the pillar. The APA chip is demonstrated with geometric tuning ability of regulating the trapping limit by altering the pillar size. Micropillar arrays with a diameter of 5 µm are demonstrated to trap 112 nm particles efficiently. Thanks to the convenience of using ultrasounds and arraying micropillars of different geometric sizes, the APA chip provides an alternative of submicron particle manipulation technique for programmable and high‐throughput trapping and patterning of particles, with potential for “lab‐on‐a‐chip” sample preparations.

As an acute inflammatory response, sepsis may cause septic shock and multiple organ failure. Rapid and reliable detection of pathogens from blood samples can promote early diagnosis and treatment of sepsis. However, traditional pathogen detection methods rely on bacterial blood culture, which is complex and time-consuming. Although pre-separation of bacteria from blood can help with the identification of pathogens for diagnosis, the required low-velocity fluid environment of most separation techniques greatly limits the processing capacity for blood samples. Here, we present an acoustofluidic device for high-throughput bacterial separation from human blood cells. Our device utilizes a serpentine microfluidic design and standing surface acoustic waves (SSAWs), and separates bacteria from blood cells effectively based on their size difference. The serpentine microstructure allows the operating distance of the acoustic field to be multiplied in a limited chip size via the "spatial multiplexing" and "pressure node matching" of SSAW field. Microscopic observation and flow cytometry analysis shows that the device is helpful in improving the flow rate (2.6 μL min-1 for blood samples; the corresponding velocity is ∼3 cm s-1) without losing separation purity or cell recovery. The serpentine microfluidic design provides a compatible solution for high-throughput separation, which can synergize with other functional designs to improve device performance. Further, its advantages such as low cost, high biocompatibility, label-free separation and ability to integrate with on-chip biosensors are promising for clinical utility in point-of-care diagnostic platforms.

Addressable trapping and manipulations of micro/nano-scale bioparticles is often necessary and critically important in microfluidic devices for biological and medical applications. While GHz bulk-acoustic-wave (BAW) resonators have shown their excellent performance in trapping, rotating, and focusing particles down to nanometers, arraying them for addressable manipulation is a great challenge due to the crosstalk among resonators. This paper presents the electrical and mechanical crosstalk analysis to GHz BAW array with proposed circuit-level models. Crosstalk mechanisms are thoroughly revealed, which contribute to clarify the design rules of GHz BAW array with low crosstalk. A $4 \times 4$ BAW array chip is designed and experimental results show the chip can achieve addressable control with negligible crosstalk, demonstrating the rationality of the analysis. The crosstalk analysis, as well as the derived design rules, will lead to the design of a high-performance GHz BAW array with great potential for applications that require massive, addressable, and precise particle manipulation. [2021-0236]