Showing papers by "Xinxin Li published in 2023"

Ultra-Responsive MEMS Sensing Chip for Differential Thermal Analysis (DTA)

Abstract: Ultra-responsive single-crystal silicon MEMS thermopiles for differential thermal analysis (DTA) are developed. Facilitated by a unique “microholes interetch and sealing (MIS)” technique, pairs of suspended thermopiles are batch fabricated in a differential form, with high-density (54 pairs) n-type/p-type single-crystal silicon thermocouples integrated within each thermopile (sample area ~0.045 mm2). The fabricated MEMS thermopile sensors exhibit outstanding power responsivity of 99.5 V/W and temperature responsivity of 27.8 mV/°C, which are more than 4 times higher than those reported for material thermal analysis. The high-responsivity MEMS DTA chips allow us to accurately measure the indium melting point at different heating rates of ~1–100 °C/s. We also perform DTA measurement of the dehydration process of CuSO4·5H2O and the crystals show three stages of losing water of crystallization before becoming anhydrous copper sulfate salt. Our high-performance, cost-effective MEMS sensing chips hold promise for rapid and accurate DTA characterization for a wide range of applications.

Cooperative Characterization of In Situ TEM and Cantilever-TGA to Optimize Calcination Conditions of MnO2 Nanowire Precursors.

Abstract: Calcination plays a vital role during material preparation. However, the calcination conditions have often been determined empirically or have been based on trial and error. Herein we present a cooperative characterization approach to optimize calcination conditions by gas-cell in situ TEM in collaboration with microcantilever-based thermogravimetric analysis (cantilever-TGA) techniques. The morphological evolution of precursors under atmospheric conditions is observed with in situ TEM, and the right calcination temperature is provided by cantilever-TGA. The proposed approach successfully optimizes the calcination conditions of fragile MnO2 nanowire precursors with multiple valence products. The cantilever-TGA shows that a calcination temperature above 560 °C is required to transform the MnO2 precursor to Mn3O4 under an N2 atmosphere, but the in situ TEM indicates that the nanowire structure is destroyed within only 30 min under calcination conditions. Our method further suggests that heating the precursor at 400 °C using an H2-containing atmosphere can produce Mn3O4 nanowires with good electrical properties.

Study on the failure mechanism between polyurethane grouting material and concrete considering the effect of moisture by digital image correlation

Abstract: The bond resistance between polyurethane (PU) grouting material and concrete consists of adhesion, friction, and mechanical interlocking and is crucial to the repaired concrete structures. During the repair of the leakage and subsidence of underground concrete pipelines by PU grouting material, the chemical adhesion between PU and concrete interfaces may be influenced by moisture caused by the pipeline leakage and groundwater. In this paper, shear tests and the digital imaging correlation (DIC) method were used to study the effect of moisture on the shear bond performance and failure process of the PU-concrete interface before and after grouting PU with different densities. The results reveal that the differences in bond strength, shear strain and horizontal displacement between the interfaces are significantly reduced with the polymer density, especially for moistened interfaces before grouting and testing. Finally, a finite element model was employed to simulate the bond strength between PU and concrete and validated based on the test results.

Catalytic Decomposition Sensing mechanism of Mesoporous gamma Alumina for Freon R134a Detection

Abstract: Freon R134a is a widely used refrigerant that can cause a severe greenhouse effect and should be detected on site. However, it is a big challenge for semiconductor gas sensors to detect the inert Freon R134a molecules. Herein, mesoporous γ-Al2O3 is synthesized and loaded on top of ZnO sensing materials to form a bilayer microsensor to realize high-performance detection of Freon R134a. The mesoporous γ-Al2O3 material first decomposes the inert R134a molecule into a large number of active radicals. The generated reactive radicals are then easily sensed by the ZnO material. The limit of detection (LOD) of the bilayer sensor reaches the ppm level, which meets the requirements for on-site detection of Freon R134a leakage. The online mass spectrum (online MS) is used to identify the produced radicals qualitatively. According to the online MS results, the catalytic mechanism of mesoporous γ-Al2O3 for Freon R134a molecules has been clearly revealed.

Reversed bond-slip model of deformed bar embedded in concrete based on ensemble learning algorithm

Abstract: A reversed bond-slip relationship that simultaneously considers key factors, such as the concrete cover, stirrups, fiber content, and lateral pressure is required to simulate the seismic response of reinforced concrete structures. In this study, the features of the hysteresis curves with different bond conditions and loading histories were discussed and analyzed, and a corresponding bond stress-slip model based on an ensemble learning (EL) algorithm, XGBoost, was then established. In this model, 10 key factors were selected as the input parameters and 4 reversed bond parameters were selected as the output results. During the training and testing process, a total of 901 sets of experimental data were collected and were randomly split into a training set and testing set at a ratio of 8:2. Compared with the empirical models and two other EL algorithms, the XGBoost method presented a high accuracy to predict the bond parameters with different bond conditions, and the proposed bond stress-slip model correlated well with the test results.

On-Demand Preparation of Gas-Sensing Materials Guided by Resonant Cantilever-Based Thermogravimetric Analysis

Abstract: In this work, the preparation conditions of Mn3O4 nanowires for formaldehyde (HCHO) sensing are optimized with a resonant cantilever-based thermogravimetric analysis (referred to as cantilever-TGA) technology. The cantilever-TGA technology only consumes about 20 ng of samples for one measurement, which is six orders of magnitude lower than the mainstream commercial-available TGA instruments, making it ideal for exploring optimal sample preparation conditions. Herein the cantilever-TGA technology has been successfully used to investigate the preparation conditions of Mn3O4 sensing material from the precursor of β-MnO2 nanowires. With the guidance of cantilever-TGA, pure-phase and morphology well-maintained Mn3O4 gas-sensing materials can be obtained under H2 atmosphere at 330°C, which is 230°C lower than N2 atmosphere. Due to the well-maintained nanowire-like structure and high mobility, the response of the Mn3O4@H2 material to HCHO is one-fold higher than that of the Mn3O4@N2 material.

Single (111)-Wafer Single-Side Microfabrication of Suspended p+Si/n+Si Thermopile for Tiny-Size and High-Sensitivity Thermal Gas Flow Sensors

Abstract: This article presents a tiny-size and high-performance thermal gas flow sensor with suspended $\text{p}^{+}$ Si/ $\text{n}^{+}$ Si thermopile formed in an ordinary non-silicon-on-insulator (SOI) (111) silicon wafer. A front-side bulk micromachining technique is herein employed to form the proposed gas flow sensor without double-side fabrication process, wafer bonding, and cavity-SOI needed. To achieve high sensitivity and quick response time, the suspended single-crystalline $\text{p}^{+}$ Si/ $\text{n}^{+}$ Si thermocouple which shows significantly higher Seebeck coefficient and lower noise compared to that of the traditional $\text{p}^{+}$ polysilicon/ $\text{n}^{+}$ polysilicon thermocouple is first used to construct the flow sensor. And the fishbone-shaped suspended SiN dielectric membrane is designed to maximize the thermal resistance between the $\text{p}^{+}$ Si heater and the silicon substrate, reducing heat dissipation from the $\text{p}^{+}$ Si heater to the silicon substrate. In addition, using high heat-conductivity Au-film to connect the cold junction and the bulk silicon acting as a heat-sink not only increases the temperature difference between the hot junction and the cold junction but also reduces the complexity of the fabrication process. Thanks to the single-side micromachining process, the sensor chip size is as small as $0.65\times0.60$ mm. Finally, the characterization of the fabricated gas flow sensor was evaluated, showing an ultrahigh normalization sensitivity of 5 V/sccm/W, a quick response time of 1.44 ms, and a minimum detectable flow velocity (MDFV) of 0.0083 sccm.

Instrumental Analysis of Advanced Catalysts Based on Resonant Microcantilevers

Abstract: Advanced catalysts are highly influential in various research and application fields. The catalytic performance parameters, such as catalytic activity and kinetics, were mainly characterized using the commercial-available TPD instruments (i.e., temperature-programmed desorption), which ex-situ measure the probe molecules in the gas flow. In this paper, a special-designed resonant microcantilever has been utilized as the mass-weighing component of a scientific instrument for characterizing advanced catalysts. Compared to the available TPD instruments, the proposed cantilever-based TPD instrument in-situ records the number of desorbed probe molecules (i.e., the mass-loss ∆m of the material) via the frequency-change ∆f during the heating process, and the bulky furnace and detector are not required. The cantilever-TPD instrument only consumes ng-level samples for one-time measurement, which is 6 orders of magnitude lower than the commercial TPD instrument. With a single-time in-situ TPD measurement, desorption activation energy can be directly calculated. Various catalysts (e.g., ZSM-5) have been successfully characterized by using the cantilever-TPD instrument, which is expected to become the next generation of TPD scientific instrument.

Non-Invasive Instant Measurement of Arterial Stiffness Based on High-Density Flexible Sensor Array

Abstract: This paper reports an innovative, non-invasive and instant method of arterial stiffness measurement. We delineate the tactile signals of arteries with varying stiffness using a dense sensor array, and analyze the factors affecting human tactility of stiffness and softness at fingertip with a deep learning model. Based on the most influential factor, an algorithm to instantaneously estimate the arterial stiffness is developed for the first time. The five stiffness grades ranked in order of the stiffness index (SI) may serve as an indicator of arterial aging and are expected to assist in early screening for certain cardiovascular diseases (CVD).

MEMS Differential Thermopiles for High-Sensitivity Hydrogen Gas Detection

Abstract: We report a MEMS differential thermopile sensor for high-sensitivity hydrogen (H2) gas detection. By exploiting the single-sided microhole inter-etch and sealing (MIS) process, pairs of MEMS single-crystalline silicon thermopiles are batch fabricated into 2×1mm2 dies. Each suspended thermopile is integrated with high-density thermocouples, allowing us to achieve a temperature sensitivity of ~27.8mV/°C. Such design ensures the detection of tiny temperature changes (down to ~1mK) caused by catalytic combustion of H2-air mixture at 120°C when the sensing thermopile is loaded with platinum nanoparticles-decorated aluminum oxide (Pt NPs@Al2O3) nanosheets. The sensors exhibit a linear response to H2 concentration from 1.0% down to 5ppm with a response time of ~2.5s and a recovery time of ~1.7s (in 1% H2), which are more sensitive than the previously reported MEMS thermopile H2 sensors. The proposed sensors are also selective against other combustible gases and remain stable after 30 days. Our highly-sensitive, cost-effective MEMS differential thermopile sensors hold promise for H2 leakage detection in industrial applications.

Wafer-Level Fabricated Tight-Coupling Dual-Solenoid Transformer Chips With Watt-Scale Power Transfer

Abstract: Reported are a novel kind of tight-coupled dual-solenoid transformers (DSTs) which are on-chip integrated by using wafer-level fabrication including a low melting-point zinc-aluminum alloy rapid microcasting technique. Without magnetic core used, the silicon-chip integrated transformer is with the two metal solenoids tightly interwound to form a highly-coupled 3-D structure, thereby performing high inductance density and featuring no concern in magnetic flux saturation. Fabricated with the wafer-level thick-metal 3-D microcasting technique, the DST exhibits sufficient inductance value and low dc resistance while maintaining tiny footprint. Various DST structures are designed, fabricated and characterized for performance optimization. The optimally designed DST chip demonstrates a compact footprint of 2 mm2, a high inductance of 193.14 nH (i.e., inductance density = 96.57 nH/mm2) and a small dc resistance of 1.09 Ω. The test shows that the chip achieves an ultrahigh coupling coefficient of 0.95 and superior maximum transformer efficiency of 87.8% at 100 MHz. More importantly, the DST achieves Watt-scale power transfer capability at 100 MHz, where no any heat dissipation treatment to the chip is used. Therefore, the on-chip DSTs are very promising for power/signal transmission in various electronic microsystems.

Simultaneous Detection of Naphthol Isomers with a 3D-Graphene-Nanostructure-Based Electrochemical Microsensor

Abstract: Naphthol is a widely used chemical and medical detection biomarker, but it is harmful to human health and the environment. Therefore, a highly sensitive detection method for naphthol is urgently required. Herein, an electrochemical microsensor for the simultaneous detection of naphthol isomers was fabricated by the in situ growth of a three-dimensional graphene network (3DGN) on screen-printed electrodes. The microsensor exhibited good electrochemical sensing responses to typical isomers of naphthol (1-NAP and 2-NAP). Using the differential pulse voltammetry (DPV) method, the microsensor successfully realized the electrochemical detection of 1-NAP, 2-NAP, and naphthol isomer mixtures. Whether detecting naphthol isomers individually or simultaneously, the microsensor exhibited a good linear relationship for 1-NAP and 2-NAP in a wide range of concentrations. For the simultaneous detection of naphthol isomers, the limit of detection (LOD) of the microsensor to 1-NAP reached 10 nM, and the LOD for 2-NAP was about 20 nM. The microsensor also showed good selectivity, reproducibility, and stability. The simultaneous quantitative detection of 1-NAP and 2-NAP was also successfully achieved in synthetic urine samples.

High-Inductance-Density MEMS 3D-solenoid Transformers with Inserted Thin-Film Ferrite Magnetic Core For On-Chip Integrated DC-DC Power Conversions

Abstract: This paper presents high-inductance-density MEMS 3D-solenoid magnetic core transformers that are wafer-level fabricated by a novel thick-metal micro-casting technique. With the embedded thin-film high-permeability ferrite core, an over 7 times boost in inductance (from 43.3 nH to 334.2 nH) and 25% increment in coupling coefficient (from 0.76 to 0.96) are achieved. For the batch-fabricated transformer in a tiny footprint of 6 mm2, an over 1.6 A saturated current and one of the best-reported power transfer efficiency of 89.5% at a lower frequency of 10 MHz are demonstrated. The proposed magnetic core transformers are ideal for high-efficiency integrated DC-DC power conversion applications.

Silicon Micromachined TSVs for Backside Interconnection of Ultra-Small Pressure Sensors

Abstract: This paper presents an ultra-small absolute pressure sensor with a silicon-micromachined TSV backside interconnection for high-performance, high spatial resolution contact pressure sensing, including flexible-substrate applications. By exploiting silicon-micromachined TSVs that are compatibly fabricated with the pressure sensor, the sensing signals are emitted from the chip backside, thereby eliminating the fragile leads on the front-side. Such a design achieves a flat and fully passivated top surface to protect the sensor from mechanical damage, for reliable direct-contact pressure sensing. A single-crystal silicon beam–island structure is designed to reduce the deflection of the pressure-sensing diaphragm and improve output linearity. Using our group-developed microholes interetch and sealing (MIS) micromachining technique, we fabricated ultra-small piezoresistive pressure sensors with the chip size as small as 0.4 mm × 0.6 mm, in which the polysilicon-micromachined TSVs transfer the signal interconnection from the front-side to the backside of the wafer, and the sensor chips can be densely packaged on the flexible substrate via the TSVs. The ultra-small pressure sensor has high sensitivity of 0.84 mV/kPa under 3.3 V of supply voltage and low nonlinearity of ±0.09% full scale (FS) in the measurement range of 120 kPa. The proposed pressure sensors with backside-interconnection TSVs hold promise for tactile sensing applications, including flexible sensing of wearable wristwatches.

How Identity Impacts Bystander Responses to Workplace Mistreatment

Abstract: Integrating a social identity approach with Cortina's (2008) theorizing about selective incivility as modern discrimination, we examine how identification—with an organization, with one's gender, and as a feminist—shapes bystanders’ interpretations and responses to witnessed incivility (i.e., interpersonal acts of disrespect) and selective incivility (i.e., incivility motivated by targets’ social group membership) toward women at work. We propose that bystanders with stronger organizational identification are less likely to perceive incivility toward female colleagues as discrimination and intervene, but female bystanders with stronger gender identification are more likely to do so. Results from two-wave field data in a cross-lagged panel design (Study 1, N = 336) showed that organizational identification negatively predicted observed selective incivility 1 year later but revealed no evidence of an effect of female bystanders’ gender identification. We replicated and extended these results with a vignette experiment (Study 2, N = 410) and an experimental recall study (Study 3, N = 504). Findings revealed a “dark side” of organizational identification: strongly identified bystanders were less likely to perceive incivility as discrimination, but there were again no effects of women's gender identification. Study 3 also showed that bystander feminist identification increased intervention via perceived discrimination. These results raise doubts that female bystanders are more sensitive to recognizing other women's mistreatment as discrimination, but more strongly identified feminists (male or female) were more likely to intervene. Although strongly organizationally identified bystanders were more likely to overlook women's mistreatment, they were also more likely to intervene once discrimination was apparent.

Aluminum Nitride Piezoelectric Micromachined Ultrasound Transducer Arrays for Non-Invasive Monitoring of Radial Artery Stiffness

Abstract: An aluminum nitride (AlN) piezoelectric micromachined ultrasound transducer (PMUT) array was proposed and fabricated for non-invasive radial artery stiffness monitoring, which could be employed in human vascular health monitoring applications. Using surface micromachining techniques, four hexagonal PMUT arrays were fabricated within a chip area of 3 × 3 mm2. The mechanical displacement sensitivity and quality factor of a single PMUT were tested and found to be 24.47 nm/V at 5.94 MHz and 278 (in air), respectively. Underwater pulse-echo tests for the array demonstrated a −3 dB bandwidth of 0.76 MHz at 3.75 MHz and distance detection limit of approximately 25 mm. Using the PMUT array as an ultrasonic probe, the depth and diameter changes over cardiac cycles of the radial artery were measured to be approximately 3.8 mm and 0.23 mm, respectively. Combined with blood pressure calibration, the biomechanical parameters of the radial artery vessel were extracted using a one-dimensional vascular model. The cross-sectional distensibility, compliance, and stiffness index were determined to be 4.03 × 10−3/mmHg, 1.87 × 10−2 mm2/mmHg, and 5.25, respectively, consistent with the newest medical research. The continuous beat-to-beat blood pressure was also estimated using this model. This work demonstrated the potential of miniaturized PMUT devices for human vascular medical ultrasound applications.

Advanced In Situ TEM Microchip with Excellent Temperature Uniformity and High Spatial Resolution

Abstract: Transmission electron microscopy (TEM) is a highly effective method for scientific research, providing comprehensive analysis and characterization. However, traditional TEM is limited to observing static material structures at room temperature within a high-vacuum environment. To address this limitation, a microchip was developed for in situ TEM characterization, enabling the real-time study of material structure evolution and chemical process mechanisms. This microchip, based on microelectromechanical System (MEMS) technology, is capable of introducing multi-physics stimulation and can be used in conjunction with TEM to investigate the dynamic changes of matter in gas and high-temperature environments. The microchip design ensures a high-temperature uniformity in the sample observation area, and a system of tests was established to verify its performance. Results show that the temperature uniformity of 10 real-time observation windows with a total area of up to 1130 μm2 exceeded 95%, and the spatial resolution reached the lattice level, even in a flowing atmosphere of 1 bar.

Functionally Collaborative Nanostructure for Direct Monitoring of Neurotransmitter Exocytosis in Living Cells.

Abstract: Neurotransmitter exocytosis of living cells plays a vital role in neuroscience. However, the available amperometric technique with carbon fiber electrodes typically measures exocytotic events from one cell during one procedure, which requires professional operations and takes time to produce statistical results of multiple cells. Here, we develop a functionally collaborative nanostructure to directly measure the neurotransmitter dopamine (DA) exocytosis from living rat pheochromocytoma (PC12) cells. The functionally collaborative nanostructure is constructed of metal-organic framework (MOF)-on-nanowires-on-graphene oxide, which is highly sensitive to DA molecules and enables direct detection of neurotransmitter exocytosis. Using the microsensor, the exocytosis from PC12 cells pretreated with the desired drugs (e.g., anticoronavirus drug, antiflu drug, or anti-inflammatory drug) has been successfully measured. Our achievements demonstrate the feasibility of the functionally collaborative nanostructure in the real-time detection of exocytosis and the potential applicability in the highly efficient assessment of the modulation effects of medications on exocytosis.

A Single-Side Micromachined MPa-Scale High-Temperature Pressure Sensor

Abstract: This paper proposes a piezoresistive high-temperature absolute pressure sensor based on (100)/(111) hybrid SOI (silicon-on-insulator) silicon wafers, where the active layer is (100) silicon and the handle layer is (111) silicon. The 1.5 MPa ranged sensor chips are designed with the size as tiny as 0.5 × 0.5 mm, and the chips are fabricated only from the front side of the wafer for simple, high-yield and low-cost batch production. Herein, the (100) active layer is specifically used to form high-performance piezoresistors for high-temperature pressure sensing, while the (111) handle layer is used to single-side construct the pressure-sensing diaphragm and the pressure-reference cavity beneath the diaphragm. Benefitting from front-sided shallow dry etching and self-stop lateral wet etching inside the (111)-silicon substrate, the thickness of the pressure-sensing diaphragm is uniform and controllable, and the pressure-reference cavity is embedded into the handle layer of (111) silicon. Without the conventionally used double-sided etching, wafer bonding and cavity-SOI manufacturing, a very small sensor chip size of 0.5 × 0.5 mm is achieved. The measured performance of the 1.5 MPa ranged pressure sensor exhibits a full-scale output of approximately 59.55 mV/1500 kPa/3.3 VDC in room temperature and a high overall accuracy (combined with hysteresis, non-linearity and repeatability) of 0.17%FS within the temperature range of −55 °C to 350 °C. In addition, the thermal hysteresis is also evaluated as approximately 0.15%FS at 350 °C. The tiny-sized high temperature pressure sensors are promising in various industrial automatic control applications and wind tunnel testing systems.

MEMS Resonant Cantilevers for High-Performance Thermogravimetric Analysis of Chemical Decomposition

Abstract: We investigate the MEMS resonant cantilevers for high-performance thermogravimetric analysis (TGA) of chemical decomposition, featuring high accuracy and minimized thermal lag. Each resonant cantilever is integrated with a microheater for sample heating near the free end, which is thermally isolated from the resonance excitation and readout elements at the fixed end. Combining finite element modeling and experiments, we demonstrate that the sample loading region can stabilize within ~11.2 milliseconds in response to a step heating of 500 °C, suggesting a very fast thermal response of the MEMS resonant cantilevers of more than 104 °C/s. Benefiting from such a fast thermal response, we perform high-performance TG measurements on basic copper carbonate (Cu2(OH)2CO3) and calcium oxalate monohydrate (CaC2O4·H2O). The measured weight losses better agree with the theoretical values with 5–10 times smaller thermal lags at the same heating rate, compared with those measured by using conventional TGA. The MEMS resonant cantilevers hold promise for highly accurate and efficient TG characterization of materials in various fields.

1ppm-detectable hydrogen gas sensors by using highly sensitive P+/N+ single-crystalline silicon thermopiles

Abstract: Abstract Hydrogen (H 2 ) is currently of strategic importance in the pursuit of a decarbonized, environmentally benign, sustainable global energy system; however, the explosive nature of H 2 requires leakage monitoring to ensure safe application in industry. Therefore, H 2 gas sensors with a high sensitivity and fast response across a wide concentration range are crucial yet technically challenging. In this work, we demonstrate a new type of MEMS differential thermopile gas sensor for the highly sensitive, rapid detection of trace H 2 gas in air. Facilitated by a unique MIS fabrication technique, pairs of single-crystalline silicon thermopiles (i.e., sensing and reference thermopiles) are batch fabricated with high-density single-crystalline silicon thermocouples, yielding an outstanding temperature sensitivity at the sub-mK level. Such devices ensure the detection of miniscule temperature changes due to the catalytic reaction of H 2 with a detection limit as low as ~1 ppm at an operating temperature of 120 °C. The MEMS differential thermopiles also exhibit a wide linear detection range (1 ppm-2%, more than four orders of magnitude) and fast response and recovery times of 1.9 s and 1.4 s, respectively, when detecting 0.1% H 2 in air. Moreover, the sensors show good selectivity against common combustible gases and volatile organics, good repeatability, and long-term stability. The proposed MEMS thermopile H 2 sensors hold promise for the trace detection and early warning of H 2 leakage in a wide range of applications.

Microcantilever-Based In Situ Temperature-Programmed Desorption (TPD) Technique.

Abstract: Temperature-programmed desorption (TPD) is an essential technique for characterizing the fundamental properties of advanced catalysts like catalytic activity and kinetics. However, the available TPD instruments are bulky and use ex situ detectors to measure the probe molecules in the elution gas flow. Herein, we demonstrate an in situ TPD technique by developing a silicon microcantilever that integrates functional elements for mass measuring and programmable sample heating. An only nanogram-level sample is required to load on the microcantilever free end, where the integrated microheater provides programmed temperatures and the desorption-induced mass change can be measured in situ. In situ TPD can continuously measure the number of desorbed molecules from the catalyst during programmed heating, without the need for ex situ detectors. With a single-time in situ TPD measurement, the desorption activation energy can be directly calculated. The proposed in situ TPD method outperforms the existing TPD techniques and is expected to enable next-generation TPD applications.

Controlling Particle Aggregation and Separation in Liquid on Membrane Resonators

Abstract: We design a dual-mode membrane resonator for non-invasively and fast manipulating microparticle aggregation and separation in liquid. By performing finite element modeling, we verify that the interaction between a pair of microspheres (d=20 μm, mimicking cancer cells) can be precisely controlled on our proposed rectangular membrane resonator. The model consists of Multiphysics coupling between mechanical vibration, fluid flow, and particle tracing. Stokes drag, acoustic radiation, and particle-particle interaction forces are analyzed to predict the microparticle trajectory (including aggregation and separation). When exciting the rectangular membrane (100×50 μm) at its 1st mode (f1,1), a pair of microspheres are observed to aggregate at the device center (antinode of f1,1). While switching to its 2nd mode (f2,1), the 2 microspheres tend to separate towards the opposite directions to 2 antinodes of f2,1. Our proposed membrane platform holds promise for high-precision, acoustically manipulating and analyzing cellular interactions in liquid.