High-throughput particle focusing and separation in split-recombination channel

Inertial microfluidic has been widely applied to manipulate particles or bio-sample based on the inertial lift force and Dean Vortices. This technology provides significant advantages over conventional technologies, including simple structure, high throughput and freedom from an external field. Among many inertial microfluidic systems, the straight microchannel is commonly used to produce inertial focusing, which is a phenomenon that particles or cells are aligned and separated based on their size under the influence of inertial lift force. Besides the inertial lift force, flow drag forces induced by the geometrical structures of microchannel can also affect particle focusing. Herein, a split-recombination microchannel, consisting of curved and straight channels, is proposed to focus and separate particles at high flow rate. As compared with the straight channel, the particle focusing in the split-recombination channel is greatly improved, which results from the combined effects of the inertial lift force, the curvature-induced Dean drag force and the structure of split and recombination. Moreover, the distribution of different-sized particles in designed microchannel is investigated. The results indicate that the proposed microchannel not only enhances the particle focusing but also enables the separation of different-sized particles with high throughput. Finally, it is discovered that the larger length of straight channel and curvature radius of curved channel can result in a more efficient particle separation. Another important feature of designed split-recombination microchannel is that it can be arranged in parallel to handle large-volume samples, holding great potential in lab-on-a-chip applications.

A Novel Piezoelectric RF-MEMS Resonator with Enhanced Quality Factor

This work presents a novel ultra-high frequency (UHF) Lamb mode Aluminum Nitride (AlN) piezoelectric resonator with enhanced quality factors (Q). With slots introduced in the vicinity of the tether support end, the elastic waves leaking from the tether sidewalls can be reflected, which effectively reduces the anchor loss while retaining size compactness and mechanical robustness. Comprehensive analysis was carried out to provide helpful guidance for obtaining optimal slot designs. For various resonators with frequencies ranging from 630 MHz to 1.97 GHz, promising Q enhancements up to 2 times have all been achieved. The 1.97 GHz resonator implemented excellent f × Q product up to 6.72 × 1012 and low motional resistance down to 340 Ω, which is one of the highest performances among the reported devices. The devices with enhanced Q values as well as compact size could have potential application in advanced RF front end transceivers.

Highly Sensitive Flexible Modulus Sensor for Softness Perception and Clinical Application

The wearable sensors for softness measuring are emerging as a solution of softness perception, which is an intrinsic function of human skin, for electronic skin and human-machine interaction. However, these wearable sensors suffer from a key challenge: the modulus of an object can not be characterized directly, which originates from the complicated transduction mechanism. To address this key challenge, we developed a flexible and wearable modulus sensor that can simultaneously measure the pressure and modulus without mutual interference. The modulus sensing was realized by merging the electrostatic capacitance response from the pressure sensor and the ionic capacitance response from the indentation sensor. Via the optimized structure, our sensor exhibits high modulus sensitivity of 1.9 × 102 in 0.06 MPa, a fast dynamic response time of 100 ms, and high mechanical robustness for over 2500 cycles. We also integrated the sensor onto a prosthetic hand and surgical probe to demonstrate its capability for pressure and modulus sensing. This work provides a new strategy for modulus measurement, which has great potential in softness sensing and medical application.

Flexible Capacitive Pressure Sensors with Micro-Patterned Porous Dielectric Layer for Wearable Electronics

Highly sensitive soft sensors play key roles in flexible electronics, which therefore have attracted much attention in recent years. Herein, we report a flexible capacitive pressure sensor with high sensitivity by using engineered micro-patterned porous polydimethylsiloxane (PDMS) dielectric layer through an environmental-friendly fabrication procedure. The porous structure is formed by evaporation of emulsified water droplets during PDMS curing process, while the micro-patterned structure is obtained via molding on sandpaper. Impressively, this structure renders the capacitive sensor with a high sensitivity up to 143.5 MPa-1 at the pressure range of 0.068~150 kPa and excellent anti-fatigue performance over 20,000 cycles. Meanwhile, the sensor can distinguish different motions of the same person or different people doing the same action. Our work illustrates the promising application prospects of this flexible pressure sensor for the security field or human motion monitoring area.

Fabrication, modeling, and characterization of soft twisting electrothermal actuators with directly printed oblique heater

Soft electrothermal actuators have drawn extensive attention in recent years for their promising applications in biomimetic and biomedical areas. Most soft electrothermal actuators reported so far demonstrated uniform bending deformation, due to the deposition based fabrication of the conductive heater layer from nanomaterial-based solutions, which generally provides uniform heating capacity and uniform bending deformation. In this paper, a soft electrothermal actuator that can provide twisting deformation was designed and fabricated. A metallic microfilament heater of the soft twisting actuator was directly printed using electrohydrodynamic (EHD) printing, and embedded between two structural layers, a polyimide (PI) film and a polydimethylsiloxane (PDMS) layer, with distinct thermal expansion properties. Assisted by the direct patterning capabilities of EHD printing, a skewed heater pattern was designed and printed. This skewed heater pattern not only produces a skewed parallelogram-shaped temperature field, but also changes the stiffness anisotropy of the actuator, leading to twisting deformation with coupled bending. A theoretical kinematic model was built for the twisting actuator to describe its twisting deformation under different actuation effects. Based on that model, influence of design parameters on the twisting angle and motion trajectory of the twisting actuator were studied and validated by experiments. Finite element analysis (FEA) was utilized for the thermal and deformation analysis of the actuator. The fabricated twisting actuator was characterized on its heating and twisting performance at different supply voltages. Using three twisting actuators, a soft gripper was designed and fabricated to implement pick-and-place operations of delicate objects.

Influence of process parameters on the characteristics of electrohydrodynamic-printed UV-curing conductive lines on the fabric

As a similar technology to the near-field static electrospinning, the emerging electrohydrodynamic (EHD) printing technology with digital printing process and compatibility of viscous particle-blended inks is one of the simplest methods of fabricating multifunctional electronic textiles.With increasing demands for textile-based conductive lines with controllable width and excellent electrical performance, it’s of great importance to know the influence of key process parameters on the morphology and electrical properties of EHD-printed UV-curing conductive lines on the fabric. This work will systematically explore the effect of the EHD printing process parameters (i.e. applied voltage, direct-writing height, flow rate and moving velocity of the substrate) on the morphology and electrical performance of the EHD-printed textile-based conductive lines, especially focus on the diffusion and penetration of inks on the rough and porous fabric. The UV-curing nano-silver ink with low temperature and fast curing features was selected, and the line width and electrical resistance of printed lines under different process parameters were observed and measured. The results showed that, unlike previous results about EHD printing on smooth and impermeable substrates, the ink diffusion related to fabric textures had a greater effect on the fabric-based conductive line width than the applied voltage and direct-writing height in the case of a stable jet. Meanwhile, the relationship between the line width and the flow rate met the equation of = 407.28 ∗ 1⁄2 , and the minimum volume on fabric per millimeter was 0.67μL to form continuous line with low electrical resistance. Additionally, the higher substrate moving velocity resulted in a smaller line width, while it deteriorated the thickness uniformity and electrical property of printed lines. Generally, due to the effect of surface structure of the fabric on the spreading and penetrating behavior of inks, the flow rate and the substrate moving velocity are two significant parameters ensuring the electrical property of printed lines. It is believed that these findings will provide some guides for applying electrohydrodynamic printing technology into flexible electronics on the woven fabric.

Evaluation of the Impact of Abnormal Grains on the Performance of Sc0.15Al0.85N-based BAW Resonators and Filters

ScxAl1-xN is a promising piezoelectric material for radio frequency communication applications with excellent electro-acoustic properties. However, the growth of abnormally oriented grains is widely observed in the Sc doped AlN films deposited by sputtering. In this work, for the first time, the impact of the abnormal grains in the Sc0.15Al0.85N films on the performance of bulk acoustic wave resonators and filters is systematically evaluated by both simulations and measurements. The correlation between the device performance and the abnormal grain parameters, including the density, dimension, crystal orientation, growth height, and the total volume of the abnormal grains, is evaluated and quantified. Simulation results show that the total volume of all abnormal grains in the whole device is the most critical factor among the parameters. Abnormal grains with randomly distributed parameters and around 6% total volume of the film can degrade the effective coupling coefficient of the resonator from 13.6% to 11%, leading to a 10.6% decrement of the filter bandwidth. Wafer-level device characterizations and measurements are performed, and the results are consistent with the simulations. This study provides a practical method for predicting the performance of the resonators and filters with abnormal grains, and a guideline for film quality evaluation.

Design and testing of a novel multipath-actuation compliant manipulator

In this paper, a novel multipath-actuation compliant manipulator (MCM) driven by piezoelectric actuators is proposed. Specifically, the monolithic MCM employs two vertically arranged compliant limbs with multipath motion transmission to actuate a symmetrically constrained planar mechanism, realizing x- and y-directional motion. For each limb, the multiple branched chains are configured in different paths but all contribute to the output motion, which results in a large displacement amplification ratio as well as a high working bandwidth. The ideal motion transmission of the proposed MCM is revealed by a specially established rigid-body kinematics model. Finite element analysis is carried out to predict the realistic static and dynamic performance of designed MCM. Moreover, a monolithic MCM prototype is fabricated, which is demonstrated to have a large displacement amplification ratio of 11.05, a high resonance frequency of 969 Hz, and a fine motion resolution of 25.48 nm. With promising static and dynamic characteristics, the proposed MCM can be widely used in practical applications.

Experimental amplitude and frequency control of a self-excited microcantilever by linear and nonlinear feedback

In recent years, measurement methods that use resonators as microcantilevers have attracted attention because of their high sensitivity, high accuracy, and rapid response time. They have been widely utilized in mass sensing, stiffness sensing, and atomic force microscopy (AFM), among other applications. In all these methods, it is essential to accurately detect shifts in the natural frequency of the resonator caused by an external force from a measured object or sample. Experimental approaches based on self-excited oscillation enable the detection of these shifts even when the resonator is immersed in a high-viscosity environment. In the present study, we experimentally and theoretically investigate the nonlinear characteristics of a microcantilever resonator and their control by nonlinear feedback. We show that the steady-state response amplitude and the corresponding response frequency can be controlled by cubic nonlinear velocity feedback and cubic nonlinear displacement feedback, respectively. Furthermore, the amplitude and frequency of the steady-state self-excited oscillation can be controlled separately. These results will expand application of measurement methods that use self-excited resonators.

A Si-based suspended tunnel structure with trapezoidal section by two - step etching

Two - step etching method is used to prepare Si-based suspended tunnel structure with trapezoidal section. In the first wet etching, surfactant Triton-X-100 is added to TMAH enchant to inhibit crystal plane characteristics. Bulk Si Rib with trapezoidal cross section is formed, with inclination of side and height being modulated by changing etching time, so as to obtain good stability. After SiO2 support layer is grown by thermal oxidation, pure 25%TMAH is used in the second wet etching to quickly lateral etch and undercut the bulk silicon under the support layer and form a suspended structure along <100> opening. Using additive-no additive two-step etching method, suspended structure with high stability and compressive strength, good insulation characteristics, high yield can be prepared. It lays a solid foundation for the development of high sensitivity photo, thermal, chemical and gas sensors.