Xiaohao Wang

Design, optimization and simulation on microelectromagnetic pump

A four-layer electromagnetic micropump was designed, and its static and dynamic characters were studied from elements to full system. The mechanical model of the electromagnetic actuator was established, and some its geometric structural parameters were then optimized. The deflection of the pump membrane caused by the varying local magnetic driving forces was analyzed in particular by ANSYS FEM. Fluid theory and experiment data were used to analyze the microvalve. Full system model of the micropump and its differential equations were set up on the basis of physical liquid transmission procedure and system function block. Pulse and periodic pulse driving current responses were evaluated. The flow-frequency characteristic shows that the most effective driving frequency is 125 Hz. The effect of driving signal duty cycle and microvalve flow resistance was studied. The transfer function of this full system of micropump was also discussed.

All-transparent graphene-based flexible pressure sensor array

In this work, we propose and demonstrate a flexible capacitive tactile sensor array based on graphene served as electrodes. The sensor array consists of 3 × 3 units with 3 mm spatial resolution, similar to that of human skin. Each unit has three layers. The middle layer with microstructured PDMS served as an insulator is sandwiched by two perpendicular graphene-based electrodes. The size of each unit is 3 mm × 3 mm and the initial capacitance is about 0.2 pF. High sensitivities of 0.73 kPa−1 between 0 and 1.2 kPa and 0.26 kPa−1 between 1.2 and 2.5 kPa were achieved on the fabricated graphene pressure sensors. The proposed flexible pressure sensor array shows a great potential on the application of electric skin or 3D touch control.

Designing, fabrication, and test of a MEMS colloid thruster

A MEMS based micro colloid thruster (including an source emitter array and an extractor) is designed, fabricated and tested. Source emitter array of the thruster is silicon column etched by ICP. The negative electrode on the extractor can be controlled separately. After bonding together, a single emitter and extractor works on an electrical colloid propulsion principle, and produce µN order thrust. Such a small and controllable thrust is the urgent requirement for a micro-satellite. Thrust test for the micro colloid thruster is made in high vacuum box. Thrust is acted on a cantilever beam, and the displacement of cantilever beam is detected by a current vortex sensor. Analysis to the recording data shows that the maxim thrust produced by a single emitter is about 2 µN, which is agreement with theory estimate.

Foldable paper electronics by direct-write laser patterning

We report a laser-ablation aided, direct-write fabrication technique that could convert non-conductive paper rinsed with metal ions and polymer solution into conductive metal carbide and graphene with a typical sheet resistance of 45.3 Ω/□. As fabricated paper electronics inherit the microfiber network from paper and have nanoscale pores and 2D metal carbide flakes due to the laser ablation process. This conducive porous structure could be potentially utilized for sensor and capacitor applications, which usually need large specific area. As preliminary demonstrations, we show a wireless moisture sensor and a supercapacitor fabricated with this foldable paper based electronics. Experimentally, the moisture changes are successfully detected in ambient environment by a paper-based moisture sensor and the paper-based supercapacitor has a measured capacitance of 1.2 mF/cm2. As such, this laser converted paper electronics could be useful for multiple applications such as sensors and energy storage devices.

High resolution flexible strain sensors for biological signal measurements

This paper presents stretchable strain sensors based on Polydimethylsiloxane (PDMS)/graphite sensing resistors for potentially a variety of wearable device applications including human biological signal measurements, such as fingertip pressure monitoring for haptic feedback and high resolution arterial pulse for health diagnostics. The strain sensor uses a serpentine electrode design that can be easily fabricated in a two-step process by direct-write laser printing and pattern transfer without any lithography process. The results demonstrate several key sensing capabilities: (1) angular motion detection with a resolution of 15-degree; (2) fingertip pressure detection up to a range of 12 kPa; (3) monitoring of human pulse waves with the clear identification of the three local peaks. As such, the proposed strain sensors can be potentially used as a biological signal input device for potential applications such in virtual reality (VR) systems.

A 3D all-solid-state microsupercapacitor with electrodes consisting of activated carbon/polymer electrolyte composite

A novel all-solid-state microsupercapacitor (MSC) with ~70-μm-thick three-dimensional electrodes consisting of activated carbon (AC) particles and polymer electrolyte (PE) was fabricated and tested in this study. Unique features of the present MSC design include: (i) a novel electrode material composed of PE and AC particles, which enhances the accessibility of the surface of AC particles by ions and results in high specific capacitance and high energy density, (ii) a short path for ions to access the nanoporous structure of AC particles via diffusion through surrounding PE, which results in high charge/discharge rate and high power density, and (iii) adequate electrode strength due to binding of the AC particles by PE. Preliminary results show that MSCs with AC/PE composite electrodes demonstrate good stability during repeated charge/discharge. The high energy density, high power density, and good cycling performance make all-solid-state MSCs with AC/PE electrodes excellent candidates for a wide range of energy storage applications.

A flexible slip sensor using triboelectric nanogenerator approach

With the rapid development of robotic technology, tactile sensors for robots have gained great attention from academic and industry researchers. Tactile sensors for slip detection are essential for human-like steady control in dexterous robot hand. In this paper, we propose and demonstrate a flexible slip sensor based on triboelectric nanogenerator with a seesaw structure. The sensor is composed of two porous PDMS layers separated by an inverted trapezoid structure with a height of 500 μm. In order to customize the sensitivity of the sensor, porous PDMS was fabricated by mixing PDMS with deionized water thoroughly and then removing water with heat. Laser-induced porous graphene and aluminium are served as the pair of contact materials. To detect slip from different directions, two sets of the electrode pair were used. Experimental results show a distinct difference between static state and the moment when a slip happens was detected. In addition, the output voltage of the sensors increased as the increase of slip velocity from 0.25 mm/s to 2.5 mm/s. The flexible slip sensor proposed here shows the potential applications in smart robotics and prosthesis.

A novel silicon/carbon nanocomposite anode for high performance lithium-ion micro-battery

This paper reports a novel nanocomposite anode for lithium-ion battery, with high initial specific capacity (1200mAh/g) and good capacity retention (850mAh/g remaining after 30 cycles). Sufficient silicon nanoparticles (SiNPs) at anode make a significant contribution to specific capacity increase. Moreover, nano void space between SiNPs and carbon scaffold provide enough space for expansion and contraction of SiNPs during the process of lithium ion intercalation and deintercalation to ensure a long cycle life. The porous carbon scaffold is obtained from Si/SiO2-templated SU-8 photoresist. As such, this design and fabrication makes it possible to implement direct prototyping of three dimensional (3D) micro-battery on chip.