Xiaoning Jiang

Micro-stereolithography of polymeric and ceramic microstructures

Abstract Micro-stereolithography (μSL) is a novel micro-manufacturing process which builds the truly 3D microstructures by solidifying the liquid monomer in a layer by layer fashion. In this work, an advanced μSL apparatus is designed and developed which includes an Ar + laser, the beam delivery system, computer-controlled precision x–y–z stages and CAD design tool, and in situ process monitoring systems. The 1.2 μm resolution of μSL fabrication has been achieved with this apparatus. The microtubes with high aspect ratio of 16 and real 3D microchannels and microcones are fabricated on silicon substrate. For the first time, μSL of ceramic microgears has been successfully demonstrated.

High-Temperature Piezoelectric Sensing

Piezoelectric sensing is of increasing interest for high-temperature applications in aerospace, automotive, power plants and material processing due to its low cost, compact sensor size and simple signal conditioning, in comparison with other high-temperature sensing techniques. This paper presented an overview of high-temperature piezoelectric sensing techniques. Firstly, different types of high-temperature piezoelectric single crystals, electrode materials, and their pros and cons are discussed. Secondly, recent work on high-temperature piezoelectric sensors including accelerometer, surface acoustic wave sensor, ultrasound transducer, acoustic emission sensor, gas sensor, and pressure sensor for temperatures up to 1,250 °C were reviewed. Finally, discussions of existing challenges and future work for high-temperature piezoelectric sensing are presented.

Micronozzle/diffuser flow and its application in micro valveless pumps

The nozzle/diffuser flow with different Reynolds number ranges and conical angles is analyzed first. It is found that the flow coefficients of nozzle/diffuser ξn and ξd vary with angle with different trends for large (> 105) and small (<50) Reynolds number ranges. The flow model of valveless pumps with nozzle/diffusers is proposed, and the relationship between nozzle/diffuser flow coefficients and the performance of the valveless pumps is investigated. In experiments, silicon nozzle/diffuser elements with conical angles of 5°, 7.5° and 10° and a silicon micro valveless pump wafer are fabricated. The experimental ξd, ξn, and ξn/ξd decrease with increasing nozzle/diffuser angles in the Re range ( 2000) of the experiment. The pumping direction of the fabricated valveless pump agrees with the nozzle/diffuser flow experiments and analysis. The pump works successfully with the output flow rate of 28 μl/min under the input power of 50 mW and 500 Hz.

Disruption of microalgal cells using high-frequency focused ultrasound.

The objective of this study was to evaluate the effectiveness of high-frequency focused ultrasound (HFFU) in microalgal cell disruption. Two microalgal species including Scenedesmus dimorphus and Nannochloropsis oculata were treated by a 3.2-MHz, 40-W focused ultrasound and a 100-W, low-frequency (20kHz) non-focused ultrasound (LFNFU). The results demonstrated that HFFU was effective in the disruption of microalgal cells, indicated by significantly increased lipid fluorescence density, the decrease of cell sizes, and the increase of chlorophyll a fluorescence density after treatments. Compared with LFNFU, HFFU treatment was more energy efficient. The combination of high and low frequency treatments was found to be even more effective than single frequency treatment at the same processing time, indicating that frequency played a critical role in cell disruption. In both HFFU and LFNFU treatments, the effectiveness of cell disruption was found to be dependent on the cell treated.

Energy harvesting using a PZT ceramic multilayer stack

In this paper, the interdisciplinary energy harvesting issues on piezoelectric energy harvesting were investigated using a ‘33’ mode (mechanical stress and/or electric field are in parallel to the polarization direction) lead zirconate titanate multilayer piezoelectric stack (PZT-Stack). Key energy harvesting characteristics including the generated electrical energy/power in the PZT-Stack, the mechanical to electrical energy conversion efficiency, the power delivered from the PZT-Stack to a resistive load, the electrical charge/energy transferred from the PZT-Stack to a super-capacitor were systematically addressed. Theoretical models for power generation and delivery to a resistive load were proposed and experimentally affirmed. In a quasi-static regime, 70% generated electrical powers were delivered to matched resistive loads. A 35% mechanical to electrical energy conversion efficiency, which is more than 4 times higher than other reports, for the PZT-Stack had been obtained. The generated electrical power and power density were significantly higher than those from a similar weight and size cantilever-type piezoelectric harvester in both resonance and off-resonance modes. In addition, our study indicated that the capacitance and piezoelectric coefficient of the PZT-Stack were strongly dependent on the dynamic stress. (Some figures may appear in colour only in the online journal)

Characterization of piezoelectric single crystal YCa4O(BO3)3 for high temperature applications

Operation at temperatures well above ambient is desired for applications such as smart structures integrated within aircraft and space vehicles. Piezoelectric yttrium calcium oxyborate single crystal YCa4O(BO3)3 (YCOB) was found to exhibit no phase transition until its melting temperature around ∼1500°C. The temperature characteristics of the resonance frequency, electromechanical coupling, and dielectric permittivity were studied in the temperature range of 30–950°C for different orientations. The electrical resistivity at 800°C was found to be greater than 2×108Ωcm. Together with its temperature independent electromechanical coupling factor (∼12%) and engineered resonance frequency behavior, these make YCOB crystals excellent candidates for sensing applications at ultra high temperatures.

5I-1 Microfabrication of Piezoelectric Composite Ultrasound Transducers (PC-MUT)

In this paper a piezoelectric composite based micromachined ultrasound transducer (PC-MUT) fabrication technology is presented. PMN-PT single crystal posts with side length of 14 mum and height of > 60 mum were fabricated using a deep dry etching method. High frequency (20-50 MHz) PMN-PT single crystal/epoxy 1-3 composites were prepared and the electromechanical coupling coefficient of the composites was ~0.72. Prototype 40 MHz ultrasound transducers showed promising sensitivity and bandwidth

A small, linear, piezoelectric ultrasonic cryomotor

A small, linear-type, piezoelectric ultrasonic cryomotor has been developed for precision positioning at extremely low temperatures (⩾−200°C). This cryomotor consists of a pair of Pb(Mg1∕3Nb2∕3)O3−PbTiO3 single crystal stacks, which are piezoelectrically excited into the rotating third-bending mode of the cryomotor stator’s center, which in turn drives a contacted slider into linear motion via frictional forces. The performance characteristics achieved by the cryomotor are: (i) a maximum linear speed of >50mm∕s; (ii) a stroke of >10mm; (iii) a driving force of >0.2N; (iv) a response time of ∼29ms; and (v) a step resolution of ∼20nm.

Laminar flow through microchannels used for microscale cooling systems

Microchannel cooling is one the prospective microscale cooling methods that can meet future needs. Many theoretical and experimental studies have been reported in the past decade. This paper presents an experimental study on the laminar flow of liquid through microchannels with different cross-sections. The experimental results for circular micropipes agree well with theoretical predictions for conventional ducts. The values of fRe (Darcy friction factor-Reynolds number product) for laminar flow of liquid in the silicon microchannels with noncircular cross-sections are smaller than those of the conventional values. The surface roughness of the silicon microchannels fabricated by surface and bulk micromachining processes is also measured. The turbulent flow and heat transfer characteristics in microchannels are to be studied in the next phase of research.

Piezoelectric accelerometers for ultrahigh temperature application

High temperature sensors are of major importance to aerospace and energy related industries. In this letter, a high temperature monolithic compression-mode piezoelectric accelerometer was fabricated using YCa4O(BO3)3 (YCOB) single crystals. The performance of the sensor was tested as function of temperature up to 1000 °C and over a frequency range of 100–600 Hz. The accelerometer prototype was found to possess sensitivity of 2.4±0.4 pC/g, across the measured temperature and frequency range, indicating a low temperature coefficient. Furthermore, the sensor exhibited good stability over an extended dwell time at 900 °C, demonstrating that YCOB piezoelectric accelerometers are promising candidates for high temperature sensing applications.