Oscillate Boiling from Electrical Microheaters

Oscillate boiling offers excellent heat transfer at temperatures above the Leidenfrost temperature. Here we realize an electrical microheater with an integrated thermal probe and resolve the thermal cycle during the high-frequency bubble oscillations. Thermal rates of $10^8\,$K/s were found indicating its applicability for compact and rapid heat transfer from micro electrical devices

Catalytic Micro/Nanomotors: Propulsion Mechanisms, Fabrication, Control, and Applications

Micro-/nanomotors are self-propelled micro-/nanomachines, which are capable of converting the surrounding fuels into mechanical movement or force. Inspired by naturally occurring biomolecular motor proteins, scientists extensively paid great attentions to synthetic micro-/nanomotors. Especially, a number of researchers devoted their efforts onto catalytic micro-/nanomotors. In the past few decades, several advanced developments and excellent contributions have been made in catalytic micro-/nanomotors. The future of this research field can be bright, but some major existing challenges such as biocompatible materials and fuels, smart controlling, and specifically practical applications are still required to be resolved. Therefore, it is essential for us to learn the state of the art of catalytic micro-/nanomotors. In this chapter, the propulsion mechanisms, fabrication methods, controlling strategies, and potential applications of catalytic micro-/nanomotors are presented and summarized

Autonomous propulsion of platinum-based catalytic micro/nanomotors

This work focuses on the investigation of platinum-based catalytic micro/nanomotors, including working mechanism, design, fabrication and related characterization. Three different categorized micro/nanomotors have been investigated, and key observations can be summarized as follows: i.A novel disk-like gold-nickel-platinum nanomotor is proposed. A bubble propulsion mechanism is employed to characterize the locomotion of the proposed nanomotor. The propulsion activities of the nanomotor are investigated at different hydrogen peroxide concentrations and different temperatures. Moreover, the magnetic effect on the propulsion of the nanomotor is also characterized. In addition, for the first time the three-dimensional propulsion of the nanomotor is characterized by using digital holographic microscope. ii. Two different types of gold-nickel-platinum nanojets are designed. One is with singular off-center nanoengine, the other one is with dual off-center nanoengines. The self-steerable propulsion activities of these two different nanojets are characterized at different hydrogen peroxide concentrations. The results show that the nanojet with singular off-center nanoengine is able to propel forward circularly; while the nanojet with dual off-center nanoengines can move forward linearly. iii.Another novel micro/nanomotor (platinum-nickel-SU-8 microrocket) is proposed. The microrocket has an eccentric nanoengine. A circularly self-steerable propulsion mechanism is proposed for characterizing the autonomous locomotion of the microrocket. The circularly steerable propulsion of the microrocket is characterized at different hydrogen peroxide concentrations. The results reveal that the speed of the microrocket increases with the increment of hydrogen peroxide concentrations. These observations prove the fabrication feasibility of newly designed micro/nanomotors. The wide applications of these micro/nanomotors can be expected.Doctor of Philosophy (MAE

MEMS Tunable Diffraction Grating for Spaceborne Imaging Spectroscopic Applications

Diffraction gratings are among the most commonly used optical elements in applications ranging from spectroscopy and metrology to lasers. Numerous methods have been adopted for the fabrication of gratings, including microelectromechanical system (MEMS) fabrication which is by now mature and presents opportunities for tunable gratings through inclusion of an actuation mechanism. We have designed, modeled, fabricated and tested a silicon based pitch tunable diffraction grating (PTG) with relatively large resolving power that could be deployed in a spaceborne imaging spectrometer, for example in a picosatellite. We have carried out a detailed analytical modeling of PTG, based on a mass spring system. The device has an effective fill factor of 52% and resolving power of 84. Tuning provided by electrostatic actuation results in a displacement of 2.7 μ m at 40 V . Further, we have carried out vibration testing of the fabricated structure to evaluate its feasibility for spaceborne instruments

Diffraction grating integrated on micromachined stepper motor for diversity implementation in imaging spectroscopy

This paper reports a monolithic fabrication of a MEMS rotary stepper motor integrated with a highly efficient diffraction grating to obtain optical transfer function diversity. The rotational motion is achieved by three phase electrostatic actuation mechanism that allows precise stepping motion which is difficult to attain with classical actuation like comb-drive design that depends on the structural resonant frequency. The micro-motor design is based on flexure mechanism to avoid frictional effects and getting the maximum angular stroke. The diffraction grating is fabricated separately by replication technique on a photosensitive material, SU-8 which becomes hard when it is cured. Finally, the replicated diffraction grating is bonded to the micro-actuator using UV-curable glue.NRF (Natl Research Foundation, S’pore)EDB (Economic Devt. Board, S’pore

Piezoelectric ZnO Thin Films for 2DOF MEMS Vibrational Energy Harvesting

Zinc oxide (ZnO) is an environmental-friendly semiconducting, piezoelectric and non-ferroelectric material, and plays an essential role for applications in microelectromechanical systems (MEMS). In this work, a fully integrated two-degree-of-freedom (2DOF) MEMS piezoelectric vibration energy harvester (p-VEH) was designed and fabricated using ZnO thin films for converting kinetic energy into electrical energy. The 2DOF energy harvesting system comprises two subsystems: the primary one for energy conversion and the auxiliary one for frequency adjustment. Piezoelectric ZnO thin film was deposited using a radio-frequency magnetron sputtering method onto the primary subsystem for energy conversion from mechanical vibration to electricity. Dynamic performance of the 2DOF resonant system was analyzed and optimized using a lumped parameter model. Two closely located but separated peaks were achieved by precisely adjusting mass ratio and frequency ratio of the resonant systems. The 2DOF MEMS p-VEH chip was fabricated through a combination of laminated surface micromachining process, double-side alignment and bulk micromachining process. When the fabricated prototype was subjected to an excitation acceleration of 0.5 g, two close resonant peaks at 403.8 and 489.9 Hz with comparable voltages of 10 and 15 mV were obtained, respectively

Self-steerable propulsion of disk-like micro-craft with dual off-center nanoengines

This paper reports a novel disk-like micro-craft with dual off-center nozzle nanoengines, consisting of three different metals: gold, nickel, and platinum. A bubble propulsion mechanism originating from momentum change induced by the detachment of oxygen bubbles is proposed to elaborate the self-steerable propulsion of the disk-like gold-nickel-platinum micro-craft. The as-proposed micro-craft is fabricated by a layer-by-layer deposition method based on the micro-electro-mechanical systems technology. Herein, the self-steerable propulsion of the fabricated micro-craft dispersed in deionized water with different hydrogen peroxide concentrations is characterized. As a consequence, the speed of the micro-craft is increased with the increment of hydrogen peroxide concentration. In addition, the micro-craft can always move forward linearly.MOE (Min. of Education, S’pore)Accepted versio

Home Care with IoT Support: Architecture Design and Functionality

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