C. D. Richards

Bio: C. D. Richards is an academic researcher from Washington State University. The author has contributed to research in topics: Heat engine & Heat transfer. The author has an hindex of 9, co-authored 42 publications receiving 268 citations.

Design, fabrication and testing of the P 3 micro heat engine

Abstract: The development and testing of a micro heat engine is presented. For the first time the production of electrical power by a dynamic micro heat engine is demonstrated. The prototype micro heat engine is an external combustion engine that converts thermal power to mechanical power through the use of a novel thermodynamic cycle. Mechanical power is converted into electrical power through the use of a thin-film piezoelectric membrane generator. This design is well suited to photolithography-based batch fabrication methods, and is unlike any conventionally manufactured macro-scale engine. # 2003 Elsevier Science B.V. All rights reserved.

A facility for characterizing the dynamic mechanical behavior of thin membranes for microelectromechanical systems

Abstract: A bulge testing system capable of applying static and dynamic loads to thin film membranes is described. The bulge tester consists of a sealed cavity, filled with a fluid, bounded on the bottom by a circular stainless steel diaphragm and on the top by the thin film membrane of interest. An actuator is used to apply either a static or a periodic force to the stainless steel diaphragm. The force is transmitted through the water to the thin film membrane. This facility provides for both accelerated lifetime testing and simulated service environment testing. The thin film membranes tested are composite stacks consisting of thin films of silicon, glass, metallic electrodes, and lead-zirconate-titanate. Pressure and deflection of a membrane are acquired simultaneously during loading. An image capture system coupled with an interferometer provides the means to capture interferograms of deflected membranes during both static and dynamic testing conditions. Images are then postprocessed to construct deflection ver...

A facility for characterizing the steady-state and dynamic thermal performance of microelectromechanical system thermal switches

Abstract: A facility to characterize microelectromechanical system (MEMS) thermal switches by measuring two pertinent figures of merit is described. The two figures of merit measured are the ratio of thermal resistance of the switch in the off and on states, Roff∕Ron, and the time required to switch from the off to the on state, τswitch. The facility consists of two pieces of equipment. A guard-heated calorimeter is used to measure heat transfer across the thermal switch under steady-state conditions. Measuring heat transfer across a thermal switch in both the off and on states then gives the thermal resistance ratio Roff∕Ron. A thin-film radial heat-flux sensor is used to measure heat transfer across the thermal switch under dynamic conditions. Measuring heat transfer across a thermal switch as the switch changes from the off to the on state gives the thermal switching time τswitch. The test facilities enable the control of the applied force on the thermal switch when the thermal switch is on, the thickness of the...

Characterization and modeling of a microcapillary driven liquid–vapor phase-change membrane actuator

Abstract: Factors affecting the efficiency of liquid–vapor phase-change actuators during dynamic operation are explored. To do this, a model actuator was specifically designed so that actuator geometry, material properties and operation could be easily varied in order to parametrically study their effects on actuator efficiency. A numerical model was developed so that the detailed energy budget within the device could be elucidated. It was found that device efficiency was maximized when the energy input to actuator was equal to the energy required to dry out the evaporator. Membrane thermal mass and compliance, as well as the thickness of the evaporating liquid layer were also found to have a large impact on efficiency. In contrast, membrane thermal conductivity was found to have a minimal effect on efficiency for dynamic operation. Based on the parameter study, a liquid–vapor phase-change membrane actuator fabricated with a 10.3 μm thick wicking structure and a 200 nm thick, 3 edge length silicon nitride actuation membrane was shown to demonstrate improved performance characteristics. The actuator generated peak pressures and deflections of 123 kPa and 167 μm when actuated with a 14.3 mJ heating pulse for a thermal efficiency of 0.15%.

Powering MEMS portable devices—a review of non-regenerative and regenerative power supply systems with special emphasis on piezoelectric energy harvesting systems

Abstract: Power consumption is forecast by the International Technology Roadmap of Semiconductors (ITRS) to pose long-term technical challenges for the semiconductor industry. The purpose of this paper is threefold: (1) to provide an overview of strategies for powering MEMS via non-regenerative and regenerative power supplies; (2) to review the fundamentals of piezoelectric energy harvesting, along with recent advancements, and (3) to discuss future trends and applications for piezoelectric energy harvesting technology. The paper concludes with a discussion of research needs that are critical for the enhancement of piezoelectric energy harvesting devices.

Group III nitride and SiC based MEMS and NEMS: materials properties, technology and applications

Abstract: With the increasing requirements for microelectromechanical systems (MEMS) regarding stability, miniaturization and integration, novel materials such as wide band gap semiconductors are attracting more attention. Polycrystalline SiC has first been implemented into Si micromachining techniques, mainly as etch stop and protective layers. However, the outstanding properties of wide band gap semiconductors offer many more possibilities for the implementation of new functionalities. Now, a variety of technologies for SiC and group III nitrides exist to fabricate fully wide band gap semiconductor based MEMS. In this paper we first review the basic technology (deposition and etching) for group III nitrides and SiC with a special focus on the fabrication of three-dimensional microstructures relevant for MEMS. The basic operation principle for MEMS with wide band gap semiconductors is described. Finally, the first applications of SiC based MEMS are demonstrated, and innovative MEMS and NEMS devices are reviewed.

Efficiency of energy conversion for a piezoelectric power harvesting system

Abstract: This paper studies the energy conversion efficiency for a rectified piezoelectric power harvester. An analytical model is proposed, and an expression of efficiency is derived under steady-state operation. In addition, the relationship among the conversion efficiency, electrically induced damping and ac–dc power output is established explicitly. It is shown that the optimization criteria are different depending on the relative strength of the coupling. For the weak electromechanical coupling system, the optimal power transfer is attained when the efficiency and induced damping achieve their maximum values. This result is consistent with that observed in the recent literature. However, a new finding shows that they are not simultaneously maximized in the strongly coupled electromechanical system.