This paper reviews the state-of-the art in vibration energy harvesting for wireless, self-powered microsystems. Vibration-powered generators are typically, although not exclusively, inertial spring and mass systems. The characteristic equations for inertial-based generators are presented, along with the specific damping equations that relate to the three main transduction mechanisms employed to extract energy from the system. These transduction mechanisms are: piezoelectric, electromagnetic and electrostatic. Piezoelectric generators employ active materials that generate a charge when mechanically stressed. A comprehensive review of existing piezoelectric generators is presented, including impact coupled, resonant and human-based devices. Electromagnetic generators employ electromagnetic induction arising from the relative motion between a magnetic flux gradient and a conductor. Electromagnetic generators presented in the literature are reviewed including large scale discrete devices and wafer-scale integrated versions. Electrostatic generators utilize the relative movement between electrically isolated charged capacitor plates to generate energy. The work done against the electrostatic force between the plates provides the harvested energy. Electrostatic-based generators are reviewed under the classifications of in-plane overlap varying, in-plane gap closing and out-of-plane gap closing; the Coulomb force parametric generator and electret-based generators are also covered. The coupling factor of each transduction mechanism is discussed and all the devices presented in the literature are summarized in tables classified by transduction type; conclusions are drawn as to the suitability of the various techniques.

/pdf/energy-harvesting-vibration-sources-for-microsystems-46t885pwdp.pdf

Energy harvesting vibration sources for microsystems applications

Auditory and non-auditory effects of noise on health

Objective:This report surveys and evaluates the scientific research on evidence-based healthcare design and extracts its implications for designing better and safer hospitals.Background:It builds o...

/pdf/a-review-of-the-research-literature-on-evidence-based-2oeftve5sd.pdf

A Review of the Research Literature on Evidence-Based Healthcare Design

Manufacturing processes that can create extremely small machines have been developed in recent years. Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than 1 mm but more than 1 micron, that combine electrical and mechanical components and that are fabricated using integrated circuit batch-processing techniques. Electrostatic, magnetic, pneumatic and thermal actuators, motors, valves, gears, and tweezers of less than 100-μm size have been fabricated. These have been used as sensors for pressure, temperature, mass flow, velocity and sound, as actuators for linear and angular motion and as simple components for complex systems such as micro-heat-engines and micro-heat-pumps The technology is progressing at a rate that fa r exceeds that of our understanding of the unconventional physics involved in the operation as well as the manufacturing of those minute devices. The primary objective of this article is to critically review the status of our understanding of fluid flow phenomena particular to microdevices. In terms of applications, the paper emphasizes the use of MEMS as sensors and actuators for flow diagnosis and control.

/pdf/the-fluid-mechanics-of-microdevices-the-freeman-scholar-4k4thaspga.pdf

The Fluid Mechanics of Microdevices—The Freeman Scholar Lecture

Understanding the ferroelectrocity in magnetic ferroelectric oxides is of both fundamental and technological importance. Here, we identify the nature of the ferroelectric phase transition in the hexagonal manganite, YMnO3, using a combination of single-crystal X-ray diffraction, thorough structure analysis and first-principles density-functional calculations. The ferroelectric phase is characterized by a buckling of the layered MnO5 polyhedra, accompanied by displacements of the Y ions, which lead to a net electric polarization. Our calculations show that the mechanism is driven entirely by electrostatic and size effects, rather than the usual changes in chemical bonding associated with ferroelectric phase transitions in perovskite oxides. As a result, the usual indicators of structural instability, such as anomalies in Born effective charges on the active ions, do not hold. In contrast to the chemically stabilized ferroelectrics, this mechanism for ferroelectricity permits the coexistence of magnetism and ferroelectricity, and so suggests an avenue for designing novel magnetic ferroelectrics.

/pdf/the-origin-of-ferroelectricity-in-magnetoelectric-ymno3-3pku3xy9v6.pdf

The origin of ferroelectricity in magnetoelectric YMnO3.

A new bond graph model for conduction heat transfer is developed, and applied to thermal energy balance in the piezoelectric thickness vibrator. In formulation of the heat conduction model, the mechanical and electrical effects are included. Hence, it can be directly applied to the temperature-dependent thickness vibrator. For the purpose of evaluation of the new method, one-dimensional heat conduction excluding other variable effects is compared with the results of the analytic solutions in simple cases. The simulation illustrates the validity and the accuracy of the model. Although the model is applied to the one-dimensional case only, the method can be easily used for general heat conduction problems.

Modeling of piezoelectric ceramic vibrators including thermal effects. Part III. Bond graph model for one-dimensional heat conduction

Spherical microphone arrays are capable of complete three‐dimensional sound field capture and robust noise cancellation [J. Meyer & G.W. Elko, ‘‘A Highly Scalable Spherical Microphone Array Based on an Orthonormal Decomposition of the Soundfield,’’ in Proc. IEEE Int. Conf. Acoust., Speech, Signal Processing, 2002, Vol. II, pp. 1781–1784]. The spherical array tested has 24 omni‐directional pressure microphones arranged on a rigid sphere. The sound pressure from each sensor is decomposed into spherical harmonics (standard eigen analysis) which results in rotationally symmetric output along any axis (three dimensionally) through the center of the sphere. An accurate impulse response of this system is important to sound localization and tracking methods. Time history can also be used to enhance the prediction model for source movement. The impulse measurements on this array were made in a semi‐anechoic chamber and are in good agreement with expected results. The three main characteristics of the impulse response that will be discussed are the delay times, amplitude differences, and frequency response.

Impulse response of a spherical microphone array (eigenmike)

The standard approach to vibration isolation analysis represents the source, isolator, and receiver by their mobilities. However, the choice of appropriate descriptor for each element is not arbitrary. Causality arguments show that whether the isolator is treated as a one‐port or a two‐port element, at least one of the system components must be represented by its impedance.

A fundamental problem with mobility analysis of vibration isolation systems

In this work, the machine dynamic response in Selective Laser Sintering is investigated with the purpose of determining the causes of scanning errors. Machine subcomponents are first investigated to determine their potential effects on the laser beam positional accuracy. The dynamics of the laser beam delivery system are identified as the major contributor to deviations in the laser beam position. The moving-iron galvanometer scanner used in SLS machines is then modeled, with the ultimate goal of understanding how its various components and parameters affect part scanning accuracy. This work should provide a better understanding of the dynamics of the laser beam delivery system and give insight on machine parameters that result in better part accuracy.

Modeling of Dynamic Effects Caused by the Beam Delivery System in Selective Laser Sintering

: Microdynamical systems have been studied for a number of years. Only limited work, however, has been completed on integrating microdynamical components into systems that satisfy mechanical tasks on macroscopic scales. In this paper, we describe microdynamical components that are needed to produce a surface which is actively deformable on local scales. In particular, we consider the design and demonstration of smart journal and thrust bearings capable of using embedded sensors and actuators to dynamically change the surface geometry. The ability to actively deform bearing surfaces allows for the design of bearings which are less prone to failure, the design of bearings with greater load carrying abilities, and a fundamental study of the effect of surface geometries and fluid conditions on bearing performance, such as start-up and shut-down conditions. Results of our new bearing designs are presented, focusing on numerical bearing models, sensor and actuator design and fabrication, and physical experimentation.

MEMS Hydrodynamic Bearings: Applications and Implications to Machine-Failure Prevention

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