Experimental comparison of macro and micro scale electromagnetic vibration powered generators

Electromagnetic vibration powered generators convert kinetic energy present in the application environment into electric energy. Such generators may be used as an alternative power supply to batteries in wireless sensor systems enabling indefinite and maintenance free operation. This paper presents an experimental comparison between macro and micro scale electromagnetic generators based upon an identical magnetic circuit and explores the influence of size on the performance and behaviour of these devices. The large scale traditionally fabricated generator exhibits the highest power density of 2615 nW/mm³ compared to the microgenerator power density of 47 nW/mm³. The macro scale device achieves the optimum damping conditions where electromagnetic damping equals parasitic damping. The level of electromagnetic damping in the micro scale generator is an order of magnitude less than the parasitic damping due to reduced electromagnetic coupling. This comparison highlights the challenges involved in scaling electromagnetic devices down in size.     

Scaling effects for electromagnetic vibrational power generators

This paper investigates how the power generated by electromagnetic based vibrational power generators scales with the dimension of the generator. The effects of scaling on the magnetic fields, the coil parameters and the electromagnetic damping are presented. An analysis is presented for both wire-wound coil technology and micro-fabricated coils. The power obtainable from electromagnetic generators in the dimension range of 1–10 mm is calculated. It is shown that the theoretical maximum power scales with the cube of the dimension. It is also shown that the high coil resistance associated with micro-coils severely restricts the power, which can be extracted.     

Engineering MEMS Resonators With Low Thermoelastic Damping

This paper presents two approaches to analyzing and calculating thermoelastic damping in micromechanical resonators. The first approach solves the fully coupled thermomechanical equations that capture the physics of thermoelastic damping in both two and three dimensions for arbitrary structures. The second approach uses the eigenvalues and eigenvectors of the uncoupled thermal and mechanical dynamics equations to calculate damping. We demonstrate the use of the latter approach to identify the thermal modes that contribute most to damping, and present an example that illustrates how this information may be used to design devices with higher quality factors. Both approaches are numerically implemented using a finite-element solver (Comsol Multiphysics). We calculate damping in typical micromechanical resonator structures using Comsol Multiphysics and compare the results with experimental data reported in literature for these devices     

Vibrational energy scavenging with Si technology electromagnetic inertial microgenerators

In this work, we present the design and optimization of an electromagnetic inertial microgenerator for energy scavenging applications, compatible with Si technology. It consists of a fixed micromachined coil and a movable magnet (inertial mass) mounted on a resonant structure (Kapton^® membrane). The modeling of the device, based on a velocity damped resonator, has allowed to make a quantitative analysis of the capabilities of this simple device structure for the development of power generators for autonomous microsystem applications. The characterization of a first (not optimized) prototype has allowed the validation of the model, which is then used as a roadmap for a number of optimizations for the final device design. For this design, the model developed shows the possibility to achieve power levels up to hundreds of μW’s, with voltage levels compatible with the requirements of standard rectifying circuits.     

Linear and non-linear behavior of mechanical resonators for optimized inertial electromagnetic microgenerators

In this work, the design, fabrication and characterization of an electromagnetic inertial microgenerator compatible with Si micro-systems technology is presented. The device includes a fixed micromachined coil and a movable magnet mounted on a resonant polymeric structure. The characterization of the fabricated prototypes has allowed to observe the presence of non-linear effects that lead to the appearance of hysteretic vibrational phenomenon and strongly affect the output of the microgenerator. These effects are likely related to the mechanical characteristics of the polymeric membrane, and determine an additional dependence of vibration frequency on the excitation amplitude. Under such non-linear conditions, power densities up to 40 μW/cm³ are obtained for devices working with low level excitation conditions similar to those present in domestic and office environment.     

A Monte Carlo Simulation approach for the modeling of free-molecule squeeze-film damping of flexible microresonators

Squeeze-film damping on microresonators is a significant damping source even when the surrounding gas is highly rarefied. This article presents a general modeling approach based on Monte Carlo (MC) simulations for the prediction of squeeze-film damping on resonators in the free-molecule regime. The generality of the approach is demonstrated in its capability of simulating resonators of any shape and with any accommodation coefficient. The approach is validated using both the analytical results of the free-space damping and the experimental data of the squeeze-film damping on a clamped–clamped plate resonator oscillating at its first flexure mode. The effect of oscillation modes on the quality factor of the resonator has also been studied and semi-analytical approximate models for the squeeze-film damping with diffuse collisions have been developed.     

NEPTUNE:并行三维全电磁粒子模拟软件

为求解具有复杂几何的高功率微波电磁场问题,本文研制了一个三维全电磁粒子并行软件NEPTUNE。本文介绍了该并行软件的基本结构和采用的一些并行算法。目前,该软件已经成功模拟了多种高功率源器件,并可扩展到数千台处理器核上运行。     

Air-damped microresonators with enhanced quality factor

It is known that the dissipative damping force due to the air film trapped between the bottom of surface micromachined resonators and the substrate on which they are fabricated decreases in magnitude as the separation between the two increases. The practical outcome of this is that microresonators located close to a substrate will have higher damping and a lower quality factor Q. In order to further investigate this effect and compare experimental findings with theory, a new test device that enables modulation of the damping interaction between a surface micromachined resonator and the substrate has been fabricated. The device consists of a surface micromachined polysilicon microresonator, which is self-elevated out of the plane of the substrate using a bimorph beam. A second, identical microresonator lying parallel to the plane of the substrate has also been fabricated. Both devices have been fabricated using the polysilicon multiuser microelectromechanical systems (MEMS) processes (polyMUMPs). The resonator-to-substrate separation of the elevated resonator is varied by changing the temperature of the bimorph beam, and the Q factors for different separations have been measured. Experimental results show that the elevated microresonators have Q values which are 65% higher than the in-plane microresonators. These experimental findings show good agreement with the theoretical model of damping used.     

Microelectromechanical systems vibration powered electromagnetic generator for wireless sensor applications

This paper presents a silicon microgenerator, fabricated using standard silicon micromachining techniques, which converts external ambient vibrations into electrical energy. Power is generated by an electromagnetic transduction mechanism with static magnets positioned on either side of a moving coil, which is located on a silicon structure designed to resonate laterally in the plane of the chip. The volume of this device is approximately 100 mm³. ANSYS finite element analysis (FEA) has been used to determine the optimum geometry for the microgenerator. Electromagnetic FEA simulations using Ansoft’s Maxwell 3D software have been performed to determine the voltage generated from a single beam generator design. The predicted voltage levels of 0.7–4.15 V can be generated for a two-pole arrangement by tuning the damping factor to achieve maximum displacement for a given input excitation. Experimental results from the microgenerator demonstrate a maximum power output of 104 nW for 0.4g (g=9.81 m s^?1) input acceleration at 1.615 kHz. Other frequencies can be achieved by employing different geometries or materials.     

Microelectromechanical systems vibration powered electromagnetic generator for wireless sensor applications

This paper presents a silicon microgenerator, fabricated using standard silicon micromachining techniques, which converts external ambient vibrations into electrical energy. Power is generated by an electromagnetic transduction mechanism with static magnets positioned on either side of a moving coil, which is located on a silicon structure designed to resonate laterally in the plane of the chip. The volume of this device is approximately 100 mm³. ANSYS finite element analysis (FEA) has been used to determine the optimum geometry for the microgenerator. Electromagnetic FEA simulations using Ansoft’s Maxwell 3D software have been performed to determine the voltage generated from a single beam generator design. The predicted voltage levels of 0.7–4.15 V can be generated for a two-pole arrangement by tuning the damping factor to achieve maximum displacement for a given input excitation. Experimental results from the microgenerator demonstrate a maximum power output of 104 nW for 0.4g (g=9.81 m s⁻¹) input acceleration at 1.615 kHz. Other frequencies can be achieved by employing different geometries or materials.

     

MEMS压电-磁电复合式振动驱动微能源的设计

在单一效应的MEMS振动驱动微能源的基础上,提出了一种MEMS压电-磁电复合振动驱动微能源器件。该微能源由八悬臂梁-中心质量块结构和永磁铁两部分组成,环境振动使中心质量块振动,PZT压电敏感单元由于压电效应产生电势差;同时中心质量块上集成的高密度线圈切割磁感线产生感应电动势,将压电转换与磁电转换相结合把振动能转换为电能。建立了该结构的数学模型并用有限分析软件Ansys12.0对该器件进行力学特性分析,最后对加工出的微能源进行性能测试。测试结果表明,该微能源谐振频率为8 Hz,易与环境发生共振;在共振条件下,施加1 gn 的加速度,器件压电发电开路输出电压峰峰值达154 mV,磁电发电开路输出电压峰-峰值达8 mV,有望为无线传感网络节点提供稳定的能源。     

Investigation of microstrip t-junction and 45° Bend Discontinuity Models from 18 to 60 GHz

A resonator technique is used to investigate the validity of microstrip t-junction and 45° bend discontinuity models over the frequency range 18–60 GHz. Models are checked against both experimental results and electromagnetic simulations using a previously described dual-resonator method to eliminate confounding variables. The method has been improved to provide results in terms of model phase error rather than a dimensionless validation parameter. Model phase errors in excess of 15° have been found. © 1998 John Wiley & Sons, Inc. Int J RF and Microwave CAE 8: 42–48, 1998.     

风致驰振型电磁俘能器输出性能仿真分析

对一种横风向驰振的电磁俘能器输出性能进行了研究。建立了风致驰振型电磁俘能器输出电流与输入风速关系数学模型,应用谐波平衡法求得了方程近似解析解。通过与龙格-库塔法数值解比较验证了解析解的正确性,随后仿真分析了激励风速和无量纲负载电阻r对驰振频率和切入风速的影响关系,并研究了机电耦合系数、线圈电感和电阻对切入风速和平均功率的影响关系。结果表明,低r值时,受高切入风速制约,俘能器不易发生驰振。俘能器驰振后,最优r值不低于1,最优功率会随着机电耦合系数的增加而增大并逐渐趋于饱和。当r取值范围为[0.01,100]时,低风速条件下,增加线圈电感值可以降低系统在低r值处的切入风速,拓宽可驰振的r值范围,改善低r值处输出功率。高风速条件下,低于49.3 mH的线圈电感对输出功率几乎无影响,随后增加的线圈电感值能明显降低俘能器在低r值处的输出功率。增加线圈电阻值能提高俘能器在低r值处的输出功率,但过量增加线圈电阻会导致系统最优功率大幅下降。研究结果为风致驰振型电磁俘能器的设计提供理论参考。     

Compact damping models for laterally moving microstructures withgas-rarefaction effects

Compact models for the viscous damping coefficient in narrow air gaps between laterally moving structures are reported. In the first part of the paper, a simple frequency-independent first-order slip-flow approximation for the damping coefficient is derived and compared with a more accurate expression obtained from the linearized Boltzmann equation. The simple approximation is slightly modified and fitted to match the accurate model. The resulting simple approximation has a maximum relative error of less than ±6% at arbitrary Knudsen numbers in viscous, transitional and free molecular regions. In the second part of the paper, dynamic models for the damping force are derived, considering again gas rarefaction, by applying various boundary conditions. The damping admittance of the first-order slip-flow model is implemented also as an electrical equivalent admittance, constructed of RC sections, to allow both frequency and time domain simulations with a circuit simulator. The dependence of the damping admittance on pressure and gap displacement is demonstrated with model simulations. The accuracy and validity range of the model are verified with comparative numerical simulations of the Navier-Stokes equation. Finally, the damping coefficient in a lateral resonator is calculated using the compact model and compared with measured data with good agreement     

Up-scaled macro-device implementation of a MEMS wideband vibration piezoelectric energy harvester design concept

In this work, we discuss a novel mechanical resonator design for the realisation of vibration Energy Harvester (EH) capable to deliver power levels in the mW range. The device overcomes the typical constraint of frequency narrowband operability of standard cantilevered EHs, by exploiting a circular-shaped resonator with an increased number of mechanical Degrees Of Freedom (DOFs), leading to several resonant modes in the range of vibrations of interest (i.e. multi-modal wideband EH). The device, named Four-Leaf Clover (FLC), is simulated in Ansys Workbench?, showing a significant number of resonant modes up to vibrations of around 2 kHz (modal eigenfrequencies analysis), and exhibiting levels of converted power up to a few mW at resonance (harmonic coupled-field analysis). The FLC mechanical structure, along with cantilevered test structure, is realised by micro-milling of an Aluminium foil. PolyVinyliDene Fluoride (PVDF) film sheet pads are assembled in order to collect first experimental feedback on generated power levels. The FLC and cantilevered EH test structures are characterised experimentally with a measurement setup purposely developed, showing encouraging performance related to the technology chosen for the realisation of EH, thus paving the way for full validation of the macro-FLC concept.     

A High-Q Widely Tunable Gigahertz Electromagnetic Cavity Resonator

This paper describes the design, fabrication and testing of a quasi-static electromagnetic cavity resonator fabricated using potassium-hydroxide (KOH) etching, shallow reactive-ion etching (RIE), metalization and wafer bonding. The resonator is distinguished by its simultaneous high-Q near 200, and wide high-frequency tuning range, 2.5-4.0 GHz for the experimental resonator presented here. When combined with an integrated actuator, it should be suitable for use in electronically tunable radio-frequency (RF) bandpass filters and oscillators. The experimental resonator, however, is tuned with an external piezoelectric actuator for simplicity     

Power processing circuits for electromagnetic, electrostatic and piezoelectric inertial energy scavengers

Inertial energy scavengers are self-contained devices which generate power from ambient motion, by electrically damping the internal motion of a suspended proof mass. There are significant challenges in converting the power generated from such devices to useable form, particularly in micro-engineered variants. This paper examines this power conversion requirement for each of the cases of electromagnetic, electrostatic and piezo-electric transduction, and presents new circuit approaches for the first two of these.     

Contactless electromagnetic switched interrogation of micromechanical cantilever resonators

A principle for contactless interrogation of passive micromechanical resonator sensors is proposed. The principle exploits an external primary coil electromagnetically air-coupled to a secondary coil which is connected to a conductive path on the resonator. The interrogation periodically switches between interleaved excitation and detection phases. During the excitation phase the resonator is driven into vibrations, while in the detection phase the excitation signal is turned off and the decaying oscillations are contactless sensed. The principle advantageously avoids magnetic properties required to the resonator, thereby ensuring compatibility with standard silicon microfabrication processes. The principle has been implemented on a MEMS SOI microcantilever resonator sensor with mechanical resonant frequency of 10.186 kHz and has been demonstrated to work over a distance of up to 1 cm. Tests based on the deposition and evaporation of a water droplet have demonstrated the capability to sense physical and chemical quantities which affect either the resonant frequency or the quality factor of the resonator.     

Numerical simulation and optimization of planar electromagnetic actuators

The design rules and characterization of planar electromagnetic actuators are presented focusing on numerical force simulation and maximization of efficiency. Theoretical simulations are carried out for circular concentric, circular eccentric and rectangular concentric placements of the magnet with respect to the coil yielding the highest forces for the circular concentric arrangement. As a result larger magnets or larger coils are not linked to higher forces in any case, thus an optimum magnet diameter for a given coil radius can be calculated and vice versa. With respect to the vertical distance of the coil to the magnet the optimum parameters are given. Dimensions and forces are derived in generalized units to facilitate scaling to other geometries. The simulations are excellently confirmed by experimental data of different coils and magnets.     

Multifingers capacitances modeling of 65‐Nm CMOS transistor by unit cell method

The multifingers' parasitic capacitances modeling of 65‐nm CMOS transistors for millimeter‐wave application is presented. The modeling is based on simulation approach, which is done by building the devices true dimension in high‐frequency structure simulator environment. The material properties of the devices as given by the foundry are used during simulation and then full electromagnetic simulations are carried out to extract the Y‐parameters of the model. Unit‐cell parameters extraction method is carried out in order to save memory and simulation time. In this case, the multifinger transistors are divided into unit‐cells and then the parasitic capacitances of the unit‐cells are calculated from the extracted Y‐parameter. Based on linear scaling, the parasitic capacitance of the multifingers transistor can be obtained with good accuracy (less than 5% error). © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2012.