Mohamed A. E. Mahmoud

Propagation of Bessel beams generated using finite-width Durnin ring

We have studied the increase of the power contained in Bessel beams generated using the Durnin ring technique, which is compatible with microelectromechanical systems technology. Increasing the ring width to increase the output power will lead to deviation from the Bessel beam profile and its diffraction properties. In this work, the effect of the ring width on the generated beam is investigated. An analytical expression for the generated beam depth of focus (DOF) is obtained. A Fourier optics model is also developed to estimate the transverse field profile. The theoretical predictions are assisted by numerical simulations and experimental measurements. The developed models allow engineering the beam diffraction properties to make the necessary compromise between the DOF and the amount of energy carried by the beam depending on the targeted application.

Electromechanical coupling in electrostatic micro-power generators

Electrostatic micro-power generators (MPGs) are modeled and analyzed with particular emphasis on electromechanical coupling and its impact on the system dynamics. We identify two qualitatively different regimes in the MPG response, dubbed slow and fast. A linearized electromechanically coupled model of an electrostatic MPG and two simplified linear models are used to study the response of the MPG. Linear models are found adequate to represent the dynamic response of fast MPGs but inadequate to represent the response of slow and mixed domain MPGs. A nonlinear model is developed and validated to describe the response of those MPGs under moderately large excitations. On the basis of this analysis, we describe a method and provide design rules for realizing wideband electrostatic MPGs, and develop closed-form formulae for the extracted power for MPGs under moderately large excitations.

Springless Vibration Energy Harvesters

A novel vibration energy harvester (VEH) architecture is developed to eliminate the need for restoring force elements (springs) in the VEH. The architecture can realize VEHs with arbitrarily low center frequency. Two prototypes were fabricated and tested to demonstrate the feasibility of this architecture. The center frequency of the first prototype was found to be 2 Hz demonstrating low frequency operation. The second prototype improve the performance by five times at much smaller footprint using thin film fabrication process and precision alignment.Copyright

Testing and evaluation of stretching strain in clamped–clamped beams for energy harvesting

In this paper, evaluation of stretching strain capabilities to harvest energy from a piezoelectric clamped–clamped beam is theoretically modeled and experimentally tested. The utilization of stretching strain has many advantages as: elimination of any substrate material, and the simple electrode configuration. The doubly clamped structure exhibits a highly nonlinear frequency response (Hardening Duffing) that widens the bandwidth during the frequency up-ward sweep. The wide bandwidth makes it suitable for practical applications. A design of ( piezoelectric material + proof mass) energy harvester was tested using PVDF (polyvinylidene fluoride) that can generate up to 15 μW from vibrations of at and 2 MΩ load. The design can also generate up to from vibrations of at and 2 MΩ load.

High-efficiency passive full wave rectification for electromagnetic harvesters

We compare the performance of four types of full-wave bridge rectifiers designed for electromagnetic energy harvesters based on silicon diodes, Schottky diodes, passive MOSFETs, and active MOSFETs. Simulation and experimental results show that MOSFET-type rectifiers are more efficient than diode-type rectifiers, reaching voltage and power efficiency of 99% for ideal voltage source with input amplitudes larger than 800 mV. Since active MOSFETs require extra components and an external DC power supply, we conclude that passive MOSFETs are superior for micro-power energy harvesting systems. We demonstrate passive MOSFET rectifiers implemented using discrete, off-shelf components and show that they outperform all electromagnetic harvester rectifiers hitherto reported obtaining a power efficiency of 95%. Furthermore, we show that passive MOSFET rectifiers do not affect the center frequency, harvesting bandwidth, or optimal resistance of electromagnetic harvesters. We demonstrate a complete power management modu...

Current source based standard-cell model for accurate timing analysis of combinational logic cells

Timing verification is an essential process in nanometer design. Therefore, static timing analysis (STA) is currently the main aspect of performance verification. Traditional STA is based on lookup tables with input slew and output load capacitance. It is becoming insufficient to accurately characterize many significant aspects of the conventional cell delays models, such as: the process variations, nonlinear waveforms, nonlinear loads, and multiple inputs switching (MIS). Therefore, the current trend in modern designs is to use current source based models (CSM), which model MOSFETs as a transconductance. This paper proposes a CSM for combinational logic cells which can accommodate single input switching (SIS) signals. It can also handle where small capacitances are connected at the gate output, while fast ramp signals are applied to the gate input. When compared with ELDO, the proposed model produces more accurate stage delay than that obtained from the standard cell lookup tables.

Out-of-Plane Continuous Electrostatic Micro-Power Generators

This paper presents an out-of-plane electrostatic micro-power generator (MPG). Electret-based continuous MPGs with different gaps and masses are fabricated to demonstrate the merits of this topology. Experimental results of the MPG demonstrate output power of 1 mW for a base acceleration amplitude and frequency of 0.08 g and 86 Hz. The MPGs also demonstrate a wideband harvesting bandwidth reaching up to 9 Hz. A free-flight and an impact mode model of electrostatic MPGs are also derived and validated by comparison to experimental results.

Optimization of the output power of a frequency-up conversion piezoelectric energy harvester

A mechanical stopper-based frequency up-conversion, FUC, piezoelectric energy harvester is designed for low frequency wideband vibrations. The primary low frequency beam is designed to have a resonance frequency as low as 15.6 Hz. Frequency up-conversion is achieved by a harvesting stopper beam which has a higher resonance frequency around 200 Hz. The effect of changing the impact point between the two beams is investigated by FEM simulations for further output power optimization. In case of using PVDF beams, the tip displacement of the stopper beam is increased from 13 μm to 32 μm when the length of the lateral overlap between the two beams is decreased from 50% to 3% of the stopper beam length for an input acceleration of 0.1g. This corresponds to a theoretical output open circuit voltage increase from 0.8V to 1.9V and a corresponding 6 times increase in the output power of the stopper beam. This proves the intuitive relationship between the effective stiffness of the two beams in the coupled vibrations phase and the position of the point of impact along the stopper.

In-plane monolithic microscanner with two synchronized, self-aligned flat mirrors and compliant springs

Abstract. This work proposes an architecture for a wide-angle, self-aligned, in-plane monolithic scanner fabricated using the deep reactive ion etching technology. The fabricated microscanner provides an optical scanning in-plane angle of about 86 deg and operates at the speed of 2.73 kHz. The scanning is achieved using two synchronized, flat mirrors coupled mechanically to allow for wide-angle scanning and connected through a compliant structure to allow the use of a linear comb actuator. This wide-angle, in-plane scanning opens the door for many applications, especially for handheld optical displays.

Staggered mode MEMS gyroscope

This paper presents a novel design concept of a MEMS gyroscope comprising a sense mode with a staggered frequency response. Considering a two-degree of freedom sense-mode structure, the bandwidth is enhanced by more than 40%. A post-fabrication electrostatic tuning mechanism based on two tuning electrodes is proposed to achieve resonance frequency trimming. The concept is applied on the design and analysis of fully decoupled gyroscope based on the SOI MUMPS process and operating around a resonance frequency of 5 kHz. The concept is extendable for multi-degree of freedom for wider bandwidth extension.