Power density

About: Power density is a research topic. Over the lifetime, 9534 publications have been published within this topic receiving 197264 citations. The topic is also known as: volumic power & volume power density.

Thinned-PZT on SOI process and design optimization for piezoelectric inertial energy harvesting

Abstract: This paper presents the design, fabrication, and testing of a thinned-PZT/Si unimorph for vibration energy harvesting. It produces a record power output and has state-of-the-art efficiency. The harvester utilizes thinning of bulk-PZT pieces bonded to an SOI wafer, and takes advantage of the similar thermal expansion between PZT and Si to minimize beam bending due to residual stress. Monolithic integration of a tungsten proof mass lowers the resonance frequency and increases the power output. The harvester dimensions, including the PZT/Si thickness ratio and the proof-mass/total-beam length ratio, are optimized via parametric multi-physics FEA. Additionally, a fabrication process for hermetic packaging of the harvester is introduced. It uses vertical Si vias for electrical feed-throughs. An unpackaged harvester with a tungsten proof mass produces 2.74 µW at 0.1 g (167 Hz), and 205 µW at 1.5 g (154 Hz) at resonance (here, g = 9.8 m/s2). The active device volume is 27 mm3 (7 × 7 × 0.55 mm3). We report the highest power output, Normalized Power Density (N.P.D.), and Figure of Merit (N.P.D. × Bandwidth) amongst reported microfabricated vibration energy harvesters.

Minimizing the instant and accumulative effects of salt permeability to sustain ultrahigh osmotic power density.

Abstract: We have investigated the instant and accumulative effects of salt permeability on the sustainability of high power density in the pressure-retarded osmosis (PRO) process experimentally and theoretically. Thin-film composite (TFC) hollow-fiber membranes were prepared. A critical wall thickness was observed to ensure sufficient mechanical stability and hence a low salt permeability, B. The experimental results revealed that a lower B was essential to enhance the maximum power density from 15.3 W/m(2) to as high as 24.3 W/m(2) when 1 M NaCl and deionized water were feeds. Modeling work showed that a large B not only causes an instant drop in the initial water flux but also accelerates the flux decline at high hydraulic pressures, leading to reduced optimal operating pressure and maximal power density. However, the optimal operating pressure to harvest energy can be greater than one-half of the osmotic pressure gradient across the membrane if one can carefully design a PRO membrane with a large water permeability, small B value, and reasonably small structural parameter. It was also found that a high B accumulates salts in the feed, leads to the oversalinization of the feed, and largely lowers both the water flux and power density along the membrane module. Therefore, a low salt permeability is highly desirable to sustain high power density not only locally but also throughout the whole module.

GaN HFET for W-band Power Applications

Abstract: In this paper we report high frequency GaN power device and measured power performance of the first W-band (75 GHz-110 GHz) MMIC fabricated in GaN material system. The first W-band GaN MMIC with 150 ?m of output gate periphery produces 316 mW of continuous wave output power (Power density = 2.1 W/m) at a frequency of 80.5 GHz and has associated power gain of 17.5 dB. By comparison the reported (1) state of the art for other solid state technologies in W-band is 427 mW measured in a pulsed mode on an InP HEMT MMIC with 1600 ?m of output periphery (Power density = 0.26 W/mm). The reported result demonstrates tremendous superiority of GaN device technology for power applications at frequencies greater than 75 GHz.

Pyroelectric waste heat energy harvesting using relaxor ferroelectric 8/65/35 PLZT and the Olsen cycle

Abstract: Waste heat can be directly converted into electrical energy by performing the Olsen cycle on pyroelectric materials. The Olsen cycle consists of two isothermal and two isoelectric field processes in the electric displacement versus electric field diagram. This paper reports on the electrical energy generated by lanthanum-doped lead zirconate titanate (8/65/35 PLZT) subjected to the Olsen cycle. The material was alternately dipped into a cold and a hot silicone oil bath under specified electric fields. A maximum energy density of 888 J l−1/cycle was obtained with a 290 µm thick 8/65/35 PLZT sample for temperatures between 25 and 160 °C and electric fields cycled between 0.2 and 7.5 MV m−1. To the best of our knowledge, this is the largest pyroelectric energy density experimentally measured with multiple cycles. It corresponded to a power density of 15.8 W l−1. The electrical breakdown strength and therefore the energy and power densities of the material increased as the sample thickness was reduced from 720 to 290 µm. Furthermore, a physical model for estimating the energy harvested by ferroelectric relaxors was further validated against experimental data for a wide range of electric fields and temperatures.