-Thermoelectric energy harvesting requires a substantial temperature difference ΔΤ to be available within the device structure. This has restricted its use to particular applications such as heat engine structural monitoring, where a hot metal surface is available. An alternative approach is possible in cases where the ambient temperature undergoes regular variation. This involves using a heat storage unit, filled with a phase change material, to create an internal spatial temperature difference from the temperature variation in time. In this paper, the key design parameters and a characterisation methodology for such devices are defined. The maximum electrical energy density expected for a given temperature range is calculated. The fabrication, characterisation and analysis of a heat storage harvesting prototype device is presented for temperature variations of a few tens of degrees around 0 °C , corresponding to aircraft flight conditions. Output energy of 105 J into a 10 Ω matched resistive load, from a temperature sweep from +20 °C to -21 °C , then to +25 °C is demonstrated, using 23 g of water as the phase change material. The proposed device offers a unique powering solution for wireless sensor applications involving locations with temperature variation, such as structural monitoring in aircraft, industrial and vehicle facilities.

Executive Summary

A metal-catalyst-free growth method of carbon nanotubes (CNTs) has been developed using chemical vapor deposition of CNTs on carbon-implanted SiGe islands on Si substrates. From scanning electron microscopy and Raman measurements, the fabricated CNTs are identified as single-walled CNTs with a diameter ranging from 1.2 to 1.6 nm. Essential parts of the substrate preparation after CVD SiGe growth and carbon implant are a chemical oxidization by hydrogen peroxide solution and a heat treatment at 1000 °C prior to CNT growth. We believe that these processes enhance surface decomposition and assist the formation of carbon clusters, which play a role in seeding CNT growth. The growth technique is a practical method of growing metal-free CNTs for a variety of applications, while at the same time opening up the prospect of merging CNT devices into silicon very-large-scale-integration technology.

Abstract-The difficulty of maximizing the proof mass, and lack of broadband operation, are key issues for miniaturized energy harvesting devices. Here, a novel electrostatic energy harvester is presented, employing an external, free-rolling proof mass to address these issues. A description of the operating principle is given and the kinetic dynamics of the cylinder are analyzed. The electrostatics of the system are simulated, identifying the device performance for different dielectric dimensions and surface specifications. The fabrication of a prototype device is presented and physical characterization results demonstrate a successful fabrication technique for dielectric sizes down to 100 nm. Capacitance measurements reveal a capacitance ratio of 4 and are in agreement with simulation results. A voltage gain of 2.4 is demonstrated. The device is suitable for energy harvesting from low frequency, high amplitude ambient motion sources, such as the human body.

This paper introduces an inductive method for harvesting energy from current-carrying structures. Numerical simulation of a structural beam shows that the skin effect can lead to significant current concentration at edges, providing a five-fold power benefit at such locations, even at frequencies below 1 kHz. The use of a rectangular ferrite core can provide a ×4 power density improvement. The adoption of funnel-like core shapes allows the reduction of core mass and coil frame size, leading to significant further power density enhancement. Magnetic field simulation and coil analysis demonstrate a power density increase of ×49 by ferrite funnels, in comparison to a coreless coil. Experimental results demonstrate rectified power over 1 mW delivered to a storage capacitor, from a 40 × 20 × 2 mm core-and-coil, in the vicinity of a spatially distributed 20 A current at 800 Hz. Rectification and impedance matching are studied experimentally using a voltage doubler circuit with input capacitor tuning to counteract the coil reactance. Experimental results from a spatially distributed 30 A current at 300 Hz and a 1:7 funnel core demonstrate power density of 36 µW/g (103 µW/cm 3 ), opening up the way to non-invasive inductive powering of systems in the vicinity of current-carrying structures.