Monday, September 15, 2014 — 11:00 AM EDT

Candidate

Mohammed AlShareef

Title

Electrically Small Particles for Energy Harvesting in the Infrared and Microwave Regimes

Supervisor

Omar Ramahi

Abstract

Harnessing energy from clean and sustainable resources is of crucial importance to our planet. Several attempts through different technologies have been pursued to achieve efficient and sustainable energy production systems. However, having systems with a high energy harvesting efficiency and at the same time low energy production cost are challenging with the existing technologies. In this research, several novel structures based on electrically small particles are proposed for harvesting the microwave and infrared energy efficiently. First, a proof of concept demonstrates a metamaterial unit cell's ability to harness the ambient electromagnetic energy. A split-ring resonator (SRR) representing the metamaterial unit cell is designed at a microwave frequency (5.8 GHz) and then fabricated by using printed circuit board technology to prove this concept. A bow-tie antenna, operating at the above frequency, is also designed to show the power efficiency improvement achieved by utilizing the SRR. More than 37% of power efficiency is achieved using SRRs-based structure compared to the 13% of the bow-tie antenna. A new efficiency term is also proposed to take into account the size reduction and efficiency advancement resulting from SRR structures. To this end, two comparable arrays of SRRs and bow-tie antennas are made. Power efficiency of 63.2% and 15.3% for the SRRs and bow-tie arrays, respectively, are achieved. Another structure composed of an ensemble of electrically small resonators for harvesting microwave energy is presented. A flower-like structure composed of four electrically small SRRs arranged in a cruciate pattern, each with a maximum dimension of less than ?o/10, is shown to achieve more than 43% microwave-to-alternating current (AC) conversion efficiency at 5.67 GHz. Even- and odd-mode currents are realized in the proposed harvester to improve the efficiency and concurrently reduce the dielectric loss in the substrate. An experimental validation is conducted to prove the harvesting capability.

To extend the work to operate at the far-infrared regime, a novel structure based on electrically small resonators is proposed for harvesting the infrared energy and yielding more than 80% harvesting efficiency. The dispersion effects of the dielectric and conductor materials of the resonators are taken into account by applying the Drude model. A new scheme to channel the infrared waves from an array of SRRs is proposed, whereby a wide-bandwidth collector is utilized by employing this new channeling concept. With the same pattern of the flower-like harvester operating in microwave regime, a new structure composed of electrically small SRRs, each of whose greatest length is less than ?o/21, is proven to achieve more than 85% of power harvesting efficiency at 0.348 THz. Furthermore, the infrared energy harvesters are fabricated using nano-fabrication tools. At last, the infrared harvesters are experimentally validated with the numerical findings using THz time-domain spectroscopy (THz-TDS).

Location 
EIT building
Room 3142

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