This paper presents a new vibration-based electromagnetic energy harvester using a mechanical frequency up-conversion method for harvesting energy from external low-frequency vibrations within a range of 1-10 Hz. The structure consists of a magnet placed on a diaphragm, a polystyrene cantilever carrying a pick-up coil, and a mechanical barrier which converts low-frequency vibrations to a higher frequency, hence increasing the efficiency of the system. The tested structure proved to generate 88.6 mV and 544.7 μW rms power output by up-converting 10-Hz external vibration to 394 Hz. The obtained power density is 184 μW/cm ³ , with a device volume of 2.96 cm ³ . An analytical model is developed to analyze the behavior of the energy harvester prototypes with various dimensions. The model predicts the performance parameters of the structures within 5% error range. The effect of scaling down the device dimensions is investigated through the developed model and fabricated prototypes. It is shown that the power density of the energy harvester is increased as its dimensions are scaled down, proving that the proposed structure is a good candidate to be used in low-power wireless microsystems operating at low-frequency vibrations.

This paper presents a vibration-based energy harvesting system composed of a compact electromagnetic (EM) power generator and highly efficient full-wave interface electronics in a system-on-package. The system harvests energy from ambient vibrations, and delivers a smooth and reliable dual rail DC supply to power up a practical load. The energy harvester module is an in-house double-coil EM transducer which generates AC voltage in response to low frequency ambient vibrations. Voltage regulation is achieved by the interface electronics at the core of the system, which is designed to rectify the input AC voltage with peak amplitude ranging from several hundred mVs to several Volts, with maximum efficiency. The interface electronics contains an active rectifier with high conversion efficiency (>;80%) for a wide range of load currents (0-42 μA). A passive network, built from low threshold-voltage chip diodes and capacitors, generates a dual supply voltage from one of the coils to power up the active rectifier. The autonomous system of 16 cm³ volume (comparable to the size of a C-Type battery), delivers 54 μW to a 37-μA load through a dual rail 1.46 V DC voltage with total system efficiency of 81%, when subjected to low frequency (8 Hz) external vibrations. The maximum overall system power density has been validated to be 6.06 μW/cm³, three times what was previously reported for a batteryless vibration driven system.

A continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell employing the element rotation method is designed and fabricated. The unit cell comprises a double layer nested ring-split ring structure realized as microfluidic channels embedded in Polydimethylsiloxane (PDMS) using soft lithography techniques. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is air. Movement of the liquid metal together with the split around the ring provides 360 ^° linear phase shift range in the transmitted field through the unit cell. A circularly polarized unit cell is designed to operate at 8.8 GHz, satisfying the necessary phase shifting conditions provided by the element rotation method. Unit cell prototypes are fabricated and the proposed concept is verified by the measurements using waveguide simulator method, within the frequency range of 8-10 GHz. The agreement between the simulation and measurement results is satisfactory, illustrating the viability of the approach to be used in reconfigurable antennas and antenna arrays.