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This paper presents a non-resonant vibration energy harvester (VEH) optimized for 0.5-1.0 Hz at 0.2g acceleration, typically associated with human motion in daily activities. Different amounts of water-based and oil-based ferrofluids as liquid bearings have been studied in an experimental setup with a precisely controllable spacing between top and bottom coil plates where the magnet array and ferrofluid bearings reside. The sub-miniature VEH (1.4cc and 3.3gram) steadily generates voltages between 0.5-1.0 Hz and is measured to produce an open-circuit voltage of Vrms = 19.5 - 31.9 mV (or 0.33-0.89 μW into a match load) from 0.2g sub-Hz applied acceleration. The highest figure of merit (FOM) of the VEH at 0.2g at 1.0 Hz is 15.5 μW/cc/g2. 

This manuscript presents airborne jet propulsion by audio sounds and ultrasounds through orifices formed by bulk-micromachining of a silicon wafer. The propeller is integrated with a small, printed circuit board (PCB) with a DC/DC converter, an oscillator, and a power amplifier, all powered by a 100F lithium-ion capacitor to make the propeller operable wirelessly. The peak propulsion force of the wireless propeller is measured to be 63.1 mg (or 618 mN) while the packaged wireless propeller’s weight is 10.6 g, including the drive electronics and adapter) when driven by 2.5kHz sinusoidal voltage with 21.4Vpp. A wired propeller (with 563 mg weight without adapter) is shown to high jump, long jump, wobbly fly, and propel objects. Also, the propeller is shown to work when driven by ultrasounds with a maximum propulsion force of 8.4 mg (82 mN) when driven by 20kHz, 20Vpp sinusoidal signal. Varying the frequency gradient of the applied sinusoidal pulses is shown to move the propeller to the left or right on demand to reach a specific location. 

This paper describes a wrist-wearable non-resonant vibrational energy harvester (1.4 cc in volume and 3.2 gram in weight, with two arrays of wound copper coils adjacent to a movable array of magnets suspended by ferrofluid bearing) for generating power from a human's walking motion. Thousand-turn coils are wound with a customized coil winding machine, and two sets of such coils are mounted on the top and bottom of a movable magnet array to obtain 20% improvement (compared to the earlier version based on an electroplated coil array) on the figure of merit (FOM) defined to be the power (delivered to a matched load) divided by the device's volume for a given acceleration of 1 g at 2 Hz.