Two types of electric power generator systems that automatically extract power from oscillating motion of a human body or vibration of machines and structures are proposed and studied. The first system utilizes self-excited rotation of an eccentric rotor that rotates in one direction in synchronization with the applied oscillating motion. Connecting an electrical load to the generator increases the damping about the rotor axis, and numerical analysis shows that there exists an upper limit to this damping to maintain the self-excited rotation mode. Excessive damping reduces the rotor to a swinging motion, resulting in decreased power output. The second type utilizes resonant vibration of a permanent magnet unit suspended by a set of springs. In order to maximize the output power, a micro controller changes the connection of the generator coils, which in effect changes the electro-mechanical damping, to keep the vibration amplitude within the allowable stroke. Theoretical analysis and experimental results are presented for both systems.
Intra-body communication is a wireless means of exchanging information within a personal area network (PAN) between wearable electronic sensors and devices. The feasibility of intra-body communication is confirmed through several experiments on signal propagation within the human body, and a human phantom is designed and used to obtain reproducible results over repeated experiments. Based on the results of these experiments, a prototype transmission system is constructed using aluminum electrodes powered by 3 V DC and operating in the 10.7 MHz frequency modulation (FM) band. This prototype is demonstrated to be capable of transmitting analog signals through the human subjects in the presence of external noise. Digital data transmission at 9600 bps is also achieved using newly fabricated 10.7 MHz frequency shift keying (FSK) transmitter and receiver devices. The carrier frequency of 10.7 MHz is the intermediate frequency of FM radio receivers, meaning that the proposed system can make use of a wide selection of inexpensive, commercial radio frequency devices.
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