Sophisticated electronics are within reach of average users. Cooperation between wireless sensor networks and existing consumer electronic infrastructures can assist in the areas of health care and patient monitoring. This will improve the quality of life of patients, provide early detection for certain ailments, and improve doctor-patient efficiency. The goal of our work is to focus on health-related applications of wireless sensor networks. In this paper we detail our experiences building several prototypes and discuss the driving force behind home health monitoring and how current (and future) technologies will enable automated home health monitoring.
To enable self-sustaining long-lasting wireless condition monitoring sensors, a small mechanical vibration energy harvester using electromagnetic transduction was constructed and used to harvest vibrations from large industrial pump motors and machine tool. The prototype harvester was roughly the size of a cube with 2.5 cm long sides. Power ranging from 0.2 to 1.5 mW was harvested from 15 to 30 kW water pump motors. For a machine tool, metal cutting vibrations and rapid jog events were explored as possible harvestable sources of energy. Power ranging from 0.9 to 1.9 mW was harvested during facemilling operations, and it was shown that rapid jog events could be harvested. The power levels harvested from the pump motors and machine tools are sufficient to provide the time-averaged power requirements of commercial wireless sensor nodes, enabling sensor nodes to overcome the finite life of replaceable batteries.
A design methodology is proposed for electronic systems powered by energy harvesting. The methodology first considers the operating environment. It then evaluates the supply-side (the attributes of the harvester), the demand-side (the engineering application or load which receives and uses the converted power), and the power conditioning needed between supply and demand. A test case is presented in which the vibrations of an electromagnetic device are harvested, converted, and used to power a wireless sensor node. Such a node is being used for the condition based monitoring of manufacturing equipment.
Most vibrational harvesting systems are resonant based systems that generate maximum power when the resonant frequency matches the fundamental mode of the ambient environment. Because microsized devices tend to have high natural frequencies, it is difficult to match the generator resonant frequency to environmentally available frequencies. This problem is addressed here by considering a multi-turned planar beam geometry for an electromagnetic resonator designed to resonant in the environmental frequency range while maintaining a small footprint on the order of 1 cm2. This work considers the application of powering wireless sensor nodes on machine tools, which are characterized by 10 m/s2 accelerations at 70Hz at the base of a 5 hp machine tool. Taking advantage of toothed iron magnetic circuit geometry, a theoretical power density of 8 mW per cubic centimeter at one g of acceleration is shown to be viable.
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