Ambient energy sources
Ambient energy sources include light, heat differentials, vibrating beams, transmitted RF signals or any other source that can produce an electrical charge through a transducer.
• Small solar panels have been powering handheld electronic devices for years and can produce 100s of mW/cm² in direct sunlight and 100s of μW/cm² in indirect light.
• Seebeck devices convert heat energy into electrical energy where a temperature gradient is present. Sources of heat energy vary from body heat, which can produce 10s of μW/cm² to a furnace exhaust stack where surface temperatures can produce 10s of mW/cm².
• Piezoelectric devices produce energy by either compression or deflection of the device. Piezoelectric elements can produce 100s of μW/cm² depending on their size and construction.
• RF energy harvesting is collected by an antenna and can produce 100s of pW/cm².
Successfully designing a completely self-contained wireless sensor system requires power-saving microcontrollers and transducers that consume minimal electrical energy from low energy environments. Now that both are readily available, the missing link is the high efficiency power conversion product capable of converting the transducer output to a usable voltage.
shows an energy harvesting power system that includes the energy source/transducer, an energy storage element and a means to convert this stored energy into a useful regulated voltage. There may also be a need for a voltage rectifier network between the energy transducer and the energy storage element to prevent energy from back-feeding into the transducer or to rectify an AC signal in the case of a piezoelectric device.