Sensors get a new role as energy scavengers

Powercast Corp.’s P2110 battery-free energy harvester converts ISM-band RF energy into a dc voltage and is used in a MiWi point-to-point wireless sensor network unit.

The race to cash in on novel energy harvesting ideas has companies outside the traditional transducer market bringing out products. For example, Japan’s Brother Industries Ltd., better known for producing printers, has developed vibration energy harvesters in form factors that let them replace AA and AAA batteries. The compact size enable the devices to generate energy with a simple shake of the controller.

Inside the battery-shaped case are an electromagnetic induction generator and a 500-mF capacitor for energy storage. The output of the AA-size generator is 10 to 180 mW. Proof-of-concept versions have reportedly produced about 1.6 and 3.2 V for the AA-size generator and 2 V for the AAA-size generator. The units are only suitable for low-duty-cycle operation as in TV remote controls which typically consume between 40 to 100 mW.

RF energy

Someday the electromagnetic transmissions beamed from your garage door opener could be a source of electrical power. That is the idea behind devices from Powercast Corp. which take advantage of widely available RF energy in the 902 - 928 MHz ISM band. This part of the RF spectrum is occupied by low-power, non-licensed devices such as simple toys, wireless security systems, wireless telemetry, and wireless automatic meter-reading systems. The Powercast devices typically use the energy they harvest to power MiWi point-to-point wireless sensor networks.

The Powercast transducers have a peak efficiency of about 70% for input power in the 20 mW to 40 mW range. They will also harvest power from signals outside the ISM band, though with diminishing sensitivity. The Powercast P2110 battery-free RF energy harvester receiver converts RF energy to a dc voltage. It mounts on a pc board that includes a Microchip Technology PIC 24 XLP microcontroller and an MRF24 radio module. On the board, which requires 3.3 V for operation, is a 50-mF capacitor for energy storage (It can be as low as 3,300 μF.), as well as discrete temperature, humidity and light sensors.

Some makers of microcontrollers, such as Microchip Technology, have developed low-power controllers with energy harvesting applications in mind. In fact, semiconductor manufacturers like Jennic in the U.K. target wireless energy harvesting by developing specific supporting parts like the firm’s JN5148 microcontroller. The unit includes a proprietary 32-bit RISC processor, a 2.4-GHz radio and 128 kbytes of RAM and peripherals.

The part harvests energy from vibration, heat, light, and RF energy. The firm teamed up with Micropelt for thermo generation; Cymbet for solar power conversion and storage; AdaptivEnergy for piezoelectric harvesting of mechanical impulse, shock and vibration; and Powercast for RF energy harvesting.

Cymbet also makes the EnerChip EP CBC 915 energy processor, which it claims is the world’s first universal energy harvesting power management unit across all energy harvesting transducer technologies, including photovoltaic, thermoelectric, piezoelectric and electromagnetic. It uses patent-pending Maximum Peak Power Tracking technology that constantly matches any energy harvester transducer input impedance. It is designed for optimal power management for Cymbet’s CBC050 EnerChip rechargeable solid-state thin-film battery that has no liquid or gel constituents.

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