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Device Captures Vibrations to Power Wireless Sensors

Energy harvesting MEMS device (Arman Hajati/MIT)

Energy harvesting MEMS device (Arman Hajati/MIT)

Engineers at MIT have designed a miniature device that harvests energy from low-frequency vibrations to power wireless sensors for industrial or environmental monitoring. Mechanical engineering professor Sang-Gook Kim and Arman Hajati, now at FujiFilm Dimatix in Santa Clara, California, published their findings last month in the  journal Applied Physics Letters (paid subscription required).

While wireless sensors can provide valuable data for a host of industrial and regulatory functions, they need power to work, and batteries have become a limiting and expensive source of electricity. To get around this constraint, researchers are trying to harness electricity from low-power sources where the sensors operate, such as vibrations from swaying bridges, humming machinery, and rumbling foot traffic.

Researchers have been able in the lab to generate electric power from ambient energy, but have run into materials, operational, and financial obstacles when they tried taking their devices out to the real world. Kim and Hajati have addressed some of those limitations in a new microelectromechanical system (MEMS) device.

The new MEMS, about the size of a quarter (pictured at top), is a microchip with a structure like a bridge that’s anchored to both ends of the chip. The chip has a single layer of piezoelectric material that naturally accumulates an electric charge in response to mechanical stress, such as vibrations.

The researchers discovered this structure could respond to a range of low frequencies, thus making it more applicable to real-world applications where vibration frequencies varied. The researchers calculated that the device was able to generate 45 microwatts of power with just a single layer of piezoelectric material, an improvement of two orders of magnitude compared to current designs.

Kim and Hajati still need to optimize the chip’s design, to accommodate even lower frequencies, and generate more power. “Our target is at least 100 microwatts,” says Hajati, adding “If you generate 100 microwatts, you can power a network of smart sensors that can talk forever with each other.”

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