Sensors get a new role as energy scavengers

Microfiber composite sensors from Smart Materials Corp. are essentially encapsulated piezo ceramics that can act as sensors and actuators in response to strain/stress.
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A car zipping over a bridge, an oven with sides warm to the touch, and a radio-controlled model car — who would have ever guessed these every-day facets of modern life could be sources of energy? That is increasingly the case, thanks to improvements in sensors that double as energy harvesting devices. Plop a vibration-harvesting sensor next to a busy roadbed and it may be able to produce enough energy to power a small circuit for keeping tabs on structural conditions. Inputs for energy scavenging sources can be found in the human body, may be emitted by machinery such motors, or be found in water and soil.

Moreover, the integrated circuits that work with such sensors are becoming smaller, are more sensitive to low-level signals, and need less power for their own operation. These qualities now make energy scavenging systems candidates for a wide range of applications in medical, automotive, environmental, military, commercial, consumer and infrastructure areas.

There are several methods for converting mechanical or thermal energy into electricity. The technologies employed to do so include piezoelectric, capacitive, RF, inductive coupling, solar, and temperature difference principles. These sensing technologies are getting more efficient, converting more physical energy to electricity.

A merging of two chips with inversely doped thin-film thermoelectric structures in this device from Micropelt GmbH forms a functional thermo-generator.
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Several IC manufacturers are trying to encourage the development of energy harvesters, particularly for powering wireless communications. Because the design of energy harvesting equipment involves working with low voltages and currents, it can be tricky to put together working circuits. To simplify the process, makers of energy harvesting ICs are joining up with sensor manufacturers to offer development kits that include demo boards, software, and firmware necessary to get up and running.

The piezoelectric effect

One of the most common forms of energy harvesting makes use of the piezoelectric effect, wherein some materials such as certain ceramics and crystals, can generate electricity in response to an applied mechanical strain. This capability is also reversible.

However, piezoelectric sensors aren’t necessarily traditional crystals. Smart Materials Corp. takes advantage of the piezoelectric effect with its macro fiber composites. It developed them at the National Aeronautics and Space Administration (NASA) in the late 1990s. These MFC sensors/actuators are aimed at picking up mechanical vibrations and body sounds and at ultrasound applications. They serve a wide range of flow-metering and structural-health monitoring uses.

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