Energy-scavenging power sensors

It can be inconvenient to replace batteries in electronic devices that need to work for a long period of time, either in biomedical monitoring systems worn by a patient or in monitors for machinery or industrial installations in remote or inaccessible situations.

But new technology being developed by MIT Prof Anantha Chandrakasan and alumnus Yogesh Ramadass PhD '09 could provide power for such sensors just from differences in temperature between the body (or other warm object) and the surrounding air, eliminating or reducing the need for a battery.

The MIT devices can harness differences of one or two degrees, producing about 100 µW but still usable electric power.

As a result of research over the last decade, the power consumption of various electronic sensors, processors and communications devices has been greatly reduced, making it possible to power such devices from very low-power energy-harvesting systems such as the wearable thermoelectric system.

Such a system, for example, could enable 24-hour-a-day monitoring of heart rate, blood sugar or other biomedical data through a simple device worn on an arm or a leg and powered just by the body's temperature, which would almost always be different from the surrounding air.

Or it could be used to monitor the warm exhaust gases in the flues of a chemical plant, or air quality in the ducts of a heating and ventilation system.

The key to the technology is a control circuit that optimises the match between the energy output from the thermoelectric material (that generates power from temperature differences) and the storage system connected to it, in this case a storage capacitor.

The present experimental versions of the device require a metal heat-sink worn on an arm or leg, exposed to the ambient air. "There's work to be done on miniaturising the whole system," Ramadass says. This might be accomplished by combining and simplifying the electronics and by improving airflow over the heat-sink.