Good vibrations

The cars and aircraft of the future will be safer and the buildings and production lines more efficient thanks to wireless sensors powered by tiny generators being developed at ANU.

Are you warm enough? Maybe you're too hot. If you're reading this inside there's a good chance that a control system is regulating your comfort.

If you're not comfortable it could well be because you are some distance away from the thermometer that is telling the system what to do.

Climate control systems are designed to keep us comfortable by monitoring the temperature and keeping it to the desired level.

Somewhere in a centrally-heated or air-conditioned home there will be a thermometer, keeping track of the temperature around it and adjusting the heating/cooling system accordingly.

Building management systems divide a modern office building into zones with a sensor in each zone monitoring the temperature.

With even the most sensitive of these systems, one area is likely to be too hot or too cold and the sensor will never know. In winter the heating will probably be too high and in summer the cooling will be overworked, wasting money and energy all because we don't have enough information.

The answer to this is simple: more sensors.

More sensors means more wires, more wires means more expense. It would be simpler and cheaper just to put the sensors wherever we need them, the problem then is how to power them.

Dr Shad Roundy from the Faculty of Engineering and Information Technology at the Australian National University, is working on tiny generators that are able to produce enough power to run a sensor and transmit its data.

The sensors won't need wires or batteries and the generators never need refuelling as they can 'scavenge' all the power they need from energy that is going to waste all around us.

A specialist in mechatronics, a combination of electronics and mechanics, Dr Roundy began his career as a mechanical engineer.

"I was working on an electronics project with some guys who were developing wireless sensors, they said they were having problems powering them - imagine the cost of paying someone to go and change all the batteries every couple of weeks," he recalls.

He began investigating scavenging power and from there he was hooked. While light and heat offer the potential for generating electricity, vibrations are the energy source he has settled on initially.

The Massachusetts Institute of Technology in the US has named wireless sensors one of the technologies that will change the world over the next 30 years.

Dr Roundy believes there are so many applications for sensors that power themselves, the tiny technology will soon be all around us.

"These can be used anywhere that sensors can improve efficiency and it is hard to run wires.

"These sensors are going to become ubiquitous. The falling cost of manufacturing electronics means it will soon be cheaper to install these than to pay someone to put in wires.

"Two of the biggest obstacles have been price and power generation, but by scavenging energy these devices don't need wires or batteries."

Without the need to install wires or change batteries the sensors can go where conventional sensors cannot, with applications ranging from vehicle safety to 'intelligent' buildings.

For example, a sensor on the inside of a car tyre could be powered by vibrations from the road and send back information on the tyre's pressure to the car's on-board computer.

In aircraft, vibrations from the wings could be made into electricity, which then powers a sensor gathering potentially lifesaving data about their condition.

The energy efficiency of a building could be increased with more data on temperature, humidity and air velocity. Furthermore, in factories, sensors along a production line could be used to monitor the performance of machinery.

Dr Roundy's generators use piezoelectric material, similar to that used in the ignition systems of some barbecues, which when stretched or compressed generates current.

The generators look like a tiny diving board with a metal weight where the diver would stand. Vibrations cause the weight to bounce on the end of the board that has piezoelectric material on either side.

As the vibrations force the board to bend, it creates current. Enough to run the sensor and transmit its data back to a central computer.

Dr Roundy has also developed a device to transform the electricity from an alternating current (a result of the bouncing motion producing peaks and troughs of current) into steady direct current, and to store the power until it is needed by the device to transmit information.

It is important to store the power, as the transmitter will only need to be operating when it has information to send back or is relaying data from another sensor.

It is likely that the sensors will be part of large networks relaying information about a vehicle or building. Power can be saved if the transmitter only needs to be strong enough to send a message a short distance.

Dr Roundy, whose pioneering research saw him named one of the world's top 100 young innovators by MIT's Technology Review magazine, is also working on tiny kinetic generators that are as small as a few hundred microns across.

These create power from movement in a similar way to watches that never need winding. He is refining these to generate enough power to run the equally tiny sensors of the future.