Combined harvester

A new era for monitoring machinery is possible with the production of microgenerators that harvest energy from the vibrations of equipment — meaning sensors no longer need wires or batteries.

'They turn the vibrations of the machine they are monitoring into an electric current to power both the sensor and the wireless transmitter which sends the data to the condition monitoring system,' said Roy Freeland, chief executive of Southampton-based Perpetuum.

Until now most sensors have had to get their energy either through wiring or from a battery. It can be costly and inconvenient to retrofit wired sensors, and there are also expenses associated with replacing batteries.

Perpetuum's combined microgenerator and sensor unit doesn't need those conventional power sources so it can simply be attached by magnet or studs to machinery. 'It is truly wireless,' said Freeland.



Detects deviation

The parasitic unit performs a neat trick. The microgenerator turns the energy from the vibrations of its host into an electrical current that powers a sensor. This detects any deviation from the signature frequency of the same host — a change that could indicate the development of a fault.

The unit converts kinetic energy from vibration of equipment running at mains frequency (50 or 60Hz) and can generate up to 100µW when attached to a surface exhibiting a minimum vibration magnitude of 16mg between 59Hz and 60Hz. This is sufficient to power a wireless transmitter sending up to six kilobytes of critical condition monitoring data every few minutes, or smaller amounts of data, such as temperature readings, several times a second.

Perpetuum, a spin-out from Southampton University, received a patent for its technology this month. It has been running trials of its pre-production units since last year, but has now started full production of more powerful models following an order from a major international oil company. The new unit, the PMG17, is capable of generating useful energy from levels of vibration that are 35 per cent lower than previously possible, and across a large bandwidth of vibration frequencies.

Each unit is 53mm in diameter and 53mm deep. It contains a static coil and a rare earth magnet. 'The university team investigated the potential of using piezo-electric materials but found they couldn't beat a coil and magnet,' said Freeland. While others have tried similar designs, Perpetuum has succeeded by damping the movement of the magnet in a clever way.

'We have combined mechanical, electro-mechanical and electronic damping in a delicate balance to optimise the movement of the magnet and get the best out of the microgenerator,' said Freeland. While the arrangement of the components inside the PMG17 are a closely-guarded secret, a patent awarded to Perpetuum and published this October shows the magnet as part of an armature whose pivot passes through a coil. Although the patent does not specify its function, a fixed block of high-permeability material placed between two arms of the armature could be tuned continually to damp movement.

Perpetuum wants a slice of a large and growing market. Shipment of radio frequency/microwave wireless products for industrial monitoring and control applications in north America alone will increase from £81m in 2004 at a compound annual growth rate of 36.6 per cent to £221m in 2007, according to a report published last year.



'Fit and forget'

The company believes its products will compete favourably with both wired and battery-powered units. 'It won't compete with a battery unit on price, but it will when the cost of replacing batteries is taken into account,' said Freeland. 'Ours is fit and forget'.

One Perpetuum package, including support, costs about £1,200, though prices could fall to as little as £100 with sufficient volume. 'It has been reckoned that the wiring of a sensor in a plant costs up to £3,000, or 10 times as much in an explosion risk area.'

An earlier version of the technology, the PMG7 (The Engineer, 27 February) has been proven in a series of field trials with Yorkshire Water, the US Navy and a major international oil company. The trials have been completed using a remote sensing module from Perpetuum's US partner, RLW of State College, Pennsylvania.

In February Perpetuum attracted £2.2m in further investment — £1.4m of it coming from UK venture capital company Quester. Henry Sallitt, an investment director at Quester, said: 'This is a very exciting opportunity in what is forecast to be a very substantial market.

'Perpetuum is a good example of the strong technology coming out of the UK's leading universities, and is indicative of the increasing number of high quality early-stage investment opportunities we are seeing.'