One of the MEMS devices tested by researchers at LNE using their harmonic distortion technique

New technique for MEMS power measurement

Researchers have discovered a new technique to accurately measure the power requirements of micro-electro-mechanical systems.

MEMS are very small devices that can be used as remotely powered sensors to measure variations in the physical environment such as changes in force, light, or motion, or conversely as actuators that convert changes in energy back into motion.

Ranging in size from 20 micrometres to a millimetre, they are made up of components that interact with the outside environment such as microsensors, and a central unit that processes data allowing MEMS to make decisions based on the information they receive.

Current applications for the devices include use in accelerometers in airbag deployment systems, inkjet printer heads, and rotation measurement systems for smartphone displays.

But development of the technology has been held back by a lack of understanding of the potential power requirements and outputs of the devices as mechanical components are often embedded in protective packaging, making them hard to access and consequently hindering developers or customers from understanding how best to use the devices.

To address this issue, Dr Alexandre Bounouh and colleagues at the EU-funded Laboratoire national de métrologie et d'essais (LNE) in France, have developed a new experimental set-up to find the mechanical values and properties of any MEMS device through electrical measurement.

“Our accurate and traceable technique could be implemented for on-line production tests and measurements,” says Bounouh.

“This could deliver key competitive edge to EU companies and support large-scale manufacturing excellence by introducing metrological principles into industrial processes.”

The technique will be presented today at the TechConnect World Conference 2013 and the researcher team, part of the European Commission-backed Metrology for Energy Harvesting Project, believe it will help improve performance, functionality, and reliability of MEMS around the world.

Dr Bounouh’s technique works by applying a current across the device with a varying frequency allowing users to analyse the harmonic content of the output voltage of the component parts.

With some additional calculations the technique electrically determines all the mechanical characteristics of the MEMs device including the damping factor (a negative impact on the amplitude of oscillations), and the frequency that determines the maximum electrical power generation from mechanical vibrations of MEMS transducers.

“It’s very easy and quick to make the measurement because all you are doing is connecting your system with two wires, applying a current and sampling the output signal,” said Dr Bounouh.

“This method doesn’t require any big investment but still delivers very precise knowledge of the parameters and limits in the performance of your device and could easily be scaled up to measure large scale energy harvesting technologies across the microscopic and macroscopic scales.”

Since its development, several MEMS devices have been tested at LNE using the technique and their mechanical resonant frequencies have been measured with only a tiny uncertainty.

In future, Dr Bounouh and his colleagues believe the technique can be used to provide feedback on production methods that will allow manufacturers to design MEMS to the needs of each particular system they operate in.

More accurate knowledge of the product output and energy requirements will also affect the choice of device from potential consumers who will now be able to select only those with optimised performance for their particular sector.

LNE is one of seven national research centres across Europe that makes up the Metrology for Energy Harvesting Project, funded by the European Commission through the European Metrology Research Programme.

The project represents the first co-ordinated international attempt to apply the principles of metrology (measurement science) to energy harvesting products and materials.

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