Europe has a one-stop shop for piezoelectric design which operates out of nine centres including two in the UK at the National Physical Laboratory and Cranfield University.
“It is an industry-academic partnership, here for people who think they need piezoelectric devices in their products,” Dr Markys Cain director of the Piezo Institute told
EW. “We develop new devices and functionality, and we organise training and conferences.”
One of the first projects within the Institute is a transducer for medical ultrasound scanning. “The beauty of the device being developed by the Piezo institute is that it is much smaller and has a wider bandwidth than the transducers used now,” said Cain. “It uses new materials and has a new structure, and there is no loss of sensitivity.”
Along with the UK: France, Germany, Italy, Switzerland, Slovenia, Denmark, Spain and Latvia are contributing. “These countries all have piezo research labs or companies that are world-renowned,” said Cain.
Another internal project is the search for alternatives to PZT - lead zirconate titanate.
“PZT is the industrial workhorse. It is so well characterised and such a good material, but it does contain lead and people want to put stickers saying lead-free on the outside of their products.” said Cain.
This does not mean to say PZT is a known hazard - it has an exemption from the RoHS directive. “The lead is locked-up as an oxide and as far as I know there are no publications that show water leaching lead out of PZT,” said Cain.
Although there are no lead-free materials that can beat PZT, they are coming close: “The alkaline niobate materials for example,” said Cain, “and it is not just ceramics and single crystals like quartz. PVDF [polyvinylidene fluoride] is a piezoelectric plastic that has less output that PZT, but is flexible.”
PVDF has been known for a long time and it used in hydrophones. According to Cain, because of its flexibility, it is being investigated from energy harvesting in clothing.
Electronic tyre pressure monitoring for cars will soon be compulsory in many countries. “This is likely to be the biggest application for piezoelectrics over the next couple of years,” said Cain. “To scavenge tens of mW you need, piezo offers you that functionality at very small length scales.”
Cain is a principle scientist at the National Physical Laboratory in Middlesex which is one of the Institute’s UK bases.
The other UK base is at Cranfield University’s Bedfordshire campus which specialises in thin and thick film piezoelectrics, and had developed devices for companies including TDK.
“We are moving away from the bulk stuff and are depositing the materials in bottom-up in films between 0.5 and 40µm,” scientist and Piezo Institute director Dr Rob Dorey told
EW.
Deposition techniques include screen printing, spray moulding and ink-jet printing of features down to 10µm.
He is looking at tiny energy harvesters that collect a small amount of energy over a long time, that can be used all at once. “So on a bridge, a transducer can collect data and energy, then transmit it all when a van with a transponder drives by once a month,” said Dorey.
Another use for film piezoelectrics could be on-chip voltage transformation. Piezoelectric transformers have been around for a while - used to power laptop backlights. Electrodes induce bulk vibrations into a block of piezo material, and electrodes at another point pick off the energy. The transformation ratio is determined by the geometry of the block and the position of the electrodes.
“A piezo transformer 2-3mm in diameter and 50-60µm thick can transform voltages higher or lower on a chip,” said Dorey. “In the lab, we have made them.”
The Piezo Institute was set-up through an EU Framework 7 research programme in 2008.
Funding comes from its industrial members and from managing research programmes on behalf of the EU.