Relying on the piezoelectric effect to convert an applied electrical field into a mechanical strain, the micro diaphragm pump generates pressure in the pump chamber by moving its silicon membrane up or down, drawing in ambient air through a valve and compressing it in the pump chamber before expelling it.
“Our smart pump measures only 25 square millimeters, making it the world’s smallest pump. That said, it still has a high compression ratio,” says Dr. Martin Richter, department head of micro dosing systems at the Fraunhofer Research Institution for Microsystems and Solid State Technologies EMFT in Munich.
Conventional micro diaphragm pumps powered by piezoelectricity generate only relatively low pressure with air; the asymmetry of the piezo effect means a lot of room is required in the pump chamber to move the membrane. This results in a high dead volume within the chamber. Richter and his team came up with a trick to reduce this dead volume and increase the pump’s suction capacity. “We use the piezo effect to specifically preload the diaphragm when assembling the piezoceramic. The advantage of this is that we no longer need a deep pump chamber. This trick enables us not only to build micropumps with high compression ratios but also to make them smaller in size.”
Not just the diaphragm but also the flap valves and the pump chamber are made of monocrystalline silicon, which offers numerous benefits over metals and plastics. For one, the metalloid – which is also used to make solar cells and computer chips – is pliable and fatigue-free. For another, the individual pump components can be etched from the silicon layer with a high degree of precision and subsequently joined together.
To circumvent the relatively high cost of silicon, the researchers aim to further reduce the size of the pump to 10 square millimetres, so it would be economically viable in mass production.
Fraunhofer envisages that such micropumps could boost the measurement accuracy of integrated gas sensors, supporting many new applications, from measuring the concentration of particulate matter, or to analyze breath for alcohol content.
Such micropumps could also find their way as a medical patch to continuously deliver tiny amounts of hormone or pain killer, but also as an implant to help regulate pressure within the eye in treating glaucoma. The pump could also supply machines with precise doses of lubricant, an application that the researchers are currently developing with a partner from industry.
As part of Fraunhofer’s Discover funding program, which supports unconventional and original ideas, Richter and his team is also looking into an additional application: adding scent information to audio and video files. “A headset fitted with our smart pump could deliver precise doses of different scents close to the nose. The gaming industry has already expressed an interest in this.”
Fraunhofer EMFT – www.emft.fraunhofer.de/en.html