As concerns over the health effects of particulate matter grow, it’s possible that in the future smartphones with an inbuilt gas sensor could be used to warn of heavy exposure. Researchers at the Fraunhofer Research Institution for Microsystems and Solid State Technologies EMFT in Munich have now developed a ‘powerful’ micro diaphragm pump which could be used to deliver ambient air to the sensor.
"Our smart pump measures only 25 square millimetres, 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 Fraunhofer, in a statement.
Richter and his team used the piezoelectric effect to convert an applied electrical field into mechanical strain, in turn generating pressure in the pump chamber. Alternating voltage helps move the silicon up and down, which in turn draws in ambient air through a valve and compresses it in the pump chamber before expressing it.
Reducing ‘dead volume’
Conventional micro diaphragm pumps powered by piezoelectricity generate relatively low pressure with air, meaning a significant amount of room is required in the pump chamber to move the membrane. This in turn results in a high dead volume – a large volume of residual gas within the chamber.
Richter and his colleagues found an innovative solution to this problem. "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."
The diaphragm, flap valves and pump chamber are all made of monocrystalline silicon, which offers benefits over metals or plastics. Used to make solar panels and computer chips, it is pliable and fatigue free. The individual pump components can be etched from the silicon layer with a high degree of accuracy, making them simple to join together.
A major downside however, is silicon’s relatively high cost. It is for this reason that the team are striving to make the pump as small as possible.
“Our goal is to reduce the size of the pump to 10 square millimeters to make its mass production profitable. We are well on track to achieving this," Richter says.
A range of applications
The microscopic pump is not just limited to gas sensors in smart phones. According to a press release from Fraunhofer, it could also be used to supply machines with precise doses of lubricant.
“This is an application that we are currently developing with a partner from industry,” Richter revealed.