I recently did a presentatiton on Low-power Piezoelectric Micropump Driving Module at the MIDEM International Conference on Microelectronics, Devices and Materials. The module was developed at the Laboratory of Microsensor Structures and Electronics. Despite its small size the module is fully capable of driving reasonably sized piezoelectric micropumps and even features arbitrary signal synthesis. It includes battery management circuitry and can also be used as a small high voltage linear amplifier. The module may be controlled by computer via USB or can work in stand-alone mode.
The micropumps are used for example in some laboratory and portable instruments and also in drug delivery. They may be used to deliver a known amount of a fluid as in staining / titrations but I have also seen them used in art projects. An art group used them in installation to draw clock / time on a river using food coloring. I think the project was called flowing time, however can’t find any link to their website.
So what are these piezoelectric micropumps (link removed due to being marked as harmful, try google searching for the term 😉 )? Micropumps are small fluid or gas pumps. They are mainly used in applications requiring small flow up to a few mililiters per minute. The micropumps can also be used in control applications where flow and/or pressure needs to be held stable or in metering applications. Their pumping action is not based on external “mechanical” actuator, but a piezoelectric material is used in pump which deflects as it is powered by applied voltage. The deflection of piezoelectric membrane makes the pumping in / out of the pump. For flow directionality some kind of valve or another type of non-linear fluidic element needs to be used (the flow in forward direction needs to be easier than backward). Pumps may also be designed with active piezoelectric valves, but these require more sophisticated drivers as multiple piezoelectric elements need to be driven. The following image shows the micropump operation principles, this page also has a neat animation of dual chamber micropump.
Piezoelectric materials can also be found in some beepers, for example those used in song cards. Depending on the thickness and needed deflection of the material varies the driving voltage. For only making sounds a low voltage is usually sufficient, however for pumping action which is more energetic and requires higher deflections of the material the voltages can be quite high – in the order of few hundred volts. As the power and currents required are not that high this is not really dangerous. It can however be quite challenging to effeciently generate such high voltages in a portable application where the system voltage is dictated by the battery type used and is usually only a few volts. The developed micropump driver overcomes these challenges and even offers arbitrary signal synthesis (you can freely choose signal shape, frequency and voltage) which is more common in larger benchtop instruments.
The module can be programmed / controlled by PC software while being connected to a computer. Also software for automatic sequencing of the output signals and for automated characterization of micropumps was developed.
When in stand-alone mode the module basically holds the last set parameters. However it can also be programmed with custom programs, for example to serve as a full microfluidic control system. A small system was set up to demonstrate the stand-alone working mode and battery management functions. Watching the micropump pump fluid at steady 1ml/min is not really that exciting and fluid pumping can also be messy (lol, as messy as spilling a few ml of colored water). Therefore I set up the driver to drive the pump with signals from 100Hz to 1kHz (normal pumping is usually somewhere in 50-200Hz) and the pump fluid connections were left unconnected. With air as the pumping media and at these higher frequencies the pump also works as a piezoelectric sounder so you can hear it “working”.
This image shows the demo system, the battery is on the left, followed by the power switch and the driver circuit. The driver circuitry measures only 25x50mm so it fits nicely on a back of double AAA holder. On the right is a micropump that is being powered by the driver.
The driver PCB has the power management section on the left hand from the battery wires up to the voltage regulator (large black element just below the red power LED). On the lower right portion the USB port can be seen and above it the processor with a crystal and a socket for programming and debugging connector. The part above the red power led is the high voltage section with DRV2667 chip. The only two bigger external components needed for the operation of the chip are the inductor and capacitor needed to produce and store the high voltages needed for the operation of the micropump. In top left corner can be seen an unpopulated connector which can be used for supplying external analog signals if the module works as a HV amplifier.
For any questions regarding the module you can contact me or any of the laboratory members directly.