Active micro valves
Bi-stable electromagnetic valveCopyright: © KEmikro
At KEmikro a bistable micro valve suitable for fabrication by ultrasonic hot embossing was developed [50, 42]. It has a cylindrical design with an outer diameter of 17 mm and a height of 3.6 mm. Into the housing fabricated this way the actuator and permanent magnets are placed and the housing is closed by ultrasonic welding.
The micro valve is electromagnetically actuated by a coil which can also be produced at low cost. The switching time of the micro valve is approximately 20 ms and an air flow rate of 880 ml/min is achieved at a pressure difference of 100 kPa over the valve. No leakage is observed up to a differential pressure of 130 kPa. The flow of both, gases and liquids, can be controlled by the micro valve. The valve material PVDF (Polyvinylidenfluoride) is not susceptible to chemically aggressive fluids. Energy is only needed while switching. Each switch of the micro valve requires 200 mJ and a voltage of 15 V. The actuator is completely separated from the fluid. Therefore, the micro valve could also be used in medicine or biology.Copyright: © KEmikro
In the housing of the micro valve there are at the upper and the lower half anular permanent magnets holding a nickel platelet in place. At the rim of the nickel platelet there is mounted an electromagnetic coil generating a magnetic field by an electrical current. The field pushes the platelet to the other side of the housing where the nickel platelet presses a silicone membrane onto a valve seat located in the center of the ring magnet. This way, a valve orifice is closed on the side where the platelet is attracted by the permanent magnet and opened on the opposite side.
96 active micro valves on a titer plateCopyright: © KEmikro
For micro titer plates with 48 wells, there was developed a micro valve system such that over each well there is placed one inlet and one outlet valve [91, 95]. Thus, this micro fluidic system includes 96 micro valves. With pneumatic systems either all inlet or all outlet valves are switched at the same time. The valves are either closed by an over pressure or opened by an under pressure.
Copyright: © KEmikro
When both valves are open, a cell culture in the corresponding well is ventilated with air. It is made sure by the dimensions of the orifice in the inlet valve that the air flow through all wells is the same. The orifices in the inlet valves are by far the narrowest part of the flow system for air ventilation of the wells.
Then first the inlet and then the outlet valves are closed and the metabolism of the cell cultures are observed by measuring the oxygen and carbon dioxide concentration with opto-chemical sensors in the wells. This way, 48 cell cultures are investigated at the same time containing besides the cells different substances at different concentrations.
The micro system was manufactured by milling the required micro structures into polymer plates form the polymer poly methyl methacrylate (PMMA). The membranes are from silicone which was casted into molds which had been milled into aluminum plates.
 A. Barth, S. Krabbe, C. Gerhardy, W.K. Schomburg
”Herstellung eines preiswerten, bistabilen Mikroventils mit niedriger Ansteuerspannung”
Proceedings Mikrosystemtechnik Kongress 2013 in Aachen, 14. bis 16. Oktober (2013) 59 – 61, ISBN 978-3-8007-3555-6.
 A. Barth, C. Gerhardy, W.K. Schomburg
”Bistable polymer micro valve with a thermo-pneumatic actuator”
Proceedings MME 2012, C14.
 S. Krabbe, D. Flitsch, J. Büchs, W.K. Schomburg
"Micro system comprising 96 micro valves on a titer plate"
Proc. Micro Mechanics Europe, 28 - 30 August 2016 in Cork, Irland, MME 2016.
 D. Flitsch, S. Krabbe, T. Lader, M. Beckers, J. Schilling, S. Mahr, U. Conrath, W.K. Schomburg, J. Büchs
“Respiration activity monitoring system for each well of a 48-well microtiter plate”
Journal of Biological Engineering (2016) 10:14, doi: 10.1186/s13036-016-0034-3.