## Publica

Hier finden Sie wissenschaftliche Publikationen aus den Fraunhofer-Instituten. # Electrohydrodynamic pumping and flow measurement

**Abstract**

A micromachined electrohydrodynamic (EHD) injection pump with improved characteristics and a novel method for flow measurement with the same structure are presented for the first time. Based on the structure of the EHD injection pump, an improved design with grid distances in the range between 10 mym and 60 mym were achieved, yielding a reduction in the required driving voltage. Grid areas of 2.5 x 2.5 qmm and 1 x 1 qmm were accomplished. The outer dimensions of the smallest pumps are 3 x 3 x 1.0 cbmm. One of the grids is etched back from the frontside and mounted upside down on the lower grid in order to reduce the grid distance. The two grids are bonded together by anodic bonding. The pump is mounted in a ceramic housing with two fluid ports. Experimental data relating to the electrical and hydrodynamic behaviour of the optimized micropump are presented. Based on the same structure a novel method for the measurement of fluid flow and velocity was developed. This technique is especial ly suited for small flow rates below 100 ml/min down to some myl/min, which is difficult to measure by known methods. The presented method is based on the measurement of the ion transit time between the two grids. Upon application of a step voltage between the two grids a cusp is observed in the associated transient space charge limited current (TSCLC). The cusp signifies the arrival of the first charge carriers at the opposite electrode, and hence the ion transit time. The transit time will now increase or decrease depending on the flow rate and direction and is therefore a direct measure of the fluid flow rate. This behavior was infered from one-dimensional calculations and subsequently confirmed by appropriate experiments. The method is not restricted to electrically isolating fluids. Volumetric flow rates down to 8 myl/min were measured with a 2.5x2.5 qmm grid area. By measuring the difference of the transit times in direction of the flow and opposite to it with two identical stru c