## 3 Results and Discussion
### Experimental Characterization
Same as for active opening, a difference of the flow rate in NO state is observed when comparing the 0.2 mm piezo-tuator valve variants ((122 \(\pm\) 9) mL/min for the basic design and (119.1 \(\pm\) 8.4) mL/min with coating) to the high force design ((83.6 \(\pm\) 4.8) mL/min). Again, this difference can be explained by the dissimilar stiffnesses of the valve diaphragms and the effect of the fluid pressure influencing the height of the valve chamber. Microvalve leakage is presented in Figure 9d. The pressure-dependent leakage characteristic of NO valves of the basic design seem to exhibit the highest of all measured leakage behaviors; however, the differences are not statistically significant (Table 2). While microvalves of the high force actuator variant exhibit the lowest leakage rates at the lowest standard deviations, better statistics are needed to assess the significance of the observed differences in order to evaluate the effect of an increased contact pressure. Since experimental leakage rates of the coated microvalves do not differ from the basic design, beneficial sealing properties as a result of the Parylene-C coating cannot be derived to this  
Figure 9: (**a**) Typical stroke measurement of the NO valve. At an applied field of approximately 1 kV/mm, the actuator diaphragm sits on the valve seat, and downwards movement is inhibited. (**b**) Typical flow characteristic of an NO valve at an inlet pressure of 20 kPa showing complete blockage of the fluidic path at approximately 1.6 kV/mm and a maximum open flow of 27 mL/min. (**c**) Average pressure-dependent flow rate in non-actuated state with an applied inlet pressure of up to 100 kPa. Error bars depict standard deviations. (**d**) Average pressure-dependent leakage with up to 20 kPa inlet pressure. Error bars depict standard deviations. date. However, the comparison of the measured leakage rates to former investigations of NO valves with soft sealing components [14] reveals that the microvalve variants presented here achieve similar leakage rates with significantly lower standard deviations. Therefore, the micromachined trenches are proven suitable for the fabrication of a microvalve with increased reliability with a view to sample-to-sample variation of the exhibited leakage rate due to higher manufacturing precision of the valve seat compared to microvalves comprising an O-ring soft sealing. Comparison of the modeled values (see Figure 8) to experimentally collected data shows an overall overestimation of expected leakage rates, which, as already mentioned, constitutes an upper limit of the theoretically expected values. While leakages of both microvalve variants without coatings are overestimated approximately by a factor of 4 and 7 (high force design and basic design, respectively), the analytically calculated leakage rates of the coated microvalves differ from experimental data only by a factor of 1.5. Future work on analytical modeling of microvalve leakage rates should consequently involve a thorough investigation of contact pressure calculation accompanied by experimental investigation of the achieved forces of piezoceramics bonded to metal diaphragms.