The PiezoHydraulic Pump (PHP) used in this work currently uses proprietary check valves that allow the PHP to be operated at 1 kHz. At a bias pressure of 500 psi and operating voltage of 1 kV, the PHP produces a mechanical power output of 46 W. The PHP was baseline tested using both the proprietary valves (internal) and external commercial passive check valves. Using the external valves at a bias pressure of 80 psi, the PHP was tested at various frequencies. At an operating frequency of 150 Hz, the maximum flow rate was 0.91 cc/s, while at 125 Hz, the maximum mechanical power output was 0.18 W (0.64 W/kg). This significant decrease in characteristics can be attributed to an increase in system compliance by moving the valves external to the pump housing and possible air entrapment within the chamber.

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This paper presents modeling, fabrication and testing results for a high flow rate and high frequency nickel titanium alloy (Nitinol) MEMS valve. ANSYS R is used to evaluate several Nitinol MEMS valve structural designs with the conclusion that a pentagonal flap with five legs produces higher frequencies and higher strengths without the inherent rotation problem present in four-leg designs. The Nitinol penta-leg design was fabricated using a novel bi-layer lift-off method. A polymethylglutarimide (PMGI) polymer layer is initially used as an underlayer while a chromium layer is used as a top layer to produce a non-rotational ortho-planar Nitinol MEMS valve array without the problems inherent in conventional Nitinol wet etching. The array consists of 65 microvalves with a single valve having dimensions of 1 mm circumference, 50 µm leg width and 8.2 µm Nitinol thickness. Each microvalve covers an orifice of 220 µm diameter and 500 µm in length and is capable of producing 150 µm vertical deflection. The Nitinol MEMS valve array was tested for flow rates in a hydraulic system as a function of applied pressure with a maximum water flow rate of 16.44 cc s −1 .

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