This paper reports on a normally open piezoelectrically actuated microvalve for high flow modulation at cryogenic temperatures. One application envisioned is to control the flow of a cryogen for distributed cooling with a high degree of temperature stability and a small thermal gradient. The valve consists of a micromachined die fabricated from a silicon-on-insulator wafer, a glass wafer, a commercially available piezoelectric stack actuator and Macor TM ceramic encapsulation that has overall dimensions of 1 × 1 × 1 cm 3. A perimeter augmentation scheme for the valve seat has been implemented to provide high flow modulation. In tests performed at room temperature the flow was modulated from 980 mL min −1 with the valve fully open (0 V), to 0 mL min −1 with a 60 V actuation voltage, at an inlet gauge pressure of 55 kPa. This range is orders of magnitude higher flow than the modulation capability of similarly sized piezoelectric microvalves. At the cryogenic temperature of 80 K, the valve successfully modulated gas flow from 350 mL min −1 down to 20 mL min −1 with an inlet pressure of 104 kPa higher than the atmosphere. The operation of this valve has been validated at elevated temperatures as well, up to 380 K. The valve has a response time of less than 1 ms and has operational bandwidth up to 820 kHz.

Future NASA missions require cooling of large structures in space. One class of thermal management solutions for providing controlled, distributed cooling would utilize actively controlled micro-scale valves that are integrated with heat exchangers and sensors in order to provide independent, local temperature control. The most attractive actuation method for these micro-valves is a multilayer piezoelectric (PZT) stack because this technology is capable of providing large force using reasonable voltages (e.g., < 100 V) with minimal power draw. In order to design a micro-valve configuration that takes advantage of this actuation technique, it is necessary to obtain information regarding the behavior of piezoelectric materials at cryogenic temperatures. This paper describes a test facility that was designed to achieve precise measurements of the coefficient of thermal expansion (CTE) and PZT stack actuator constant (33 d) from 40 K to room temperature. The operation of the facility is validated by measuring the CTE of a copper alloy with wellknown behavior. Experimental measurements are subsequently presented for a commercially available PZT stack.

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