Richard C. Givler

Passive MEMS Valves With Preset Operating Pressures for Microgas Analyzer

In this paper, we present integrated disk-in-cage poppet valves with tuned spring stiffness for gas flow control of a microgas analyzer. The valves require zero power and close at preset offset pressures (0-35 psig) to switch from gas sample loading onto a preconcentrator to concentrated constituent sample injection into a microgas chromatograph. Air flow rates of 4.5 mL/min at pressures of - 2.5--5 psig (vacuum sample loading) were measured. Hydrogen leak rates of 0.1 muL/s (0.006 mL/min) were measured with valves closed at 15 psig. Analytical and numerical modeling was used to guide design of valve spring constants (ranging from 10 to 1500 N/m) that control the valve open position, flow rate, and closing pressure. The parameter design space is limited to a range of seat overlap, valve size, and spring stiffness that will allow adequate flow rate, sealing, and closing at predictable pressures. A linear curve defining closing pressure as a function of spring constant, valve gap, valve size, and seat overlap fit measured closing pressure data and can be used to predict closing pressure for future designs.

Efficient Runner Networks for Investment Castings

We present a computational method that finds an efficient runner network for an investment casting, once the gate locations have been established. The method seeks to minimize a cost function that is based on total network volume. The runner segments are restricted to lie in the space not occupied by the part itself. The collection of algorithms has been coded in C and runner designs have been computed for several real parts, demonstrating substantial reductions in rigging volume.

Predicted optical performance of the high-altitude balloon experiment (HABE) telescope in an adverse thermal environment

The High-Altitude Balloon Experiment telescope was designed to operate at an ambient temperature of -55 degree(s)C and an altitude of 26 km, using a precooled primary mirror. Although at this altitude the air density is only 1.4 percent of the value at sea level, the temperature gradients within the telescope are high enough to deform the optical wavefront. This problem is considerably lessened by precooling the primary mirror to -35 degree(s)C. This paper describes the application of several codes to determine the range of wavefront deformation during a mission.