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Tests of a 200-mhz surface acoustic wave mass monitor in a space environment

A surface acoustic wave (SAW) crystal has been tested to demonstrate its usefulness in a space environment. The testing was done in a vacuum space chamber. The temperature of the heat sink on which the SAW was supported was varied over the anticipated temperature range that the SAW would be subjected to in space (from 100 C to LN2 temperature). The repeatability of frequency, the stability of the device and the long term drift were important features of the test. An empirical determination of mass sensitivity (mass/frequency change) of the SAW was accomplished by measuring the water-vapor outgassing rate of the chamber walls with not only the SAW but also a 10-MHz QCM with a known mass sensitivity. This test not only measured the mass sensitivity by comparison but it also allowed the measurement of the linearity of the SAW''s total dynamic range.