Radiation Tests

RSC-164 chips from Sensory Inc., memory chips and microphones of the type we expect to use were exposed to 10 krad radiation. These are "interplanetary" level doses similar to those used for Mars Global Surveyor tests. Neither microphones nor chips showed significant degradation following the exposure.

Thermal Tests

During 1/20-23/97 thermal tests were carried out on operating RSC-164 chips, microphones, and board surface-mounted electronics components of the type that we expect to use. The test chamber containing air at atmospheric pressure was cycled between +100 degrees F (~38 C) and -115 degrees F (-82C) six times over the four-day period. Equipment outside of the chamber was used to monitor the health of all components continuously. The fan inside the chamber provided the noise source for the microphone. A test unit also supplied by Sensory Inc. was used to verify the operation of the RSC-164 chip. The five capacitors and resistors on the surface-mount test board were wired in parallel so that one measurement each could verify their integrity. The four surface-mounted diodes were wired in series with their forward voltage measured.

Over the six temperature cycles no failures occurred. The resistors repeatedly changed in value by only 0.3% over the entire temperature range, while the capacitors changed by approximately 22% (an expected change for the dielectric). The diode voltage varied with the chamber temperature in the expected manner. A new RISC-164 chip was cycled three times, after which a 10 krad exposed chip was cycled twice, and a different 10 krad exposed chip was used during the last single cycle (the chip test unit holds only one chip at a time).

Pressure Tests

During 1/16-17/97 initial pressure tests were carried out on the microphone to determine how its response is affected by ambient pressure. The microphone was connected to a test circuit for power and signal amplification and mounted with a loudspeaker at a fixed distance on an assembly placed in a vacuum chamber. A signal generator was used to drive the loudspeaker at frequencies between 100 and 4000 Hertz at signal amplitudes equivalent to ~1 Volt. The output voltage was measured as a function of frequency at fixed pressures between ~10 mbar (as expected on the Martian surface) and atmospheric pressure (1 bar). We determined that the output signal scales approximately linearly with the pressure. The frequency response measurement has not yet been completed because of interference from resonances generated in the pressure chamber. We are looking into the control of this test-setup-related interference at this time. Such resonances, of course, will not be a problem in the "open" Lander environment.