Since Rohacell is susceptible to changes in relative humidity, a series of experiments were performed to test the suitability of this material for the support structure. Although the MVD will operate under constant environmental conditions, it is important to test a worse-case scenario in which environmental controls fail. These tests also help in defining the handling, machining and transportation procedures for the Rohacell, as well as the MVD.
Rohacell C-cages, with and without silicon wafers, and with and without Parylene coating, were tested. Coated cages had only the 0.50 mil thickness of Parylene. Cages stored at 50% relative humidity were placed in an environmental chamber and subjected to humidities between 30 and 40% then to humidities between 80 and 90%. In each case, cages were allowed to reach equilibrium with their environment. During the duration of the test, the radial distances, widths and lengths of the cages (See figure 2) were measured several times using a caliper with a 1 mil accuracy.