APPLICATIONS OF MICROWAVES IN THE NONDESTRUCTIVE TESTING OF SOLID PROPELLANTS,

Power employed was less than 0.1 watt at frequencies between 8 and 24 Gc. Results with dummy propellant formulations were evaluated in terms of signal attenuation. Attenuation in a polymer-filled waveguide decreased during polymerization by a factor of from 2 to 10 depending upon the material tested. Disregarding standing wave effects, which were pronounced and unpredictable, powdered aluminum 6.4 - 13. 0 microns dm produced attenuation at normal incidence to the signal path between horn antennas, attenuation increased by about 0.144 decibels per centimeter of propellant thickness per weight percent of aluminum. With the same arrangement, and propellant containing aluminum staple maximum attenuation was obtained when the staple length was an integral multiple of the half-wavelength of the signal in the propellant. Rotation of cubical test samples in the plane-polarized microwave beam showed effects of preferred staple orientation superimposed on effects of random orientation. Propellant-propellant interfaces between slabs produced detectable attenuation by reflection only at high angles of incidence with the electric field of the test signal perpendicular to the plane of incidence.