Microwave Phonon Attenuation in Magnesium Aluminate Spinel

Abstract
Measurements are reported of the attenuation of microwavephonons of various modes in magnesium aluminate spinel (MgAl2O4). The attenuation of certain modes is lower than in any other material measured and permits the observation of 9000 MHz echo patterns at room temperature. Some possible applications of this discovery are discussed. The attenuation at room temperature is interpreted in terms of an effective viscosity damping mechanism and approximate values of the components of the viscosity matrix are given.