Microwave interferometry of shock waves. I. Unreacting porous media

Abstract

Microwave interferometry appears to be a promising method for the study of wave and mass velocity in shocked dielectric materials. This paper discusses the mathematics concerning the frequencies and amplitudes in the microwave reflections from the shock wave and from an impacting piston which drives the shock into a nonreacting porous solid. Methods for the determination of the state variables in the compressed region between the shock wave and the piston are given. In this paper, these methods have been confirmed by experimental measurements in nonenergetic materials in which there is no ionization from chemical reaction. The microwave reflection from the shock wave traveling through an inert media is shown to result from a dielectric discontinuity at the wave front. Studies on energetic materials (explosives and propellants) are considered in a companion paper where ionization associated with the chemical reactions is required to explain the increased reflection from the shock front.

Detonation failure characterization of non-ideal explosives

“…This is a modified method from previous work calculating the velocity of shock waves [5]. The spatial resolution is limited to the frequency of the interference signal with this method due to the calculation of the detonation front relying on each zero-crossing.…”

Using time-frequency analysis to determine time-resolved detonation velocity with microwave interferometry

“…This technique is used to measure the phase and amplitude of microwave signals that are transmitted through an unreacted explosive and reflected back at locations of interest. These reflection points are located at dielectric discontinuities such as a shock wave or a reaction front 1,2 which occur in the media during a detonation event. The phase measurements can then be used to infer the relative position and velocity of the phenomena.…”

“…3 Furthermore, the shock or detonation wave may be a nonplanar reflector due to sample diameter effects as well as material heterogeneities 4 resulting in poor signal quality. Other factors which may affect the signal quality include the possibility of a decoupled shock-reaction zone (e.g., shock initiation and detonation failure) giving rise to multiple harmonic frequencies, 1 as well as the confinement of the test explosive acting as a waveguide for the MI signal. 3 When several of these non-idealities are present simultaneously, it may still be possible to extract useful velocity information with an advanced time-frequency analysis.…”

Reactive flow modeling of small scale detonation failure experiments for a baseline non-ideal explosive

“…Specifically, this technique records the phase and amplitude of microwave signals that are transmitted through an unreacted explosive and reflected back at dielectric discontinuities, such as a shock wave or reaction front. 14,15 In the present study, explosive-filled waveguides are used to propagate only the lowest microwave mode through an optically transparent media. An explosive booster is used to initiate samples of ANFO, where the confiner (i.e., waveguide) wall thickness and sound speed are varied to tailor the behavior of the shock velocity profile corresponding to detonation failure.…”