Static and Dynamic Permittivity Measurement of High Explosives in the W Band to Investigate Shock and Detonation Phenomena

Abstract

Radio interferometry techniques are often used to investigate shock and detonation phenomena thanks to the radio‐transparency of high explosives in the gigahertz frequency band. These techniques require the knowledge of the permittivity of studied explosives. Although the permittivity has been thoroughly studied for many materials, very few data are available at high frequencies (>75 GHz) for high explosives. In this paper, we report static measurement data of the permittivity for various reactive materials using the standard line transmission method between 75 GHz and 110 GHz (W frequency Band), and we present dynamic measurement results at 94 GHz obtained from the so‐called detonation wavefront tracking method. It is shown that the measurement results provided by these two methods are in good agreement. As a consequence, this work validates the detonation wavefront tracking method for the dynamic measurement of high explosives permittivity, and shows that the static experimental results are relevant for shock wave propagation analysis from millimeter‐wave measurement techniques.

Review of the Wedge Test and Single Curve Initiation Principle Applied to Aluminized High Explosives

“…Concerning the shot CA18139, the Chapman-Jouguet detonation velocity registered is roughly 500 m/s higher than its theoretical one; which leads to a deviation of 7 %. According to Rougier et al [7], the uncertainty on the dielectric relative permittivity may account for 1.3 % of deviation on the velocity recorded. That does not explain the high detonation velocity registered.…”

“…The key issue is to know the dielectric relative permittivity of the high explosives. Rougier et al [7] proposed a comparison between two methods of determination the relative permittivity and give some high explosives data.…”

“…The posttreatment was made with the dielectric relative permittivity given by Rougier et al [7]. In these shots, the RIF recorded the whole shock motion from the base to the end of the wedge, while it did not with non-aluminized high explosive.…”

Development of a Shock and Detonation Velocity Measurement System Using Chirped Fiber Bragg Gratings

“…The hole diameter for the CFBG was 0.8 mm; therefore, the CFBG was glued with a thin Teflon tube following the same process as in the first wedge test (Section 6.3.1). A microwave interferometer (internally called RIF for radio interferometer) [31,32] with a 94-GHz frequency was also used. The microwave signal from the RIF was brought to the sphere through a dielectric waveguide (Teflon), and the output beam was expanded up to an 18-mm-diameter area through a cone directly glued on the outer sphere surface.…”

“…(b) Picture of the cylinder end with 24 ESPs positioned in a cross shape. The white cone is connected to a microwave interferometer[31,32].…”