Capacitive sensing for measuring the conduction zone of low density pentaerythritol tetranitrate (PETN)

• Published in: Journal of applied physics Vol. 134; no. 18
• Main Authors: Edgeley, James, Braithwaite, Chris, Lee, Elizabeth, Drake, Rod
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 14.11.2023
• Subjects: Coupling; Density; Detonation; Detonators; Diagnostic systems; Electrical noise; Explosives; Explosives detection; Low conductivity; PETN; Temporal resolution
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/5.0175481

We present a novel diagnostic system, based on the principle of capacitive sensing, capable of detecting the conduction zone of detonating explosives. The method relies on measuring the change in the capacitive coupling between a printed circuit and its surroundings, induced by an increase in local conductivity. A high frequency wave generator provides the driving signal, which is modified by the change in coupling. This method boasts greater sensitivity than existing conductivity-based techniques, with comparable spatial and temporal resolution. The subject material was pentaerythritol tetranitrate (PETN) powder, pressed into low density (50%–85% theoretical maximum density) cylindrical columns. Previous attempts to measure the reaction zone of low density PETN have faced difficulties because of its short length and low conductivity compared to other explosives. The PETN was initiated using a laser flyer detonator in order to reach detonation promptly and with a minimum of electrical noise. Application of the capacitive sensor diagnostic and subsequent analysis yielded a density dependent steady-state reaction zone length of between 45 and 78  μm.