Analysis of Electrical Noise from Shock Loading a Steel Flatpack Soil Stress Gage

Abstract

Extremely high electrical noise in the output of a carbon steel flatpack soil stress gage interferes with the desired piezoresistive shock wave signal at stresses above and, to a lesser extent, below about 10 GPa. Examples of this noise are indicated in stress histories of 17 GPa impact experiments performed by P. S. DeCarli1 and shown in Fig. 1. Fig. 1(a) shows electrical noise on the stress signal obtained from a manganin gage experiment with a very short carbon steel flatpack, and a repeated experiment with the gage replaced by a constantan shorting element. The gage is clearly not the source of the noise. Fig. 1(b) shows results of repeated experiments with a very short stainless steel flatpack. No noise is present. The noise must therefore be due to the carbon steel flatpack. The purpose of this paper is to give a quantitative explanation for this noise, especially in the field flatpack configuration.