Technique for Measuring the Electrical Conductivity of Wakes of Projectiles at Hypersonic Speeds

Abstract

A technique is described for measuring the electrical conductivity of hypersonic wakes and any conducting medium by measurement of the Joule losses produced by the oscillating magnetic field of a circular coil surrounding it. The apparatus consists of a symmetrical rf bridge, two arms of which contain identical coils. A conducting medium inserted into one of the coils unbalances the bridge, changing the apparent impedance of the coil. Although the apparatus was designed specifically to investigate the conductivity of hypersonic wakes, it has also been used to measure the conductivity of electrolytic solutions, electrical discharges, flames, and plasmas produced in shock tubes. The measurements on electrolytic solutions gave results in satisfactory agreement with their known conductivities and provided a convenient check on the calibration of the apparatus. The shock tube measurements were made in air and agreed well with the results of Lamb and Lin [L. Lamb and S. C. Lin, J. Appl. Phys. 28, 754 (1957)]. Results of the measurements of the conductivity of electrolytic solutions, shock tube heated plasmas, and hypersonic wakes of 0.22‐in.‐diam nylon spheres in argon are presented.