Design considerations for a passive magnetic induction signal generator for sensing hypervelocity projectile passage

Measurement of projectile passage after hypervelocity launch is an important measurement and/or trigger needed for electromagnetic launcher development. One method is to use a magnetic induction technique which takes advantage of the fact that a metal object passing through a magnetic field can move the magnetic flux aside and thereby produce a voltage in a coil. This type of system can be designed to use permanent magnets and thereby be totally passive. In addition, this passive system can be designed to be insensitive to the high electromagnetic fields generated during the operation of electrothermal guns and railguns. This diagnostic has been used to trigger other electrically sensitive data acquisition equipment including flash X-rays and to determine the velocity of the projectile. This report discusses the results of tests and a comparison of data with a simple model for calculating the expected signal output of such a device.<>