The IPS JFET-L1 from Micro Oscillator Inc., Bala Cynwyd, PA, is an inductive proximity sensor that uses JFET transistors to create a radiation-hardened device. You can build proximity sensors using bipolar, JFET, or MOS-style transistors from most semiconductor process technologies; additional ruggedness is provided by the patented technique that uses passive component (r, c, l) ratios rather than tight transistor parameters or matching. You can use one or more inductors in the circuit and tune them to respond between various metals, such as ferrous and nonferrous metals, or tune it to a specific metal. Transistor gain and offset are not critical.
Micro Oscillator Inc.