Design and Development of Extremely Low Frequency Electromagnetic Sensor

Abstract

This research work starts with the basic description of inductive sensor operating for extremely low frequency (ELF) range from 7 Hz to 30 Hz. This induction coil magnetometer sensor consists of multilayer solenoid having very stable and linear electrical characteristics but limited sensitivity. An air coil (also known as Helmholtz pick up coil) sensor has a large diameter but relatively short in length. It is optimized in typical environment for best electrical response. Some modifications in using other material/s to develop this inductive coil sensor are opted for getting high electromagnetic sensitivity. Experiments are carried out for coil with a ferromagnetic core to justify its design resulting into larger sensitivity but they are found to be relatively less stable. newlineThese are mechanically longer and thinner in diameter so we observe low demagnetization effects. Modern low noise induction coil usually works in current and power output modes. Low noise voltage or current preamplifier is usually mounted in close proximity to the induction coil and is an integrated part of this sensor proposed for research. Here, the air core coils together with integrator (flux-meter) are used to map the d.c. induction effects by an extraction method and that also measures the magnetic field intensity for the coil-sensor at ELF. newlineOne of the most important applications is the electromagnetic compatibility (EMC) to measure the ELF magnetic field effects at the power frequency. It helps measuring the wideband root mean square (rms) output typically, for 7 Hz to 30 Hz. Also, this will prove to be one of the widely known sensitivity calibration techniques. The coil constant can be reliably calculated for only simple air coil with well-defined geometry to make the design a future compatible technology. In this research, I have studied all types of sensors (e.g. Resistive, Inductive and Capacitor sensors). The very first inductive sensor was developed in 1933. newlineIt detects and senses electromagnetics signal but it is not stable and has