7.2. Magnetometer

A magnetometer or magnetic sensor is an instrument that measures magnetism either the magnetization of a magnetic material like a ferromagnet, or the direction, strength, or relative change of a magnetic field at a particular location [66].

In 1962, Hill and Bostick presented a report about a magnetometer (with their own words micropulsation sensor) that had laminated mumetal core based on the resistance of winding and the character of the output signal. Aim of the design was a sensor with a lower impedance than the 1000 ohm source impedance. Therefore, the length and resistance of the coil in the sensor had been studied in detail. Within the core, eddy current and hysteresis losses and Within the winding, losses caused by skin effect, proximity effect, distributed capacity, and wire resistance were considered [27].

In 1977 an induction coil magnetometer that contains mumetal rod core, several partial coils, and a preamplifier circuit was patented. Critical dimensions of magnetometer that coil width to core width ratio, coil diameter to core diameter ratio, and core diameter to core length ratio were given. In addition, manufacturing of magnetometer was described in details. The invention was that increasing the resolution of the magnetometer [42].

Patents:

Year	Name	Patent Number
1977	Magnetometer	DE2625964A1
1985	Magnetisches Sondentripel	EP0154129B1

7.2.1. Magnetotelluric

Magnetotelluric is a device that measure the electric and magnetic fields arising from natural sources (electromagnetic sounding of the Earth) at the surface of the earth over broad frequency bands and is based upon the skin depth effect in conductive media. Stanley and Tinkler investigated a practical, low-noise coil system for magnetotellurics. Aim of the work was implementation of the magnetometer with low-cost, light weight, broad bandwidth, ease of construction and reliability. Manufacturing steps were given in detail. A chopper amplifier had been improved according to existing systems [56].