Magnetometric techniques for the measurement of initial susceptibility and for non-contact sensing of displacement

Abstract

Part 1 of the thesis describes a new instrument that simultaneously measures the real magnetic susceptibility X' and the imaginary magnetic susceptibility X". The instrument measures the temperature dependences of X' and X" in rock samples between 16°C and 800°C; natural developments are working down to -200°C and measuring the anisotropy of susceptibility. The instrument's heart is a tuned circuit driven at its natural frequency by a 5MHz crystal oscillator. The tuned circuit's inductance is a sample coil that encloses-a furnace. The random noise level in the signal for X' is 7.4 x l0-13 m3 r. m. s., the noise level in the signal for X" is 2x 10 ^12 m3 r. m. s. Sample volumes are 0.1 cm3 or less. Equations describing the instrument are derived and verified, particular attention is paid to the sample coil. Circuit diagrams are included. Some results are presented and equations that broadly describe the observed temperature dependences of X' and X" are developed. Some methods for substantially improving the instrument's performance are outlined. Part 2 of the thesis describes a new method for non-contact sensing of displacement. A magnet is mounted on the object whose displacement is to be measured. The magnet's field is sensed and fed to a 6502 microprocessor programmed to display the distance between the magnet and the sensor; intervening barriers with a permeability very close to unity do not affect the readings. The accuracy is better than 2.0% of full scale deflection (FSD) over the useful range of 250 mm and better than 0.1% FSD over a range of 110 mm. The magnet's volume is 4.00 mm3 and the moment is 3.1 x 10-7 Vbm. Circuit diagrams are presented and a complete software listing is included, the design will work with any magnet and magnetometer. There are directions for greatly improving the instrument's performance.