Electromagnetic measurements

This thesis addresses the electromagnetic analyses of two structures. The first structure, a low frequency loop antenna recommended for use by national standards on electromagnetic compatibility (EMC), is incorrectly specified to have the same voltage to magnetic field conversion ratio (antenna factor) when used with a 50 ohm receiver in lieu of a high impedance type ($>$600 ohm). Two independent measurement sets were performed to demonstrate the prevailing discrepancy, and a corrected antenna factor is presented for use with a 50 ohm receiver. The second structure, a partial spiral "pancake" applicator used to generate high EM fields in its vicinity, was evaluated for its (induction) reactive near-field electromagnetic characteristics. Construction of an induction zone measurement system including the development of an electrically small electric field is described. Measured data on three dimensional EM field contours over the face of the applicator, are presented.

As part of a project to study internal waves, FAU plans to utilize an AUV to tow a magnetometer to study electromagnetic signatures from internal waves. This research is focused on the electromagnetic noise issues related to using an AUV to tow the magnetic sensor package. There are active sources of electromagnetic noise caused by an AUV that are present in addition to those induced by the Earth's magnetic field and permanent magnets. To characterize the magnetic noise associated with the AUV magnetometer tow system, the various active source elements were identified, the orientation sensitivity of the sensors being used was determined, and the magnetic anomaly of a similar AUV which may be eventually be used in a magnetic sensing arrangement was measured. The results are used to show the proposed sensing arrangement will likely not achieve the necessary sensitivity to measure subtle internal wave signals.

A magnetometer with a sensitivity of 0.01nT will be towed through the thermocline by a 2.87 meter long, 0.533 meter diameter autonomous underwater vehicle (AUV) to measure the magnetic fluctuations generated by oceanic internal waves. At this point, no research has been found that suggests towed magnetometer measurements have been done using an AUV. Simulations of the AUV, tow cable, and towfish are performed to provide an understanding of the effects of changing different input parameters, such as towing speed (0.5-2m/s), cable length (5-15m), vehicle trajectory (circle and vertical zig zag maneuvers), and current (0.25-1.25m/s). The AUV-cabletowfish system and equations of motion needed for the simulations are described herein. Results show that a 5m tow cable provides better towfish maneuvering than the longer cable lengths. High towfish pitch angle is decreased by decreasing the distance between CG and CB. Surface currents speed of 0.25m/s change the AUV and towfish circle maneuver to a spiral trajectory, while 1.25m/s current speed cause a zig zag trajectory.