Reid Worthen and Professor Richard Selfridge, Electrical and Computer Engineering
The project that was proposed, by my professor and I, was to calculate the current density, that passes through an electrical circuit, by using an advanced technique that utilizes an optical fiber that has a slab crystal that is coupled to the core of a D-shaped optical fiber. By using this set up, we hoped to calculate the current density in a flat wire using an electronic output voltage. The advantage of using this method is that the only other ways to collect data on the current density is to take physical measurements of the wire itself which can result in high amounts of error if not physically measured correctly. Thus this new method would result in much faster, precise, and accurate ways to measure the current density of any object in the electrical world.
In order to achieve the results we wanted, we needed to test our device under severe and extreme conditions to prove the concept. Before we dive into the methodology of how we set up the experiments, it is vital to understand various concepts about electromagnetics from a physics and engineering view point. The main concept to understand about electromagnetics is that when a current is induced into a wire, the wire will exhibit two very important properties. A magnetic and electric field will be produced tangential and around (circumscribing) the wire. Both the magentic and electric field will be tangential to the direction of propogation and to each other. (see figure 1) Another important concept on top of the tangential fields is that in the structure of a wire, the magnetic field rotates around the wire in a clockwise motion in reference to the direction of propogation. Since we know that the magnetic field rotates around the wire and the electric field is tangential to both the magnetic field and the magnetic field, then we know that the electric field propogates itself 100% tangent/normal to the surface of the conductor. So if we used a very flat and wide conductor as our wire then we would achieve very exagerated electric fields that would be about 99% vertical by nature of the flat wire that we use, thus leading us to a much more concentrated electric field to be detected by the optical sensor.
Another key aspect to getting a very high current density, to help our results is to get a very large voltage, reduce all resistance to a minimum, and finally to create a high energy pulse using a switch for a high concentrated current. We reduced the resistance by using thick stranded gauge wire (6-8 AWG) while using nuts/bolts for contact points and using high pressured copper clamps on the thin metal strip. For the high voltage, we used a high voltage 2k Volt vacuum tube supply into 2 VERY large high capacitance capacitors that held a charge of about 1k volts. We would charged the capacitors to the 1000 Volts and then discharge them using a switch to complete the circuit. With an overall DC resistance of about 0.01 Ohms and a voltage of about 1k, we were able to achieve a rough current of about 10,000 Amps into our very thin strip of metal to produce a large electric field on the metal strip so we could use our optical sensor. The final key about this design is that the optical sensor can be placed anywhere on the circuit and NOT induce any extraneous about of noise or RF that is caused by the high amounts of voltage and current arcing from the switch. Figure 2 shows the overall final setup of the circuit with the metal strip, capacitors, and switch.
When all was said and done, and after a long process of problem solving and repairing we very recently got results from our tests. We found small spikes in our noise floor and they seemed to correspond to the exact time delay of the sensor picking up the electric field signal from the circuit. This was showing that we finally had a proof of concept on our idea and that it is very possible to alter and tweak this technique into something much more practical. This was one of the very last results we got and is as far as we have come in the past year of testing and doing research, hence why we have not offically published anything on the topic yet, but we seem hopeful in finishing this project for a publication.
Some of the problems we ran into ranged from high current, contact points, RF noise/faraday cage type isolation, and switching mechanisms. One of the biggest problems at hand was far too much current being passed through the tiny metal strip, thus causing it to explode, spontaneous combust into fire, or warp its physical structure and move the sensor. Arcing was a big problem and at first we had used a mechanical motorized blade switch, but it was far too dangerous since it would weld the contact points together and cause molten particles to fly into the air. We replaced it with a solenoid type switch that would be submerged into transformer oil to reduce the size of the arc.
To conclude, we found that after various amounts of testing, we were able to capture a delayed signal that produced a spike indicating the electric field produced by the current flowing through the metal strip. Knowing that we had proved this small concept makes us believe that it is very possible to finish the results from where we left off to show that this setup and system can capture the current density of any conducting material using the slab coupled optical sensor.