As a part of DOD/DOE-funded grants, EHT has worked to understand, develop, and optimize systems that allow for "pulse compression". Pulse compression generally uses reactive circuit elements to compress the rising edge of a pulse, in order to decrease the rise-time. An example of a simple, single-stage, lumped-element pulse compression circuit can be seen at right, in which L1 is a saturable inductor. The circuit functionality is described in more detail below.
My coworker, Akel, and I worked to develop an understanding of the different parameters that dictated the relationship between the values of C1, L1, and RL. Particularly, we focused on designing saturable inductors with different numbers of series windings, parallel windings, and cores. This involved a great deal of testing and data analysis to develop a model that would allow us to create additional compression stages on-demand. It also involved the characterization of a number of types of saturable inductor material, as information was often scare from manufacturers.
Skills Demonstrated / Gained
- Data analysis, to parameterize the behavior of saturable inductor-based pulse compression circuits.
- Experiment design and test setup
- High voltage/frequency measurement
- Use of nonlinear saturable inductors and capacitors
- Conducting extensive literature review
The circuit diagram for a single stage pulse compression circuit using a saturable inductor can be seen in Figure A. The basic idea is that once the switch closes, the source capacitor will charge the first stage capacitor (C1) in some time Tcharge. The saturable inductor L1 is constructed to saturate at the same time it takes C1 to charge and has a large unsaturated impedance such that it dominates the voltage divider ratio with the output load resistor (RL) pre-saturation. Once C1 charges to peak output voltage, L1 ideally saturates very quickly and all of the charge on C1 is transferred to RL as fast as possible. This also assumes that the saturated impedance of L1 significantly less than RL so that RL dominates the voltage divider ratio with L1 post-saturation. In theory, any number of stages can be added in parallel to the first stage for further pulse compression.