I’m a graduate student in the Electrical Engineering department at the University of Colorado, Boulder. This summer I am working on a project in which we are trying to understand how faults occur on chips. I’ve been tasked with creating a multiphysics simulation (using COMSOL) of the ChipShouter and I want to make sure that the models of the injection tips are accurate. I’ve read through the manual for the ChipShouter and the picoEMP. There are a few details which I cannot find, and I am not allowed to dissect the tips we have:
- Is 1mm the actual diameter of the ferrite rod on the 1mm tip?
- Which ferrite rod is used? I would like to know the permeability.
- What is the length of the ferrite rod?
- What gauge of wire is used in the 1mm injection tip that comes with the ChipShouter?
- How many turns of wire are used on the 1mm injection tip?
- Has anyone connected the 1mm injection tip to an LCR meter and if so, what was the measured inductance and DC resistance?
This is sure to be an interesting project!
Thanks in advance for any help.
Sorry on the lag here. Hopefully the following diagram answers the questions w.r.t. winding:
The core itself is Fair-Rite 3078990831
I haven’t done the LCR test, will check if we can measure accurately enough to be usable. I have a low-cost VNA that could generate that or S11 parameters too (not sure they will be that accurate, but give you an idea).
Thanks for the specs! For the 1mm probe, we were able to measure an inductance of 423nH +/- 20nH. We built a model of the probe in COMSOL using the provided dimensions, and the simulated inductance (426nH) is in close agreement with the inductance of the simulated coil. That’s all good news.
I’m now trying to build a very simple approximation of the High Voltage portion of the ChipShouter in LTSPICE and in COMSOL. Are you able to share the part number for the NMOS transistor designated Q4 in the schematic?
The BOM has it as the IXFT50N85XHV.
I updated the geometry and material characteristics of the model to better match the data provided in this post. It agrees with measured data. That’s good…
Wow - that is amazingly close! Very cool, look forward to seeing what you learn about the EM field stuff here.
Thanks! Creating a model of the 1mm injection probe was the easy part. The challenge I’m currently facing is how to excite the probe using the simulation software. I need to figure out a simplified circuit which would take the place of the gate driver, MOSFET, and pulse shaping BJT/inductor (Q11/L4). The goal is to have a simulated voltage across the modeled injection tip which has close agreement to measurements taken from the oscilloscope connection ports of the ChipShouter. I’ve been experimenting in LTSPICE (because it is fast), replacing the FET with a simple switch, but have not yet modeled a circuit that approximate the ChipShouter output voltages.
Any thoughts on how I can do this would be greatly appreciated!