Recent content by decaf14

Dang it. That's exactly it. I don't know why I didn't think of that. Thank you! Sometimes it helps to get an extra set of eyes. Here's the simulation output that verifies this (I set vsupp to 5 gig-volts and v- is -5 gig-volt). Impedance drops to 56k like expected.

I'm having trouble finding it as the pspice model simply shows this for the lm358. I'm fairly certain it should be negligible compared to the 10u capacitor in series, though. If I simply test the opamp with a series resistance, I should be able to intuit the capacitance to ground based on the...

You may be able to neglect the effect of the ground plane if you simply pick the distance to be extremely large. This would yield a small capacitance according to the parralel plate model. In calculus, you would take the limit as the distance to the ground plane approaches infiinity. Naturally...

Hello, I am simulating the input impedance of a high-pass filter with the output voltage of the filter input to the non-inverting pin of an op amp. I'm confused as to why the input impedance can possibly dip below the resistance of the high-pass filter resistor. Please see the following circuit...

L is referred to simply as the "effective inductance ... for each coil" . No units are listed, but based on the context, I think it's simply units of henries. Especially since they list this equation for resonant frequency that we know to be true (taken directly as a .jpeg from the text):

Nope. There is no mention of what kind of integral. They don't even name what " r' "actually means, but I'm assuming it's a derivative. They sort of just introduce the equation out of nowhere. It's a very highly cited (2.6k citations) paper in the field, so it's a reputable paper. I just can't...

Hello, I would like to replicate the results from the paper "wireless power transfer via strongly coupled magnetic resonances", but I'm having trouble interpreting their equations. I'm creating a MATLAB script to do so. In the paper, they get to a point where L and C are to be calculated in a...

Here is a paper detailing exactly your question if I understood correctly. The key search term here is "microstrip". Here is the phrase I googled if you want to up your google-fu: "two microstrip capacitance" https://cecas.clemson.edu/cvel/emc/expert_systems/PCB/summaries/Mutual_LC_summary.pdf

Thanks for this berkeman. Also thanks Tom for the input on making a bifilar coil to create a purely resistive load. I've run some simulations using the model they provided and my target frequency should be much, much, higher based on the dimensions of my Rx coil. The small inner diameter lends...

Thanks. I'm not quite sure what the load circuit will look like. I have a design consideration to make for it. It's going to be a heating element, so right now I'm thinking that I can keep the ~MHz signal as is and gain additional heating via skin effect. It may have some slight inductance...

Hi Marcus, The Rx coil is 2mm inner diameter. The transmitter is 25mm diameter. The load is 20 ohms. The characteristic impedance (system impedance to which I should match to) is 50 ohms. You can visualize the load in the circuit schematic (it's 40 pF in series with 25 uH and 20 ohms). To be...

Thank you guys for all the responses. This is a great idea. I can't think of an analog way to do so, but digitally, I could place a small current sense resistor and use a microcontroller to continuously adjust the frequency until the current is highest. I think this is ringing a bell from a...

Hello, Some trouble came up today with designing a 50 ohm system for a wireless powering project. I'd like to increase the frequency range for which my system impedance is 50 ohms in order to reduce power losses due to mismatch. I've simulated two RLC circuits in OrCAD SPICE to demonstrate my...

Thanks for this! Ampacity was the keyword I needed. I had seen these charts before, but they were rated for 30 C. 60, 75, and 90 seems far more useful. I'll engineer around this as a rough estimate and better hone in on actual temperature rise experimentally.

Ahh, yes. Let's assume we are working with air, then. I'm still struggling to find an equation I can apply to this system. My closest guess is the specific heat equation, Q = m*c*dT. I could calculate the mass of the wire based on it's dimensions, then input the specific heat constant. The issue...