Model for finger touching a microstrip

Hi everyone,

I would like to know how you guys would model a microstrip with a finger touching the microstrip? The microstrip is connected at one end to a circuit and serves as a variable C/L. The variation occrs when a finger touches the strip. To model this, should I consider the strip is left open at the point where the finger touches the strip, or is it rather shortened to ground at the contact point?

Thanks for your help

Hi,

Hope you meen human finger used to de-bug some circuit? To my experience, the finger mainly attenuates thus it adds matching the same way as attenuater does.

flyhigh

No I don't mean to debug. What I mean is that I have a transmission line opened at one end and it behaves as a capacitor whose value is controlled by design. Now I'm wondering what is the equivalent circuit of this same line once a finger touches it?

Thanks for your help

I don't agree with flyhigh in that a finger touching the microstrip acts as a attenuator. If this would be true, every frequency should be attenuated evenly, which is not the case in real world. The effect is somehow similar to the capacitive loading of the microstrip (perhaps distributed at the length where finger is touchinh the microstrip line).

Thanks rfmw, so the model would be to add a capapcitor to ground at the contact point. Do you agree?