5 ms·

The way I rationalize impedance matching is like the Index of refraction. The analogue to two pieces of wire with different impedance is two pieces of glass wi

by rocqua 7y ago

The way I rationalize impedance matching is like the Index of refraction. The analogue to two pieces of wire with different impedance is two pieces of glass with different index of refraction. What happens when you shine in light is a partial reflection at the boundary of the two pieces of glass, which also means less light gets through. Impedance matching is just trying to match these indices of refraction to me. Sadly, I have no good analogue for a balun or impedance matching circuit. I have no idea whether this is mathematically correct, but it gives me some intuition for why it matters.

MayeulC 7y ago
It is technically correct, but might not be the easiest way to understand it intuitively (this will be different for everyone, but I didn't quite get the explanations in the thread). I'll try to make it simple: for now, let's admit impedance is resistance. It is just a way to express how much the medium will slow a propagation down. This works with multiple fields: thermal resistance, soundwaves, lightwaves (refraction index is c/v), or you can just imagine yourself going trough different mediums: when diving, you encounter some resistance where the medium starts slowing you more. You lose energy there. If instead the resistance was the same all the way (if you were already swimming), there would be no interface to lose energy at. Diving championships use bubblers to soften the water, that's adapting impedance, in a sense. Of course, this analogy is a bit extreme at our scale, due to the high absorption and terminal velocity differences between the two mediums. But you have the same with soundwaves: a wall will reflect your speech because sound has a lot higher speed in concrete. Some surfaces will do it better than others. And to avoid that kind of parasite reflection during ultrasound imaging, a gel is employed to match impedance between the emitter and the body [1] (avoiding a thin air layer in between). OK, now for real (actually complex) impedance, you have to take into account that the speed inside the medium varies based on frequency. That's called dispersion in optics and acoustics, and is sometimes compensated by employing mediums with an inverted dispersion relationship [2]. OK, I'll admit that propagation speed isn't strictly what impedance is, but it is pretty close, and they probably have an intimate relationship (which I can't reflect on right now, but feel free to elaborate below, if you feel like it). This actually sent me down a small rabbit hole in wikipedia: https://en.wikipedia.org/wiki/Impedance_analogy https://en.wikipedia.org/wiki/Impedance_analogy [1]: https://en.wikipedia.org/wiki/Medical_ultrasound https://en.wikipedia.org/wiki/Medical_ultrasound [2]: https://en.wikipedia.org/wiki/Dispersion_(optics)#Dispersion_control https://en.wikipedia.org/wiki/Dispersion_(optics)#Dispersion... [2]: http://www.m2optics.com/blog/bid/61431/Chromatic-Dispersion-in-Optical-Fibers http://www.m2optics.com/blog/bid/61431/Chromatic-Dispersion-...

by rocqua 7y ago

MayeulC 7y ago

It is technically correct, but might not be the easiest way to understand it intuitively (this will be different for everyone, but I didn't quite get the explanations in the thread). I'll try to make it simple: for now, let's admit impedance is resistance. It is just a way to express how much the medium will slow a propagation down. This works with multiple fields: thermal resistance, soundwaves, lightwaves (refraction index is c/v), or you can just imagine yourself going trough different mediums: when diving, you encounter some resistance where the medium starts slowing you more. You lose energy there. If instead the resistance was the same all the way (if you were already swimming), there would be no interface to lose energy at. Diving championships use bubblers to soften the water, that's adapting impedance, in a sense. Of course, this analogy is a bit extreme at our scale, due to the high absorption and terminal velocity differences between the two mediums. But you have the same with soundwaves: a wall will reflect your speech because sound has a lot higher speed in concrete. Some surfaces will do it better than others. And to avoid that kind of parasite reflection during ultrasound imaging, a gel is employed to match impedance between the emitter and the body [1] (avoiding a thin air layer in between). OK, now for real (actually complex) impedance, you have to take into account that the speed inside the medium varies based on frequency. That's called dispersion in optics and acoustics, and is sometimes compensated by employing mediums with an inverted dispersion relationship [2]. OK, I'll admit that propagation speed isn't strictly what impedance is, but it is pretty close, and they probably have an intimate relationship (which I can't reflect on right now, but feel free to elaborate below, if you feel like it). This actually sent me down a small rabbit hole in wikipedia: https://en.wikipedia.org/wiki/Impedance_analogy https://en.wikipedia.org/wiki/Impedance_analogy [1]: https://en.wikipedia.org/wiki/Medical_ultrasound https://en.wikipedia.org/wiki/Medical_ultrasound [2]: https://en.wikipedia.org/wiki/Dispersion_(optics)#Dispersion_control https://en.wikipedia.org/wiki/Dispersion_(optics)#Dispersion... [2]: http://www.m2optics.com/blog/bid/61431/Chromatic-Dispersion-in-Optical-Fibers http://www.m2optics.com/blog/bid/61431/Chromatic-Dispersion-...