Resonator Q factor and current - Page 1
Forum section: electronics / beginners

author: fonograph
author_rank: Frequent Contributor
timestamp: August 07, 2018, 08:58:40 pm
content: If I have resonator with Q factor 10 with peak at 10 Hz,if I supply that resonator with 1 volt 1 amp 10 Hz sinewave from signal source,how high would the current inside that resonator get? Would the current be 1 amp or 10 amps?

author: bson
author_rank: Unknown
timestamp: August 07, 2018, 11:34:20 pm
content: For a passive resonator, 1A.Look up Kirchhoff's current law: what goes in must go out, and what goes out must come from somewhere. Hence if it sits in a circuit the current inside it can't exceed the current at its terminals.For an active resonator you need to include the supply current(s).

author: rfeecs
author_rank: Frequent Contributor
timestamp: August 08, 2018, 12:21:36 am
content: Quote from: bson on August 07, 2018, 11:34:20 pmNo, for a parallel LC for example, the current circulating around the loop between L and C would be about Q times the current from the signal source, or 10 amps.

author: rfeecs
author_rank: Frequent Contributor
timestamp: August 08, 2018, 12:37:13 am
content: Here's an example:

author: fonograph
author_rank: Frequent Contributor
timestamp: August 08, 2018, 07:04:59 am
content: bson says 1 amp,rfeeces 10 amps... so which one is true? I dont understand that circuit picture,but I think two of these probes say 10 while two say 1,so I guess thats proof that the circulating current inside resonator is the current of the signal source times the Q factor.

author: rfeecs
author_rank: Frequent Contributor
timestamp: August 08, 2018, 05:52:51 pm
content: bson is correct that if you have 1A going into the input node of a resonator, you will have a total of 1A going out of that node.Butinsidethe resonator circuit, in the case of the parallel LC resonator, you can have higher currents. Since the current through the L and C are 180 degrees out of phase, they can cancel.Note that this is one example where you have higher current. Different types of resonators will be different. A series LC will have higher voltage across individual elements, but they will all have the same current. A cavity resonator is different again.

author: fonograph
author_rank: Frequent Contributor
timestamp: August 08, 2018, 07:03:27 pm
content: Today I tried to learn about parallel LC resonator and I saw its not really a resonator,but a band reject filter.Can it even resonate at resonance like serial resonator can?Also the circulating currents inside resonator,you say they cancel inside,but how strong is their magnetic field? Would it be 1 amp magnetic field or 10 amp magnetic field?Feel free to tell me about cavity resonator differences,I am interested in that too.My goal is to make resonstor that will create strong magnetic field,I see the that serial LC resonator,a bandpass filter have the single frequency selectivity,but I read the voltage inside it gets higher,not the current,so the magnetic field doesnt get boosted by the extra strong circulating currents right? I read that parallel resonator gets high currents inside,but its band reject so cant resonate at single frequency.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 08, 2018, 07:19:45 pm
content: You are missing one critical parameter: impedance.A resonator is an RLC component, so you need three parameters to define them. Any (linearly independent) combination will do, but the most important are R, L and C, and Zo, Fo and Q:R = Zo * Q (for parallel, Zo / Q for series)L = Zo / (2*pi*Fo)C = 1 / (2*pi*Fo*Zo)With this, you can fully describe the system and calculate its properties.Tim