Inductive Coupling

CaptainP

Hi Guys,

I'm not sure if this is the best place to post this thread but hopefully someone can help me out there. The problem is that i want to design an inductive link so that max power is transfered across link. it requires impedance matching.I was just wondering if anyone had any experience in this field and if so could they point me in the right direction.

Captain P

nesf

Hmm, I think this would possibly get more replies if it was in engineering.

Thread moved.

SparkyLarks

you using resonant ccts??

CaptainP

Yea i'm using resonant ccts. Basically i have a class e amplifier connected to a series resonant circuit in the primary.This is linked to a secondary which has a parallel resonant tank. I want to know basically the best way to transfer power from the secondary to the primary.I have seen some papers and stuff that try to "match the impedance" of the load and source. They don't explain it very well.Also do i need to keep the same resonant frequency on both the primary and secondary in order to obtain max power transfer.
Any help is greatly appreciated,
Captain P

SparkyLarks

I am assuming that you want max power to go to a load rather than maximum power to transfer across the link.

to maximise power across a link have a huge inductor( however a higher inductor has a huge impedance and thus the current flowing in it will be small and so the power to the load will be small.

If you want to maximisse the power to the load
First off you want to match the impedance of the secondary to the load.

Too big and the current induced will be small.
Too small and no current will flow through the load as the resistance of the resonant cct is lower .

After that is optimised then you optimise the Source(transmitter) inductance.
I think it pretty much works out that the optimum transmitter inductance is equal to the reciever inductance

CaptainP

Yea i want to transfer power to the load as efficiently as possible. you say to match the impedance of the secondary to the load.
I have some papers that say you must match the output impedance of a source to the input impedance of a load to attain maximum power transfer. I was just wondering the effect of the mutual impedance Xm. where does this come in to the equation. Do you have to keep the same resonant frequency on both sides.
To give u a better idea of my circuit i have
-On the primary side i have a class E power amp. then a series tuned resonant circuit (a cap and an inductor)
-On the secondary side i have a parallel resonant circuit (a cap and an inductor) followed by a resistive load.
I basically need to choose these values of C&L in order transfer as much power to the load as possible.

Thank for all your help so far its just i'm finding this subject a bit confusing,

SparkyLarks

firstly, the resonant frequency is determined by the frequency of the AC current flowing in the primary inducrot, The series capacitor reduces the impedance of your transmitter cct, which increases the magnetic field transmitted, and hence the power transmitted.

The secondary inductor then picks up a voltage which is dependant on the strength (and frequency of the mag field) This voltage will be at the same freq of the mag field and the primary current. The current flowing through the inductor will be at this frequency.

With no cap the current flowing through the load is determined the voltage inducedand the totalimpedance. So the bigger the inductance. The bigger the voltage induced. However the increased impedance will decrse the current flowing in the cct and hence power to the load then reduce the voltage to such a degree that the power to the load is now low, despite the high voltage being induced.
impedance matching is about optimising the inductance to maximise the current flowing in the cct.

Putting in the parallel resonant cap increases the current flowing in the load. It's hard to get to grips with how that happens, and I can't remember enough to expalin it. But it is akin to lowering the internal impedance of a bettery.

From what I remember.( I'll try to check it out tonight)
the power source for your load is the secondary inductor.
you match that impeddance to the load.

that gives you and inductance. value.
The value for the paralled capacitor is determinded by the transmission frequency.

Set your primary inductor to the same value as the secondary

Choose your primary cap to to achieve resonance at the tramnsmission freq with your primary inductor.
Voilla
Loads of power to the load.

Xm is your mutual inductance, you don't tweak it really, or use it to tweak. set you inductance as above you coupling is determinaed by the size positioning and orientaion of your coile, and your mutiual inductance is a product of those.

You do need to have the same resonant freqqency on both sides as both sides operate at the same frequency.

furqan

hello

My PROJECT is same like you but i have just started. I also need to maximize the power transfer to load through inductive coupling. Would you please forward me papers you have searched in this regard.

Thanks in advance

Furqan Noor