Inductive Coupling Coefficient

how long?

5mm rods, how long? what orientation? end to end? side by side?

audio ferrites? low perm ferrites?

I don't know. What would be best? ~100kHz sinusoidal drive ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

obviously, best orientation depends on length.

from memory rods usually are 4:1 up to 10:1 aspect ratio rarely longer, they break pretty easily. surprisingly the aspect ratio determines more the 'effective' permeability much more than the basic permeability, like with a 4:1 anything with more than 100 rel perm makes NO difference.

do you have any way to 'close' the magnetic path just a bit? Tuning makes a BIG difference! on getting a huge voltage out of it.

I can make some 'guesses' or spend some time to look at it in a bit more detail over night and get back to you with justifications for why do this versus do that.

Cross talk you can get some good estimates. If this is for a 'communication' at all; we should discuss that a bit too.

This is an RFQ for a slow speed (~100bps) data link "magnetically", with ~5mm gap.

I'm just wondering feasibility before sticking my neck out. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Data? That can't miss at 5 mm. I've used similar geometries to transfer enough power to run a microprocessor-based electric meter

*and* send the data back over the same path, more like 25 mm.

Get an assortment of small unshielded drum-core inductors from Digikey and measure things. Drums have a nice geometry for axial coupling. Resonating both ends will help keep the power requirement down. 10 to

50 KHz carrier should be fine. You could get volts at the receive coil.

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John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

That's pretty much what I expected. But I also have a 5mm "above the PCB" maximum... do drum/pot cores come that small a diameter? ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Full-duplex? piece of cake! I've done that using air core PCB coils [no winding necessary] and operate over a distance of 8 inches using less than

3.3Vdc, 5mA per TxRx pair. Also, no tuning required, no 'touchy' high tolerance analog parts. PLUS, not even catch the attention of FCC, operate in a true don't care band. 100bps! I'ved designed systems that communicate MILES, through salt water to do that!

no 5mm, 100bps full-duplex, piece of cake.

Big hint: communication between two entities should NEVER be treated like a radio transmitter/radio receiver pair. leave THAT for the broadcast industry where ONE talks to many. Rather THINK SYSTEM! where BOTH must communicate hand in hand, not simply throwing information out there hoping the other stumbles over it. Thinking system will get reliable cheap communication that even instantly flags you as the link starts to weaken!

Sorry, have to get offline for a bit, painting here.

Thanks! ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Me, too! IKEA bookcases ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Take a look at the unshielded ones, ME2200 or DO1608C. Coilcraft is great for sampling.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Stop it! you're going to optimize a weak design following this path. If you want to avoid FCC scrutiny stay below 10KHz. Don't even use ferrites, no real need. You aren't transferring energy, you're transferring 'information', where almost NO power still will tell you stuff.

ARRRGGG!

I've got a system in mind that will cost less than $1 each in volumes of

100, and if you have some left over uController power, like inside TI's MSP430, the rest is FREE! jeeesh!

ferrites?! barbaric! plus weight, mounting, wrapping, vibration etc etc .... stay away from antique concepts, PLEASE!

I'm guessing 50% or less.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

See reply to what3rd who did an excellent 'rule-of-thumb' estimate.

I was VERY surprised to see approximately 0.1 coupling!

If you're stuck on using this approach, and need a model; I've already got the .asc running for various positions. However, it's easy to do a curve fit and produce k vs position, too.

Is this for isolation? high voltage separation? Have you thought of using those cheap LED 'handheld remote controllers' They transmit quite a distance, cost nothing and run on nothing, ...well almost. but you get to piggy back on VOLUME production costs. Bunch of chipsets out there.

This is one of those "I wouldn't do it this way", but I'm looking into it at the insistence of the client. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

whew! but still, will have your name on it when finished.

However, I just confirmed that using a rod that is 5mm diameter by 1cm long and the permeability changes from 2000 down to 1000 you only get about 0.3% change in inductance. [remember I said a function of aspect ratio?] which means *if* you tune the inductor, it will stay pretty much in tune. At least for a Q of 100 and that should be good enough for peaking the signal AND getting 1kHz through on a 100kHz carrier. [more possible but allow some sloppiness] and 1kHz sidebands means at least

2kb/s. and that means at least 200+ Full Duplex so you're done.

The answer is yes it can be done that way.

That's OK. If I design it... it _will_ work >:-}

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Wasn't questioning that aspect, just the "why did he do it this way?" aspect. and NOT even use vacuum tubes!