From: dash@ast.COM (Darrell Shively)
Newsgroups: sci.physics,sci.electronics
Subject: Wireless power transmission question
Keywords: wireless power transmission electronics physics
Date: 9 Oct 92 01:33:59 GMT
Followup-To: poster
Organization: AST Research, Systems Software Engineering, Irving, CA


Greetings:

    I have been experimenting with short range wireless power transmission.  
I have constructed a setup that allows me to transmit a limited amount of 
power a short distance, but I'm having trouble locating the equations that 
would allow me to analyze my design.

    Consider the following:

  /-----\                     /-----\
 |      /|                   |      /|
 |     / |                   |     / |
 |   R1  |                   |   R2  |
 |       | --------D-------- |       |
 |       |                   |       |
  \-----/                     \-----/
     T1                          T2
     G1                          G2

    Two coils are placed colinearly separated by a  distance D (typically 
2-6 inches).  Coil one (C1) has radius R1 and T1 turns of wire of guage G1.  
Coil two (C2) has similar parameters.  There are no ferrous materials in the 
system.  What equations describe the following?
    1)  Current induced in C2 in terms of a current driven into C1.
    2)  Efficiency of power transmission from C1 to C2.
    3)  Effect of frequency on 1) and 2).

    What are the general steps I can take to accomplish the following
    1)  Select the location and width of the efficiency vs. frequency 
        response curve.
    2)  Minimize the total mass of wire.
    3)  Maximize distance D.

    What can I do to my active electronics to maximize efficiency?  I have a 
vague notion that I can affect the power factor to tailor this, but I don't 
know how to go about this.  Would transformers between my active electronics 
and C1 help to compensate for impedence mismatch, or are there better 
approaches?  Also, would the addition of ferrous materials in the center of 
one or both loops (but not in the space between them) raise the efficiency?  

    Finally, is this different from a radio transmitter?  My intent was to 
avoid generating radio waves (free photons) by sticking in the magnetic 
domain (so to speak).  Did I achieve this goal, or does everything that 
doesn't transfer to C2 go out as RFI?  Are there likely to be health 
consequences to driving power out a setup such as this?

    Feel free to respond with vagueness, handwaving, and references.  This 
isn't an assignment, I just want to understand my demented little project 
better.  I have tried cracking my old Halliday and Resnick, but it just 
didn't seem to have a cogent discussion of what I'm doing.

    Thanks in advance for all of your informative responses.  Please 
respond by mail (rodentia@alr.com) as I don't have news access.

Regards,
 -Tom
---
Thomas Roden                 | e-mail: rodentia@alr.com
Advanced Logic Research, Inc.| FAX:    (714)581-7951
9401 Jeronimo                |
Irvine, CA  92718            |

-- 
Darrell M. Shively II  | internet: dash@ast.com      |
AST Research Inc.      |     uucp: ..uunet!legs!dash |
16215 Alton Pkwy       +-----------------------------+----------------------+
Irvine, CA  92713-9658 | "These are my opinions.  No one else shares them." |