[Keelynet] phase conjugation for mapping space and objects!

[Jerry Decker - KN]

Hola Folks!

To 'relieve the tension' about the SG/desulphate question..<LOL>...this 
is just an amazing little acoustic/wave trick....what happens if the 
surface gets dirty or something is placed on it that might alter the 
reflective properties???

(I happen to think it IS desulphation which restores power since it is 
generated as a chemical process, but need to do experiments like Roamer 
and Bedini have done.)

A senior engineer everyone called Pops, who worked at Mostek when I did 
was great to talk with.  I was a total newbie, still in electronics 
school and wide open to learning lots of goodies...and of course full of 
questions.

So I asked Pops how would you measure the natural resonant frequency of 
a mass without altering it.  He thought about it and said, 'hmmm....I 
guess I would use a dual trace scope, attach a speaker to one side of 
the test mass and a microphone to the other side."

He would connect the speaker signal to one scope channel and the 
microphone to the other scope channel, the run a frequency generator 
slowly up the scale and watch for when the microphone signal reached the 
same amplitude as the speaker signal...that would be one of the 
resonance points...of course the greatest amplitude match would be at 
the true resonant frequency.

I tried this but never found with a big limestone block I paid $200 to 
have cut, but never got anything that made sense...still have that block 
and a granite block of similar size that cost $300...have to do that again.

11/25/05 - Localization of finger impacts using acoustic time-reversal 
process

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APPLAB000087000020204104000001&idtype=cvips&gifs=Yes

Time reversal in acoustics is a very efficient solution to focus sound 
back to its source in a wide range of materials including reverberating 
media. It expresses the following properties: A wave still has the 
memory of its source location.

The concept presented in this letter first consists in detecting the 
acoustic waves in solid objects generated by a slight finger knock. In a 
second step, the information related to the source location is extracted 
from a simulated time reversal experiment in the computer.

Then, an action (turn on the light or a compact disk player, for 
example) is associated with each location. Thus, the whole system 
transforms solid objects into interactive interfaces. Compared to the 
existing acoustic techniques, it presents the great advantage of being 
simple and easily applicable to inhomogeneous objects whatever their 
shapes.

The number of possible touch locations at the surface of objects is 
shown to be directly related to the mean wavelength of the detected 
acoustic wave. An acoustics sensor and analyzer that localizes finger 
impacts on a surface and maps them to computer commands.

The system taps time-reversal acoustics to analyze reverberations within 
a solid object in order to trace a sound back to its point of origin.

The system works with rigid materials like glass, metal, hard plastics 
and ceramics, and can work with irregularly-shaped objects. The system 
is made up of a single acoustic receiver and a personal computer, and 
can identify contact points as small as a square centimeter.

The system can be used to turn a desk top into a computer keyboard, a 
coffee table into a remote control, and a spot on a wall into a light 
switch.
--
              Jerry Decker - http://www.keelynet.com
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