The basic concept for this project was that the energy in a microwave beam would be focused on a flexible cell filled with ammonia. The flexible cell would expand as it absorbed the microwave energy, thereby producing mechanical pressure. This might have applications in switching the position of "gates" at remote or inaccessible sites, or for the conversion of modulated microwave energies for such devices as "large audience" hearing aids, or "wireless" controls of toys.
On October 6, 1969 I wrote a memo to a friend suggesting a possible product line which would use flexible ammonia-filled cells, illuminated by microwave energy, for producing mechanical effects at a distance. That memo was based on reading the following article:
"Thermal and Acoustic Effects Attending Absorption of Microwaves by Gases," by W.D. Hershberger, E.T. Bush and G. W. Leck in "RCA Review," Vol. 7, No. 3, Sept. 1946, pg. 422-31.
The article was about the absorption of microwave energy by different gases. The key points that I focused on were as follows:
I decided to set up a home experiment to determine a practical use for this phenomenon. K-band (24 gigahertz) microwave transmitters were available for use in rain studies and mapping (at 15 to 125 milliwatts). Diodes were available in the milliwatt range at lower S band frequencies (2 gigahertz), and semiconductors were available in S band or X band frequencies at low power in the gigahertz frequency range.
I also scouted around for sources of ammonia and other candidate gases that might absorb energy in the broadcast frequency range.
As you probably guessed, these efforts turned out to require more work and time than I could spend on them. So the project went into my "Someday To Do" file. Today I pulled it out, dusted it off, and am describing it to you in the hope that you might carry it further. I think it has commercial possibilities.
An easy way to understand what this project is about is to imagine the following experiment.
Fill a small balloon with ammonia gas. Then take a microwave radio transmitter that can be modulated by voice inputs. Aim the transmitter at the balloon so that the microwave energy causes the ammonia in the balloon to expand and contract, thereby producing sounds at those voice frequencies. If you place your ear near the balloon, you will hear the voice signal that is modulating the microwave energy. You don't need an amplifier!
That gives you a general idea of how the system would work. However, instead of a balloon, you must design a device that holds small flexible cells of gas against a person's ears (say, in a helmet, or an in a headphone configuration). If the cells are close to the ear it won't be necessary to provide any amplification energy at the passive "ammonia receiver"
Also, you should select a gas (other than ammonia) that will respond to lower radio frequencies in the same way that ammonia responds to microwave frequencies. The frequency will depend on the directivity required for the application. Lower frequencies provide omnidirectional coverage (such as for calling the kids somewhere in the neighborhood). Higher frequencies provide greater directional selectivity (such as aiming the transmitter at the helmets of football players who you want to control).
I haven't followed the significant changes in the technologies for miniaturized transmitters, or the encapsulation of gases in flexible cells (similar to those air bubbles in plastic sheets used for packaging). But it seems to me that this project might produce profitable results if pursued further by the right person. Run with it! Good luck!
[ Home Page ] [ Perspectives ] [ Projects ] [ Speculations ] [ Books ]
Comments or suggestions? mortgale@comcast.net
Copyright © Mort Gale, 2003 All rights reserved.