The American Seal
In the book “The future of the mind“, Dr. Michio Kaku talks about a Russian spying incident involving the American seal and an unwitting US ambassador in the erstwhile USSR. A group of young kids had donated an American seal, similar to the one shown here, as a “friendship” gesture to the American ambassador in Moscow for helping the great bear during World war II. This seal which was prominently displayed inside the American embassy in Moscow from 1946 until it was taken down in 1952 had been surreptitiously transmitting conversations happening within the embassy corridors. What prevented this bugging device from not being detected for so long was that it didn’t require any direct source of power.
Any hunter worth his salt knows that the best place to find his hunt is near a watering hole. Machine or beast they all require a source of power and following this supply route is the surefire way to track a beast or kill a terrorist. However, this cunning piece of contraption had no wire connecting to a power source. A simple diaphragm to capture sound waves and a long metallic nail that acted like an antenna are all that was inside this “Great American Seal” bug. The simplicity of this design was yet another reason why this remained undetected for long.
The Great American Seal Bug
Very early on it was known that metallic objects act like mirrors to radio waves. Depending on the dimension of the metal, it will reflect back some of the radio waves falling on it. This is the principle behind radars, the anti-theft devices used by big-box retailers and so on. The only thing this spying device needed to start transmitting the audio signal was a high energy radio wave beamed at it from far and some sensitive radio equipments to monitor the reflections. The operation of this device is very simple and is based on a phenomenon called back scattering. When soundwave falls on the diaphragm, it causes it to vibrate which in turn causes the metallic nail to vibrate. This vibration induces a very small change in the reflected radio waves that a Russian spy comfortably sitting in a building across the embassy could listen to Uncle Sam’s game plan to checkmate the big bear.
Sound wave through glass
This ingenious Russian contraption got me thinking about extending this idea into an interesting domain. What if we can do the same thing with light? After all light is nothing but radio wave (electromagnetic wave) operating at much higher frequency and the greatest source of this energy, Sun, is readily available. Additionally, our eyes operate by capturing backscattered light. Or in plain speak, we see stuff around us because our eyes detects the light reflected off of objects. When sound waves, which are pressure waves, fall on objects in our surroundings, it causes small vibrations on its surface. If we have a very sensitive, high speed camera, then technically it is possible to record these tiny surface vibrations. It would then be a matter of some trivial signal processing to recreate the original sound from these high speed frames of video data. I am calling this as a What You Hear Is What You See (WYHIWYS) device or an Audio Telescope. Think of the immense possibilities that such a device would open up…. For astronomy, a brand new powerful telescope with an attached high speed camera that can not only bring to you the vivid images of a storm raging deep within Jupiter’s giant red spot but also reproduce its deafening roar. For military and covert operations, this would be an indispensable tool. For entertainment, an episode of cheaters or some trashy reality show would feature the exploits of a transgressing spouse with video and audio feed in real time captured from far and so on…
Edgertronic High Speed Camera
While researching on this idea, I came across this cool high speed camera project on Kickstarter developed by a two men team called Edgertronic. Their 10cm x 10cm camera is capable of capturing video at an astonishing rate of 18,000 frames per second. This limits the maximum audio frequency that could be detected using this camera at 9000Hz (Nyquist Limit). Luckily, this is near the upper limit of an adult human’s auditory abilities. Additionally, I came across this conference paper submitted last year at the Acoustics Society of America describing an experiment that involved using a high speed camera zoomed at the throat of a subject to pick up spoken words. We have all the tools in place and it is only a matter of time before someone puts them all into a neat little package crowdsourced on kickstarter. The future of this area of research is exciting and as the cliche goes… “The only limitation is your imagination”.
Capturing spoken word from throat vibrations
Akutsu, Mariko, Yasuhiro Oikawa, and Yoshio Yamasaki. “Extract voice information using high-speed camera.” Proceedings of Meetings on Acoustics. Vol. 19. No. 1. Acoustical Society of America, 2013.