A device that converts the wail of a baby into a ‘sonic bullet’ exceeding the human pain threshold could finally allow the widespread use of sound as a non-lethal weapon.
While blasts from previous sonic weapons affected all within earshot, the HyperSonic Sound system from San Diego-based American Technologies uses an ultrasonic beam to divert the sound at a precise target.
The device plays the sound of a baby’s cry at 140dB, 20dB above the human pain threshold and similar in intensity to a jet engine during take-off.
Those hearing it experience symptoms similar to a migraine, disorientating or incapacitating them.
However, the system also has commercial applications and could enable the introduction of personalised advertising by allowing vending machines and retail stores to single out potential clients from a crowd.
‘Initial applications for HSS include shop displays, vending machines, kiosks, in-store advertising, museum guides and trade show exhibits,’ said Bob Todrank, vice-president of business development.
The technology relies on non-linear distortion. In effect this means that when a sound wave travels through the atmosphere it distorts and in effect produces new frequencies or sounds around the original.
The level of distortion is predictable, so it is possible to generate a second sound through the natural distortion of another.
HSS uses ultrasound to create the ‘new’ frequencies and carry them to the target. Because ultrasound is itself at such a high frequency it can be directed like a beam of light, and for the same reason it cannot be detected by the human ear. Only the distortion it produces can be heard by the target.
Using this technique, the company has taken music, speech or the noise of a baby crying and converted it via an ultrasonic transducer into a highly complex signal. This is then amplified and emitted as a beam along which the non-linearity of the air produces distortion in the form of the sound that was originally converted.
The new frequencies do not spread outside the ultrasound column which means only those in direct line of the emitter will be able to hear the noise, unless it has been directed to bounce off a solid object such as a wall.