UFO?

An electroacoustic device for transducing electrical energy to acoustic energy and vice-versa, and, more particularly, to such devices which operate at ultrasonic frequencies. It has been 'found that a suitable device of this character, which is operable at ultrasonic frequencies, generally comprises a hemispherical vibratory shell, a pair of magnetostriction rods having their ends secured to the inner wall of the shell, and a magnetostriction winding on each of the rods.

Magnetostriction is the change in dimension produced in a magnetic material, such as iron or nickel or alloys, upon being magnetized, in this instance by the winding which causes the rods to effect vibration of the shell when the device is used as a transmitter. When the device is used as a sound pick-up, vibration of the shell changes the rods in dimension, which in turn changes the magnetization in the rods in a manner to alternate the same and generate electrical oscillations in the winding around the rods.

In both cases, the energy transduced to another form depends upon the motion of the shell, and, in so transducing energy, maximum efficiency is desirable to transmit the vibrations of the rods as airwaves of maximum power and to pick-up the 'full power of such a wave.

Note: Magnetostriction is used in Electronic article surveillance (EAS) type of system used to prevent shoplifting The tag can also be deactivated by demagnetizing the strip. Same, like those little things you stick to your Nephew's back, then exit the store to see what happens.

More Information on this particular device:

Patent US2832952A Status: Expired - Lifetime