ULTRASONIC WAVES DETECT UNDER WATER PERILS OF OCEAN

Manawatu Times, Volume LIV, Issue 6843, 22 February 1929, Page 8

ULTRASONIC WAVES DETECT UNDER WATER PERILS OF OCEAN

Finding Depths and Signalling

Sound vibrations that the human ear is capable of hearing range from about 15 a second to, about 20,000 a second. Beyond this point the ear is no longer a detector, and it is perhaps because of this that the whole region beyond this point was neglected by experimenters. Now this region has been shown to be of peculiar interest. Waves above the audible are used to find the ocean’s depth from travelling steamers, for un-der-water signalling, for iceberg detection and so on. These waves have been found to kill fish and other small animals, and produce chemical reactions, and the investigation of the uses of such waves has really just begun.

Study Begin in 1912,

The development of the study of these high-frequency short sound waves, a study of what is called ultrasonics, was instigated by the sinking of tho Titanic in 1912. It was then proposed to use high-frequency sound waves for detection of icebergs, so that disasters of this sort might bo avoided. At that time Lewis Richardson, an English scientist, clearly outlined the whole procedure that is now 7 used for tho detection of rocks, icebergs, submarines and wrecks, but the methods in use for production of ultrasonic beams of sufficient intensity for the purpose were not then available.

Reach Ocean’s Depths. j Beams of sound of short high-fre-. quency and corresponding short-wave length when directed to the bottom of] the ocean, are returned as if reflected, from an almost perfect reflector. If ( the time it takes tlur-sound to go to the! bottom is carefully measured, andj knowing the speed at which it travels,! it is a simple calculation to find how far the sound must have travelled to ; make tho return trip, and thus find the depth of the ocean. If is possible to] map very small changes in contour of the ocean bed as tho ship proceeds, and, unlike the sounding load, docs no-t re-; quire that tho ship come to rest to take measurements. The reflected sound method for finding depths is also used for detection of submarines, mines,etc.

A directed beam under »water may bo used for a secret dot-dash system of; telegraphy, or by superimposing the voico on the beam it may be used for telephony by a method analogous to i broadcasting. It may bo asked how : the wave can be detected if it is of too high pitch to be heard. The system is electrical and is known as heterodyning. A wave of nearly the same frequency as that to be received is produced at the receiving end, and the ear hears a frequency which is between these two. Thus if the incoming wave has a frequency of 200,000 vibrations a second and that produced at the receiving end is 200,500, the ear will' hoar a sound of 500 vibrations a sec- ( ond. i

Fatal to Fish,

Recent experiments, while perhaps of a less practical nature, are probably more interesting. Particularly is this so of the experiments on animals in which it was found that fish could no-t survive exposure to these short waves of high intensity. It is believed by seme bacteriologists that this is due to breaking down the membrames of the cells.

If a long, tapered glass rod is dipped into oil in which there are present ul-tra-sonic waves the oil will creep up the glass, and at the end, which is made about the 1 diameter of a needle, the oil is sprayed off as invisible vapour. If touched at this needle-like end the glass will burn the fingers. Tho point will boro its way through wood or even glass. An under-water ultrasonic beacon to guide ships coming into harbaurs was installed in the Port of Calais, France, and proved successful. Ships suitably equipped can pick up the beam and follow it past obstacles. It is limited to a straight channel. Messages can be sent at the same time from ship to shore, or from ship to ship.

“An incidental result is that the receivers at tho short station have been able to detect vibrations from a shoal of pebbles situated off the shore not far away,” says Professor Boyle. “It is thought that these vibrations are due to tho rolling and colliding of the pebbles against one another by the motion of the water. The explanation is a reasonable one, since the dimensions of the pebbles would be about right to cause in one another elastic vibrations of ultrasonic pitch.”