Depth of Sea:
Ultrasonic waves of high frequency are used to determine the depth of the sea. A Piezo- electric quartz oscillator is used for this purpose. The crystal is placed between two metal plates and the plates are connected to a spark oscillator, producing damped oscillations. The frequency of the damped oscillator is tuned to be the same as the natural frequency of the quartz crystal. The quartz crystal itself acts as a transmitter and a receiver of the ultrasonic waves. The ultrasonic waves transmitted by the crystal are directed towards the bed of the sea. These waves are reflected back from the bed and the echo is detected by the crystal itself. In this case, the metal plates are automatically connected to an amplifier and a canoed ray oscillograph. The time interval between the emitted signal and the echo is determined with the help of the oscillograph. Knowing the velocity of sound through sea water and the time interval, the depth of the sea can be calculated. Suppose, t is the time interval between the transmission of the ultrasonic wave and receipt of the echo and the velocity of sound waves through sea water, then depth of the sea,
h = v x t/2
This method is also suitable to detect the presence and depth of submarines, rocks etc., from the surface of sea water. The instrument directly calibrated to show the depth of sea is called a fathometer or echo meter.
Signalling:
Ultrasonic waves are used for directional signaling. The frequency of ultrasonic waves is higher than the audible sound waves. There- fore, the wavelength is comparatively small. Due to the small wavelength, ultrasonic waves can be sent in the form of a short beam. If a quartz crystal, taken in the form a disc of radius r, is used as a source of ultrasonic waves, the angle of the cone containing these waves is given by
sin 0 = 0.61 λ / r
For small wavelengths, e is small. Even for a small amplitude of the vibrating crystal, large amount of energy is radiated whereas it is not possible in the case of audio frequency waves. Recently, ultrasonic microscope has been invented. It is used to detect concealed objects. The frequency is very high so that the wave length is of the order of the wavelength of visible light.
Heating effects
When a beam of ultrasonic waves is passed through a substance, it gets heated. If ultrasonic waves pass through water at 0°C, water can be made to boil. Mechanical effects
Ultrasonic drills are used to bore holes in steel and other metals or their alloys. Here the drill oscillates with ultrasonic frequency and can bore any hard metal.
Cracks in metals
Ultrasonic waves can be used to detect cracks or discontinuity in metal structures. In this case, an emitter and detector of ultrasonic waves are used. Ultrasonic waves from the emitter are directed towards the metal. The reflected beam is detected by the detector. If there is a crack or discontinuity, there will be rise in energy received by the detector, if the emitter and the detector are on the same side. If the emitter and the detector are on the opposite sides of the metal, there will be fall in energy at the regions of cracks or discontinuity.
Formation of alloys
Alloys of uniform composition are obtained by subjecting the constituents to an ultrasonic beam. The two constituents are well mixed up by ultrasonic waves, even though the constituents differ in density.
Chemical effect
Ultrasonic waves act like catalytic agents and accelerate chemical reactions. They bring about a number of chemical changes. Some of the chemical applications are as follows:
- When potassium iodide is subjected to ultrasonic waves, it liberates iodine.
- Water is decomposed into hydrogen and hydroxyl ions, by the action of ultrasonic waves.
- Ultrasonic waves reduce mercuric chloride into mercurous chloride.
- Water and oil are immiscible. An emulsion of water and oil is obtained when the mixture is subjected to ultrasonic waves. Similarly, an emulsion of water and mercury can be prepared.
- Ultrasonic waves accelerate crystallization.
- Ultrasonic waves explode nitrogen iodide.
Soldering
Aluminum cannot be soldered by ordinary soldering method. To solder aluminium, ultrasonic waves are used in addition to the electrical soldering iron. The ultrasonic waves remove the oxide film and facilitates soldering.
Medical applications
Ultrasonic waves have a large number of applications in the field of medicine. Some of the important applications are as follows:
- Neuralgic pain. Ultrasonic waves are useful for relieving neuralgic and rheumatic pains. The affected portion of the body is exposed to ultrasonic waves. The waves produce a soothing massage action and relieves pain.
- Arthritis. Ultrasonic waves are used to relieve pain due to arthritis. Here a small metal head, vibrating with a frequency of more than 10° hertz is moved over the skin of the patient. These vibrations after passing through the tissues, produce a deep massage action. The patient is relieved of the pain.
- Contracted fingers. Ultrasonic waves are used to restore the contracted fingers. They are also used to loosen up the scar tissues in various parts of the human body.
- Broken teeth. Ultrasonic waves are used by dentists for the proper extraction of broken teeth.
- Bloodless surgery. Ultrasonic waves are used in bloodless surgery. Here the ultrasonic waves are focused on a sharp instrument and the tissues are destroyed without any loss of blood. American doctors have used such instruments for conducting bloodless brain operations.
Sterilization
Ultrasonic waves can destroy unicellular organisms. is Bacteria perishing under the action of ultrasonic waves. Ultrasonic waves are used in the sterilization of water and milk.
Enemy of lower life.
When some lower animals like rats, frogs, fish, etc., are exposed to ultrasonic waves, they become lame.
Ultrasonic waves are having more and more practical applications in all fields. Active research work is still in progress to study the effect of ultrasonic waves in mechanical, biological, chemical, physical and industrial fields.