Ultrasound Technology: Principles, Applications & Medical Uses

Ultrasonics Browse the article Ultrasonics

Ultrasonics

Ultrasonics, the branch of physics and engineering dealing with highfrequency sound waves. The waves are produced by objects vibrating more than 20,000 times a second, creating ultrasoundsound that is beyond the range of human hearing. (The term ultrasound is also used for a type of medical test, discussed later in this article.) Ultrasonic waves have numerous medical and industrial uses. They are used in tools for cutting, cleaning, mixing, inspecting, and soldering.

Ultrasonic vibrations may be created electronically, by passing alternating current through a quartz or ceramic crystal ; mechanically, with special sirens; or magnetically, by the action of an alternating magnetic field on a hollow metal rod.

Uses of Ultrasonics

Pierre Curie discovered how to produce ultrasonic vibrations in 1890. By World War II their first practical applicationthe detection of submarines underwaterhad been developed. Today ultrasonic waves have many important applications.

Medical

In a technique called ultrasonography (also referred to as simply sonography), a probe placed against the skin directs low-energy ultrasonic waves into the body. The same probe detects waves reflected by tissues in the body and converts the waves into electrical signals. The signals are used to form an image of internal structures on a viewing screen similar to that of a television set. Ultrasonography is useful for detecting certain tumors and for diagnosing disorders of the gall bladder, kidney, liver, and certain other organs. It is also used during pregnancies to monitor the development of the fetus; and to determine whether there is more than one fetus in the womb; and to detect certain birth defects. A test using ultrasonography is popularly called an ultrasound.

Ultrasonic energy can heat deep tissues, much like diathermy. The method has been used to treat arthritis, bursitis, muscular dystrophy, and other diseases. High-energy ultrasonic waves can be focused into a pinpoint "scalpel" for bloodless brain surgery. In dentistry, ultrasonic devices are sometimes used to remove calcium deposits from the surface of teeth.

Cleaning

Ultrasonic vibrations in a liquid cause millions of bubbles to form and collapse thousands of times a second. This process, called cavitation, blasts clean the surface of objects immersed in the liquid. Applications of this process include sterilization of surgical instruments and the scouring of precision metal parts.

Machining

Diamonds, tungsten carbide, and tool steel are readily carved and drilled by ultrasonic techniques. The material to be machined is fixed in place and the cutting tool is lowered until it is in contact with the surface. Then a liquid abrasive is poured over the material in a steady stream. The tool vibrates at an ultrasonic frequency and drives tiny particles of the abrasive against the material with tremendous impact. This bombardment, together with cavitation, grinds an exact counterpart of the tool face into the material being machined. Oddshaped cuts not possible with other methods can be made.

Other Uses

Sound waves beamed into solid materials will not readily cross air barriers such as cracks. When a crack or other defect is encountered, the sound waves are reflected to a measuring instrument. This form of inspection has replaced the use of X rays in many industries.

Ultrasound is used in some types of burglar alarms and remote-control television tuners. It is also sometimes used in welding and soldering metals, mixing liquids, and dyeing and bleaching textiles.