Sound consists of vibrations that can be heard by humans and other animals. Ultrasound is a type of sound frequency that cannot be heard by humans. Since "ultrasonic" is a word used to describe ultrasound frequency, the terms ultrasound transducer and ultrasonic transducer are used interchangeably.
An ultrasound or ultrasonic transducer is a device that converts energy -- such as electricity -- into ultrasound vibrations. These vibrations bounce off of material, such as body tissue and water, to create echoes or computerised images for medical or industrial analysis.
There are many types of ultrasound transducers that are generally labelled according to their design or intended usage. For example, contact transducers are used by applying them directly to, or having contact with, a solid surface for analysis. Some contact transducers are named according to their general design, such as a dual element, a linear array or a convex transducer. Contact transducers can also be named according to what they are used for, such as trans-vaginal transducers.
Unlike contact transducers that are applied directly to solid surfaces, immersion transducers are submerged into liquids such as water and oil for analysis.
However, regardless of the general names and specialised varieties of ultrasound transducers, all ultrasound transducers are ultimately classified in one of two fundamental groups: piezoelectric or magnetostrictive.
Piezoelectric transducers operate from the piezoelectric effect. The piezoelectric effect occurs when energy is produced by applying mechanical stress between two non-conducting surfaces. Non-conducting surfaces are surfaces that do not conduct -- or are resistant to -- electricity. The non-conducting surfaces used in piezoelectric transducers are crystals, which are primarily made from quartz, Rochelle salt or ceramics.
Piezoelectric transducers are considered to be the most versatile type of ultrasonic transducer. Some piezoelectric transducers are used for vibration control and pressure sensors. These can be found in audio equipment speakers, printing devices, space platforms and aircraft. The medical industry commonly uses piezoelectric transducers for diagnostic imaging, such as in sonograms.
Magnetostrictive transducers use oscillating magnetic fields to expand and contract various kinds of magnetic materials within the transducer. The magnetic materials primarily used within these transducers are nickel and nickel alloys. The magnetic expansion and contraction of these materials generate high-frequency mechanical vibrations.
Magnetostrictive transducers are used in numerous industrial environments, such as steel and paper mills. These transducers are also utilised for ultrasound cleaners, underwater sonar and surgical tools.
Most manufacturers of ultrasound systems use piezoelectric transducers. Proponents of piezoelectric transducers cite that magnetostrictive transducers are larger, less energy-efficient and may require special cooling methods. However, others counter that magnetostrictive transducers are more durable, facilitate better multiposition measurements and that piezoelectric transducers have a greater propensity to lose power over an extended period of time.
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