Ultrasound: properties, applications, and overview
Ultrasound denotes sound waves at frequencies above the human hearing range. This article explains its physics, major applications in medicine and industry, history, and safety considerations.
Ultrasound refers to mechanical sound waves with frequencies higher than those detectable by most humans. In general usage, frequencies above the commonly cited upper limit of human hearing are considered ultrasonic; that limit is often given as around 20 kilohertz. The concept connects to basic ideas of sound and frequency, and to discussions of the upper limit of human hearing.
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Characteristics and how it works
Ultrasound propagates as longitudinal pressure waves in gases, liquids and solids. Devices that generate or detect ultrasound typically use piezoelectric transducers: electrical signals drive crystal deformation to produce mechanical vibrations, and returning echoes convert mechanical motion back into electrical signals. Frequency, wavelength and amplitude determine resolution and penetration; higher frequencies give finer detail but shorter range.
Common applications
- Medical imaging: Diagnostic sonography produces real-time images of soft tissues, fetal development and organs. Doppler ultrasound measures blood flow and velocity.
- Therapeutic uses: Focused ultrasound can heat or disrupt tissue (e.g., targeted ablation) and low-intensity ultrasound is used in physical therapy.
- Industrial uses: Non-destructive testing finds flaws in metals and composites; ultrasonic cleaning uses cavitation to remove contaminants.
- Navigation and biology: Sonar systems and animal echolocation (bats, dolphins) operate at ultrasonic frequencies for ranging and navigation.
Other areas include ultrasonic welding, sensors for distance measurement, and acoustic emulsification in manufacturing. Advantages of ultrasound are safety (non-ionizing energy), portability and real-time feedback; limitations include lower penetration at high frequencies and difficulty imaging through bone or gas.
Historically, ultrasound technology developed through 20th-century advances in electronics and materials. Early sonar work, wartime research, and the refinement of piezoelectric materials and signal processing led to modern medical and industrial equipment. Regulatory bodies set device standards and clinical guidelines to ensure effective and safe use.
Safety considerations emphasize minimizing unnecessary exposure and following established clinical protocols. Biological effects can be thermal or mechanical; when used properly in diagnostics the procedure is widely regarded as safe, while therapeutic and high-intensity applications require controlled conditions and specialist oversight.
For further reading on fundamentals and applications, consult technical literature and authoritative reviews that cover acoustic physics, device design and clinical practice.
Generation and registration of ultrasonic waves
Dynamic and electrostatic loudspeakers are suitable for generating ultrasound in air, as are piezoelectric loudspeakers in particular, i.e. membrane-coupled plates made of piezoelectric ceramics which are excited to vibrate by reversing the piezoelectric effect. Piezoelectric plastics (PVDF) can also be used to directly drive membranes, which results in improved transmission behavior.
Ultrasound in liquids and solids was initially generated only with magnetostrictive transducers (the first echo sounders worked in this way). Today, piezoelectric quartz or ceramic transducers are increasingly used. An alternating voltage with their natural resonance frequency (or a harmonic thereof) is applied to them. The oscillations are then transmitted, e.g. via the bottom of an ultrasonic bath, into the liquid.
Not too high frequency ultrasound can also be generated by galton whistles.
In principle, ultrasonic waves can be received using the same electrical transducers as are used to generate them.
To make bat calls audible, there are bat detectors that record the calls with a microphone, shift the frequency range of the calls that are in the ultrasonic range into the audible range, and play back these signals through a speaker or headphones.
Applications
Ultrasound has various applications in technology and medicine:
- Time-of-flight measurement of emitted ultrasonic pulses:
- Sonar, echo sounder: Depth measurement and seabed survey from water and underwater vehicles, fish finder.
- Early rangefinders (in air), such as for autofocus lenses (Polaroid)
- non-contact level measurement
- Sonography and echocardiography for the examination of humans and animals
- Parking aids, distance warning
- Underwater direction finder for flight recorders
- Exploitation of the Doppler effect:
- Measurement of wind speed with ultrasonic anemometer
- Ultrasonic flow sensor for pipes and ducts
- Motion detector
- Measurement of blood flow velocity by Doppler effect
- Ultrasonic density measurement
- Material processing:
- Ultrasonic vibrating lobe
- Ultrasound cleaning
- Ultrasonic welding
- Ultrasonic cutting
- Fiber digestion
- Ultrasonic microscope
- Ultrasonic motors / drives
- Contactless handling with ultrasound
- Information processing and transmission
- Early remote controls (late 1950s to about the mid-1970s) for television sets.
- Acoustic delay lines for signal delay in electronic circuits
- Surface acoustic wave filters, sensors, ceramic transducers, oscillating crystals
- Materials testing and structural investigations:
- Ultrasonic testing devices: unwanted inclusions, blowholes or cracks can be detected via reflections at discontinuity points of the density and their signal propagation time
- Coating thickness measurement, also on non-metallic substrates and with multi-layer systems
- Ultrasound therapy
- Ultrasonic cell disruption, production of protein crude extracts from microbiological samples (mainly bacteria, both in research and industry) by ultrasound, as the sound waves lead to lysis of the cell wall
- High-intensity focused ultrasound: ulcer treatment, stone disintegration (lithotripsy)
- Removal of tartar through water-cooled, high-frequency oscillating metal tip
- Ultrasonic nebulizers: atomizing, nebulizing, emulsifying, dispersing and mixing of liquids (for example in air humidifiers, fog machines)
- Degassing of liquids
- Acousto-optic modulators (AOM)
- Determination of the sound velocity of liquids using the Debye-Sears effect
- Devices for deterring martens (marten repellent) and other animals that are supposed to flee from ultrasound
- Dog whistles
- Communication with bats and dolphins for research purposes
- Recording of ultrasonic vocalization in rats and mice is used in psychopharmacological research as well as in neurobehavioral research.
- Double sheet control with ultrasound in printing technology
- Apparative cosmetics: micromassage and regeneration of the skin and introduction of cosmetic active ingredients (sonophoresis / phonophoresis)
Author
AlegsaOnline.com Ultrasound: properties, applications, and overview Leandro Alegsa
URL: https://en.alegsaonline.com/art/102701