Ultrasound - Wikiparency

# Ultrasound > On the **[[PORTAL_Acoustics|Acoustics]]** spine · article face [[Acoustics]]. Microsim queued; the physics is complete.  ## Microsims — p5.js ### Ultrasound (p5.js) · `> 20 kHz` <div class="microsim-player"> <iframe src="https://editor.p5js.org/sciencenibber/full/DhWu_2JUd" width="100%" height="480" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" title="Ultrasound — p5.js microsim"></iframe> </div> *Sound above hearing, used to image the body and measure distance by echo.* **Open in the editor:** [▶ fork this sketch](https://editor.p5js.org/sciencenibber/sketches/DhWu_2JUd) · movement *VII · Antennas, waves & RF propagation* · library `p5js` ### Related microsims Live sims on neighbouring articles: - [[Sonar]] - [[Reverberation]] *Sim hosted off-article; the article owns the reference, not the runtime (WIKI_RULES §10.4). Placed by `g08_place_microsims.py`.*  ## Microsim — queued <p class="wt-pending"><strong>Microsim in the draft queue.</strong> The interactive p5.js sim for this station is being built via the two-queue pipeline; the sourced physics below is complete and citable now.</p> ## Overview ### What it is Ultrasound is sound at frequencies above the roughly 20 kHz upper limit of human hearing, widely used for imaging and sensing. ### How it works / why it matters A piezoelectric transducer emits short high-frequency pulses into a medium and detects the echoes reflected from internal boundaries; the delay gives depth and the echo strength gives contrast, building an image line by line. Higher frequencies improve resolution but are absorbed sooner, so frequency trades resolution against penetration. Ultrasound enables radiation-free medical imaging, Doppler blood-flow measurement, industrial flaw detection, and distance sensing. **On the spine:** [[Sound]] · [[Wave]] · [[Oscillation]] · [[Vibration]] · [[Acoustic_wave]] · [[Mechanical_wave]] · [[Plane_wave]] · [[Wave_equation]] · [[Harmonic_oscillator]] · [[Doppler_effect]] · [[Fourier_analysis]] · [[Digital_signal_processing]] · [[Acoustics]] · [[Reverberation]] · [[Sonar]] · portal [[PORTAL_Acoustics]]. ## History The idea that some animals use sound beyond human hearing is older than the physics that explains it: the Italian physiologist Lazzaro Spallanzani first deduced, from experiments with blinded bats, that bats find their way by something other than sight, and Donald Griffin confirmed in 1938 that the mechanism is ultrasonic [[Sound|sound]] used for navigation.[^ultrasoundbook-preface] The measurement that made ultrasound quantifiable came earlier still: in 1826 the Swiss physicist Jean-Daniel Colladon used a submerged bell in Lake Geneva to show that sound travels faster through water than through air, timing its arrival against the flash of gunpowder fired at the same instant.[^ultrasoundbook-preface] Two more nineteenth-century discoveries supplied the rest of the toolkit still used today: Christian Doppler's 1842 proposal that a wave's observed frequency shifts with the relative motion of source and observer, now the [[Doppler_effect|Doppler effect]], and Pierre and Jacques Curie's 1880 discovery of the piezoelectric effect, the ability of certain crystals to generate an electric charge under mechanical stress and, run in reverse, to vibrate under an applied voltage.[^ultrasoundbook-preface] The push to detect icebergs and submarines during the First World War drove the next step: Paul Langevin built a working piezoelectric transducer for underwater ranging, the direct ancestor of both [[Sonar|sonar]] and the medical probe.[^ultrasoundbook-preface] Medical use followed within a generation. Karl Dussik, a neurologist, began using ultrasound transducers to diagnose brain tumors in 1942; George Ludwig applied it to diagnosing gallstones in 1948; and by the early 1960s obstetric ultrasound was in clinical use, with the 1950s marking the start of digital two-dimensional B-mode imaging, described below under Imaging.[^ultrasoundbook-preface] Ultrasound has since spread from a handful of specialties into routine use across anesthesiology, cardiology, emergency medicine, obstetrics and gynecology, and surgery.[^ultrasoundbook-preface] ## Definition Sound waves are classified by frequency into three bands: infrasonic, below about 20 Hz; audible, from roughly 20 Hz to 20 kHz; and ultrasonic, above about 20 kHz.[^ultrasoundbook-ch1] **Ultrasound** is therefore [[Wave|sound]] pitched above the top of ordinary human hearing — a longitudinal pressure wave in a fluid or gas, carrying the same physics as audible sound but at a frequency too high for a human ear to register. It is the same mechanical disturbance described by [[Acoustic_wave_equation|the acoustic wave equation]]; only the frequency, not the underlying physics, sets it apart from ordinary sound. ## Perception ### Humans The upper edge of human hearing is not a fixed wall. Younger listeners typically hear tones up to about 20 kHz, while the ear's sensitivity falls with age, and several ear conditions — otitis media, otosclerosis, Menière's disease among them — can narrow the range further.[^ultrasoundbook-ch1] Above that edge, ultrasound is inaudible to essentially everyone regardless of age, which is exactly what makes it useful: a diagnostic pulse or an industrial test signal can be as loud as the equipment allows without a patient or a factory floor ever hearing it. ### Animals Several animals both produce and use ultrasound that people cannot perceive. Bats navigate and hunt by ultrasonic echolocation, the very behavior Spallanzani and later Griffin identified, and dolphins and other toothed whales use an analogous biosonar underwater; both are treated in full at [[Animal_echolocation|animal echolocation]]. At the other end of the spectrum, elephants, whales and some other large animals communicate with infrasound below human hearing rather than above it — the mirror-image case to ultrasound, and part of the wider field of [[Bioacoustics|bioacoustics]].[^ultrasoundbook-ch1] ## Detection and ranging ### Non-contact sensor A [[Transducer|transducer]] that emits a short ultrasonic pulse and times its echo can measure a distance, a level, or a presence without ever touching the object, which is why ultrasonic sensors show up in parking-assist systems, tank-level gauges and obstacle detectors: the same pulse–echo arithmetic that turns an echo's delay into a depth inside the body turns it into a distance in open air. ### Motion sensors and flow measurement The same principle, combined with the Doppler effect, measures motion rather than distance: a continuous ultrasonic beam reflected from a moving target, or from blood cells and other particles suspended in a moving fluid, returns at a shifted frequency proportional to the target's velocity along the beam, the basis of ultrasonic flow meters and of the [[Doppler_effect|Doppler]] techniques used throughout medical imaging. ### Nondestructive testing Inspectors use pulse–echo ultrasound to find flaws and measure wall thickness inside metal parts exactly as a clinician images tissue, reading the delay and strength of echoes from cracks, voids and back walls; the technique, its equipment and its standards are treated in full at [[Ultrasonic_testing|ultrasonic testing]]. ### Ultrasonic range finding Beyond fixed sensors, handheld and vehicle-mounted ultrasonic rangefinders apply the same *d* = *ct*/2 relation used throughout this article — the travel time of a single round trip, multiplied by the medium's sound speed and halved — to read a distance directly off a timed echo. ### Ultrasound Identification (USID) Ultrasound has also been proposed and used as a short-range positioning signal: a tag emits an ultrasonic chirp that one or more fixed receivers time, giving a location fix indoors where radio-based positioning is unreliable, in effect a miniature, indoor sonar network. ## Imaging ### Acoustic microscopy At very high frequencies — hundreds of megahertz to gigahertz — the same pulse–echo principle resolves features far smaller than any medical probe can, imaging the internal structure of microelectronic components and biological cells with an acoustic beam rather than light or electrons. ### Human medicine A diagnostic probe fires a short pulse, usually built from several cycles of a chosen frequency, into the body and listens for the echoes each tissue boundary returns; the delay of an echo gives its depth, assuming the standard soft-tissue [[Speed_of_sound|sound speed]] of 1,540 m/s, and its amplitude gives the boundary's contrast, set by the [[Acoustic_impedance|acoustic-impedance]] mismatch at that boundary.[^ultrasoundbook-ch1] Frequency sets the fundamental trade the whole modality turns on: abdominal, cardiac and brain scanning typically use 2–5 MHz probes for the depth they need to reach, while superficial structures such as the eye and peripheral vessels use 5–15 MHz probes for finer detail, and diagnostic imaging as a whole spans roughly 2–20 MHz.[^ultrasoundbook-ch1] Two of the classic display modes make the trade visible directly: A-mode plots echo amplitude against depth along a single line, historically used for the eye, liver and brain, while B-mode converts each echo into a bright dot whose position is its depth and whose brightness is its strength, sweeping many such lines into the gray-scale cross-sectional image now standard in obstetric and abdominal sonography.[^ultrasoundbook-ch2] *Try: raise the probe frequency from 2 MHz toward 15 MHz and watch the echo from bone sink into the noise floor as the fat layer thickens; toggle time-gain compensation off to see every later echo arrive weaker simply because it has traveled farther and lost more of its energy to attenuation along the way.* ### Veterinary medicine The same pulse–echo physics, transducers and display modes carry over directly to animal patients, with frequency and probe choice adapted to the size and depth of the structures being imaged rather than to any different underlying principle. ## Processing and power ### Physical therapy At lower intensities than imaging uses, ultrasound is applied therapeutically to warm and increase blood flow in soft tissue, using the same absorption of acoustic energy that, at diagnostic intensities, is a nuisance to be corrected for and, at higher intensities still, becomes the therapy itself. ### Ultrasonic impact treatment High-power ultrasonic impact treatment drives a tool tip against a metal surface at ultrasonic frequency to relieve residual stress and improve fatigue life in welds, a mechanical rather than thermal use of the same piezoelectric drive that powers a diagnostic probe. ### Processing Industrial ultrasonic processing covers a family of techniques — emulsification, extraction, and the acceleration of chemical and physical processes — that all exploit the same intense, localized energy delivery that also drives cleaning and disintegration. ### Ultrasonic manipulation and characterization of particles Acoustic radiation forces from a standing ultrasonic field can trap, sort or align small particles and cells without touching them, and the same fields can be used to characterize a suspension's particle size from how it scatters and attenuates the sound passing through it. ### Ultrasonic cleaning Ultrasonic cleaners drive a bath at ultrasonic frequency to generate and collapse microscopic cavitation bubbles throughout a liquid, and the resulting local scrubbing action — a smaller, more controlled version of the cavitation the safety literature is careful to keep away from patients — dislodges contamination from surfaces and crevices a brush cannot reach.[^ultrasoundbook-ch4] ### Ultrasonic disintegration At still higher intensity, focused ultrasound is used to lyse cells and break up particles and biological aggregates, again through the same cavitation mechanism, now driven hard enough to do mechanical damage on purpose rather than to avoid it. ### Ultrasonic humidification An ultrasonic humidifier vibrates a small volume of water at its resonant frequency to atomize it into a fine mist without heating it, a low-power application of the same piezoelectric transducers used everywhere else in this article. ### Ultrasonic welding Ultrasonic welding clamps two workpieces, usually plastic or thin metal, and drives an ultrasonic [[Vibration|vibration]] between them until local frictional heating fuses the joint, welding without an open flame or a separate heat source. ### Sonochemistry Sonochemistry uses the same cavitation collapse that damages tissue and cleans instruments to drive chemical reactions, because the brief, intense local pressures and temperatures a collapsing cavitation bubble produces can exceed what a beaker's bulk conditions ever reach. ## Other uses ### Wireless communication Ultrasonic signals have also been used to carry data over short distances underwater and through solid structures, where radio propagates poorly or not at all, trading the very low frequency (and low bit rate) of a [[Sound|sound]] wave for the ability to get a signal through a medium radio cannot cross. ## Safety Ultrasound's two recognized biological effects are thermal (heating from absorbed energy) and mechanical (cavitation and the streaming that goes with it), and diagnostic machines display two indicators built to track them: the thermal index (TI) and the mechanical index (MI).[^ultrasoundbook-ch4] The TI is the ratio of the acoustic power the transducer produces to the power that particular tissue and application would need to raise its temperature by 1 °C, so a TI of 1 marks the acoustic power needed for a 1 °C rise and a higher TI means a higher thermal risk; separate soft-tissue (TIS), bone (TIB) and cranial-bone (TIC) indices exist because a beam passing near bone heats faster than one that only crosses soft tissue, and reported TI values above 1.5 can occur during pulsed Doppler exams, which is why prolonged pulsed Doppler is discouraged for especially sensitive tissue such as the embryo, eye, brain and spine.[^ultrasoundbook-ch4] The MI tracks the risk of cavitation — the growth and violent collapse of gas bubbles under the ultrasound field's rarefaction pressure — and is more of a concern at lower frequencies; bioeffects from cavitation have been observed in animal tissue at MI values above 0.3, while no bioeffects have been reported in skeletal muscle, fat, myocardium, kidney, liver or intestine at MI values up to 1.9, so operators are still advised to keep both indices as low as diagnosis allows, particularly around gas-containing tissue such as neonatal lung.[^ultrasoundbook-ch4] ## See also - [[Medical_ultrasound]] - [[Ultrasonic_testing]] - [[Sonar]] - [[Animal_echolocation]] - [[Doppler_effect]] - [[Acoustic_wave_equation]] - [[PORTAL_Acoustics]] ## References [^ultrasoundbook-preface]: *Ultrasound Physics and its Application in Medicine* (2024), Preface, pp. vii–viii: Spallanzani's bat experiments and Griffin's 1938 confirmation of echolocation; Colladon's 1826 Lake Geneva speed-of-sound-in-water measurement; Doppler's 1842 proposal; the Curies' 1880 discovery of the piezoelectric effect; Langevin's First World War transducer; Dussik's 1942 use of ultrasound for brain-tumor diagnosis; Ludwig's 1948 use for gallstone diagnosis; and the (book-stated) early-1960s start of obstetric use. On the [[PORTAL_Acoustics]] book shelf. [^ultrasoundbook-ch1]: *Ultrasound Physics and its Application in Medicine* (2024), Chapter 1, §1.6 "Audible and Ultrasound Waves," pp. 6–7 (frequency bands; age-related hearing loss; 3.5–20 MHz range stated for medical imaging in this section) and §1.8 "Propagation of Ultrasound Through Tissues," p. 9 (2–20 MHz clinical range; 1,540 m/s assumed soft-tissue sound speed). [^ultrasoundbook-ch2]: *Ultrasound Physics and its Application in Medicine* (2024), Chapter 2, §2.11 "Image Display Modes," pp. 47–48 (A-mode: 2–5 MHz abdominal/cardiac/brain, 5–15 MHz eye and peripheral vessels; B-mode as the basis of modern grayscale imaging). [^ultrasoundbook-ch4]: *Ultrasound Physics and its Application in Medicine* (2024), Chapter 4, "Ultrasound Bioeffects and Safety," §4.3.1 "Thermal Index" and §4.3.2 "Mechanical Index," pp. 79–84 (TI as the ratio of acoustic power to the power needed for a 1 °C rise; TIS/TIB/TIC; TI > 1.5 on pulsed Doppler; MI-related bioeffects observed above 0.3 in animal tissue with gas bodies present, none reported up to MI 1.9 in the tissues listed; cavitation as bubble growth and collapse under the wave's rarefaction phase, used harmlessly by design in ultrasonic cleaning at much lower intensity, §4.2).  **Microsim — three.js (Wikitube framework):** *Ultrasound* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/acoustics/Ultrasound.html" data-title="Ultrasound"></div> *Built from `MICROSIM_GUIDE/specs/acoustics/sims/Ultrasound.json`; part of the [[PORTAL_Acoustics|Acoustics portal]] spine (section sims and See-also variants).*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Ultrasound) : [Wikitube](https://en.wikitube.io/wiki/Ultrasound) --- *Repopulated 2026-08-05 · text transfer from legacy Signal-Processing lane · sim queued · 0 deletions.*