Ultrasound

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For the application to medicine, see Medical ultrasound. Ultrasound_sentence_0

For other uses, see Ultrasound (disambiguation). Ultrasound_sentence_1

Not to be confused with Supersonic. Ultrasound_sentence_2

Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound_sentence_3

Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. Ultrasound_sentence_4

This limit varies from person to person and is approximately 20 kilohertz (20,000 hertz) in healthy young adults. Ultrasound_sentence_5

Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz. Ultrasound_sentence_6

Ultrasound is used in many different fields. Ultrasound_sentence_7

Ultrasonic devices are used to detect objects and measure distances. Ultrasound_sentence_8

Ultrasound imaging or sonography is often used in medicine. Ultrasound_sentence_9

In the nondestructive testing of products and structures, ultrasound is used to detect invisible flaws. Ultrasound_sentence_10

Industrially, ultrasound is used for cleaning, mixing, and accelerating chemical processes. Ultrasound_sentence_11

Animals such as bats and porpoises use ultrasound for locating prey and obstacles. Ultrasound_sentence_12

History Ultrasound_section_0

Acoustics, the science of sound, starts as far back as Pythagoras in the 6th century BC, who wrote on the mathematical properties of stringed instruments. Ultrasound_sentence_13

Echolocation in bats was discovered by Lazzaro Spallanzani in 1794, when he demonstrated that bats hunted and navigated by inaudible sound, not vision. Ultrasound_sentence_14

Francis Galton in 1893 invented the Galton whistle, an adjustable whistle that produced ultrasound, which he used to measure the hearing range of humans and other animals, demonstrating that many animals could hear sounds above the hearing range of humans. Ultrasound_sentence_15

The first technological application of ultrasound was an attempt to detect submarines by Paul Langevin in 1917. Ultrasound_sentence_16

The piezoelectric effect, discovered by Jacques and Pierre Curie in 1880, was useful in transducers to generate and detect ultrasonic waves in air and water. Ultrasound_sentence_17

Definition Ultrasound_section_1

Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz". Ultrasound_sentence_18

In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less. Ultrasound_sentence_19

Perception Ultrasound_section_2

Humans Ultrasound_section_3

The upper frequency limit in humans (approximately 20 kHz) is due to limitations of the middle ear. Ultrasound_sentence_20

Auditory sensation can occur if high‐intensity ultrasound is fed directly into the human skull and reaches the cochlea through bone conduction, without passing through the middle ear. Ultrasound_sentence_21

Children can hear some high-pitched sounds that older adults cannot hear, because in humans the upper limit pitch of hearing tends to decrease with age. Ultrasound_sentence_22

An American cell phone company has used this to create ring signals that supposedly are only audible to younger humans, but many older people can hear the signals, which may be because of the considerable variation of age-related deterioration in the upper hearing threshold. Ultrasound_sentence_23

The Mosquito is an electronic device that uses a high pitched frequency to deter loitering by young people. Ultrasound_sentence_24

Animals Ultrasound_section_4

Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey. Ultrasound_sentence_25

They can detect frequencies beyond 100 kHz, possibly up to 200 kHz. Ultrasound_sentence_26

Many insects have good ultrasonic hearing, and most of these are nocturnal insects listening for echolocating bats. Ultrasound_sentence_27

These include many groups of moths, beetles, praying mantids and lacewings. Ultrasound_sentence_28

Upon hearing a bat, some insects will make evasive manoeuvres to escape being caught. Ultrasound_sentence_29

Ultrasonic frequencies trigger a reflex action in the noctuid moth that causes it to drop slightly in its flight to evade attack. Ultrasound_sentence_30

Tiger moths also emit clicks which may disturb bats' echolocation, and in other cases may advertise the fact that they are poisonous by emitting sound. Ultrasound_sentence_31

Dogs and cats' hearing range extends into the ultrasound; the top end of a dog's hearing range is about 45 kHz, while a cat's is 64 kHz. Ultrasound_sentence_32

The wild ancestors of cats and dogs evolved this higher hearing range to hear high-frequency sounds made by their preferred prey, small rodents. Ultrasound_sentence_33

A dog whistle is a whistle that emits ultrasound, used for training and calling dogs. Ultrasound_sentence_34

The frequency of most dog whistles is within the range of 23 to 54 kHz. Ultrasound_sentence_35

Toothed whales, including dolphins, can hear ultrasound and use such sounds in their navigational system (biosonar) to orient and to capture prey. Ultrasound_sentence_36

Porpoises have the highest known upper hearing limit at around 160 kHz. Ultrasound_sentence_37

Several types of fish can detect ultrasound. Ultrasound_sentence_38

In the order Clupeiformes, members of the subfamily Alosinae (shad) have been shown to be able to detect sounds up to 180 kHz, while the other subfamilies (e.g. herrings) can hear only up to 4 kHz. Ultrasound_sentence_39

Ultrasound generator/speaker systems are sold as electronic pest control devices, which are claimed to frighten away rodents and insects, but there is no scientific evidence that the devices work. Ultrasound_sentence_40

Detection and ranging Ultrasound_section_5

Non-contact sensor Ultrasound_section_6

An ultrasonic level or sensing system requires no contact with the target. Ultrasound_sentence_41

For many processes in the medical, pharmaceutical, military and general industries this is an advantage over inline sensors that may contaminate the liquids inside a vessel or tube or that may be clogged by the product. Ultrasound_sentence_42

Both continuous wave and pulsed systems are used. Ultrasound_sentence_43

The principle behind a pulsed-ultrasonic technology is that the transmit signal consists of short bursts of ultrasonic energy. Ultrasound_sentence_44

After each burst, the electronics looks for a return signal within a small window of time corresponding to the time it takes for the energy to pass through the vessel. Ultrasound_sentence_45

Only a signal received during this window will qualify for additional signal processing. Ultrasound_sentence_46

A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera, which included a lightweight transducer system to focus the camera automatically. Ultrasound_sentence_47

Polaroid later licensed this ultrasound technology and it became the basis of a variety of ultrasonic products. Ultrasound_sentence_48

Motion sensors and flow measurement Ultrasound_section_7

A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects a person's approach and opens the door. Ultrasound_sentence_49

Ultrasonic sensors are also used to detect intruders; the ultrasound can cover a wide area from a single point. Ultrasound_sentence_50

The flow in pipes or open channels can be measured by ultrasonic flowmeters, which measure the average velocity of flowing liquid. Ultrasound_sentence_51

In rheology, an acoustic rheometer relies on the principle of ultrasound. Ultrasound_sentence_52

In fluid mechanics, fluid flow can be measured using an ultrasonic flow meter. Ultrasound_sentence_53

Nondestructive testing Ultrasound_section_8

See also: Macrosonic and Ultrasonic testing Ultrasound_sentence_54

Ultrasonic testing is a type of nondestructive testing commonly used to find flaws in materials and to measure the thickness of objects. Ultrasound_sentence_55

Frequencies of 2 to 10 MHz are common, but for special purposes other frequencies are used. Ultrasound_sentence_56

Inspection may be manual or automated and is an essential part of modern manufacturing processes. Ultrasound_sentence_57

Most metals can be inspected as well as plastics and aerospace composites. Ultrasound_sentence_58

Lower frequency ultrasound (50–500 kHz) can also be used to inspect less dense materials such as wood, concrete and cement. Ultrasound_sentence_59

Ultrasound inspection of welded joints has been an alternative to radiography for nondestructive testing since the 1960s. Ultrasound_sentence_60

Ultrasonic inspection eliminates the use of ionizing radiation, with safety and cost benefits. Ultrasound_sentence_61

Ultrasound can also provide additional information such as the depth of flaws in a welded joint. Ultrasound_sentence_62

Ultrasonic inspection has progressed from manual methods to computerized systems that automate much of the process. Ultrasound_sentence_63

An ultrasonic test of a joint can identify the existence of flaws, measure their size, and identify their location. Ultrasound_sentence_64

Not all welded materials are equally amenable to ultrasonic inspection; some materials have a large grain size that produces a high level of background noise in measurements. Ultrasound_sentence_65

Ultrasonic thickness measurement is one technique used to monitor quality of welds. Ultrasound_sentence_66

Ultrasonic range finding Ultrasound_section_9

Main article: Sonar Ultrasound_sentence_67

A common use of ultrasound is in underwater range finding; this use is also called Sonar. Ultrasound_sentence_68

An ultrasonic pulse is generated in a particular direction. Ultrasound_sentence_69

If there is an object in the path of this pulse, part or all of the pulse will be reflected back to the transmitter as an echo and can be detected through the receiver path. Ultrasound_sentence_70

By measuring the difference in time between the pulse being transmitted and the echo being received, it is possible to determine the distance. Ultrasound_sentence_71

The measured travel time of Sonar pulses in water is strongly dependent on the temperature and the salinity of the water. Ultrasound_sentence_72

Ultrasonic ranging is also applied for measurement in air and for short distances. Ultrasound_sentence_73

For example, hand-held ultrasonic measuring tools can rapidly measure the layout of rooms. Ultrasound_sentence_74

Although range finding underwater is performed at both sub-audible and audible frequencies for great distances (1 to several kilometers), ultrasonic range finding is used when distances are shorter and the accuracy of the distance measurement is desired to be finer. Ultrasound_sentence_75

Ultrasonic measurements may be limited through barrier layers with large salinity, temperature or vortex differentials. Ultrasound_sentence_76

Ranging in water varies from about hundreds to thousands of meters, but can be performed with centimeters to meters accuracy Ultrasound_sentence_77

Ultrasound Identification (USID) Ultrasound_section_10

Ultrasound Identification (USID) is a Real-Time Locating System (RTLS) or Indoor Positioning System (IPS) technology used to automatically track and identify the location of objects in real time using simple, inexpensive nodes (badges/tags) attached to or embedded in objects and devices, which then transmit an ultrasound signal to communicate their location to microphone sensors. Ultrasound_sentence_78

Imaging Ultrasound_section_11

Main article: Medical ultrasound Ultrasound_sentence_79

The potential for ultrasonic imaging of objects, with a 3 GHz sound wave producing resolution comparable to an optical image, was recognized by Sokolov in 1939, but techniques of the time produced relatively low-contrast images with poor sensitivity. Ultrasound_sentence_80

Ultrasonic imaging uses frequencies of 2 megahertz and higher; the shorter wavelength allows resolution of small internal details in structures and tissues. Ultrasound_sentence_81

The power density is generally less than 1 watt per square centimetre to avoid heating and cavitation effects in the object under examination. Ultrasound_sentence_82

High and ultra high ultrasound waves are used in acoustic microscopy, with frequencies up to 4 gigahertz. Ultrasound_sentence_83

Ultrasonic imaging applications include industrial nondestructive testing, quality control and medical uses. Ultrasound_sentence_84

Acoustic microscopy Ultrasound_section_12

Acoustic microscopy is the technique of using sound waves to visualize structures too small to be resolved by the human eye. Ultrasound_sentence_85

Frequencies up to several gigahertz are used in acoustic microscopes. Ultrasound_sentence_86

The reflection and diffraction of sound waves from microscopic structures can yield information not available with light. Ultrasound_sentence_87

Human medicine Ultrasound_section_13

See also: Medical ultrasound Ultrasound_sentence_88

Medical ultrasound is an ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons, and many internal organs to capture their size, structure and any pathological lesions with real time tomographic images. Ultrasound_sentence_89

Ultrasound has been used by radiologists and sonographers to image the human body for at least 50 years and has become a widely used diagnostic tool. Ultrasound_sentence_90

The technology is relatively inexpensive and portable, especially when compared with other techniques, such as magnetic resonance imaging (MRI) and computed tomography (CT). Ultrasound_sentence_91

Ultrasound is also used to visualize fetuses during routine and emergency prenatal care. Ultrasound_sentence_92

Such diagnostic applications used during pregnancy are referred to as obstetric sonography. Ultrasound_sentence_93

As currently applied in the medical field, properly performed ultrasound poses no known risks to the patient. Ultrasound_sentence_94

Sonography does not use ionizing radiation, and the power levels used for imaging are too low to cause adverse heating or pressure effects in tissue. Ultrasound_sentence_95

Although the long-term effects due to ultrasound exposure at diagnostic intensity are still unknown, currently most doctors feel that the benefits to patients outweigh the risks. Ultrasound_sentence_96

The ALARA (As Low As Reasonably Achievable) principle has been advocated for an ultrasound examination – that is, keeping the scanning time and power settings as low as possible but consistent with diagnostic imaging – and that by that principle nonmedical uses, which by definition are not necessary, are actively discouraged. Ultrasound_sentence_97

Ultrasound is also increasingly being used in trauma and first aid cases, with emergency ultrasound becoming a staple of most EMT response teams. Ultrasound_sentence_98

Furthermore, ultrasound is used in remote diagnosis cases where teleconsultation is required, such as scientific experiments in space or mobile sports team diagnosis. Ultrasound_sentence_99

According to RadiologyInfo, ultrasounds are useful in the detection of pelvic abnormalities and can involve techniques known as abdominal (transabdominal) ultrasound, vaginal (transvaginal or endovaginal) ultrasound in women, and also rectal (transrectal) ultrasound in men. Ultrasound_sentence_100

Veterinary medicine Ultrasound_section_14

See also: Preclinical imaging Ultrasound_sentence_101

Diagnostic ultrasound is used externally in horses for evaluation of soft tissue and tendon injuries, and internally in particular for reproductive work – evaluation of the reproductive tract of the mare and pregnancy detection. Ultrasound_sentence_102

It may also be used in an external manner in stallions for evaluation of testicular condition and diameter as well as internally for reproductive evaluation (deferent duct etc.). Ultrasound_sentence_103

By 2005, ultrasound technology began to be used by the beef cattle industry to improve animal health and the yield of cattle operations. Ultrasound_sentence_104

Ultrasound is used to evaluate fat thickness, rib eye area, and intramuscular fat in living animals. Ultrasound_sentence_105

It is also used to evaluate the health and characteristics of unborn calves. Ultrasound_sentence_106

Ultrasound technology provides a means for cattle producers to obtain information that can be used to improve the breeding and husbandry of cattle. Ultrasound_sentence_107

The technology can be expensive, and it requires a substantial time commitment for continuous data collection and operator training. Ultrasound_sentence_108

Nevertheless, this technology has proven useful in managing and running a cattle breeding operation. Ultrasound_sentence_109

Processing and power Ultrasound_section_15

High-power applications of ultrasound often use frequencies between 20 kHz and a few hundred kHz. Ultrasound_sentence_110

Intensities can be very high; above 10 watts per square centimeter, cavitation can be inducted in liquid media, and some applications use up to 1000 watts per square centimeter. Ultrasound_sentence_111

Such high intensities can induce chemical changes or produce significant effects by direct mechanical action, and can inactivate harmful microorganisms. Ultrasound_sentence_112

Physical therapy Ultrasound_section_16

Main article: therapeutic ultrasound Ultrasound_sentence_113

Ultrasound has been used since the 1940s by physical and occupational therapists for treating connective tissue: ligaments, tendons, and fascia (and also scar tissue). Ultrasound_sentence_114

Conditions for which ultrasound may be used for treatment include the follow examples: ligament sprains, muscle strains, tendonitis, joint inflammation, plantar fasciitis, metatarsalgia, facet irritation, impingement syndrome, bursitis, rheumatoid arthritis, osteoarthritis, and scar tissue adhesion. Ultrasound_sentence_115

Biomedical applications Ultrasound_section_17

Ultrasound also has therapeutic applications, which can be highly beneficial when used with dosage precautions. Ultrasound_sentence_116

Relatively high power ultrasound can break up stony deposits or tissue, accelerate the effect of drugs in a targeted area, assist in the measurement of the elastic properties of tissue, and can be used to sort cells or small particles for research. Ultrasound_sentence_117

Ultrasonic impact treatment Ultrasound_section_18

Ultrasonic impact treatment (UIT) uses ultrasound to enhance the mechanical and physical properties of metals. Ultrasound_sentence_118

It is a metallurgical processing technique in which ultrasonic energy is applied to a metal object. Ultrasound_sentence_119

Ultrasonic treatment can result in controlled residual compressive stress, grain refinement and grain size reduction. Ultrasound_sentence_120

Low and high cycle fatigue are enhanced and have been documented to provide increases up to ten times greater than non-UIT specimens. Ultrasound_sentence_121

Additionally, UIT has proven effective in addressing stress corrosion cracking, corrosion fatigue and related issues. Ultrasound_sentence_122

When the UIT tool, made up of the ultrasonic transducer, pins and other components, comes into contact with the work piece it acoustically couples with the work piece, creating harmonic resonance. Ultrasound_sentence_123

This harmonic resonance is performed at a carefully calibrated frequency, to which metals respond very favorably. Ultrasound_sentence_124

Depending on the desired effects of treatment a combination of different frequencies and displacement amplitude is applied. Ultrasound_sentence_125

These frequencies range between 25 and 55 kHz, with the displacement amplitude of the resonant body of between 22 and 50 µm (0.00087 and 0.0020 in). Ultrasound_sentence_126

UIT devices rely on magnetostrictive transducers. Ultrasound_sentence_127

Processing Ultrasound_section_19

Main article: Sonication Ultrasound_sentence_128

Ultrasonication offers great potential in the processing of liquids and slurries, by improving the mixing and chemical reactions in various applications and industries. Ultrasound_sentence_129

Ultrasonication generates alternating low-pressure and high-pressure waves in liquids, leading to the formation and violent collapse of small vacuum bubbles. Ultrasound_sentence_130

This phenomenon is termed cavitation and causes high speed impinging liquid jets and strong hydrodynamic shear-forces. Ultrasound_sentence_131

These effects are used for the deagglomeration and milling of micrometre and nanometre-size materials as well as for the disintegration of cells or the mixing of reactants. Ultrasound_sentence_132

In this aspect, ultrasonication is an alternative to high-speed mixers and agitator bead mills. Ultrasound_sentence_133

Ultrasonic foils under the moving wire in a paper machine will use the shock waves from the imploding bubbles to distribute the cellulose fibres more uniformly in the produced paper web, which will make a stronger paper with more even surfaces. Ultrasound_sentence_134

Furthermore, chemical reactions benefit from the free radicals created by the cavitation as well as from the energy input and the material transfer through boundary layers. Ultrasound_sentence_135

For many processes, this sonochemical (see sonochemistry) effect leads to a substantial reduction in the reaction time, like in the transesterification of oil into biodiesel. Ultrasound_sentence_136

Substantial ultrasonic intensity and high ultrasonic vibration amplitudes are required for many processing applications, such as nano-crystallization, nano-emulsification, deagglomeration, extraction, cell disruption, as well as many others. Ultrasound_sentence_137

Commonly, a process is first tested on a laboratory scale to prove feasibility and establish some of the required ultrasonic exposure parameters. Ultrasound_sentence_138

After this phase is complete, the process is transferred to a pilot (bench) scale for flow-through pre-production optimization and then to an industrial scale for continuous production. Ultrasound_sentence_139

During these scale-up steps, it is essential to make sure that all local exposure conditions (ultrasonic amplitude, cavitation intensity, time spent in the active cavitation zone, etc.) stay the same. Ultrasound_sentence_140

If this condition is met, the quality of the final product remains at the optimized level, while the productivity is increased by a predictable "scale-up factor". Ultrasound_sentence_141

The productivity increase results from the fact that laboratory, bench and industrial-scale ultrasonic processor systems incorporate progressively larger ultrasonic horns, able to generate progressively larger high-intensity cavitation zones and, therefore, to process more material per unit of time. Ultrasound_sentence_142

This is called "direct scalability". Ultrasound_sentence_143

It is important to point out that increasing the power of the ultrasonic processor alone does not result in direct scalability, since it may be (and frequently is) accompanied by a reduction in the ultrasonic amplitude and cavitation intensity. Ultrasound_sentence_144

During direct scale-up, all processing conditions must be maintained, while the power rating of the equipment is increased in order to enable the operation of a larger ultrasonic horn. Ultrasound_sentence_145

Ultrasonic manipulation and characterization of particles Ultrasound_section_20

A researcher at the Industrial Materials Research Institute, Alessandro Malutta, devised an experiment that demonstrated the trapping action of ultrasonic standing waves on wood pulp fibers diluted in water and their parallel orienting into the equidistant pressure planes. Ultrasound_sentence_146

The time to orient the fibers in equidistant planes is measured with a laser and an electro-optical sensor. Ultrasound_sentence_147

This could provide the paper industry a quick on-line fiber size measurement system. Ultrasound_sentence_148

A somewhat different implementation was demonstrated at Pennsylvania State University using a microchip which generated a pair of perpendicular standing surface acoustic waves allowing to position particles equidistant to each other on a grid. Ultrasound_sentence_149

This experiment, called acoustic tweezers, can be used for applications in material sciences, biology, physics, chemistry and nanotechnology. Ultrasound_sentence_150

Ultrasonic cleaning Ultrasound_section_21

Main article: Ultrasonic cleaning Ultrasound_sentence_151

Ultrasonic cleaners, sometimes mistakenly called supersonic cleaners, are used at frequencies from 20 to 40 kHz for jewellery, lenses and other optical parts, watches, dental instruments, surgical instruments, diving regulators and industrial parts. Ultrasound_sentence_152

An ultrasonic cleaner works mostly by energy released from the collapse of millions of microscopic cavitations near the dirty surface. Ultrasound_sentence_153

The bubbles made by cavitation collapse forming tiny jets directed at the surface. Ultrasound_sentence_154

Ultrasonic disintegration Ultrasound_section_22

Similar to ultrasonic cleaning, biological cells including bacteria can be disintegrated. Ultrasound_sentence_155

High power ultrasound produces cavitation that facilitates particle disintegration or reactions. Ultrasound_sentence_156

This has uses in biological science for analytical or chemical purposes (sonication and sonoporation) and in killing bacteria in sewage. Ultrasound_sentence_157

High power ultrasound can disintegrate corn slurry and enhance liquefaction and saccharification for higher ethanol yield in dry corn milling plants. Ultrasound_sentence_158

Ultrasonic humidifier Ultrasound_section_23

The ultrasonic humidifier, one type of nebulizer (a device that creates a very fine spray), is a popular type of humidifier. Ultrasound_sentence_159

It works by vibrating a metal plate at ultrasonic frequencies to nebulize (sometimes incorrectly called "atomize") the water. Ultrasound_sentence_160

Because the water is not heated for evaporation, it produces a cool mist. Ultrasound_sentence_161

The ultrasonic pressure waves nebulize not only the water but also materials in the water including calcium, other minerals, viruses, fungi, bacteria, and other impurities. Ultrasound_sentence_162

Illness caused by impurities that reside in a humidifier's reservoir fall under the heading of "Humidifier Fever". Ultrasound_sentence_163

Ultrasonic humidifiers are frequently used in aeroponics, where they are generally referred to as foggers. Ultrasound_sentence_164

Ultrasonic welding Ultrasound_section_24

In ultrasonic welding of plastics, high frequency (15 kHz to 40 kHz) low amplitude vibration is used to create heat by way of friction between the materials to be joined. Ultrasound_sentence_165

The interface of the two parts is specially designed to concentrate the energy for maximum weld strength. Ultrasound_sentence_166

Sonochemistry Ultrasound_section_25

Main article: Sonochemistry Ultrasound_sentence_167

Power ultrasound in the 20–100 kHz range is used in chemistry. Ultrasound_sentence_168

The ultrasound does not interact directly with molecules to induce the chemical change, as its typical wavelength (in the millimeter range) is too long compared to the molecules. Ultrasound_sentence_169

Instead, the energy causes cavitation which generates extremes of temperature and pressure in the liquid where the reaction happens. Ultrasound_sentence_170

Ultrasound also breaks up solids and removes passivating layers of inert material to give a larger surface area for the reaction to occur over. Ultrasound_sentence_171

Both of these effects make the reaction faster. Ultrasound_sentence_172

In 2008, Atul Kumar reported synthesis of Hantzsch esters and polyhydroquinoline derivatives via multi-component reaction protocol in aqueous micelles using ultrasound. Ultrasound_sentence_173

Ultrasound is used in extraction, using different frequencies. Ultrasound_sentence_174

Weapons Ultrasound_section_26

Ultrasound has been studied as a basis for sonic weapons, for applications such as riot control, disorientation of attackers, up to lethal levels of sound. Ultrasound_sentence_175

Wireless communication Ultrasound_section_27

In July 2015, The Economist reported that researchers at the University of California, Berkeley have conducted ultrasound studies using graphene diaphragms. Ultrasound_sentence_176

The thinness and low weight of graphene combined with its strength make it an effective material to use in ultrasound communications. Ultrasound_sentence_177

One suggested application of the technology would be underwater communications, where radio waves typically do not travel well. Ultrasound_sentence_178

Ultrasonic signals have been used in "audio beacons" for cross-device tracking of Internet users. Ultrasound_sentence_179

Other uses Ultrasound_section_28

Ultrasound when applied in specific configurations can produce short bursts of light in an exotic phenomenon known as sonoluminescence. Ultrasound_sentence_180

This phenomenon is being investigated partly because of the possibility of bubble fusion (a nuclear fusion reaction hypothesized to occur during sonoluminescence). Ultrasound_sentence_181

Ultrasound is used when characterizing particulates through the technique of ultrasound attenuation spectroscopy or by observing electroacoustic phenomena or by transcranial pulsed ultrasound. Ultrasound_sentence_182

Audio can be propagated by modulated ultrasound. Ultrasound_sentence_183

A formerly popular consumer application of ultrasound was in television remote controls for adjusting volume and changing channels. Ultrasound_sentence_184

Introduced by Zenith in the late 1950s, the system used a hand-held remote control containing short rod resonators struck by small hammers, and a microphone on the set. Ultrasound_sentence_185

Filters and detectors discriminated between the various operations. Ultrasound_sentence_186

The principal advantages were that no battery was needed in the hand-held control box and, unlike radio waves, the ultrasound was unlikely to affect neighboring sets. Ultrasound_sentence_187

Ultrasound remained in use until displaced by infrared systems starting in the late 1980s. Ultrasound_sentence_188

Safety Ultrasound_section_29

Occupational exposure to ultrasound in excess of 120 dB may lead to hearing loss. Ultrasound_sentence_189

Exposure in excess of 155 dB may produce heating effects that are harmful to the human body, and it has been calculated that exposures above 180 dB may lead to death. Ultrasound_sentence_190

The UK's independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). Ultrasound_sentence_191

This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). Ultrasound_sentence_192

See also Ultrasound_section_30

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Ultrasound.