Ultrasound

Ultrasound is a vibrational wave, like sound, but at a frequency that is too high to be perceived by the human ear. Indeed, the human ear can only perceive sounds with a frequency of between 16 and 20 kHz (kilohertz). Above these thresholds is infrasound, while ultrasound lies above 20 kHz. Although the human ear can't detect ultrasound, we've known about its existence since the 19th century thanks to the scholar Francis Galton and the military, which began using it during the First World War to locate enemy submarines using sonar.

Ultrasound and animals

Although the human ear can't hear ultrasound, many animals can. This is the case with dogs and dolphins for example. Some animals even emit these high frequencies and use them to communicate and pinpoint their location. Bats, whales and mice use ultrasound every day.

There are also ultrasound emitters that repel animal species considered nuisances. These include devices that produce ultrasound to repel insects (ants, cockroaches, mosquitoes, etc.), cats, rats, etc. These emitters are used indoors, in gardens (to repel moles, mice and rabbits), to protect the engine compartments of vehicles or protect certain buildings from damage caused by birds, notably pigeons.

Ultrasound production

To use ultrasound, different emitters are used to produce the high frequencies. All of these devices are based on the same principle: converting electrical energy into mechanical energy.

• Piezoelectric generators: strips of quartz are bonded between two steel discs connected to an alternating current. This current deforms the strips and produces vibrations at a frequency identical to the voltage applied.
• Magnetostrictive generators: the dimensions of the ferromagnetic materials change in the presence of a magnetic field. This is known as magnetorestriction. The contraction caused produces a high-frequency vibration that can reach 50 kHz.
• Electrostrictive emitters: these use the electrostriction phenomenon, i.e. the change in the dimension of certain ceramics in the presence of a variable electric field. These variations produce high-frequency vibrations and therefore ultrasound.
  Ultrasound can be detected and measured by these same devices, which then become ultrasound receivers. The electric voltage produced by the ultrasound mechanical vibrations is measured.

The properties of ultrasound

Ultrasound has a wide variety of applications thanks to its versatile properties, as it propagates in the air, gases and liquids. The frequency and pressure variations produce various effects depending on the propagation medium: a change in the refractive index, luminescence, ultrasonic cavitation, the breakdown of matter, the halting of fermentation, the depolymerisation and fragmentation of molecules, etc. Although these terms look obscure, they explain how ultrasound is used in many fields: industry, health, chemistry, medicine, etc. Discover all our products

The different applications of ultrasound

Ultrasound is a very frequently used tool, whether in technical fields, medicine, industry, the military, meteorology, etc.

• Ultrasound and obstacle detection

By emitting high-frequency waves and measuring the interval between the time ultrasound is emitted and the time its echo is received after being reflected off an obstacle, bodies present in an environment can be detected. Widely used in underwater detection, whether to locate enemy submarines or icebergs, this technique uses devices called sonars.

• Industrial applications of ultrasound

High-frequency sounds are used in engineering during the machining, drilling and welding of certain parts. Ultrasound is also very useful for exploring the surface of materials, detecting invisible machining defects (inside a part for example) and measuring or checking the thickness of materials. High-frequency waves are also used to treat parts in aeronautics and mechanics, and to clean precision instruments in fields like jewellery and watch-making. The food industry sometimes also uses ultrasound technology to clean equipment.

• Medical applications of ultrasound

Ultrasound forms the very basis of sonography: this technology is used to non-invasively explore the soft organs in the human body through a probe placed on the skin. Sonography is a very common diagnostic tool used on different parts of the body (urinary tract, gynaecology, the joints, etc.) and is used to locate anomalies and lesions such as cysts, calculi and fibroids. Sonography is a very useful imaging technology for doctors and researchers for establishing a diagnosis, as well as producing reference images.

Another medical technology that uses ultrasound is the Doppler test, which allows doctors to observe arterial and venous circulation.

However, the medical applications of ultrasound aren't restricted to health diagnostics. Ultrasound technology is also used to treat various conditions. It can destroy unwanted tissue (fibroadenomas and tumours for example) or break up urinary stones non-invasively using lithotripsy to make them easier to flush out.

High-frequency waves are also used therapeutically in physiotherapy to reduce certain local inflammations in the muscles, ligaments and tendons. An ultrasound generator is used to improve the circulation and ease pain thanks to the heat produced.

Lastly, ultrasound is used for cleaning certain medical devices in an ultrasound bath: the microbubbles that form in the cleaning solution remove the dirt. Nevertheless, the equipment still needs to be sterilised when necessary.

Ultrasound and measuring the wind

High-frequency sound is also used in meteorology, notably to measure the wind direction and speed. Wind gauges - measuring devices included in weather stations alongside a thermometer, rain gauge and other instruments such as a wind vane - contain ultrasound transducers. An ultrasound signal is sent on north-south and west-east axes, and the reception speed and orientation of the return signal determine the speed and direction of the wind.

Other applications of ultrasound

However, these applications aren't the only ones, and ultrasound waves provide solutions in many other fields: they're used for locating mineral deposits, producing stable emulsions in biology or photography, creating holograms, etc. Some products even include ultrasound technology to aid the mobility of blind or partially sighted people: when an obstacle is detected it triggers sounds that tell the wearer about his or her environment.