Humans

The upper frequency limit in humans (approximately 20 kHz) is due to limitations of the middle ear. The auditory sensation can occur if high-intensity ultrasound feeds directly into the human skull and reaches the cochlea through bone conduction, bypassing the middle ear.[5]​.

Children can hear some high-pitched sounds that adults cannot perceive, since in humans the upper limit pitch of hearing tends to decrease with age.[6] An American mobile phone company used this principle to create telephone call signals that were supposedly only audible to younger people,[7] but many older people could perceive them, which was due to the considerable variation in age-related impairment in upper limit hearing. The Mosquito") is an electronic device that uses a high-pitched frequency to deter young people from loitering.

Animals

Some species such as certain insects and mammals (dolphins and bats) use it in a similar way to radar for orientation; This phenomenon is known as echolocation. It is known that the waves emitted by these animals are so high that they easily “bounce” off all the objects around them, allowing them to create an “image” of what is around them so they can easily orient themselves.

Likewise, ultrasonic emitting devices are frequently used as anti-pest methods in order to scare away rodents and insects.

Physics

Ultrasound is defined as a series of mechanical waves, generally longitudinal, originated by the vibration of an elastic body (piezoelectric crystal) and propagated through a material medium (tissues and body organs) with a frequency that exceeds that of sound audible to humans, greater than 20kHz. Its frequency consists of the number of cycles or pressure changes that occur per second, which is quantified in cycles per second or hertz.[8]​.

Applications in Predictive Maintenance

High-frequency ultrasound is used in predictive maintenance programs to detect leaks in compressed air systems, partial discharges in electrical equipment and early failures in bearings. This technique allows identifying incipient problems that are not noticeable through visual inspection or vibration analysis.[9]​.

The characteristics of ultrasound are:.

1. • Frequency: determined by the source of the sound and the medium passed through. In medicine, for diagnostic purposes, frequencies between 2 and 30MHz are used.

2. • Propagation speed: varies depending on the density and compressibility of the material. That is, the molecules in the most comprehensible tissues will be very separated so their transmission is slower.

3. • Interaction with matter, through stimulation of molecules that transmit energy between them when interacting.

4. • Wavelength. When passing through tissue, the reflection of ultrasonic beams towards a transducer, called "echo", occurs.

5. • Acoustic impedance. Provides evidence of the identity of different materials or tissues that pass from one medium to another. This gives rise to an interface between these materials.

6. • Angle of incidence. The intensity with which the US beam is reflected will depend on the angle. This technique requires an exact angle for correct detection by the receiving source.

7. • Attenuation.

8. • Pulse repetition frequency.

When exposing living tissues to ultrasound, they will undergo the following processes:

• - Attenuation: Sound waves within a material suffer attenuation and therefore it is impossible for us to perceive them with the same intensity.

• - Refraction: Depending on the interface crossed, the direction of the refracted sound wave will depend on the orientation of the interface with respect to the incident one (Snell's law).

• - Dispersion or Scattering: Part of the sound waves when they encounter an interface are reflected in all directions. Provides noise and artifacts in images (undesirable effects).

• - Reflection: Part of the sound waves when encountering an interface are reflected with a similar angle to the incident. Phenomenon provided by the echo.

From here, for diagnostic imaging, the most important effect is reflection.

Acoustic microscopy is the technique of using sound waves to visualize structures too small to be resolved by the human eye. Frequencies up to several gigahertz are used in acoustic microscopes. The reflection and diffraction of sound waves from microscopic structures can provide information not available with light.

The following steps are essential to obtain an image of these pulses of ultrasonic waves:.

Step 1: Emission of a wave pulse.

Step 2: Measurement of echo time and intensity.

Acoustic echo occurs between two materials with different acoustic properties. Less echo will be produced for materials with a lower reflection coefficient (i.e., water, grease, soft tissues...)[11]​.

Step 3: Reconstruction using known wave propagation speed.

The images obtained will be different depending on the attenuation coefficient of the matter crossed.

Denser materials have greater atomic bonds, which slows the speed of sound propagation.

The wavelength determines the minimum resolution of the instrument, which determines the finest detail that can be detected:

The resolution thus allows us to understand the size of a tissue of different density depending on the sensitivity of the detection instrument. This increases depending on the frequency and its penetration power decreases with frequency.

The basic ultrasound device consists of the following parts:.

Probe that sends and receives sound waves using the piezoelectric effect (receives the echoes)

In the probe there are one or more quartz crystals called piezoelectric crystals. When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of crystals produce sound waves. When sound waves hit the crystals, they emit electrical current in turn. In this way, they can be used to emit and receive sound waves.

It is important to note that these US waves are produced in pulses because the crystals are used dually. In the time between the emission and reception of these pulses, the waves pass through the tissue or matter, and then the echoes produced deform the crystals and produce the electrical signal to be interpreted as an image on the monitor.

Important: The probe has a sound-absorbing substance to eliminate reflections from the probe and an acoustic lens to help focus the emitted sound waves.

In addition, there are different types of probes: linear or sector-based. This classification is due to the arrangement of the crystals (matrix) and the shape of the image field produced on the monitor.

The number of glass elements and the shape of the probe determines its field of view and the frequency of the emitted waves: it determines penetration capacity and image resolution. As an example, multi-element probes, each crystal has its own circuit which allows the light beam to be directed and its timing changed. On the other hand, there are probes adaptable to specific areas of the body in order to obtain greater proximity to the organ in question.

Sector transducers are most useful for imaging deeper structures. They are considered common multipurpose.

Computer that does all the calculations and contains the electrical power supplies for itself and the transducer probe.

The CPU contains the microprocessor, memory, amplifiers, and power supplies for the microprocessor and transducer probe. The CPU sends electrical currents to the transducer probe to emit sound waves, and also receives the electrical pulses that were created from the return echoes. The CPU performs all the calculations involved in processing the data. Once the data is processed, the CPU forms the image on the monitor. The CPU can also store the processed data and/or image to disk.

Changes the amplitude, frequency and duration of the pulses emitted by the transducer probe.

The transducer pulse controls allow the operator to set and change the frequency and duration of the ultrasound pulses, as well as the scan mode of the machine. The operator's commands are translated into changing electrical currents that are applied to the piezoelectric crystals in the transducer probe.

Ultrasound machines have several controls to alter the image:.

• - The control that alters the intensity of the ultrasound beam is called power control. This control alters the amount of voltage delivered to the piezoelectric crystals and therefore the intensity of the ultrasound beam and return echoes. To increase the echo signal without creating unwanted artifacts, it is advisable to keep the power as low as possible and adjust the echo amplification instead. This can be done by adjusting the Time Gain Compensation (TCG) control.

• - The time-gain (TCG) compensation control allows adjustment of the amplification of return echoes at various depths. This control usually appears as a column of sliders. Each slider controls a particular section of the monitor, with the first slider altering the shallower echoes and each successive slider controlling deeper echoes.[12]​.

• - The gain control uniformly alters the brightness of all echoes on the monitor, regardless of their location.

• - A depth control allows you to control the depth of the image display. It may be necessary to change the depth control to place the structure of interest in the center of the monitor to optimize its display.

Displays the image of the ultrasound data processed by the CPU.

The mode used for visualization depends on the type of device, the information to be obtained, and the organ being examined.

• - Amplitude Mode: Echoes are displayed on the monitor as peaks originating from a vertical or horizontal baseline. The depth of the echo is determined by the position of the peak on the axis (higher or to the left will be shallower, lower or to the right will be further away). The height of the peak depends on the amplitude of the echo. This mode is not frequently used except in ophthalmology.

• - Brightness mode: Echoes are represented by points on a line that forms the basis of a two-dimensional image. The brightness of each point indicates the amplitude of the recorded echo. Its location relative to the transducer is shown along the vertical axis of the monitor, with the top of the monitor representing closest to the transducer. With each pass of the ultrasound beam, multiple lines of dots are generated on the monitor, producing a complete image. Because several beam sweeps are performed per second, a moving, changing image is generated "in real time."

Enter data and take measurements from the screen.

Prints the image from the displayed data. Whether in color or black and white.

Stores the acquired images.

Medicine

Medical ultrasound "Ultrasound Therapy (medicine)") is an ultrasound-based 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. As currently applied in the medical field, properly performed ultrasound poses no known risks to the patient. Ultrasound does not use ionizing radiation, and the power levels used for imaging are too low to cause adverse heating or pressure effects on tissues.[14]​.

It is very simple for the GP to determine, for example, when a patient requires urgent surgery and when he or she does not require it. Likewise, it simplifies the diagnosis quickly and rules out possible defects in softer tissues.

Ultrasounds have been used by radiologists and sonographers to image the human body for at least 50 years and have become a widely used diagnostic tool. The technology is relatively cheap and portable, especially when compared to other techniques, such as magnetic resonance imaging (MRI) and computed tomography (CT).

Ultrasound is also increasingly used in trauma and first aid cases, with emergency ultrasound becoming a staple of most EMT response teams. Additionally, ultrasound is used in remote diagnostic cases where teleconsultation is required, such as scientific experiments in space or diagnosis of mobile sports equipment.

It is also used to visualize fetuses during routine prenatal and emergency care. These diagnostic applications used during pregnancy are called obstetric ultrasound, which we will see below.

Although the long-term effects of ultrasound exposure at diagnostic intensity are still unknown, most physicians currently consider the benefits to patients to outweigh the risks. The ALARA principle (as low as reasonably achievable) is recommended for ultrasound examinations, in order to keep scan time and power settings as low as possible but consistent with diagnostic imaging in non-medical uses.[15]​.

As an improvement, Doppler ultrasound is based on the effect of the same name. When the object reflecting the ultrasound waves moves, the frequency of the echoes changes, increasing in frequency if it moves toward the probe and decreasing in frequency if it moves away from the probe. How much the frequency changes depends on how fast the object is moving. Doppler ultrasound measures the change in the frequency of echoes to estimate how fast an object is moving. It is primarily used to measure the speed of blood flow through the heart and major arteries. We will see below its application in cardiology, mainly.

This diagnostic technique is also known as ultrasound or sonography.[16]​.

The ultrasound machine has piezoelectric crystals that, when stimulated by electricity, vibrate, producing high-frequency sound waves that echo in the body structures, returning to the crystals that, now stimulated again by ultrasound, produce small voltages that are processed according to their intensity and return time by a computer that has a digital scanning converter, thus creating the images. Unlike X-rays, this examination does not involve any exposure to ionizing radiation and no risk has been detected when used with appropriate diagnostic devices. Currently there are ultrasound machines the size of a cell phone that can be used for immediate diagnosis.[17]​.

Typical frequencies used for applications in the abdomen can range from 2.0 MHz to 5.0 MHz while for regions such as breast, musculoskeletal, thyroid, etc., frequencies can range between 8.0 MHz to 16.0 MHz. Higher frequencies are used for measurement of very small and superficial structures.

At intensities and application times much higher than those used in ultrasound diagnosis, cavitation (bubble formation) and an increase in temperature have been detected, as well as sonoluminescence, which is the emission of light through ultrasound stimulation.

Doppler is a variety of traditional ultrasound, its most useful use being visualization of fluid flow within the body. In addition, the color representation is used to determine the direction and speed of the liquid flow. Doppler is now used very little in obstetrics because its power is much higher and can produce adverse effects on the fetus.

Echocardiography is located within this area, which also allows obtaining a presentation in the form of a range of colors according to the speed of a fluid, such as blood. This technique has special impact on:

• - Dilation of parts of the heart and function of ventricles and heart valves.

• - Transthoracic echocardiogram: In this case, the echocardiography transducer (or probe) is placed on the subject's chest wall (or thorax), and images are taken through the chest wall.

• - Transesophageal echocardiogram: A probe ending in a transducer is passed through the patient's esophagus. This allows evaluation of an image directly behind the heart. They are most commonly used when transthoracic images are of poor quality.

It measures the amount of fluid retained in the patient's bladder.

Pelvic sonograms show the organs of the pelvic region: uterus, ovaries, urinary bladder, prostate and testicles.

There are two methods to perform a pelvic ultrasound: external or internal. Internal pelvic ultrasound is performed transvaginally (in a woman) or transrectal (in a man).

Tendons, muscles, nerves, ligaments, soft tissue masses and bone surfaces. It is an alternative to radiography in the detection of wrist, elbow and shoulder fractures for patients up to 12 years of age.

Most structures in the neck, including the thyroid and parathyroid glands, lymph nodes, and salivary glands, are well visualized by high-frequency ultrasound with high-quality images. Ultrasound is an imaging modality with special incidence in thyroid lesions.[19]​.

Many other benign and malignant conditions in the head and neck can be evaluated and managed with the help of diagnostic ultrasound and ultrasound-guided procedures.

In abdominal ultrasound, images are formed of the solid organs of the abdomen such as the pancreas, aorta, inferior vena cava, liver, gallbladder, bile ducts, kidneys, and spleen. Sound waves are blocked by gas in the intestine and attenuated in different degrees of fat, so there are limited diagnostic capabilities in this area. The appendix can sometimes be seen when it becomes inflamed.[20]​.

Vet

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 mare's reproductive tract and pregnancy detection.[21] It can also be used externally in stallions for evaluation of testicular condition and diameter, as well as internally for reproductive evaluation (vas deferens, etc.).

At the turn of the century, the beef cattle industry began using ultrasound technology to improve animal health and the performance of livestock operations. Ultrasound is used to evaluate fat thickness, costal eye area, and intramuscular fat in live animals. It is also used to evaluate the health and characteristics of unborn calves.

Ultrasound technology provides a means for livestock producers to obtain information that can be used to improve livestock breeding and breeding. This technology can be expensive and requires a significant time commitment for ongoing data collection and operator training. However, this technology has proven to be useful in managing and running a livestock farming operation.[22]​.

Therapy

In physical therapy it has been used since the 1940s especially to reduce pain or improve inflammation in deep muscles, treat connective tissue: ligaments, tendons and fascia (and also scar tissue).[23]​ Specifically, therapists use this technique to treat ligament sprains, muscle strains, tendinitis, joint inflammation, plantar fasciitis, metatarsalgia, facet irritation, impingement syndrome, bursitis, rheumatoid arthritis, osteoarthritis and scar tissue adhesion.

It is used with more powerful intensities and high frequencies, around 1-3 MHz. There are a large number of doctors who distrust the program and do not recommend it to their patients.[24] There are not a large number of studies carried out in this regard, and the design of those that exist does not allow confirming or denying the effectiveness in the treatment of pathologies of the musculoskeletal system; It is therefore necessary to continue studying.[25]​.

Its use is analgesic, regenerative, anti-inflammatory, and its rebound wave travels up to 100% of the bone. We must be very careful in the application of this medium, due to the complications that it entails, with greater concern in women and children, which, like all physical agents in rehabilitation, can produce mutations in the cells of the human body (altering the cells and even altering some types of tumors), which is why this type of equipment should be used exclusively by highly trained professionals, to avoid all the complications that it entails. both to patients and to those who apply it.

Another example of its use in medicine is extracorporeal shock wave lithotripsy, a therapeutic technique for the treatment of kidney stones.

Contactless sensor

This is a detection system that does not require contact with the target. In multiple processes in the medical, pharmaceutical, military and general industries, this is an advantage over in-line sensors that can contaminate the liquids inside a container or tube since these have the disadvantage that they can be obstructed by the product.

Both continuous wave and pulsed systems are used. The principle behind a pulsed ultrasonic technology is that the transmission signal consists of short bursts of ultrasonic energy. After each explosion, the electronics look for a return signal within a small time window corresponding to the time it takes for energy to pass through the material. Only a signal received during this window will be taken into account for processing an additional signal.[26]​.

A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera, which included a fine transducer system to automatically focus the camera. This ultrasound technology was later licensed by Polaroid and became the basis for a variety of ultrasonic products.[27]​.

Industry: Ultrasonic testing

Ultrasonic testing is a type of non-destructive testing commonly used to find defects in materials and to measure the thickness of objects. Frequencies between 2 and 10 MHz are commonly used, but for more specific purposes other frequencies are used. Inspection can be manual or automated and is an essential part of modern manufacturing processes. Most metals can be inspected, as well as plastics and aerospace composites. Low-frequency ultrasound (50–500 kHz) can also be used to inspect less dense materials such as wood, concrete, and cement.

Ultrasonic inspection of welded joints has been an alternative to radiography for non-destructive testing since the 1960s. This technique eliminates the use of ionizing radiation, benefiting the safety and cost of these tests. On the other hand, ultrasound can also provide additional information, such as the depth of defects in a welded joint.

These tests have evolved from manual methods to computerized systems that automate much of the process. An ultrasound test of a joint can identify the existence of flaws, measure their size, and identify their location. 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 equipment is also used in civil engineering to detect possible anomalies, as well as to clean objects, such as carburetors.

Navigation: Sonar

Sonar can be used as a means of acoustic location, functioning in a similar way to radar, with the difference that instead of emitting electromagnetic waves it uses sound impulses. In fact, acoustic localization was used in air before GPS, with SODAR (vertical aerial scanning with sonar) still being applicable for atmospheric research. The acoustic signal can be generated by piezoelectricity or by magnetostriction.[28]​.

In maritime navigation it is used to detect obstacles and objects underwater using sonar, this use was extended to the air applied in mobile robots.[29] An ultrasonic pulse is generated in a particular direction. 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. By measuring the time difference between the pulse being transmitted and the echo being received, it is possible to determine the distance.

The measured travel time of probe pulses in water is highly dependent on water temperature and salinity. The ultrasonic range is also applied to measure in air and for short distances. For example, handheld ultrasonic measuring tools can quickly measure the layout of rooms.

Ultrasonic Identification (USID)

Ultrasonic Identification") (USID) is a real-time location system (RTLS) or indoor positioning system (IPS) technology used to automatically track and identify the location of objects in real time using simple and inexpensive nodes, attached or integrated into objects and devices, which then transmit an ultrasound signal to communicate their location to microphonic sensors.

Motion sensors and flow measurement

A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects the proximity of a person and opens the door in response. Ultrasonic sensors are also used for sensing in a passenger compartment: ultrasound can cover a wide area from a single point.

On the other hand, flow in pipes or open channels can be measured using ultrasonic flow meters, which measure the average velocity of the flowing liquid.

In rheology, an acoustic rheometer is based on the principle of ultrasound. In fluid mechanics, fluid flow can be measured using an ultrasonic flow meter.

Others

An ineffective and very popular application of ultrasound consists of its use as a repellent for insects (especially mosquitoes). There are devices and software programs that allow these acoustic signals to be generated. FACUA asks to withdraw these devices from the market due to misleading advertising, since there are multiple studies that demonstrate their ineffectiveness.[30]​.

Humans

The upper frequency limit in humans (approximately 20 kHz) is due to limitations of the middle ear. The auditory sensation can occur if high-intensity ultrasound feeds directly into the human skull and reaches the cochlea through bone conduction, bypassing the middle ear.[5]​.

Children can hear some high-pitched sounds that adults cannot perceive, since in humans the upper limit pitch of hearing tends to decrease with age.[6] An American mobile phone company used this principle to create telephone call signals that were supposedly only audible to younger people,[7] but many older people could perceive them, which was due to the considerable variation in age-related impairment in upper limit hearing. The Mosquito") is an electronic device that uses a high-pitched frequency to deter young people from loitering.

Animals

Some species such as certain insects and mammals (dolphins and bats) use it in a similar way to radar for orientation; This phenomenon is known as echolocation. It is known that the waves emitted by these animals are so high that they easily “bounce” off all the objects around them, allowing them to create an “image” of what is around them so they can easily orient themselves.

Likewise, ultrasonic emitting devices are frequently used as anti-pest methods in order to scare away rodents and insects.

Physics

Ultrasound is defined as a series of mechanical waves, generally longitudinal, originated by the vibration of an elastic body (piezoelectric crystal) and propagated through a material medium (tissues and body organs) with a frequency that exceeds that of sound audible to humans, greater than 20kHz. Its frequency consists of the number of cycles or pressure changes that occur per second, which is quantified in cycles per second or hertz.[8]​.

Applications in Predictive Maintenance

High-frequency ultrasound is used in predictive maintenance programs to detect leaks in compressed air systems, partial discharges in electrical equipment and early failures in bearings. This technique allows identifying incipient problems that are not noticeable through visual inspection or vibration analysis.[9]​.

The characteristics of ultrasound are:.

1. • Frequency: determined by the source of the sound and the medium passed through. In medicine, for diagnostic purposes, frequencies between 2 and 30MHz are used.

2. • Propagation speed: varies depending on the density and compressibility of the material. That is, the molecules in the most comprehensible tissues will be very separated so their transmission is slower.

3. • Interaction with matter, through stimulation of molecules that transmit energy between them when interacting.

4. • Wavelength. When passing through tissue, the reflection of ultrasonic beams towards a transducer, called "echo", occurs.

5. • Acoustic impedance. Provides evidence of the identity of different materials or tissues that pass from one medium to another. This gives rise to an interface between these materials.

6. • Angle of incidence. The intensity with which the US beam is reflected will depend on the angle. This technique requires an exact angle for correct detection by the receiving source.

7. • Attenuation.

8. • Pulse repetition frequency.

When exposing living tissues to ultrasound, they will undergo the following processes:

• - Attenuation: Sound waves within a material suffer attenuation and therefore it is impossible for us to perceive them with the same intensity.

• - Refraction: Depending on the interface crossed, the direction of the refracted sound wave will depend on the orientation of the interface with respect to the incident one (Snell's law).

• - Dispersion or Scattering: Part of the sound waves when they encounter an interface are reflected in all directions. Provides noise and artifacts in images (undesirable effects).

• - Reflection: Part of the sound waves when encountering an interface are reflected with a similar angle to the incident. Phenomenon provided by the echo.

From here, for diagnostic imaging, the most important effect is reflection.

Acoustic microscopy is the technique of using sound waves to visualize structures too small to be resolved by the human eye. Frequencies up to several gigahertz are used in acoustic microscopes. The reflection and diffraction of sound waves from microscopic structures can provide information not available with light.

The following steps are essential to obtain an image of these pulses of ultrasonic waves:.

Step 1: Emission of a wave pulse.

Step 2: Measurement of echo time and intensity.

Acoustic echo occurs between two materials with different acoustic properties. Less echo will be produced for materials with a lower reflection coefficient (i.e., water, grease, soft tissues...)[11]​.

Step 3: Reconstruction using known wave propagation speed.

The images obtained will be different depending on the attenuation coefficient of the matter crossed.

Denser materials have greater atomic bonds, which slows the speed of sound propagation.

The wavelength determines the minimum resolution of the instrument, which determines the finest detail that can be detected:

The resolution thus allows us to understand the size of a tissue of different density depending on the sensitivity of the detection instrument. This increases depending on the frequency and its penetration power decreases with frequency.

The basic ultrasound device consists of the following parts:.

Probe that sends and receives sound waves using the piezoelectric effect (receives the echoes)

In the probe there are one or more quartz crystals called piezoelectric crystals. When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of crystals produce sound waves. When sound waves hit the crystals, they emit electrical current in turn. In this way, they can be used to emit and receive sound waves.

It is important to note that these US waves are produced in pulses because the crystals are used dually. In the time between the emission and reception of these pulses, the waves pass through the tissue or matter, and then the echoes produced deform the crystals and produce the electrical signal to be interpreted as an image on the monitor.

Important: The probe has a sound-absorbing substance to eliminate reflections from the probe and an acoustic lens to help focus the emitted sound waves.

In addition, there are different types of probes: linear or sector-based. This classification is due to the arrangement of the crystals (matrix) and the shape of the image field produced on the monitor.

The number of glass elements and the shape of the probe determines its field of view and the frequency of the emitted waves: it determines penetration capacity and image resolution. As an example, multi-element probes, each crystal has its own circuit which allows the light beam to be directed and its timing changed. On the other hand, there are probes adaptable to specific areas of the body in order to obtain greater proximity to the organ in question.

Sector transducers are most useful for imaging deeper structures. They are considered common multipurpose.

Computer that does all the calculations and contains the electrical power supplies for itself and the transducer probe.

The CPU contains the microprocessor, memory, amplifiers, and power supplies for the microprocessor and transducer probe. The CPU sends electrical currents to the transducer probe to emit sound waves, and also receives the electrical pulses that were created from the return echoes. The CPU performs all the calculations involved in processing the data. Once the data is processed, the CPU forms the image on the monitor. The CPU can also store the processed data and/or image to disk.

Changes the amplitude, frequency and duration of the pulses emitted by the transducer probe.

The transducer pulse controls allow the operator to set and change the frequency and duration of the ultrasound pulses, as well as the scan mode of the machine. The operator's commands are translated into changing electrical currents that are applied to the piezoelectric crystals in the transducer probe.

Ultrasound machines have several controls to alter the image:.

• - The control that alters the intensity of the ultrasound beam is called power control. This control alters the amount of voltage delivered to the piezoelectric crystals and therefore the intensity of the ultrasound beam and return echoes. To increase the echo signal without creating unwanted artifacts, it is advisable to keep the power as low as possible and adjust the echo amplification instead. This can be done by adjusting the Time Gain Compensation (TCG) control.

• - The time-gain (TCG) compensation control allows adjustment of the amplification of return echoes at various depths. This control usually appears as a column of sliders. Each slider controls a particular section of the monitor, with the first slider altering the shallower echoes and each successive slider controlling deeper echoes.[12]​.

• - The gain control uniformly alters the brightness of all echoes on the monitor, regardless of their location.

• - A depth control allows you to control the depth of the image display. It may be necessary to change the depth control to place the structure of interest in the center of the monitor to optimize its display.

Displays the image of the ultrasound data processed by the CPU.

The mode used for visualization depends on the type of device, the information to be obtained, and the organ being examined.

• - Amplitude Mode: Echoes are displayed on the monitor as peaks originating from a vertical or horizontal baseline. The depth of the echo is determined by the position of the peak on the axis (higher or to the left will be shallower, lower or to the right will be further away). The height of the peak depends on the amplitude of the echo. This mode is not frequently used except in ophthalmology.

• - Brightness mode: Echoes are represented by points on a line that forms the basis of a two-dimensional image. The brightness of each point indicates the amplitude of the recorded echo. Its location relative to the transducer is shown along the vertical axis of the monitor, with the top of the monitor representing closest to the transducer. With each pass of the ultrasound beam, multiple lines of dots are generated on the monitor, producing a complete image. Because several beam sweeps are performed per second, a moving, changing image is generated "in real time."

Enter data and take measurements from the screen.

Prints the image from the displayed data. Whether in color or black and white.

Stores the acquired images.

Medicine

Medical ultrasound "Ultrasound Therapy (medicine)") is an ultrasound-based 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. As currently applied in the medical field, properly performed ultrasound poses no known risks to the patient. Ultrasound does not use ionizing radiation, and the power levels used for imaging are too low to cause adverse heating or pressure effects on tissues.[14]​.

It is very simple for the GP to determine, for example, when a patient requires urgent surgery and when he or she does not require it. Likewise, it simplifies the diagnosis quickly and rules out possible defects in softer tissues.

Ultrasounds have been used by radiologists and sonographers to image the human body for at least 50 years and have become a widely used diagnostic tool. The technology is relatively cheap and portable, especially when compared to other techniques, such as magnetic resonance imaging (MRI) and computed tomography (CT).

Ultrasound is also increasingly used in trauma and first aid cases, with emergency ultrasound becoming a staple of most EMT response teams. Additionally, ultrasound is used in remote diagnostic cases where teleconsultation is required, such as scientific experiments in space or diagnosis of mobile sports equipment.

It is also used to visualize fetuses during routine prenatal and emergency care. These diagnostic applications used during pregnancy are called obstetric ultrasound, which we will see below.

Although the long-term effects of ultrasound exposure at diagnostic intensity are still unknown, most physicians currently consider the benefits to patients to outweigh the risks. The ALARA principle (as low as reasonably achievable) is recommended for ultrasound examinations, in order to keep scan time and power settings as low as possible but consistent with diagnostic imaging in non-medical uses.[15]​.

As an improvement, Doppler ultrasound is based on the effect of the same name. When the object reflecting the ultrasound waves moves, the frequency of the echoes changes, increasing in frequency if it moves toward the probe and decreasing in frequency if it moves away from the probe. How much the frequency changes depends on how fast the object is moving. Doppler ultrasound measures the change in the frequency of echoes to estimate how fast an object is moving. It is primarily used to measure the speed of blood flow through the heart and major arteries. We will see below its application in cardiology, mainly.

This diagnostic technique is also known as ultrasound or sonography.[16]​.

The ultrasound machine has piezoelectric crystals that, when stimulated by electricity, vibrate, producing high-frequency sound waves that echo in the body structures, returning to the crystals that, now stimulated again by ultrasound, produce small voltages that are processed according to their intensity and return time by a computer that has a digital scanning converter, thus creating the images. Unlike X-rays, this examination does not involve any exposure to ionizing radiation and no risk has been detected when used with appropriate diagnostic devices. Currently there are ultrasound machines the size of a cell phone that can be used for immediate diagnosis.[17]​.

Typical frequencies used for applications in the abdomen can range from 2.0 MHz to 5.0 MHz while for regions such as breast, musculoskeletal, thyroid, etc., frequencies can range between 8.0 MHz to 16.0 MHz. Higher frequencies are used for measurement of very small and superficial structures.

At intensities and application times much higher than those used in ultrasound diagnosis, cavitation (bubble formation) and an increase in temperature have been detected, as well as sonoluminescence, which is the emission of light through ultrasound stimulation.

Doppler is a variety of traditional ultrasound, its most useful use being visualization of fluid flow within the body. In addition, the color representation is used to determine the direction and speed of the liquid flow. Doppler is now used very little in obstetrics because its power is much higher and can produce adverse effects on the fetus.

Echocardiography is located within this area, which also allows obtaining a presentation in the form of a range of colors according to the speed of a fluid, such as blood. This technique has special impact on:

• - Dilation of parts of the heart and function of ventricles and heart valves.

• - Transthoracic echocardiogram: In this case, the echocardiography transducer (or probe) is placed on the subject's chest wall (or thorax), and images are taken through the chest wall.

• - Transesophageal echocardiogram: A probe ending in a transducer is passed through the patient's esophagus. This allows evaluation of an image directly behind the heart. They are most commonly used when transthoracic images are of poor quality.

It measures the amount of fluid retained in the patient's bladder.

Pelvic sonograms show the organs of the pelvic region: uterus, ovaries, urinary bladder, prostate and testicles.

There are two methods to perform a pelvic ultrasound: external or internal. Internal pelvic ultrasound is performed transvaginally (in a woman) or transrectal (in a man).

Tendons, muscles, nerves, ligaments, soft tissue masses and bone surfaces. It is an alternative to radiography in the detection of wrist, elbow and shoulder fractures for patients up to 12 years of age.

Most structures in the neck, including the thyroid and parathyroid glands, lymph nodes, and salivary glands, are well visualized by high-frequency ultrasound with high-quality images. Ultrasound is an imaging modality with special incidence in thyroid lesions.[19]​.

Many other benign and malignant conditions in the head and neck can be evaluated and managed with the help of diagnostic ultrasound and ultrasound-guided procedures.

In abdominal ultrasound, images are formed of the solid organs of the abdomen such as the pancreas, aorta, inferior vena cava, liver, gallbladder, bile ducts, kidneys, and spleen. Sound waves are blocked by gas in the intestine and attenuated in different degrees of fat, so there are limited diagnostic capabilities in this area. The appendix can sometimes be seen when it becomes inflamed.[20]​.

Vet

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 mare's reproductive tract and pregnancy detection.[21] It can also be used externally in stallions for evaluation of testicular condition and diameter, as well as internally for reproductive evaluation (vas deferens, etc.).

At the turn of the century, the beef cattle industry began using ultrasound technology to improve animal health and the performance of livestock operations. Ultrasound is used to evaluate fat thickness, costal eye area, and intramuscular fat in live animals. It is also used to evaluate the health and characteristics of unborn calves.

Ultrasound technology provides a means for livestock producers to obtain information that can be used to improve livestock breeding and breeding. This technology can be expensive and requires a significant time commitment for ongoing data collection and operator training. However, this technology has proven to be useful in managing and running a livestock farming operation.[22]​.

Therapy

In physical therapy it has been used since the 1940s especially to reduce pain or improve inflammation in deep muscles, treat connective tissue: ligaments, tendons and fascia (and also scar tissue).[23]​ Specifically, therapists use this technique to treat ligament sprains, muscle strains, tendinitis, joint inflammation, plantar fasciitis, metatarsalgia, facet irritation, impingement syndrome, bursitis, rheumatoid arthritis, osteoarthritis and scar tissue adhesion.

It is used with more powerful intensities and high frequencies, around 1-3 MHz. There are a large number of doctors who distrust the program and do not recommend it to their patients.[24] There are not a large number of studies carried out in this regard, and the design of those that exist does not allow confirming or denying the effectiveness in the treatment of pathologies of the musculoskeletal system; It is therefore necessary to continue studying.[25]​.

Its use is analgesic, regenerative, anti-inflammatory, and its rebound wave travels up to 100% of the bone. We must be very careful in the application of this medium, due to the complications that it entails, with greater concern in women and children, which, like all physical agents in rehabilitation, can produce mutations in the cells of the human body (altering the cells and even altering some types of tumors), which is why this type of equipment should be used exclusively by highly trained professionals, to avoid all the complications that it entails. both to patients and to those who apply it.

Another example of its use in medicine is extracorporeal shock wave lithotripsy, a therapeutic technique for the treatment of kidney stones.

Contactless sensor

This is a detection system that does not require contact with the target. In multiple processes in the medical, pharmaceutical, military and general industries, this is an advantage over in-line sensors that can contaminate the liquids inside a container or tube since these have the disadvantage that they can be obstructed by the product.

Both continuous wave and pulsed systems are used. The principle behind a pulsed ultrasonic technology is that the transmission signal consists of short bursts of ultrasonic energy. After each explosion, the electronics look for a return signal within a small time window corresponding to the time it takes for energy to pass through the material. Only a signal received during this window will be taken into account for processing an additional signal.[26]​.

A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera, which included a fine transducer system to automatically focus the camera. This ultrasound technology was later licensed by Polaroid and became the basis for a variety of ultrasonic products.[27]​.

Industry: Ultrasonic testing

Ultrasonic testing is a type of non-destructive testing commonly used to find defects in materials and to measure the thickness of objects. Frequencies between 2 and 10 MHz are commonly used, but for more specific purposes other frequencies are used. Inspection can be manual or automated and is an essential part of modern manufacturing processes. Most metals can be inspected, as well as plastics and aerospace composites. Low-frequency ultrasound (50–500 kHz) can also be used to inspect less dense materials such as wood, concrete, and cement.

Ultrasonic inspection of welded joints has been an alternative to radiography for non-destructive testing since the 1960s. This technique eliminates the use of ionizing radiation, benefiting the safety and cost of these tests. On the other hand, ultrasound can also provide additional information, such as the depth of defects in a welded joint.

These tests have evolved from manual methods to computerized systems that automate much of the process. An ultrasound test of a joint can identify the existence of flaws, measure their size, and identify their location. 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 equipment is also used in civil engineering to detect possible anomalies, as well as to clean objects, such as carburetors.

Navigation: Sonar

Sonar can be used as a means of acoustic location, functioning in a similar way to radar, with the difference that instead of emitting electromagnetic waves it uses sound impulses. In fact, acoustic localization was used in air before GPS, with SODAR (vertical aerial scanning with sonar) still being applicable for atmospheric research. The acoustic signal can be generated by piezoelectricity or by magnetostriction.[28]​.

In maritime navigation it is used to detect obstacles and objects underwater using sonar, this use was extended to the air applied in mobile robots.[29] An ultrasonic pulse is generated in a particular direction. 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. By measuring the time difference between the pulse being transmitted and the echo being received, it is possible to determine the distance.

The measured travel time of probe pulses in water is highly dependent on water temperature and salinity. The ultrasonic range is also applied to measure in air and for short distances. For example, handheld ultrasonic measuring tools can quickly measure the layout of rooms.

Ultrasonic Identification (USID)

Ultrasonic Identification") (USID) is a real-time location system (RTLS) or indoor positioning system (IPS) technology used to automatically track and identify the location of objects in real time using simple and inexpensive nodes, attached or integrated into objects and devices, which then transmit an ultrasound signal to communicate their location to microphonic sensors.

Motion sensors and flow measurement

A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects the proximity of a person and opens the door in response. Ultrasonic sensors are also used for sensing in a passenger compartment: ultrasound can cover a wide area from a single point.

On the other hand, flow in pipes or open channels can be measured using ultrasonic flow meters, which measure the average velocity of the flowing liquid.

In rheology, an acoustic rheometer is based on the principle of ultrasound. In fluid mechanics, fluid flow can be measured using an ultrasonic flow meter.

Others

An ineffective and very popular application of ultrasound consists of its use as a repellent for insects (especially mosquitoes). There are devices and software programs that allow these acoustic signals to be generated. FACUA asks to withdraw these devices from the market due to misleading advertising, since there are multiple studies that demonstrate their ineffectiveness.[30]​.