Ultrasonic Waves
Introduction:
Sound waves with a frequency greater than 20,000 Hz are termed ultrasonic waves. The audible range is between 20 and 20,000 Hz. The frequency below 20 Hz is the infrasonic wave. Let us look into some properties of ultrasonic waves.
- Require a material medium to travel
- They are reflected, refracted, and absorbed like ordinary sound waves.
- Possess very high energy
- Can be transmitted over long distances without much loss of energy [2]
The frequency (20 kHz) is the approximate upper audible limit of human hearing in healthy young adults. The upper-frequency limit in humans (20 kHz) is due to limitations of the middle ear. 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. [4]
Children can hear some high-pitched sounds that older adults cannot. It is because in human beings the upper limit pitch of hearing tends to decrease with age. [5] An American cell phone company has used this to create ring signals that, are only audible to younger humans. [6] The physical principles of acoustic waves apply to any frequency range, including ultrasound. Ultrasonic devices operate with frequencies from 20 kHz up to several gigahertz [3].
Ultrasound has applications in many different fields.
Ultrasonic devices have many uses:
- The detection of objects and measuring distances.
- Ultrasound imaging or sonography in medicine.
- In the nondestructive testing of products and structures.
- Used to detect invisible flaws.
- Industrially, for cleaning, mixing, and accelerating chemical processes.
- Animals such as bats and porpoises use ultrasound to locate prey and obstacles. [2]
Do you know what the middle ear is?
The eardrum lies between the middle ear and the outer ear. The mammalian middle ear contains three ossicles (malleus, incus, and stapes), which transfer the vibrations into waves in the fluid and membranes of the inner ear. The auditory tube joins the tympanic cavity with the nasal cavity, allowing pressure to equalize between the middle ear and throat.
The primary function of the middle ear is to efficiently transfer acoustic energy from compression waves in air to fluid–membrane waves within the cochlea. [2]
A dog whistle, used to train dogs and other animals, emits sound in the ultrasonic range.
Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey. They can detect frequencies beyond 100 kHz, possibly up to 200 kHz.[7]
Many insects have good ultrasonic hearing. They are nocturnal insects listening for echolocating bats. These include many groups of moths, beetles, praying mantises, and lacewings. Upon hearing a bat, some insects will make evasive maneuvers to escape being caught. [8] Ultrasonic frequencies trigger a reflex action in the noctuid moth that causes it to drop slightly in its flight to evade the attack. [9] Tiger moths also emit clicks, which may disturb the bat's echolocation. [10][11] In other cases, they may advertise that they are poisonous by emitting sound. [12][13]
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. [22][23][24] The wild ancestors of cats and dogs evolved this higher hearing range to hear high-frequency sounds made by their preferred prey, small rodents. [14]
- A dog whistle is a whistle that emits ultrasound used for training and calling dogs.
- The frequency of most dog whistles is within the range of 23 to 54 kHz.[15]
Bats use ultrasounds to navigate in the darkness [2]
Non-contact sensor
An ultrasonic level or sensing system requires no contact with the target.
Both continuous wave and pulsed systems are in use. The principle behind pulsed-ultrasonic technology is that the transmit signal consists of short bursts of ultrasonic energy. After each burst, the electronics look for a return signal within a small window of time, corresponding to the time it takes for the energy to pass through the vessel. Only a signal received during this window will qualify for additional signal processing. [2]
- A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera, which included a lightweight transducer system to focus the camera automatically.
Polaroid later licensed this ultrasound technology, and it became the basis of several ultrasonic products.
- An automatic door opener is an application of ultrasound, where an ultrasonic sensor detects a person's approach and opens the door.
- To detect intruders, we can use ultrasonic sensors. The ultrasound can cover a wide area from a single point.
We can measure the flow in pipes or open channels using ultrasonic flowmeters. That measures the average velocity of flowing liquid. In rheology, an acoustic rheometer relies on the principle of ultrasound. In fluid mechanics, fluid flow is measurable using an ultrasonic flow meter.
Ultrasound Identification (USID)
- Ultrasound Identification is an indoor positioning system (IPS).
- This technology automatically identifies the location of objects.
The approach uses inexpensive nodes (badges/tags) attached to the surface of persons, objects, and devices. That transmits an ultrasound signal to communicate their locations to microphone sensors.
Because ultrasound signal wavelengths have a short reach, they are within a lesser distant location than wireless transmissions with higher susceptibility to multiple reflections, multipath, and through-the-wall multiple-room responses. Hence, ultrasound-based RTLS is considered a more robust alternative to passive radio-frequency identification (RFID) and even to active radio-frequency identification (RFID) in complex indoor environments (such as hospitals), where radio waves get multiply transmitted and reflected, thereby compromising the positioning accuracy. [2]
Imaging:
Ultrasonic imaging uses frequencies of 2 megahertz and higher. Resolution of small internal details in structures and tissues is possible with shorter wavelengths. The power density is generally less than 1 watt per square centimeter to avoid heating and cavitation effects in the object under examination. [20] Ultrasonic imaging applications include industrial nondestructive testing, quality control, and medical uses. [21]
Human medicine
Medical imaging techniques are applied to visualize muscles, tendons, and many internal organs to capture their size, structure, and pathological lesions with real-time tomographic images. It is a widely used diagnostic tool.
Features:
- The technology is relatively inexpensive and portable.
- To visualize fetuses during routine and emergency prenatal care.
- Proper ultrasound poses no known risks to the patient. [25]
- 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. [26][27]
- Although the long-term effects of ultrasound exposure at diagnostic intensity are still unknown,[28]
- We can use it for remote diagnosis cases for teleconsultation, such as scientific experiments in space or mobile sports team diagnosis.[29]
- Tool for trauma and first aid cases, emergency ultrasound, has become a staple of most EMT response teams.
According to RadiologyInfo,[43] ultrasound is a tool for detecting pelvic abnormalities. Vaginal (transvaginal or endovaginal) ultrasound in women and rectal (transrectal) ultrasound in men are widely used tools.
Once, I have been treated for a ligament one month years ago. Ultrasound has been used since the 1940s by physical and occupational therapists for treating connective tissue: ligaments, tendons, and fascia (and also scar tissue).[30]
Conditions for which ultrasound may be a tool for treatment include the following examples: ligament sprains, muscle strains, tendonitis, joint inflammation, plantar fasciitis, metatarsalgia, facet irritation, impingement syndrome, bursitis, rheumatoid arthritis, osteoarthritis, and scar tissue adhesion.
- Relatively high-power ultrasound can break up stony deposits or tissue, increase skin permeability, accelerate the effect of drugs in a targeted area, measure the elastic properties of tissue, and sort cells or small particles for research. [31]
Longitudinal waves (compressional waves):
In this wave, particles of the medium vibrate parallel to the wave’s propagation direction. Longitudinal waves travel through a material medium as compressions and rarefactions. It can propagate through solids, liquids, and gases.
Transverse waves (shear waves):
In this wave, particles of the medium vibrate perpendicular to the wave’s propagation direction. It can propagate only through solids.
Rayleigh wave (surface wave):
These waves are neither longitudinal nor transverse. They are analogous to the water waves. It can travel only on the surface layer of solids. There is no particle motion at greater depths during the wave’s existence.
Lamb waves (flexural waves):
Thin metals produce these waves. These waves are also known as plate waves.
With a magnetostriction oscillator and Piezoelectric oscillator, we can produce ultrasonic waves. I will tell you briefly, the magnetostriction effect and piezoelectric effect.
Magnetostriction effect:
- When we apply a strong magnetic field parallel to the length of a rod made of ferromagnetic material (Nickel or Iron), the size of the rod varies.
Piezoelectric effect:
If we stretch a crystal-like quartz, tourmaline, etc., along an axis, the crystal produces a potential difference along a perpendicular axis. This phenomenon is the piezoelectric effect. Piezoelectricity is the electric charge in certain solid materials in response to applied stress.
Detection of ultrasonic waves:
Thermal detection:
When ultrasonic waves travel through a medium, the temperature increases at compression and decreases at rarefactions. Platinum is very sensitive to temperature changes. When ultrasonic waves pass through platinum, the wire is alternatively heated and cooled throughout its length. This temperature variation causes the variation of resistance in the platinum wire. With the help of a bridge arrangement, we can note the variation in resistance
.
Piezoelectric detection:
When a quartz crystal receives ultrasonic waves at one pair of faces, the other pair (faces) produce charges. The corresponding voltage is small. Hence, it is amplified and detected.
Sonar (Sound Navigation And Ranging):
SONAR is a method to determine the depth of oceans, locate submarines, etc. Ultrasonic waves are a little scattered by water. Send a sharp ultrasonic beam under the water to the ocean bed and collect the reflected beam by a detector. The received signal is amplified and analyzed by a CRO. If the object is moving, there will be a change in the frequency of the echo signal. It will help us to find its velocity and direction of motion.
Let d be the depth, t is the time taken for to and fro motion, and v is the velocity in seawater.
We know that distance, 2d=vt or d=vt/2, is the depth of the water body.
The measured travel time of Sonar pulses in water depends on the temperature and salinity of the water. Ultrasonic ranging also applies for measurement in air and short distances. For example, hand-held ultrasonic measuring tools can rapidly measure the layout of rooms.
Range finding underwater is performed at sub-audible and audible frequencies for long distances (1 to several kilometers). For short-distance measurement, we can use ultrasonic range finding for accurate measurement. Ranging in water varies from hundreds to thousands of meters but can be performed with centimeters to meters accuracy. [2]
NDT (Non-Destructive Testing):
NDT is a technique to find imperfections to evaluate the quality of a material. The most common ultrasonic testing system is the pulse-echo system.
- In this method, short pulses (high frequency) from a transducer are allowed to pass through the testing material through a couplant (it is a liquid as oil or silicon grease placed in between the transducer surface to reduce the loss in ultrasonic energy due to reflection at the air and metal interface).
- Collect the reflected ultrasonic pulses from the flaws inside the material by a receiving transducer.
- The transducer converts the ultrasonic wave into an electrical signal.
- These signals are amplified and fed to a CRO. CRO analyzes the signal and gives size, shape, and other details of cracks, voids, non-metallic inclusion, etc.
Frequencies usually used for testing are 2 to 10 MHz.
Other frequencies are in use for particular cases.
Inspection may be manual or automatic. It is an essential part of modern manufacturing processes.
Ultrasound applies to testing metals, plastics, and aerospace composites. To inspect less dense materials such as wood, concrete, and cement, low-frequency ultrasound (50–500 kHz) can also be used. [2]
Ultrasound inspection of welded joints has been an alternative to radiography for testing since the 1960s.
- Ultrasonic inspection eliminates the ionizing radiation, with safety and cost benefits.
- Ultrasound can also provide information such as the depth of flaws in a welded joint.
- An ultrasonic test of a joint can identify the existence of flaws, measure their size, and spot their location.
Ultrasonic thickness measurement is one technique used to monitor the quality of welds.
Ultrasonic drilling:
In ultrasonic drilling, the drill bit is not cutting the material directly. Ultrasonic waves activate the drill bit to vibrate vertically. With the help of an abrasive slurry, we can do cutting. The slurry is circulated continuously between the drill bit and the material. The pounding action of the drill bit causes the underlying material to chip away, leaving a hole. Using the ultrasonic drilling technique, we can make holes of any shape (square or non-circular). This method is very effective for drilling brittle materials like glass, ceramics, etc.
Welding:
Two thin pieces of metal are held in contact and let high-intensity ultrasonic waves pass through the metal plates. It causes an increase in the temperature of the metal plates. The two surfaces melt and join together. It applies to cell phones, disposable medical tools, etc.
Soldering:
To solder glasses, steel, ceramics, etc., we use this technique of ultrasonic soldering. A filler material applies for this purpose
.
Mixing:
For mixing a colloidal solution of two non-mixable liquids like oil and water, we can use ultrasonic mixing
For cleaning jewelry, lenses, and other optical parts, watches, dental instruments, surgical instruments, diving regulators, and industrial parts, ultrasonic cleaners at frequencies 20 to 40 kHz are used. An ultrasonic cleaner works by energy released from the collapse of millions of microscopic cavitation bubbles near the dirty surface. The collapsing bubbles form tiny shockwaves that break up and disperse contaminants on the object's surface. [2]
.Safety
- Occupational exposure to ultrasound over 120 dB may lead to hearing loss.
- Exposure over 155 dB may produce heating effects that are harmful to the human body.
- Exposures above 180 dB may lead to death. [32]
In medical ultrasound, guidelines exist to prevent inertial cavitation from happening.
Medical Applications:
Using ultrasonic waves, monitoring the shape and movement of organs in the human body is possible. Ultrasonic waves reflected from moving objects, namely blood cells, exhibit a Doppler shift. From this data, we can estimate blood flow. This technique applies in monitoring the function of the heart. It helps to get information about size, location, velocity, etc., without surgery or with the use of harmful radiation.
In dentistry, an ultrasound scrubber is combined with a water jet to remove plaque from teeth
.
Recent developments:
The latest research and advances in ultrasound applications show that this technique can help accelerate processes, reduce energy requirements, increase productivity, and produce better-quality food materials in fruits, juices, and dairy products.
References
1 Sciencedirect.com
14^ Coile DC, Bonham MH (2008). "Why Do Dogs Like Balls?: More Than 200 Canine Quirks, Curiosities, and Conundrums Revealed". Sterling Publishing Company, Inc: 116. ISBN 978-1-4027-5039-7.
15^ Whitlow WL (1993). The sonar of dolphins. Springer. ISBN 978-0-387-97835-2. Retrieved 13 November 2011.
16^ Kastelein RA, Bunskoek P, Hagedoorn M, Au WW, de Haan D (July 2002). "Audiogram of a harbor porpoise (Phocoena phocoena) measured with narrow-band frequency-modulated signals". The Journal of the Acoustical Society of America. 112 (1): 334–44. Bibcode:2002ASAJ..112..334K. doi:10.1121/1.1480835. PMID 12141360
17^ Mann DA, Higgs DM, Tavolga WN, Souza MJ, Popper AN (June 2001). "Ultrasound detection by clupeiform fishes". The Journal of the Acoustical Society of America. 109 (6): 3048–54. Bibcode:2001ASAJ..109.3048M. doi:10.1121/1.1368406. PMID 11425147.
18Jump up to:a b Krantz L (2009). Power of the Dog: Things Your Dog Can Do That You Can't. MacMillan. pp. 35–37. ISBN 978-0-312-56722-4.
^
23 Jump up to: a b Krantz L (2009). Power of the Dog: Things Your Dog Can Do That You Can't. MacMillan. pp. 35–37. ISBN 978-0-312-56722-4.
31 ^ Rapacholi MH, ed. (1982). Essentials of Medical Ultrasound: A Practical Introduction to the Principles, Techniques and Biomedical Applications. Humana Press.
33^ AGNIR (2010). Health Effects of Exposure to Ultrasound and Infrasound. Health Protection Agency, UK. pp. 167–170. Archived from the original on 8 November 2011. Retrieved 16 November 2011.
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