Lena Torres
Ultrasonic and infrasonic sound waves are two ends of the sound spectrum. Ultrasonic waves are defined as inaudible sound waves with frequencies greater than 20 kHz, while infrasonic waves are sound waves with frequencies below 20 Hz. Ultrasonic waves are used in a variety of fields, including medicine, industry, and pest control, while infrasonic waves are used in the study of earthquakes, volcanoes, and the human cardiovascular system. Many animals, such as dogs, cats, and whales, can hear ultrasonic sound waves, while some animals are believed to perceive infrasonic waves and use them as an early warning system for natural disasters.
| Characteristics | Values |
|---|---|
| Infrasonic sound frequency | Less than 20Hz |
| Ultrasonic sound frequency | Greater than 20,000Hz or 20 kHz |
| Infrasonic sound sources | Volcanoes, earthquakes, avalanches, explosions, geomagnetic variations, meteors, ocean waves, severe weather, elephant herds, aircraft, industrial machinery |
| Ultrasonic sound sources | Bats, SONAR, medical imaging, ultrasonic transducers |
| Human ear audible frequency range | 20Hz to 20,000Hz or 20 kHz |
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What You'll Learn
- Ultrasound imaging or sonography is used in medicine
- Animals such as bats, porpoises, and toothed whales use ultrasound for navigation and locating prey
- Ultrasonic pest controllers emit loud sounds to drive away pests
- Infrasound is used to monitor earthquakes, volcanoes, and to study the human cardiovascular system
- Some animals communicate over long distances using infrasound
Ultrasound imaging or sonography is used in medicine
Ultrasound imaging, also called sonography or ultrasonography, is a non-invasive imaging technique used in medicine to create images or videos of the body in real time. It is a safe, effective, and commonly used imaging test that employs high-frequency sound waves to visualise soft tissues, internal organs, and blood flow without the use of radiation.
Ultrasound imaging has a wide range of medical applications. It is most commonly associated with pregnancy and obstetric ultrasonography, where it is used to visualise the fetus and assess facial features, skeletal issues, and other body parts. However, ultrasound is also used in emergency medicine, gastroenterology, colorectal surgery, and anesthesiology. For example, abdominal sonography can image major organs such as the pancreas, liver, and kidneys, while ultrasound can also assist in differentiating causes of abdominal pain, such as gallstones or kidney stones.
Ultrasound imaging can be used to guide interventional procedures, such as biopsies or draining fluid collections, and is valuable in vascular access procedures like cannulation of large central veins. In anesthesiology, ultrasound helps guide the placement of needles for local anaesthetic injections near nerves. Transcranial Doppler, a type of Doppler sonography, is used by neuro-anesthesiologists to assess flow velocity in the basal cerebral vessels.
Ultrasound imaging offers several advantages over other imaging modalities. It is portable, relatively low cost, and can be brought to the bedside. However, it also has limitations, including a narrow field of view, difficulty imaging structures obscured by bone or gas, and a requirement for skilled operators. Ultrasound energy can also slightly heat tissues and produce small gas pockets in body fluids or tissues (cavitation), although the long-term consequences of these effects are unknown. Therefore, it is essential to minimise patient exposure while maintaining diagnostic quality.
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Animals such as bats, porpoises, and toothed whales use ultrasound for navigation and locating prey
Sound is produced by a sudden local compression of a gas, liquid, or solid. The compression may be a single pulse, a group of pulses, or a periodic pulse. Sound is only audible to the average human ear if the frequencies lie between 20Hz and 20kHz. Sounds with frequencies below 20Hz are infrasonic, while those above 20kHz are ultrasonic.
Bats, porpoises, and toothed whales are among the animals that use ultrasound for navigation and locating prey. They emit ultrasonic clicks and listen to the echoes that bounce back from objects around them. This process is called echolocation, which is used for navigation and to locate and identify objects.
Bats use echolocation to navigate and hunt for insects, often in total darkness. They generate ultrasound via the larynx and emit the sound through their open mouths or, rarely, their noses. The returning echoes enable them to determine the distance, size, shape, density, and movement of objects. Some bat species can modify their call intensity mid-call to prevent the returning echo from deafening them.
Porpoises emit short and powerful ultrasonic clicks about 20 times a second when swimming and searching for prey. The high frequencies and narrow beam enable them to focus sound on the target while reducing echoes from nearby objects. The echoes also help them determine the distance and direction of the prey.
Toothed whales use intense ultrasonic clicks to echolocate their prey, such as cephalopods. They emit short ultrasonic clicks with source sound pressure levels around 220 dB re 1 μPa. It has been hypothesized that these intense sound pulses may also acoustically debilitate their prey, making them easier to capture.
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Ultrasonic pest controllers emit loud sounds to drive away pests
The use of audible sound to deter pests is not a new strategy. The ancient Chinese, for instance, used mechanically operated sensory-repellent devices to keep rodents away from agricultural crops and buildings. However, ultrasound, which is defined by sound frequencies beyond the upper limit of human hearing, has only been used for pest control in recent decades.
Ultrasonic pest repellers are electronic devices that emit high-frequency sounds designed to repel, injure or kill common household pests, such as rodents and insects. These devices are plugged into electrical outlets and emit sounds that are disruptive to pests. The sound is thought to induce a physiological response called audiogenic seizure response, which causes non-directional running, convulsions, and possibly death from cerebral hemorrhage. The theory is that rodents, confused by the disruption, will eventually flee when prevented from gathering food, breeding, building nests or communicating.
However, the effectiveness of these devices has been disputed by testing labs and the U.S. Federal Trade Commission (FTC). One extensive test by Kansas State University in 2002 found that while the devices were effective at repelling some insects, such as crickets, they had little effect on cockroaches, and no effect on ants and spiders. Pests that are bothered by the noise may soon become accustomed to it as they realize it is harmless. Furthermore, signal strength can be significantly weakened in real-world environments due to blockage from walls and furniture.
Safety concerns have also been raised regarding the use of ultrasonic pest repellers. The sound emitted by these devices can interfere with telephone conversations, burglar alarm systems, and cause muting in hearing aids. It may also cause distress to pet animals such as rabbits, guinea pigs, and hamsters.
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Infrasound is used to monitor earthquakes, volcanoes, and to study the human cardiovascular system
Infrasound refers to sound waves with a frequency below the lower limit of human audibility, which is generally 20 Hz. As frequency decreases, hearing becomes gradually less sensitive, so for humans to perceive infrasound, the sound pressure must be high. While the ear is the primary organ for sensing low sound, at higher intensities, it is possible to feel infrasound vibrations in various parts of the body.
Infrasound is used to monitor earthquakes and volcanoes. Infrasound waves are produced by earthquakes and volcanic eruptions, and because they can travel long distances without being absorbed, they are useful for detecting and monitoring these events. Infrasound sensors can detect small acoustic (pressure) waves in the atmosphere, and by using multiple sensors, the source of the sound can be located. This helps to provide early warnings to nearby populations.
Infrasound is also used to study the human cardiovascular system. This application is known as ballistocardiography and seismocardiography, which are methods to study the mechanics of the human cardiovascular system.
In addition, infrasound is used in other areas such as monitoring compliance with the Comprehensive Nuclear Test Ban Treaty and in research on the impact of sound emissions from wind turbines on nearby populations.
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Some animals communicate over long distances using infrasound
Sound is produced by a sudden local compression of a gas, liquid, or solid. Sound waves with frequencies above 20 kHz are known as ultrasonic sound waves, while those below 20 Hz are called infrasonic sound waves. Infrasonic waves are not easily absorbed, allowing for detection across large distances.
Some animals have evolved to take advantage of infrasonic waves for long-distance communication. For example, whales, elephants, hippopotamuses, rhinoceroses, giraffes, okapis, peacocks, and alligators are known to use infrasound to communicate over distances—up to hundreds of miles in the case of whales.
African elephants, in particular, have been recorded communicating with each other over distances of up to 4 km. They are also able to hear gathering thunderstorms more than 100 km away, which is an important skill to have in sub-Saharan Africa, where water is a scarce resource at the end of the dry season.
Cassowaries, large flightless birds living in dense rainforests in Papua New Guinea and northern Australia, also use infrasound for communication. This is an ideal way for them to communicate over long distances in their challenging habitat of dense forests and rough terrain.
Additionally, some birds use infrasound to detect coming storms from hundreds of miles away, which serves as a cue to leave the area and start migrating. Crocodilians also use infrasound in their 'water dance' to attract mates and warn off other crocodiles.
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Frequently asked questions
Ultrasonic sounds are sounds with frequencies above the upper limit of human hearing (20,000 Hz or 20 kiloHertz). Infrasonic sounds are sounds with frequencies below the lower limit of human hearing (20 Hz).
Ultrasonic sounds are produced by sources such as bats, SONAR, and medical imaging equipment. Natural sources of infrasonic sounds include volcanoes, earthquakes, avalanches, meteors, ocean waves, and severe weather. Elephants also use infrasonic waves to communicate with each other over long distances.
Ultrasonic transducers are used to produce and detect ultrasonic waves. They change their physical size when an electric potential is applied to them, sending out compression waves at the same frequency as the applied electric potential. Infrasonic waves can be detected by specialised microphones.
