Compiled By : Aamarpali Puri
Sound waves with frequencies higher than upper audible limit of human ear and which cannot be heard by humans are called ultrasound waves. Human hearing limit is between 20Hz – 20,000Hz. Humans cannot hear sounds having frequency less than 20 Hz and greater than 20,000Hz. Infrasound has frequency less than 20 Hz. Ultrasound has frequencies more than 20,000Hz. Ultrasound refers to anything above the frequencies of audible sound, and nominally includes anything over 20,000 Hz.
Ultrasound has application in various fields.
Ultrasonic humidifier: one type of nebulizer is a popular type of humidifier. The ultrasonic pressure waves nebulize not only the water but also materials in the water including calcium and other minerals.
Ultrasonic door opener: A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects a person’s approach and opens the door.
Ultrasound generator/speaker systems are sold as electronic pest control devices, which frighten away rodents and insects.
Whales and dolphins, can hear ultrasound waves and use such sounds in their navigational system to orient and capture prey.
Ultrasound is also used to visualize fetuses during routine and emergency prenatal care. Such diagnostic applications used during pregnancy are referred to as obstetric sonography.
Medical sonography 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 images.
In this context, let us talk about whistling. Dog can hear ultra sound; dog whistle emits a high frequency sound to call to a dog. Many such whistles emit sound in the upper audible range of humans.
Bats use ultrasounds to navigate in the darkness. Bats use a variety of ultrasonic ranging techniques to detect their prey. They produce high pitched ultrasound squeaks. These high pitched squeaks are reflected by objects such as preys and returned to the bat’s ear. This allows bat to know the distance of his prey. They can detect frequencies beyond 100 KHz, possibly up to 200 kHz.
Ultrasound can also provide additional information such as the depth of flaws in a welded joint. Ultrasonic inspection has progressed from manual methods to computerized systems that automate much of the process. An ultrasonic test of a joint can identify the existence of flaws, measure their size, and identify their location.
Defects in metal blocks can be detected using ultrasound. Defects do not allow ultrasound to pass through them and they are reflected back as a result, it doesn’t get detected by the detector.
Diagnostic ultrasound is used externally in horses for evaluation of soft tissue and tendon injuries, and internally in particular for reproductive system.
Ultrasound is used to evaluate fat thickness, rib eye area, and intramuscular fat in living animals. It is also used to evaluate the health and characteristics of unborn calves
Ultrasonic cleaners frequency 20 to 40,000 Hz, are used to clean jewelry, lenses, optical instruments, watches and surgical instruments etc. An ultrasonic cleaner works mostly by energy released from the collapse of millions of microscopic cavities near the dirty surface. Objects to be cleaned are put in a cleaning solution and ultrasound waves are passed through that solution. The high frequency of these ultrasound waves detaches the dirt from the objects.
It is also used in killing bacteria in sewage. Ultrasonic cleaning is the rapid and complete removal of contaminants from objects by immersing them in a tank of liquid flooded with high frequency sounds waves. These non-audible sound waves create a scrubbing brush action within the fluid.
SONAR (Sound Navigation And Ranging) is an acoustic device used to measure the depth, direction and speed of under-water objects (submarines etc) with the help of Ultrasounds. It is used in measuring the depth of seas too. A beam produces by this device is passed through sea. This beams gets reflected and the echo is recorded by the detector, which converts it to electrical signals. This method is termed as ‘echo – ranging’.