History and Definition of Ultrasound - Acoustics dates back to Pythagoras in the 6th century BC - Lazzaro Spallanzani discovered echolocation in bats in 1794 - Francis Galton invented the Galton whistle in 1893 - Chilowski proposed submarine detection during World War I - Paul Langevin built an ultrasound transducer using the piezoelectric effect - Ultrasound is sound with frequencies greater than 20kHz - Ultrasound can be generated at very high frequencies, up to multiple hundreds of kilohertz - Medical imaging equipment uses frequencies in the MHz range - UHF ultrasound waves have been generated in the gigahertz range - Extremely high-frequency ultrasound poses challenges due to wave steepening and shock waves

Perception of Ultrasound - Humans have an upper frequency limit of approximately 20kHz - Children can hear higher-pitched sounds than older adults - Some cell phone signals are designed to be audible only to younger humans - Bats use ultrasounds for navigation and prey detection - Dogs, cats, and toothed whales can hear ultrasound

Ultrasound in Animals - Bats can detect frequencies beyond 100kHz, possibly up to 200kHz - Nocturnal insects listen for echolocating bats - Moths and tiger moths have defense mechanisms against bats - Dogs and cats have a hearing range that extends into ultrasound - Porpoises have the highest known upper hearing limit at around 160kHz

Applications of Ultrasound - Ultrasonic sensors can be used for non-contact sensing - Pulsed-ultrasonic technology is used for level or sensing systems - Ultrasonic sensors are used in motion sensors and flow measurement - Polaroid SX-70 camera used ultrasonic technology for focusing - Ultrasonic sensors can be used for automatic door openers and intruder detection - Ultrasonic testing is commonly used to find flaws in materials and measure object thickness - Frequencies of 2 to 10MHz are common in ultrasonic testing - Ultrasonic range finding is used for shorter distances and finer accuracy - Ultrasonic imaging uses frequencies of 2 megahertz and higher - Acoustic microscopy uses sound waves to visualize structures too small to be resolved by the human eye - Medical ultrasound is a diagnostic imaging technique used to visualize muscles, tendons, and internal organs - Diagnostic ultrasound is used externally and internally in veterinary medicine - High-power ultrasound frequencies range from 20kHz to a few hundred kHz - Ultrasonic impact treatment enhances the mechanical and physical properties of metals - Ultrasonication improves mixing and chemical reactions in various applications and industries - Ultrasonic standing waves can trap and orient particles in equidistant planes - Ultrasonic cleaners are used for cleaning jewelry, lenses, watches, dental instruments, and industrial parts - High-power ultrasound can disintegrate biological cells, including bacteria - Ultrasonic humidifiers are a type of nebulizer that creates a fine spray

Processing and Power of Ultrasound - Intensities above 10 watts per square centimeter can induce cavitation in liquid media - Some applications use up to 1000 watts per square centimeter - Ultrasonic treatment can break up stony deposits, increase skin permeability, and assist in drug effectiveness - Ultrasonic impact treatment results in controlled residual compressive stress, grain refinement, and grain size reduction - Ultrasonication generates alternating low-pressure and high-pressure waves in liquids, causing cavitation - Ultrasonic manipulation and characterization of particles have applications in various fields - Ultrasonic disintegration has uses in biological science, analytical chemistry, and ethanol production - Ultrasonic disintegration can enhance liquefaction and saccharification in corn milling plants