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