The world is full of sounds we cannot hear. Beyond the range of human hearing โ limited between 20 Hz and 20,000 Hz โ there is a rich acoustic world inhabited by animals and also utilized by modern technology for extraordinary purposes. This is the world of ultrasound.
Ultrasound is sound with a frequency higher than 20,000 hertz (20 kHz). Although human ears cannot detect it, many animals can produce and hear ultrasound, using it as a tool for navigation, hunting, and communication. The most famous example is bats.
Bats use a system called echolocation to navigate in total darkness and hunt prey. They emit high-frequency ultrasound (between 20,000 and 200,000 Hz) through their mouths or noses. These sounds travel through the air, hit objects in the surroundings, and echo back to the bat's ears. By analyzing the time it takes for the echo to return, the strength of the echo, and the frequency changes caused by the Doppler effect, the bat's brain can create a detailed three-dimensional map of its environment โ including the location, size, and movement direction of even tiny insects like mosquitoes.
Dolphins and toothed whales also use echolocation in water, producing ultrasonic clicks that can reach frequencies of up to 150,000 Hz. Dolphin echolocation systems are so advanced that they can distinguish the size, shape, and even the composition of objects with remarkable accuracy. Research has shown that dolphins can detect objects hidden in the sand or differentiate between objects even when they are concealed behind barriers.
In the field of medicine, ultrasound technology or ultrasonography has become one of the most valuable and widely used diagnostic tools. Medical ultrasound scanners use frequencies between 2 and 18 MHz โ much higher than bats. A transducer (probe) sends sound pulses into the body. These sounds travel through body tissues and reflect back differently depending on the tissue density. Computers analyze these reflections and create two- or three-dimensional images of internal body structures.
Medical ultrasound is an incredibly useful tool because it is safe (it does not use ionizing radiation like X-rays), portable, relatively inexpensive, and can show real-time images. It is widely used in prenatal care to monitor fetal development, in cardiology to examine the heart (echocardiogram), in gastroenterology to examine the liver, pancreas, and gallbladder, and in many emergency situations to quickly assess internal injuries.
In addition to medicine, ultrasound is also used in industry for non-destructive testing โ detecting cracks or hidden defects in metals, plastics, and other materials without needing to cut or damage the tested object. Ultrasonic cleaners use cavitation bubbles generated by ultrasound to clean delicate objects such as jewelry and surgical instruments. Ultrasound supporters in the field of therapeutic sonography are used to heat deep tissues to relieve pain and accelerate healing.
Recent studies have also revealed that many other animals we did not expect use ultrasound โ including some species of frogs, mice, and even cats that emit ultrasonic sounds while playing. This inaudible acoustic universe is nothing less than a hidden dimension of our world.