What is Ultrasound?
Ultrasound is sound waves with frequencies above the upper limit of the human hearing range (above about 20000 Hz, hertz)
Ultrasound travels in a longitude wave. This can be demonstrated using a slinky spring.
Key Features of Waves
The key features of waves are:
- Rarefaction - area of low pressure.
- Compression - area of high pressure.
- Wavelength - the distance between corresponding points on two succesive disturbances.
- Frequency - the number of waves produced (or that pass a particular point) in 1 second.
- Amplitude - the maximum disturbance caused by a wave.
Applications of Ultrasound
Ultrasound can be used in medicine. Scanning the body with ultrasound waves can build up a picture of the body's organs, including the heart, lungs and liver.
Ultrasound waves can down kidney stones so they can be removed from the body naturally. This avoids the need for surgery.
Ultrasonic waves cause the kidney stones to vibrate. The stones break up, are dispersed, and can then be passed out of the body in the urine.
Ultrasound can be used:
- to measure the speed of blood flow.
- to detect gallstones and tumors.
- for pre-natal scanning because there is less risk to mother or baby than using X-rays.
More on Ultrasound
Ultrasound waves are partly reflected at a boundary as they pass from one medium to another. The time taken for these reflections to be detected can be used to calculate the depth of the reflected surface. The reflected waves are usually processed to produce a visual image on the screen.
Ultrasound has two main advantages over X-ray imaging:
- It's able to produce images of soft tissue.
- It doesn't damage living cells.
Particle Motion in Waves
All waves transfer energy from one point to another without transferring any particles of matter. In the Following diagrams, each coil of the slinky spring represents one particle. There are two types of wave - longitude and transverse.