Ultrasound (Edexcel GCSE Physics Combined Science): Revision Notes
Ultrasound
Ultrasound refers to sound waves with a frequency above 20,000 Hz, which is higher than what humans can hear.
Electrical devices can generate electrical oscillations at any frequency, which can then be converted into mechanical vibrations to produce ultrasound waves.
Key Concepts:
Partial Reflection:
When an ultrasound wave passes through different media (e.g., from air to water), part of the wave is reflected at the boundary between the two media, while the rest is transmitted (and may be refracted).
This property allows us to detect boundaries between substances. By sending a pulse of ultrasound at an object, the waves are reflected back at each boundary, providing information about the location of the boundary.
Detecting Distance:
The time it takes for the reflections (echoes) to return to the detector can be used to calculate how far away the boundary is.
This technique is particularly useful for imaging objects or identifying materials with hidden flaws.
Ultrasound Applications:
1. Medical Imaging:
Example: Prenatal scanning of a foetus. Ultrasound waves are sent through the body. When they meet a boundary between two different media (like the fluid in the womb and the skin of the foetus), some waves are reflected back.
The timing and distribution of these echoes are processed by a computer to create a video image of the foetus.
2. Industrial Imaging:
Example: Finding flaws in materials (like metal or wood).
Ultrasound waves are sent into a material. Typically, these waves reflect back from the far side of the material.
If there is a crack or flaw inside the material, the ultrasound waves will be reflected sooner, indicating a problem.