Sailors can use ultrasound to find the depth of the sea using an echo-sounder or S.O.N.A.R. The sound used by the sonar is too high for us to hear. It is called ultrasound. (Sound waves above 18,000 Hz) Slide 3
Dolphins make high pitched squeaks and listen to the echoes. Bats also use ultrasonic sounds, to echo-locate their flying food (moth). Slide 4
Slide 6 Ultrasound scanners have advantages over X rays: * X rays are ionising and can damage cells * Ultrasound is reflected at boundaries between different types of tissue so they can be used to scan organs To obtain an echo at a boundary: tissue densities must be different. (The acoustic impedance of the two tissues must be different = product of speed x density)
Detecting faults inside metal objects A A B B C C D D Slide 7
Whales ‘sing’ messages to each other over hundreds of miles. Their sex life is being disturbed by noisy ships. Sound travels further and faster in water than in air because………... Slide 8
Geologists use echo-sounding to search for oil and gas Q1. Which microphone will receive the sound first? Q2. How deep is the hard rock layer? t = 0 s t = 0. 2 s Speed of sound in rock is 4000 m/s Slide 9
Most students should be able to: Compare ultrasound to audible sound waves. Describe a range of uses of ultrasound, including cleaning and detecting cracks. Some students should also be able to: Explain how ultrasound can be used for medical scanning and the advantages of ultrasound over X-ray techniques. Work out the distance between interfaces from diagrams of oscilloscope traces.