To prevent this, the transducer that produces the ultrasonic waves is placed on the skin using a special gel. This difference would normally mean that a large part of the ultrasound energy is reflected away from the body and wasted. This means that there is an acoustic impedance difference between the air and the body. The speed of sound in air is much less than that in water (and the human body is mostly water!). Photo: West ga obgyn – Baby, CC BY-SA 3.0 This small wavelength allows a very high degree of image detail to be recorded. Ultrasound is chosen because high frequency sounds have small wavelength. Ultrasound is very high-frequency acoustic waves, typically between 1 and 3 MHz – much higher than the frequency range audible to humans (20 Hz -20 kHz). Stealth devices are those which attempt to make an object non-reflective – if the waves do not bounce off your aircraft, then no-one will know it is there! You also get sound radar, called SODAR which plays chirping sounds and use these to detect wind speed and temperature in the atmosphere! The B-2 stealth bomber flies over the Utah Testing and Training Range (Photo by Bobbie Garcia) UltrasoundĪn adaptation of sonar is used to create images of structures inside the human body – this is called medical ultrasound. From this they can detect nearby reflective objects. Both systems send out waves (sound waves in water and electromagnetic waves in air, respectively) and record the time it takes for the reflections to arrive back. This is the sound underneath the dome of a mosque in Iran.Įchoes are used in Sonar and Radar. The problem is even worse when there is a curved surface. Diffusers could also help the problem by dispersing the reflection causing the echo. To overcome this problem, absorbers can be put on the rear wall to stop the sound reflecting, as was done in the Royal Festival Hall, London shown below. Sometimes this sound can be heard by the audience as an echo. If a trumpet plays on the stage, the sound can reflect off the back wall and return to the front of the seating (stalls) still quite loud.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |