Distance to remote object

 

Radar, Ultrasound & Sonar

(You would almost certainly not use the Ultrasound spin under this heading)

  • A pulse of carrier wave is dispatched at intervals determined by the clock. 

  • The energy will spread out (inverse square law) and be partially absorbed by the medium. These diminutions in signal strength must be taken into account.

  • A portion of the energy will be reflected by any discontinuities that exist on a line from the transmitter perpendicular to its aperture. The return time and strength will be noted by the system.

  • The next pulse will be dispatched in a different direction (perhaps by using a rotating aerial, or perhaps by using an array of emitters and introducing a progressive phase shift into the signals supplied to them so as to do a kind of diffraction grating in reverse) so as to return information about discontinuities in a different part of space.

  • A CRT has an electron beam making a sweep under the control of the timebase, which is synchronised to start just as the pulse starts its journey.

  • The mixed signal is fed to the grid of the CRT so as to affect the brightness of the trace. Reflected signals cause an increase of brightness.

  • The timebase is organised to sweep the beam across the screen in a direction related to the direction in which the signal is transmitted. In this way a map is built up.

Radar

The transducer is a radio aerial, often letterbox-shaped so as to give a wide diffraction pattern vertically and a narrow pattern horizontally (remember that pattern width varies inversely with slit width). Since the resulting image is a map, this gives good resolution in the plane of the map while ensuring that everything in a vertical direction is picked up.

Ultrasound 

The transducer is a piezo-electric crystal, which vibrates when a pd is applied across it (and vice-versa). 

Sonar

The transducer is a piezo-electric crystal, which vibrates when a pd is applied across it (and vice-versa). I don't think you sweep through different angles with sonar, but I'm not going to take the time off to look just at the moment.