I'm in need of a long-range sonar circuit or a long-range ultasonic beam transmitter and detector circuit.

Question

The required range is in kilometers. Where can i find such circuits? Please help!

Answer 1

You are probably better off going with infrared, or lasers, unless you are planning an underwater application, in with case such units are relatively easy to come by, if you have the money.

Unlike light, sound waves have a bad tendency to always spread out in all directions, the same way that ripples in water do, because they are simply small variations in air pressure. In most cases it is not practical to project a sound more than a few hundred meters in air. Sound waves cannot be concentrated into a cohesive "beam" without some pretty sophisticated tricks, and even then they still spread out along the edges and lose intensity very quickly.

The simplest model of this tendency to "spread out" is the inverse square law:
l = L /( k * r² )
Where l is the observed sound intensity, L is the sound intensity at the source, r is the distance, and k is the coefficient of attenuation, which is usually calculated by taking measurements.

In the case of air, k is relatively large, so sound cannot travel very far before it is indistinguishable from background noise. In water, k is much smaller, sound can travel much longer distances, up to hundreds of kilometers if it is powerful enough.

Answer 2

In a medium like air, kilometer range sonar or ultrasonic transmitter/receivers are not practical because of air currents, thermal distortion and other atmospheric factors, You will be much happier with the stability offered by light or lazer setups.