On Mon, 23 Nov 1998, Andy Kunz wrote:

> I have a PIC project customer who is looking for a sonar transducer.  Some
> sort of hydrophone which will be rather non-directional.  They tried fish
> locator ones, but they're too directional.

Use an acoustical lens with the directional one. This is easy to make once
you know what you want but will require some precision machining or
plastic molding. A turning mill (engl?)  is enough usually. With the
directional transducer + acoustical lens you can do almost whatever you
want with the beam, including pick up so much background with each echo so
as to render it totally useless. The biggest sin is to open it more than
180 degrees (get surface reflections in each return). I haven't got much
experience in this, just tinkering in an empty (empty of people, not
water) swimming pool, so ask some more. A good acoustics book will cover
acoustical lenses. Stuff that applies to 20kHz dome and horn tweeters
mostly applies to 30-40kHz ultrasonics, with the usual caveats (water, not
air, thus the wavelength is MUCH shorter).

Peter