Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!cs.utexas.edu!math.ohio-state.edu!news.acns.nwu.edu!ftpbox!mothost!lmpsbbs!NewsWatcher!user
From: eck001@email.mot.com (Chris Kerlin)
Subject: Re: Ultraonic Transducers/Acceptance Angles
Organization: Motorola Land Mobile
Date: Mon, 21 Mar 1994 22:08:20 GMT
Message-ID: <eck001-210394165117@145.2.119.41>
Followup-To: comp.robotics
References: <2miivo$2kh@bigboote.WPI.EDU>
Sender: news@lmpsbbs.comm.mot.com (Net News)
Nntp-Posting-Host: 145.2.119.41
Lines: 57

In article <2miivo$2kh@bigboote.WPI.EDU>, jpeskin@bear.WPI.EDU (Jonah
Peskin) wrote:

>      I've looked at the FAQ for transducer sources, but I was wondering
> if anyone knows of a company which sells omni-directional transducers with
> essentially an acceptance andle of 360 degrees.  I have heard of techniques
> which involve cones to accomplish this (Figure follows):
>  _______________
>   \    Cone    /
>     \        /---<------- Sound
>       \    / |
>         \/   |
>   ________________
>   |              |
>   |  Transducer  |
>   |              |
>   ----------------
> 
> With the above setup (which is apparently used for sonar in submarines) you 
> can acheive a 360 degree acceptance angle.  I have tried this setup but have
> found that the received signal is relatively weak.  I believe this is due to
> the fact that the above receiver would only receive sound that travels along
> a specific horizontal plane.  
>      Anyone know of a transducer that is inherantly like this or another 
> technique that may work better?
> 
> JP

Typical beam pattern for 1.513 in dia transducer at 50kHz is something like
this:

  Beam Pattern
              |
              +              0dB
             +|+
        +   + | +   +      -25dB
      +    +  |  +    +    -35dB
--------------+-------------
         -12  0  12
   Degrees (theta) off axis

The central peak (called Airy disk in optics) can be found by the equation

sin (theta) = 1.22 * wavelength / diameter

A 50 kHz transducer transmitting through a .27 inch diameter
aperture would have a beam of +- 90 deg; or 180 deg coverage

Several transducers grouped together and excited simultaneously
with an effective diameter of 3.8 in would have a beam of +- 5 deg

with a .466 in dia aperture, four transducers could cover 
180 deg of horizon...

---------+---------+---------+---------+---------+---------+---------+
Chris Kerlin                         ECK001@email.mot.com
Motorola Land Mobile Products        Fort Lauderdale, Florida
