Newsgroups: comp.robotics
Path: brunix!uunet!mdisea!mothost!lmpsbbs!ECK001@email.mot.com
From: ECK001@email.mot.com (Chris_Kerlin)
Subject: Re: Polaroid Range Finders
Organization: Motorola_Adv_Mfg_Tech
Date: Thu, 20 May 1993 20:34:44 GMT
Message-ID: <1993May20.203444.22325@lmpsbbs.comm.mot.com>
References: <1993May17.195445.17138@cs.tulane.edu>
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In article <1993May17.195445.17138@cs.tulane.edu>, preslan@bourbon.ee.tulane.edu (Kenneth Preslan) writes:
> 
> 	I've been having a problem with my polaroid ultrasonic range finder
> and I thought someone out there might be able to help me.
>  
>         The beam of sound sent out by the Polaroid range finder is too broad
> for what I want to do.  The manual says that an acoustic horn can be used to
> focus the beam.  Does anybody know where I could get one?
>  
>  
> Kenneth Preslan
> preslan@bourbon.ee.tulane.edu
> 
> 

I suggest making one:
Beam pattern is governed by diffraction at the circular aperture of the
transducer, i.e. the first maximum is given by
sin theta = 1.22 * (wavelength / diameter)
With the 1.513 inch diameter transducer, at 50kHz, and
wavelength .26 in this gives a beam half-angle of about 12 degrees.
This agrees with their published _Typical_Beam_Pattern_ showing -30db
at about 12 degrees. To narrow to 5 degrees you will need about a 3.6 inch
diameter aperture. Experiment with different lengths of cone-shaped horn,
maybe then try curved sides....
-----------------------------------------------------------------------------CK

