Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!zaphod.mps.ohio-state.edu!think.com!snorkelwacker.mit.edu!bloom-beacon!eru!hagbard!sunic!sics.se!fuug!mcsun!corton!mirsa!ravel.inria.fr!vdputten
From: vdputten@ravel.inria.fr (Frits Van Der Putten)
Newsgroups: comp.robotics
Subject: Re: Getting narrow-beam range data
Message-ID: <11763@mirsa.inria.fr>
Date: 12 Jun 91 12:46:21 GMT
References: <1291@sousa.ltn.dec.com> <1991Jun9.051512.29194@mintaka.lcs.mit.edu>
Sender: news@mirsa.inria.fr
Organization: INRIA, Sophia-Antipolis (Fr)
Lines: 45
Nntp-Posting-Host: ravel.inria.fr

In article <1991Jun9.051512.29194@mintaka.lcs.mit.edu>, jpexg@gaak.lcs.mit.edu (John Purbrick) writes:
> >In article <160412.13057@timbuk.cray.com>, 
> >	kilian@cray.com (Alan Kilian) writes...
> >> I can understand that the beam divergence could be proportional to the
> >> transducer width but I don't see how a larger transducer can produce a
> >> narrower beam. Is this really true?
> >> Also how does an array of transducers produce a narrow beam?
> 

-- skipped a part --

> A team at the University of Nottingham, England, invented a phased-array 
> sonar system; once the target was located they would "steer" their beam
> across its surface by firing the transducers at the right times so that at the
> desired point on the target all the beams would be in phase, while at all other
> points the beams would cancel at least partly.
> 
> John Purbrick

At our instrumentation department we have quite a lot of experience using
ultrasound for underwater, air or seismic applications.
One of the devices we develloped a few years agoo was a phased array of 32x32
ultrasonic transduces for underwater acoustics. By means of using phase shifts in
firing the transducers the beam could be pointed at any location hence acting
as an directional acoustic antenna. Please contact mr. G. Boersma (phone:
+31.15.69.23.31) at our department in Delft for more details.
The same techniques can also be applied in air. I agree completely with the
rough explanation by John Purbick that small devices will act as point sources
and larger devices will spread plane waves. However, we used a parallel set of
six polaroid transduces and did not use any sophisticated phase shifting in
steering those devices. Thus we obtained a beamwith of approximately 6 degrees
and an accuracy of 0.4 mm in axial direction. This development was done by
my collegue mr. R. Breeuwer (also in Delft, phone: +31.15.69.22.20)


-- 
                           Frits van der Putten

  TNO, Institute of Applied Physics        INRIA
  Stieltjesweg 1                           2004 Route des Lucioles
  Delft                                    06561 Valbonne, Cedex
  The Netherlands                          France
  Tel: + 31.15.69.20.00                    Tel: + 33.93.65.78.57
  Fax: + 31.15.69.21.11                    Fax: + 33.93.65.78.58
  e-mail: vdputten@tpdsun.tno.nl           e-mail: vdputten@mirsa.inria.fr