On Thu, 2006-12-07 at 20:24 -1000, Ken Brown wrote:
> It's news to me that SAWs are processors. I would be more inclined to
> believe that a SAW filter may be used in front of some type of dsp
> processor.
>
> Last time I read about Surface Acoustic Wave devices they were basically
> bandpass filters, that work similarly to Collins mechanical filters. The
> electrical signal is converted into a mechanical signal using some type
> of electromechanical transducer (like a piezoelectric device, or a moving
> coil device) and then propagated through some mechanically resonant
> parts, later to be converted back to an electrical signal by another
> electromechanical transducer. In the case of Collins mechanical filters
> the signal travels as torsion in a rod, which has resonant disks
> attached. In a SAW the signal travels as, you guessed it, a surface
> acoustic wave, and the surface it travels across has some resonant
> pieces either etched out or deposited upon it.
>
> I've probably got some of the details, or maybe even the whole concept,
> wrong. I'd love to hear about it from someone who has a better, more
> authoritative explanation of either mechanical filters or SAWs. Is a SAW
> a processor? Or is it just another way to make a bandpass filter?
>
> DE N6KB
> > In the military applications for example, SAW processors (Surface
> > Acoustic Wave) handle this nicely, as do various hard wired ASICS. The
> > latter are comparatively cheap. Neither do much actual processing, as the
> > algorithm is pretty much hard wired in.
> >
> >
SAW devices can do the autocorrelation process. Might be two input
transducers, at different distances from the output transducer. The
distance chosen to put a preferred frequency in phase, but noise out of
phase. So it accomplishes the correlation function of adding the signal
and a time delayed signal so that the repetitive signal adds, but the
random noise doesn't add. Just its not adjustable for delay, and picking
that delay is how the DSP adjusts the process to adapt.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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