Re: Negative doppler shift

On May 28, 11:01 pm, "La N" <nilita2004NOS...@xxxxxxxxx> wrote:
"Frogwatch" <dboh...@xxxxxxxxxxxxxx> wrote in message

news:64b797ea-c009-464b-93fe-4046d189becf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Been reading about negative index of refraction materials.  These are
materials with features made in them so as to bend light the "wrong"
way.  They have only recently been developed and I do not think are
yet being used for anything.  However, they can have negative doppler
shift so that if such an object was approaching you, a radar gun would
shift its wavelength to LONGER wavelength instead of shorter.  This
would really mess with police radar if your car was coated with it.
Would it be worthwhile to coat vessels or AC?  I think it would still
cause a radar return but any measurement of doppler would indicate the
object was going the opposite direction it really was.
Some of these materials exhibit a backwards "Snells Law" (reflection
at wrong way wrt perpendicular) but as most current radars are
monostatic this should not effect them.  It would screw with Bistatic
radar.

Any relation to the Doppler ultrasound that evaluates blood flow in a
person's body via sound waves?

- nilita

Same wave concept. Doppler radar, doppler ulttra-sound and even the
so-called "red shift" used by astronomers are all caused by a shift of
wavelength (frequency) of the source because of its movement. It is
exactly the effect of a car horn as it approaches you getting higher
pitch and then lower pitch as it passs you and goes away.
When I taught EM lab, I had a simple Gunn Diode (emits microwaves) and
a detector the Gunn diode aimed at the upper blades of a fan (so they
illuminated only the upper blades and not the lower ones). By
observing the shift of wavelength (with an appropriate tunable
waveguide in front of the detector) one could extremely accurately
measure the blade speed and hence the variation of the 60 cycle
building voltage, it was an interesting practical demo.
Can one have a similar reverse doppler for sound? You should be able
to get such although the mechanisms of Electromagnetic wave reflection
and sound reflection are different.
La N, now you've screwed up my night cuz I'll be pondering that one
all eve.
.

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