The received signal will be frequency modulated but at any "instant" the
received frequency is Doppler related to the instantaneous speed and the
(constant) transmitted frequency. If you are using a common ultrasonic
frequency of about 40 kHz, a period is then about 25 microseconds.
Electronics can be used to measure this (varying) period, or a finite
wavetrain can be captured and analyzed on a scope, or it could be
digitized and computer analyzed for this frequency vs time info.
Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net http://www.velocity.net/~trebor
----- Original Message -----
From: "Gonzalez-Espada, Wilson" <wilson.gonzalezespad@MAIL.ATU.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, January 30, 2003 3:21 PM
Subject: Doppler Effect (constant acceleration)
| Hello all:
|
| Have any one heard of an easy way to measure the change in the frequency
of a sound source when the source is moving linearly with constant
acceleration toward a stationary observer? As you know, the Doppler effect
describes, among other scenarios, the change in perceived frequency of a
sound source when the object is moving with constant speed toward a
stationary observer. A colleague and I were having a discussion about
that. Since he is a physicist and I am a science educator, I am almost
sure he is correct when he argues it cannot be done. However, common sense
tells me that if a sound-emitting object is moving with constant
acceleration, the perceived sound frequency should change in a predictable
way. This case should not be confused with a common demonstration of
Doppler effect using a rotating sound source.
|
| Thanks for your comments,
|
| Wilson J. Gonzalez-Espada, Ph.D.