How to find time of flight

Hi, I am doing a project for measuring the time of flight required by a sound signal when it passes through air. A transmitter will send a sine wave and it will be received by the receiver. So I need to determine the time taken by the sound signal to reach the receiver from the transmitter in the presence of wind having a speed of 340 m/s. How will I do this in simulink?

[Star Strider]

The ‘wind having a speed of 340 m/s’ is approximately the velocity of sound at sea level standard atmosphere.

[Walter Roberson]

Which direction is the wind blowing relative to the direction of travel of the sound?

Say... how does that work for sound? If there is a wind traveling at the speed of sound traveling directly in opposition to the direction the sound has to go, does that imply the sound can never get there? If there is a wind traveling at the speed of sound traveling directly towards the direction the sound has to go, does that imply the sound travels twice as fast as normal?

Answer 1

[Roger Stafford]

It is possibly easier to think of this problem as having the air stand still and both the transmitter and the receiver moving in the same direction at the same speed of 340 m/s. It’s then a problem in geometry figuring out how a sound wave emitted by the transmitter at an appropriate angle can arrive at the receiver at just the right time.

Answer 2

[John BG]

1.

http://practicalphysics.org/measuring-speed-sound-using-echoes.html

suggests to measure distance to a sound reflecting surface, measure distance, and measure delay between clapping and respective echoes.

2.

http://www.bbc.co.uk/education/guides/z8d2mp3/revision/3

BBC Bitsize suggests connecting 2 microphones to a computer, then measure distance between microphones generating sound far away from one side of the generator. The generator should be away but lined up with the 2 microphones to avoid having to involve an additional measurement of the angle between the the line joining both microphones and the line from generator to mid point between microphones.

3. Pulse better than CW

Please note that in any case, pulsed rather than sinusoidal is recommended kind of ping signals, because sin(w*t) is a continuous wave, which means that 1 measured delay generates a series of possible sound speeds, that only one may make sense, but why generating uncertainty when choosing the right signal helps read one and only one valid measurement.

4. this project measures ultrasound speed with an Arduino board

http://www.instructables.com/id/Measuring-the-speed-of-sound-with-Arduino-microcon/

5. measure air pressure and air density and calculate sound speed from there: v(P,ro)

v=(Ks/ro)^0.5

Ks is a measurement of how compressible a substance is. It's called bulk modulus or the modulus of the bulk elasticity.

P: air pressure ro: air density

Note that sound velocity through a gas is function of both gas density and material stiffness.

.

for instance with adiabatic K, and air density 1.2922 kg/m^3 then

v=(1.42e5/1.2922)^.5 = 3.314967720658979e+02

331m/s which is not exactly the expected speed of 343m/s but of course I took air pressure from Wikipedia for sea level who-knows-where-what-season spot.

6. Air density

air density calculator https://www.gribble.org/cycling/air_density.html

inside the Troposphere the air temperature is approximated with

T=T0-L*h

the air pressure as function of altitude

P=P0*(1-L*h/T0)^(g*M/(R*L))

    P0 = sea level standard atmospheric pressure, 101.325 kPa
    T0 = sea level standard temperature, 288.15 K
    g = earth-surface gravitational acceleration, 9.80665 m/s2
    L= temperature lapse rate, 0.0065 K/m
    R = ideal (universal) gas constant, 8.31447 J/(mol·K)
    M = molar mass of dry air, 0.0289644 kg/mol

and the air density then is:

    ro=P*M/(R*T)

if you find these lines useful would you please mark my answer as Accepted Answer?

thanks in advance for time and attention

John BG

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