The range of ultrasonic is more than the 20khz
Then why does the HC-SR04 states 40hz what is it??
in datasheet it is specified as working frequency?
Also the frequency of sound depends on the medium
then what is this 40Hz?
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2 Answers
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Looks like a typo.
The frequency of the ultrasonic is specified as 40kHz, and they recommend no shorter than 60ms between trigger pulses (16.7Hz)
answered Apr 10, 2015 at 15:50
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\$\begingroup\$ Sir,I want to drive the transducer manually to measure the reflection coefficient, in water how should i design the ultrasonic transducer driver. \$\endgroup\$– MaMbaCommented Apr 10, 2015 at 15:58
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\$\begingroup\$ Reflection coefficient? I would have thought Doppler.. but in any case this module (and the transducers is uses) do not seem to be very appropriate for making an ultrasonic flowmeter for use in water. \$\endgroup\$ Commented Apr 10, 2015 at 16:03
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The 40Hz is most likely the speed at which you can take measurements. Ie you have to wait 1/40th of a second before you take the next reading. This is to ensure that the ultrasonic sound you made in the previous reading have died out , or else you'll receive the sound and get incorrect readings.
The frequency of a wave is independent of medium. The wavelength does become shorter though. But the frequency of sound is purely a time based property. ie a 40Hz wave makes 40 cycles in a second.
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\$\begingroup\$ I believe I have the same module at home. I can hook it up to my scope and signal generator if that would be usefull. \$\endgroup\$– PasswordCommented Apr 10, 2015 at 9:01
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\$\begingroup\$ Max range = 4m x 2 return = 8m. At 340 m/s sound speed time for transit < = 8/340 = 1/42.5th of a second. So 1/4oth is slightly slower than that. \$\endgroup\$– Russell McMahon ♦Commented Apr 10, 2015 at 11:57
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1\$\begingroup\$ That Was a typing mistake ...... Its really a wonder that you even found a explanation....and also some master of the subject up voted it. \$\endgroup\$– MaMbaCommented Apr 11, 2015 at 15:57