# Distance measurements with ultrasonic sensors

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#### gonsays

##### Newbie level 5
Hello guys,

I’m doing a lab regarding Sensors & Actuators, using a ultrasonic 40 kHz piezoelectric emitter-receiver board, in order to do distance measurements, velocity of the sound an thickness measurements.

The modulating signal will be a square-wave with 10 Hz and a duty cycle of 20%.
The carrier will be a 40 kHz sinusoidal signal.

I have some doubts regarding some theoretical questions, if you could help me it would be great:
• Why is it used a 40 kHz signal for the carrier?
• Why is it used a square modulation signal?
• Why is it used a low duty-cycle (20%)?
• Why is it used a DC offset voltage for the modulated signal? [I think it is to prevent overmodulation, right?]
• What is the maximum theoretical distance that can be measured with this signal (carrier 40kHz, modulating signal 10Hz)?

Thank you very much in advance.

Best regards,
G

#### gonsays

##### Newbie level 5
[Moved]Ultrasonic sensor - Theoretical Question

Hello guys,

I would like to ask your help regarding a theorical question regarding an ultrasonic 40 kHz piezoelectric emitter-receiver board, in order to perform distance, velocity of the sound and thickness measurements.

The modulating signal will be a square wave with 10 Hz and a duty cycle of 20%.

The carrier will be a 40 kHz sinusoidal signal.

Having this information, what would be the maximum theoretical distance that can be measured with this signal?

I have found an expression:

va=2.D/ta [velocity of propagation=2*Distance/Time-Of-Flight]

What would be the maximum Distance? Is there any way to relate Time-Of-Flight and the frequency of the carrier/modulating signal?

Any help or tip would be really appreciated.