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Original question:

TIDA-00322: Buying the TIDA-00322 board for testing purpose

TDC1000: how do you determine the number of cycle in ultrasound

Quang Nguyen
Prodigy 20 points
Part Number: TDC1000

Hi TI team,

I'm reading application note How to Select and Mount Transducers in Ultrasonic Sensing for Level Sensing and (Rev. A) (link https://www.ti.com/lit/an/snaa266a/snaa266a.pdf?ts=1620784050823&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTDC1000): one of formula in page 2: Axial resolution =  (λ * cycles)/2  but I'm confused how to determine the number of cycles in this formula.  so could you please help me to clarify this parameter because i have not found any other information about it in the document!

  • 0
    TI__Mastermind 23045 points

    Hello Quang,

    Thank you for your question. Sorry it was not explained thoroughly in the documentation. But what is referred to as  "#cycles" in the document, is the number of cycles in the transmitted pulses. Essentially the number of cycles is how many periods are in the entire burst train. The figure below illustrates a cycle and how they can be measured in different places just like the period of a wave.

    The formula to calculate axial resolution is dependent on how many total cycles can be found in the ultrasonic burst that was transmitted. I hope this answers your question. 

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    Prodigy 20 points

    Hi Isaac Lara,

    thanks for your answer, 

    Based on your explanation, the resolution is dependent on the distance between transducer and target object because as I understand, more distance is, more the cycles there are. Is this correct?

  • 0 in reply to Quang Nguyen
    TI__Mastermind 23045 points

    Hello Quang,

    Not quite, the distance between the objects does not indicate there will be more cycles because the ultrasonic waves propagating to the object are the same ones that were created at the burst. Essentially it is the same cycles traveling through the medium and the ones you see returned are still the same cycles.

    Instead the resolution is dependent on the frequency of the transducer, because this will determine the size of the actual wavelength. A lower frequency transducer will have a larger wavelength and higher frequency one will have smaller wavelengths. Additionally the amount of cycles produced also depends on the transducer dampening being one of the main factors determining how many cycles get produced.

    I find this formula for resolution below, to be a little more helpful, since it does take into consideration the speed of sound of the medium. The end result is similar giving us the smallest measurement possible between two items in an ultrasonic system. The main difference being that these values for the transducer frequency and the speed of sound are much easier to find. A data sheet for a transducer will not give you the amount of cycles the transducer produces.

    Hope this helps!

    Best,

    Isaac