SLOA341 October   2024 LOG300

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Description
    1. 2.1 Basics of Ultrasound Sensing
    2. 2.2 Advantages and Disadvantages of Ultrasonic Sensing
    3. 2.3 Ultrasonic Transducer
      1. 2.3.1 Transducer Construction
      2. 2.3.2 Transducer Frequencies
    4. 2.4 Transducer Topologies
    5. 2.5 Blind Zone Effect on Minimum Distance
    6. 2.6 Transducer Drive
    7. 2.7 Ultrasonic Echo and Signal Processing
      1. 2.7.1 Digital Gain or Fixed Gain
      2. 2.7.2 Time-Varying-Gain
      3. 2.7.3 Automatic Gain Control or Logarithmic Amplifier
      4. 2.7.4 Logarithmic Amplifier vs Logarithmic Detector
  6. 3LOG Detector Amplifier and the Advantages Over Conventional Opamps
  7. 4Application
    1. 4.1 Double Paper Feed and Paper Thickness Detector
      1. 4.1.1 Schematic Implementation
      2. 4.1.2 Material Thickness Detector
    2. 4.2 Bubble Detector
    3. 4.3 Material Detection
    4. 4.4 Distance or Proximity Detection
  8. 5Summary
  9. 6References

2.3.2 Transducer Frequencies

Most piezoelectric ultrasonic transducer are optimized to work at a particular narrow band of frequency range, this frequency is known as resonance frequency and depends on the construct of the transducer. For most air-couples application this ranges from 30Khz to 480Khz while liquid level sensing, transducers in the 1MHz range are often used. The transducer frequency selection needs to be based on application and requirement.

As the frequency increases the resolution and directive also increase but at the same time reduces the distance the sound signal can travel. This is because the attenuation of higher frequency signal is much higher compared to lower frequency signal as the frequency travels through a medium.

Table 2-2 Low Frequency vs High Frequency : Benefits and Drawbacks
Type Low Frequency High Frequency
Benefit
  • Maximize long range performance
  • Large off-the-shelf selection for purchase
  • Maximize resolution (typically <5mm)
  • Short blind-zone in mono static topology because of reduced ring decay time
  • Transmission concentrated into forward facing
Drawbacks
  • Long blind-zone in mono static topology
  • Low resolution (typically >5mm)
  • Reduced maximum detectable range due to higher attenuation
  • Limited off-the-shelf selection for purchase