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

2.3.1 Transducer Construction

There are mainly two types of transducers available: closed-top and open-top.

Type selection needs to be based on the ambient environment conditions.

Table 2-1 Close top vs Open top: Benefits and Drawbacks
Type Close top Open top
Benefits
  • Piezoelectric membrane protected against water (hermetically sealed), heat, and humidity
  • Constructed to mitigate ESD strikes
  • Designed for outdoor or harsh environments
  • Piezoelectric membrane directly couples to air for
  • Increased receiver sensitivity
  • Small driving voltage to generate maximum SPL
  • Large off-the-shelf selection for purchase
  • Low-cost
Drawbacks
  • Requires large driving voltage enabled by transformer
  • Limited off-the-shelf selection for purchase
  • High-cost
  • Limited to indoor or protected environments