Air-Coupled Ultrasonic Ferroelectret Receiver With Additional Bias Voltage

Area of Science:

• Materials Science
• Nondestructive Testing
• Sensor Technology

Background:

• High sensitivity is crucial for air-coupled ultrasonic sensors in materials testing.
• Charged cellular polypropylene (PP) offers better acoustic impedance matching to air compared to piezoelectric materials.
• Piezoelectric properties in charged cellular PP stem from polarization, creating internal voltage.

Purpose of the Study:

• To develop the first ultrasonic sensor utilizing charged cellular PP with an integrated high-voltage DC bias module.
• To investigate the effect of DC bias voltage on sensor sensitivity and signal-to-noise ratio.
• To establish a new method for determining the internal voltage of ferroelectrets.

Main Methods:

• Development of a charged cellular PP ultrasonic sensor with a DC bias module (up to 2 kV).
• Application of DC bias voltage to enhance sensor performance.
• Testing the sensor's capability in nondestructive testing (NDT) of a rotor blade segment and glued-laminated timber.

Main Results:

• The DC bias voltage increased the signal-to-noise ratio by up to 15 ± 1 dB.
• A new method for measuring internal voltage in ferroelectrets was proposed based on bias voltage response.
• Successful imaging of internal structures in 4 cm thick specimens was achieved.

Conclusions:

• Charged cellular PP is a promising material for high-sensitivity air-coupled ultrasonic sensors.
• The integrated DC bias module significantly improves sensor performance for NDT applications.
• The developed sensor system enables effective imaging of internal structures in composite materials and timber.