Miniature Ferroelectret Microphone Design and Performance Evaluation Using Laser Excitation.

Area of Science:

• Acoustics
• Materials Science
• Sensor Technology

Background:

• Miniature microphones for ultrasonic measurements above 100 kHz are often expensive, lack sensitivity, or are too large.
• Existing solutions do not meet the requirements for precise ultrasonic wave field scans in air.

Purpose of the Study:

• To develop a miniature, sensitive, and cost-effective ultrasonic microphone using ferroelectret (FE) film.
• To evaluate the performance of the novel FE microphone for ultrasonic measurements.

Main Methods:

• Constructed a 0.5-mm-diameter needle-style ultrasonic microphone utilizing FE film.
• Evaluated performance through sensitivity area mapping using laser-induced thermoelastic ultrasound, directivity, AC response, and absolute sensitivity calibration via three-transducer reciprocity.
• Compared FE microphone performance with a polyvinylidene difluoride (PVDF) microphone.

Main Results:

• The FE microphone demonstrated high sensitivity and a broad frequency range suitable for ultrasonic measurements.
• Sensitivity map revealed micrometer-scale granularity of the FE material.
• Laser-based methods provided reliable AC response measurements, validated by reciprocity calibration.

Conclusions:

• Ferroelectret film is a promising material for constructing miniature, high-performance ultrasonic microphones.
• The developed FE microphone offers a cost-effective and sensitive alternative for ultrasonic field measurements.
• Novel laser-based characterization techniques were successfully employed for microphone evaluation.