Acoustical Sensitivity and Linearity of an Air-Coupled 3D-Printed Ferroelectret Ultrasonic Receiver

3D-printed ferroelectret transducers, utilizing poly-lactic acid (PLA), present an eco-friendly alternative to ceramic-based transducers, which predominantly employ lead zirconate titanate (PZT). We demonstrate using 3D-printed ferroelectret ultrasonic transducers made from PLA featuring well-defined cavities as a sound receiver by developing a simple amplifier circuit and measure the resulting linearity and sensitivity. The quasi-permanently trapped surface charges inside the air cavities of the ferroelectret ultrasonic transducer serve as an electrical bias, resulting in a mechanical pre-stress due to the electrostatic force. The amplifier for the microphone does not need to provide a DC-Bias and is based on a charge amplifier with a flat amplification curve between 20 kHz and 80 kHz. We test the receiver in an anechoic chamber at a distance of 30 cm. We excite with a broadband electrostatic transducer over different frequencies and sound pressures. The receiver exhibits a linear relationship between output voltage and sound pressure, with a mean square error of 102.14 mV² at 50 kHz. The sensitivity varies with frequency, peaking at 29 kHz with -25 dB/VPa and has a 6 dB-bandwidth of 32 kHz. These results underscore the potential of easily manufacturable and adaptable ferroelectret transducers as viable, eco-friendly alternatives to traditional piezoelectric devices.