DESIGN AND DEVELOPMENT OF PVDF HYDROPHONE FOR UNDERWATER APPLICATION

Abstract

In recent years, underwater acoustic measurement has gained significant importance due to the increasing need for detecting and monitoring underwater objects such as marine life and vehicles. Acoustic waves remain the most efficient method for transmitting information across long distances underwater. Consequently, extensive research has been directed towards the development of hydrophones and acoustic sensors that can address the requirements of diverse underwater applications and conditions. These devices are crucial in areas like marine biology, underwater exploration, and naval defense. Efforts are being made by researchers to enhance the precision and dependability of these sensors to ensure optimal performance across various underwater settings. Continuous progress in this technology is enhancing our ability to understand and engage with the underwater realm. Polyvinylidene fluoride (PVDF) film stands out among acoustic sensing materials due to its remarkable piezoelectric characteristics and acoustic impedance, which closely matches that of water. PVDF possesses attributes that make it an excellent choice for underwater acoustic sensors. Although PVDF is commonly used in hydrophone applications, its exact sensing mechanism in underwater sound environments is not yet completely understood. This thesis aims to explore the behavior of PVDF film in underwater sound fields and leverage the findings to design both a hydrophone and an acoustic vector sensor using PVDF. Recent progress in underwater acoustic sensors has been driven by the growing need for improved detection and localization in underwater operations, such as acoustic noise monitoring, target identification, and object tracking. Acoustic waves, capable of traveling over long distances underwater, are significantly more effective for communication and sensing in aquatic environments compared to electromagnetic waves. To enhance these abilities, a new Micro-Electro-Mechanical System (MEMS) has been developed, inspired by the auditory functions of a bionic fish's lateral line organ. This system includes a piezoelectric polymer-based acoustic vector hydrophone made from PVDF, which captures vector information from the underwater acoustic sound field. PVDF is a highly suitable material for underwater applications due to its flat frequency response, excellent mechanical flexibility, and ideal acoustic impedance. This study concentrates on the design and analysis of a PVDF-based hydrophone sensor, with its performance validated using analytical models. The hydrophone has been optimized through simulation and parametric sweeps, showing notable improvements in its functionality. The findings indicate that the vector hydrophone offers a flat frequency response and optimal sensitivity, especially for detecting the direction of low frequency acoustic waves. These characteristics are crucial for various underwater applications, including sonar systems and navigation. The sensor's performance shows a marked improvement over previous models, with sensitivity enhanced by 5 dB, achieving a sensitivity level of -186 dB and a frequency bandwidth ranging from 20 Hz to 1.5 kHz (0 dB = 1V/μPa). These findings highlight the advancements made by the novel PVDF hydrophone, offering improved detection capabilities and accuracy for low-frequency sound waves in underwater environments. This represents a significant step forward in the field of underwater acoustic sensing technology.