Directional sound transmission using ultrasonic array

• Main Author: Loh, Jian Hao
• Other Authors: Li King Ho Holden
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/149261
• Institution: Nanyang Technological University

Acoustic as a form of long-range non-lethal directional energy transmission in sonic, ultrasonic or infrasonic range has been researched for long time. Commercial acoustic devices or systems developed in the past decade are capable of directional sonic transmission for extended range and can cover audio frequency of around 0.1kHz to 10kHz. They are mainly used for crowd control and long distance hailing with acceptable sound quality fidelity. These proprietary products have limited technical information for extending their capability for other applications. This project was to explore methods for potential long-range directional acoustic transmission at higher frequency range (i.e. 15 kHz to 25 kHz) with sufficient intensity or energy to induce disruption or self-destruction of MEMS devices used in autonomous systems such as Unmanned Aerial Systems (UAS) or drones, Autonomous Guided Vehicles (AGV). This frequecy range is to target the resonance frequency of those MEMS devices with the frequency range of 17-25 kHz typically. The MEMS devices are used for self navigation in the autonomous systems and disruption in the MEMS device operation would usually result in stalking the systems. The major requirement for this application is high sound pressure level (SPL) while the acoustic quality fidelity is not important. Ultrasonic waves generally exhibit much better directionality as compared to audio sound waves. Commercial 40kHz ultrasonic transducers were used in different array configurations in this study for possible two beams directional transmission of sonic energy closer to the ultrasonic frequency range. Experiments were carried out to understand the ultrasonic sound waves from these 40kHz ultrasonic air transducers and how sonic pressure level (SPL) vary with distance and driving signal frequency. Subsequently, ultrasonic transducer arrays of different configurations were built and tested for SPL performance at different frequencies. The experimental results from the transducer array testings did provide useful insights in terms of ultrasonic array design for two beams directional acoustic transmission. In conclusion, it is worth noting the exploratory nature of this study and the results should be used as a basis for further research before being translated into practical applications, especially for the purpose of targeting MEMS devices.