Design and analysis of a passive omni-directional acoustic switch
This thesis details the creation of a novel acoustic device, one which requires no power and is activated by the frequency of an acoustic wave. This device, named an acoustic switch in this paper, lays dormant until a continuous wave acoustic signal excites it at its specific design frequency, at which point it outputs a voltage. There currently are devices, namely hydrophones, that yield similar results, but are not activated by a specific frequency. The acoustic switch can be used in applications that require acoustic communications where power usage is critical, such as in battery powered unmanned underwater vehicles. The acoustic switch operates based on the principles of resonance induced by acoustic signals. Resonance creates large displacement harmonic motion in a mass spring system and this displacement can be converted to electrical signals. This thesis lays out the mechanical design of three different types of acoustic switches, each acting on different modes of resonance. The designs are analyzed numerically and through finite element analyses to determine the resonance frequency of each as a function of size, and the sensitivity of each design. A proof of concept prototype is constructed and successfully tested in the acoustic laboratory at Boston University to prove that an acoustic switch can work. The analyses show that designs can be created in the diameter range of 5 cm to 200 cm with actuation frequencies from 2,000 Hz to 50,000 Hz, where the size is inversely proportional to the actuation frequency. The designs can have sensitivities up to 15,000 Volts per Pascal of peak pressure amplitude. The voltage output from the switch can either be used as is or be fed to an ultra low power signal conditioning unit. The signal conditioning units use energy efficient active electronics and have a battery life of up to 46 years. The acoustic switch can usher in the development of a new category of low power sensors that can be used in commercial, military, and consumer applications.