A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. For example, state-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously "retuning" the state-switched absorber to a new frequency. This paper briefly develops the fundamental analysis tools for a Single-Degree-of-Freedom state-switchable device, and then considers the application of such a device for the purpose of vibration control in a 2-DOF system. Simulation results indicate that state-switched vibration absorbers may be advantageous over classical passive tuned vibration absorbers under certain conditions.
In order to produce high-amplitude, low-frequency signals, an underwater transducer must generate a relatively large volume displacement. Since water exerts a large reaction force back on the transducer, ''conventional wisdom'' dictates that such a transducer would have to be a high Q resonant device and thus not be broadband. However, a transducer does not have to be broadband in the conventional sense to meet the requirements of communication and sonar systems. A transducer that is capable of instantaneously switching between two discrete frequencies is adequate for communication and transmission of coded signals; one that is capable of switching among several frequencies could produce the chirp signals commonly used in active sonars. Ordinarily, a broadband transducer is needed to accomplish the frequency switching rapidly. A way around this difficulty is the ''state-switched'' source concept originally proposed by Walter Munk in 1980 which permits instantaneous frequency switching of a high Q resonant transducer while always maintaining the resonance state. The objective of this research has been to investigate this novel approach to the design of high-power, low-frequency, broadband transducers for use in long-range underwater communication, active sonar, and underwater research applications. This paper presents a practical realization of a ''state-switched'' source.
To produce high amplitude low-frequency signals, an underwater transducer must generate a relatively large volume displacement. Since water exerts a large reaction force back on the transducer, ‘‘conventional wisdom’’ dictates that such a transducer would have to be a high Q resonant device and thus not be broadband as seemingly required for many applications. However, a transducer does not have to be broadband in the conventional sense to work in communication and SONAR systems. A transducer capable of switching between two discrete frequencies is adequate for communication and one capable of switching among several frequencies could produce chirp signals for active sonars. Ordinarily, a broadband transducer is needed to switch frequencies rapidly. It is theoretically possible, however, to instantaneously switch frequencies with a high Q resonant system provided that the system’s resonant and drive frequencies are altered simultaneously. Such a ‘‘state-switched’’ transducer [Munk, Webb, Birdsall, unpublished (1980), (1981)] would retain the advantages (high power, high efficiency, and large displacements) of a high Q resonant transducer without the accompanying disadvantage of slow response time. A state-switched acoustic source with an active spring of PZT has been built to demonstrate the state switching concept. [Research supported by ONR 334.]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.