|Ph.D Student||Dolev Amit|
|Subject||Parametrically Excited Mechanisms for Selective Detection|
Identification and Actuation in Distributed
|Department||Department of Mechanical Engineering||Supervisor||Professor Izhak Bucher|
|Full Thesis text|
Effective methods, based on parametric excitation (PE), for selective amplification, detection and identification of certain dynamics in distributed systems were developed in this research. These methods are employed and demonstrated experimentally for two types of systems: parametrically excited mechanical amplifiers and standing wave acoustic levitators.
The dissertation's first part deals with a novel scheme of tunable, nonlinear and dual-frequency parametric amplifiers. The scheme designation is to alter physical systems' dynamical response; allowing one to amplify weak and slow physical components of the dynamical response in-situ. This is achieved by applying a precisely tuned PE and nonlinear feedback along with a direct excitation, which is considered as the input signal to be amplified. By employing dual-frequency PE, two types of resonance are produced: combination and principal parametric. The former projects the direct excitation onto a selected vibration mode of the system, and the latter significantly amplifies the response. The tuned nonlinear feedback comprises quadratic and cubic stiffness terms, which cause the system to behave in a pseudo-linear manner. The developed parametric amplifiers are capable of enhancing low oscillations by transforming low-frequency motions into high-frequency ones, yielding a tailored mechanical response. The natural resonances of the systems are harnessed to enable amplification of low amplitude and frequency signals that cannot be detected otherwise, thus giving way to a new type of ultra-sensitive sensing approach.
To achieve the research goals, analytical models were developed, and the governing nonlinear equations were analytically solved using the asymptotic method of multiple scales. These solutions were then compared to numerical simulations for verification. Once verified, experimental rigs were designed and built to conduct experiments for validation and refinement of the models and theory as needed.
The dissertation's second part deals with standing wave acoustic levitation and noncontact particle manipulation (NPM). NPM is realized here by parametrically exciting acoustically levitated spherical particles in strong, nonlinear and complex ultrasonic fields. The underlying principle allowing levitation and PE is based on acoustic radiation forces, which are generated due to nonlinear phenomena in strong ultrasound wave fields. An improved analytical model, describing the parametrically excited sphere's nonlinear dynamics is derived and solved using the method of multiple scales. The suggested model is novel because it takes into consideration the nonlinear dissipative and conservative forces.
A single-axis ultrasonic levitator comprising an emitter and a matching concave reflector were used to study the spherical particle dynamics experimentally. With this setup, and employing PE, the following was demonstrated: 1) ejection of a particle from an acoustic trap, and 2) selection and oscillation of a specific particle while multiple particles are levitated, using only a single actuator. The proposed NPM technique differs from other works; because, the acoustic traps remain in place.