| PhD Viva

Name of the Speaker: Ms. Visalakshi V (EE12D021)
Guide: Dr. Bharath Bhikkaji
Co-Guide: Prof. Boby George
Online meeting link: https://meet.google.com/dhg-zwzr-ojd
Date/Time: 29th January 2024 (Monday), 3:00 PM
Title: Sensing, Modeling and Control of Resonant Structures

Abstract

First part of the research concentrated on modeling and control of resonant structures. A flexible structure with collocated sensor/actuator pairs is considered. The resonant modes of the collocated structure are damped by designing a suitable Positive Position Feedback (PPF) Controller. The control design frame work involves matching the eigen- structure of a desired reference system with that of the closed loop system. Matching of the eigen-structure reduces to solving a set of over determined linear equations in the controller parameters. If the linear equations do not have solution, then a least squares solution under stability constraints (both closed loop and controller stability) is computed. The stability constraints are found to be Linear Matrix Inequalities (LMIs) in the controller parameters; thus, making the control design convex. Second part of research concentrated on the design of controllers for highly resonant systems which are non-collocated. The plant and controller are written in a second order form, and their states are concatenated to form a closed loop. The controller parameters are determined by matching the eigen-values and eigen-vectors of the closed loop with that of a desired plant as in collocated system. Here also convex design of controllers in an optimization frame work was carried out ensuring the stability of both closed loop system and controller. To suppress vibrations of resonant structures, first the vibrations are to be measured. So, the research concentrated on a novel sensing scheme which was not explored earlier.

Tunneling Magneto-Resistance sensor as a pick-up element for string instruments, in particular for guitars, is proposed in research. TMR based pick up showed several clear advantages compared to the presently used inductive pick-ups. The proposed scheme is less sensitive to the disturbing electromagnetic fields, mainly because each string is excited using an AC current source at specific frequency and the signal conditioning circuit for the TMR sensor kept underneath the corresponding string is tuned to be sensitive to that particular frequency. This reduces the cross-coupling effects, significantly. In addition, the output is not sensitive to the residual magnetic field of the string. The proposed sensor unit is compact compared to the conventional pick up. The TMR sensor is placed just below the guitar string and the output was recorded. For the feasibility study, the output signals are acquired using LABVIEW environment. After extracting the vibration information from the TMR sensor, with the help of envelope detection and look up table, the data is compared with the output from a Laser Distance Sensor that directly measures the string vibration simultaneously. The results are matching.