314 Int. J. Automation and Control, Vol. 1, No. 4, 2007 Copyright © 2007 Inderscience Enterprises Ltd. Reduced-order models for a smart plate G. Jayaprasad* and C. Sujatha Machine Design Section, Department of Mechanical Engineering, IIT Madras, Chennai 600036, India Fax: +91-44-2257-4652 E-mail: jayaprasad@iitm.ac.in E-mail: sujatha@iitm.ac.in *Corresponding author Abstract: A Single Input Single Output (SISO) state space model has been developed in MATLAB using a smart plate model realised in ANSYS ® . The frequency response due to a unit force, for the full model as well as the reduced unsorted and sorted models was studied. Dc gain is used as the criterion for sorting. Simple reductions as well as ‘modred’ option of MATLAB were used for model reduction. In this paper a method of reducing modes, ‘balanced reduction’ will also be introduced. The method will be compared with dc and peak gain ranking methods using a smart plate model. The step and impulse responses for all the models were also studied. The model with minimum number of modes retained, and with minimum deviation from full model characteristics was identified analytically. It is proposed to use this model subsequently for vibration control applications. Keywords: smart plate; model reduction; modred; controllability grammian; balanced reduction. Reference: to this paper should be made as follows: Jayaprasad, G. and Sujatha, C. (2007) ‘Reduced-order models for a smart plate’, Int. J. Automation and Control, Vol. 1, No. 4, pp.314–341. Biographical notes: G. Jayaprasad is a Research Scholar in the Department of Mechanical Engineering, IIT Madras, India. He received a Post Graduate degree in Mechanical Engineering, and has 14 years of teaching experience in the field of Mechanical Engineering. C. Sujatha is a Professor in the Department of Mechanical Engineering, IIT Madras, India. She received a PhD in Applied Mechanics (IIT Madras) and has 20 Years of research and teaching and consulting experience, with numerous publications in international journals and conferences. 1 Introduction Model reduction is a technique widely used in part of dynamic analysis and design of structures. Flexible structures are described by partial differential equations, and a common practice is to represent their equation of motion via linear ordinary differential equations using the finite element discretisation technique. Typically a model with a