Multi-point vibration measurement using PVDF piezoelectric film with application to direct sensing of modes in structures

Direct methods of sensing modal participation factors in thin vibrating structures making use of distributed or multi-point piezoelectric PVDF films to measure surface strains are investigated. The principle of modal sensing, originally developed for beams, is extended to the case of plates. The validity of this concept is proven in its generality, while underlying orthogonality relationships are derived and applied to the case of plates with common boundary conditions. By discretizing the system, a computational method for the design of such sensors is obtained. A similar approach incorporating experimental results is illustrated in the case of a beam. Two practical ways of fabricating a modal sensor in two dimensional geometries are presented. The first method uses photolithographic techniques and multilayered polymer films. The second one involves the embedding of active electronic components in conjunction with a modulation scheme. These findings give a general means for designing modal sensors for thin elastic plates, and also illustrate a methodology which may be generalized to the construction of a modal sensor for a thin shell.