Review of Modal Sensing and Actuation Techniques

Abstract

The linear behavior of continuous structures is characterized by the combined response of infinite individual modal responses. Knowledge of the contribution of each individual mode to the overall dynamic response simplifies many applications, such as vibration control, shape estimation, and structural health monitoring. Unfortunately, most transducers simultaneously measure a combination of modes, and hence extracting the contribution of an individual mode can be difficult. The concept of modal transducers was developed in the late 1970s to overcome this limitation and allow for the simplified design of active control laws. Modal transducers seek to address individual vibration modes on a structure through the intelligent design of transducers, reducing the apparent system complexity. These modal transducers, also known as modal sensors and modal actuators, greatly simplify the problems of vibration control and shape estimation. This paper reviews the literature concerning the design and implementation of spatial modal sensors and actuators. Construction techniques initially focused on large-area sensors physically shaped to provide the desired spatial coupling. Modern techniques use arrays of transducer elements that have their signals weighted to provide the desired filtering. While temporal modal sensors exist, their use in real-time vibration control, shape estimation, and health monitoring is limited due to large time lags resulting from the temporal filtering. This critical review aims to illuminate the main characteristics, advantages, and limitations of the different techniques and provides an extensive list of references on the subject.