A New Transducer for Rotational and Translational Impedance Measurement

Measurement of rotational frequency response functions (FRFs) is important for a complete description of a dynamic system, as a full description requires consideration of both translational and rotational excitations. However, so far rotational FRFs have usually been neglected from analysis due to the absence of reliable and accurate measurement transducers and methods. This study presents a novel bimorph impedance transducer (BIT), which can accurately and easily measure rotational FRFs as well as translational ones. Through careful design, this transducer is only sensitive to one translational and one rotational degree of freedom (DOF) at a structural point, which are further decoupled from each other through controlling the phase of the electrical excitation supplied to the transducer. To investigate the effectiveness of the transducer, experiments using a one-dimensional beam as a test structure are carried out. The results show that the BIT is accurate in measuring both rotational and translational impedance of elastic structures. The measurement is performed simply by measuring the input electrical parameters of the BIT; consequently the direct measurement of moment/force and linear velocity/angular velocity, which are usually difficult to conduct in experiments, is avoided. As this transducer functions actuating and sensing simultaneously during measurement, the measurement system is also greatly simplified and the accurate driving-point measurement is achieved.