Virtualization of sensors using laser vibrometer-based sensor synthesis

Effective application of ultrasonic guided waves in structural health monitoring requires systematic selection and placement of elastic wave transducers, acting as actuators and sensors, to maximize sensitivity of the system while minimizing the number of its elements. Non-contact space–time wavefield measurements performed using scanning laser Doppler vibrometry (SLDV) are often utilized to replace physical sensors in sensor network optimization studies. However, on their own, these measurements do not accurately represent the characteristics of complex transducers, which are commonly used in guided waves-based applications. In this work, we propose two methods for constructing virtual sensors that can be applied to space–time wavefield measurements to accurately represent elastic wave transducer behavior in sensing. These methods, namely, direct matrix inversion (DMI) and directional filter (DF), estimate a set of weighting coefficients that describe the directivity pattern of the required arbitrary physical transducer for a given excitation. The DMI method involves inversion of transducer’s constitutive equations, while the DF method implements a directional filter in the wavenumber domain. In this paper, the effectiveness of both the proposed approaches is investigated using three different types of complex transducers, with numerical simulations and subsequent experimental validation using SLDV measurements. The results show that the responses predicted by the proposed methods have high agreement with those of the physical transducers; with the DMI method achieving higher accuracy and the DF method offering lower computational complexity.