## 1 Introduction  
In the last half-a-century, there has been an exponential surge in the volume of research on SHM with at least 17,000 papers published in the last decade alone [1]. The major reason can be attributed to the enormous rise in the global demand for (a) wired and wireless sensing techniques, (b) miniaturization of analyzers, (c) energy harvesting of sensors and actuators, and (d) robotic applications. The efficiencies of many SHM techniques improved rapidly due to advancements in the designs of sensors, especially those made of smart materials [2; 3; 4; 5]. Most such sensors can be classified as either FO sensors [6; 7] or non-FO sensors [8; 9] or their combinations [1; 10; 11]. The input of EMradiations or electrical power or magnetic field either remotely or directly to most smart material sensors via analysers/devices, produce diagnosable output signals. If such sensors are attached to or embedded in any CMA structures, they can probe the structures' health in either continuous real time domain or discontinuous frequency domain [12]. Any deviation in the output signal from the healthy stage signal indicates possible anomalies in the CMA engineering structure under investigation. However, handling of (a) heavy and bulky input-output analysers or devices, (b) various types of smart material sensors from their installation to collection of usable output data, and (c) post processing output signals, are all important tasks requiring labour or engineers. The advent of automation, especially the application of robots coupled with miniaturized devices has greatly reduced such human tasks and increased the demand for qualitative SHM. Recently, Technavio analysts, a well-known market research company estimated the global SHM market to surge from the current US $ 1.48 billion to US $ 3.38 billion by 2023, at a CAGR of 17.93% [13].  
This shows that the demand for SHM, especially the popular smart materials such as FO sensors and their operational designs, viz., (a) (FBG) sensors, and (b) modulated sensors are on the rise [14]. Usually the modulations are induced in intensity, wavelength, phase, polarizations, and gratings. Similarly, adaptable and innovative designs of non-FO smart materials such as metamaterial and piezoelectric materials are also on the rise. For example, the market for metamaterials and piezoelectric materials are expected to grow rapidly at a CAGR of more than 22% and 13%, respectively [15; 16]. Furthermore, the global automation and robotics market in the automotive industry is expected to post a CAGR of close to 8% [17]. The fusion of such smart material sensors with automation can increase the overall market enormously and shape the future to a great extent [18]. Thus, this invited review paper presents a positive perspective of non-FO materials especially metamaterials with brief discussion on characteristic features of EM near field and far field; and evolution of EM metamaterial designs with relevance to these fields for SHM applications. Additionally, our recent work related to near field setup using a few near field metamaterial designs, a portable meta setup, and their functionalities along with a novel piezoelectric catchment sensor are discussed.