Abstract
Flexible substrates have become essential in order to provide increased flexibility in wearable sensors, including polymers, plastic, paper, textiles and fabrics. This study is to comprehensively summarize the bending capabilities of flexible polymer substrate for general Internet of Things (IoTs) applications. The basic premise is to investigate the flexibility and bending ability of polymer materials as well as their tendency to withstand deformation. We start by providing a chronological order of flexible materials which have been used during the last few decades. In the future, the IoT is expected to support a diverse set of technologies to enable new applications through wireless connectivity. For wearable IoTs, flexibility and bending capabilities of materials are required. This paper provides an overview of some abundantly used polymer substrates and compares their physical, electrical and mechanical properties. It also studies the bending effects on the radiation performance of antenna designs that use polymer substrates. Moreover, we explore a selection of flexible materials for flexible antennas in IoT applications, namely Polyimides (PI), Polyethylene Terephthalate (PET), Polydimethylsiloxane (PDMS), Polytetrafluoroethylene (PTFE), Rogers RT/Duroid and Liquid Crystal Polymer (LCP). The study includes a complete analysis of bending and folding effects on the radiation characteristics such as S-parameters, resonant frequency deviation and the impedance mismatch with feedline of the flexible polymer substrate microstrip antennas. These flexible polymer substrates are useful for future wearable devices and general IoT applications.
Highlights
Over the last few decades, Flexible Electronic System (FES,) known as flex circuits, have been growing rapidly in industries and organisations such as medical healthcare, energy and power, aerospace, industrial automation, military and defence, sports and entertainment are the array of various devices are generally comprised of organic substances as a substrate
The area of investigation includes the primary and secondary research, focusing on the most efficient and relevant polymer substrates in terms of bending and flexibility, which is a key challenge for flexible Internet of Things (IoTs) and wearable applications and includes polymers such as PI, Polyethylene Terephthalate (PET), PDMS, PTFE and Liquid Crystal Polymer (LCP) which cover more than 90% of the polymer-based flexible wearable industry
This review gives emphasis on a detailed comparative analysis of the physical, electrical, thermal and chemical properties of the flexible polymer materials which have been used as substrates during the last few decades to provide flexibility, which, in the process of appropriate substrate selection for flexible antennas, simultaneously serves as a beneficial guide to better match their compatibility with specific wearable applications
Summary
Over the last few decades, Flexible Electronic System (FES,) known as flex circuits, have been growing rapidly in industries and organisations such as medical healthcare, energy and power, aerospace, industrial automation, military and defence, sports and entertainment are the array of various devices are generally comprised of organic substances as a substrate. Researchers have incorporated a variety of materials for providing improved flexibility in electronic systems, including the application of polymers, plastics, paper, textiles and fabrics as substrates of these systems. Each of these materials has its own characteristics in terms of how efficiently they can be safely bent, twisted and/or crumpled. For certain electronic and communication applications, the flexible characteristic of different materials is of great importance, with extensive use spreading into flexible displays, smart tags and wearable products as well as the flexible antenna developments [3,4].
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