Novel Flexible Wearable Antennas Based on Advanced Materials and Fabrication Techniques.

PhD Theses.Wearable technology has evolved gradually in parallel with other technological advancements, and nowadays, it plays a key role in a wide range of applications. New antenna designs within wearable environments should explore solutions using exible materials, remaining ergonomic and comfortable but o ering mechanical robustness at the same time. Among these materials, carbon-based materials are up-and-coming candidates for these types of solutions and fabrics to fully integrate into e-textiles and smart clothing. The target of this research is to develop novel designs for exible antennas that will provide solutions to overcome the challenges associated with wearable technology by using modern fabrication techniques and materials. A comprehensive literature review regarding fabrication methods, together with material characterisation techniques is presented. A lack of experimental work was noticed, and for the rst time, a full campaign of measurements was carried out to accurately describe the temperature's impact on fabric-based devices using resonator antenna structures. Wearables in general and e-textiles, in particular, are about to tackle tremendous environmental and sustainability challenges. In the context of exploring sustainable materials in e-textiles, a novel soft and conformal textile-based antenna using multi-layer graphene sheets has been thoroughly analysed, describing its performance, the e ects of bending, and proximity to the human body. Within this research, printing techniques have been considered as an alternative to assembly processes. Two antenna designs (PICA/LOOP) with the advantages of carbon nanotubes inks and screen-printing methods, such as lightness, malleable and washability are characterized. In addition, a quasi-Yagi-Uda design has been optimized, fabricated, and characterised. The specimen was inkjet printed on Kapton substrate using graphene ink. A post-numerical analysis was used to characterise the e ect of a not ideal fabrication. The measured data was post-processed in order to overcome some of the associated challenges of measurements for exible devices in a wearable environment. The outcomes of this research ful l the gap between the use of carbon-based alternatives and fabrication procedures on di erent exible substrate

Screen printing carbon nanotubes textiles antennas for smart wearables

Electronic textiles have become a dynamic research field in recent decades, attracting attention to smart wearables to develop and integrate electronic devices onto clothing. Combining traditional screen-printing techniques with novel nanocarbon-based inks offers seamless integration of flexible and conformal antenna patterns onto fabric substrates with a minimum weight penalty and haptic disruption. In this study, two different fabric-based antenna designs called PICA and LOOP were fabricated through a scalable screen-printing process by tuning the conductive ink formulations accompanied by cellulose nanocrystals. The printing process was controlled and monitored by revealing the relationship between the textiles’ nature and conducting nano-ink. The fabric prototypes were tested in dynamic environments mimicking complex real-life situations, such as being in proximity to a human body, and being affected by wrinkling, bending, and fabric care such as washing or ironing. Both computational and experimental on-and-off-body antenna gain results acknowledged the potential of tunable material systems complimenting traditional printing techniques for smart sensing technology as a plausible pathway for future wearables

Smart nanotextiles for communication

Together with wireless technology, advances in nanotechnology and rapid and scalable synthesis of nanomaterials including the 2D graphene has transformed the realms of biomedical sciences. Recent research in the areas of drug delivery, cancer therapy, bio-sensing and bio-imaging have exploited the unique structural and physiological features of graphene and its different forms. Along with the Graphene, several other nanomaterials including carbon nanotubes (CNTs), make excellent candidates for applications associated with loading of drugs, cellular imaging, sensing other molecules and in-vivo cancer studies due to their biocompatibility and stability. Assimilating from the fundamentals of electromagnetic, wireless communication, medical and material science, a novel concept of nanonetworks was first introduced in 2008, which stems from the concept that a collection of nanodevices have the potential to harness the innate communication capabilities of the human body, thereby allowing them to cooperate and share information. It is anticipated that the advanced healthcare diagnosis can be realised if an efficient communication mechanism and data transfer are established between these nanodevices. The human body is a good example of a naturally existing communication network. For instance, the nervous system is composed of nerve cells, i.e. neurons that communicate the external stimulus to the brain and enable the communication between different systems by conveying information with a molecular impulse signal known as a spike. The human body needs communication amongst different cells to survive, the proposed intra- and inter-body nanonetworks ensure their stability without mechanically (or physically) disturbing the harmony of the in-built molecular structure of the body. Moreover, in several cases, the medicine technology fails to understand the root cause of the problem but once we have a monitoring network established in our body, we can extract various unknowns and treat them effectively. The vision of nanoscale networking attempts to achieve the functionality and performance of the internet with the exception that node size is measured in nanometres and channels are physically separated by up to hundreds or thousands of nanometres. In addition, nodes are assumed to be mobile and rapidly deployable. Nodes (or nanodevices) are expected to be either self-powered or spread in and around the specific location. In a visionary sense, an ultimate application of nanoscale networking would be an automated process, where the nano-nodes are in motion communicating in a complex dynamic environment of living organisms monitoring diseased or sensitive parts of the body

Graphene-based soft wearable antennas

Electronic textiles (e-textiles) are about to face tremendous environmental and resource challenges due to the complexity of sorting, the risk to supplies and metal contamination in textile recycling streams. This is because e-textiles are heavily based on the integration of valuable metals, including gold, silver and copper. In the context of exploring sustainable materials in e-textiles, we tested the boundaries of chemical vapour deposition (CVD) grown multi-layer (ML) graphene in wearable communication applications, in which metal assemblies are leading the way in wearable communication. This study attempts to create a soft, textile-based communication interface that does not disrupt tactile comfort and conformity by introducing ML graphene sheets. The antenna design proposed is based on a multidisciplinary approach that merges electromagnetic engineering and material science and integrates graphene, a long-lasting alternative to metal components. The designed antenna covers a wide bandwidth ranging from 3 GHz to 9 GHz, which is a promising solution for a high data rate and efficient communication link. We also described the effects of bending and proximity to the human body on the antenna's overall performance. Overall, the results suggested that graphene-based soft antennas are a viable solution for a fully integrated textile-based communication interface that can replace the current rigid, restrictive and toxic approaches, leading to a future where eco-friendliness and sustainability is the only way forward

Numerical and experimental analyses of wearable antennas, including novel fabrication and metrology techniques

Most fifth-generation (5G) mobile network applications require wearable antennas to be unobtrusive, low-profile, low-power and electrically small. Such antennas are a crucial element in wearable body-centric wireless system designs for delivering 5G user’s experience. Wearable antennas can be employed in a wide range of applications from communicating, harvesting energy to sensing capabilities. For this purpose, fabrics and novel materials such as graphene are been explored in order to cope with the wearable device demands in terms of flexibility, conformability and lightweight. Similarly, novel fabrication techniques for wearable antenna prototyping such as screen printing, inkjet printing, embroidery and cutters are been investigated to exploit the unique characteristics of various materials. These innovative fabrication methods allow a high degree of fabrication precision enabling their uptake for 5G applications. Due to power absorption by lossy human body tissues, a distorted radiation pattern and lower radiation efficiency are envisaged when they are worn on and at proximity to the body. Furthermore, when designing the antenna, the body proximity effects must be considered to prevent significant antenna detuning and the consequent mismatch. Numerical and experimental human body phantoms are used with a view to simulate its impact. This chapter presents an analysis of novel fabrication methods for wearable antennas, methodologies and measurement techniques to characterise their performance in a dynamic body-worn communication environment. This chapter delivers a review of different novel fabrication techniques for wearable antennas such as various printing processes, machine embroidery and laser methods. Follow by a metrology section, where numerical and experimental human phantoms are explained and durability tests described. Three examples of 5G wearable antennas for different frequencies and their on-body performance characterisation are provided.Finally, it is closed with a summary of the outcomes achieved in this chapter and future prospects of the research

Graphene-based textile ultra wideband antennas for integrated and wearable applications

This paper presents an ultra-wideband antenna using graphene as a conductive patch. In order to provide flexibility, the cotton fabric is used as a substrate. The proposed antenna covers a bandwidth of 2–8 GHz. Simulated antenna efficiency is approximately 60% in overall bandwidth. The attractive features of conformity, lower design complexity, and fabrication ease as well as integration of an environment friendly and low cost graphene have suggested the proposed antenna well-suited for body-centric, biomedical and wearable applications