Printed energy harvesting solutions for textile-based applications

Nowadays, the pursuit of sustainability and sustainable products and services has become a reality in several industrial sectors, including automotive industry. Current products with added value and functionality, such as monitoring devices, tend to be battery dependent, leading to a continuous increase in environmental pollution and resource extraction (e.g. raw materials such as cobalt and lithium). Therefore, the development of energy harvesting solutions that can increase the lifetime of batteries and, simultaneously, lead to the fabrication of self-sustainable devices is recognized as a promising approach to address this issue.

Continental’s interest in the development of printed energy harvesting solutions is set within this context, where, through the combination of advanced textile processes and printed electronics technologies, the development of autonomous devices is intended that can monitor different parameters of several textile and rubber based products – in a sustainable and environmental friendly approach.

ContiTex project

The Continental AG, Hanover/Germany, is recognized worldwide for its expertise in the development of rubber-based solutions for several sectors and for its strong know-how in the development of textile reinforcement structures. This strong expertise combined with its investment and interest in innovation and new functionalities for its products, allowed the creation of the Portuguese nationally funded project ContiTex.

Printed thermoelectric energy harvester applied in a rubber-based product (Source: Continental/CeNTI)

The ContiTex project aims at the development of textile-based smart labels, with embedded energy harvesting, sensors and wireless communication systems, through a combination of advanced textile processes and printed electronics. The proposed smart label concept presents a modular aspect in terms of sensors (e.g. temperature and strain) and energy harvesters (e.g. piezoelectric and thermoelectric), allowing its application within different areas of the Continental group, namely automotive interiors and rubber-based products such as hoses, power transmission belts and air springs.

The targeted project devices aim to provide smart functionalities to these products, through the monitoring of critical parameters such as temperature and strain level, taking advantage of the mechanical or thermal events to which the products are submitted to harvest energy, ensuring self-sustainability of the smart label.

To develop this solution, Continental is collaborating with the Centre for Nanotechnology and Smart Materials (CeNTI), Vila Nova de Famalicão/Portugal, a R&D centre with expertise in nanotechnology and smart materials with application in different sectors, including the automotive industry.

Making printed electronics and textile processes compatible

The merging of printed electronics and textile processes is currently a reality in the field of smart textiles, allowing the development of smart textile-based devices with application in different industrial sectors such as sports, construction and, of course, the automotive industry. The ContiTex project aims to reinforce the benefits that printed electronics can add when combined with textile applications, through the integration of disruptive technologies, such as energy harvesting, without compromising the mechanical stability and adaptability of the targeted textile structures. Simultaneously, the project includes the application of the developed printed harvesters in textile reinforced rubber composites, demonstrating the versatility of printed electronics and the added value of its implementation. “To ensure the compatibility of the processes and technologies applied, the developments focused not only on the study of different materials, namely functional inks, textile fibres, adhesives and coatings, but also in the customisation of knitting and screen-printing processes, bringing the solutions one step closer to industrialisation,” explained researcher Kevin Rodrigues.

Printed piezoelectric harvesters

Considering the development of printed piezoelectric energy harvesters, this type of devices exhibits a high potential of application in several sectors, converting mechanical vibrations/deformations in electrical energy. The efficiency in the energy conversion of these devices is based on piezoelectric coefficients of the applied materials, being polyvinylidene (PVDF) and its co-polymers as the most explored in printed electronics. Therefore, the printed piezoelectric devices developed were produced in a layer-by-layer screen-printing process, through the application of PVDF functional inks and silver ink electrodes. “During this work different PVDF piezoelectric inks were developed and studied in order to increase the energy harvesting performance of the devices. This study involved not only inks formulation, but also the analysis of the best printing parameters and curing conditions,” explained researcher Daniela Campanhã.

Printed thermoelectric harvesters

Regarding thermoelectric harvesters (TEGs), these devices can convert thermal gradients in electrical energy through Seebeck effect, achieved by n-type and p-type semiconductors. Since the performance of the developed devices is dependent of the selected thermoelectric materials, during this work different bismuth telluride Bi2Te3 (n-type and p-type) thermoelectric inks were developed, applying silver ink electrodes in the device’ construction. “The development of the thermoelectric inks included the test of different Bi2Te3 powders, as the study of different ink formulation and processing parameters such as Bi2Te3 particle size, ink matrix, printing conditions and inks curing/sintering. Simultaneously, different device’ designs were studied, since this parameter has a critical role in the energy harvesting performance,” explains researcher Cristina Furtado.

Energy harvester performance in textile reinforced rubber-based products

To achieve self-sustainable devices, it is necessary that the developed printed piezoelectric and thermoelectric harvesters are optimized either considering their energy harvesting performance but also in terms of its integration in the final application (e.g. textile structure, hose, power transmission belt). This final aspect has a critical impact in the harvesters’ performance since the energy output is dependent of the external thermal gradients or mechanical events to which the printed devices are exposed. “Thus, to characterise the performance of the developed harvesters, different characterisation apparatus capable of accommodate different Continental products such as power transmission belts and fluid hoses were produced, simulating the real operating conditions of these products, guaranteeing that the printed harvesters integrated were exposed to the most similar thermal/mechanical events,” explained researcher Miguel Peixoto. Simultaneously, the ContiTex project included the development of customised electronic solutions to interact with the developed energy harvesters, supplying the electrical energy to the sensing and wireless communication systems that constitute the smart label concept presented.