*Proceeding Paper* **A Screen-Printed 8** *×* **8 Pixel Electroluminescent Display on Fabric †**

**Huanghao Dai \*, Thomas Greig, Russel Torah and Steve Beeby**

† Presented at the 4th International Conference on the Challenges, Opportunities, Innovations and Applications in Electronic Textiles, Nottingham, UK, 8–10 November 2022.

**Abstract:** A screen-printed electroluminescent (EL) matrix display on fabric is presented. This work demonstrates the fabrication of a screen-printed multilayer display with a matrix of 8 × 8 pixels, as well as the design and construction of integrated drive electronics capable of operating the EL display and achieving good visibility. Each pixel is 1 mm × 1 mm, which is smaller than in previously reported literature. The EL matrix was successfully printed and laminated on fabric at this higher resolution, improving the visual effect and decreasing the overall display size, and reducing the impact on the flexibility and breathability of the underlying fabric. This proof-of-concept demonstrator EL display shows the potential for more complex pixel displays for e-textile and printed electronic applications, such as interactive clothing, and information displays in applications, such as the automotive field, architecture, and point of sale advertising.

**Keywords:** electroluminescent devices; e-textiles; screen printing; smart fabrics; flexible electronics

#### **1. Introduction**

Printed electroluminescence (EL) materials are widely used for the fabrication of longlasting, high-intensity light-emitting devices on flexible substrates [1]. The main benefits are the ease of fabrication of an EL multilayer structure via screen printing, which has a higher layer-thickness tolerance compared with equivalent printed OLEDs. In addition, the polymer inks required for fabrication are more widely available. The previous literature has successfully implemented an EL display on fabrics to fabricate a watch [2] and a traffic signal system on a backpack [1]. To achieve improved high-resolution display performance, the pixel pitch, which is the distance from the centre of a pixel to the centre of the adjacent pixel, is a critical dimension. A lower pixel pitch results in an image with smoother edges, finer detail, and smaller dimensions in the flexible display, increasing the comfort of wearable e-textile applications.

#### **2. Materials and Methods**

#### *2.1. Electroluminescent (EL) Lamp Structure*

A standard parallel plate capacitor configuration is used to make EL lamps, with a light-emitting phosphor layer sandwiched between the two electrodes. To allow light to be emitted, one of the electrodes is transparent. Because the phosphor layer would electrically break down at high field strengths, a dielectric layer is also placed between the electrodes to prevent a short circuit. Figure 1 shows the cross-section structure of a complete EL lamp with the materials used for each layer, which consists of four layers [2]. A bus-bar layer is added between the phosphor and the translucent conductor (PEDOT) layer for improved electric field distribution in this design to create an 8 × 8 pixels array.

**Citation:** Dai, H.; Greig, T.; Torah, R.; Beeby, S. A Screen-Printed 8 × 8 Pixel Electroluminescent Display on Fabric. *Eng. Proc.* **2023**, *30*, 2. https:// doi.org/10.3390/engproc2023030002

Academic Editors: Kai Yang and Theodore Hughes-Riley

Published: 19 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

School of Electronics & Computer Science, University of Southampton, Southampton SO17 1BJ, UK

**<sup>\*</sup>** Correspondence: hd2m19@soton.ac.uk

**Figure 1.** Schematic diagram of the cross-section structure of printed EL lamp with inks used from Smart Fabric Inks Ltd. for each layer, which are labelled in red.

#### *2.2. EL Pixel Arrays Fabrication*

The screen-printing method was used to print the flexible EL lamps array with high printing resolution and low cost compared with the clean room facilities typically required for OLED production.

#### 2.2.1. Screen Design

The first step of printing EL lamps is manufacturing the screen. In this project, to test the resolution limitation of screen-printing method, two layouts for the displays were designed using Tanner L-Edit software. The screen design is shown in Figure 2A, which has a print area of 10 cm × 10 cm. It consists of seven large pixel arrays (one of which is labelled with the red shaded area in Figure 2A) and eight combinations of nine small pixel arrays (one of which is labelled with the blue shaded area in Figure 2A), plus six alignment patterns to aid registration of the various layers in the printing process. The screen details (mesh size and emulsion thickness) are given below for each layer.

**Figure 2.** Screen design, which consists of overall layout (**A**), larger 8 × 8 pixels arrays, (**B**) and smaller 3 × 3 pixels arrays (**C**).

In the large pixel 8 × 8 array, the size of each pixel is 1000 μm × 1000 μm with a gap of 500 μm, which is shown in Figure 2B. The linewidth of the connecting tracks is 500 μm, while the width of the connector pitch is 2540 μm to match the flexible printed circuit (FPC) connector used for testing.

The smaller pixel arrays were designed to test the resolution limits of the screen printing. The size of each pixel in the 3 × 3 pixels arrays is 800 μm × 800 μm, with a gap of 300 μm (Figure 2C, left part). The sizes of the connecting tracks of nine different arrays were designed to vary from 100 microns to 400 microns, which is shown in Figure 2C (right part), to explore the printing resolution limitation of screen-printing method.

#### 2.2.2. Screen Printing Process

The EL lamps array was fabricated using five functional layers as detailed below. The schematic pictures of the patterns after printing each layer are shown in Figure 3. A 120-34 polyester screen with 5 μm emulsion thickness was used for each screen except for the busbar, which had 30 μm emulsion to aid the print step across the layers, and the PEDOT layer, which used a 140-30 mesh, identified as the optimum mesh by the ink manufacturer.

**Figure 3.** Top views of the EL lamps after the printing of each layer: (**A**) silver layer, (**B**) dielectric layer, (**C**) phosphor layer, (**D**) bus-bar layer, (**E**) PEDOT layer.

The printing process used to produce the EL lamp is:


#### **3. Results and Discussions**

The EL pixels arrays were printed on 120 μm Policrom film and then laminated on to the fabric to achieve the flexible EL display screen on the fabric. The lamps were tested using a standard EL driving circuit, shown in Figure 4, which shows the visibility of each pixel and the retained flexibility of the fabric.

**Figure 4.** Powering the larger EL pixels arrays in flat (**A**) and bent (**B**) conditions.

The optical properties of the blue emitter were also assessed, which is shown in Figure 5A. The emission peak is at a wavelength of ~550 nm, with a brightness of ~200 cd/m2. The detected colour of emitting light was shown in CIE 1931 colour space in Figure 5B, of which the coordinates are (0.156, 0.426).

**Figure 5.** Measured luminance (**A**) and CIE 1931 colour space (blue circle) (**B**).

The smaller 3 × 3 pixels arrays were also tested, and the arrays of sizes greater than or equal to 150 μm were successful. There were defects in the printed 100-microns tracks, which caused open circuits, meaning the pixels could not be lit up. The printed performance of nine different sizes of tracks indicates that the screen-printing method is suitable for fabricating devices with track widths of more than 150 μm.

#### **4. Conclusions**

This work improved the screen-printed resolution of electroluminescent (EL) lamps on fabric and is capable of reducing the size of displays whilst retaining the flexible property of fabrics, which helps in reducing the size limit of wearable display devices. However, the limitation is that the screen-printing resolution must be 150 μm to achieve operational displays. Thus, future work must investigate an alternative printing method, namely reverse-offset printing, and use it to fabricate EL lamps to reduce their size by a factor of at least two whilst maintaining good performance.

**Author Contributions:** H.D. carried out the experiment design and implementation and wrote the manuscript draft. T.G. provided technical support in building the driving circuit. R.T. provided supervision for the research work, screen design, material selection, and electronics and edited the manuscript draft. S.B. supervised the research and edited the manuscript draft. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by EPSRC grant Wearable and Autonomous Computing for Future Smart Cities: A Platform Grant (EP/P010164/1).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** No new data were created or analyzed in this study. Data sharing is not applicable to this article.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

**Paula Veske \*, Frederick Bossuyt, Filip Thielemans and Jan Vanfleteren**

Centre for Microsystems Technology (CMST), Interuniversity Microelectronics Centre (IMEC), Ghent University, 9000 Ghent, Belgium

**\*** Correspondence: paula.veske@ugent.be

† Presented at the 4th International Conference on the Challenges, Opportunities, Innovations and Applications in Electronic Textiles, Nottingham, UK, 8–10 November 2022.

**Abstract:** The current work presents a testing machine built from off-the-shelf components to test for conductive yarns' (or textiles') durability to repeated bending that can occur during general wear-and-tear or domestic washing procedures. The testing method is explained with an example and results, comparing two different conductive yarns weaved into polyester-based narrow fabric.

**Keywords:** wearables; e-textiles; electronics; testing; reliability

#### **1. Introduction**

Conductive yarns are an essential part of e-textile (electronic textiles) applications [1,2]. Nevertheless, integrated electronics often create high-stress areas at the electronics encapsulation–textiles transition points. Thus, measuring their ability to withstand repeated bending is essential. Contrary to domestic washing tests, bending tests help to identify the exact moment(s) when the conductive yarns are breaking, thus helping to compare their durability more accurately and in uniform conditions.

This work presents a bending tester that can be assembled from off-the-shelf components together with a testing method to test e-textiles interconnection materials' durability. The study exemplifying the method includes two different conductive yarns weaved into narrow fabric in six rows with a pitch of 1.27 mm. For testing purposes, a non-functional printed circuit board was encapsulated with a casting material on the narrow fabric creating rigid–soft (encapsulation–textile) transition areas and accumulated stress for the conductive yarns (Figure 1).

**Figure 1.** Final sample encapsulation; red markings highlight the transition/high-stress areas.

#### **2. Materials and Methods**

The materials are divided into two categories: testing samples and testing machine. The methods explain the testing process in more detail.

#### *2.1. Samples*

The testing samples were based on a narrow fabric weaved in conductive yarns. The yarns were integrated into the narrow fabric in 6 rows, with a pitch of 1.27 mm to create a communication bus for the I2C communication protocol. Two different yarns were tested during this work:

**Citation:** Veske, P.; Bossuyt, F.; Thielemans, F.; Vanfleteren, J. Measuring the Flex Life of Conductive Yarns in Narrow Fabric. *Eng. Proc.* **2023**, *30*, 3. https:// doi.org/10.3390/engproc2023030003

Academic Editors: Steve Beeby, Kai Yang, Russel Torah and Theodore Hughes-Riley

Published: 19 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).


A CO2 laser was used to create an opening in the yarn for an electrical connection with electronic parts. A rigid PCB (printed circuit board) was glued onto the narrow fabric and connected to the conductive yarns through soldering. The integrated electronics were encapsulated with a polyurethane-based flexible potting compound through the low-pressure injection-molding process. The encapsulation was designed to have a smooth transition from thick to thin. However, the difference in the encapsulation material and the textile flexibility properties created transition points with higher mechanical stress. The final outcome of the sample and the highlighted stress areas are seen in Figure 1.

The conductive-yarn endings on each side were stripped from the Teflon cover. On one side, the conductive-yarn endings were coupled together and soldered to make 3 loops. On the second side, the conductive-yarn endings were soldered on an interposer PCB with female pins (Figure 2).

**Figure 2.** Testing set-up where the motor is at the top left side where also the 180-degree rotation takes place. (**a**) Machine set-up highlighting the connection between ADC and sample and where the 180-degree bending takes place. (**b**) Sample set-up highlighting the connections between interposer board/yarns and interposer board/ADC board.

#### *2.2. Machine*

The tester was developed using off-the-shelf components and a specially milled frame (Figure 2). The fixed part of the machine consisted of:


The stepper motor was attached to the top and connected to the Arduino UNO/ Motorshield V2 board. The connections between Motorshield and Arduino board did not allow connecting the sample to the microcontroller. Thus, the ADC board was connected in between to read out the data. The male pins on the ADC board allowed connection and disconnection of the sample easily to the machine.

#### *2.3. Testing Method*

A sample with a weight clamp was attached from the (black) encapsulated part to the motor and flexed 180 degrees. Since the yarns were coupled together, one ending of the loop received the power input and the other end was used to read the output. During the test, the samples were flexed 180 degrees for 100,000 cycles or until it was observed that at least two yarn loops' voltage dropped and was not regained for 10 seconds.

The ADC was used to convert digital signals to analogue signals to read every voltage value measured, whether the signal was there or not. If the yarn was damaged in between, the voltage drop would indicate it. Data read-out included: the voltage of the yarns (V), the number of cycles performed, and time (s). The data transmission was read out and saved using PuTTY (an open-source terminal emulator) through the serial port [3]. The data were logged in a CSV file that is easily usable for analysis.

However, resistance rise is often a more desired measurement for failure analysis. Resistance can be measured using Ohm's law by first defining the current (I).

The original resistance of a yarn (RY) loop was 1.2 Ω. The voltage input was always 5 V and the original voltage output (Vout) was always 4.95 V. Thus, the voltage loss (Vloss) at the start was always 50 mV. Based on that, the current was calculated:

$$\text{I} = \frac{\text{V}\_{\text{loss}}}{\text{R}\_{\text{Y}}} = \frac{50 \text{ mV}}{1.2 \text{ }\Omega} = 41 \text{ mA} \tag{1}$$

when the resistance of the yarns stays within 10% of the load resistance, the current stays stable and it can be assumed the same. To calculate the load resistance (RL), the following formula can be used:

$$R\_{\rm L} = R\_{\rm Y} \times \frac{V\_{\rm out}}{V\_{\rm loss}} = 1.2 \,\Omega \times \frac{4.95 \text{ V}}{0.05 \text{ V}} = 120 \,\Omega \tag{2}$$

Thus, if the RY changes over 12 Ω, then the current will also change. When the yarn resistance changes over the 12 Ω during the tests (voltage drops), the resistance should be calculated accordingly:

$$\mathcal{R}\_{\text{V}} = \frac{(\text{5 V} - \text{V}\_{\text{out}}) \times \mathcal{R}\_{\text{L}}}{\text{V}\_{\text{out}}} \tag{3}$$

Thus, the resistance of the yarn loops can be also plotted during failure analysis (Figure 3b,d).

**Figure 3.** Results with red dotted line highlighting the failure points. (**a**) Yarn 1 (Ni-plated copper yarn) showing voltage drops. (**b**) Yarn 1 (Ni-plated copper yarn) showing resistance changes. (**c**) Yarn 2 (copper-plated steel yarn) showing voltage drops. (**d**) Yarn 2 (copper-plated steel yarn) showing resistance changes.

#### **3. Results**

As mentioned earlier, the samples were flexed 180 degrees for 100,000 cycles or until the voltage dropped in at least two yarn loops for 10 seconds after bending. The failure points were based on the final needs of the application. Voltage under 3.5 V or resistance rise to 50 ohms was considered a failure point. The voltage drops are seen in Figure 3a,c comparing two different conductive yarns during the bending tests.

It was also observed that if more than one yarn was breaking during the tests, the second failure appeared quite fast. Moreover, the copper-plated steel yarn (yarn 2) durability was considerably better than the Ni-plated copper yarn (yarn 1). Voltage drops were smaller and more stable, indicating how steel and a larger quantity of filaments provide much better durability than conductive yarns.

Moreover, the data showed how earlier resistance rises were reduced back to original measurements (Figure 3a,c between 20,000 and 30,000 cycles). The stable connections were lost due to the filaments breaking during the bending tests. However, it was still possible for the yarn to regain some connection with other filaments, which resulted in a regain of voltage output as well. Voltage drops increase in size and persistence when filaments break. It was observed that a yarn with a larger number of filaments (yarn 2) regained the original conductivity more, was more stable, and started to break later. Thus, higher numbers of filaments together with less sensitivity to plastic deformation under bending the base material (steel or copper) support stable connections longer.

#### **4. Conclusions and Future Work**

This work introduced a bending tester aimed to determine conductive yarns' breaking points. The testing method was also explained by bending two different conductive yarns weaved into a narrow fabric. The results show how the two yarns degraded differently and at what exact point they started to degrade. The tool presents an opportunity to test for a proof-of-concept without ordering expensive machines and tests. Future work will include alternative testing features, such as a slower or faster bending cycle or a different weight clamp.

**Author Contributions:** Conceptualization, P.V., F.T. and F.B.; methodology, P.V. and F.B.; software, P.V. and F.B.; validation, P.V. and F.B.; formal analysis, P.V., F.B. and J.V.; investigation, P.V. and F.B.; resources, P.V. and F.B.; data curation, P.V.; writing—original draft preparation, P.V.; writing—review and editing, P.V., F.T., F.B. and J.V.; visualization, P.V.; supervision, F.B. and J.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article. Please contact the authors for additional information.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

**Sanju Ahuja \* and Jyoti Kumar**

Department of Design, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India


**Abstract:** The role of e-textiles has been discussed widely for health sensing applications. However, the ethical aspects of health sensing e-textiles have received less attention in the literature. In this contribution, we aim to identify the ethical concerns that emerge from the collection and use of health data from e-textiles. To identify these concerns, we draw upon the literature on health wearables and m-health applications. We propose that four ethical concerns need to be accounted for in the design of e-textiles that collect health data. These are privacy, discrimination, autonomy, and harm. We discuss the need to address these ethical concerns during the design process.

**Keywords:** health sensing; e-textiles; ethics; surveillance

#### **1. Introduction**

E-textiles are being widely developed for health sensing applications, such as smart health, healthy ageing, sports, fitness, and wellness [1]. Sensing technologies can be integrated within e-textiles, such as into the fabric or the yarn, to collect a wide range of health data. E-textiles can communicate with smartphones and computers to collect, display, store, and process physiological information such as heart rate, temperature, breathing, stress, movement, acceleration, or even hormone levels. The use of e-textiles in the health domain can help users monitor health conditions, treat diseases, maximize cognitive and physical function, and promote social engagement and interactions [2]. They can also be used in specialized medical settings to monitor patients' health, postures, and physiological states in real time.

In the health sensing domain, e-textiles have been argued to be the next level of technology after mobile health and wearables [3]. Mobile health (m-health) refers to mobile applications in the health domain, such as fitness apps, weight-watching apps, exercise apps, etc. [4]. Mobile applications collect data through both embedded sensors and self-logging by users. Health wearables refer to devices such as smartwatches and pedometers with sensors for capturing health-related data. The literature has discussed several ethical concerns pertaining to m-health applications and wearables, even though they are voluntarily adopted by millions of users across the globe. However, ethical aspects of e-textiles have received relatively less attention in the literature. This is potentially because e-textiles are an emerging technology that is yet to become as ubiquitous or accessible [4]. However, there is a need to anticipate potential ethical issues in advance. In this paper, we argue that the ethical concerns posed by m-health applications and wearables extend to health sensing applications of e-textiles. To identify these concerns, we draw upon the existing literature from these domains [5,6]. We identify four major ethical concerns, which are privacy, discrimination, autonomy, and harm. We show how these concerns are replicated or exacerbated in the context of e-textiles.

#### **2. Background**

Ethical concerns have been discussed widely in the domain of m-health and health wearables. It has been argued that through the use of m-health applications, users become

**Citation:** Ahuja, S.; Kumar, J. Ethical Aspects of Health Sensing Applications in E-Textiles. *Eng. Proc.* **2023**, *30*, 4. https://doi.org/ 10.3390/engproc2023030004

Academic Editors: Steve Beeby, Kai Yang, Russel Torah and Theodore Hughes-Riley

Published: 20 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

subjects of both surveillance and persuasion [4]. They present their body and their self as open to continual measurement and assessment. Wieczorek et al. [5] conducted a literature review of health wearables and identified areas of opportunities and concerns associated with self-tracking. Sharon [6] discussed the disciplining and disempowering effects of wearables, outlining their impact on values of autonomy, solidarity, and authenticity.

In this paper, we argue that ethical concerns pertaining to m-health and health wearables extend to the health sensing applications of e-textiles as well. Since the data collected by e-textiles are potentially more intimate, accurate, and sensitive, in many cases, these concerns might be exacerbated. However, critical literature has not emerged in this area. Therefore, there is a need to understand the ethical aspects pertaining to the design of e-textiles for health sensing applications.

#### **3. Ethical Aspects of Health Sensing Applications in E-Textiles**

In this paper, we draw upon the literature on m-health and health wearables to identify the ethical aspects of health sensing applications in e-textiles. We discuss how these concerns might operationalize in different application contexts. We discuss four ethical aspects of e-textiles: privacy, discrimination, autonomy, and harm (Figure 1).

**Figure 1.** Ethical concerns in health sensing applications in e-textiles.

#### *3.1. Privacy*

Inarguably, the most pronounced concern that emerges for health sensing e-textiles is that of privacy [5]. Privacy has emerged as a significant concern across different types of sensing and surveillance technologies. Health sensing technologies can collect a wide range of data, from trivial to intimate. While some health wearables may collect less sensitive data such as the number of steps walked by a user, the data collected by e-textiles are more intimate by design. E-textiles may collect highly sensitive health data such as body temperature, perspiration rates, stress levels and movement patterns [1]. On one hand, these datasets may be better suited for functional purposes. On the other hand, privacy concerns are higher due to the intimate nature of the data. As users adopt e-textiles for several health and fitness purposes, they may inadvertently end up sharing sensitive private information with technology companies, service providers, and third parties.

#### *3.2. Discrimination*

The data collected from health-sensing e-textiles poses not only privacy concerns, but also concerns about data-driven discrimination. Health data collected from various sources are often processed for decision-making purposes in different industries. The more

sensitive the data are, the more they can be used for inferential decision-making purposes in areas where users least expect it or are not prepared for it. Health data collected by e-textiles can be used for decision-making in markets or in medical setups. When private data are shared with different stakeholders, users may end up being discriminated against by algorithms used in insurance, advertising, treatment, pricing, etc. [7,8]. For example, within insurance, it may so happen that users who are unaware of their own pre-existing conditions are sold insurance plans at the highest prices. Health data may also be used as a justification to discriminate in medical treatments, for example, to prioritize patients in limited-resource settings. In the domain of advertising, algorithms may exploit users' health vulnerabilities to suggest targeted products, which users are tempted to buy out of fear but do not really need.

#### *3.3. Autonomy*

Another concern that has surfaced prominently in the literature is that of autonomy. The value of autonomy is often invoked to articulate both the benefits and the concerns about health wearables [6]. Health sensing is surrounded by the empowerment narrative, promising greater self-knowledge through numbers [5]. Advertising of health wearables seeks to convince customers to gain control over their health, weight, and sleep, facilitated by troves of data. However, the empowerment narrative is accompanied by perceptions of individual responsibility. In the workplace, employers are encouraging employees to adopt wearables [9]. Insurance companies commonly offer discounts to customers who self-track [8]. In such arrangements, the line between voluntary and compulsory participation often blurs [7]. The normalization of e-textiles for health sensing and their integration within socio-economic systems may force users into involuntary participatory arrangements. Users may be forced to adopt e-textiles in schools and workplaces, akin to the current push towards wearables [9]. Another autonomy-related critique of health sensing concerns the value of authenticity. Data-driven approaches to health have been criticized in the literature as unidirectional and reductive [5,6]. It has been argued that these approaches prevent individuals from exploring alternate means of health management.

#### *3.4. Harm*

Lastly, the data collected through e-textiles may be used intentionally or unintentionally to cause harm. For example, e-textiles with sensors that detect users' stress levels may share their data with advertising companies, promoting the sale of addictive medication while a user is in their most vulnerable state. Health sensing data may be used as a justification to deny users medical treatments. E-textiles may also cause unintended harm. They may inadvertently expose users to information about underlying medical conditions without them seeking out this information. They may cause users undue mental distress with false positives about underlying medical conditions. In contrast, they may fail to detect an ongoing medical emergency, such as a heart attack, giving users a false sense of comfort even when their symptoms tell them otherwise.

#### **4. Discussion and Conclusions**

The ethical aspects highlighted in this paper apply to nearly all use cases of healthsensing e-textiles. There is a need for designers to actively mitigate these concerns. For this purpose, it is important that designers are able to anticipate these concerns in advance, during the design activity, a process termed moral imagination [10]. Moral imagination allows designers to anticipate ethical concerns using ethics frameworks such as the one presented in this paper. Designers can systematically assess whether their sensing applications violate users' privacy or autonomy, or whether they can be used to perpetuate discrimination or cause any harm. Addressal of these concerns is important to build users' trust in technology, especially when several technology products are facing a 'crisis of ethics' [11]. We believe that this contribution is a timely one to initiate a discussion on the ethical aspects of e-textiles, and foreground ethical concerns in the design activity.

**Author Contributions:** This research was conducted as part of the doctoral dissertation of S.A. and was supervised by J.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Prime Minister Doctoral Research Fellowship granted by the Ministry of Human Resource Development, Government of India.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

**Kristel Fobelets \*, Christoforos Panteli and Ghena Hammour**

Department of Electrical and Electronic Engineering, Imperial College London, Exhibition Road, London SW7 2BT, UK

**\*** Correspondence: k.fobelets@imperial.ac.uk

† Presented at the 4th International Conference on the Challenges, Opportunities, Innovations and Applications in Electronic Textiles, Nottingham, UK, 8–10 November 2022.

**Abstract:** Simultaneous recording of breathing and heart rate signals was carried out on a healthy volunteer with a fully knitted, non-sports-type garment. Breathing was recorded using two knitted respiratory inductive plethysmography (RIP) sensors. Electrocardiogram (ECG) recordings were obtained from three knitted electrodes. The knitted garment design was customised for the specific requirements of RIP and ECG by adapting the needle size and/or introducing knit-in-elastic in the sensor areas. RIP was read out using an in-house-developed cross-coupled complementary oscillator circuit. The ECG was recorded using the commercial OpenBCI board. The sensors produced excellent signal quality that allowed for simple signal processing to extract information on heart and breathing rates, showing good correlation between the two.

**Keywords:** respiratory inductive plethysmography; ECG; e-wearable sensor; knitting; oscillator

#### **1. Introduction**

Among service prices, population growth and aging, chronic conditions play a major role in substantially increasing healthcare costs. Wearable technology is attractive for continuous health monitoring and thus reduces the costs associated with doctor–patient interactions. Knitting offers the possibility to integrate different sensors for non-invasive and real-time breathing and heart rate monitoring in wearable garments. This can be achieved by tracking changes in chest/abdomen circumference using transduction methods such as resistance changes [1,2] or inductance changes of a coil wound around the body [3]. In most cases, RIP (respiratory inductive plethysmography) is implemented in elastic belts that are strapped around the chest and/or the abdomen, shown in Figure 1a. For ECG, gelled electrodes are normally taped on the body. A more wearable implementation comes in the form of dry knitted electrodes [4]. In our implementation, knitted RIP and ECG were optimised in conjunction with the garment to increase sensitivity and reduce motion artifacts, illustrated in Figure 1b.

**Citation:** Fobelets, K.; Panteli, C.; Hammour, G. Simultaneous Breathing and ECG Measurements with e-Knits. *Eng. Proc.* **2023**, *30*, 5. https://doi.org/10.3390/ engproc2023030005

Academic Editors: Steve Beeby, Kai Yang, Russel Torah and Theodore Hughes-Riley

Published: 20 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

**Figure 1.** (**a**) Classical RIP implementation using elastic belts with one metal winding strapped around the chest and abdomen. (**b**) Knitted implementation of RIP in a halter top, on the chest and on the abdomen. The ECG electrodes and their positions on the inside of the garment are shown with arrows. Inset show the knitted electrodes.

#### **2. Materials and Methods**

#### *2.1. Knitted Breathing Sensors*

In our previous work, RIP sensors were integrated into a garment by a thin, circular knitted, insulated metal wire with yarn [5], achieving ultra-wearability and higher sensitivity proportional to the number of knitted rows with metal [6]. Figure 1b shows the implementation of two knitted coils, at the chest and the abdomen level. The RIP sensors were knitted using a needle size appropriate for the yarn, allowing the knit's natural elasticity to accommodate the stretch when inhaling. Knit-in-elastic is added to force the knit to return to its minimum circumference when exhaling.

#### *2.2. RIP Read-Out Electronics*

A complementary cross-coupled pair oscillator translates the coil's inductance to frequency [7]. For a wide range of coil dimensions to be recorded, the oscillator is followed by a rail-to-rail comparator that converts the sine-wave oscillations to a rectangular waveform. An esp32 microcontroller counts the frequency and logs the data to a micro-SD card [8].

#### *2.3. Knitted ECG Electrodes*

The ECG electrodes were knitted using Ag-coated polyester thread with a size equivalent to commercial pads. The different implementations are given in Table 1.


**Table 1.** Five different types of knitted electrodes. The four on the right were knitted by hand.

\* Commercially knitted Shieldex fabric [9]. + Shieldex threads (235/36 × 2 HCB in catalogue [9]).

By knitting different yarn thicknesses and adapting the needles' size, the roughness of the rib side of the electrodes can be controlled while maintaining a similar stitch density, unlike in the previous work [10]. The rib side of the knit is placed against the skin to reduce movement artifacts and improve signal quality. To decrease the movement artifacts in the ECG signals further, the regions in the knitted garment where the electrodes are sewn in, are knitted with a smaller needle size. This reduces the elasticity of the knit in those areas, reducing movement against the body. The ECG signals were recorded using the OpenBCI board [11]. The quality of the electrodes was defined by comparing the mean and median

signal and signal frequency histogram that must be non-Gaussian. The electrode with 3 Shieldex threads and 2 mm needles gave the best performance.

#### **3. Results**

#### *3.1. Breathing of the Volunteer*

The performance parameters for a range of coils are given in Table 2. A larger number of windings *N* results in larger sensitivity *s* and smaller current *icoil*. Thus, although *Q* is low for high *N*, a reduced *icoil* is better for user safety. Using coils with *N* = 8 in the knit of Figure 1, different breathing patterns, normal, slow and fast, were recorded from a healthy volunteer and are given in Figure 2.

**Table 2.** Characteristics of the knitted coil: *c* circumference, *N* number of windings, *s* sensitivity, *fosc* oscillator frequency, *Q* quality factor and *icoil* the RMS current through the coil at *fosc*.


\* Machine knitted on a Kniterate [12] machine by Ecoknitware [13].

**Figure 2.** Frequency variations of the chest (blue) and abdomen (orange) (colour available online) coils due to breathing. (**a**) Normal breathing, (**b**) deep and slow breathing and (**c**) fast breathing.

Breathing parameters (Table 3) were extracted using signal processing in MATLAB. The signal amplitude is related to the effort from the chest and abdomen. The phase difference during fast breathing mirrors minor hyperventilation and is the result of the increased work of breathing and the use of accessory muscles.

**Table 3.** Breathing parameters. BPM: breaths per minute, Ti/Ttot the ratio of the inhalation time to the total time of one breath, |A| the mean amplitude of one breath and Δφ the phase difference between the signal from the chest and the abdomen.


#### *3.2. ECG on the Volunteer*

Figure 3 shows 10 s ECG snapshots of 1 min measurements using the dry knitted contacts as implemented in Figure 1b during normal, fast and slow breathing. Typical signal parameters were extracted in MATLAB, as given in Table 4. In Figure 3, we observe that the amplitude of the R-peaks (the peaks with the largest amplitude) is modulated by the breathing signal. Breathing in, increases the resistance of the chest and breathing out decreases it. The breathing rate associated to this modulation is similar to that reported in Table 3.

**Figure 3.** 10 s ECG recordings for (**a**) normal, (**b**) deep and (**c**) fast breathing. All recorded using dry knitted electrodes.

**Table 4.** ECG parameters. *R*: distance between R-peaks, *σ*: standard variation on the R-peak position and HR: heart rate in beats per second (bps).


#### **4. Conclusions**

Knitted RIP sensors and ECG electrodes were implemented in a garment and were used to record breathing and ECG signals simultaneously. This implementation gave good quality recordings and health parameters in a relatively relaxed fitting garment when the wearer sat still.

**Author Contributions:** Conceptualization, K.F.; methodology, K.F., C.P. and G.H.; software, K.F. and G.H.; validation, K.F.; formal analysis, K.F.; investigation, K.F. and C.P.; resources, K.F.; data curation, K.F. and C.P.; writing—original draft preparation, K.F.; writing—review and editing, C.P.; visualization, K.F.; supervision, K.F.; project administration, K.F.; funding acquisition, K.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Ethical review and approval were waived for this study as the dataset is not related to clinical trials.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Data can be requested from K.F.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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