Advances in Flexible Electronics toward Wearable Sensing

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Electrical, Electronics and Communications Engineering".

Deadline for manuscript submissions: closed (30 April 2023) | Viewed by 16281

Special Issue Editor


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Guest Editor
School of Electronic Engineering, Dublin City University, Dublin, Dublin 9, Ireland
Interests: smart textiles; wearable sensors; connected health; human–computer interaction; physiological monitoring; sports performance; sustainable design

Special Issue Information

Dear Colleagues,

We are inviting submissions to the Special Issue on “Advances in Flexible Electronics toward Wearable Sensing”. 

Wearable sensing can be used to assess an individual’s health and wellbeing in an everyday setting, at work, home or during sports and leisure activities. Wearable sensing has a strong role to play in digitizing healthcare and connecting home and hospital care from the early stages of prevention through to disease management and aftercare, including rehabilitation. Furthermore, such technologies may also monitor the wearer’s environment and monitor pollution or other hazards in the surroundings.

Flexible electronics enable the design of wearable sensors that truly conform to the body and may take the form of epidermal patches or smart textiles. Flexible sensor design ensures a comfortable and secure connection with the body which is essential to optimize signal acquisition (e.g., heart rate, temperature, force) and ensures reliable sampling methods in the case of chemical sensing (e.g., collection of sweat, saliva, tears, breath). 

To support sensing elements, power requirements need to be considered and also integrated in a flexible form, necessitating flexible batteries and energy harvesting methods. Data management is also required for the sensed information and may require the integration of flexible antennae for wireless communications.

In this Special Issue, you are invited to submit contributions on the latest developments in flexible electronics for wearable applications. The scope of this Special Issue includes new materials and manufacturing methods, sensors, actuators, haptics, data communication, power supply, energy harvesting and storage, integration and interconnections, microfluidics, biocompatibility, and sustainable design.

Dr. Shirley Coyle
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • flexible electronics
  • wearable sensors
  • smart textiles
  • electronic skin
  • advanced manufacturing
  • physiological monitoring

Published Papers (6 papers)

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Editorial

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2 pages, 170 KiB  
Editorial
Special Issue on Advances in Flexible Electronics toward Wearable Sensing
by Shirley Coyle
Appl. Sci. 2023, 13(13), 7842; https://0-doi-org.brum.beds.ac.uk/10.3390/app13137842 - 04 Jul 2023
Viewed by 683
Abstract
Flexible electronics enable the design of wearable sensors that truly conform to the body [...] Full article
(This article belongs to the Special Issue Advances in Flexible Electronics toward Wearable Sensing)

Research

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17 pages, 1114 KiB  
Article
Toward Real-Time, Robust Wearable Sensor Fall Detection Using Deep Learning Methods: A Feasibility Study
by Haben Yhdego, Christopher Paolini and Michel Audette
Appl. Sci. 2023, 13(8), 4988; https://0-doi-org.brum.beds.ac.uk/10.3390/app13084988 - 16 Apr 2023
Cited by 2 | Viewed by 1996
Abstract
Real-time fall detection using a wearable sensor remains a challenging problem due to high gait variability. Furthermore, finding the type of sensor to use and the optimal location of the sensors are also essential factors for real-time fall-detection systems. This work presents real-time [...] Read more.
Real-time fall detection using a wearable sensor remains a challenging problem due to high gait variability. Furthermore, finding the type of sensor to use and the optimal location of the sensors are also essential factors for real-time fall-detection systems. This work presents real-time fall-detection methods using deep learning models. Early detection of falls, followed by pneumatic protection, is one of the most effective means of ensuring the safety of the elderly. First, we developed and compared different data-segmentation techniques for sliding windows. Next, we implemented various techniques to balance the datasets because collecting fall datasets in the real-time setting has an imbalanced nature. Moreover, we designed a deep learning model that combines a convolution-based feature extractor and deep neural network blocks, the LSTM block, and the transformer encoder block, followed by a position-wise feedforward layer. We found that combining the input sequence with the convolution-learned features of different kernels tends to increase the performance of the fall-detection model. Last, we analyzed that the sensor signals collected by both accelerometer and gyroscope sensors can be leveraged to develop an effective classifier that can accurately detect falls, especially differentiating falls from near-falls. Furthermore, we also used data from sixteen different body parts and compared them to determine the better sensor position for fall-detection methods. We found that the shank is the optimal position for placing our sensors, with an F1 score of 0.97, and this could help other researchers collect high-quality fall datasets. Full article
(This article belongs to the Special Issue Advances in Flexible Electronics toward Wearable Sensing)
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16 pages, 2941 KiB  
Article
Magnesium Nanoparticle Synthesis from Powders via Pulsed Laser Ablation in Liquid for Nanocolloid Production
by Anesu Nyabadza, Mercedes Vázquez, Shirley Coyle, Brian Fitzpatrick and Dermot Brabazon
Appl. Sci. 2021, 11(22), 10974; https://0-doi-org.brum.beds.ac.uk/10.3390/app112210974 - 19 Nov 2021
Cited by 18 | Viewed by 3195
Abstract
Magnesium nanoparticles of various mean diameters (53–239 nm) were synthesised in this study via pulsed laser ablation in liquid (PLAL) from millimetre sized magnesium powders within isopropyl alcohol. It was observed via a 3 × 3 full factorial design of experiments that the [...] Read more.
Magnesium nanoparticles of various mean diameters (53–239 nm) were synthesised in this study via pulsed laser ablation in liquid (PLAL) from millimetre sized magnesium powders within isopropyl alcohol. It was observed via a 3 × 3 full factorial design of experiments that the processing parameters can control the nanoparticle distribution to produce three size-distribution types (bimodal, skewed and normal). Ablation times of 2, 5, and 25 min where investigated. An ablation time of 2 min produced a bimodal distribution with the other types seen at higher periods of processing. Mg nanoparticle Ultraviolet–Visible spectroscopy (UV–Vis) absorbance at 204 nm increased linearly with increasing ablation time, indicating an increase in nanoparticle count. The colloidal density (mg/mL) generally increased with increasing nanoparticle mean diameter as noted via increasing UV–Vis absorbance. High laser scan speeds (within the studied range of 3000–3500 mm/s) tend to increase the nanoparticle count/yield. For the first time, the effect of scan speed on colloidal density, UV–Vis absorbance and nanoparticle diameter from metallic powder ablation was investigated and is reported herein. The nanoparticles formed dendritic structures after being drop cast on aluminium foil as observed via field emission scanning electron microscope analysis. Dynamic light scattering was used to measure the size of the nanoparticles. Magnesium nanoparticle inks show promise for use in the fabrication conductive tracks or thermal insulation in electronics. Full article
(This article belongs to the Special Issue Advances in Flexible Electronics toward Wearable Sensing)
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5 pages, 1443 KiB  
Article
E-Textile Metamaterials: Stop Band Pass Filter
by Bahareh Moradi, Raul Fernández-García and Ignacio Gil Gali
Appl. Sci. 2021, 11(22), 10930; https://0-doi-org.brum.beds.ac.uk/10.3390/app112210930 - 19 Nov 2021
Cited by 5 | Viewed by 1667
Abstract
In this paper, the utilization of common fabrics for the manufacturing of e-textile metamaterial is investigated. The proposed design is based on a transmission line loaded with split-ring resonators (SRRs) on a cotton substrate for filter signal application. The proposed design provides a [...] Read more.
In this paper, the utilization of common fabrics for the manufacturing of e-textile metamaterial is investigated. The proposed design is based on a transmission line loaded with split-ring resonators (SRRs) on a cotton substrate for filter signal application. The proposed design provides a stop band between 2.7 GHz and 4.7 GHz, considering a four stage SRR topology. Experimental results showed stop band levels higher than −30 dB for the proposed compact embroidered metamaterial e-textiles. The validated results confirmed embroidery as a useful technique to obtain customized electromagnetic filter properties, such as transmitted signal filtering and control, on wearable tech device applications. Full article
(This article belongs to the Special Issue Advances in Flexible Electronics toward Wearable Sensing)
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19 pages, 5687 KiB  
Article
The Impact of Bending on Radiation Characteristics of Polymer-Based Flexible Antennas for General IoT Applications
by Muhammad Usman Ali Khan, Raad Raad, Faisel Tubbal and Panagiotis Ioannis Theoharis
Appl. Sci. 2021, 11(19), 9044; https://0-doi-org.brum.beds.ac.uk/10.3390/app11199044 - 28 Sep 2021
Cited by 11 | Viewed by 2886
Abstract
Flexible wearable wireless devices have found practical uses as their cost has fallen and Internet of Things applications have gained further acceptance. These devices are gaining further use and acceptance in the consumer and wearable space for applications such as logistical tracking and [...] Read more.
Flexible wearable wireless devices have found practical uses as their cost has fallen and Internet of Things applications have gained further acceptance. These devices are gaining further use and acceptance in the consumer and wearable space for applications such as logistical tracking and maintaining sensor information, including temperature, humidity, and location. In such applications, antennas are exposed to bending and crumbling. Therefore, flexible substrate antennas for use with polymer-based flexible devices are an important area of research that needs to be addressed. In this study, the bending capabilities of flexible polymer substrate antennas for general IoT applications were practically analyzed by fabricating flexible antennas on Polyethylene Terephthalate (PET), Polytetrafluoroethylene (PTFE) Teflon, and Polyvinylchloride (PVC) substrates operating at 2.45, 4.45, and 7.25 GHz frequencies. The basic premise was to investigate the flexibility and bending ability of polymer materials, and their tendency to withstand deformation. In the current paper, we start by providing an equivalent model for the flexible microstrip patch antenna under bent conditions, followed by outlining the process of designing flexible antennas on polymer substrates. Finally, the fabricated flexible antennas were tested in an anechoic chamber for various radiation characteristics such as reflection coefficients, operating frequency shifts, and impedance mismatch with the transmission line, under bending conditions up to 7 mm. The practical outcomes were then compared with our recent investigation on flexible polymer substrate antennas for wearable applications. This study provides a means to select a suitable polymer substrate for future wearable sensors and antennas with high bendability. Full article
(This article belongs to the Special Issue Advances in Flexible Electronics toward Wearable Sensing)
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Review

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30 pages, 3588 KiB  
Review
Review of Materials and Fabrication Methods for Flexible Nano and Micro-Scale Physical and Chemical Property Sensors
by Anesu Nyabadza, Mercedes Vázquez, Shirley Coyle, Brian Fitzpatrick and Dermot Brabazon
Appl. Sci. 2021, 11(18), 8563; https://0-doi-org.brum.beds.ac.uk/10.3390/app11188563 - 15 Sep 2021
Cited by 23 | Viewed by 5018
Abstract
The use of flexible sensors has tripled over the last decade due to the increased demand in various fields including health monitoring, food packaging, electronic skins and soft robotics. Flexible sensors have the ability to be bent and stretched during use and can [...] Read more.
The use of flexible sensors has tripled over the last decade due to the increased demand in various fields including health monitoring, food packaging, electronic skins and soft robotics. Flexible sensors have the ability to be bent and stretched during use and can still maintain their electrical and mechanical properties. This gives them an advantage over rigid sensors that lose their sensitivity when subject to bending. Advancements in 3D printing have enabled the development of tailored flexible sensors. Various additive manufacturing methods are being used to develop these sensors including inkjet printing, aerosol jet printing, fused deposition modelling, direct ink writing, selective laser melting and others. Hydrogels have gained much attention in the literature due to their self-healing and shape transforming. Self-healing enables the sensor to recover from damages such as cracks and cuts incurred during use, and this enables the sensor to have a longer operating life and stability. Various polymers are used as substrates on which the sensing material is placed. Polymers including polydimethylsiloxane, Poly(N-isopropylacrylamide) and polyvinyl acetate are extensively used in flexible sensors. The most widely used nanomaterials in flexible sensors are carbon and silver due to their excellent electrical properties. This review gives an overview of various types of flexible sensors (including temperature, pressure and chemical sensors), paying particular attention to the application areas and the corresponding characteristics/properties of interest required for such. Current advances/trends in the field including 3D printing, novel nanomaterials and responsive polymers, and self-healable sensors and wearables will also be discussed in more detail. Full article
(This article belongs to the Special Issue Advances in Flexible Electronics toward Wearable Sensing)
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