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Special Issue "Wearable and Implantable Sensors and Electronics Circuits"

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: 15 April 2019

Special Issue Editors

Guest Editor
Prof. Dr. Maaike Op de Beeck

Program manager biomedical systems at imec and at CMST, associated imec laboratory at Ghent University
Professor at Ghent University, Faculty of Engineering and Architecture
Website | E-Mail
Interests: implantable electronics; advanced packaging and integration technologies for wearable and implantable electronics; hermetic encapsulation technologies for implantable electronics; flexible electronics
Guest Editor
Dr. Frederik Bossuyt

Centre for Microsystems Technology, Ghent University, Belgium
Website | E-Mail
Interests: advanced packaging technologies for wearable electronics; integration of electronics in objects to realize smart objects; flexible and stretchable electronic systems

Special Issue Information

Dear Colleagues,

The miniaturization of MEMS and electronics opened the door for the development of very small, lightweight devices. When combined with flexible or stretchable packaging and integration techniques, electronics can be shaped to be conformal with non-flat and even moving surfaces such as human skin, enabling the fabrication of wearable devices for medical applications. Using low-power electronics and/or a system design with low power consumption in mind enables the use of small batteries while still realizing a considerable battery lifetime. In combination with wireless data transmission, very interesting wearable electronic devices can be constructed, allowing for regular follow-up of biomedical parameters even outside a hospital setting. Obviously, these devices need to be equipped with reliable sensors (e.g., skin electrodes, chemical sensors, optical sensors, etc.) to monitor relevant bio-signals. With an aging population, such devices will be more than welcome to enable a longer period of independent living for the elderly without jeopardizing their health. Additionally, younger people suffering from a disease which needs constant monitoring (e.g., diabetes) and healthy people who prefer to sport in a controlled manner enjoy the existence of high-quality wearable health monitoring devices. Although several wearable sensors are now on the market, there is still plenty of room for improvement: more reliable sensors, new sensor technologies, smaller and more flexible devices which offer higher user comfort, sensors not causing skin irritation even after prolonged use, smaller batteries due to battery improvement or lower power consumption enabling lightweight devices, etc.

Electronics are also very interesting as implantable devices, combining electronic intelligence with extreme miniaturization. However, bringing electronics inside the body has severe consequences for the integration and packaging of the electronic device: the device needs to be hermetically sealed from the body fluids to avoid corrosion, while the sealing should also protect the body from direct contact with the non-biocompatible materials used to compose the electronic device. Furthermore, this bidirectional device encapsulation should be biostable during the total implantation time of the system. In spite of this hermetic device encapsulation, sensors of the device should still be able to monitor relevant biomedical parameters. Hence, a direct contact between the local tissue and the sensing part of the electronic device is often essential, and therefore the hermetic seal needs to have locally “hermetic windows”. Electronic implants challenge scientists even more: the biostability of the sensors should be guaranteed during the lifetime of the device, which is often difficult, since proteins or other components of the local body tissue tend to react with the surface of sensors, which might change their electronic readout. Testing of this biostability is often challenging, especially for long-term implants for which relevant accelerated testing procedures have to be developed. Furthermore, the sensing part of a device might have to be placed in a tiny area in the body (e.g., electrodes placed inside the brain or a nerve bundle for the recording or stimulation of nerve cells). The fabrication of such sensing parts requires a very high degree of miniaturization. Finally, ultralow power consumption is a must for electronic implants—heat generation in the body needs to be firmly avoided, and the use of a small battery is essential. Rechargeable batteries can reduce this problem, although energy/signal transport towards implants located deeper in the body is still a challenge due to absorbing body tissue. Energy scavenging is a possibility, although important technical improvements are essential to match the device power consumption with the energy efficiency of current scavenging techniques.

The immense potential of electronics as wearable or implantable sensing devices for better health and improved healthcare is obvious, but many hurdles still have to be overcome. Reports on investigations related to the issues as explained above are very welcome in this Special Issue of Sensors, which aims to highlight relevant advancements in the development and testing of wearable and implantable sensing devices at the component level as well as at the system level.

Prof. Dr. Maaike Op de Beeck
Dr. Frederik Bossuyt
Guest Editors

Manuscript Submission Information

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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. Sensors 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 1800 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

  •    biomedical sensors
  •    wearable sensors
  •    implantable devices
  •    device miniaturization for wearable/implantable devices
  •    sensor biocompatibility
  •    sensor biostability
  •    device hermeticity
  •    testing and accelerated testing procedures for wearables/implants
  •    wireless powering of electronic implants
  •    energy scavenging for implants

Published Papers (4 papers)

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Research

Open AccessArticle Motion Artifact Reduction for Wrist-Worn Photoplethysmograph Sensors Based on Different Wavelengths
Sensors 2019, 19(3), 673; https://doi.org/10.3390/s19030673
Received: 31 December 2018 / Revised: 3 February 2019 / Accepted: 5 February 2019 / Published: 7 February 2019
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Abstract
Long-term heart rate (HR) monitoring by wrist-worn photoplethysmograph (PPG) sensors enables the assessment of health conditions during daily life with high user comfort. However, PPG signals are vulnerable to motion artifacts (MAs), which significantly affect the accuracy of estimated physiological parameters such as [...] Read more.
Long-term heart rate (HR) monitoring by wrist-worn photoplethysmograph (PPG) sensors enables the assessment of health conditions during daily life with high user comfort. However, PPG signals are vulnerable to motion artifacts (MAs), which significantly affect the accuracy of estimated physiological parameters such as HR. This paper proposes a novel modular algorithm framework for MA removal based on different wavelengths for wrist-worn PPG sensors. The framework uses a green PPG signal for HR monitoring and an infrared PPG signal as the motion reference. The proposed framework includes four main steps: motion detection, motion removal using continuous wavelet transform, approximate HR estimation and signal reconstruction. The proposed algorithm is evaluated against an electrocardiogram (ECG) in terms of HR error for a dataset of 6 healthy subjects performing 21 types of motion. The proposed MA removal method reduced the average error in HR estimation from 4.3, 3.0 and 3.8 bpm to 0.6, 1.0 and 2.1 bpm in periodic, random, and continuous non-periodic motion situations, respectively. Full article
(This article belongs to the Special Issue Wearable and Implantable Sensors and Electronics Circuits)
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Open AccessArticle A Fetal ECG Monitoring System Based on the Android Smartphone
Sensors 2019, 19(3), 446; https://doi.org/10.3390/s19030446
Received: 20 December 2018 / Revised: 18 January 2019 / Accepted: 21 January 2019 / Published: 22 January 2019
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Abstract
In this paper, a fetal electrocardiogram (ECG) monitoring system based on the Android smartphone was proposed. We designed a portable low-power fetal ECG collector, which collected maternal abdominal ECG signals in real time. The ECG data were sent to a smartphone client via [...] Read more.
In this paper, a fetal electrocardiogram (ECG) monitoring system based on the Android smartphone was proposed. We designed a portable low-power fetal ECG collector, which collected maternal abdominal ECG signals in real time. The ECG data were sent to a smartphone client via Bluetooth. Smartphone app software was developed based on the Android system. The app integrated the fast fixed-point algorithm for independent component analysis (FastICA) and the sample entropy algorithm, for the sake of real-time extraction of fetal ECG signals from the maternal abdominal ECG signals. The fetal heart rate was computed using the extracted fetal ECG signals. Experimental results showed that the FastICA algorithm can extract a clear fetal ECG, and the sample entropy can correctly determine the channel where the fetal ECG is located. The proposed fetal ECG monitoring system may be feasible for non-invasive, real-time monitoring of fetal ECGs. Full article
(This article belongs to the Special Issue Wearable and Implantable Sensors and Electronics Circuits)
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Open AccessArticle Capturing Electrocardiogram Signals from Chairs by Multiple Capacitively Coupled Unipolar Electrodes
Sensors 2018, 18(9), 2835; https://doi.org/10.3390/s18092835
Received: 27 July 2018 / Revised: 18 August 2018 / Accepted: 21 August 2018 / Published: 28 August 2018
Cited by 1 | PDF Full-text (14167 KB) | HTML Full-text | XML Full-text
Abstract
A prototype of an electrocardiogram (ECG) signal acquisition system with multiple unipolar capacitively coupled electrodes is designed and experimentally tested. Capacitively coupled electrodes made of a standard printed circuit board (PCB) are used as the sensing electrodes. Different from the conventional measurement schematics, [...] Read more.
A prototype of an electrocardiogram (ECG) signal acquisition system with multiple unipolar capacitively coupled electrodes is designed and experimentally tested. Capacitively coupled electrodes made of a standard printed circuit board (PCB) are used as the sensing electrodes. Different from the conventional measurement schematics, where one single lead ECG signal is acquired from a pair of sensing electrodes, the sensing electrodes in our approaches operate in a unipolar mode, i.e., the biopotential signals picked up by each sensing electrodes are amplified and sampled separately. Four unipolar electrodes are mounted on the backrest of a regular chair and therefore four channel of signals containing ECG information are sampled and processed. It is found that the qualities of ECG signal contained in the four channel are different from each other. In order to pick up the ECG signal, an index for quality evaluation, as well as for aggregation of multiple signals, is proposed based on phase space reconstruction. Experimental tests are carried out while subjects sitting on the chair and clothed. The results indicate that the ECG signals can be reliably obtained in such a unipolar way. Full article
(This article belongs to the Special Issue Wearable and Implantable Sensors and Electronics Circuits)
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Open AccessArticle A 10-Bit 300 kS/s Reference-Voltage Regulator Free SAR ADC for Wireless-Powered Implantable Medical Devices
Sensors 2018, 18(7), 2131; https://doi.org/10.3390/s18072131
Received: 29 April 2018 / Revised: 19 June 2018 / Accepted: 22 June 2018 / Published: 3 July 2018
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Abstract
This paper presents a reference-voltage regulator free successive-approximation-register analog-to-digital converters (SAR ADC) with self-timed pre-charging for wireless-powered implantable medical devices. Assisted by a self-timed pre-charging technique, the proposed SAR ADC eliminates the need for a power-hungry reference-voltage regulator and area-consuming decoupling capacitor while [...] Read more.
This paper presents a reference-voltage regulator free successive-approximation-register analog-to-digital converters (SAR ADC) with self-timed pre-charging for wireless-powered implantable medical devices. Assisted by a self-timed pre-charging technique, the proposed SAR ADC eliminates the need for a power-hungry reference-voltage regulator and area-consuming decoupling capacitor while maintaining insensitivity to the supply voltage fluctuation. Fabricated with a 0.18-µm complementary metal–oxide–semiconductor (CMOS) technology, the proposed SAR ADC achieves a Signal To Noise And Distortion Ratio (SNDR) of 53.32 dB operating at 0.8 V with a supply voltage fluctuation of 50 mVpp and consumes a total power of 2.72 µW at a sampling rate of 300 kS/s. Including the self-timed pre-charging circuits, the total figure-of-merit (FOM) is 23.9 fJ/conversion-step and the total area occupied is 0.105 mm2. Full article
(This article belongs to the Special Issue Wearable and Implantable Sensors and Electronics Circuits)
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