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Development and Characterization of Large Area Pressure Sensors and Sitting Posture Monitoring Systems
Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.ORCID iD: 0000-0001-7395-3687
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the emergence of the Internet and rapid development of science and technology over the past few decades, many individuals worldwide now rely on the Internet to conduct daily activities ranging from education, business and creativity to communication and shopping. As we tend to spend more and more time on the Internet and engage less in physical activities, this persistent behaviour could result in some health-related issues within a relatively short period of time. This behaviour, known as sedentary lifestyle, may be related to a higher risk of cardiovascular disease, osteoporosis, obesity, anxiety, pressure ulcers and many other illnesses. As a consequence, there has been great interest in developing non-invasive and unobtrusive measurement techniques for a variety of health care-monitoring applications, such as for blood oxygen saturation, stress levels, electrocardiograms and glucose monitoring. In such systems, wearable and flexible electronics technologies may enable monitoring of vital signs, offering significant potential for early screening as well as long-term behaviour modelling.

In this thesis, large area pressure sensors based on non-conventional materials are proposed and realised by screen printing technique for monitoring sitting postures. The developed pressure sensing system measures distributed pressure when an individual sits on a chair equipped with a pressure sensor array. This technology could provide grounding for the advancement of health-related monitoring systems for both able-bodied and disabled individuals and inform them of their sitting time and sitting posture, and this could be used to establish a sitting pattern. To accomplish this, pressure sensors have been designed using non-conventional flexible electronics. A blend of non-conductive and low-resistance ink is used as pressure-sensitive material to enable the realization of screen-printed sensors. To characterise the performance of the suggested pressure sensor, several tests, such as repeatability, drift and flexibility, are conducted. The sensor has also been exposed to different humidity and temperature conditions in a climate chamber to examine its functionalities.

A graphical user interface was developed for real-time demonstration of data from distributed pressure points in the form of a pressure map to display the pressure values. Four sitting postures are identified: forward, backward, left, and right leaning. Furthermore, a stretchable pressure sensor is proposed that could follow slight stretching with regard to changes in the shape of the human skin. Machine learning algorithms have been employed to further enhance the sitting posture identification, and accuracy of 99.03% is attained. A standalone embedded system capable of illustrating real-time pressure data has been developed with the potential to be used in portable health monitoring systems. In summary, this work provides a promising framework for measuring pressure distribution and identifying irregular sitting postures that may help to reduce the potential risks of developing health-related issues associated with prolonged sitting time.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2021. , p. 50
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 355
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:miun:diva-43754ISBN: 978-91-89341-33-3 (print)OAI: oai:DiVA.org:miun-43754DiVA, id: diva2:1612320
Public defence
2021-11-30, C310, Mittuniversitetet, Sundsvall, 13:00 (English)
Opponent
Supervisors
Available from: 2021-11-18 Created: 2021-11-17 Last updated: 2021-11-18Bibliographically approved
List of papers
1. Sitting Posture Recognition using Screen Printed Large Area Pressure Sensors
Open this publication in new window or tab >>Sitting Posture Recognition using Screen Printed Large Area Pressure Sensors
2017 (English)In: Proceedings of IEEE Sensors, IEEE, 2017, p. 232-234Conference paper, Published paper (Refereed)
Abstract [en]

In the biomedical sector, pressure sensors exhibit an important role towards monitoring and recognition of sitting posture for wheelchair users, which is helpful for pressure ulcer prevention and cure.  In this paper, a flexible and inexpensive screen printed large area pressure sensing system is presented. The large area sensor comprise three layers, is able to cancel-out false pressure detection, and achieves a sitting classification accuracy over 80 percent. The sensor matrix contains 16 sensors distributed over an area of 23.5 cm × 21.5 cm and the pressure points are monitored at a scanning rate of 77 Hz. The sensor system provides wireless communication and a Windows based GUI is developed that allows real-time presentation of pressure data by means of a pressure map. The presented sensor design targets smart wheelchairs but is suitable for any low cost and high throughput pressure distribution monitoring systems. 

Place, publisher, year, edition, pages
IEEE, 2017
Series
IEEE Sensors, ISSN 1930-0395
Keywords
Wheelchair, pressure sensors, conductive inks, pressure mapping, sitting posture recognition
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-32324 (URN)10.1109/ICSENS.2017.8233944 (DOI)000427677500077 ()2-s2.0-85044326019 (Scopus ID)978-1-5090-1012-7 (ISBN)
Conference
16th IEEE SENSORS Conference, ICSENS 2017; Scottish Event Campus (SEC) Glasgow; United Kingdom; 30 October 2017 through 1 November 2017
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Available from: 2017-12-07 Created: 2017-12-07 Last updated: 2022-03-31Bibliographically approved
2. Screen Printed Piezoresistive Sensors for Monitoring Pressure Distribution in Wheelchair
Open this publication in new window or tab >>Screen Printed Piezoresistive Sensors for Monitoring Pressure Distribution in Wheelchair
2019 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 19, no 6, p. 2055-2063Article in journal (Refereed) Published
Abstract [en]

Prolonged sitting inadequacies cause pressure ulcer to many individuals, especially to disadvantaged with reduced mobility. The measurement of distributed pressure and detection of irregular sitting postures is essential for preventing the risk of developing pressure ulcer. In this paper, a pressure sensing system capable of recognizing sitting postures by means of measuring interface pressure through printed pressure sensors is presented. A thin and flexible large area sensor is screen-printed using silver flake and carbon particle inks and comprises 16 sensing elements. For the evaluation of practical usability, the sensor characterization is carried out by conducting stability, repeatability, drift and bending tests. The performance of the sensor is checked under varying environmental conditions. Sitting posture detection accuracy above 80 % is achieved using a classification algorithm for four different sitting postures. Pressure distribution is monitored at a scanning rate of 10 Hz. A low power and small form factor of read-out electronics enables a compact packaging inside the seat cushion. The presented sensor design targets smart wheelchairs, but it is extendable to much larger areas, for example to be used in beds. The proposed sensing system would be of a great assistance for caregivers and health professionals.

Place, publisher, year, edition, pages
IEEE, 2019
Keywords
Pressure sensors, wheelchair, conductive inks, sitting posture recognition, pressure mapping, screen-printing
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-35133 (URN)10.1109/JSEN.2018.2885638 (DOI)000459513100009 ()2-s2.0-85058158693 (Scopus ID)
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2022-03-31Bibliographically approved
3. An Analysis of Screen-Printed Stretchable Conductive Tracks on Thermoplastic Polyurethane
Open this publication in new window or tab >>An Analysis of Screen-Printed Stretchable Conductive Tracks on Thermoplastic Polyurethane
2019 (English)In: FLEPS 2019 - IEEE International Conference on Flexible and Printable Sensors and Systems, Proceedings, 2019, article id 8792266Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-36146 (URN)10.1109/FLEPS.2019.8792266 (DOI)2-s2.0-85071395576 (Scopus ID)978-1-5386-9304-9 (ISBN)
Conference
IEEE Fleps 2019, IEEE International Conference on Flexible and Printable Sensors and Systems, Glasgow, Scotland, July 7-10, 2019
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Available from: 2019-05-15 Created: 2019-05-15 Last updated: 2022-03-31Bibliographically approved
4. A Proposal of Implementation of Sitting Posture Monitoring System for Wheelchair Utilizing Machine Learning Methods
Open this publication in new window or tab >>A Proposal of Implementation of Sitting Posture Monitoring System for Wheelchair Utilizing Machine Learning Methods
2021 (English)In: Sensors, E-ISSN 1424-8220, Vol. 21, article id 6349Article in journal (Refereed) Published
Abstract [en]

This paper presents a posture recognition system aimed at detecting sitting postures of a wheelchair user. The main goals of the proposed system are to identify and inform irregular and improper posture to prevent sitting-related health issues such as pressure ulcers, with the potential that it could also be used for individuals without mobility issues. In the proposed monitoring system, an array of 16 screen printed pressure sensor units was employed to obtain pressure data, which are sampled and processed in real-time using read-out electronics. The posture recognition was performed for four sitting positions: right-, left-, forward- and backward leaning based on k-nearest neighbors (k-NN), support vector machines (SVM), random forest (RF), decision tree (DT) and LightGBM machine learning algorithms. As a result, a posture classification accuracy of up to 99.03 percent can be achieved. Experimental studies illustrate that the system can provide real-time pressure distribution value in the form of a pressure map on a standard PC and also on a raspberry pi system equipped with a touchscreen monitor. The stored pressure distribution data can later be shared with healthcare professionals so that abnormalities in sitting patterns can be identified by employing a post-processing unit. The proposed system could be used for risk assessments related to pressure ulcers. It may be served as a benchmark by recording and identifying individuals’ sitting patterns and the possibility of being realized as a lightweight portable health monitoring device.

Place, publisher, year, edition, pages
MDPI, 2021
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-43192 (URN)10.3390/s21196349 (DOI)000759972000005 ()34640669 (PubMedID)2-s2.0-85115393331 (Scopus ID)
Available from: 2021-09-27 Created: 2021-09-27 Last updated: 2022-06-03Bibliographically approved
5. Stretchable Pressure Sensor Using Thermoplastic Polyurethane and Conductive Inks
Open this publication in new window or tab >>Stretchable Pressure Sensor Using Thermoplastic Polyurethane and Conductive Inks
2021 (English)In: Proceedings of IEEE Sensors, IEEE, 2021, article id 1310Conference paper, Published paper (Refereed)
Abstract [en]

The development of wearable health devices is an emerging technology, and pressure sensors have been widely used in several of these applications. Plenty of research within pressure sensors is focused on tactile sensing and artificial skin. In this paper, a highly flexible and stretchable pressure sensor is presented. The sensor comprises stretchable thermoplastic polyurethane (TPU) film as substrate and stretchable conductive inks as electrodes and sensing material. Screen printing is used to fabricate electrodes and pressure sensing components on TPU sheets. Electrical and mechanical properties of the fabricated sensors indicate good mechanical and electrical stability while retaining pressure sensing properties and marginal deterioration even after 100 elongation cycles. The findings show that the presented stretchable pressure sensor has a great potential for usage on surfaces where bending and stretching will occur while retaining nearly all of its electrical and mechanical capabilities. The proposed sensor may be employed as a wearable device to detect human movements.

Place, publisher, year, edition, pages
IEEE, 2021
National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:miun:diva-43193 (URN)10.1109/SENSORS47087.2021.9639852 (DOI)000755468300308 ()2-s2.0-85123589662 (Scopus ID)978-1-7281-9501-8 (ISBN)
Conference
IEEE Sensors 2021, Sydney, Australia, [DIGITAL], October 30 - November 4, 2021.
Available from: 2021-09-27 Created: 2021-09-27 Last updated: 2022-06-03Bibliographically approved

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Ahmad, Jawad

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