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  • 1.
    Andersson, Tom
    et al.
    Mälardalen University.
    Persson, Niklas
    Mälardalen University.
    Fattouh, Anas
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin C.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    A loop shaping method for stabilising a riderless bicycle2019In: 2019 European Conference on Mobile Robots, ECMR 2019 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2019, article id 8870965Conference paper (Refereed)
    Abstract [en]

    Several control methods have been proposed to stabilise riderless bicycles but they do not have sufficient simplicity for practical applications. This paper proposes a practical approach to model an instrumented bicycle as a combination of connected systems. Using this model, a PID controller is designed by a loop shaping method to stabilise the instrumented riderless bicycle. The initial results show that the bicycle can be stabilised when running on a roller. The work presented in this paper shows that it is possible to self stabilise a riderless bicycle using cascade PI/PID controllers.

  • 2.
    Bergblomma, Marcus
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering.
    Björkman, Mats
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering.
    Gerdtman, Christer
    Motion Control AB, Västerås, Sweden .
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    A wireless low latency control system for harsh environments2012In: IFAC Proceedings Volumes (IFAC-PapersOnline): Vol. 11, PART 1, 2012, p. 17-22Conference paper (Refereed)
    Abstract [en]

    The use of wireless communication technologies in the industry offer severaladvantages. One advantage is the ability to deploy sensors where they previously could noteasily be deployed, for instance on parts that rotate. To use wireless communication in industrialcontrol loops, demands on reliability and latency requirements has to be met. This in anenvironment that may be harsh for radio communication. This work presents a reliable, lowlatency wireless communication system. The system is used in a wireless thyristor control loopin a hydro power plant generator. The wireless communication is based on Bluetooth radiomodules. The work shows a latency analysis together with empirical hardware based latencyand packet error rate measurements. The background noise of a hydro power plant station isalso investigated. The average latency between the Bluetooth modules for the proposed systemis 5.09 ms. The packet error rate is 0.00288 for the wireless low latency control system deployedin a hydro power plant.

  • 3.
    Bergblomma, Marcus
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering.
    Garcia Castaño, Javier
    Mälardalen University, School of Innovation, Design and Engineering.
    Björkman, Mats
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    Wireless ECG network2009In: WORLD CONGRESS ON MEDICAL PHYSICS AND BIOMEDICAL ENGINEERING, VOL 25, PT 5, 2009, p. 244-247Conference paper (Refereed)
    Abstract [en]

    This paper presents a time synchronized wireless ECG sensor network with reliable data communication. Wireless ECG systems are a popular research area where several research groups have presented point-to-point solutions. Alongside the wireless ECG research, the wireless sensor network research has created an increasing interest for secure, low power and predictable network applications. Combining these research areas is a natural step for the evolution of secure wireless monitoring of physiological parameters. In this study the Bluetooth radio standard has been chosen for its versatility. This paper focuses on both the hardware and the software development for a functional multihop ECG network using Bluetooth. The presented wireless ECG network is reliable up to link loss and is easily configured to send more or different types of signals. The system has been tested and verified for secure multihop communication.

  • 4.
    Ehn, Maria
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Derneborg, Mattias
    Region Västmanland, Sweden.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Johansson, Ann-Christin
    Mälardalen University, School of Health, Care and Social Welfare, Health and Welfare.
    Inter- disciplinary and -sectorial cooperation for development of technology supporting behavioral change: Peer reviewed poster abstract2017Conference paper (Other academic)
  • 5.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering.
    Towards Predictable and Reliable Wireless Communication in Harsh Environments2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wireless communication in industrial, scientific and medical applications have several benefits. The main benefits when using wireless technologies include ease-of-deployment, the simplicity to introduce new units into the network and mobility. However it also put higher demands on the communication, including reliability and predictability compared to wired communication. The reliability issues correlate to the radio communication and the possibility to ensure that the user data is received, and within the time frame of the system requirements. This doctoral thesis presents an empirical measurement approach to investigate and model the behaviour linked to reliability and predictability. The focus of the work presented is energy consumption, packet-error-rate and latency studies. This is performed for various radio technologies and standards in (radio?) harsh environments. The main contributions of this thesis are the measurements platforms and procedures that have been developed to meet the requirements to investigate modern radio technologies in terms of predictability and reliability. This thesis show that it is possible to predict wireless communication in radio harsh environments. However it is necessary to determine the characteristics of the environment to be able to choose a suitable radio technology. The measurement procedures presented in this thesis alongside the platform developed enable these types of investigations. In this thesis a model of the energy consumption for a Bluetooth radio in low-duty-cycle applications with point-to-multipoint communication is presented. The measurements show that distance and transmission power will not effect the energy consumption for a Bluetooth nor ZigBee module. However the packet-error-rate and number of retransmissions will affect the overall energy consumption, and these parameters can be correlated to distance and foremost the environmental characteristics. This thesis also presents two application-based solutions, a time synchronized ECG network with reliable data communication as well as a low-latency wireless I/O for a hydro plant.

  • 6.
    Ekström, Martin
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Bergblomma, Marcus
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    Björkman, Mats
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Mikael
    Edith Cowan University, Bunbury, Australia.
    A Bluetooth Radio Energy Consumption Model for Low Duty-Cycle Applications2012In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 61, no 3, p. 609-617Article in journal (Refereed)
    Abstract [en]

    This paper presents a realistic model of the radio energy consumption for Bluetooth-equipped sensor nodes used in a low-duty-cycle network. The model is based on empirical energy consumption measurements of Bluetooth modules. This model will give users the possibility to optimize their radio communication with respect to energy consumption while sustaining the data rate. This paper shows that transmission power cannot always be directly related to energy consumption. Measurements indicate that, when the transmission power ranges from $-$5 to $+$10 dBm, the difference in consumed energy can be detected for each transmission peak in the sniff peak. However, the change is negligible for the overall energy consumption. The nonlinear behavior of the idle state for both master and slave when increasing the interval and number of attempts is presented. The energy consumption for a master node is in direct relation to the number of slaves and will increase by approximately 50% of the consumption of one slave per additional slave, regardless of the radio setting.

  • 7.
    Ekström, Martin
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Bergblomma, Marcus
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    Björkman, Mats
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering.
    Comparison study of ZigBee and Bluetooth with regards to power consumption, packet-error-rate and distanceManuscript (preprint) (Other academic)
    Abstract [en]

    This paper present a empirical measurement comparison study of ZigBee and Bluetooth. The parameters investigated are power consumption, packet-error-rate or retransmissions and distance in different environments. This study shows the differences and similarities for the two different short range radio technologies. A measurement set-up and procedure that makes it possible to investigate power consumption of the radio module, retransmissions and packet-error-rate as well as ambient noise is presented. For both the Bluetooth and the ZigBee modules used in this study the distance itself have no influence of the power consumption. However the retransmission rate and packet-error-rate have a large influence on the power consumption. This study have show that the environment has a great impact on the range of the radio modules and the behaviour concerning the retransmission rate and packet-error-rate.

  • 8.
    Ekström, Martin
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Bergblomma, Marcus
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    Björkman, Mats
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering.
    Development of Programmable Micro Power Meter Testbed for Radio ModulesManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents the POMPOM testbed for high precision power consumption \textit{in situ} measurements for interchangeable radio modules.The main requirements for the development have been;

    Interchangeable radio modules to enable the same hardware testbed to be used independently of the radio standard used make comparison studies possible.

    The testbed should be programmable so that the need for hardware development should be minimized. The testbed must be able to act as a controller for the communication and simultaneously make accurate \textit{in situ} measurements of the energy consumption of the radio.

    The required sample rate must be at least 50 kSamples per second. The range of the current measurement should cover at least 0.2~$\mu$Ampere to 60~mAmpere with at least 14-bit resolution.

    Mobility, low cost and small size are vital for the testbed. It must be possible to deploy several measurement testbeds to act as sensor nodes in a wireless sensor network to capture the behavior of the entire network.

    The results for test measurement setup for POMPOM is presented to illustrate a typical usage of the testbed. The results presented show how the testbed can be used to investigate the correlation between distance, packet-error-rate and current consumption for a Zigbee radio.

  • 9.
    Ekström, Martin
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Berglomma, Marcus
    Mälardalen University, School of Innovation, Design and Engineering.
    Reliable Wireless ECG Sensor Network2009Conference paper (Refereed)
  • 10.
    Ekström, Martin
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Blom, Marcus
    Mälardalen University, School of Innovation, Design and Engineering.
    Garcia Castaño, Javier
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering.
    Bluetooth energy characteristics in wireless sensor networks2008In: 2008 3RD INTERNATIONAL SYMPOSIUM ON WIRELESS PERVASIVE COMPUTING, VOLS 1-2, 2008, p. 198-202Conference paper (Refereed)
    Abstract [en]

    In this paper a measurement system to create an experimental model and a tool box for simulations concerning both the energy consumption and the time aspect when creating wireless sensor networks using Bluetooth 2.0 + enhanced data rate has been developed. Further energy and time characteristics for critical events when using Bluetooth 2.0 in wireless sensor networks are investigated experimentally, with the main events; create connection, send data, receive data, and idle state. Results show that when allowing higher latencies for the connection in the Wireless Sensor Networks the power consumption drops drastically when using low power mode as sniff.

  • 11.
    Hellstrom, Per Anders Rickard
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Carlén Eriksson, Lennie
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Scharff Willners, Jonatan
    Folke, Mia
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Intelligent Wireless Body Area Network System for Human Motion Analysis2015Conference paper (Refereed)
    Abstract [en]

    Human motion analysis provides several important applications. Examples are fall risk assessment, sports biomechanics, physical activity monitoring and rehabilitation. This work in progress paper proposes an intelligent wireless body area network system for motion and gait symmetry analysis. A Bluetooth network with accelerometers, gyroscopes and in-shoe force sensing resistors gathers data and sends it to a web server after intelligent pre-processing and filtering. The system is flexible and adaptable for different use cases including combinations of gait analysis, gait symmetry and pressure measurements between foot and shoe.

  • 12.
    Hellstrom, Per Anders Rickard
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Folke, Mia
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Wearable Weight Estimation System2015In: Procedia Computer Science, vol. 64, 2015, Vol. 64, p. 146-152Conference paper (Refereed)
    Abstract [en]

    Heavy working conditions, as well as sedentary behaviour, are risk factors for health. There is a lack of wearable measurement systems for monitoring carried loads while walking. Pedobarography, the study of force fields acting between the plantar surface of the foot and a supporting surface, is supposed to be useable for estimating carried loads. Purpose. The aim of this paper is to present a novel method for selecting appropriate measurement samples for weight estimation of carried load during walk and a wearable system, based on pedobarography, consisting of commercial off the shelf components. The main idea is to choose samples when half of the total weight is on the forward sensors and the other half is on the heel sensor “equipoise” in one foot while the other foot not touches the ground. Methods. The system consists of insoles with force sensing resistors, data acquisition with IOIO-OTG and analysis in Excel. Each subject was weighed on an electronic floor scale. Three walks were performed on level ground. The first walk without any added load and then with two increases of carried load. Equipoise was defined as having half the weight distributed on the heel and the other half over the metatarsal pad. An equipoise value of 0.5 represents equilibrium regarding the weight distribution on one foot, with the other foot in the air. Samples were chosen in the equipoise region of 0.5±0.1 and then the average of the samples collected during one minute estimated the total weight. Results. The system can detect increases in carried loads but has a tendency to overestimate them. The estimated value was always larger with increased weight but the system was not always linear. The average overestimation error was 16.7 kg. Discussion. This study shows that this type of wearable system is usable for estimating carried load during walk after calibration of the system to the body weight force distribution on the sensors. There is still need for future development to obtain real-time analysis and direct feedback. A smaller and lighter measurement system is also desirable. Conclusion. This study shows that the novel method, equipoise, is usable for selecting appropriate measurement samples for weight estimation of carried load during walk. This study also shows that the wearable system, consisting of commercial off the shelf components, can be used for these measurements. However, there is a tendency to overestimate the loads.

  • 13.
    Hellstrom, Per Anders Rickard
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Åkerberg, Anna
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    FOLKE, MIA
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems. Mälardalen University, School of Health, Care and Social Welfare.
    Evaluation of the IngVaL Pedobarography System for Monitoring of Walking Speed2018In: Healthcare Informatics Research, ISSN 2093-3681, E-ISSN 2093-369X, ISSN 2093-3681, Vol. 24, no 2, p. 118-124Article in journal (Refereed)
    Abstract [en]

    Objectives

    Walking speed is an important component of movement and is a predictor of health in the elderly. Pedobarography, the study of forces acting between the plantar surface of the foot and a supporting surface, is an approach to estimating walking speed even when no global positioning system signal is available. The developed portable system, Identifying Velocity and Load (IngVaL), is a cost effective alternative to commercially available pedobarography systems because it only uses three force sensing resistors. In this study, the IngVaL system was evaluated. The three variables investigated in this study were the sensor durability, the proportion of analyzable steps, and the linearity between the system output and the walking speed.

    Methods

    Data was collected from 40 participants, each of whom performed five walks at five different self-paced walking speeds. The linearity between the walking speed and step frequency measured with R2 values was compared for the walking speed obtained ‘A’ only using amplitude data from the force sensors, ‘B’ that obtained only using the step frequency, and ‘C’ that obtained by combining amplitude data for each of the 40 test participants.

    Results

    Improvement of the wireless data transmission increased the percentage of analyzable steps from 83.1% measured with a prototype to 96.6% for IngVaL. The linearity comparison showed that the methods A, B, and C were accurate for 2, 15, and 23 participants, respectively.

    Conclusions

    Increased sensor durability and a higher percentage of analyzed steps indicates that IngVaL is an improvement over the prototype system. The combined strategy of amplitude and step frequency was confirmed as the most accurate method.

  • 14.
    Hellstrom, Per Anders Rickard
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Åkerberg, Anna
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Folke, Mia
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Walking Intensity Estimation with a Portable Pedobarography System2016In: Studies in Health Technology and Informatics, IOS Press , 2016, Vol. 224, p. 27-32Conference paper (Refereed)
    Abstract [en]

    The aim of this pilot study was to investigate the possibility to find a correlation between the output from a portable pedobarography system and the walking intensity expressed as walking speed. The system uses shoe insoles with force sensing resistors and wireless transmission of the data via Bluetooth. The force-time integral, at the toe-off phase of the step, for the force sensors in the forward part of the right foot was used to measure impulse data for 10 subjects performing walks in three different walking speeds. This data was then corrected by multiplication with the step frequency. This pilot study indicates that the portable pedobarography system output shows a linear relationship with the walking intensity expressed as walking speed on an individual level.

  • 15.
    Hozhabri, Melika
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Otterskog, Magnus
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Petrović, Nikola
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Experimental Comparison Study of UWB Technologies for Static Human Detection2016In: IEEE International Conference on Ubiquitous Wireless Broadband (ICUWB 2016) ICUWB 2016, 2016Conference paper (Refereed)
    Abstract [en]

    This paper compares two dominant Ultra Wide Rand(UWB) radar technologies Impulse and M-sequence for static human being detection in free space. The hardware and software platform for each system is described separately. These two radar platform performances are tested in real conditions and the results show that M-sequence UWB radar is better suited for detecting the static human target in larger distances.

  • 16.
    Koshmak, Gregory
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    A smart-phone based monitoring system with health device profile2012Conference paper (Refereed)
  • 17.
    Koshmak, Gregory
    et al.
    Mälardalen University, School of Innovation, Design and Engineering.
    Ekström, Martin
    Mälardalen University, School of Innovation, Design and Engineering.
    Lindén, Maria
    Mälardalen University, School of Innovation, Design and Engineering.
    A smart-Phone Based Monitoring System with Health Device Profile for Measuring Vital Physiological parameters2012Conference paper (Refereed)
  • 18.
    Tidare, Jonatan
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Åstrand, Elaine
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Martin C.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Evaluation of closed-loop feedback system delay a time-critical perspective for neurofeedback training2018In: BIODEVICES 2018 - 11th International Conference on Biomedical Electronics and Devices, Proceedings; Part of 11th International Joint Conference on Biomedical Engineering Systems and Technologies, BIOSTEC 2018, SciTePress , 2018, p. 187-193Conference paper (Refereed)
    Abstract [en]

    Neurofeedback in real-time has proven effective when subjects learn to control a BCI. To facilitate learning, a closed-loop feedback system should provide neurofeedback with maximal accuracy and minimal delay. In this article, we propose a modular system for real-time neurofeedback experiments and evaluate its performance as a function of increased stress level applied to the system. The system shows stable behavior and decent performance when streaming with many EEG channels (36-72) and 500-5000 Hz, which is common in BCI setups. With very low data loads (1 channel, 500-1000 Hz) the performance dropped significantly and the system became highly unpredictable. We show that the system delays did not correlate linearly with the stress-level applied to the system, emphasizing the importance of system delay tests before conducting real-time BCI-experiments. 

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