Special Session FO-9
Wearable and Implantable Sensors and Body Sensor Networks

Session FO-9.1 - Sensor Technology

FO-9.1:IL02  A Wearable Computer Platform "Wewear" for Healthcare Monitoring
G.K. STYLIOS, L. LUO, RIFleX, Heriot Watt University, Galashiels, UK

The synergy of modern IT and SMART materials will play a major role to the ever increasing socioeconomic and environmental demands of modern life. Research is advancing rapidly for the provision of wearable computer based systems for health and well-being, military and sports. In this effort challenges still exist in a number of areas of data stability and integration, in energy and size and in aesthetics so that obtrusiveness and comfort are realised. The "WeWear" wearable computer platform, reported in this paper, is designed and developed by taking on board these challenges and its effectiveness is demonstrated in the provision of a high quality care system for monitoring ECG, respiration and temperature.
The hardware platform consists of a 24-bit ADC with integrated analog front end chip, a highly flexible multi-protocol system on chip of a 32 bit ARM Cortex M0 CPU and an antenna. The system is small size and ideally suited for 2.4GHz ultra low power wireless applications. Bluetooth Low Energy protocol stack or ANT protocol stack can be integrated in this platform for different applications. There are bespoke respiration sensors and electrodes based on a SMART fabric designed with high frictional properties to enhance stability of contact with the skin. Single frequency spectrum process and coding/de-coding is performed during communication by using compression/de-compression techniques so that energy is minimised, whilst data fusion is performed to ensure precise and complete data. A remote server database has been developed to synchronize with a local database on a SMART phone or Tablet PC by Cloud link. Portable interfaces for SMART phones or Tablet PCs have been written having in mind the user needs and experience. The controlling of the energy is evident is every aspect of the system from the sensor design, in CPU hardware and software control, right through to communication design and in the control of battery charge/discharge. The system is based on wireless charge, and is also capable to work with solar energy. The latter has been achieved by modelling of the behaviour of the solar cell to enable maximum solar power output for optimum charging the battery. Final integration is done with a SMART garment or with a wearable belt. Special attention is given to a multilayer fabric design which is needed for communication, for energy and for electromagnetic masking.
The typical package of the ECG/respiration system is 28X35X8 mm including the 3.7 V 200 mAh battery cell and its continuous operation prior to charging 5 days. The system will be demonstrated at the conference in real life.


Session FO-9.2 - Smart Fabrics and Wearables

FO-9.2:IL01  Tools for Care of Elderly People
T. TAMURA, Department of Biomedical Engineering, Osaka Electro-communication University, Neyagawa, Osaka, Japan

Assistive devices have been used to improve the quality of life in elderly society, and information technology and robotics have been applied extensively. In this study, wearable technologies for use in elderly society are proposed. Wearable inertial sensors were applied to detect and prevent a fall. The threshold of acceleration and angular velocity were used to detect falls. We developed a wearable air-bag system using an accelerometer, angular velocity and airbags to prevent falls. The subjects wore the airbag vest with a motion detection belt. When the subject fell, the combination of acceleration and angular velocity signals detected the fall and inflated the airbag. A wearable pulse monitor with a green light emitting diode (LED) was also developed for cardiovascular safety. Pulse rates were monitored during exercise and daily activities. The motion artifact during exercise was lower with the use of the green LED. A sudden increase in pulse rate posted a warning. Furthermore, we monitored circadian rhythms, physical activates and prevented mental and digestive diseases such as stomachache using a wearable deep body thermometer in conjunction with measuring acceleration and pulse rate.


FO-9.2:IL02  Electronic Textile Platforms for Monitoring in Physiological Parameter
R. PARADISO, Smartex srl, Cascina (PI), Italy

In the last decade significant advances have been made in building lighter and more versatile devices for rehabilitation and assistance in a remote environment. Continuous daily monitoring of the functional performances of subjects in their physical interaction with the environment is essential for guiding training and rehabilitation therapy, by means of remote professionals assistance. The integration into clothes of biosensors for health monitoring provides daily physiological parameters through a continuous and personalized detection of vital signs, while fabrics with strain- and stress-sensing capabilities enable the analysis of the kinematic variables of interest. E textile platforms comprise fabric electrodes and textile sensors that can detect bioelectrical and biomechanical signals like electrocardiogram, ElectroMyoGraphy (EMG), respiratory signal, bio-impedance, skin conductivity, joint angles and gesture. Sensing clothes or part of it, like gloves or knee sleeves can be used for ambulatory therapy for different movement disorders, in a remote setting. Furthermore, textile electrodes fully integrated in fabric, allow remote Functional Electrical Stimulation (FES) therapy and EMG measurements. This lecture focuses on the results that have been achieved in the frame of the European project INTERACTION, a project aiming at a continuous daily monitoring of the functional performances of after-stroke patients and of their physical interaction with the environment. Monitoring is based on ambulatory and context awareness sensing of the subjects motor control by using textile sensors combined with inertial platforms. In particular, textile electrodes, piezoresistive sensors and wearable electrogoniometers are fully integrated in the sensing system that includes instrumented trousers, sweatshirt and gloves. This system enables the a remote clinical team to evaluate the performances, coach the patient and to influence the training via a telematic connection.


FO-9.2:IL03  On-Body Chem/Bio-Sensing - Opportunities and Challenges
D. DIAMOND, INSIGHT, National Centre for Sensor Research, Dublin City University, Dublin, Ireland

In recent years, there has been significant progress in a number of sensing technologies related to on-body measurements, such as platforms for monitoring respiration, heart rate, location and movement. In these cases, these are based on highly effective transducers that are increasingly integrated into garments such that they are becoming innocuous to the user. In contrast, the area of on-body chemical sensing remains highly under-developed. In this paper, I will address the significant challenges that are inhibiting the practical realisation of reliable chemical sensors and biosensors capable of generating accurate data in real time. I will also discuss the central role that materials science (and particularly the trend towards more biomimetic platforms) can play in overcoming these challenges, and present some idea and concepts that could point the way forward.


FO-9.2:IL04  Stretchable Circuits with Horseshoe Shaped Conductors Embedded in Elastic and Thermoplastic Polymers 
J. VANFLETEREN, F. BOSSUYT, T. VERVUST, M. JABLONSKI, B. VAN KEYMEULEN, I. CHTIOUI, B. PLOVIE, R. VERPLANCKE, A. JAHANSHAHI, J. DE BAETS, CMST, Ghent University and imec, Ghent, Belgium  

This contribution will give an overview of the latest progress at imec on the development of technologies for elastic and thermoplastic electronics and sensor circuits. Common properties of these technologies are :
• The use of horseshoe shaped metallic conductors, usually supported by a flexible polymer film for increased mechanical reliability and embedded in elastic or thermoplastic polymers like silicone rubbers (PDMS) or polyurethanes. When deforming the polymer the embedded conductors are elongated or contracted, thus acting as two-dimensional springs, and maintaining their electrical connectivity and functionality. Elongation can be dynamic for elastic circuits or single time for thermoplastic circuits.
• The use of commercially available components-off-the-shelf (COTS), which can be assembled on the stretchable substrate using conventional lead-free soldering technology or adhesive assembly.
• The use of carefully designed transitions from (normally) rigid components or component islands to flexible substrate parts and from these flexible to the stretchable parts of the circuits. It is extremely important to include smooth transitions between zones of changing mechanical stiffness in order to ensure a good mechanical reliability under repeated deformations.
• In general, the use of technologies for circuit fabrication, component assembly and polymer embedding, which are close to industrial practice and indicate a clear route to industrialization of the processes, developed in the research laboratory.
Two different technologies will be presented :
• A Printed Circuit Board (PCB) based technology, using standard low resistivity Cu conductors (thickness : 17µm or 35µm) and standard soldered components
• A fine-pitch (< 100µm), thin-film (typ. thickness 300nm) Au conductor based technology for biocompatible circuit applications (see photograph below, middle)


Session FO-9.3 - Wearable and Implantable Sensor Systems

FO-9.3:IL01  Ambulatory Sensing in Balance Control and Fall Prevention; Application in Parkinson's Disease
L. CHIARI, Department of Electrical, Electronic, and Information Engineering - Guglielmo Marconi (DEI) & Health Sciences and Technologies - Interdepartmental Center for Industrial Research (HST-ICIR) Università di Bologna, Bologna, Italy

Inertial sensors are getting popular, especially to characterize human gait or classify physical activities. Only few studies, nevertheless, have so far employed inertial sensors to investigate balance control or to quantify fall risk. Postural instability, gait disturbances and falls are leading causes of morbidity and mortality among older adults, especially those with neurodegenerative diseases like Parkinson's (PD). While much is known about the multifactorial nature of gait disturbances and falls not equally known is the best therapeutic mean of improving these impairments and thus reducing falls. At the Biomedical Engineering Group of the University of Bologna we have been working for many years in the design of smart wearable systems with a minimal set-up which can account for reliable estimates of balance and mobility by minimizing information loss compared to more complex systems. We're currently leading European projects aimed at better understanding and prevention of falls (FARSEEING) and at the design of innovative ICT-based solutions to treat postural instability and gait disturbances in persons with PD (CuPiD). This talk will present a critical survey of ambulatory solutions we've proposed so far, with a specific emphasis on their application in persons with PD.


FO-9.3:L02  Fluctuations in Frequency Composition of Neural Activity Observed by Portable Brain Intention Detection Device
R.A. SHOURESHI, New York Institute of Technology, Old Westbury, New York, USA; C.M. AASTED, Center for Pain and the Brain, Harvard Medical School and P.A.I.N. Group, Boston Children's Hospital, Boston, MA, USA

As part of the goal of developing wearable sensor technologies, we have continued the development of a headset system for monitoring activity across the primary motor cortex of the brain. Through the combination of electroencephalography (EEG) and near-infrared spectroscopy (NIRS), the headsets are capable of monitoring event-related potentials and hemodynamic activity, which are wirelessly transmitted to a computer for real-time processing to generate control signals for a motorized prosthetic limb or a virtual embodiment of one or more limbs. This paper focuses on recent observations that have been made regarding the frequency content of EEG data, which we believe is responsible for the high performance we have previously reported using artificial neural networks to infer user's intentions. While the inference engine takes advantage of frequency content from 0-128 Hertz (Hz), distinct fluctuations in alpha (8-13 Hz), beta (13-30 Hz), and gamma (30-100 Hz) frequency bands are human-observable across varying upper limb motor exercises when observed at the group level. In addition to prosthetic limbs, this technology is continuing to be investigated for application in areas including pain treatment, robotic arm control, lie detection, and more general brain-computer interfaces.


FO-9.3:L03  Metallization on Polymer Substrates for Functional Contact Lenses
S. TINKU, C. COLLINI, S. PEDROTTI, L. LORENZELLI, Center for Materials and Microsystems, Fondazione Bruno Kessler, Trento, Italy; R.S. DAHIYA, Electronics and Nanoscale Engineering, University of Glasgow, UK

Functional multi-purpose contact lenses have recently attracted attention as suitable means to exploit the characteristics of eyes to diagnose diseases and for drug delivery. This is made possible by developing functional contact lens with micro sensors placed on it, which can be worn on the eye surface. However there are several challenges that need to be addressed before reaching the final functional contact lens with incorporated micro devices and micro sensors for biomedical applications. One such challenge is related to the metallization on polymer substrates. In this work, we present the first results in the direction of realizing robust metal patterns on polymer substrates. The metal patterns presented here are electrodes for connecting different devices and micro antenna loops. We also compare the metallization techniques on different polymer substrates like PDMS, PET to name a few and different metals patterned like Ag, Au etc. Specific steps and solutions to issues like crack formation and adhesion of the metal on the polymer substrates are also discussed.


FO-9.3:L04  Mobile Health: Design of In-body Wearable Sensor System by Flexible and Stretchable Electronics
C.C.Y. POON^{1, 2}, NINGQI LUO², NI ZHAO², ¹Department of Surgery, The Chinese University of Hong Kong, HKSAR; ²Department of Electronic Engineering, The Chinese University of Hong Kong, HKSAR 

Wearable and implantable sensors have emerged as an active area of research, especially when integrated with mobile and wireless technologies, to provide new ways for the pervasive management of acute and chronic health conditions. Traditionally, wearable systems were thought to be used for sensing health information on the body surface, while implantable systems were used to collect information inside the body. Recent advancement in flexible and stretchable electronics has opened up new opportunities for designing sensor that can be worn inside the body. Studies have shown that optoelectronic sensors, fabricated on flexible elastomeric substrate in micrometres, can be transferred and adhered to the epidermis for non-invasive monitoring of physiological signals such as electrocardiogram. Due to the flexibility of these sensor systems, they have the ability to conform well to the rough surface of biological tissues. Similar concept can be used in designing sensor system for the gastrointestinal (GI) tract, where traditionally, an invasive implant design must be used to anchor the system to the GI wall. The usages of in-body wearable sensor systems in the GI tract have huge potentials, including the detection of occult bleeding and pH monitoring in patients with reflux diseases.
This work is supported by the Hong Kong Innovation and Technological Fund (ITS/159/11; ITS/197/12) and the CUHK Direct Grant (Grant No. 4054058).


FO-9.3:IL06  Pervasive Sensors for Real Time Monitoring
F. DI FRANCESCO¹, P. SALVO¹, N. CALISI¹, B. MELAI¹, S. GHIMENTI¹, V. CASTELVETRO¹, S. BIANCHI¹, A. PUCCI¹, C. CHIAPPE¹, R. FUOCO¹, M. CORREVON², G. DUDNIK², G. VOIRIN², I. TEXIER³, P. MARCOUX³, P. PHAM³, N. BUE⁴, J. CRISTENSEN⁴, M. LAURENZA^{5, 6}, A. RAPTOPOULOS⁷, A. BARTZAS⁷, D. SOUDRIS⁸, C. SAXBY⁹, T. NAVARRO¹⁰, M. ROMANELLI¹¹, V. DINI¹¹, A. PAOLICCHI¹², M. MULLER¹³, P.-Y. BENHAMOU¹³, L. LYMPEROPOULOS⁷, ¹University of Pisa, Dipartimento di Chimica e Chimica Industriale, Pisa, Italy; ²Centre Suisse d'Electronique et de Microtechnique, Neuchâtel, Switzerland; ³CEA Leti, MINATEC Campus, Grenoble, France; ⁴European Wound Management Association, Frederiksberg, Denmark; ⁵Euroresearch, Milano, Italy; ⁶Haemopharm Biofluids, Tovo di S. Agata, Italy; ⁷EXUS, Athens, Greece; ⁸National Technical University of Athens / ICCS, School of Electrical & Computer Engineering, Athens, Greece; ⁹Smith and Nephew Wound Management, Hull, UK; ¹⁰Swissinnov, Gland, Switzerland; ¹¹University of Pisa, Wound healing research unit, Clinica Dermatologica, Pisa, Italy; ¹²University of Pisa, Department of Translational Research and New Technologies in Medicine and Surgery, Pisa, Italy; ¹³Clinique d'Endocrinologie Diabetologie, Pôle DigiDune, CHU de Grenoble, Grenoble, France  

Sensors can be a valid tool to improve efficiency and quality of healthcare. They can be used in diagnostics and therapeutics, and in particular to extend the application possibilities of telemedicine. The integration of sensor data within health information systems and decision support systems may allow the delivery of personalized treatments at decreased cost. Chronic wounds such as diabetic foot ulcers and venous leg ulcers represent an interesting field of application for this technology. These pathologies, often caused by diabetes and vascular problems with the co-morbidity influence of many other diseases, affect in Europe more than 10 million people, a number which is expected to grow due to the aging of the population. The EU FP7 SWAN-iCare project is developing an integrated autonomous device for the remote monitoring and management of chronic wounds based on non-invasive integrated micro-sensors, capable to monitor many wound parameters and early identify infections, and micro-actuators, to supplement the negative pressure wound therapy with an innovative personalized two-line therapy. The SWAN-iCare system will be outlined with a particular emphasis on sensors and their potential impact in the area of wound management.


FO-9.3:L07  Soft Conductive Polymer Dry Electrodes for High-quality and Comfortable ECG/EEG Measurements
YUN-HSUAN CHEN¹, M. OP DE BEECK², L. VANDERHEYDEN³, H. VANDORMAEL³, C. VAN HOOF¹, ¹imec & Electrical Engineering Department, KU Leuven, both at Leuven, Belgium; ²imec, Leuven, Belgium; ³Department of R&D and Innovation, Datwyler Sealing Solutions, Alken, Belgium

Wet gel electrodes are widely used for ECG/EEG monitoring, their low impedance results in high-quality signals. But they have important drawbacks too, such as time-consuming electrode set-up for EEG followed by a painful removal, skin irritation by the gel and signal degradation due to gel drying. Hence various dry electrode types are investigated, such as hard metal electrodes with low impedance but limited patient comfort/safety. We focus on flexible conductive polymer-based electrodes to combine low impedance, user comfort and safety. The composition of the conductive polymers is optimized to improve various properties such as conductivity, which directly affects signal quality and sensitivity to motion artifacts, and mechanical properties of the electrodes, important with respect to patient comfort. Electrode impedance and ECG/EEG signal recordings are evaluated using various polymer compositions and compared to wet gel electrode results. Additive optimization to improve processability of the conductive formulations is performed by dedicated flow studies, and will result in a high electrode fabrication yield. Very promising results are obtained regarding impedance, EEG/ECG signal quality, user comfort and fabrication yield.


Session FO-9.4 - Energy Harvesting and Management

FO-9.4:IL02  Tailoring the Electrical and Optical Properties of Graphene for Energy Harvesting
M. CRACIUN, Centre for Graphene Science, University of Exeter, Exeter, UK

Graphene -a single layer of carbon atoms with honeycomb structure- has emerged as a new paradigm in condensed matter physics due to the gamut of unique physical properties which also make it the ideal platform for novel transparent and flexible opto-electronic devices. These unique properties can be further tailored to fit specific device functionalities by means of chemical bonding of a molecule or a chemical element to the pristine graphene. For example functionalization with fluorine makes graphene a wide gap semiconductor [1-3]. This gap can be tuned be adjusting the fluorine content using electron beam irradiation [2,3]. At the same time, functionalization with FeCl3 of few-layer graphene results in a new system which is the best known flexible and transparent material able to conduct electricity [4]. In this talk I will review our most recent contributions to engineer the electrical and optical properties of graphene materials via chemical functionalization and the development of whole-graphene optoelectronics [5].
[1] Nanoscale Research Letters 6, 526 (2011);
[2] Nano Lett. 11, 3912 (2011);
[3] New Journal of Physics 15, 033024 (2013)
[4] Advanced Materials 24, 2844 (2012);
[5] ACS Nano, (6), 5052 (2013).


FO-9.4:IL03  Power Management for Vibrational Energy Harvesters
S. STANZIONE, C. VAN LIEMPD, IMEC-NL, Eindhoven, The Netherlands; C. VAN HOOF, IMEC-NL, The Netherlands, and KU Leuven, Belgium

Vibrational energy harvesting is an enabling technology for wireless sensor networks in industrial and automotive applications. In the past years, much effort has been devoted to finding solutions for efficiently interfacing piezoelectric and electrostatic energy harvesters. Both types of harvesters produce AC output power, but their internal impedances are quite different. Piezoelectric energy harvesters are characterized by source resistances of few hundreds of kOhms. As a consequence, in a piezoelectric power management interface the most critical block is the AC-DC converter, because diode threshold voltages and quiescent current significantly lower system efficiency. We have designed a power management interface capable to work from 1uW to 1mW, consuming only 40nA and employing a novel zero-bias active diode. Alternatively, electrostatic energy harvesters are characterized by much larger source resistances. This means that the most critical power management block is the DC-DC conversion. We have implemented a High voltage inductive step-down converter capable to interface up to 60V input voltage with 88% peak efficiency and including a fully analog Maximum Power Point Tracking algorithm with more than 99% peak efficiency.


FO-9.4:L04  Hybrid Energy Harvesting using Electroactive Polymers Combined with Piezoelectric Materials
A. CORNOGOLUB, L. PETIT, P.-J. COTTINET, INSA de Lyon, LGEF, Villeurbanne, France

Electroactive polymers (EAP) are relatively soft and flexible materials, easy to integrate and able to undergo large deformations by applying an electric field (usually some 10 V/µm). This coupling between strain and electric field (quadratic) as well as particular mechanical properties has already been used advantageously to design actuators. As energy harvesters EAP have also shown good abilities by providing energy densities up to 0.4 J/g. Moreover, they present some advantages over other techniques as electromagnetic or piezoelectric as they have low resonance frequency response and high elasticity which enable them to be used in situations where large displacements are available. The main drawback of EAP as energy harvesters is that they don't experience direct coupling between stress and electric field, such as the piezoelectric effect.
It is therefore essential to use an external electrical polarization source in order to create an energy c ycle induced by the EAP capacitance variations when it is subject to external stress.
The goal of this work is to combine the EAP and piezoelectric materials using the advantages of both, for hybrid energy harvesting. Different systems are simulated and a study of performances is done as well as a comparison with existing techniques.

 
Session FO-9.5 - Antennas, Data Transmission, Signal Processing

FO-9.5:IL02  Combination of Body Sensor Networks and On-body Signal Processing Algorithms
J. LUPRANO, CSEM SA, Neuchâtel, Switzerland

Non-obtrusive body sensing has made large progress during the last decade. From sensing nodes with distributed miniaturized sensors to so-called smart fabrics intelligent textiles (SFIT), where the term smart refers to materials that sense and respond in a pre-defined way to environmental stimuli. In each case, the goal is to collect information from the body and its environment, and process it to inform or take action.
Typical physiological measurements for medical applications include electrocardiogram, respiration or body temperature. Activity, movements and position are typical measurements for other applications.
Body sensor network technology supports an increase of the number of sensors allowing the use of less performing and expensive sensors, at the price of additional processing algorithms, not only to filter the signals but also to combine them.
Gathering, combining and making use of these signals to derive higher-level comprehensive and useful information requires an interconnection of the sensors, wired or wireless, local intelligence for on-body signal processing and an interface to the user. The necessity to keep nodes and electronics small, the interoperability feature and the trade-offs between on-body and off-body processing (electronic size, power consumption, energy storage and autonomy, wireless communication…) are challenges of wearable systems. Several projects and results will be used during the lecture to illustrate the subject.


FO-9.5:IL04  Signal Processing for Ultra Low Power Communications: Capsule Endoscope
I. BALASINGHAM, Oslo University Hospital & Norwegian University of Science and Technology, Oslo, Norway

Recent developments in the field of wireless radio technology has enhanced the way diagnosis is done for patients with gastroenterological disorders such as anal bleeding, Crohn's disease, Celiac disease, and intestinal tumors. Currently, physicians rely on the insertion of flexible tubes containing cameras to examine hard-to-reach parts of the digestive tract. This technique, however, can examine the upper portion of the digestive tract only, while colonoscopies help to visualize the lower part (colon). There is a large portion (ca. 6 meters) of the small intestine that cannot be inspected. Capsule endoscopes help to fill this gap with significantly less discomfort for the patient. A capsule endoscope is a camera with the size and shape of a pill that is swallowed in order to visualize the gastrointestinal tract. They originally were devised to transmit still images of the digestive tract for subsequent diagnosis and detection of gastrointestinal diseases. In this talk, we will demonstrate wireless transmission of high definition real-time video of the digestive tract using high data rate radio interface. The signal processing techniques have been carefully designed and developed taking into the consideration of the ultra wideband radio channel and the small onboard battery.
 
 
Poster Presentation

FO-9:P01  Wearable Chemical Sensing - Sensor Design and Sampling Techniques for Real-time Sweat Analysis
J.A. DEIGNAN, S. COYLE, G. MATZEU, C. O'QUIGLEY, C. ZULIANI, D. DIAMOND, INSIGHT, National Centre for Sensor Research, Dublin City University, Glasnevin, Dublin, Ireland; P. FITZPATRICK, G. WARRINGTON, School of Health and Human Performance, Dublin City University, Glasnevin, Dublin, Ireland

Wearable chemical sensors have the potential to provide new methods of non-invasive physiological measurement. The nature of chemical sensors involves an active surface where a chemical reaction must occur to elicit a response. This adds complexity to a wearable system which creates challenges in the design of a reliable long-term working system.
This work presents the design of a real-time sweat sensing platform to analyse sweat loss and composition. Sampling methods have an impact on composition therefore skin encapsulation needs to be avoided so as not to disrupt normal sweating patterns. Sensors ideally need to be placed close to the sampling site which may be subject to motion artefacts [1]. The design of this device takes into account sample collection and delivery, sensor placement and associated electronics. The overall design is ergonomic to interface with the contours of the body. Results of lab-based simulations and real-time exercise trials are presented.
This device can offer valuable information regarding hydration status and electrolyte balance which may be especially important for optimised rehydration during or after sports activities.
[1] Curto, V. F. S. Coyle, R. Byrne, N. Angelov, D. Diamond, F. Benito-Lopez., Sens. Actuators, B, 2012, 175, 263-270.