N. F. de Rooij

École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland

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Publications (1000)1012.48 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an analytical and experimental study of a compact configuration to harvest energy from a rotating gear using piezoelectric microelectromechanical system harvesters. The reported configuration realizes a contact-type frequency up-conversion mechanism in order to generate useful electrical energy. The up-conversion mechanism was achieved using an atomic force microscope (AFM)-like piezoelectric cantilever plucked by the teeth of the rotating gear that could be eventually driven by an oscillating mass. This paper describes relevant design guidelines for harvesting energy from the low-frequency mechanical movement of a rotating gear through analytical modeling and finite element method (FEM) simulation followed by experimental validation. Different harvester configurations are investigated to identify the optimal configuration in terms of the output energy and energy conversion efficiency. The latter results are reported for the first time because of the implementation of an original concept based on the coupling of the harvester with a rotational flywheel. The experimental results reveal that free vibrations of the harvester after plucking contribute significantly to the output energy and efficiency. By adding a proof mass, the efficiency of the system can be greatly improved. For plucking speeds between 3 and 19 r/s, average output powers in the order of tens of microwatts were obtained for continuous plucking. By combining interaction energy, friction, and energy absorption, between the harvester and inertial mass, the maximum efficiency of the impact piezoelectric harvesters was found to be 1.4%. The efficiency results obtained were compared with the noncontact magnetic plucking approach further demonstrating the potential of our concept. Finally, different tip-gear materials combinations were evaluated showing the importance of their nature on the reliability of the presented configuration. [2014-0102]
    Journal of Microelectromechanical Systems 06/2015; 24(3):742-754. DOI:10.1109/JMEMS.2014.2349794 · 1.92 Impact Factor
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    ABSTRACT: This paper presents the optimization of a micro gas preconcentrator (µ-GP) system applied to atmospheric pollution monitoring, with the help of a complete modeling of the preconcentration cycle. Two different approaches based on kinetic equations are used to illustrate the behavior of the micro gas preconcentrator for given experimental conditions. The need of a high adsorption flow and heating rate, a low desorption flow and detection volume is demonstrated through this paper. Preliminary to this optimization, the preconcentration factor is discussed and a definition is proposed.
    Analytical Chemistry 03/2015; 87(8). DOI:10.1021/acs.analchem.5b00400 · 5.83 Impact Factor
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    ABSTRACT: Point-of-care (PoC) applications require small, fast, and low power sensors with high reliability. Despite showing promising performances, nanomechanical sensors have not yet demonstrated the excellent reproducibility of measurements necessary to be incorporated in such systems. Coffee-ring effect usually occurs during the deposition of the functionalization layer and produces an inhomogeneous and poorly repeatable profile on the sensor surface. In this study, we investigated how cantilever-based sensors and the previously developed membrane-type surface stress sensor (MSS) are affected by an inhomogeneous functionalization. We functionalized 8 piezoresistive cantilevers and 16 MSS with a dextran solution that formed an inhomogeneous layer due to the coffee ring effect. During expositions to humidity pulses, MSS were five times more reproducible (standard deviations between 5% and 6%) compared to the cantilever-based sensors (standard deviations between 25% and 28%). In fact, the cantilever-based sensors were as reproducible as their functionalization layer while the reproducibility of MSS was only limited by the tolerances of their fabrication. This sensor-to-sensor reproducibility, combined with a high sensitivity, makes the MSS a promising bio/chemical sensor platform for reliable and label-free detection of substances to be integrated into PoC systems.
    Sensors and Actuators A Physical 03/2015; 228. DOI:10.1016/j.sna.2015.02.039 · 1.94 Impact Factor
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    ABSTRACT: In this paper we report on the fabrication of spin-coated biodegradable polylactic acid (PLA) thin films to be used as substrates for the realisation of all-solution-processed organic electronic devices. The full mechanical and electrical characterisation of these substrates shows that they exhibit good mechanical and dielectric properties and are therefore suitable for the fabrication of disposable electronics. To demonstrate practically the functionality of such PLA thin films, organic electronic devices were realised on the top of them, exclusively by means of solution-process fabrication techniques and in particular inkjet-printing. Also, a photonic curing procedure is here presented as a means for sintering the conductive inks without heating up the PLA substrates. Two types of organic transistors were fabricated on the top of PLA: organic field-effect transistors (OFETs), where the PLA film was used not only as a substrate but also as the gate dielectric, and all-inkjet-printed organic electrochemical transistors (OECTs). The second typology of transistors exhibited one of the highest transconductance reported so far in the literature (up to 2.75 mS). This study opens an avenue for the fabrication of disposable, low-cost organic electronic devices.
    Organic Electronics 02/2015; 17:77-86. DOI:10.1016/j.orgel.2014.11.010 · 3.83 Impact Factor
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    ABSTRACT: Additive microcontact printing of self-assembled monolayers of gold nanoparticles.•Plasma sintering of thiol-capped gold nanoparticles printed on plastic foil.•Solvent-less printing of the top electrode of a parallel-plates organic capacitor.•Miniaturization and optimization of fully-printed humidity capacitive sensors.
    Organic Electronics 01/2015; 16. DOI:10.1016/j.orgel.2014.10.041 · 3.83 Impact Factor
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    ABSTRACT: Monitoring metabolism fluctuations inside a cell culture is a valuable method for assessment of the cells vitality. Enzyme-based biosensors can provide selective measurement of metabolites such as glucose, lactate, glutamate and choline. However, integration of these biosensors inside a cell culture is a challenging issue that can disrupt the properties of the cells microenvironment or influence the biosensors’ enzyme functioning. Herein, a technique for measuring the abovementioned metabolites in a cell culture without affecting the enzymes or the cells is presented. In this study, SU-8 is investigated as a suitable substrate for a simple enzyme immobilization. Two SU-8 microreactors are designed inside a microfluidic cartridge and functionalized with different enzymes. The implemented microreactors are used for detection of two metabolites simultaneously in a few microliters of a sample extracted from the cell-culture medium. Sub-micromolar concentrations are detectable using this device. The results of measuring variations in glucose and lactate concentration inside a cell culture, before and after exposing the cells to three different toxicants, are presented. In order to eliminate the enzymes disruption by the toxicants present inside the medium, a protocol for a toxicant-free sampling is investigated.
    Microfluidics and Nanofluidics 01/2015; DOI:10.1007/s10404-015-1562-8 · 2.67 Impact Factor
  • 6th European Conference of the International Federation for Medical and Biological Engineering; 01/2015
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    ABSTRACT: This work presents an approach for increasing operational bandwidth of a vibration energy harvester in low-frequency environments by effectively exploiting contact-based frequency up-conversion. It was implemented by a couple of low-frequency resonators with appropriately spaced natural frequencies impacting high-frequency piezoelectric generators when the device is harmonically excited in 10-40 Hz range. A proof of concept was designed, modeled, fabricated and characterized, demonstrating improved power and bandwidth performance (up to 37 μW and 9 Hz at 1 g) with respect to traditional single-resonator designs.
    Procedia Engineering 12/2014; 87:1517-1520. DOI:10.1016/j.proeng.2014.11.587
  • Journal of Microelectromechanical Systems 12/2014; 23(6):1417-1427. DOI:10.1109/JMEMS.2014.2314702 · 1.92 Impact Factor
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    ABSTRACT: Conducting polyaniline-based chemiresistors on printed polymeric micro-hotplates were developed, showing sensitive and selective detection of ammonia vapor in air. The devices consist of a fully inkjet-printed silver heater and interdigitated electrodes on a polyethylene naphthalate substrate, separated by a thin dielectric film. The integrated heater allowed operation at elevated temperatures, enhancing the ammonia sensing performance. The printed sensor designs were optimized over two different generations, to improve the thermal performance through careful design of the shape and dimension of the heater element. A vapor-phase deposition polymerization technique was adapted to produce polyaniline sensing layers doped with poly(4-styrenesulfonic acid). The resulting sensor had better thermal stability and sensing performance when compared with conventional polyaniline-based sensors, and this was attributed to the polymeric dopant used in this study. Improved long-term stability of the sensors was achieved by electrodeposition of gold on the silver electrodes. Response to sub-ppm concentrations of ammonia even under humid conditions was observed.
    Analytical Chemistry 08/2014; 86(18). DOI:10.1021/ac501908c · 5.83 Impact Factor
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    ABSTRACT: A new and versatile fabrication process of insulated gold tip probes for atomic force microscopy (AFM) is presented by Wu et al. (In-plane fabricated insulated gold-tip probe for electrochemical and molecular experiments, in: 2013 IEEE 26th International Conference on Micro Electro Mechanical Systems (MEMS), IEEE, 2013, pp. 492–495). The novelty of the process lies in the fact that the length and the thickness of the cantilever are defined by photolithography and Si etching from the wafer top surface. Width of the cantilever is defined by the device layer of a silicon-on-insulator (SOI) wafer. The tip is fabricated in the wafer top plane. E-beam lithography was employed outlining the gold nanowire tip. The chip body is formed with the handling layer of the SOI by deep reactive ion etching in later steps. In a practical operation, the probe chip is rotated by 90 degree. The tip radius of curvature is approximately 20 nm. The high-quality insulation on the probe was demonstrated by performing electrodeposition of gold on the tip-end. The spring constant of the cantilever was obtained by measuring resonance frequency of the cantilever. With this in-plane fabrication process, probes with different spring constants ranging from 0.05 N/m to 13.67 N/m were fabricated on the same wafer.
    Sensors and Actuators A Physical 08/2014; 215:184–188. DOI:10.1016/j.sna.2013.08.043 · 1.94 Impact Factor
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    ABSTRACT: We present a microfabricated alkali vapor cell equipped with an anti-relaxation wall coating. The anti-relaxation coating used is octadecyltrichlorosilane and the cell was sealed by thin-film indium-bonding at a low temperature of 140 °C. The cell body is made of silicon and Pyrex and features a double-chamber design. Depolarizing properties due to liquid Rb droplets are avoided by confining the Rb droplets to one chamber only. Optical and microwave spectroscopy performed on this wall-coated cell are used to evaluate the cell's relaxation properties and a potential gas contamination. Double-resonance signals obtained from the cell show an intrinsic linewidth that is significantly lower than the linewidth that would be expected in case the cell had no wall coating but only contained a buffer-gas contamination on the level measured by optical spectroscopy. Combined with further experimental evidence this proves the presence of a working anti-relaxation wall coating in the cell. Such cells are of interest for applications in miniature atomic clocks, magnetometers, and other quantum sensors.
    Applied Physics Letters 07/2014; 105(4):043502-043502-4. DOI:10.1063/1.4891248 · 3.52 Impact Factor
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    ABSTRACT: Taking advantage of the sensor interface capabilities of a Radiofrequency Identification (RFID) chip, the integration of different types of sensors on printed Ultra High Frequency (UHF) RFID tags is investigated. The design, development and testing of printed smart sensing tags compatible with the RFID standard Electronic Product Code (EPC) Gen 2 is presented. Two different strategies are employed to interface the sensors: passive single-chip and semi-passive architectures. Both strategies provide sensor data by directly answering to the RFID reader inquiries or by using a data logging mechanism to store the sensor data in the RFID chip memory. Temperature read out is measured using the embedded sensor in the RFID chip. Additionally a light sensor and a pressure sensor interfaced to a microcontroller are implemented in the passive and semi-passive tags versions, respectively. For the employed RFID chip, two different UHF antennas are designed and printed using inkjet and screen printing to compare their radiofrequency performances. Finally, the fabricated smart tags are fully validated through measurements in an anechoic chamber and their behaviors are compared to numerical simulation. The screen printed semi-passive RFID tag with loop antenna shows a better reading range than the inkjet-printed one, whereas the passive tag can be considered as the most cost-effective system.
    IEEE Sensors Journal 07/2014; 14(12). DOI:10.1109/JSEN.2014.2335417 · 1.85 Impact Factor
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    ABSTRACT: We have experimentally studied the variation in electrical resistance of flexible platinum lines patterned on polyimide foil when they are subjected to circular bending constraints. The lines were patterned by means of standard photolithography and sputtering deposition. Two different photolithography masks were used for comparative evaluation: an un-expensive transparency mask and a standard chromium mask. Measurements of the temperature coefficient of resistance (TCR) and time stability of the resistance have been acquired for lines bent down to 1.25 mm radius of curvature on a customized bending setup, showing good reliability results. The robustness of the lines has been also assessed by registering their change in resistance while bending at different radii of curvature. The lines showed reliability issues for radii of curvature below 1.25 mm, presenting a resistance variation of 19% for transparency mask-fabricated lines and 9% for chromium mask-fabricated lines. The worse reliability performances of transparency mask lines, compared to the chromium mask ones, was found to be due to their imperfect edges, which promoted the formation and propagation of cracks during bending. The results of the experiments in this work permitted to compare the performances of flexible conductive lines with different geometry and fabricated with two different masks, establishing quantitative and qualitative bending limits for their appropriate operation in flexible electronics systems.
    Microelectronics Reliability 07/2014; 54(11). DOI:10.1016/j.microrel.2014.06.015 · 1.43 Impact Factor
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    ABSTRACT: We present a complete wafer level microfabrication process for the production of unimorph MEMS energy harvesters based on thinned bulk piezoelectric ceramic, lead zirconate titanate (PZT), sheets. This process eliminates the need for individual bonding of PZT pieces and proof masses at the chip level while still benefitting from the excellent properties of bulk PZT. With the process presented in this paper, 20 piezoelectric energy harvesters have been fabricated in parallel at the wafer level by bonding a single bulk (PZT) sheet onto a silicon-on-insulator (SOI) wafer using a low-temperature process and structuring the bonded stack with standard microfabrication techniques including thinning of the bulk PZT sheet using mechanical grinding as well as electrodeposition to deposit a thick nickel proof mass on the tip of each cantilever. A single fabricated harvester with an effective volume of 47.82 mm3 is capable of generating a normalized power density of 3346 μW cm−3 g−2 with an average power of 1.6 μW under an excitation of 0.1 g (1 g = 9.81 m s−2) at a resonant frequency of 100 Hz through an optimal resistive load of 11.8 kΩ. Thinned bulk PZT exhibits high power and a useable voltage while maintaining a low optimal resistive load, demonstrating the potential of high performance piezoelectric MEMS energy harvesters using bulk PZT sheets fabricated at the wafer level.
    Sensors and Actuators A Physical 04/2014; 210. DOI:10.1016/j.sna.2014.01.032 · 1.94 Impact Factor
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    ABSTRACT: Over the past decade, different designs of micro gas preconcentrators (µ-GP) have been proposed in literature for targeting diverse applications from medical diagnostic to explosives detection [1,2,3, 4]. The common point of all these developments is that the design of the µGP is driven by its future use. Therefore, we address here the technical aspect of the development of μGP for meeting the requirement of both pollution monitoring and explosives detection applications. In this paper, we have proposed four different designs of silicon μGP optimized from fluidic and thermal simulations but also from experimental results in regards to the chosen application. Beside the choice of the adsorbent material and the experimental parameters, the efficiency of a μGP is closed related to its shape and size. In General the μGP needs to be small enough to fit with fast desorption heating rate requiring a low thermal mass device and not too much small for allowing high flow rates during the adsorption and thus reducing the duration of preconcentration cycle
    IMCS 2014, Buenos Aires, Argentina; 03/2014
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    ABSTRACT: Forward osmosis (FO) is a well-established process that has been used for different applications like desalination of water, concentration of foods or drugs, and energy harvesting. We exploited this process in a fully automatic system to adjust osmolality of environmental water samples that are to be tested by cell-based biosensors. In cell-based biosensors, samples are brought into contact with living cells. Therefore, the samples0 osmolality and pH should be in a range that is tolerable for the cells. Controlling these parameters has been a significant challenge especially in environmental monitoring, where the biosensors are required to work on-site. In this paper, we introduce a low-cost portable fluidic system that works automatically, and adjusts the osmolality and pH of environmental samples without diluting or denaturizing the ingredients of the samples. We report the performance of this system in adjusting the osmolality and pH of Swiss environmental waters with a natural osmolality of 471 mmol/kg and a pH of 7.8470.02.
    Journal of Membrane Science 03/2014; 454:470–477. DOI:10.1016/j.memsci.2013.12.041 · 4.91 Impact Factor
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    ABSTRACT: The design optimization through modeling of a thinned bulk-PZT-based vibration energy harvester on a flexible polymeric substrate is presented. We also propose a simple foil-level fabrication process for their realization, by thinning the PZT down to 50 μm and laminating it via dry film photoresist onto a PET substrate at low temperature (<85 °C). Two models, based on analytical and finite element modeling (FEM) methods, were developed and experimentally validated. The first, referred to as the hybrid model, is based mainly on analytical equations with the introduction of a correction factor derived from FEM simulations. The second, referred to as the numerical model, is fully based on COMSOL simulations. Both models have exhibited a very good agreement with the measured output power and resonance frequency. After their validation, a geometrical optimization through a parametric study was performed for the length, width, and thicknesses of the different layers comprising the device. As a result, an output power of 6.7 μW at 49.8 Hz and 0.1 g, a normalized power density (NPD) of 11 683 μW g−2 cm−3, and a figure of merit (FOM) of 227 μW g−2 cm−3 were obtained for the optimized harvester.
    Smart Materials and Structures 03/2014; 23(4):045041. DOI:10.1088/0964-1726/23/4/045041 · 2.45 Impact Factor
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    ABSTRACT: We report the modeling, and geometrical and electrical characterization, of inkjet and screen-printed patterns on different polymeric substrates for use as antennas in radio-frequency identification (RFID) applications. We compared the physical and electrical characteristics of two silver nanoparticle-based commercial inkjet-printable inks and one screen-printable silver paste, when deposited on polyimide (PI), polyethylene terephthalate (PET), and polyetherimide (PEI) substrates. First, the thickness of the inkjet-printed patterns was predicted by use of an analytical model based on printing conditions and ink composition. The predicted thickness was confirmed experimentally, and geometrical characterization of the lines was completed by measuring the root-mean-square roughness of the patterns. Second, direct-current electrical characterization was performed to identify the printing conditions yielding the lowest resistivity and sheet resistance. The minimum resistivity for the inkjet-printing method was 8.6 ± 0.8 μΩ cm, obtained by printing four stacked layers of one of the commercial inks on PEI, whereas minimum resistivity of 44 ± 7 μΩ cm and 39 ± 4 μΩ cm were obtained for a single layer of screen-printed ink on polyimide (PI) with 140 threads/cm mesh and 90 threads/cm mesh, respectively. In every case, these minimum values of resistivity were obtained for the largest tested thickness. Coplanar waveguide transmission lines were then designed and characterized to analyze the radio-frequency (RF) performance of the printed patterns; minimum transmission losses of 0.0022 ± 0.0012 dB/mm and 0.0016 ± 0.0012 dB/mm measured at 13.56 MHz, in the high-frequency (HF) band, were achieved by inkjet printing on PEI and screen printing on PI, respectively. At 868 MHz, in the ultra-high-frequency band, the minimum values of transmission loss were 0.0130 ± 0.0014 dB/mm for inkjet printing on PEI and 0.0100 ± 0.0014 dB/mm for screen printing on PI. Although the resistivity achieved is lower for inkjet printing than for screen printing, RF losses for inkjetted patterns were larger than for screen-printed patterns, because thicker layers were obtained by screen printing. Finally, several coil inductors for the HF band were also fabricated by use of both printing techniques, and were used as antennas for semi-passive smart RFID tags on plastic foil capable of measuring temperature and humidity.
    Journal of Electronic Materials 02/2014; 43(2). DOI:10.1007/s11664-013-2893-4 · 1.68 Impact Factor
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    ABSTRACT: We present a portable microsystem to quantitatively detect cocaine in human saliva. In this system, we combine a microfluidic-based multiphase liquid–liquid extraction method to transfer cocaine continuously from IR-light-absorbing saliva to an IR-transparent solvent (tetrachloroethylene) with waveguide IR spectroscopy (QC-laser, waveguide, detector) to detect the cocaine on-chip. For the fabrication of the low-cost polymer microfluidic chips a simple rapid prototyping technique based on Scotch-tape masters was further developed and applied. To perform the droplet-based liquid–liquid extraction, we designed and integrated a simple and robust droplet generation method based on the capillary focusing effect within the device. Compared to well-characterized and commonly used microfluidic H-filters, our system showed at least two times higher extraction efficiencies with potential for further improvements. The current liquid–liquid extraction method alone can efficiently extract cocaine and pre-concentrate the analytes in a new solvent. Our fully integrated optofluidic system successfully detected cocaine in real saliva samples spiked with the drug (500 μg/mL) and allowed real time measurements, which makes this approach suitable for point-of-care applications.
    Analytical Chemistry 01/2014; 85(15). DOI:10.1021/ac404081j · 5.83 Impact Factor

Publication Stats

10k Citations
1,012.48 Total Impact Points

Institutions

  • 2–2015
    • École Polytechnique Fédérale de Lausanne
      • • Sensors, Actuators and Microsystems Laboratory
      • • Institute of Microengineering
      Lausanne, Vaud, Switzerland
  • 2000–2013
    • Centre Suisse d'Electronique et de Microtechnique
      • Centre Suisse d’Electronique et de Microtechnique SA (CSEM)
      Neuenburg, Neuchâtel, Switzerland
  • 2012
    • Universität Luzern
      Luzern, Lucerne, Switzerland
  • 2011
    • University of Western Macedonia
      • Department of Engineering Informatics and Telecommunications
      Kozani, West Macedonia, Greece
  • 1988–2010
    • Université de Neuchâtel
      • Laboratoire Temps-Fréquence (LTF)
      Neuenburg, Neuchâtel, Switzerland
  • 2006
    • The University of Tokyo
      Tōkyō, Japan
    • Hochschule Reutlingen
      Reutlingen, Baden-Württemberg, Germany
  • 2005
    • Intel
      Santa Clara, California, United States
    • Delft University of Technology
      Delft, South Holland, Netherlands
  • 2003
    • Tohoku University
      • Department of Nanomechanics
      Japan
  • 1999
    • Universität Basel
      Bâle, Basel-City, Switzerland
  • 1998
    • Sumitomo Heavy Industries, Ltd
      Edo, Tōkyō, Japan
  • 1996–1998
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 1989
    • University of Geneva
      • Faculty of Medicine
      Genève, Geneva, Switzerland
  • 1987
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1977–1980
    • Universiteit Twente
      • Department of Electrical Engineering
      Enschede, Overijssel, Netherlands