A. K. Skrivervik

École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland

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Publications (202)68.14 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We propose an autonomous battery-less wireless sensor node that combines on a single printed circuit board an ultra-wideband (UWB) transmitter and its printed antenna, together with a piezoelectric cantilever and a solar cell array to harvest vibrations and light energy, respectively. The co-design of the solar cell array with the printed UWB antenna allows a prototype size of only 85 × 35 mm2, i.e., less than 65% of a credit card size. Low-cost is achieved by using inexpensive FR4 dual-layer substrate, standard-ceramic capacitors, and low-cost harvesters. The vibrational energy scavenger is fabricated at the wafer scale based on commercially available bulk polycrystalline Lead Zirconate Titanate (PZT), and the solar cells are fabricated by depositing amorphous-Si on 0.5 mm thick glass substrate. The cold-startup time of the demonstrator is about 42 min under indoor-ambient light conditions, and about 34 min under 700 mg vibrations at a frequency of 100 Hz. Once started, the sensor requires only 12.6 μW to allow a transmission rate of one temperature sensor readout every 34 s, thanks to the UWB transmitter that consumes only 206 pJ per pulse and a custom protocol with a reduced overhead.
    No preview · Article · Jan 2016 · Sensors and Actuators A Physical
  • Anja K. Skrivervik · Antonio Alves Moreira · Mohsen Koohestani
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    ABSTRACT: This study reports an experimental study of the system fidelity factor (SFF) of ultra-wideband wireless body area network antennas in an on-body environment. This study also investigates the influence in the SFF because of the antenna polarisation with respect to the body. For this purpose, two antennas having different polarisations are compared: a mono-cone antenna with the polarisation perpendicular to the wearer and a printed monopole with the polarisation either parallel or perpendicular to the wearer. A phantom made of pork meat was considered as a model for the wearer's body, and five different communication scenarios involving each pair of antennas were considered. On-body experimental results show that the time-domain behaviour of the transmission is better for two different antenna types having the same polarisation, but, more importantly, that the SFF (and thus the time-domain fidelity of the signal) is better for a link having a polarisation perpendicular to the body.
    No preview · Article · Apr 2015 · IET Microwaves Antennas & Propagation
  • Mohsen Koohestani · Ahmed Hussain · Antonio A. Moreira · Anja K. Skrivervik
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    ABSTRACT: This paper presents an experimental investigation of diversity gain influenced by polarization and spatial diversity techniques in ultrawideband (UWB) radio technology. To this aim, two different coplanar-fed UWB diversity antennas having the same size and employing identical monopoles were taken and both effective and apparent diversity gain were measured in a reverberation chamber. To extract the diversity gain, three commonly used approaches to combine diversity (i.e., selection, equal gain, and maximal ratio) have been considered. Results showed that >1 dB (~ 26 %) improvement in diversity gain is obtained over most of the considered band for polarization diversity case as compared with spatial case, showing the usefulness of polarization diversity for future UWB diversity applications.
    No preview · Article · Jan 2015
  • Marko Bosiljevac · Zvonimir Sipus · Anja K. Skrivervik
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    ABSTRACT: The Wireless Body Area Network (WBAN) has become an important part of the wireless communication world in the past decade leading to the need for efficient antennas for In-, On- and Off-Body links. The design of such antennas depends critically on the understanding of their interaction with the host body, and thus on the propagation of waves in inhomogeneous lossy media of finite dimensions. To this aim, we propose a simplified spherical multishell model of the lossy body, and study its interaction with elementary sources placed within or on the latter.
    No preview · Article · Jan 2015 · IEEE Antennas and Wireless Propagation Letters
  • Jovanche Trajkovikj · Anja K. Skrivervik
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    ABSTRACT: This letter presents a study on the Specific Absorption Rate (SAR) evaluation of UHF wearable antennas. A Planar Inverted F Antenna (PIFA) intended to operate in Wireless Body Area Networks (W-BAN) is taken as an example for the investigation. The presence of the ground plane introduces isolation between the body and the wearable antenna and decouples the antenna from the body, thus resulting in lower SAR values. The performed analysis of the proposed PIFA antenna indicate increased near-field regions close to the shorting wall, which directly leads to increased SAR values. This can be avoided if alternative current paths are provided, e.g. extending the ground plane slightly. The dielectric materials used as substrates partially reduce the SAR by confining part of the fields inside the dielectric. All the suggested solutions are easily applicable for a practical implementation.
    No preview · Article · Dec 2014 · IEEE Antennas and Wireless Propagation Letters
  • Source
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    ABSTRACT: We present our studies on a compact high-performance continuous wave (CW) double-resonance (DR) rubidium frequency standard in view of future portable applications. Our clock exhibits a short-term stability of 1.4 × 10(-13) τ(-1/2), consistent with the short-term noise budget for an optimized DR signal. The metrological studies on the medium- to longterm stability of our Rb standard with measured stabilities are presented. The dependence of microwave power shift on light intensity, and the possibility to suppress the microwave power shift is demonstrated. The instabilities arising from the vapor cell geometric effect are evaluated, and are found to act on two different time scales (fast and slow stem effects). The resulting medium- to long-term stability limit is around 5.5 × 10(-14). Further required improvements, particularly focusing on medium- to long-term clock performance, are discussed.
    Full-text · Article · Nov 2014 · IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control
  • [Show abstract] [Hide abstract]
    ABSTRACT: This work presents performance of robust wearable antennas intended to operate in Wireless Body Area Networks (W-BAN) in UHF, TETRAPOL communication band, 380-400 MHz. We propose a Planar Inverted F Antenna (PIFA) as reliable antenna type for UHF W-BAN applications. In order to satisfy the robustness requirements of the UHF band, both from communication and mechanical aspect, a new technology for building these antennas was proposed. The antennas are built out of flexible conductive sheets encapsulated inside a silicone based elastomer, Polydimethylsiloxane (PDMS). The proposed antennas are resistive to washing, bending and perforating. From the communication point of view, opting for a PIFA antenna type we solve the problem of coupling to the wearer and thus improve the overall communication performance of the antenna. Several different tests and comparisons were performed in order to check the stability of the proposed antennas when they are placed on the wearer or left in a common everyday environ- ment, on the ground, table etc. S11 deviations are observed and compared with the commercially available wearable antennas. As a final check, the antennas were tested in the frame of an existing UHF TETRAPOL communication system. All the measurements were performed in a real university campus scenario, showing reliable and good performance of the proposed PIFA antennas.
    No preview · Conference Paper · Nov 2014
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    ABSTRACT: Nowadays mobile and battery-powered applications push the need for radically miniaturized and low-power frequency standards that surpass the stability achievable with quartz oscillators. For the miniaturization of double-resonance rubidium ( (^{87}) Rb) atomic clocks, the size reduction of the microwave cavity or resonator (MWR) to well below the wavelength of the atomic transition (6.835 GHz for (^{87}) Rb) is of high interest. Here, we present a novel miniaturized MWR, the (mu ) -LGR, for use in a miniature DR atomic clock and designed to apply a well-defined microwave field to a microfabricated Rb cell that provides the reference signal for the clock. This (mu ) -LGR consists of a loop-gap resonator-based cavity with very compact dimensions (<0.9 cm (^{3}) ). The (mu ) -LGR meets the requirements of the application and its fabrication and assembly can be performed using repeatable and low-cost techniques. The concept of the proposed device was proven through simulations, and prototypes were successfully tested. Experimental spectroscopic evaluation shows that the (mu ) -LGR is well-suited for use in an atomic clock. In particular, a clock short-term stability of (7times 10^{-12} tau ^{-1/2}) was measured, which is better than for other clocks using microfabricated cells and competitive with stabilities of compact Rb clocks using conventional glass-blown cells.
    No preview · Article · Sep 2014 · IEEE Sensors Journal
  • A. K. Skrivervik · D. D. Cara · J. Trajkovikj · J-F. Zurcher
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    ABSTRACT: A major issue in Wireless Body Area Networks (W-BAN) is the reliability of the transmission in all conditions, thus in all locations and positions of the wearer. One way to achieve this is to design communication systems as independent as possible to the presence of the wearer, and to use multiple antennas (diversity, MIMO) to overcome fading. Polarization diversity is a good candidate for W-BAN, as it allows for the design of compact antennas having potentially a good diversity gain. Ultra Wide Band (UWB) has proved to be good candidate for W-BAN, in the case where high data rates over short ranges are targeted. In order to achieve polarization diversity, both UWB antennas having a polarization orthogonal and parallel to the surface of the wearer are required. While the latter are easy to design, it is not obvious design low profile UWB antennas with a vertical polarization. Moreover and for both cases, the design of antenna elements coupling as little as possible to each other or to the wearer is a key issue to the final quality of the system. In this contribution, we present a low profile UWB antenna having a polarization orthogonal to the wearer, which inherently minimizes the coupling to the body.
    No preview · Conference Paper · Aug 2014
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    ABSTRACT: This work presents a novel technology for the fabrication of soft and flexible antennas that can be used for Wireless Body Area Networks (W-BAN). By using standard lab facilities we are proposing a technique on how to build robust antennas intended to work in a harsh environment. A silicon based elastomer Polydimethylsiloxane (PDMS) has been used as a substrate material while copper meshes are used as a conductive material. The initial fluid state of the PDMS allows several degrees of freedom during the fabrication process, both from the electric and mechanic point of view. The dielectric properties of the substrate are adjusted by loading the PDMS with inclusions having a permittivity lower/higher than the PDMS istelf. From the mechanic point of view, liquid PDMS allows the shaping of the antennas in custom prepared moulds, and provides a complete encapsulation of the conductive parts inside the substrate. Moreover, the final antenna prototype is completely sealed and encpasulated inside the PDMS. Several antenna prototypes have been built, measured and characterized. The built antennas are flexible and resistant to different external influences like dust, water or humidity. As a examples of environmental tests, the antennas were exposed to washing, bending and real body (environment) measurements.
    No preview · Conference Paper · Jul 2014
  • Mohsen Koohestani · Antonio A. Moreira · Anja K. Skrivervik
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    ABSTRACT: Since its introduction the fidelity concept has been used to evaluate the time behavior of UWB antennas. However, fidelity has been employed with different meanings. This paper clarifies the differences between fidelity factor, system fidelity factor, and fidelity factor of the system. A recently developed UWB antenna has been taken as a representative one to illustrate the differences among these concepts.
    No preview · Conference Paper · Jul 2014
  • Anja K. Skrivervik
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    ABSTRACT: W-BAN applications have been around since a long time, but have been experiencing a tremendous growth during the last decades. This results in the need of dedicated antennas, which are designed and optimized taking into account their lossy surroundings. Design considerations and several examples will be presented in this paper.
    No preview · Conference Paper · May 2014
  • Anja K. Skrivervik
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    ABSTRACT: This contribution starts with a short overview on classic Integral Equation techniques for the analysis of periodic structures. Then, an efficient iterative procedure will be presented for periodic and quasi periodic structures.
    No preview · Conference Paper · Apr 2014
  • Mohsen Koohestani · Antonio A. Moreira · Anja K. Skrivervik
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    ABSTRACT: This paper reports a study of the feeding structure influence on impedance matching and system fidelity factor of two loaded UWB antennas when placed near a human arm. To this aim, two identical dielectric loaded versions of the same UWB antenna designs with different feeding structures, CPW-and microstrip (MS)-fed, were studied and placed 3 mm away from a human arm. Results of the considered antennas show that, in body proximity scenarios, the CPW-fed antenna detunes ∼39% less than the MS-fed. Moreover, the feeding structure has minimal effect on pulse distortion with a 2% and 0.4% average system fidelity factor deviation from CPW- to MS-fed in free space and in arm proximity, respectively. Furthermore, the system fidelity factor near the arm is almost unchanged when compared to free-space with an average deviation of 1.5% and 0.2% for CPW- and MS-fed antennas, respectively.
    No preview · Conference Paper · Apr 2014
  • Source
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    ABSTRACT: This paper proposes a novel, low-profile UWB antenna for wireless body area network (WBAN) applications. The antenna has a polarization perpendicular to the body-free-space interface, which is interesting in order to minimize the coupling into the body. Its structure comprises a modified mono-cone with a top-cross-plate and is coaxially fed through the ground plane. The higher frequency band |S11| performance is due to the mono-cone while the top-cross-plate is responsible for the lower frequency band. This plate also leads to a height reduction when compared to conventional mono-cone antennas. A comprehensive parametric study is done to provide design guidelines. Both frequency- and time-domain results have been measured and presented to validate the design. Results show that the antenna operates from 3.06 to beyond 12 GHz based on |S11| ≤ -10 dB, radiates omni-directionally in the H-plane, and has a radiation efficiency over 95%. The system-fidelity factor for UWB signals is adequate for pulse transmission. Finally, the influence of the human proximity on the antenna matching was tested. Results show that its impedance is nearly unchanged as compared to free-space.
    Preview · Article · Mar 2014 · IEEE Transactions on Antennas and Propagation
  • [Show abstract] [Hide abstract]
    ABSTRACT: A new compact coplanar-fed antenna suitable for polarization diversity in ultrawideband (UWB) applications is presented. The antenna consists of two identical monopoles that are printed on a low-loss substrate with 3 mm spacing and positioned perpendicular to each other. Both frequency- and time-domain results have been measured and presented to validate the design. Results show that the proposed antenna has not only ultra-wide bandwidth ( ${sim}115hbox{%}$ for port 1 and ${sim}107hbox{%}$ for port 2), but also good port isolation above 22 dB over the entire band of interest. Moreover, radiation patterns demonstrate good orthogonal polarization operation. Furthermore, the system fidelity factor is adequate for pulse transmission with averages of 85% and 75% for port 1 and 2, respectively. Finally, the envelope correlation coefficient $(rho_{e})$ has been calculated to evaluate the diversity performance. Results indicate that $rho_{e} leq {-}$20 dB across the ultra-wide bandwidth. These results show the suitability of the proposed antenna for future UWB diversity applications.
    No preview · Article · Jan 2014 · IEEE Antennas and Wireless Propagation Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present our studies on a compact high-performance continuous wave (CW) double-resonance (DR) rubidium frequency standard in view of future portable applications. Our clock exhibits a short-term stability of 1.4 x 10(-13) tau(-1/2), consistent with the short-term noise budget for an optimized DR signal. The metrological studies on the medium- to long-term stability of our Rb standard with measured stabilities are presented. The dependence of microwave power shift on light intensity, and the possibility to suppress the microwave power shift is demonstrated. The instabilities arising from the vapor cell geometric effect are evaluated, and are found to act on two different time scales (fast and slow stem effects). The resulting medium-to long-term stability limit is around 5.5 x 10(-14). Further required improvements, particularly focusing on medium-to long-term clock performance, are discussed.
    No preview · Article · Jan 2014
  • Mohsen Koohestani · Nuno Pires · Anja K. Skrivervik · Antonio A. Moreira
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    ABSTRACT: ABSTRACTA dielectric sandwich loading technique is proposed to enhance impedance matching bandwidth of an antenna when it is placed close to the human body. This technique mitigates the body influence by confining the reactive fields in the dielectric loads. This has no side effects on the antenna performance. Unloaded and loaded prototypes of a recently developed UWB antenna have been measured both in free space and near a human arm. Free space results confirm that loading the antenna neither detune |S11| nor decrease efficiency. It was found that in a body proximity scenario, loading the antenna increases the impedance matching by 22% with respect to the unloaded antenna. These results show the suitability of this technique to design antennas for WBAN applications. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2965–2967, 2013
    No preview · Article · Dec 2013 · Microwave and Optical Technology Letters
  • Source
    Mohsen Koohestani · Nuno Pires · Anja K. Skrivervik · Antonio A. Moreira
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    ABSTRACT: This letter studies the frequency- and time-domain performance of a recently developed printed coplanar-fed ultrawideband (UWB) monopole antenna aiming at predicting its behavior close to a human arm. The input reflection coefficient (|S11|) and fidelity factor of the antenna were evaluated in free space and close to an arm. Simulations using three simplified arm models with different cross sections (flat, rectangular, and elliptical) were compared to measurements. All models include the relevant human tissue layers: skin, fat, muscle, and bone. It was found that an accurate model requires the inclusion of the tissues broadband dispersion characterization. Moreover, the skin layer has a major impact in |S11|, and a small effect on fidelity, while the models can be simplified by discarding the bone. Furthermore, the geometry of the models is less relevant than dispersion characterization. It has also been observed that using the simplified models with proper broadband tissues dispersion yields good performance predictions, and that the fidelity factor increases as the antenna gets closer to the arm.
    Preview · Article · Dec 2013 · IEEE Antennas and Wireless Propagation Letters
  • Jovanche Trajkovikj · Jean-Francois Zurcher · Anja K. Skrivervik
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    ABSTRACT: This paper describes a new technology for the realization of soft, flexible, and robust antennas intended to operate in a harsh environment. One of the main characteristics of the proposed technology is the ease of fabricating antennas in a simple lab environment. The method is based on the use of a silicon-based elastomer, polydimethylsiloxane (PDMS), for the substrate material, and copper meshes or any kind of perforated metal plates as flexible conductive materials. The initial liquid state of the PDMS allows a lot of freedom in the fabrication process, both from the electrical and mechanical points of view. The electrical and mechanical properties of the substrate can be adjusted by loading the PDMS with inclusions having low or high permittivity and/or density, thus controlling the permittivity and the rigidity. Another good characteristic of the initial low viscosity of PDMS is the possibility of shaping the antennas and substrates in in-house fabricated moulds. Copper meshes or perforated metal structures enable good adhesion between the substrate and 288 IEEE Antennas and Propagation Magazine, Vol. 55, No. 5, October 2013 conductor, and improve the overall flexibility. Measured results showed good repeatability of the substrate samples, both with or without inclusions. To demonstrate the versatility of the proposed technique, several antenna prototypes were built and characterized. All the antennas were flexible and showed good radiation characteristics. The antennas were exposed to tests such as washing and bending, in order to assess their robustness to environmental changes.
    No preview · Article · Oct 2013 · IEEE Antennas and Propagation Magazine

Publication Stats

1k Citations
68.14 Total Impact Points

Institutions

  • 1989-2016
    • École Polytechnique Fédérale de Lausanne
      • Electromagnetics and Acoustics Laboratory
      Lausanne, Vaud, Switzerland
  • 2013
    • Université de Rennes 1
      Roazhon, Brittany, France
  • 2007
    • Centre Suisse d'Electronique et de Microtechnique
      Neuenburg, Neuchâtel, Switzerland
  • 1997
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland