V. Lakafosis

Georgia Institute of Technology, Atlanta, GA, United States

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Publications (42)13.87 Total impact

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    ABSTRACT: An innovative wearable, partially self-powered, health monitoring and indoor localization shoe-mounted sen-sor module is presented. The system's novel shoe sole serves the double role of (i) medical-grade temperature probe for human body monitoring and (ii) renewable energy scavenger, which transforms the human motion to electrical energy. Mounted on the shoe is also an NFC reader for proximity-based localization purposes. An Adidas TM -logo-shaped dual-band communication antenna is fabricated that exhibits great performance despite the close proximity to the high lossy human body. The proposed platform can be extended to other sensors applications, for example by embedding into the sole normal and/or shear force sensors in order to monitor the sport performances of the athletes as well as to improve the rehabilitation techniques.
    Wireless and Sensor Networks (WiSNet) 2013, Austin, TX; 01/2013
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    ABSTRACT: In this paper, we present various novel techniques for the performance enhancement of nanotechnology-enabled wireless platforms utilizing inkjet-printed carbon-based thin films, especially for gas sensing applications. The key advancements include surface modification techniques to drastically reduce film thickness (from micron to nm) and a unique in-house developed nano-patterning process to increase porosity of the thin film resulting in increased surface contact area with gas. We have improved the performance by nearly one order of magnitude (a factor of around 10), increasing the sensitivity to 4.8% at 60 ppm, compared to previously reported results (6% sensitivity after exposure to 500 ppm NH3). We also propose a novel technique for carbon-based material growth on top of pre-printed patterns. The proposed graphene-based thin film approach could set the foundation for a plethora of novel wireless sensing and gas-reconfigurable communication platforms.
    Microwave Conference (EuMC), 2013 European; 01/2013
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    ABSTRACT: Inkjet-printing is a very promising technology for the development of microwave circuits and components. Inkjet-printing technology of conductive silver nanoparticles on an organic flexible paper substrate is introduced in this study. The paper substrate is characterised using the T-resonator method. A variety of microwave passive and active devices, as well as complete circuits inkjet-printed on paper substrates are introduced. This work includes inkjet-printed artificial magnetic conductor structures, a substrate integrated waveguide, solar-powered beacon oscillator for wireless power transfer and localisation, energy harvesting circuits and nanocarbon-based gas-sensing materials such as carbon nanotubes and graphene. This study presents an overview of recent advances of inkjet-printed electronics on paper substrate.
    IET Microwaves Antennas & Propagation 01/2013; 7(10):858-868. · 0.84 Impact Factor
  • Microwave Journal 02/2012; · 0.17 Impact Factor
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    ABSTRACT: Remote Frequency identification (RFID) enables both the realization of very low-cost integration platforms with multifunctional capabilities and the implementation of low-power wireless communications. Common photo paper is investigated in this paper as the first “green” ultra-low-cost organic substrate, on which the RFID tag circuitry and antenna are inkjet-printed with conductive silver nano-particle ink. Fully integrated, RFID-enabled modules on paper are demonstrated for a wide range of wireless sensing and anti-counterfeiting applications. These paper-based devices could potentially set the foundation for the truly convergent wireless sensor ad-hoc networks of the future.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
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    ABSTRACT: In this paper we demonstrate the design and development of a family of low-cost, self-powered, wireless sensor solutions utilizing both analog and digital principles. The sensors will utilize Graphene-based thin films integrated directly into the structure. For an immediately deployable digital sensing solution compatible with current commercial technologies we will utilize the Intel WISP platform, which can be read with current COTS products. Our thin films are produced from water-based, inkjet printed graphene oxide (GO) on paper/Kapton, developed using both conventional thermal and laser reduction techniques. In addition to reporting the first ever integration of inkjet-printed water soluble GO inks into low cost, flexible RF electronics, we also bring gas sensing capabilities to RFID tags relying on purely wireless digital transmission. The introduction of low cost, mass producible, eco-friendly, reduced graphene oxide (RGO) films on paper substrates lays the foundation for the development of a wide range of new low-cost, high performance Graphene-based electronic devices.
    Sensors, 2012 IEEE; 01/2012
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    ABSTRACT: In this research, folded patch antennas are investigated as low-cost and wireless smart-skin sensors that monitor the strain and crack in metallic structures. A radio frequency identification (RFID) chip is used for signal modulation. When the antenna is under strain/deformation, its resonance frequency varies accordingly. The variation can be easily interrogated and recorded by a reader that wirelessly delivers power for the antenna operation. Therefore, the antenna sensor can measure strain/crack. This paper reports latest test results on the strain and crack sensing performance of the antenna. In particular, tensile tests show that the wireless antenna sensor can detect small strain changes lower than 20 με, and can perform well at large strains higher than 10,000 με. In the crack test, a growing sub-millimeter crack is successfully detected by the antenna sensor.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
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    ABSTRACT: This paper will discuss recent advances in state-of-the-art inkjet printing of novel materials for wireless sensing applications. The work includes development of a prototype sensor based on high performance inkjet printed graphene thin films. The thin films were fabricated from direct write of environmentally friendly, water soluble graphene oxide (GO) inks, which were then reduced to obtain the final film. The resulting sensor demonstrates excellent sensitivity compared to existing thin films, along with remarkable recovery time at room temperature without the use of high temperature or UV treatments as reported in literature. In a response to ammonia gas (NH3), we observed a 6% change in normalized resistance after an exposure to 500 ppm of NH3. In addition, over 30% of material restoration is observed within five minutes in ambient conditions.
    Electromagnetics in Advanced Applications (ICEAA), 2012 International Conference on; 01/2012
  • Taoran Le, Vasileios Lakafosis, Ziyin Lin, C. P. Wong, M. M. Tentzeris
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    ABSTRACT: In this paper we demonstrate the use of graphene as the basis for design and development of low-cost, self-powered, battery-less, wireless sensor solutions utilizing thin films produced from environmentally friendly, water-based, inkjet printed graphene oxide (GO) ink. The in-house developed novel sensor material demonstrates good response to ammonia gas (NH3), yielding a 6% normalized resistance change within 15 minutes of exposure to a concentration of 500 ppm. In addition, excellent recovery time is achieved using the RGO thin films, with over 30% of material recovery observed within 5 minutes without exposure to high temperature or any UV treatments. Finally, we present in this work important distinctive characteristics in the behavior of the RGO sensor when exposed to different types of gases, including the hard-to-detect CO gas, that can be exploited in order to further enhance the applicability of the material. The introduction of mass producible, stable, environmentally friendly, inkjet-printable GO on organic paper/kapton substrates lays the foundation for the development of a wide range of new low-cost, high performance graphene-based devices, such as inkjet-printed diodes, capacitors and transistors.
    Proceedings - Electronic Components and Technology Conference 01/2012;
  • Taoran Le, Vasileios Lakafosis, Ziyin Lin, C. P. Wong, M. M. Tentzeris
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    ABSTRACT: In this paper we demonstrate the design and development of a low-cost, self-powered, wireless sensor solution based on the WISP platform and utilizing thin films produced from environmentally friendly, water-based, inkjet printed graphene oxide (GO) ink. The sensor demonstrates good response to ammonia gas (NH3), yielding a 6% normalized resistance change within 15 minutes after exposure to a concentration of 500 ppm. In addition, excellent recovery time is achieved using the graphene thin films, with over 30% of material recovery observed within 5 minutes without exposure to high temperature or any UV treatments. In addition to reporting the first ever integration of inkjet-printed water soluble GO inks into low cost RF electronics fabricated on flexible substrates, we also bring gas sensing capabilities to RFID tags relying on purely wireless digital transmission of the sensed information. The introduction of mass producible, stable, environmentally friendly, inkjet printable GO on organic paper/Kapton substrates lays the foundation for the development of a wide range of new low-cost, high performance graphene-based devices, such as inkjet-printed diodes, capacitors and transistors.
    01/2012;
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    ABSTRACT: Real-time and distributed sensing of large amounts of data, environmental, social or other, collected by very small and low-cost sensors is becoming a critical feature in more and more applications. In this paper, we are demonstrating with our developed prototypes that it is possible to deploy Wireless Sensor Network (WSN) nodes in-between prototype sensors and the Internet gateways. As a proof of concept, sensors in location tracking, health monitoring and secure identity verification applications are enhanced with essential WSN features. These sensing devices can be considered as some of the first Internet-of-Things nodes that bring the ubiquitous cognition vision closer and closer.
    01/2012;
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    ABSTRACT: Maximizing the Radio Frequency IDentification (RFID) performance is one of the main challenges for a wide variety of applications, where the overall throughput can be significantly affected by undesired Tag-Tag collision events. The UHF EPC Class-1 Generation-2 (Gen2) protocol only specifies algorithms to avoid the collisions but makes no provision for their resolution. In this paper, performance enhancement of the RFID EPC Gen2 protocol exploiting Tag collision recovery is demonstrated, for the first time, in real time with measurements. Two simple and effective approaches to handle successful Tag acknowledgments of recovered collided packets are proposed and implemented on a software-defined Reader and programmable Tags. The overall throughput per time slot is increased by 72% over the standard Gen2 MAC scheme. The validity of such result is confirmed by the good agreement with simulations reported in the literature.
    Wireless Communication Systems (ISWCS), 2012 International Symposium on; 01/2012
  • 01/2012;
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    ABSTRACT: Maximizing the identification speed of Radio Frequency Identification (RFID) tagged items is one of the main challenges in the area than can bring significant benefits to a vast array of applications. The dominating UHF EPC Gen2 protocol only specifies collision avoidance algorithms and, although collision recovery techniques have been investigated by researchers in the past, no attempt has been made to leverage the application of such techniques with minor modifications to the RFID protocol and, hence, realistically improve its performance. In this paper, we show that a significant reduction of 26% in the inventory time with collision recovery is feasible in real time relying, for the first time, on actual measurements taken with a software-defined RFID Reader and off-the-shelf programmable Tags. Among the numerous applications that can benefit from an increased reliable RFID reading rate, we are highlighting the advantages of deploying our working prototype testbed in moving conveyor belt systems. In brief, we achieve a 26% belt speed increase maintaining the exact same reading reliability and up to 84% of RFID Reader power consumption savings.
    Microwave Symposium Digest (MTT), 2012 IEEE MTT-S International; 01/2012
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    ABSTRACT: This paper introduces antenna-based “smart skin” sensors that are integrated with RFIDs for wireless sensor networks. Furthermore, the paper shows wireless energy harvesting capabilities to enable battery-less, or sustainable, wireless sensor networks with “smart skin” sensor nodes. These sensors are highly applicable for industrial applications: carbon-nanotube-based gas sensor, pressure sensor, and strain sensor. The low-profile, flexible sensors can be attached to surfaces as a “smart skin” with various sensing capabilities. These antenna-based sensors have the unique property of having a dual function of sensing and communication within a single device, which thereby enables RFID functionality to be integrated. Utilizing wireless sensor networking, it is possible to increase range and area of sensing. All prototypes have been designed, fabricated, and measured, the results of which show high sensitivity.
    01/2012;
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    ABSTRACT: In this talk, inkjet-printed flexible antennas, RF electronics and sensors fabricated on paper and other polymer (e.g. LCP)substrates are introduced as a system-level solution for ultra-low-cost mass production of UHF Radio Frequency Identification (RFID) Tags and Wireless Sensor Nodes (WSN) in an approach that could be easily extended to other microwave and wireless applications. The talk will cover examples from UHF up to the millimeter-wave frequency ranges. A compact inkjet-printed UHF "passive-RFID" antenna using the classic T-match approach and designed to match IC's complex impedance, is presented as a the first demonstrating prototype for this technology. Then, Prof. Tentzeris will briefly touch up the state-of-the-art area of fully-integrated wireless sensor modules on paper or flexible LCP and show the first ever 2D sensor integration with an RFID tag module on paper, as well as numerous 3D multilayer paper-based and LCP-based RF/microwave structures, that could potentially set the foundation for the truly convergent wireless sensor ad-hoc networks of the future with enhanced cognitive intelligence, anti-counterfeiting capabilities and "rugged" packaging. We will discuss issues concerning the power sources of "near-perpetual" RF modules, including flexible minaturized batteries as well as power-scavenging approaches involving thermal, EM, vibration and solar energy forms. The final step of the presentation will involve examples from wearable (e.g. biomonitoring) antennas and RF modules, as well as the first examples of the integration of inkjet-printed nanotechnology-based (e.g. CNT) sensors on paper and organic substrates. It has to be noted that the talk will review and present challenges for inkjet-printed organic active and nonlinear devices as well as future directions in the area of environmentally-friendly ("green") RF electronics and "smart-skin' conformal sensors.
    General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
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    ABSTRACT: The inadequacy of the traditional, digitally encoded RFID tags in combating counterfeiting prompts us to investigate new hardware-enabled technologies that can complement the remote identification functionality of typical RFIDs in an effective and very low cost way. In this paper, we present RFID-CoA; a system that aims to render typical RFID tags physically unique and hard to near-exactly replicate by complementing them with random 3D scattering structures, which serve as certificates of authenticity (CoA). The unique near-field response, or “fingerprint”, of the CoAs is extracted as a set of S<sub>21</sub> curves by our reader prototype, the design and development details of which are discussed. The results of our performance analysis show that the intersection probability of the false positive and false negative error probability curves is inconceivably small (<;10<sup>-200</sup>). The RFID-CoA tag's lifecycle from fabrication site to store is presented, and a strategy to block potential attacks is discussed. Our system bridges the world of RFID with a large array of anti-counterfeiting applications by exploiting “hardware-enabled”, modified-material scattering characteristics in the near-field. Based on our multifaceted analysis, we firmly believe that the demonstrated RFID-CoA technology can prove a valuable tool for the low-cost ubiquitous applicability of RFID technology against counterfeiting.
    RFID (RFID), 2011 IEEE International Conference on; 05/2011
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    ABSTRACT: Rendering typical RF identification (RFID) tags physically unique and hard to near-exactly replicate by complementing them with unique RF certificates of authenticity (RF-CoAs) can prove a valuable tool against counterfeiting. This paper introduces a new robust RFID system with enhanced hardware-enabled authentication and anticounterfeiting capabilities that relies on the near-field RF effects between a 5 × 5 antenna array and the uniquely modified substrate of the RF-CoAs. A microcontroller-enabled, low-power, and low-cost reader is used to accurately extract the near-field response (“RF fingerprint”) of the certificates meant to complement typical RFID tags in the 5-6-GHz frequency range. The RF characterization of all the reader's components, with an emphasis on the accuracy provided, has been performed. The state diagram of the fast and accurate reader operation is outlined. Rigorous performance and security test results are presented and verify the unique features of this technology.
    IEEE Transactions on Microwave Theory and Techniques 03/2011; · 2.23 Impact Factor
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    ABSTRACT: In this talk, inkjet-printed flexible antennas, RF electronics and sensors fabricated on paper and other polymer (e.g. LCP) substrates are introduced as a system-level solution for ultra-low-cost mass production of UHF Radio Frequency Identification (RFID) Tags and RFID-enabled Wireless Sensor Nodes (WSN's) in an approach that could be easily expanded to other microwave and wireless “cognition” applications. The talk will also touch up the state-of-the-art area of fully integrated wireless sensor modules on paper or LCP and demonstrate the 2D and the first ever 3D sensor integration in the form of module-on-paper, that could potentially set the foundation for the truly convergent wireless sensor ad-hoc networks of the future with enhanced cognitive intelligence and “rugged” packaging. Various examples encompassing temperature sensors, carbon-nanotube-enabled inkjet printed gas sensors and crack detection sensors will be covered in detail.
    Microwave Conference Proceedings (APMC), 2010 Asia-Pacific; 01/2011
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    ABSTRACT: In this paper, a novel power scavenging mote to harness wireless power in the UHF frequencies between 470 and 570 MHz is presented. A broadband monopole antenna prototype inkjet printed on a paper based substrate is used transduce the incident wireless power from its Electromagnetic wave form to a RF AC signal. A conjugately matched voltage multiplier and RF transformer are used to rectify and store the RF input power in a low leakage capacitor for powering on a microcontroller unit and wireless transceiver end-device thereby making the entire operation of this mote battery-less.
    01/2011;