Sangwook Nam

Seoul National University, Sŏul, Seoul, South Korea

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Publications (183)156.95 Total impact

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    ABSTRACT: Implantable endovascular devices such as bare metal, drug eluting and bioresorbable stents have transformed interventional care by providing continuous structural and mechanical support to many peripheral, neural and coronary arteries affected by blockage. Although effective in achieving immediate restoration of blood flow, the long term re-endothelialisation and inflammations induced by mechanical stents are difficult to diagnose or treat. Here we present nanomaterial designs and integration strategies for the bioresorbable electronic stent with drug-infused functionalized nanoparticles to enable flow sensing, temperature monitoring, data storage, wireless power/data transmission, inflammation suppression, localized drug delivery, and hyperthermia therapy. In vivo and ex vivo animal experiments as well as in vitro cell studies demonstrate the previously unrecognized potential for bioresorbable electronic implants coupled with bioinert therapeutic nanoparticles in the endovascular system.
    ACS Nano 04/2015; 9(6). DOI:10.1021/acsnano.5b00651 · 12.88 Impact Factor
  • Dong-yeon Kim · Youngjoon Lim · Hee-Sung Yoon · Sangwook Nam
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    ABSTRACT: A W-band 8 × 8 slot array antenna is proposed and fabricated by electroforming for high-precision manufacturing. The external mutual coupling between radiating shunt slots is compensated for input impedance matching and a uniform held distribution. The overall antenna aperture area is 473.1 mm2 with slot spacings of 2.8 and 2.64 mm in the transverse and longitudinal direction, respectively. The measured maximum gain is 26.8 dBi and the corresponding antenna efficiency is 81.9% at 94 GHz. The measured impedance bandwidth when the VSWR is less than 2.0 (-10 dB) is 8.3%, with a range from 89.9 to 97.6 GHz.
    IEEE Transactions on Antennas and Propagation 04/2015; 63(4):1854-1857. DOI:10.1109/TAP.2015.2398129 · 2.18 Impact Factor
  • IEEE Transactions on Microwave Theory and Techniques 01/2015; DOI:10.1109/TMTT.2015.2477343 · 2.24 Impact Factor
  • Sumin Yun · Dong-Yeon Kim · Sangwook Nam
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    ABSTRACT: A folded, cavity-backed crossed-slot antenna is proposed for antenna miniaturization. The cavity dimensions of a conventional cavity-backed crossed-slot antenna are about a half-guided-wavelength along each side, which is unsuitable in many applications like a handheld device or body area network (BAN). To reduce the size of the cavity, a folded cavity is proposed in this letter. The center plate that divides the cavity into the upper cavity and the lower cavity increases the effective length inside the cavity. Compared to the conventional cavity-backed crossed-slot antenna, a 72.8% size reduction can be achieved using the proposed structure. The proposed antenna also has circular polarization and wideband characteristics, which are the main advantages of a cavity-backed crossed-slot antenna. The proposed technique is especially useful for reducing the lateral dimensions of the cavity.
    IEEE Antennas and Wireless Propagation Letters 01/2015; 14:36-39. DOI:10.1109/LAWP.2014.2354517 · 1.58 Impact Factor
  • Youngjoon Lim · Sangwook Nam
    12/2014; 14(4):405-410. DOI:10.5515/JKIEES.2014.14.4.405
  • Jongmin Park · Sangwook Nam
    10/2014; 25(10):959-965. DOI:10.5515/KJKIEES.2014.25.10.959
  • H.-R. Ahn · Byungjoon Kim · Sangwook Nam
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    ABSTRACT: A compact UHF 3 dB power divider (PD) is presented. It consists of two identical asymmetric impedance transformers (MCCTs) and one isolation circuit with resistance and capacitance. The MCCT is composed of two different transmission-line sections and one open stub, and good frequency performance may be achieved by the combination of transmission-line sections and open stub. One PD is fabricated at a design center frequency of 500 MHz, of which total transmission-line sections are only 39.68$^{circ}$ long. The measured bandwidth with 15 dB return loss is about 68%.
    IEEE Microwave and Wireless Components Letters 07/2014; 24(7):445-447. DOI:10.1109/LMWC.2014.2316213 · 1.70 Impact Factor
  • Byungjoon Kim · Duksoo Kim · Sangwook Nam
    06/2014; 14(2):47-53. DOI:10.5515/JKIEES.2014.14.2.47
  • Kihyun Kim · Junghee Choi · Munkyo Seo · Sangwook Nam
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    ABSTRACT: A 500 MHz On-Off Keying (OOK) transmitter integrated with a high-efficiency wideband power amplifier (PA) is designed for low-power/high-data rate applications. The PA biased in Class C region, employs a bias current-reused and an RF current-combining structure to achieve a high-efficiency and high-data rate. The transmitter is fabricated using a 0.13 $mu$m CMOS process. The chip size is 0.6 mm$^{2}$ and the measured drain efficiency of the PA reaches 59.5% at 500 MHz with 1.62 dBm output power while consuming only 2.52 mW dc power from a 3 V power supply. The efficiency of the transmitter is 38.4% and the energy usage is 22 pJ/bit at a data rate of 100 Mbps with ${-}0.75$ dBm average output power.
    IEEE Microwave and Wireless Components Letters 06/2014; 24(6):424-426. DOI:10.1109/LMWC.2014.2310486 · 1.70 Impact Factor
  • Yoon Goo Kim · Sangwook Nam
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    ABSTRACT: A method is presented to analyze the maximum power transfer efficiency of a wireless power transfer system and its electromagnetic fields via spherical modes. The Z-parameter and Y-parameter for two coupled antennas are derived using the antenna scattering matrix and an addition theorem. In addition, formulas for calculating the maximum power transfer efficiency and optimum load impedance are presented. A formula is derived to calculate the electromagnetic field generated by a wireless power transfer system from the antenna scattering matrix.
    IEEE Transactions on Antennas and Propagation 06/2014; 62(6):3054-3063. DOI:10.1109/TAP.2014.2312419 · 2.18 Impact Factor
  • Junhyuk Choi · Byungjoon Kim · Duksoo Kim · Jaeyong Ko · Sangwook Nam
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    ABSTRACT: This paper presents a dual band CMOS power amplifier (PA) for an S/X band high resolution radar system. Reconfigurable band-switchable matching networks and a dual band Wilkinson power combiner (impedance transformer) are used for an output matching network. The PA is fabricated using a UMC 0.13 μm CMOS process. It provides a saturated output power of 24.8 dBm and 25.3 dBm with the power-added-efficiency (PAE) of 27.2 % and 36.4 % at 8.4 GHz and 3.0 GHz, respectively. The 3-dB bandwidth is 2.5 GHz (7.4-9.9 GHz) and 2.3 GHz (2.7-5.0 GHz). This amplifier achieves a fractional bandwidth of 29% and 60 % at each band, and shows suitable performance for use in a high resolution radar system.
    2014 IEEE Radio Frequency Integrated Circuits Symposium (RFIC); 06/2014
  • Byungjoon Kim · Sangwook Nam · Hee-Ran Ahn · Jae-Hoon Song
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    ABSTRACT: This letter proposes a wideband compact DC block design technique. This DC block has a wide pass-band and wide stop-band and transforms termination impedances. It comprises a pair of coupled lines on a defected ground structure (DGS) with capacitor loading. A periodic DGS pattern increases coupling, and, consequently, a wideband DC block design is allowed with a microstrip process on a high dielectric low height substrate. A DC block with equal termination impedances of 50 Ω and another that transforms 50 into 30 Ω are fabricated. The measured fractional bandwidths are 48% and 47%. The size of the DC block is 16.8× 15 mm2(0.057λ0× 0.051λ0).
    IEICE Transactions on Electronics 01/2014; E97.C(9):915-917. DOI:10.1587/transele.E97.C.915 · 0.28 Impact Factor
  • Dong-yeon Kim · Sangwook Nam
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    ABSTRACT: A sidelobe suppression method for a series slot array antenna which radiates 45 degrees-inclined linear polarization is proposed. Axial displacements are employed to create arbitrary excitation coefficients for individual centered-inclined radiating slots along the center line of a broad wall. To verify the proposed design method, we design two types of center-fed linear slot array antennas with a Dolph-Chebyshev distribution for -20 dB and -26 dB sidelobe levels (SLLs) in the Ka band. Furthermore, a cross-validation process involving an equivalent circuit model analysis and electromagnetic full-wave simulation using CSTM WS is utilized. The entire structure of the proposed series slot array antenna is fabricated on printed circuit boards ( PCBs), including drilling and chemical etching, to secure advantages of miniaturization and cost reduction. The measured realized gains are 15.17 and 15.95 dBi and SLLs are -18.7 and -22.5 dB respectively for two types of fabricated antennas. It demonstrates the validity of the proposed sidelobe suppression method.
    IEEE Transactions on Antennas and Propagation 11/2013; 61(11):5807-5812. DOI:10.1109/TAP.2013.2277711 · 2.18 Impact Factor
  • Hee-Ran Ahn · Sangwook Nam
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    ABSTRACT: A 3-dB power divider (PD) terminated in equal complex impedances is presented. It consists of two identical 90 ° transmission-line sections and an isolation circuit, being composed of resistance and capacitance, or resistance and inductance, depending on the termination impedances. If the termination impedance has capacitance, the isolation impedance should consist of inductance, and therefore, the isolation circuit should be implemented with a chip inductor. However, the chip inductor contains additional stray capacitance and resistance, which lead to undesired frequency performance. To avoid the usage of the chip inductors, even with arbitrary termination impedances, three design methods by adding transmission-line sections, adding open stubs, and adding short stubs are introduced. The PDs designed by the three methods can have not only desired isolation impedances, but also the total size of the PDs can be reduced. To verify the suggested theory, three PDs are measured. For one PD with adding transmission-line sections, the measured reflection coefficients at all ports are -43.29, -41.55, and -51.69 dB, the isolation is 56.7 dB, and the power division is -3.042 dB at a design center frequency of 1 GHz, which agree quite well with those predicted.
    IEEE Transactions on Microwave Theory and Techniques 11/2013; 61(11):3872-3883. DOI:10.1109/TMTT.2013.2281101 · 2.24 Impact Factor
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    Hyun-Jin Shim · Jong-Min Park · Sangwook Nam
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    ABSTRACT: The effective way of estimation and analysis of EMI(Electromagnetic Interference) in Wireless Power Transfer System operating at 13.56 MHz is proposed. In this paper methodology of driving magnetic field strength and electric loop current of two antennas which are in free space and on PEC plane using image theory and duality is proposed. Perfect electric conductor(PEC) is planar, infinite in extent, and perfectly conducting plane. And we will refer it as PEC plane. A equivalent circuit model is used to analyze. Using this theoretical analysis, we can derive maximum magnetic field strength of the far-field region numerically using measured data of near-field maximum magnetic field strength. The experimental results using commercial numerical simulation tool are in agreement with the theoretical results. Also, using the derivation of maximum magnetic field strength in the far-field region, we can easily estimate the maximum allowable power dissipation that meets EMI regulations.
    09/2013; 24(9). DOI:10.5515/KJKIEES.2013.24.9.873
  • Yoon Goo Kim · Sangwook Nam
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    ABSTRACT: A method to determine the generalized scattering matrix of an antenna using characteristic modes is presented. When the characteristic currents flowing at a feed point, the radiation patterns of the characteristic currents, and the eigenvalues are known, the generalized scattering matrix can be calculated. It is shown that an antenna whose behavior is dominated by a single characteristic mode becomes a minimum scattering antenna. The formula is verified using a two wavelength dipole antenna and a bow-tie antenna.
    IEEE Transactions on Antennas and Propagation 09/2013; 61(9):4848-4852. DOI:10.1109/TAP.2013.2269763 · 2.18 Impact Factor
  • Yoon Goo Kim · Sangwook Nam
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    ABSTRACT: The concept of a minimum-scattering antenna was introduced by Dicke more than 60 years ago, and Khan and Kurss redefined it. The theory of minimum-scattering antennas was considerably extended later. The minimum-scattering antenna is one which does not scatter electromagnetic fields when its feeding ports are terminated in a suitable set of reactances. Modeling an antenna as a minimum-scattering antenna simplifies antenna analysis. P. G. Rogers demonstrated that lossless antennas whose scattering behavior is dominated by a single characteristic mode can become minimum-scattering antennas (P. G. Rogers, IEEE Trans. Antennas Propag., vol. 34, no. 10, pp. 1223-1228, Oct. 1986). To the best of our knowledge, there is no literature that derives a condition where lossy antennas become minimum-scattering antennas. In this study, we investigate whether lossy antennas can become minimum-scattering antennas and determine a condition where antennas become minimum-scattering antennas.
    2013 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium); 07/2013
  • Hee-Ran Ahn · Sangwook Nam
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    ABSTRACT: Wideband coupled-line ring hybrids are presented for high power-division ratios. For this, an equivalent circuit to make the characteristic impedance of a transmission-line section lower is firstly investigated, based on a Π-type lumped-element equivalent circuits. Design formulas of four types of equivalent circuits (LΠ-, LT-, LS2-, and LS1-types) are then derived, and N is introduced for more design flexibility and wideband performance. The LS2-type with N=1 is composed of one transmission-line section and two identical series inductances at both ends, which cannot be used for the ring hybrids with the high power-division ratios. To avoid the problem, modified LS2-type (MLS2-type) with N is additionally suggested, and that with N=1 is intensively discussed. Using two of those, LS1-type with N=2 and MLS2-type with N=1, the coupled-line ring hybrids with 13- and 11-dB power-division ratios are fabricated. The measured results show good agreement with those predicted.
    IEEE Transactions on Microwave Theory and Techniques 05/2013; 61(5):1768-1780. DOI:10.1109/TMTT.2013.2251654 · 2.24 Impact Factor
  • Source
    Dong-Yeon Kim · Sangwook Nam
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    ABSTRACT: The 4 by 4 series slot sub-array antenna is proposed using substrate integrated waveguide(SIW) technology for 35 GHz of Ka band application. The proposed antenna is realized with multi-layered structure for compact size and easy integration features. 4 by 4 radiating slots are arrayed on top PCB with equal spacing and the feeding SIWs are arranged on middle and bottom PCBs for uniform power distribution. The multi-layered antenna is realized using RT/Duroid 5880 that has dielectric constant of 2.2 and the total antenna size is . The individual parts such as radiators and feeding networks are simulated using full-wave simulator CST MWS. Furthermore, the total sub-array antenna also fabricated and measured the electrical performances such as impedance bandwidth under the criteria of -10 dB(490 MHz), maximum gain(18.02 dBi), sidelobe level(SLL)(-11.0 dB), and cross polarization discrimination (XPD)(-20.16 dB).
    04/2013; 24(4). DOI:10.5515/KJKIEES.2013.24.4.365
  • Source
    Yoon Goo Kim · Jongmin Park · Sangwook Nam
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    ABSTRACT: We derive the Z-parameters for the two coupled antennas used for wireless power transfer under the assumption that the antennas are canonical minimum scattering antennas. Using the Z-parameter and the maximum power transfer efficiency formula, we determine the maximum power transfer efficiency of wireless power transfer systems. The results showed that the maximum power transfer efficiency increases as the mode number or the radiation efficiency increases. To verify the theory, we fabricate and measure two different power transfer systems: one comprises two antennas generating mode; the other comprises two antennas generating mode. When the distance between the centers of the antennas was 30 cm, the maximum power transfer efficiency of the antennas generating the mode increased by 62 % compared to that of the antennas generating the mode.
    03/2013; 13(1). DOI:10.5515/JKIEES.2013.13.1.38

Publication Stats

2k Citations
156.95 Total Impact Points


  • 1995–2015
    • Seoul National University
      • • Department of Electrical and Computer Engineering
      • • School of Electrical Engineering and Computer Sciences
      Sŏul, Seoul, South Korea
  • 2009
    • Sungkyunkwan University
      • College of Information and Communication Engineering (SoICE)
      Sŏul, Seoul, South Korea
  • 2008
    • Samsung Thales
      Sŏul, Seoul, South Korea
  • 2007
    • Chung-Ang University
      • School of Electrical and Electronics Engineering
      Sŏul, Seoul, South Korea
  • 2004
    • Chonbuk National University
      • Department of Electronic Engineering
      Seoul, Seoul, South Korea
  • 2003
    • Soon Chun Hyang University Hospital
      Sŏul, Seoul, South Korea
  • 2002
    • Electronics and Telecommunications Research Institute
      Sŏul, Seoul, South Korea
  • 2000–2002
    • Soonchunhyang University
      • Department of Electrical and Electronic Engineering
      Onyang, Chungcheongnam-do, South Korea
  • 1997
    • Institute For New Media
      Frankfurt, Hesse, Germany