About

Sun Young Lee is an Associate Professor in the Department of Communication at the University of Maryland and serves as Co-Director of Graduate Studies for enrolled students. She earned her Ph.D. in journalism and mass communication from the University of North Carolina, Chapel Hill in 2012. Her research interests include visual strategies in corporate social responsibility (CSR) messages, strategies to engage the public with CSR activities, and the effects of CSR practices in crisis contexts. Her work has been published in journals such as the Journal of Business Ethics, Communication Research, and Public Relations Review. Lee’s current projects focus on the role of emotions and public empowerment in the co-creation of social value through CSR activities. Prior to her position at Maryland, she was on the faculty at Texas Tech University. Her research explores how organizations can develop and implement CSR and creating shared value (CSV) initiatives, with case studies including Yuhan-Kimberly’s response to Korea’s aging society. She also investigates visual framing in disaster relief social media, consumer engagement in CSR campaigns, and the effectiveness of advertising imagery, contributing to both theoretical understanding and practical applications in strategic communication and corporate social advocacy.

Research topics

• Physics
• Optics
• Materials science
• Optoelectronics
• Astrophysics

Selected publications

• Green's Function Analysis of Spatially Discrete Traveling-Wave Modulated (Parametric) Loop Networks

  2025-06-15

  article

  This paper explores the analysis and design of spatially discrete traveling-wave modulated (SDTWM) loop networks, which are commonly used to achieve parametric effects and functionalities such as nonreciprocal propagation. We present an efficient method for analyzing the spatial Green's function of SDTWM loop networks using the Interpath Relation (a space-time boundary condition) and modal analysis. The method is applied to design a non-magnetic circulator, demonstrating enhanced performance, twice the fractional bandwidth, and a 2 dB improvement in insertion loss over a previous design in literature. The study highlights the versatility of SDTWM in creating compact, cost-efficient, and high-performance nonreciprocal devices and offers insights into their design.

  PublisherDOI

• Characterization and Modeling of Varactor Diodes for Parametric Circuits

  IEEE Microwave Magazine · 2025-08-06 · 1 citations

  articleSenior author

  Hyperabrupt-junction varactor diodes, for which dopant concentration decreases with distance from the p-n junction, possess favorable characteristics in time-varying systems. These diodes can exhibit a more linear relationship between reverse-bias voltage and capacitance than their abrupt-junction and linear-junction counterparts. This feature makes them attractive for parametrically time-varying circuits when low distortion is desired. However, hyperabrupt-junction diodes are inadequately represented by standard reverse-bias diode models, which were developed primarily for abrupt and linear-junction diodes. We propose a modified diode model that uses a voltage-dependent grading coefficient to more accurately reproduce the junction capacitance over a wide range of bias voltage. Using experimentally extracted junction capacitance from ten commercially available varactor diodes, we demonstrate the improved performance of the proposed Polynomial Grading Coefficient model compared to the conventional SPICE model with a constant grading coefficient. A sample implementation of the proposed diode model is presented using a Symbolically Defined Device for use within the commercial circuit solver Keysight ADS.

  PublisherDOI

• Modal and Driven Solutions to Spatially-Discrete Traveling-Wave Modulated Networks

  2025-03-18

  preprintOpen access

  Spatially discrete traveling wave modulated (SDTWM) networks are a class of parametric circuits in which a circuit or material parameter in adjacent, discrete unit cells is staggered by a constant time delay. Like continuous traveling-wave modulated structures, SDTWM networks can exhibit a wide range of phenomena, including frequency conversion, parametric amplification, and non-reciprocity. Here, we present a method for efficiently simulating finite SDTWM electrical networks using the Interpath Relation: a space-time boundary condition governing N-path networks. First, we present the concept of a multi-harmonic Bloch impedance derived from a generalized eigenvalue problem for infinite SDTWM networks. Subsequently, we introduce solutions to SDTWM networks driven by a phased array of sources. Finally, we show how to analyze SDTWM networks driven by a single source using two different analytical approaches: Analytic Array Scanning (AAS) and Eigenmode Decomposition (EMD). To demonstrate the utility of the methods, non-reciprocal and frequency-converting devices are analyzed and designed. The Interpath Relation allows the proposed methods to analyze only a single unit cell, which significantly reduces computational time.

  PublisherOA PDFDOI

• Increasing the Efficiency-Bandwidth Product and Impedance Bandwidth of Electrically-Small Antennas Through Parametric Space-Time Variation

  2024-03-17 · 1 citations

  article

  A method for improving the efficiency-bandwidth product of electrically-small antennas (ESAs) through space-time variation is reported. By coupling radiative and non-radiative modes of the ESA using spatially-discrete traveling wave modulation (SDTWM), the time-varying antenna is made to radiate efficiently over an operating band that is 4.5 times larger than its LTI counterpart. Judicious choice of the modulation parameters allows this bandwidth enhancement to be obtained while keeping the reflected power more than 10 dB below the incident power.

  PublisherDOI

• Spatio-Temporal Modulation of Multimode Electrically-Small Antennas for Efficiency-Bandwidth Enhancement

  2024-07-14

  article

  Electrically-small antennas (ESAs) have known limits on their resonant bandwidth, which constrains the information rate that can be transmitted or received through them (C. Pfeiffer and B. I. Wu, “On the Max-imum Communication Data Rate of Resonant Antennas,” IEEE Trans. Commun., vol. 71, issue 3, March 2023). The bandwidth of a singly-resonant ESA is inversely related to its quality factor, and while this is not strictly true for multi-resonant antennas, their matched bandwidths are ultimately constrained by the Bode-Fano bound on passive impedance matching (R. M. Fano, “Theoretical Limitations on the Broadband Matching of Arbitrary Impedances,” J. Frank. Inst., vol. 249, issue 1, 1950). Since the Bode-Fano bound as-sumes linearity and time invariance, it can be surpassed using active elements (as in non-Foster approaches) or parametric time variation. Here, we report an ESA with spatio-temporally-modulated capacitive elements that shows a 5.5x improvement in the efficiency-bandwidth product compared to a time-invariant antenna of the same size and shape. The spatially-discrete traveling-wave modulation couples radiative and non-radiative modes of the ESA, which avoids the need for external idler resonators while suppressing radiation of spurious harmonics.

  PublisherDOI

• Space–Time Modulation of a Multimode Electrically Small Antenna for Increased Matching and Efficiency Bandwidths

  IEEE Transactions on Antennas and Propagation · 2024-12-09 · 2 citations

  article

  In this work, a method for increasing the efficiency-bandwidth product of an electrically small antenna (ESA) by using spatially discrete traveling-wave modulation (SDTWM) is introduced. This method applies generally to electrically small antennas possessing N-fold rotational symmetry. To illustrate the method, it is applied to a top-hat loaded monopole antenna that supports a fundamental radiating mode as well as non-radiating modes that are analogous to discrete orbital angular momentum (OAM) modes. Time-modulated capacitors, placed in each sector, couple these modes using SDTWM. The modulation scheme is similar to that of a classic negative-resistance parametric amplifier, but instead of using the modulation to obtain gain from the system, the modulation parameters are chosen to enhance the matching bandwidth of the antenna. We show how this can be done by choosing an appropriate combination of the modulation depth and modulation frequency. After extending the definition of radiation efficiency and mismatch loss to the case of a parametrically time-varying antenna, the extended definitions are used to characterize the simulated performance of the time-varying antenna under two different SDTWM modulation schemes. The first modulation scheme couples the radiative mode to a single non-radiative mode, while the second modulation scheme couples the radiative mode to two different non-radiative modes. Both schemes yield efficiency-bandwidth products that are 6.4–7.6 dB larger than that of the time-invariant version of the antenna.

  PublisherDOI

• Characterization and Modeling of Varactor Diodes for Parametric Circuits

  2024-10-07 · 1 citations

  preprintOpen accessSenior author

  Hyperabrupt-junction varactor diodes, for which dopant concentration decreases with distance from the PN junction, possess favorable characteristics in time-varying systems. These diodes can exhibit a more linear relationship between reverse-bias voltage and junction capacitance than their abruptjunction and linear-junction counterparts. This feature makes them attractive for parametrically time-varying circuits when low distortion is desired. However, hyperabrupt-junction diodes are inadequately represented by standard reverse-bias diode models, which were developed primarily for abrupt and linear-junction diodes. We propose a modified diode model that uses a voltagedependent grading coefficient to more accurately reproduce the junction capacitance over a wide range of bias voltage. Using experimentally extracted junction capacitance from ten commercially available varactor diodes, we demonstrate the improved performance of the proposed Polynomial Grading Coefficient (PGC) model compared to the conventional SPICE model with a constant grading coefficient. A sample implementation of the proposed diode model is presented using a Symbolically Defined Device for use within the commercial circuit solver Keysight ADS.

  PublisherOA PDFDOI

• Nanoscale architecture for frequency-resolving single-photon detectors

  Communications Physics · 2023-04-15 · 3 citations

  articleOpen access1st authorCorresponding

  Abstract Single photon detectors play a key role across several basic science and technology applications. While progress has been made in improving performance, single photon detectors that can maintain high performance while also resolving the photon frequency are still lacking. By means of quantum simulations, we show that nanoscale elements cooperatively interacting with the photon field in a photodetector architecture allow to simultaneously achieve high efficiency, low jitter, and high frequency resolution. We discuss how such cooperative interactions are essential to reach this performance regime, analyzing the factors that impact performance and trade-offs between metrics. We illustrate the potential performance for frequency resolution over a 1 eV bandwidth in the visible range, indicating near perfect detection efficiency, jitter of a few hundred femtoseconds, and frequency resolution of tens of meV. Finally, a potential physical realization of such an architecture is presented based on carbon nanotubes functionalized with quantum dots.

  PublisherOA PDFDOI

• Increasing the Efficiency-Bandwidth of Small Antennas by Coupling Radiative and Non-Radiative Modes Using Time-Variation

  2023-01-10 · 2 citations

  article

  Time-variation is one possible method that may be used to contravene the Chu limit, which constrains the bandwidth of electrically-small antennas. Here, insights gained from the analysis of parametric circuits are applied to the design of a time-varying antenna in such a way that the antenna exhibits an increased efficiency-bandwidth product over the matched linear time-invariant (LTI) benchmark antenna. Both the time-varying antenna and the benchmark LTI antenna are a sectored version of the common top-hat loaded monopole antenna. The methods demonstrated in this work rely upon coupling radiative (bright) modes of the antenna to poorly radiating (dark) modes of the antenna through spatio-temporal modulation. By confining intermediary frequencies from the parametric processes in the dark modes, their radiation is suppressed.

  PublisherDOI

• Global Localization of Energy-Constrained Miniature RF Emitters using Low Earth Orbit Satellites

  2023-11-12 · 2 citations

  article

  Daily tracking of small objects or animals anywhere on earth for long time-periods is a long sought-after goal. Recently, the emergence of low earth orbit (LEO) satellites offers a unique pathway to achieve this goal. However, to date, LEO trackers have not achieved cm-size. While the integrated chip can be readily scaled to sub-cm size, the size of trackers remains limited by their battery and antenna size. To address these two fundamental size limiting factors, this paper presents a LEO satellite localization system that is specifically optimized to reduce antenna size and transmit power, thereby reducing battery size. To reduce power, a new cooperative waveform is designed which enhances the localization accuracy, combined with an increased packet length to enable low transmit power while maintaining packet energy. However, this long packet length introduces a intra-packet Doppler shift which we address by proposing a localization algorithm that includes a Doppler shift correction. The final result is a 50 kHz periodic BPSK signal with 23 dBm equivalent isotropic radiation power (EIRP), and 120 ms packet length (> 10 × longer than conventional), at a 60 s interval. The proposed solution enables 7 months operation on a 2.5 × 1.2 cm LiPo battery within a North American search area. To address the antenna size, the optimal transmit frequency was studied and a 1 cm loop antenna with 65% radiation efficiency was designed with internal matching to 50 Ohm. Using the proposed techniques, three satellite flyover experiments were performed to confirm the accuracy of the proposed tracking system and localization algorithms using a USRP-X310, a custom 1 cm-size antenna, and a commercial satellite cluster. The measured average localization error is 320 - 840 m depending on satellite trajectories, demonstrating an improved accuracy in real life measurements compared to prior art with experimental result while simultaneously achieving 15 -- 26 dB lower transmit power and > 3 × lower packet energy.

  PublisherDOI

Frequent coauthors

• Anthony Grbic

  University of Michigan–Ann Arbor

  26 shared

• J. S. Kaastra

  SRON Netherlands Institute for Space Research

  23 shared

• S. Geier

  19 shared

• J. S. Schimoia

  Universidade Federal de Santa Maria

  17 shared

• P. Uttley

  University of Amsterdam

  17 shared

• M. Vestergaard

  17 shared

• J. M. Gelbord

  Spectral Sciences (United States)

  17 shared

• E. Dalla Bontà

  17 shared

Labs

• Center for Political Communication & Civic LeadershipPI

Education

• Ph.D., Journalism and Mass Communication

  University of North Carolina

  2012