Workshop/Tutorial Session

EunMi Choi is a professor in department of electrical engineering at Ulsan National Institute of Science and Technology (UNIST). She is currently leads the THz Vacuum Electronics and Applied Electromagnetics (TEE) laboratory as a principle investigator since 2010. Her main contribution in the field includes high power vacuum electronics development (gyrotrons, TWTs, etc) and its application for nuclear fusion plasma heating and current drive, remote detection of radioactive materials experimentally, and energy recirculating microfabricated vacuum electronics amplifier source development. Her current research interests span from development of electron beam based high power millimeter and THz sources, ultra-compact THz sources at 300 GHz and beyond by means of micro-fabrication techniques, orbital angular momentum (OAM) beams generation for communication system and exotic electromagnetic waves generation, to their possible applications in novel technique in remote detection of radioactive materials, and plasma interaction with exotic electromagnetic waves.

High-power microwave (HPM) sources based on relativistic electron beams remain essential platforms for generating gigawatt-level microwave radiation in pulsed regimes. This workshop will provide a focused tutorial on the physics, design, and experimental validation of HPM oscillators driven by intense electron beams, with particular emphasis on backward wave oscillators (BWOs), magnetically insulated line oscillators (MILOs), and associated pulsed power technologies. The session will begin with a concise review of beam–wave interaction physics in slow-wave structures, including dispersion engineering, synchronism conditions, and nonlinear saturation mechanisms in relativistic regimes. Special attention will be given to beam instabilities that influence mode competition, efficiency, and spectral stability. Practical design considerations for BWO and MILO systems will be discussed, covering slow-wave structure optimization, impedance matching, magnetic insulation, and output coupling strategies.
A dedicated segment will address pulsed power drivers for HPM sources, including pulse forming networks, Marx generators, and high-voltage switching technologies. The interplay between pulse shaping, beam quality, and microwave generation efficiency will be analyzed from both theoretical and experimental perspectives. Measurement techniques for gigawatt-class microwave characterization—such as calibrated antenna diagnostics, attenuation chains, and time-resolved spectral analysis—will also be introduced.
By bridging classical vacuum electronic device theory with modern numerical modeling and experimental validation, this tutorial aims to provide participants with a systematic understanding of HPM source development. The session is designed for researchers and engineers working on advanced electromagnetic systems who seek both foundational insight and practical guidance for next-generation HPM platforms.

This session presents the fundamentals of an electromagnetic particle-in-cell algorithm coupled with a finite-element time-domain field solver on irregular meshes. The method is based on differential geometry and discrete exterior calculus, ensuring consistent discretization of Maxwell’s equations, exact charge conservation, and structure preservation.

Abstract The increasing incidence of armed violence, such as stabbings and active shootings, in crowded public spaces highlights an urgent need for widely deployable weapon detection systems. Detecting concealed weapons requires precise imaging, rather than simple metal detection, to distinguish weapons from everyday metallic items. However, existing imaging systems, such as airport body scanners, rely on costly hardware and require cooperative subjects to pause during the scanning process. Consequently, these systems are confined to controlled checkpoints with explicit queuing, hindering large-scale deployment.
In this talk, I will present a low-cost, walk-through weapon detection system utilizing a commodity mmWave radar paired with a passive metasurface. The core idea of our system is to employ a transmissive metasurface that spatially encodes the reflection map of the scene, enabling the reconstruction of the target image from limited mmWave measurements without requiring costly hardware or mechanical scanning. To translate these measurements into high-fidelity images, we incorporate a physics-informed diffusion model to generate target images consistent with the reflected mmWave signals, allowing the system to infer the concealed object’s shape and type.
Preliminary simulation results suggest our system achieves a spatial resolution of up to several wavelengths, even for moving targets. Finally, this talk will detail remaining challenges, concluding with a discussion of future work for deployment in public spaces.

Monitoring everyday events in the home can help computational systems provide timely assistance without requiring constant user effort. However, existing solutions involve important trade-offs. Cameras introduce privacy concerns, and wearables depend on consistent use and regular charging. Tag-based approaches are often more practical, but many require periodic battery replacement, depend on non-ubiquitous transceivers, or need multiple receivers per room because of limited sensing range.
In this talk, I will present AcousTag, a batteryless, 3D-printed tag that can be sensed by widely deployed smart speakers such as Amazon Echo Dots to detect interactions with hinged or sliding objects from a distance. AcousTag includes two main technical contributions: (1) a batteryless tag design that harvests motion energy to produce unique, identifiable acoustic reflections, and (2) a receiver-side software system that retrofits commodity smart speakers to detect these reflections in real time, enabling room-scale sensing and differentiation of multiple object interactions.
We evaluate AcousTag through real-world deployments across two homes, where it achieves an average activation accuracy of over 94%. We also show that tags can be detected at distances up to 11 m, while remaining robust during multi-speaker operation and simultaneous tag activations.

The prevalence of counterfeit infant formulas poses serious threats to infant health and safety, a concern highlighted by the notorious Melamine Milk Scandal that affected hundreds of thousands of children. The primary challenge in detecting counterfeit formulas lies in their sophisticated adulteration and substitution techniques. Such detection is feasible only in laboratory settings, making it nearly impossible for average
consumers to test the formula before feeding their infants. In this talk, I will present PowDew, a novel and practical system that enables counterfeit infant formula detection using only a commodity smartphone. PowDew operates by capturing and analyzing the interaction of a water droplet with the powdered formula, focusing on the droplet motion, namely its spreading and penetration. Our key insight is that the droplet motions are governed by powder-specific properties such as wettability and porosity. PowDew analyzes the subtle differences in droplet motions and infers the formula’s authenticity. To demonstrate PowDew’s effectiveness, we implement PowDew and conduct comprehensive real-world experiments under varying conditions with different brands of powdered infant formula and adulterants. Our extensive real-world evaluation, comprising 12,000 minutes of video recordings across various brands of authentic and altered infant formulas under different conditions, demonstrates that PowDew achieves a detection accuracy of up to 96.1%.

This tutorial will introduce or reappraise the audience with the need for and the potential solutions for HPEM resilience and protection of critical infrastructure assets. We will provide an overview of relevant transient HPEM ‘threat’ environments including High altitude Electromagnetic Pulse (HEMP) and Intentional Electromagnetic Interference (IEMI) environments. We will describe what critical infrastructure is and how it has particular challenges, which could make it vulnerable to HPEM environments. Finally, we will discuss some practical protection solutions and introduce the concept of moving towards a resilience based, rather than protection-dominated, approach to HPEM threat mitigation.
We will reference published information such as the standards of International Electrotechnical Commission (IEC) 77C and, in particular, the newly published IEC standard 61000-5-6. We will also reference other relevant authoritative documents and provide a bibliography for further reading