arXiv subjects

Juan Rivas-Davila

Publications and source records attributed to Juan Rivas-Davila.

11 recordsLinked to original sources

arXiv2026

EasyRider: Mitigating Power Transients in Datacenter-Scale Training Workloads

Large-scale AI model training workloads use thousands of GPUs operating in tightly synchronized loops. During synchronous communication, start-up, shut-down, and checkpointing, GPU power consumption can swing from peak to idle within milliseconds. Such steep power ramp rates induce reactive power transients, leading to voltage and frequency shifts that can damage transformers, generators, and protection equipment on the broader power grid. To solve this problem, we introduce EasyRider, a power architecture to mitigate power fluctuations at the rack level. EasyRider uses passive and active hardware components to attenuate rack power swings and rack-scale energy storage for the large amounts of energy needed to smooth high-power racks. A software system continually monitors the energy storage system to maximize its lifetime in the presence of frequent charge/discharge cycles. EasyRider filters rack power variations to be within grid safety requirements without requiring software modifications to AI training frameworks or wasting energy. We evaluate EasyRider on a 10kW/400VDC-rated rack-scale prototype system, demonstrating its effectiveness across heterogeneous power levels and workload power profiles.

cs.AR↗

arXiv2026

Induction-heated resonant reactors for electrified thermochemistry

We present induction-heated resonant reactors, a new concept in electrified thermochemistry in which the reactor itself serves as a volumetric electromagnetic resonator heated through resonant wireless power transfer. We use the Swiss roll resonator as a model system and show that it can be designed to support uniform volumetric heating profiles and enhanced heat transfer characteristics, creating opportunities for process intensification in scaled systems. Compared to conventional (i.e., non-resonant) induction heating systems, resonant reactors can achieve exceptionally high system efficiencies through the combination of near-unity power-to-heat efficiencies and low thermal losses, both enabled by the utilization of resonant energy transfer. These concepts demonstrate how the integration of electromagnetic power transduction with thermochemical reaction engineering enables new opportunities for utilizing green electricity in sustainable chemical conversion.

eess.SY↗

arXiv2026

Spurious-Free Lithium Niobate Bulk Acoustic Wave Resonator with Grounded-Ring Electrode

High-performance piezoelectric resonators are promising energy storage elements for piezoelectric power conversion due to their compact footprint and low loss at frequencies where conventional magnetic components become bulky and inefficient. However, their practical use is often limited by the trade-off between a high electromechanical coupling coefficient (k^2) for wide-band operation and the emergence of spurious acoustic modes that limit the resonators' inductive bandwidth. This work reports a spurious-free thickness-extensional (TE)-mode bulk acoustic wave (BAW) resonator in single-crystal lithium niobate (LN) based on a grounded-ring electrode architecture. The proposed structure is analyzed through simulation and experimentally validated using electrical characterization and laser Doppler vibrometry (LDV). The results show that the grounded ring modifies the effective boundary conditions of the acoustic device, enabling a piston-like modal response that suppresses lateral spurious modes across the inductive band. The demonstrated device operates at 10.14 MHz and achieves an electromechanical coupling coefficient of 29.6%, a maximum in-band Bode quality factor (Q_Bode) of 5230, and a figure of merit (FoM, Q*k^2) of 1548. These results establish the grounded-ring TE-mode LN BAW resonator as a practical platform for piezoelectric power conversion and a broader design approach for realizing high-performance spurious-free acoustic resonators.

eess.SY↗

arXiv2026

Single-Crystal AlN Wafer-Based Bulk Acoustic Resonators for Piezoelectric Power Conversion

In this work, we demonstrate the first single-crystal aluminum nitride (AlN) wafer-based thickness-extensional (TE) mode bulk acoustic resonator for piezoelectric power conversion. The device exhibits a high series resonance 3-dB quality factor ($Q$) of 1677 and an electromechanical coupling coefficient ($k^2$) of 6.1%, highlighting the strong potential of AlN resonators for efficient power conversion. To suppress in-band spurious modes, a grounded ring structure is proposed and experimentally validated. The measured frequency-domain impedance response shows a spurious suppression of the spectrum above the resonance at 13.52 MHz. A comparative analysis with prior PZT, LN, and LT-based resonators indicates that AlN achieves a competitive figure of merit and $f \cdot Q$ product, while its material thermal conductivity is orders of magnitude higher than that of the incumbent piezoelectric power-converter resonators. The power-handling capability is expected to be superior in AlN single-crystal wafers and will be demonstrated in ongoing experiments. These results suggest that AlN offers a promising platform for compact, robust piezoelectric power converters and next-generation power electronic systems.

physics.app-ph↗

arXiv2025

Radial Mode Lithium Niobate Rosen Transformer

In this work, we demonstrate the first two-port radial-mode Rosen transformer based on 36$^{\circ}$Y-cut lithium niobate (LN) for piezoelectric power conversion. The device achieves a high transformation ratio (TF) of 16, a high electromechanical coupling factor ($k^2$) of 16.8\% and a quality factor ($Q$) of 2500, yielding an outstanding figure of merit (FoM = $Q \cdot k^2$) of 420. The fabricated transformer features a large effective turns ratio of 16 and delivers an open-circuit voltage gain of 45.56 (unloaded) and 40.57 with a load of 1 M$Ω$ in parallel with 0.1 pF, validating its ability to provide efficient passive voltage amplification. An equivalent circuit model was developed to accurately fit both finite-element-simulated and measured admittance spectra, enabling reliable parameter extraction. These results establish LN radial-mode resonators as a promising high-performance, magnetic-less transformer platform.

physics.app-ph↗

arXiv2025

Scale Up Analysis of Inductively Heated Metamaterial Reactors

Inductively heated metamaterial reactors, which utilize an open cell lattice baffle structure as a heating susceptor for magnetic induction, are promising candidates for scaled electrified thermochemical reactor operation due to their ability to support volumetric heating profiles and enhanced heat transfer properties. In this work, we present a systematic scale up analysis of inductive metamaterial reactors where we utilize a combination of analytic modeling, numerical simulations, and experiments to project the capabilities and performance of scaled reactors. We use reverse water gas shift as a model reaction system and show that for reactor configurations featuring a uniform metamaterial susceptor, the total system efficiency increases with scale. However, the throughput of these scaled reactors is limited by radial temperature gradients. We further show this bottleneck can be overcome by tailoring the radial effective conductivity profile of the susceptor, which can enable scaled reactors with nearly ideal plug flow-like capabilities. These concepts provide a pathway towards scaled electrified thermochemical reactors with optimal chemical conversion capabilities.

eess.SY↗

arXiv2025

Periodically Poled Piezoelectric Lithium Niobate Resonator for Piezoelectric Power Conversion

As the demand for compact and efficient power conversion systems increases, piezoelectric power converters have gained attention for their ability to replace bulky magnetic inductors with acoustic resonators, enabling higher power density and improved efficiency. Achieving optimal converter performance requires resonators with high quality factor ($Q$), strong electromechanical coupling ($k^2$), high power handling capability, and a spurious-free response. Lithium niobate (LN) has emerged as a promising material in this context due to its high figure of merit (FoM = $Q \cdot k^2$). While previous studies on single-layer LN resonators have demonstrated high FoM values, they typically operate at relatively low resonance frequencies ($f_s$). Recently, periodically poled piezoelectric film (P3F) structures, formed by stacking piezoelectric layers with alternating crystal orientations, have shown the potential to both scale up the operating frequency and enhance the FoM compared to single-layer counterparts in piezoelectric power conversion. This work presents the first P3F thickness-extensional (TE) LN resonator for power conversion, operating at 19.23 MHz, with a large \textit{$k^2$} of 29\% and a high \textit{Q} of 3187, achieving a state-of-the-art (\textit{ $f_s \cdot Q$}) product among piezoelectric power resonators. A high-power testing procedure is performed to systematically study the nonlinear behavior and power handling of P3F LN for power applications. With further optimization, P3F TE resonators have the potential to open up a new design space for high-power and high-frequency power conversion.

physics.app-ph↗

arXiv2024

Lithium Niobate Resonators for Power Conversion: Spurious Mode Suppression Via an Active Ring

In an effort to shift the paradigm of power conversion, acoustic resonators pose as compact alternatives for lossy magnetic inductors. Currently, the acoustic resonator's restricted inductive region between its series and parallel resonances constitutes a major bottleneck, which is further diminished due to spurious modes. Prior work has partially addressed this issue by the introduction of various design guidelines tailored to the material and the mode of interest, but can only provide a limited spurious-free region. Alternatively, a separated grounded ring on LN operating in the first order symmetric lamb mode (S1), maintains optimal device performance with a large fractional spurious mode suppressed region, but has been shown to experience voltage breakdown at high power near the ring at different potentials. Hence, we propose a new spurious mode suppressing design leveraging a thickened active ring in lithium niobate (LN), maintaining high Q and k2 while also reducing resistance at resonance (Rr), and mitigating breakdown effects.

physics.app-ph↗

arXiv2023

Spurious-Free Lithium Niobate Bulk Acoustic Resonator for Piezoelectric Power Conversion

Recently, piezoelectric power conversion has shown great benefits from replacing the bulky and lossy magnetic inductor in a traditional power converter with a piezoelectric resonator due to its compact size and low loss. However, the converter performance is ultimately limited by existing resonator designs, specifically by moderate quality factor (Q), moderate electromechanical coupling (kt2), and spurious modes near resonance. This work reports a spurious-free lithium niobate (LiNbO3) thickness-extensional mode bulk acoustic resonator design, demonstrating Q of 4000 and kt2 of 30% with a fractional suppressed region of 62%. We first propose a novel grounded ring structure for spurious-free resonator design, then validate its performance experimentally. Upon further work, this design could be extended to applications requiring spurious suppression, such as filters, tunable oscillators, transformers, etc.

eess.SP↗

arXiv2021

High Voltage Generation by Fiber-Coupled Pulsed Laser for a Simple Receiver Circuit Structure

Almost all high-voltage dc generation for low-power applications is done by either electrostatic machines or voltage multipliers. Electrostatic machines use mechanically moving parts to transfer charge and energy from the low-voltage side to the high-voltage side. Voltage multipliers use capacitive and inductive networks to achieve the same purpose of energy transfer. Considering the pros and cons inherent in those mechanical, capacitive, and inductive energy transfer, a new means of energy transfer may provide a superior design of a high voltage dc generator. Here we investigate the design of high voltage generators based on optical power transfer. Optical power delivered via fiber-optic cable allows extensive input-to-output dc insulation and spatial separation. These characteristics lead to advantages with respect to ease of insulation, ease of electromagnetic shielding, and scalability. We experimentally validate the idea by building and testing a 5.5 kV dc generator module solely powered by a 20 kHz pulsed laser, and cascading three of those modules to obtain 14.7 kV dc output voltage. We then discuss possible improvements to the circuit design to make it useful for real-world applications. Finally, we demonstrate an optically powered electroadhesion gripper to show the practicality of the proposed high voltage generator.

physics.app-ph↗

arXiv2021

Plasma-fixated nitrogen as fertilizer for turf grass

We investigated the use of plasma-fixated nitrogen, which produces nitrates (NO3-) in water, as a possible nitrogen fertilizer for recreational turf such as ryegrass and bentgrass. Experiments were carried out to study the effects of nitrate concentration on growth, the further effects of adding phosphorous (P) and potassium (K) to the plasma nitrated solution to make an N-P-K complete fertilizer, and to compare the efficacy of plasma-fixated nitrogen to sodium nitrate (NaNO3) and potassium nitrate (KNO3). The results indicate that the growth and biomass of the plants were strongly dependent on the concentration of the plasma-fixated nitrogen. Adding P-K to the plasma-fixated nitrogen improved grass growth. Grass that was supplied plasma-fixated nitrogen had improved growth compared to those supplied with equal amounts of NaNO3and KNO3. This work highlights the potential use of plasma-fixated nitrogen as a fertilizer source for commonly used turf grass.

physics.plasm-ph↗