arXiv subjects

Zachary Taylor

Publications and source records attributed to Zachary Taylor.

15 recordsLinked to original sources

arXiv2026

Permittivity Characterization of 3D-Printed Materials at Millimeter Waves

In this study, we characterize the permittivity of various commercially available materials commonly used in 3D printing over the millimeter-wave frequency range of 70-110 GHz. The open-waveguide extraction method is employed to efficiently determine the permittivity of these 3D-printed materials, and key strategies for improving its accuracy are discussed. This methodology can be readily applied to the characterization of similar materials and extended to higher frequency ranges. The resulting permittivity data are expected to support advances in 6G and beyond wireless communication technologies, in which 3D-printed materials and millimeter-wave frequencies are anticipated to play an increasingly important role in the development of novel antennas and metasurfaces.

physics.optics↗

arXiv2025

Roadmap towards Personalized Approaches and Safety Considerations in Non-Ionizing Radiation: From Dosimetry to Therapeutic and Diagnostic Applications

This roadmap provides a comprehensive and forward-looking perspective on the individualized application and safety of non-ionizing radiation (NIR) dosimetry in diagnostic and therapeutic medicine. Covering a wide range of frequencies, i.e., from low-frequency to terahertz, this document provides an overview of the current state of the art and anticipates future research needs in selected key topics of NIR-based medical applications. It also emphasizes the importance of personalized dosimetry, rigorous safety evaluation, and interdisciplinary collaboration to ensure safe and effective integration of NIR technologies in modern therapy and diagnosis.

physics.med-ph↗

arXiv2025

Quasioptic, Calibrated, Full 2-port Measurements of Cryogenic Devices under Vacuum in the 220-330 GHz Band

A quasi-optical (QO) test bench was designed, simulated, and calibrated for characterizing S-parameters of devices in the 220-330 GHz (WR-3.4) frequency range, from room temperature down to 4.8 K. The devices were measured through vacuum windows via focused beam radiation. A de-embedding method employing line-reflect-match (LRM) calibration was established to account for the effects of optical components and vacuum windows. The setup provides all four S-parameters with the reference plane located inside the cryostat, and achieves a return loss of 30 dB with an empty holder. System validation was performed with measurements of cryogenically cooled devices, such as bare silicon wafers and stainless-steel frequency-selective surface (FSS) bandpass filters, and superconducting bandpass FSS fabricated in niobium. A permittivity reduction of Si based on 4-GHz resonance shift was observed concomitant with a drop in temperature from 296 K to 4.8 K. The stainless steel FSS measurements revealed a relatively temperature invariant center frequency and return loss level of 263 GHz and 35 dB on average, respectively. Finally, a center frequency of 257 GHz was measured with the superconducting filters, with return loss improved by 7 dB on average at 4.8 K. To the best of our knowledge, this is the first reported attempt to scale LRM calibration to 330 GHz and use it to de-embed the impact of optics and cryostat from cryogenically cooled device S-parameters.

physics.ins-det↗

arXiv2025

A Telecentric Offset Reflective Imaging System (TORIS) for Terahertz Imaging and Spectroscopy

Terahertz (THz) imaging has emerged as a promising technology in medical diagnostics due to its non-ionizing radiation and high sensitivity to water content. However, conventional THz imaging systems face limitations such as slow mechanical scanning, restricted field of view, and poor telecentricity. To overcome these challenges, we introduce the Telecentric Offset Reflective Imaging System (TORIS), a novel dual-mirror scanning design optimized for high-speed, distortion-free imaging. The system employs a telecentric f-theta lens and is validated using ray tracing and physical optics simulations. It achieves uniform resolution across a 50 mm x 50 mm field of view without the need for mechanical translation stages. Broadband spectral imaging of a USAF resolution test target across WR-2.2 (325-500 GHz) and WR-1.5 (500-700 GHz) frequency bands demonstrates consistent beam focus and minimal distortion, with a maximum deviation of 2.7 degrees from normal incidence and a beam waist of 2.1 lambda at the field edge in the WR-1.5 band. The system's sensitivity to hydration dynamics is further validated through imaging of wet tissue paper, capturing temporal changes in water content. In vivo imaging of human skin after capsaicin patch application reveals localized hydration variations due to biochemical response and adhesive removal. These findings confirm the system's potential for real-time hydration sensing and dermatological evaluation. TORIS sets a new benchmark in THz imaging, with applications in clinical diagnostics, wound assessment, and material characterization.

physics.optics↗

arXiv2023

Mie Scattering with 3D Angular Spectrum Method

Mie theory is a powerful method to model electromagnetic scattering from a multilayered sphere. Usually, the incident beam is expanded to its vector spherical harmonic representation defined by beam shape coefficients, and the multilayer sphere scattering is obtained by the T-matrix method. However, obtaining the beam shape coefficients for arbitrarily shaped incident beams has limitations on source locations and requires different methods when the incident beam is defined inside or outside the computational domain or at the scatterer surface. We propose a 3D angular spectrum method for defining beam shape coefficients from arbitrary source field distributions. This method enables the placement of the sources freely within the computational domain without singularities, allowing flexibility in beam design. We demonstrate incident field synthesis and spherical scattering by comparing morphology-dependent resonances to known values, achieving excellent matching and high accuracy. Additionally, we present mathematical proof to support our proposal. The proposed method has significant benefits for optical systems and inverse beam design. It allows for the analysis of electromagnetic forward/backward propagation between optical elements and spherical targets using a single method. It is also valuable for optical force beam design and analysis.

physics.optics↗

arXiv2021

Coupling to longitudinal modes in spherical thin shells illuminated by submillimeter wave Gaussian beam: applications to corneal sensing

Coupling to longitudinal modes of thin spherical shells, under Gaussian-beam illumination, was explored with a theoretical method based on Fourier-optics analysis and vector spherical harmonics. The illumination frequency band was fixed between 100-600 GHz and the outer spherical shell radius of curvature and thickness are 7.5 mm and 0.5 mm, respectively. The shell material was either the lossless cornea or an aqueous effective media representing the cornea. Six different beam-target strategies were introduced being potential candidates for maximum coupling. Two dispersion-tuned beam ensembles with strongly frequency-dependent phase center location have been created with a fixed incident beam 1/e radius and radius of curvature called forward strategies. These computations of different alignments were continued with four beam ensembles of frequency-invariant phase center, constructed from fits to experimental data, oriented at four different axial locations with respect to the spherical shell center of curvature, they are called reverse strategies. Coupling efficiency for all strategies was calculated for different targets including PEC sphere, air-core, and PEC core covered by a cornea loss-free layer and cornea. All scattering strategies contrasted to scattering from equivalent planar targets as a reference with maximum coupling. The results show that, under an ideal calibration, forward strategies are a closer approximation to the plane-wave condition. However, target properties influence the coupling efficiency remarkably for instance the observed difference in cornea scattering is vanishingly small as dielectric loss limits walk-off loss. Furthermore, under perturbed calibration, the forward strategies showed less sensitivity.

physics.med-ph↗

arXiv2020

An Open-Source System for Vision-Based Micro-Aerial Vehicle Mapping, Planning, and Flight in Cluttered Environments

We present an open-source system for Micro-Aerial Vehicle autonomous navigation from vision-based sensing. Our system focuses on dense mapping, safe local planning, and global trajectory generation, especially when using narrow field of view sensors in very cluttered environments. In addition, details about other necessary parts of the system and special considerations for applications in real-world scenarios are presented. We focus our experiments on evaluating global planning, path smoothing, and local planning methods on real maps made on MAVs in realistic search and rescue and industrial inspection scenarios. We also perform thousands of simulations in cluttered synthetic environments, and finally validate the complete system in real-world experiments.

cs.RO↗

arXiv2020

Towards Efficient Full Pose Omnidirectionality with Overactuated MAVs

Omnidirectional MAVs are a growing field, with demonstrated advantages for aerial interaction and uninhibited observation. While systems with complete pose omnidirectionality and high hover efficiency have been developed independently, a robust system that combines the two has not been demonstrated to date. This paper presents VoliroX: a novel omnidirectional vehicle that can exert a wrench in any orientation while maintaining efficient flight configurations. The system design is presented, and a 6 DOF geometric control that is robust to singularities. Flight experiments further demonstrate and verify its capabilities.

cs.RO↗

arXiv2020

Design and optimal control of a tiltrotor micro aerial vehicle for efficient omnidirectional flight

Omnidirectional micro aerial vehicles are a growing field of research, with demonstrated advantages for aerial interaction and uninhibited observation. While systems with complete pose omnidirectionality and high hover efficiency have been developed independently, a robust system that combines the two has not been demonstrated to date. This paper presents the design and optimal control of a novel omnidirectional vehicle that can exert a wrench in any orientation while maintaining efficient flight configurations. The system design is motivated by the result of a morphology design optimization. A six degrees of freedom optimal controller is derived, with an actuator allocation approach that implements task prioritization, and is robust to singularities. Flight experiments demonstrate and verify the system's capabilities.

cs.RO↗

arXiv2018

C-blox: A Scalable and Consistent TSDF-based Dense Mapping Approach

In many applications, maintaining a consistent dense map of the environment is key to enabling robotic platforms to perform higher level decision making. Several works have addressed the challenge of creating precise dense 3D maps from visual sensors providing depth information. However, during operation over longer missions, reconstructions can easily become inconsistent due to accumulated camera tracking error and delayed loop closure. Without explicitly addressing the problem of map consistency, recovery from such distortions tends to be difficult. We present a novel system for dense 3D mapping which addresses the challenge of building consistent maps while dealing with scalability. Central to our approach is the representation of the environment as a collection of overlapping TSDF subvolumes. These subvolumes are localized through feature-based camera tracking and bundle adjustment. Our main contribution is a pipeline for identifying stable regions in the map, and to fuse the contributing subvolumes. This approach allows us to reduce map growth while still maintaining consistency. We demonstrate the proposed system on a publicly available dataset and simulation engine, and demonstrate the efficacy of the proposed approach for building consistent and scalable maps. Finally we demonstrate our approach running in real-time on-board a lightweight MAV.

cs.RO↗

arXiv2018

Sparse 3D Topological Graphs for Micro-Aerial Vehicle Planning

Micro-Aerial Vehicles (MAVs) have the advantage of moving freely in 3D space. However, creating compact and sparse map representations that can be efficiently used for planning for such robots is still an open problem. In this paper, we take maps built from noisy sensor data and construct a sparse graph containing topological information that can be used for 3D planning. We use a Euclidean Signed Distance Field, extract a 3D Generalized Voronoi Diagram (GVD), and obtain a thin skeleton diagram representing the topological structure of the environment. We then convert this skeleton diagram into a sparse graph, which we show is resistant to noise and changes in resolution. We demonstrate global planning over this graph, and the orders of magnitude speed-up it offers over other common planning methods. We validate our planning algorithm in real maps built onboard an MAV, using RGB-D sensing.

cs.RO↗

arXiv2018

Safe Local Exploration for Replanning in Cluttered Unknown Environments for Micro-Aerial Vehicles

In order to enable Micro-Aerial Vehicles (MAVs) to assist in complex, unknown, unstructured environments, they must be able to navigate with guaranteed safety, even when faced with a cluttered environment they have no prior knowledge of. While trajectory optimization-based local planners have been shown to perform well in these cases, prior work either does not address how to deal with local minima in the optimization problem, or solves it by using an optimistic global planner. We present a conservative trajectory optimization-based local planner, coupled with a local exploration strategy that selects intermediate goals. We perform extensive simulations to show that this system performs better than the standard approach of using an optimistic global planner, and also outperforms doing a single exploration step when the local planner is stuck. The method is validated through experiments in a variety of highly cluttered environments including a dense forest. These experiments show the complete system running in real time fully onboard an MAV, mapping and replanning at 4 Hz.

cs.RO↗

arXiv2018

Voliro: An Omnidirectional Hexacopter With Tiltable Rotors

Extending the maneuverability of unmanned areal vehicles promises to yield a considerable increase in the areas in which these systems can be used. Some such applications are the performance of more complicated inspection tasks and the generation of complex uninterrupted movements of an attached camera. In this paper we address this challenge by presenting Voliro, a novel aerial platform that combines the advantages of existing multi-rotor systems with the agility of omnidirectionally controllable platforms. We propose the use of a hexacopter with tiltable rotors allowing the system to decouple the control of position and orientation. The contributions of this work involve the mechanical design as well as a controller with the corresponding allocation scheme. This work also discusses the design challenges involved when turning the concept of a hexacopter with tiltable rotors into an actual prototype. The agility of the system is demonstrated and evaluated in real- world experiments.

cs.RO↗

arXiv2017

Voxblox: Incremental 3D Euclidean Signed Distance Fields for On-Board MAV Planning

Micro Aerial Vehicles (MAVs) that operate in unstructured, unexplored environments require fast and flexible local planning, which can replan when new parts of the map are explored. Trajectory optimization methods fulfill these needs, but require obstacle distance information, which can be given by Euclidean Signed Distance Fields (ESDFs). We propose a method to incrementally build ESDFs from Truncated Signed Distance Fields (TSDFs), a common implicit surface representation used in computer graphics and vision. TSDFs are fast to build and smooth out sensor noise over many observations, and are designed to produce surface meshes. Meshes allow human operators to get a better assessment of the robot's environment, and set high-level mission goals. We show that we can build TSDFs faster than Octomaps, and that it is more accurate to build ESDFs out of TSDFs than occupancy maps. Our complete system, called voxblox, will be available as open source and runs in real-time on a single CPU core. We validate our approach on-board an MAV, by using our system with a trajectory optimization local planner, entirely on-board and in real-time.

cs.RO↗

arXiv2009

Turbulent flow over a house in a simulated hurricane boundary layer

Every year hurricanes and other extreme wind storms cause billions of dollars in damage worldwide. For residential construction, such failures are usually associated with roofs, which see the largest aerodynamic loading. However, determining aerodynamic loads on different portions of North American houses is complicated by the lack of clear load paths and non-linear load sharing in wood frame roofs. This problem of fluid-structure interaction requires both wind tunnel testing and full-scale structural testing. A series of wind tunnel tests have been performed on a house in a simulated atmospheric boundary layer (ABL), with the resulting wind-induced pressures applied to the full-scale structure. The ABL was simulated for flow over open country terrain where both velocity and turbulence intensity profiles, as well as spectra, were matched with available full scale measurements for this type of terrain. The first set of measurements was 600 simultaneous surface pressure measurements over the entire house. A key feature of the surface pressure field is the occurrence of large, highly non-Gaussian, peak uplift (suctions) on the roof. In order to better understand which flow features cause this, PIV experiments were performed on the wind tunnel model. These experiments were performed with time-resolved PIV (sampling rate of 500 Hz) for a duration of 30 seconds. From the fluid dynamics videos (low- and high-resolution) generated from the PIV data it is clear that strong circulation is generated at the windward edge of the roof. These vortices are eventually shed and convect along the roof. It is the presence of this concentrated circulation which is responsible for the peak loading observed.

physics.flu-dyn↗