Dielectric-based Components and Methods for Terahertz Sensing

[ES] En el presente trabajo, se investigan algunos aspectos de la interacción de los materiales dieléctricos con ondas de THz. La banda de THz, que incluye las frecuencias de 100 GHz a 30 THz, ha despertado un gran interés sobre todo por su baja energía y su buena capacidad de penetración en materiales de uso diario como tejidos y plásticos. Las características peculiares de estas ondas permiten su aplicación en diversos campos tecnológicos, especialmente como herramientas científicas y para la inspección de control de calidad. Para avanzar en la aplicación práctica de la radiación THz, la presente tesis doctoral investigó varios caminos. En primer lugar, se trataron métodos alternativos de bajo coste para la fabricación de componentes pasivos de THz, centrándose en los polarizadores. El interés en el control de la polarización nace de la demanda de un mayor control sobre las características físicas de los haces de THz. Asimismo, se han investigado los polarizadores wire grid flexible basados en el efecto de absorción dicroica. Se han fabricado polarizadores con grafito y GaIn24,5 depositados en materiales ordinarios utilizados como sustratos (papel y polímeros como PVA y PVC). Mediante la colaboración con el grupo de investigación chino dirigido por el profesor Liu de la Universidad de Tsinghua, se investigaron procesos de fabricación alternativos. Todos los componentes se simularon mediante un simulador comercial basado en la técnica de integrales finitas FIT (CST Microwave Studio). En segundo lugar, se investigó el potencial de la técnica de fixed delay para la detección rápida de elementos homogéneos y transparentes con posible aplicación en la inspección de calidad industrial. En este esquema, la variación de corriente del haz de THz en un punto específico está relacionada con la variación de sus parámetros ópticos, por lo que se demostró la capacidad de detectar defectos, así como de estimar sus volúmenes bajo ciertas condiciones. Por último, un enfoque diferente para el beam profile basado en un slit dieléctrico fue evaluada como alternativa a los métodos convencionales utilizados en la región de THz y la óptica. Todas las mediciones, tanto la espectroscopia como el control de la polarización, se hicieron por medio de un sistema basado en fibra TDS-THz, con antenas fotoconductoras (PCA), tanto para la generación como para la detección de THz.[EN] In the present work, some aspects of the role of dielectric materials when interacting with THz waves were investigated. The THz bandgap, which covers the frequencies from 100 GHz to 30 THz, has aroused great interest mainly due to its low energy and its good penetration capacity in some materials of daily use such as fabrics and plastics. The peculiar features of terahertz waves enable their application in various technological fields, especially as scientific tools and for quality control inspection. To advance in the practical application of THz radiation, the present doctoral thesis researched several paths. Firstly, alternative low-cost methods for manufacturing THz passive components, in particular, THz polarizers was treated. The interest in polarization control is derived from the demand for greater control over the physical characteristics of THz beams. Flexible wire grid polarizers based on the dichroic absorption effect have been investigated. The polarizers have been manufactured using graphite and GaIn24.5 deployed on ordinary materials used as substrates (paper and polymers such as PVA and PVC). Through a collaboration undertaken with the Chinese research group led by Professor Liu at Tsinghua University, alternative manufacturing processes were researched. All components were simulated through a commercial simulator based on the FIT finite integrals technique (CST Microwave Studio). Secondly, the potential of the fixed delay technique was investigated for rapid sensing of homogeneous and transparent items with possible application to industrial quality inspection. In this scheme, the current variation of the THz beam at a specific point is related to the variation of its optical parameters, thus it was demonstrated the ability of the method in detecting voids as well as in roughly estimating their volumes under certain conditions. Finally, a different approach for beam profiling based on a dielectric slit aperture was evaluated, as an alternative to the conventional methods used in the THz region and optics All measurements, both spectroscopy and polarization control, were made by means of a TDS-THz fibre-based system, with photoconductive antennas (PCA), both for the generation and detection of THz.[CA] En el present treball, s'investiguen alguns aspectes del paper dels materials dielèctrics quan interactuen amb ones de THz. El bandgap de THz, que cobreix les freqüències de 100 GHz a 30 THz, ha despertat un gran interés principalment a causa de la seua baixa energia i la seua bona capacitat de penetració en alguns materials d'ús diari com els teixits i els plàstics. Les característiques peculiars de les ones de terahertz permeten la seua aplicació en diversos camps tecnològics, especialment com a eines científiques i per a la inspecció de control de qualitat. Per a avançar en l'aplicació pràctica de la radiació THz, la present tesi doctoral investiga diversos camins. En primer lloc, es s'han tractat mètodes alternatius de baix cost per a la fabricació de components passius de THz, centrant-se principalment en polaritzadors de THz. L'interés en el control de la polarització es deriva de la demanda d'un major control sobre les característiques físiques dels feixos de THz. Així mateix, s'han investigat els polaritzadors amb reixes de filferro flexible basats en l'efecte d'absorció dicroica. Els polaritzadors s'han fabricat utilitzant grafit i GaIn24,5 desplegats en materials ordinaris utilitzats com a substrats (paper i polímers com el PVA i el PVC). Mitjançant una col·laboració empresa amb el grup d'investigació xinés dirigit pel professor Liu de la Universitat de Tsinghua, es van investigar processos de fabricació alternatius. Tots els components es van simular mitjançant un simulador comercial basat en la tècnica d'integrals finites FIT (CST Microwave Studio). En segon lloc, s'ha investigat el potencial de la tècnica de retard fix per a la detecció ràpida d'elements homogenis i transparents amb possible aplicació a la inspecció de qualitat industrial. En aquest esquema, la variació actual del feix de THz en un punt específic està relacionada amb la variació dels seus paràmetres òptics, per la qual cosa es va demostrar la capacitat del mètode per a detectar els buits així com en l'estimació aproximada dels seus volums sota certes condicions. Finalment, un enfocament diferent per al perfil de feix basat en una obertura d'escletxa dielèctrica ha sigut avaluada, com a alternativa als mètodes convencionals utilitzats a la regió de THz i l'òptica.Tots els mesuraments, tant l'espectroscòpia com el control de la polarització, es van fer per mitjà d'un sistema basat en fibra TDS-THz, amb antenes fotoconductores (PCA), tant per a la generació com per a la detecció de THz.Colleoni, MPM. (2020). Dielectric-based Components and Methods for Terahertz Sensing [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/149569TESI

NASA Tech Briefs, February 2009

Tech Briefs are short announcements of innovations originating from research and development activities of the National Aeronautics and Space Administration. They emphasize information considered likely to be transferable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. Topics covered include: Measuring Low Concentrations of Liquid Water in Soil; The Mars Science Laboratory Touchdown Test Facility; Non-Contact Measurement of Density and Thickness Variation in Dielectric Materials; Compact Microwave Fourier Spectrum Analyzer; InP Heterojunction Bipolar Transistor Amplifiers to 255 GHz; Combinatorial Generation of Test Suites; In-Phase Power-Combined Frequency Tripler at 300 GHz; Electronic System for Preventing Airport Runway Incursions; Smaller but Fully Functional Backshell for Cable Connector; Glove-Box or Desktop Virtual-Reality System; Composite Layer Manufacturing with Fewer Interruptions; Improved Photoresist Coating for Making CNT Field Emitters; A Simplified Diagnostic Method for Elastomer Bond Durability; Complex Multifunctional Polymer/Carbon-Nanotube Composites; Very High Output Thermoelectric Devices Based on ITO Nanocomposites; Reducing Unsteady Loads on a Piggyback Miniature Submarine; Ultrasonic/Sonic Anchor; Grooved Fuel Rings for Nuclear Thermal Rocket Engines; Pulsed Operation of an Ion Accelerator; Autonomous Instrument Placement for Mars Exploration Rovers; Mission and Assets Database; TCP/IP Interface for the Satellite Orbit Analysis Program (SOAP); Trajectory Calculator for Finite-Radius Cutter on a Lathe; Integrated System Health Management Development Toolkit

NASA Tech Briefs, May 2011

Topics covered include: 1) Method to Estimate the Dissolved Air Content in Hydraulic Fluid; 2) Method for Measuring Collimator-Pointing Sensitivity to Temperature Changes; 3) High-Temperature Thermometer Using Cr-Doped GdAlO3 Broadband Luminescence; 4)Metrology Arrangement for Measuring the Positions of Mirrors of a Submillimeter Telescope; 5) On-Wafer S-Parameter Measurements in the 325-508-GHz Band; 6) Reconfigurable Microwave Phase Delay Element for Frequency Reference and Phase-Shifter Applications; 7) High-Speed Isolation Board for Flight Hardware Testing; 8) High-Throughput, Adaptive FFT Architecture for FPGA-Based Spaceborne Data Processors; 9) 3D Orbit Visualization for Earth-Observing Missions; 10) MaROS: Web Visualization of Mars Orbiting and Landed Assets; 11) RAPID: Collaborative Commanding and Monitoring of Lunar Assets; 12) Image Segmentation, Registration, Compression, and Matching; 13) Image Calibration; 14) Rapid ISS Power Availability Simulator; 15) A Method of Strengthening Composite/Metal Joints; 16) Pre-Finishing of SiC for Optical Applications; 17) Optimization of Indium Bump Morphology for Improved Flip Chip Devices; 18) Measuring Moisture Levels in Graphite Epoxy Composite Sandwich Structures; 19) Marshall Convergent Spray Formulation Improvement for High Temperatures; 20) Real-Time Deposition Monitor for Ultrathin Conductive Films; 21) Optimized Li-Ion Electrolytes Containing Triphenyl Phosphate as a Flame-Retardant Additive; 22) Radiation-Resistant Hybrid Lotus Effect for Achieving Photoelectrocatalytic Self-Cleaning Anticontamination Coatings; 23) Improved, Low-Stress Economical Submerged Pipeline; 24) Optical Fiber Array Assemblies for Space Flight on the Lunar Reconnaissance Orbiter; 25) Local Leak Detection and Health Monitoring of Pressurized Tanks; 26) Dielectric Covered Planar Antennas at Submillimeter Wavelengths for Terahertz Imaging; 27) Automated Cryocooler Monitor and Control System; 28) Broadband Achromatic Phase Shifter for a Nulling Interferometer; 29) Super Dwarf Wheat for Growth in Confined Spaces; 30) Fine Guidance Sensing for Coronagraphic Observatories; 31) Single-Antenna Temperature- and Humidity-Sounding Microwave Receiver; 32) Multi-Wavelength, Multi-Beam, and Polarization-Sensitive Laser Transmitter for Surface Mapping; 33) Optical Communications Link to Airborne Transceiver; 34) Ascent Heating Thermal Analysis on Spacecraft Adaptor Fairings; 35) Entanglement in Self-Supervised Dynamics; 36) Prioritized LT Codes; 37) Fast Image Texture Classification Using Decision Trees; 38) Constraint Embedding Technique for Multibody System Dynamics; 39) Improved Systematic Pointing Error Model for the DSN Antennas; 40) Observability and Estimation of Distributed Space Systems via Local Information-Exchange Networks; 41) More-Accurate Model of Flows in Rocket Injectors; 42) In-Orbit Instrument-Pointing Calibration Using the Moon as a Target; 43) Reliability of Ceramic Column Grid Array Interconnect Packages Under Extreme Temperatures; 44) Six Degrees-of-Freedom Ascent Control for Small-Body Touch and Go; and 45) Optical-Path-Difference Linear Mechanism for the Panchromatic Fourier Transform Spectrometer

THz Imaging for Food Inspections: A Technology Review and Future Trends

Terahertz imaging is the newest among non-invasive sensing technologies and currently huge attention is pointed towards its use in several applications. Among possible applications, food inspection represents one of the most prominent cases, due to the possible dangerous impact on human safety. Hence, significant efforts are currently addressed towards the exploitation of THz imaging as a tool to improve the effectiveness of food quality surveys. This chapter deals with the exploitation of THz imaging technology for food quality control and assessment. In particular, the chapter aims at reviewing the latest developments regarding THz imaging, both in terms of measurement systems and data processing methodologies. Moreover, the chapter summarizes experiments available in literature and presents some purposely designed experiments to address the discussion on currently open issues

Extraordinary Optical Transmission in Aligned Carbon Nanotube Devices at Terahertz Frequencies.

In the phenomenon known as extraordinary optical transmission (EOT), a narrow band of selected frequencies are transmitted when incident on an array of subwavelength periodic apertures where the resonant frequency is determined by the geometry of the array of apertures and optical properties of the metal-dielectric interface. This takes place due to the excitation of surface plasmon polaritons (SPPs) at the metal and dielectric interface. Using the COMSOL Multiphysics software RF Module, a unit cell of a carbon nanotube (CNT) based EOT device is modeled in order to verify theoretical calculations of the resonant frequency using S-parameter calculations. The simulation of the interaction of the THz light with the CNT EOT device exhibits a resonant transmission at 235 GHz. Further, the transmission falls exponentially with increasing device thickness of the device, and the transmission peak reaches its maximum value at the skin depth. Although some of the transmission features, such as Wood’s anomalies, are seen in the modeled device only, the other numerical results show good agreement with the experimental observations reported in literature. The fabricated single-walled carbon nanotube devices with 100 nm thickness do not indicate any resonances; however any such resonances might be weak due to the thin nature of the samples

Recent advances in active infrared thermography for non-destructive testing of aerospace components

Active infrared thermography is a fast and accurate non-destructive evaluation technique that is of particular relevance to the aerospace industry for the inspection of aircraft and helicopters’ primary and secondary structures, aero-engine parts, spacecraft components and its subsystems. This review provides an exhaustive summary of most recent active thermographic methods used for aerospace applications according to their physical principle and thermal excitation sources. Besides traditional optically stimulated thermography, which uses external optical radiation such as flashes, heaters and laser systems, novel hybrid thermographic techniques are also investigated. These include ultrasonic stimulated thermography, which uses ultrasonic waves and the local damage resonance effect to enhance the reliability and sensitivity to micro-cracks, eddy current stimulated thermography, which uses cost-effective eddy current excitation to generate induction heating, and microwave thermography, which uses electromagnetic radiation at the microwave frequency bands to provide rapid detection of cracks and delamination. All these techniques are here analysed and numerous examples are provided for different damage scenarios and aerospace components in order to identify the strength and limitations of each thermographic technique. Moreover, alternative strategies to current external thermal excitation sources, here named as material-based thermography methods, are examined in this paper. These novel thermographic techniques rely on thermoresistive internal heating and offer a fast, low power, accurate and reliable assessment of damage in aerospace composites

Pulsed Free Space Photonic Vector Network Analyzers

Terahertz (THz) radiation (0.1–10 THz) has demonstrated great significance in a wide range of interdisciplinary applications due to its unique properties such as the capacity to penetrate optically opaque materials without ionizing effect, superior spatial resolution as compared to the microwave domain for imaging or ability to identify a vast array of molecules using THz fingerprinting. Advancements in generation and detection techniques, as well as the necessities of application-driven research and industry, have created a substantial demand for THz-range devices and components. However, progress in the development of THz components is hampered by a lack of efficient and affordable characterization systems, resulting in limited development in THz science and technology. Vector Network Analyzers (VNAs) are highly sophisticated well-established characterization instruments in the microwave bands, which are now employed in the lower end of the THz spectrum (up to 1.5 THz) using frequency extender modules. These modules are extremely expensive, and due to the implementation of hollow metallic waveguides for their configuration, they are narrowband, requiring at least six modules to achieve a frequency coverage of 0.2–1.5 THz. Moreover, they are susceptible to problems like material losses, manufacturing and alignment tolerances etc., making them less than ideal for fast, broadband investigation. The main objective of this thesis is to design a robust but cost-effective characterization system based on a photonic method that can characterize THz components up to several THz in a single configuration. To achieve this, we design architectures for the Photonic Vector Network Analyzer (PVNA) concept, incorporating ErAs:In(Al)GaAs-based photoconductive sources and ErAs:InGaAs-based photoconductive receivers, driven with a femtosecond pulsed laser operating at 1550 nm. The broadband photonic devices replace narrowband electronic ones in order to record the Scattering (S)-parameters in a free space configuration. Corresponding calibration and data evaluation methods are also developed. Then the PVNAs are configured, and their capabilities are validated by characterizing various THz components, including a THz isolator, a distributed Bragg Reflector, a Split-Ring Resonator array and a Crossed-Dipole Resonator (CDR) array, in terms of their S-parameters. The PVNAs are also implemented to determine the complex refractive index or dielectric permittivity and physical thickness of several materials in the THz range. Finally, we develop an ErAs:In(Al)GaAs-based THz transceiver and implement it in a PVNA configuration, resulting in a more compact setup that is useful for industrial applications. The feasibility of such systems is also verified by characterizing several THz components. The configured systems achieve a bandwidth of more than 2.5 THz, exceeding the maximum attainable frequency of the commercial Electronic Vector Network Analyzer (EVNA) extender modules. For the 1.1-1.5 THz band, the dynamic range of 47-35 dB (Equivalent Noise Bandwidth (ENBW) = 9.196 Hz) achieved with the PVNA is comparable to the dynamic range of 45-25 dB (ENBW = 10 Hz) of the EVNA. Both amplitude and phase of the S-parameters, determined by the configured PVNAs, are compared with simulations or theoretical models and showed excellent agreement. The PVNA could discern multi-peak and narrow resonance characteristics despite its lower spectral resolution (∼3-7 GHz) compared to the EVNA. By accurately determining the S-parameters of multiple THz components, the transceiver-based PVNA also demonstrated its exceptional competence. With huge bandwidth and simpler calibration techniques, the PVNA provides a potential solution to bridge the existing technological gap in THz-range characterization systems and offers a solid platform for THz component development, paving the way for more widespread application of THz technologies in research and industry

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Nondestructive Evaluation of Aircraft Composites Using Terahertz Time Domain Spectroscopy

Terahertz (THz) time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Material properties of glass fiber composite were measured using both transmission and reflection configuration. The interaction of THz with a glass fiber composite was then analyzed, including the effects of scattering, absorption, and the index of refraction, as well as effective medium approximations. THz TDS, in both transmission and reflection configuration, was used to study composite damage, including voids, delaminations, mechanical damage, and heat damage. Measurement of the material properties on samples with localized heat damage showed that burning did not change the refractive index or absorption coefficient noticeably; however, material blistering was detected. Voids were located by THz TDS transmission and reflection imaging using amplitude and phase techniques. The depth of delaminations was measured via the timing of Fabry-Perot reflections after the mail pulse. Evidence of bending stress damage and simulated hidden cracks was also detected with terahertz imaging

Terahertz imaging and quantum cascade laser based devices

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 108-114).The terahertz (THz) frequency range (f=0.3-10 THz, [lambda]=30-1000 lam) is much less technologically developed that the adjacent microwave and infrared frequency ranges, but offers several advantages for imaging applications: THz wavelengths offer better spatial resolutions than microwave frequencies, and THz radiation is able to penetrate materials that are opaque at infrared frequencies (e.g. packaging, plastics, paints and semiconductors). These features, combined with the unique THz spectral signatures of chemicals have lead to the development of terahertz imaging systems for non-destructive test. However, the weak radiation sources in these existing systems result in single pixel scanning architectures requiring minutes to acquire images or enhanced speed at the expense of signal to noise ratio (SNR). In this thesis, a system for real-time imaging is demonstrated using recently developed terahertz quantum-cascade laser (QCL) sources, along with commercial, focal plane array thermal detectors. The system uses a high power (48 mW) 4.3-THz QCL, which is also used to characterize the focal plane array, resulting in a noise equivalent power (NEP) of 320 pW/Hz. The source and detector are used in a synchronous detection scheme, resulting in an SNR of ~25 dB/pixel at a 20-Hz frame rate. This represents a two order of magnitude improvement in speed over previous systems at comparable SNRs. Real-time imaging over a 25-m distance is described, using a QCL adjusted for emission in the narrow 4.9 THz atmospheric transmission window.(cont.) The challenges posed by the long THz wavelengths in QCL waveguide design leads to a tradeoff between high temperature operation (<186K) and high power/good beam patterns (248 mW peak, l2deg FWHM). To mitigate these tradeoffs, a technique for buttcoupling a metal-metal waveguide QCL to an index matched lens is developed. The resulting device achieves the highest reported power for a MM waveguide (145 mW peak) and while retaining a high operating temperature (160 K) and achieving a narrow beam pattern (<5deg). The lens coupling technique is also used to add spectroscopic capability to the system, through the development of an external cavity QCL. The butt-coupling of an antireflection coated lens to a semi-insulating surface plasmon waveguide QCL results in increased optical losses and suppression of lasing. Lasing is recovered using an external optical system with a reflective grating for frequency selective feedback. A device is characterized showing 4% tuning range at ~4.4 THz, and is among the first demonstrations of tunable THz QLCs.by Alan Wei Min Lee.Ph.D