We present high-transmittance, narrow bandwidth band-pass terahertz filters fabricated on 1-μm-thick freestanding, yet robust cyclic olefin copolymer (TOPAS) films integrated on 3D printed frames of the same material. This approach allows for very flexible customization of the shape and dimensions of the filters as well as cost-effective scaling of their fabrication volume.

Achieving full-spectrum lighting is a major challenge for phosphor-converted light-emitting diodes (pc-LEDs), which are crucial for solid-state lighting. This study presents the synthesis of polycrystalline Eu-doped Y3Al5O12 (YAG) phosphors through a sol-gel method and flame synthesis process, leading to XRD amorphous microspheres. The amorphous nature of the microspheres allows the reduction of Eu3+ to Eu2+ at a significantly lower temperature (800 °C) than the reduction of crystalline samples described in the literature (1400 °C). The presence of Eu2+ in the YAG lattice was confirmed by X-ray photoelectron spectroscopy (XPS). The X-ray diffraction (XRD) of samples annealed in reducing atmosphere confirmed partial crystallization of pure YAG in all examined samples. The Eu-doped YAG phosphor embedded in residual glass microspheres exhibited a broadband emission spectrum over the wavelength range 450–800 nm peaking at 565 nm, corresponding to the 4f65d1→ 4f7 electron transition within the Eu2+ ions.

A small, novel, integrated SHM system has been deployed during full-scale testing of a wing fatigue test for several weeks and a fuselage pressurisation test for several months. Complementary NDE measurement techniques were combined, with inputs from visible and infrared optical sensors, as well as resistance strain gauges. Sensor units were deployed at regions of interest and integrated board computers permitted near real-time data processing. The outputs were full-field measurement datasets from digital image correlation and thermoelastic stress analysis systems. Changes in these datasets in the regions of interest were successfully quantified using orthogonal decomposition and were indicative of changes in the condition of the structure. The results from these case studies demonstrate that this system can be successfully deployed in spatially restricted areas within airframe structures to monitor crack growth. The low cost and small footprint of the system presents the opportunity for installation of arrays of similar sensors for both test and in-service data collection. Near real-time data processing would allow timely reporting to service engineers, informing maintenance or operational decisions.

Until today, disassembling cylindrical 18650 cells commonly involved using a pipe cutter and pliers, with a risk of short-circuiting and mechanical damage to the electrode materials. This study presents a novel laser ablation assisted disassembly method with X-ray and optical validation for opening cylindrical battery cells without damaging the jelly roll. The objective is to develop a safe, efficient, and reproducible approach for cell disassembly enabling post-mortem analysis of failure mechanisms and investigation of aging effects. X-ray and tube micrometer measurements are used to estimate the cell wall thickness, with good agreement between the two methods. Laser ablation is calibrated to determine the optimal number of laser cycles for achieving the desired ablation depth. In situ temperature measurements are conducted. Various cooling parameters are investigated, maintaining the cell temperature within a safe range of 17( degrees)C to 35 C-degrees during operation. The temperature remains significantly below the reported onset temperature of 57 C-degrees for solid electrolyte interphase (SEI) decomposition. Depth analysis and surface morphology are conducted using confocal microscopy with interferometry and a fully automated digital microscope system. The cells are disassembled within an inert argon atmosphere. Challenges such as redeposition of ablated material and side trench formation are addressed. Overall, this method offers a safe, reproducible and efficient approach for opening cylindrical battery cells. This innovative approach fills a gap in the literature and contributes to advancements in failure analysis and degradation research for the benefit of cell producers, testing laboratories and research institutes.

We present a fabrication concept for freestanding THz filters and other photonic elements. It uses a polymer film substrate onto which a designed metamaterial is processed using standard clean-room processes. Elements are framed to custom dimensions and shapes using 3D printing. The resulting freestanding elements are robust, easy to handle, and mountable. We assessed the performance of the fabricated band-pass filters using THz time-domain spectroscopy. The process is adaptable to other wavelength ranges and has the potential for upscaling in manufacturing.

Large‐area flexible transparent conductive electrodes (TCEs) featuring excellent optoelectronic properties (low sheet resistance, R s , at high transparency, T) are vital for integration in transparent wearable electronics (i.e., antennas, sensors, supercapacitors, etc.). Solution processing (i.e., printing and coating) of conductive inks yields highly uniform TCEs at low cost, holding great promise for commercially manufacturing of transparent electronics. However, to formulate such conductive inks as well as to realize continuous conductive films in the absence of percolation issue are quite challenging. Herein, the scalable slot‐die coating of Ti 3 C 2 T x MXene aqueous inks is reported for the first time to yield large‐area uniform TCEs with outstanding optoelectronic performance, that is, average DC conductivity of 13 000 ± 500 S cm −1 . The conductive MXene nanosheets are forced to orientate horizontally as the inks are passing through the moving slot, leading to the rapid manufacturing of highly aligned MXene TCEs without notorious percolation problems. Moreover, through tuning the ink formulations, such conductive MXene films can be easily adjusted from transparent to opaque as required, demonstrating very low surface roughness and even mirror effects. These high‐quality, slot‐die‐coated MXene TCEs also demonstrate excellent electrochemical charge storage properties when assembled into supercapacitors.

Light beams with Orbital Angular Momentum (OAM) are explored in applications from microscopy to quantum communication, while the Talbot effect revives in applications from atomic systems to x-ray phase contrast interferometry. We evidence the topological charge of an OAM carrying THz beam in the near-field of a binary amplitude fork-grating by means of the Talbot effect, which we show to persist over several fundamental Talbot lengths. We measure and analyze the evolution of the diffracted beam behind the fork grating in Fourier domain to recover the typical donut-shaped power distribution, and we compare experimental data to simulations. We isolate the inherent phase vortex using the Fourier phase retrieval method. To complement the analysis, we assess the OAM diffraction orders of a fork grating in the far-field using a cylindrical lens.

We report a technological concept for freestanding photonic elements based on metamaterials fabricated on polymer films by clean-room processes and framed using 3D printing. A spin-coated cyclic olefin copolymer (TOPAS) of variable thickness down to one micrometer was used as the substrate onto which metamaterials were fabricated using optical lithography. We demonstrate the possibility of applying a second TOPAS layer to protect the device or to allow for stacking another metamaterial layer. To obtain freestanding elements, frames were 3D printed directly on top of the metamaterial before lift-off from the carrier wafer. This ensured maintaining the flatness of the elements. Both the cleanroom process and the 3D printing enabled the design and manufacturing of elements in different sizes and shapes, e.g., to adapt to specific experimental set-ups and holder geometries or to be compatible with standard optical mounts. While TOPAS is transparent for wavelengths from UV to the far infrared, except for a few infrared absorption lines, we illustrate the concept with the simulation and manufacturing of THz band-pass filters. The performance of the fabricated filters was assessed using THz time-domain spectroscopy. The process is scalable to other wavelength ranges and has the potential for upscaling in manufacturing.

THz-Time domain spectroscopic imaging is demonstrated combining a robotic scanning method with continuous signal acquisition and holographic reconstruction of the object to improve the imaging resolution. We apply the method to a metallic Siemens star in order to quantify resolution and to wood samples to demonstrate the technique on a non-metallic object with an unknown structure.

We present the 3D printing of microfluidic devices suitable for the THz regime using TOPAS filaments. We assessed the 3D-printed microfluidic devices with THz time-domain spectroscopy and X-ray microscopy. We compared the results of polished and unpolished windows of the 3D printed devices for studying the quality of the 3D printing in the THz and VIS regimes. Spectroscopic measurements were performed of water and lysozyme dissolved in water. We found that the results from the polished and unpolished devices were similar in the THz regime. A detailed calculation of the measurement uncertainty revealed that the dominant component of the measurement uncertainly was the gap thickness. Because of their optical and mechanical properties, we are convinced that 3D printing from TOPAS offers a cost-effective and rapid production of microfluidic devices usable in X-ray, UV, VIS, NIR, and THz regimes.

The extent of the domain over which a model validation demonstrates the reliability of a model is discussed and a simple schematic diagram is used to illustrate the domain. The schematic diagram can also be used to optimise the physical test campaign required to demonstrate the reliability of a model for its context of use. The connections to existing validation approaches and procedures are discussed.

Polarized THz time domain spectroscopy was used to study the anisotropic properties of wood-based materials for potential optical elements in the THz range, such as half-wave and quarter-wave plates. Wood samples of different species and sample thickness were studied experimentally showing high birefringence but rather high absorption. We elaborate on two approaches to optimize the optical properties for use as wave plates and assess them based on a figure of merit describing their efficiency as a function of birefringence and absorption. The first approach is to dry the wood samples, which significantly improves the efficiency of wave plates. The second approach is the use of artificially produced cellulose samples using 3D printing and freeze drying techniques, which also show birefringence caused by their similar macroscopic cellulose fibre structure. These materials have the potential as cost effective THz elements that are easy to tailor and produce for use at specific frequencies.

Polarized THz time domain spectroscopy was used to study the anisotropic properties of wood-based materials for potential optical elements in the THz range, such as half-wave and quarter-wave plates. Wood samples of different species and sample thickness were studied experimentally showing high birefringence but rather high absorption. We elaborate on two approaches to optimize the optical properties for use as wave plates and assess them based on a figure of merit describing their efficiency as a function of birefringence and absorption. The first approach is to dry the wood samples, which significantly improves the efficiency of wave plates. The second approach is the use of artificially produced cellulose samples using 3D printing and freeze drying techniques, which also show birefringence caused by their similar macroscopic cellulose fibre structure. These materials have the potential as cost effective THz elements that are easy to tailor and produce for use at specific frequencies.

Near-field diffraction from periodic structures leads to self-imaging (the Talbot effect), while dedicated quasi-periodic structures are used to generate orbital angular momentum in THz beams. However, the image stack taken in regular steps of increasing distance behind the grating suffers from experimental effects such as inhomogeneous laser power, parasitic interferences, or misalignment. We circumvent these flaws by evaluating the image stacks in the Fourier domain to identify the Talbot distance. We show how a Fourier transform also allows the identification of the topological charge. We report results on linear, ring and fork gratings.

Cyclic olefin copolymer (TOPAS) is a polymer transparent for frequencies up to 10 THz. TOPAS can be used for various THz devices and components. This work reports the 3D printing and the microfabrication of THz devices from TOPAS, namely microfluidic devices, lenses, flexible detectors, and freestanding THz filters.

Background: In the Clean Sky 2 project DIMES, the cyclic loading of a section of an A320 wing with pre-existing damage was carried out. Methods: We present a Digital Image Correlation (DIC) prototype system to monitor crack propagation in the aircraft wing. This system includes a mount for easy installation and adjustment in a confined space. Results: Strain localization and evaluation due to crack propagation was successfully observed in the Region-of-Interest (ROI) during cyclic fatigue loading. The results from the DIC prototype system were supported by conventional contact Resistance Strain Gauge (RSG) sensors acting as a far-field monitor. Conclusions: Future improvements, the combination of two DIC modules for a stereo DIC system and the potential of the DIC system for ground-based tests and Structural Health Monitoring (SHM) applications are also discussed.

The Talbot effect has been revived in many fields of modern optics. As a key number of self-imaging, the fundamental Talbot length plays a crucial role in many applications. However, the inspection of the Talbot carpet for determining the Talbot length is applicable only if the 2D field distribution behind the grating is represented by a 1D cross section. In this Letter, we show an effective way to overcome this limitation to explore the self-imaging of gratings with complex 2D periodicities. For that purpose, the near-field diffraction is analyzed using the Pearson correlation coefficient of the intensity distribution in Fourier space. We report results on linear, ring, and spiral gratings.

The limited availability and environmental issues of materials resources call for the development of biodegradable devices, which also applies to THz devices. Here, we present our work developing THz wave-plates based on cellulose nanofibers and Ag nanomaterials. Emphasis is put on optimizing the wave plate efficiency based on the arrangement and orientation of the nanofibers and the type and concentration of Ag nanoparticles.

Computational models of structures are widely used to inform decisions about design, maintenance and operational life of engineering infrastructure, including airplanes. Confidence in the predictions from models is provided via validation processes that assess the extent to which predictions represent the real world, where the real world is often characterised by measurements made in experiments of varying sophistication dependent on the importance of the decision that the predictions will inform. There has been steady progress in developing validation processes that compare fields of predictions and measurements in a quantitative manner using the uncertainty in measurements as a basis for assessing the importance of differences between the fields of data. In this case study, three recent advances in a validation process, which was evaluated in an inter-laboratory study 5 years ago, are implemented using a ground-test on a fuselage at the aircraft manufacturer’s site for the first time. The results show that the advances successfully address the issues raised by the inter-laboratory study, that the enhanced validation process can be implemented in an industrial environment on a complex structure, and that the model was an excellent representation of the measurements made using digital image correlation.