Renishaw (United Kingdom)

Abstract In this article we present an integration of a Raman spectroscopy system with a scanning electron microscope (SEM) and present several applications demonstrating the advantages of correlative microscopy using these technologies. Combining Raman and SEM allows direct collection of data describing the molecular and lattice vibrations in materials and the spatial distribution of different chemical species from the same sample area at high resolution. Examples include analysis of carbon types in a carbon-based battery electrode, SEM EDS analysis of a geological sample, and identification of contaminants on a fuel injector. The information provided by Raman spectroscopy complements the ultrastructural details from SEM imaging, and together the data provide comprehensive insights into the chemistry and structure of the samples.

This paper presents an axially stacked coil structure for use in heating metal powders used in additive manufacturing. This structure acts as a quarter wavelength transmission line resonator providing H field hot spots evenly distributed across the structure. Using COMSOL Multiphysics and bench top measurements, these resonant modes and peak H fields are identified then used to efficiently heat 200cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> of Ti-6Al-4V nowder to 100°C.

BackgroundThere is a dearth of research to support the treatment of people with postural tachycardia syndrome (PoTS). Despite expert consensus suggesting exercise is recommended for this patient group, there are no randomised control trials examining this rigorously. The aim was to co-create a feasibility trial protocol and a rehabilitation intervention for people living with PoTS.MethodsThe intervention and feasibility trial design were co-created as part of the PostUraL tachycardia Syndrome Exercise (PULSE) study. We used the ‘three co’s framework’ of co-define, co-design and co-refine. Recruitment included key national charities and National Health Service Trusts treating people living with PoTS in the UK. Eighteen patient and public involvement members attended the co-define session, and 16 co-creators with a mix of expertise attended the subsequent co-design and co-refine sessions. Seven intervention practitioners were trained in the rehabilitation intervention, providing feedback for further co-refinement.ResultsThe final co-created intervention comprises online physical activity, and lifestyle and behaviour change support sessions. It is based on functional movement activities using a patient-centred approach tailored to individual needs. Physical activity intensity is guided by individuals’ perception of effort rather than by objective measures. Recumbent bikes are provided for home use. Patients deemed randomisation to be acceptable because research in this area was considered important.ConclusionsAn innovative approach was used to co-create the PULSE intervention and feasibility trial protocol to meet the evidence-based and logistical needs of people living with PoTS, clinicians, service deliverers, third-sector organisations, academics and funders. This can be used as a successful example and template for future research internationally. People living with PoTS were recognised as experts and involved in every aspect of conceptualisation, design and refinement. This complex rehabilitation intervention is currently being tested in a randomised feasibility trial comparing the PULSE intervention with best-practice usual care for people living with PoTS.Trial registrationISRCTN45323485 was registered on April 7, 2020.

Dual-comb ranging techniques employ a ‘probe’ comb of repetition frequeny, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{rep}$</tex> to sample the distance between reference (R) and target (T) optics, and a ‘local oscillator’ (LO) comb with a repetition frequency, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{rep}+\Delta f_{rep}$</tex> to temporally gate the returning probe pulses. When conventional detection is used, the result is a series of interferograms requiring high-bandwidth digitisation and post-processing to derive the distance values. Conversely, in two-photon dual-comb LiDAR, the probe and LO combs are combined with orthogonal polarisations and detected via two-photon absorption to create optical cross-correlations [3]. The carrier-free nature of these signals allows them to be conditioned to act as triggers for a microcontroller, enabling an ultra-precise data collection paradigm where the microcontroller acts as a stopwatch recording the time between the detection of subsequent cross-correlations, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\tau_{i}$</tex> [4]. The raw data take the form of a string of integers written to the serial port, allowing real-time distance calculations. The transition from digitising the full optical signal to time-stamping pulses using a microcontroller-based stopwatch significantly reduces the data burden associated with dual-comb techniques, whilst maintaining a comparable level of measurement precision.

We have measured the Raman spectra of some oligothiophenes (bithiophene, terthiophene, quarterthiophene, sexithiophene and octithiophene) and polythiophene with wavelengths from 325–1064 nm (3.815–1.165 eV). All of the materials give good quality spectra with 1064 nm excitation, although there is weak background fluorescence for some of them. The UV lines of 405 and 324 nm generally provide good-quality spectra, albeit with significant fluorescence for bithiophene and quarterthiophene. Surprisingly, there is little difference between the relative intensities (i.e., the ratio of a band’s intensity as compared to the strongest band) of the spectra with the different excitation wavelengths. However, close inspection of the 2000–3200 cm−1 region of octithiophene and polythiophene with 325 and 405 nm excitation shows several modes in this region that can be assigned to combinations and overtones involving the ~1440 cm−1 C–C ring stretch that do not appear with 1064 nm excitation. The presence of overtones and combinations with anomalously large intensities is a hallmark of resonance Raman spectroscopy.

This paper presents a deformed elliptical cavity resonator that allows the control of transmission zeros (TZs) over an extensive frequency range. These TZs can improve filter selectivity and suppress spurious modes to give the filter a wide stopband with high rejection. A building block is analysed, and the theory explained with control of TZ illustrated. Two Ku-band bandpass filter models, 4- and 8-pole, are presented. The 4-pole model was 3D printed using Selective Laser Melting (SLM) and tested without any internal surface post-processing. The measured results agree well with the simulations.

While Laser powder bed fusion (L-PBF) machines have greatly improved in recent years, the L-PBF process is still susceptible to several types of defect formation. Among the monitoring methods that have been explored to detect these defects, camera-based systems are the most prevalent. However, using only photodiode measurements to monitor the build process has potential benefits, as photodiode sensors are cost-efficient and typically have a higher sample rate compared to cameras. This study evaluates whether a combination of photodiode sensor measurements, taken during L-PBF builds, can be used to predict measures of the resulting build quality via a purely data-based approach. Using several unsupervised clustering approaches build density is classified with up to 93.54% accuracy using features extracted from three different photodiodes, as well as observations relating to the energy transferred to the material. Subsequently, a supervised learning method (Gaussian Process regression) is used to directly predict build density with a RMS error of 3.65%. The study, therefore, shows the potential for machine-learning algorithms to predict indicators of L-PBF build quality from photodiode build measurements only. This study also shows that, relative to the L-PBF process parameters, photodiode measurements can contribute to additional information regarding L-PBF part quality. Moreover, the work herein describes approaches that are predominantly probabilistic, thus facilitating uncertainty quantification in machine-learnt predictions of L-PBF build quality.

Additive manufacturing (AM) enables freedom of design, part complexity, and customization with minimal added cost, by fusing materials layer upon layer. AM, in general, is considered to have great potential in complementing conventional manufacturing methods. Functional parts with high strength to weight ratio generated using structural topology optimization can be eventually realized by AM. Limitations of AM parts related to surface finish and dimensional accuracy can be overcome by post-machining of critical features and surfaces in order to achieve a specific tolerance and surface quality. To minimize the trial and error efforts, accurate AM and post-machining simulations are essential for effective planning of the synergized processes. The goal of this study is to propose a process workflow which can be used as a guideline for successful production of complex parts manufactured via laser powder bed fusion (LPBF) and post-processed via CNC (computer numerical control) machining. The workflow is deployed and iterated through a case study of the manufacturing of a surgical navigation tracker, where the holistic manufacturing process involves a digital design utilizing structural topology optimization, AM part geometric distortion simulation, machining process planning, fabrication, and validation.KeywordsAdditive manufacturingTopology optimizationSimulationProcess planningPost-machining

Plasmonic nanowires are key building-blocks for plasmonic based devices, such as nano-sources and nano-sensors. They can take advantage of the propagative nature of surface plasmon polaritons (SPP) in a guided way, and the strong field enhancement at the nanowire tips. Here, the proof-of-concept of a SPP-mediated remote Raman effect with a coaxial nanowire is reported [1]. The remote Raman spectroscopy consists in probing a species at a distanced place from the excitation. The metallic nanowire geometry promotes a guiding of the surface plasmon polaritons along several micrometers, while the required momentum matching for exciting SPP is allowed by the discontinuity at the nanowire tip. The proposed systems are cylindrical coaxial nanowires consisting of a gold core to propagate SPP and a Raman-emitting shell of poly(3,4-ethylene-dioxythiophene) (PEDOT) grown only at one tip of the gold nanowire. A second challenge has been tackled, dealing with the weakness of the Raman signal to be detected. It was proposed to enlarge the nanowire tips in order to enhance the in-coupling of an excitation optical signal with the nanowire, and the out-coupling of the plasmon-mediated signal at a remote location. It has been achieved by transforming the gold nanowire tips with dry laser heating treatments to obtain dumbbell-like nanowires. The plasmonic properties of these original nanowires have been determined by an EELS-STEM study and interpreted by finite-element modeling. The benefits of these enlarged tips on the optical signal has been investigated by a Rayleigh backscattering study. [1] D. Funes-Hernando, M. Peláez-Fernández, D. Winterauer, J.-Y. Mevellec, R. Arenal, T. Batten, B. Humbert and J.L. Duvail Nanoscale (2018) 10, 6437 – 6444