A comprehensive review on various non-isolated power converter topologies for a light-emitting diode driver

Light-emitting diode (LED) lighting applications aided by an electronic power control have become very attractive in the recent years. For LED lighting applications, it is essential to design a converter with single/multi-output for handling multiple loads. As the LED load is more sensitive to the change in input/converter parameters, it is necessary to regulate the current concerning the design specifications. In this paper, several LED topologies are reviewed with a focus on power density, single/multi-load operation, size, and reliability. Several converter topologies are reviewed and compared in terms of power rating, number of semiconductor switches, isolation, and efficiency. Various modulation techniques used for dimming control are described in brief. The salient features of each converter topology are discussed with the power rating and application for which the topology can be preferred. So, the selection of the power factor correction (PFC) and low source side harmonics converter topology is presented. This paper will be helpful to the researchers who are working on the development of LED drivers

The 30 GHz solid state amplifier for low cost low data rate ground terminals

This report details the development of a 20-W solid state amplifier operating near 30 GHz. The IMPATT amplifier not only met or exceeded all the program objectives, but also possesses the ability to operate in the pulse mode, which was not called for in the original contract requirements. The ability to operate in the pulse mode is essential for TDMA (Time Domain Multiple Access) operation. An output power of 20 W was achieved with a 1-dB instantaneous bandwidth of 260 MHz. The amplifier has also been tested in pulse mode with 50% duty for pulse lengths ranging from 200 ns to 2 micro s with 10 ns rise and fall times and no degradation in output power. This pulse mode operation was made possible by the development of a stable 12-diode power combiner/amplifier and a single-diode pulsed driver whose RF output power was switched on and off by having its bias current modulated via a fast-switching current pulse modulator. Essential to the overall amplifier development was the successful development of state-of-the-art silicon double-drift IMPATT diodes capable of reproducible 2.5 W CW output power with 12% dc-to-RF conversion efficiency. Output powers of as high as 2.75 W has been observed. Both the device and circuit design are amenable to low cost production

Wireless magnetoelectrically powered organic light-emitting diodes

This work was supported by a scholarship to J.F.B. donated by Beverly and Frank MacInnis to the University of St Andrews, the European Union Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement no. 101023743 (PolDev to A.M.), The Leverhulme Trust (RPG-2017-231), the Alexander von Humboldt Foundation (Humboldt Professorship to M.C.G.), the DFG-funded Research Training Group “Template-Designed Organic Electronics (TIDE)” (RTG2591), and the EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207).Compact wireless light sources are a fundamental building block for applications ranging from wireless displays to optical implants. However, their realization remains challenging because of constraints in miniaturization and the integration of power harvesting and light-emission technologies. Here, we introduce a strategy for a compact wirelessly powered light-source that consists of a magnetoelectric transducer serving as power source and substrate and an antiparallel pair of custom-designed organic light-emitting diodes. The devices operate at low-frequency ac magnetic fields (~100 kHz), which has the added benefit of allowing operation multiple centimeters deep inside watery environments. By tuning the device resonance frequency, it is possible to separately address multiple devices, e.g., to produce light of distinct colors, to address individual display pixels, or for clustered operation. By simultaneously offering small size, individual addressing, and compatibility with challenging environments, our devices pave the way for a multitude of applications in wireless displays, deep tissue treatment, sensing, and imaging.Peer reviewe

Investigations of chiral effects in molecular spectroscopy

A consequence of the chiral weak interaction is that the enantiomers of a chiral molecule will differ in energy by the minute parity-violating energy difference (PVED). The enantiomers of a chiral iron complex were prepared and characterized with various spectroscopies, including x-ray photoelectron spectroscopy and x-ray diffraction. Measurements of the Mossbauer spectra show a small difference in the energy of the two enantiomers (~10-10 eV). This energy difference nears the expected order of magnitude of the parity-violating energy difference for a molecule in which the chiral center is a high Z atom. Sodium chlorate has been known to form chiral crystals from achiral aqueous solutions for over one hundred years. Typically, equal numbers of right- and left-handed crystals are produced in unstirred crystallizations. Data has been taken that show an excess of right-handed crystals are produced when crystallizations occur under the influence of a beta source. The beta particles are spin polarized due to the chiral weak interaction which is responsible for beta decay. Preliminary results indicate that the influence of positrons (which are spin polarized oppositely to beta particles) is in the opposite direction. Finally, measurements of mass resolved resonant and non-resonant multiphoton ionization of the chiral 2-butylamine entrained in a nozzle jet expansion into a linear time-of-flight mass spectrometer constructed in house were obtained using right- and left-circularly polarized laser light. In addition, ratios of ionization rates for linearly and circularly polarized light were measured

Spectroscopic study of optical confinement and transport effects in coupled microspheres and pillar cavities

In this thesis we investigated the spatial and spectral mode profiles, and the optical transport properties of single and multiple coupled cavities. We performed numerical modeling of whispering gallery modes (WGMs) in such cavities in order to explain recent experiments on semiconductor micropillars. High quality (Q up to 20 000) WGMs with small mode volumes V ~0.3 µm3 in 4-5 µm micropillars were reproduced. The WGM spectra were found to be in a good agreement with the experimental data. The coupling between size-matched spheres from 2.9 to 6.0 µm in diameter was characterized using spectroscopy. We observed peculiar kites in the spectral images of such coherently coupled bispheres. The origin of these kites was explained due to the coupling of multiple pairs of azimuthal modes. We quantified the coupling constant for WGMs located in the equatorial plane of spheres parallel to the substrate which plays the most important role in the transport of WGMs in such structures. It was shown that in long (>10 spheres) chains of size-disordered polystyrene microspheres the transmission properties are dominated by photonic nanojet-induced modes (NIMs) leading to periodic focusing of light along the chain. In the transmission spectra of such chains we observed Fabry-Pe´rot fringes with propagation losses of only 0.08 dB per sphere at the maxima of the transmission peaks. The fringes of NIMs are found to be in a good agreement with the results of numerical modeling. These modes can be used in various biomedical applications requiring tight focusing of the beams

LASER Tech Briefs, Spring 1994

Topics in this Laser Tech Brief include: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Mechanics, Fabrication Technology, and books and reports

Present and future of surface-enhanced Raman scattering

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article

Nuclear Dynamics in the Molecular Convergent Close-Coupling Method

Theoretical and computational modelling of collisions between electrons and the hydrogen molecule (H2) as well as its five isotopologues has been conducted. The technique applied is the molecular convergent close-coupling (MCCC) method, with a particular focus on the treatment of nuclear dynamics in the MCCC calculations. Cross sections for over 60,000 vibrationally-resolved transitions have been calculated within the adiabatic-nuclei approximation, and a new vibrational-electronic close-coupling method has been developed to study resonant electron-molecule collisions

Shedding New Light on Cancer with Non-Linear Optical Microscopy

Oesophageal cancer, one of the most aggressive cancer types is considered the seventh most common cancer in terms of incidence and the sixth most common cause of cancer deaths worldwide due to late diagnosis. In the UK, the oesophageal cancer incidence rate has increased by approximately 10% since the 1990s. At present, histopathology is the gold standard method for the diagnosis of oesophageal cancer, which rely on biopsy collection using an endoscopy procedure followed by the histological sample’s preparation. This method is invasive, time-consuming, and largely based on the pathologist's experience of diagnosis. Therefore, new diagnostic techniques are required to provide non-invasive methods for early and rapid diagnosis. Raman scattering has the potential to replace histopathology as the gold standard for diagnosis for a wide range of diseases. Raman scattering provides stain-free imaging with chemical-specificity derived from the intrinsic vibrational signatures of biomolecules. However, the low scattering cross-section severely limits the image acquisition speeds and like conventional histopathology, requires tissue sectioning to provide morphological imaging below the surface of tissue biopsies. Stimulated Raman scattering (SRS) has recently appeared as a powerful technique for (near)real-time Raman imaging in intact tissue samples. Thework in this thesis aimed to develop the stimulated Raman scattering (SRS) for rapid wavelength tuning and chemical imaging of clinical samples, such as cancer biopsies. This was achieved by making modification to a laser cavity to reduce the time of the wavelength tuning by approximately 35 times compared to the original cavity design. Furthermore, the cavity modification led to the spectra being separated efficiently and the wavelength tuning controlled by cavity length changes only. The improved design was applied to image frozen oesophageal tissues, which have four major pathology groups, normal, inflammation, columnar-lined (Barrett's) oesophagus (CLO) and low-grade dysplasia. A large area imaging was performed using the SRS technique at 2930 cm-1 for four different oesophageal tissues, which presented the morphological and structural information. However, histopathological diagnosis depends on the visualisation of the cell nucleus in the tissue. This component was not highlighted until the stimulated Raman histology approach was developed for small regions of interest in the CLO and the low-grade dysplasia sample, which required two different frequencies at 2840 cm-1 and 2930 cm-1. All SRS images were compared to haematoxlin and eosin (H&E) stained sections. Further comparisons were made between SRS and Raman imaging techniques, with SRS offering faster acquisition times and a higher spatial resolution. The spectral signature for the different pathological groups in the oesophageal tissues were explored in the high wavenumber (2800 – 2930 cm-1) region using hyperspectral SRS and compared with the spectra from the Raman. K-means clustering analysis was used to explore the morphochemical information using the CLO and low-grade dysplasia sections. Both techniques were able to demonstrate unique information such as the epithelial cells that form the oesophagus glands and surrounding connective tissue. It is concluded that SRS has the power to be one of the ideal imaging modalities to gather the molecular information in biological samples. However, it still needs more development due to the complexity of the system