Order Of 100μm Research Articles

Approximation method for fast calculation of transmission in multi-mode waveguides.

Freeform dielectric waveguides connect optical chips made of different materials in fully integrated photonic devices. With a spatial extent in the order of 100µm, they constitute a computational challenge and make Maxwell full-wave solvers unhandy for the accelerated design. Therefore, it is of utmost importance to have tools that permit the fast prediction of waveguide loss to enable the rapid optimization of waveguide trajectories. Previously developed methods relied on the assumption that only a single mode propagates in the waveguide. However, the propagation of higher-order modes is not just unavoidable due to the geometry of the waveguides, but also, sometimes, beneficial as it increases the number of channels to transmit information. In this contribution, we present an approximate method for the fast calculation of transmission that accommodates the presence of higher-order waveguide modes, and assess its liability by describing light propagation through selected devices.

Fast Timing MPGD for ToF-PET

Positron emission tomography (PET) is an effective functional imaging technique especially for cancer diagnosis. Its performance is strictly connected to the ability to detect and reconstruct photons emitted by the positron–electron annihilation. Its sensitivity is enhanced when time information is included (time-of-flight (ToF) PET). The measure of the detection time difference between the annihilation of the two photons leads to a higher contrast image and more accurate diagnoses. We describe the studies for a possible development of a ToF-PET based on Micro Pattern Gas Detector (MPGD). This kind of detector has a very good spatial and time resolution (order of 100μm and few ns, respectively) and very low price, making it suitable for a full-body scanner. Further improvement in the time precision (suitable goal is to achieve values of the order of 100 ps) could be reached thanks to the Fast Timing MPGD (FTM) design, where multiple layers of MPGD compete in better measuring time information.

Fractal scan strategies for selective laser melting of ‘unweldable’ nickel superalloys

The high thermal gradients experienced during manufacture via selective laser melting commonly result in cracking of high γ/γ′ Nickel based superalloys. Such defects cannot be tolerated in applications where component integrity is of paramount importance. To overcome this, many industrial practitioners make use of hot isostatic pressing to ‘heal’ these defects. The possibility of such defects re-opening during the component life necessitates optimisation of SLM processing parameters in order to produce the highest bulk density and integrity in the as-built state.In this paper, novel fractal scanning strategies based upon mathematical fill curves, namely the Hilbert and Peano-Gosper curve, are explored in which the use of short vector length scans, in the order of 100μm, is used as a method of reducing residual stresses. The effect on cracking observed in CM247LC superalloy samples was analysed using image processing, comparing the novel fractal scan strategies to more conventional ‘island’ scans. Scanning electron microscopy and energy dispersive X-ray spectroscopy was utilised to determine the cracking mechanisms.Results show that cracking occurs via two mechanisms, solidification and liquation, with a strong dependence on the laser scan vectors. Through the use of fractal scan strategies, bulk density can be increased by 2±0.7% when compared to the ‘island’ scanning, demonstrating the potential of fractal scan strategies in the manufacture of typically ‘unweldable’ nickel superalloys.

Spatiotemporally resolved heat transfer measurements for flow boiling in microchannels

Spatiotemporally resolved wall heat transfer measurements can provide valuable insight into the fundamental mechanisms affecting flow boiling in microchannels. Operating at the microscale, necessitates resolving changes in local and instantaneous heat transfer characteristics on the order of 100μm and 1kHz, respectively. Straightforward interpretation of transient temperature measurements is often challenging due to the conjugate conduction effects in the substrate, which can dampen the measured and inferred heat transfer quantities. These damping effects are described using a slip coefficient (S), which represents the fraction of the change in the local heat transfer that is registered by a sensor (negligible thermal mass) located on a given substrate. Using S, arguments are presented that the conduction patterns in the substrate are predominantly 1-D (i.e. into the substrate) at suitable spatiotemporal-scales. Building on these fundamental considerations, a numerical procedure is adopted to allow a time varying estimate of the local convective heat flux and heat transfer coefficient from transient temperature measurements. Examples of this framework are showcased with experimental results and discussions for interactions observed during flow boiling of HFE 7000 in a single microchannel (hydraulic diameter=370μm). At the relatively low mass flux of 200kg/m2s reported in this work, liquid evaporation was found to dictate the local heat transfer trends. High rates of heat transfer were observed to accompany the growth of bubbles and evaporation of the liquid film under vapor slugs. Local dryout was routinely observed in the bubbly and slug flow regime and found to initially enhance heat transfer (i.e. at the creation and subsequent propagation of the three-phase contact line) and present near-zero heat transfer rates in the dried-out domain.

Phase shifting masks in Displacement Talbot Lithography for printing nano-grids and periodic motifs

High-resolution periodic structures with geometric shapes such as squares or triangles cannot be readily produced with low-cost photolithography methods like interference or proximity photolithography. We present a method for robust printing of such patterns with Displacement Talbot Lithography (DTL) using phase shifting masks. This combination effectively yields high-contrast images that extend to large distances from the mask. It therefore enables uniform images to be printed over large, non-flat substrates without loss of resolution. Phase masks with several different motifs have been designed, fabricated and tested using DTL exposures. High-fidelity grid and island type structures with square and triangular motifs and sub-micron feature sizes were printed into different types of photoresists using wafer–mask gaps on the order of 100μm. The experimental results show good agreement with calculated image intensity distributions. The method is suitable for low-cost production of high-quality patterned growth substrates and photonic structures among other applications.

Fluidic oscillator-mediated microbubble generation to provide cost effective mass transfer and mixing efficiency to the wastewater treatment plants

Aeration is one of the most energy intensive processes in the waste water treatment plants and any improvement in it is likely to enhance the overall efficiency of the overall process. In the current study, a fluidic oscillator has been used to produce microbubbles in the order of 100μm in diameter by oscillating the inlet gas stream to a pair of membrane diffusers. Volumetric mass transfer coefficient was measured for steady state flow and oscillatory flow in the range of 40–100l/min. The highest improvement of 55% was observed at the flow rates of 60, 90 and 100l/min respectively. Standard oxygen transfer rate and efficiency were also calculated. Both standard oxygen transfer rate and efficiency were found to be considerably higher under oscillatory air flow conditions compared to steady state airflow. The bubble size distributions and bubble densities were measured using an acoustic bubble spectrometer and confirmed production of monodisperse bubbles with approximately 100μm diameters with fluidic oscillation. The higher number density of microbubbles under oscillatory flow indicated the effect of the fluidic oscillation in microbubble production. Visual observations and dissolved oxygen measurements suggested that the bubble cloud generated by the fluidic oscillator was sufficient enough to provide good mixing and to maintain uniform aerobic conditions. Overall, improved mass transfer coefficients, mixing efficiency and energy efficiency of the novel microbubble generation method could offer significant savings to the water treatment plants as well as reduction in the carbon footprint.

Advanced Fiber Laser Perforation Technology for Thermoplastic Pre-Preg Material

A study concerning the application of fiber laser to perforate thermoplastic pre-pregs is presented. An IPG fiber laser was used to drill arrays of holes in PEKK carbon-fiber composite pre-preg material. Perforated holes were of the order of 100μm. The effects of laser perforation process parameters including the number of pulses on the geometry of the resultant holes and the thermal damage to the matrix and fibres have been investigated. Dimensional analysis and experimental results have been used to construct the laser perforation process model. Keywords: Laser perforation; Fibre laser; Process modelling; Polymer matrix composites.

Noncontact scanning impedance imaging in an aqueous solution

We present a method for imaging based on noncontact electrical impedance measurements and mechanical scanning. Measurement results are shown for an initial system based on this concept. An impedance probe design is presented, applicable to the test system. Line-scan data plots of high impedance contrast structures show a good fit to a theoretical physical model. Image resolutions on the order of 100μm are indicated for the initial system. Two-dimensional impedance images of biological tissue generated by this technique are shown.

Electron density measurements in an atmospheric pressure air plasma bymeans of infrared heterodyne interferometry

An infrared heterodyne interferometer has been used to measure thespatial distribution of the electron density in direct current, atmosphericpressure discharges in air. Spatial resolution of the electron density in thehigh-pressure glow discharge with characteristic dimensions on the order of100 µm required the use of a CO2 laser at a wavelength of 10.6 µm.For this wavelength and electron densities greater than 1011 cm-3the index of refraction of the atmospheric air plasma is mainly determined byheavy particles rather than electrons. The electron contribution to therefractive index was separated from that of the heavy particles by taking thedifferent relaxation times of the two particle species into account. With thedischarge operated in a repetitive pulsed mode, the initial rapid change ofthe refractive index was assumed to be due to the increase in electrondensity, whereas the following slower rise is due to the decrease in gasdensity caused by gas heating. By reducing the time between pulses, directcurrent conditions were approached, and the electron density as well as thegas density, and gas temperature, respectively, were obtained throughextrapolation. A computation inversion method was used to determine the radialdistribution of the plasma parameters in the cylindrical discharge. For adirect-current filamentary discharge in air, at a current of 10 mA, theelectron density was found to be 1013 cm-3 in the centre, decreasingto half of this value at a radial distance of 0.21 mm. Gaussian temperatureprofiles with σ = 1.1 mm and maximum values of 1000-2000 K in the centrewere also obtained with, however, larger error margins than for electrondensities.

Design of a Wide Field High Sensitivity Imaging System for Quantitative Analysis of CGHA Micro-Arrays.

Abstract Comparative Genomic Hybridization (CGH) is a quantitative technique for determining relative copy numbers of DNA sequences in whole-genomic test samples. In conventional CGH, test DNA labelled with one fluorochrome and reference DNA labelled with a spectrally different fluorochrome are hybridized to metaphase chromosomes. by measuring the ratio of intensities of the two fluorochromes, a relative copy number of sequences in the test DNA can be calculated for each point along each chromosome. While this approach is very useful for rapid surveying of the entire test genome, the spatial and dynamic resolution are compromised by the dense packing of DNA in the metaphase state. CGHa (array-based CGH) uses spots of cloned DNA arrayed onto a microscope slide which represent the entire genome or interesting sections thereof. Spatial resolution and dynamic range are now only limited by the size of the clones used. See the abstract by Pinkel et al. for more detail. We designed an imaging system for analyzing fluorescence signals from micro-arrays containing targets on the order of 100μm in diameter spaced at similar intervals.

Low-voltage phase modulation in GaAs/AlGaAs quantum well optical waveguides

We report GaAs/AlGaAs quantum well waveguide phase modulators with high phase shift coefficients, as large as 520 degrees per V mm. By operating at wavelengths far below the bandedge and applying DC bias we achieve large electrooptic modulation with low absorption loss in device lengths on the order of 100μm and drive voltages on the order of 1 V.

Non-local conduction by charge-density waves in niobium triselenide

The threshold field E T for the onset of nonlinear conduction in NbSe 3 has been measured using both the normal 4-terminal arrangement, and a transposed version with current flow between the inner pair and voltage measured between the outer. When the distance between the inner terminals is small, and the temperature between 60 and 110 K, E T is significantly greater for the transposed than for the normal arrangement. The phenomenon is thought to demonstrate that the nonlinear conduction, which arises from motion of the charge-density wave (CDW) forming at 144 K, is non-local over distances of the order of 100μm. Further experiments indicate that E T is greater with the transposed arrangement because the CDW then has to be broken near the inner terminals, in order that its central section might move independently. Evidence is presented that the breaking process at an inner terminal depends on whether current flows from or towards it, and that above 110 K breaking occurs even when the normal configuration is used, apparently because the CDW is then too weak to overcome the pinning introduced by the contact material. No corresponding effects have been observed in nonlinear conduction by the CDW which forms at 59 K.