Browsing by Author "Tiwari, Divya"

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    Ammonia sensing using lossy mode resonances in a tapered optical fibre coated with porphyrin-incorporated titanium dioxide
    (Society of Photo-optical Instrumentation Engineers (SPIE), 2016-05-30) Tiwari, Divya; Mullaney, Kevin; Korposh, Sergiy; James, Stephen W.; Lee, Seung-Woo; Tatam, Ralph P.
    The development of an ammonia sensor, formed by the deposition of a functionalised titanium dioxide film onto a tapered optical fibre is presented. The titanium dioxide coating allows the coupling of light from the fundamental core mode to a lossy mode supported by the coating, thus creating lossy mode resonance (LMR) in the transmission spectrum. The porphyrin compound that was used to functionalise the coating was removed from the titanium dioxide coating upon exposure to ammonia, causing a change in the refractive index of the coating and a concomitant shift in the central wavelength of the lossy mode resonance. Concentrations of ammonia as small as 1ppm was detected with a response time of less than 1min. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
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    An ammonia sensor based on Lossy Mode Resonances on a tapered optical fibre coated with porphyrin-incorporated titanium dioxide
    (Elsevier, 2017-04) Tiwari, Divya; Mullaney, Kevin; Korposh, Sergiy; James, Stephen W.; Lee, Seung-Woo; Tatam, Ralph P.
    The development of a highly sensitive ammonia sensor is described. The sensor is formed by deposition of a nanoscale coating of titanium dioxide, containing a porphyrin as a functional material, onto a tapered optical fibre. The titanium dioxide coating allows coupling of light from the fundamental core mode to a lossy mode supported by the coating, thus creating a Lossy Mode Resonance (LMR) in the transmission spectrum. A change in the refractive index of the coating caused by the interaction of the porphyrin with ammonia causes a change in the centre wavelength of the LMR, allowing concentrations of ammonia in water as low as 0.1 ppm to be detected, with a response time of less than 30 s.
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    An ammonia sensor based on Lossy Mode Resonances on a tapered optical fibre coated with porphyrin-incorporated titanium dioxide
    (Cranfield University, 2016-11-28 09:12) Tiwari, Divya; Mullaney, Kevin; James, Stephen; Tatam, Ralph
    Data presented in: An ammonia sensor based on Lossy Mode Resonances on a tapered optical fibre coated with porphyrin-incorporated titanium dioxide, Tiwari et al Sensors and Actuators B 2016 - http://dx.doi.org/10.1016/j.snb.2016.11.092 Figure3.xlsx - The transmission spectrum obtained in air and water from a typical 40 µm non-adiabatic (a), a 17 µm non-adiabatic (b), a 40 µm adiabatic (c) and a 17 µm adiabatic (d) tapered optical fibre. Figure 4.zip - transmission spectra of a non-adiabatic tapered optical fibre of waist diameter 17 microns with time and thus increasing thickness of the TMPyP-TiO2 coating. Figure 5_6_7.zip - transmission spectrum of an adiabatic tapered optical fibre of waist diameter 17 microns with time and thus increasing thickness of the TMPyP-TiO2 coating. Figure 8 and 9.zip transmission spectra when an adiabatic tapered optical fibre of diameter 17 microns was immersed in differing concentrations of ammonia
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    Fibre Bragg grating sensors for the analysis of pressure distribution at a disc brake/pad interface
    (SPIE, 2017-04-24) Major, B. T.; Tiwari, Divya; Correia, Ricardo; James, Stephen W.; Tirovic, Marko; Tatam, James P.
    The use of optical fibre Bragg gratings (FBGs) to monitor the Interface Pressure Distribution (IPD) on an automotive disc brake pad under a variety of loading conditions is studied. The results demonstrate successful strain transfer from the brake pads to the attached FBG sensors under static loading, with a linear response to increasing pressure, and with the measured IPD showing good agreement with that recorded using pressure sensitive paper. Results are also presented demonstrating that changes in the IPD as a result of torque acting on the brake pads can be monitored by the FBG sensors.
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    Impact of Zr/Ti ratio in the PZT on the photoreduction of silver nanoparticles.
    (Elsevier, 2009-06-03) Tiwari, Divya; Dunn, Steve; Zhang, Qi
    Silver nanoparticle deposition from an aqueous solution of silver nitrate onto the surface of PZT thin films of stoichiometric compositions PbZr0.3Ti0.7O3 and PbZr0.52Ti0.48O3 has been investigated. The impact of Zr/Ti ratio on the photochemical properties of PZT is shown by the preferential growth of silver nanoparticles onto the surface. Photoreduction of silver occurs on both c+ and c− domains on PbZr0.52Ti0.48O3 whereas it occurs only on c+ domains on a PbZr0.3Ti0.7O3 surface. The difference in deposition pattern is attributed to difference in magnitude of spontaneous polarization, effective hole concentration and band gap of the two samples which impacts shape and width of space charge layer in the two samples resulting in a change in band bending at the surface.
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    Influence of annealing on the photochemical deposition of silver onto PZT thin films under UV irradiation
    (Elsevier Science B.V., Amsterdam., 2009-10-31T00:00:00Z) Tiwari, Divya; Dunn, Steve
    Silver nanoparticle deposition from an aqueous solution of 0.01 M silver nitrate solution onto the c+ domain of PZT (30/70) thin films has been investigated for samples annealed at a variety of temperatures from 530 to 690 °C. The impact of annealing was to increase the deposition of photoreduced silver on the surface. When the PZT samples were annealed in air at temperatures ranging from 530 to 690 °C the silver deposition increased by more than 200%. The increase in the deposition of the silver is attributed to increase in the defect concentration due to the volatilisation of components from the PZT, most importantly PbO. Variations in the Pb concentration of the sample are measured using EDX and show a marked change, reduction in Pb, with annealing temperature.
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    Influence of ferroelectricity on the photoelectric effect of LiNbO3.
    (American Institute of Physics (AIP), 2008-09) Dunn, Steve; Tiwari, Divya
    A comparison between the influence of domain dependent photochemical and photoelectric cation reduction on the surface of LiNbO3 is presented. The reduction of the photoelectric threshold for LiNbO3 due to the polar nature of the crystal allows high energy UV irradiation to produce free electrons that can participate in photochemical reduction of silver nitrate on the surface. This is in addition to the previously understood phenomenon of domain directed photophysics, where influences on space charge layer due to the internal dipole of a ferroelectric determine the carrier at the surface. We show that the interaction of photoelectric and domain dependent influences can be observed in LiNbO3 due to the low electron affinity (ca 2eV) and large band bending (0.8eV).
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    Insights into the relationship between inherent materials properties of PZT and photochemistry for the development of nanostructured silver.
    (Royal Society of Chemistry, 2007-09-25) Dunn, Steve; Tiwari, Divya; Jones, Paul M.; Gallardo, Diego E.
    Recently there has been great interest in using patterned ferroelectric materials for the photochemical growth of metal nanostructures. Variations in surface and sub-surface structure influence the photochemical processes. Here we show that crystallography, and hence remnant polarization, of the ferroelectric affects photo-deposition. The ratio of metal growth on c– and c+ domains varies from 1 : 2 for [100] to 1 : 100 for [111]. This is shown to be dependent on the variations in the band structur
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    Photochemical growth of metal nanoparticles on domain patterned ferroelectric surfaces
    (Cranfield University, 2009) Tiwari, Divya; Dunn, S. C.
    In this work, the growth of metal nanoparticles on domain patterned ferroelectric Pb(ZrxTi1-x)O3 and LiNbO3 by photochemical reaction is demonstrated. The photochemical properties and phenomena occurring on the surface of Pb(ZrxTi1-x)O3 and LiNbO3 under ultraviolet illumination are investigated. Ferroelectric materials possess a reversible spontaneous polarisation that has an effect on photochemical reactivity of a surface. Since the spontaneous polarisation is reversible, a desired pattern can be drawn on a ferroelectric surface in the form of domains. A combination of domain patterning and domain specific surface reactions can lead to fabrication of complex nanostructures. It is found that on a PZT (30/70) thin film, under UV irradiation, metal deposition occurred only on C + domains and no deposition occurred on C - domains. Hence, the chemical reactivity of ferroelectric surface was found to be dependent on the polarisation of domain that is underlying the surface. Annealing of PZT samples at high temperatures alters the defect concentration of the PZT as shown by an increase in the deposition of silver on the surface. When the PZT samples were annealed in air at temperatures ranging from 530-690°C the silver deposition increased by more than 150% and the size of deposited silver clusters increased by four times. The photochemical properties of PZT thin films of different compositions PbZr0.3Ti0.7O3, PbZr0.52Ti0.48O3 and PbZr0.7Ti0.3O3 were investigated by undertaking silver nanocluster deposition experiments. The composition of PZT film (Zr/Ti ratio) affects silver deposition such that on PbZr0.3Ti0.7O3 silver deposits only on C + domains, whereas PbZr0.52Ti0.48O3 and PbZr0.7Ti0.3O3 experience deposition on both C + and C - domains. This difference in silver deposition pattern is shown to be due to the difference in width of the space charge region and bandii gap of the three samples. The impact of size of poled pattern on silver deposition at the surface is shown. It is found that for smaller size of C + domains (smaller than 1 μm) the amount and size of deposited silver decreased with the decrease in domain size. On a PZT surface, formation of spherical, triangular and hexagonal nanoplates of gold via photoreduction has also been demonstrated. Silver cation reduction on C + and C - domains of ferroelectric lithium niobate (LN) by photochemical and photoelectric process is demonstrated. The interaction of photoelectric and domain dependent influences can be observed in LiNbO3 due to the low electron affinity (ca 1.1-1.5eV). The impact of composition of LN on the photoreduction of silver has been shown. It is found that the photochemical reactivity of MgO-doped LN is significantly higher as compared to non-doped LN. The energy and intensity of incident photon is also found to have an impact on the photoreduction of silver on LN surface. In addition to this, deposition of Al and Mn nanoparticles on LN surface by means of photoreduction reaction has been demonstrated. It is shown that for a metal to photoreduce on C + domain of a ferroelectric material, the reduction potential of the metal has to be within the band-gap of the material. It is shown that under atmospheric conditions, it is possible to selectively adsorb molecules of opposite charge on the surface of LN due to uncompensated polarisation charge.
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    Simulation to enable a data-driven circular economy
    (MDPI, 2019-06-19) Charnley, Fiona; Tiwari, Divya; Hutabarat, Windo; Moreno, Mariale; Okorie, Okechukwu; Tiwari, Ashutosh
    This paper presents an investigation on how simulation informed by the latest advances in digital technologies such as the 4th Industrial Revolution (I4.0) and the Internet of Things (IoT) can provide digital intelligence to accelerate the implementation of more circular approaches in UK manufacturing. Through this research, a remanufacturing process was mapped and simulated using discrete event simulation (DES) to depict the decision-making process at the shop-floor level of a remanufacturing facility. To understand the challenge of using data in remanufacturing, a series of interviews were conducted finding that there was a significant variability in the condition of the returned product. To address this gap, the concept of certainty of product quality (CPQ) was developed and tested through a system dynamics (SD) and DES model to better understand the effects of CPQ on products awaiting remanufacture, including inspection, cleaning and disassembly times. The wider application of CPQ could be used to forecast remanufacturing and production processes, resulting in reduced costs by using an automatised process for inspection, thus allowing more detailed distinction between “go” or “no go” for remanufacture. Within the context of a circular economy, CPQ could be replicated to assess interventions in the product lifecycle, and therefore the identification of the optimal CE strategy and the time of intervention for the current life of a product—that is, when to upgrade, refurbish, remanufacture or recycle. The novelty of this research lies in investigating the application of simulation through the lens of a restorative circular economic model focusing on product life extension and its suitability at a particular point in a product’s life cycle.