Optical fibre long period grating gas sensor modified with metal organic framework thin films

An optical fibre long period grating (LPG) modified with a thin film of ZIF-8, zeolitic immidazol framework material, a subgroup of metal organic framework (MOF) family, was employed for the detection of organic vapours. ZIF-8 film was deposited onto the surface of the LPG using in-situ crystallization technique by mixing freshly prepared 12.5 mM zinc nitrate hexahydrate and 25 mM of 2-metyl-imidazole solutions in methanol. ZIF-8 film was characterized by scanning electron microscope (SEM) images, thickness and refractive index (RI) has been calculated with use of ellipsometer for films containing of 1,2,3,5 and 10 growth cycles. The crystallinity of the film was confirmed by x-ray diffraction pattern (XRD). The LPG sensor was designed to operate at the phase matching turning point to provide the highest sensitivity. The sensing mechanism is based on the measurement of the RI change induced by the penetration of the chemical molecules into the ZIF-8 pores. LPG modified with 2 and 5 growth cycles of ZIF-8 responded to exposure to methanol, ethanol, 2-propanol and acetone. The sensitivity of the measurements to humidity as an interfering parameter was also investigated

Metal-organic framework thin films on a surface of optical fibre long period grating for chemical sensing

An optical fibre long period grating (LPG) modified with a thin film of HKUST-1, a material from metal organic framework (MOF) family, was employed for the detection of carbon dioxide. The sensing mechanism is based on the measurement of the change of the refractive index (RI) of the coating that is induced by the penetration of CO2 molecules into the HKUST-1 pores. The responses of the resonance bands in the transmission spectrum of an LPG modified with 40 layers of HKUST-1 upon exposure to carbon dioxide in mixture with nitrogen were investigated

The complex polynomial method with a least-squares fit to boundary conditions

We present a new application of the complex polynomial method variant of the complex variable boundary element method. Instead of fitting the boundary conditions using collocation points, we minimize the error of fit in the l 2 norm to minimize the least-squares error. This approach greatly enhances the utility and efficiency of the method, allowing us to apply the method to a variety of engineering problems. Published by Elsevier Ltd

The complex polynomial method with a least-squares fit to boundary conditions

We present a new application of the complex polynomial method variant of the complex variable boundary element method. Instead of fitting the boundary conditions using collocation points, we minimize the error of fit in the l 2 norm to minimize the least-squares error. This approach greatly enhances the utility and efficiency of the method, allowing us to apply the method to a variety of engineering problems. Published by Elsevier Ltd

A complex variable boundary element method for a class of boundary value problems in anisotropic thermoelasticity

A boundary element method based on the Cauchy's integral formulae, called the complex variable boundary element method (CVBEM), is proposed for the numerical solution of boundary value problems governing plane thermoelastic deformations of anisotropic elastic bodies. The method is applicable for a wide class of problems which do not involve inertia or coupling effects and can be easily and efficiently implemented on the computer. It is applied to solve specific test problems.W.T. Ang, D.L. Clements & T. Cook

Multi-parameter measurements using optical fibre long period gratings for indoor air quality monitoring

An array of three long period gratings (LPGs) fabricated in a single optical fibre and multiplexed in the wavelength domain was used to measure simultaneously temperature, relative humidity (RH) and volatile organic compounds (VOCs), which are key indoor air quality (IAQ) indicators. Each LPG sensor was designed with optimised response to a particular measurand. The first, with no surface modification, was used to measure temperature. The second, modified by a mesoporous coating of silica nanoparticles (SiO2 NPs), was used to measure RH and the third, modified with a coating of SiO2 NPs infused with a functional material, p-sulphanatocalix[8]arene (CA[8]), was employed to monitor VOC concentration. The LPGs were fabricated with periods such that they operated at or near the phase matching turning point. The sensors were calibrated in the laboratory and the simultaneous measurement of the key indoor air quality parameters was undertaken in laboratory and office environments. It was demonstrated successfully that the data produced by the LPG sensor array under real conditions was in a good agreement with that produced by commercially available sensors. The average differences between values obtained by the optical fibre sensor and standard temperature and RH sensors were better than 0.5 °C and 5% respectively. Further, the potential application of fibre optic sensors for VOC detection at high concentrations has been demonstrated