Single-Mode Fiber Refractive Index Sensor Based on Core-Offset Attenuators

Mach-Zehnder and Michelson interferometers using core-offset attenuators were demonstrated. As the relative offset direction of the two attenuators in the Mach-Zehnder interferometer can significantly affect the extinction ratio of the interference pattern, single core-offset attenuator-based sensors appear more robust and repeatable. A novel fiber Michelson interferometer refractive index (RI) sensor was subsequently realized by a single core-offset attenuator and a layer of ~ 500-nm gold coating. The device had a minimum insertion loss of 0.01 dB and maximum extinction ratio over 9 dB. The sensitivity (0.333 nm) of the new sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of an identical long period gratings pair Mach-Zehnder interferometric sensor, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.

Efficient Path Key Establishment For Wireless Sensor Networks

Key pre-distribution schemes have been proposed as means to overcome Wireless Sensor Networks constraints such as limited communication and processing power. Two sensor nodes can establish a secure link with some probability based on the information stored in their memories though it is not always possible that two sensor nodes may set up a secure link. In this paper, we propose a new approach that elects trusted common nodes called ”Proxies” which reside on an existing secure path linking two sensor nodes. These sensor nodes are used to send the generated key which will be divided into parts (nuggets) according to the number of elected proxies. Our approach has been assessed against previously developed algorithms and the results show that our algorithm discovers proxies more quickly which are closer to both end nodes, thus producing shorter path lengths. We have also assessed the impact of our algorithm on the average time to establish a secure link when the transmitter and receiver of the sensor nodes are ”ON”. The results show the superiority of our algorithm in this regard. Overall, the proposed algorithm is well suited for Wireless Sensor Networks.

Difference equation sensor characterization algorithms for two-thermocouple probes

The characterization of thermocouple sensors for temperature measurement in variable flow environments is a challenging problem. In this paper, novel difference equation-based algorithms are presented that allow in situ characterization of temperature measurement probes consisting of two-thermocouple sensors with differing time constants. Linear and non-linear least squares formulations of the characterization problem are introduced and compared in terms of their computational complexity, robustness to noise and statistical properties. With the aid of this analysis, least squares optimization procedures that yield unbiased estimates are identified. The main contribution of the paper is the development of a linear two-parameter generalized total least squares formulation of the sensor characterization problem. Monte-Carlo simulation results are used to support the analysis.

Extraction of electrode kinetic parameters from microdisc voltammetric data measured under transport conditions intermediate between steady-state convergent and transient linear diffusion as typically applies to room temperature ionic liquids

The extraction of electrode kinetic parameters for electrochemical couples in room-temperature ionic liquids (RTILs) is currently an area of considerable interest. Electrochemists typically measure electrode kinetics in the limits of either transient planar or steady-state convergent diffusion for which the voltammetic response is well understood. In this paper we develop a general method allowing the extraction of this kinetic data in the region where the diffusion is intermediate between the planar and convergent limits, such as is often encountered in RTILs using microelectrode voltammetry. A general working surface is derived, allowing the inference of Butler-Volmer standard electrochemical rate constants for the peak-to-peak potential separation in a cyclic voltammogram as a function of voltage scan rate. The method is applied to the case of the ferrocene/ferrocenium couple in [C(2)mim][N(Tf)(2)] and [C(4)mim][N(Tf)(2)].

Voltammetric characterization of the ferrocene vertical bar ferrocenium and cobaltocenium vertical bar cobaltocene redox couples in RTILs

Ferrocene, Fc, and cobaltocenium hexafluorophosphate, CcPF(6), have been recommended for use as internal reference redox couples in room-temperature ionic liquids (RTILs), as well as in more conventional aprotic solvents. In this study, the electrochemical behavior of Fc and CcPF(6) is reported in eight commonly used RTILs; [C(2)mim][NTf2], [C(4)mim][NTf2], [C(4)mim][BF4], [C(4)mim][PF6], [C(4)mim][OTf], [C(4)mim][NO3], [C(4)mpyrr][NTf2], and [P-14,P-6.6,P-6][FAP], where [C(n)mim](+) = 1-butyl-3-methylimidazolium, [NTf2](-) = bis(trifluoromethylsulfonyl)imide, [BF4](-) = tetrafluoroborate, [PF6](-) = hexafluorophosphate, [OTf](-) = trifluoromethylsulfonate, [NO3](-) = nitrate, [C(4)mpyrr](+) = N-butyl-N-methylpyrrolidinium, [P-14,P-6,P-6,P-6](+) = tris(ri-hexyl)-tetradecylphosphonium and [FAP](-) = trifluorotris(pentafluoroethyl)phosphate, over a range of concentrations and temperatures. Solubilities and diffusion coefficients, D, of both the charged and neutral species were determined using double potential-step chronoamperometry, and CcPF(6) (36.5-450.0 mM) was found to be Much more Soluble than Fc (27.5-101.8 mM). It was observed that classical Stokes-Einstein diffusional behavior applies for Fc and CcPF(6) in all eight RTILs. Diffusion coefficients of Fc and CcPF(6) were calculated at a range of temperatures, and activation energies calculated. It was also determined that D for Fc and CcPF(6) does not change significantly with concentration. This supports the use of both Fe and CcPF(6) to provide a well-characterized and model redox couple for use as a voltammetric internal potential reference in RTILs contrary to previous literature reports in the former case.

Voltammetric studies of gold, protons, and [HCl2](-) in ionic liquids

The comparative study of the voltammetry of H[NTf2], HCl and H[AuCl4] in [C(4)mim][NTf2] has provided an insight into the influence of protons on the reduction of [AuCl4](-) at Au, Pt or glassy carbon (GC) electrodes, and has allowed the identification of an unprecedented proton-induced electroless deposition of Au on relatively inert GC surfaces. For the first time, clear evidence of the quantitative formation of [HCl2](-) has been obtained in HCl/[C(4)mim][NTf2] mixtures, and the electrochemical behavior of these mixtures analyzed. In particular, a significant shift of the dissociation equilibrium toward the formation of chloride and the solvated proton (H-IL(+)), following electrochemical reduction of H-IL(+) has been observed in the time-scale of the experiments.

Use of room temperature ionic liquids in gas sensor design

The attainable steady-state limiting currents and time responses of membrane-covered and membrane-independent gas sensors incorporating different electrode and electrolyte materials have been compared. A new design comprising a membrane-free microelectrode modified with a thin layer of a room temperature ionic liquid is considered. While the use of ionic liquid as electrolyte eliminates the need for a membrane and added supporting electrolyte, the slower diffusion of analyte within the more viscous medium results in slower time responses. Such sensors do, however, have potential application in more extreme operating conditions, such as high temperature and pressure, where traditional solvents would volatise.