Search

The BICEP/Keck experiment (BK) is a series of small-aperture refracting telescopes observing degree-scale Cosmic Microwave Background (CMB) polarization from the South Pole in search of a primordial $B$-mode signature. This $B$-mode signal arises from primordial gravitational waves interacting with the CMB, and has amplitude parametrized by the tensor-to-scalar ratio $r$. Since 2016, BICEP3 and the Keck Array have been observing with 4800 total antenna-coupled transition-edge sensor detectors, with frequency bands spanning 95, 150, 220, and 270 GHz. Here we present the optical performance of these receivers from 2016 to 2019, including far-field beams measured in situ with an improved chopped thermal source and instrument spectral response measured with a field-deployable Fourier Transform Spectrometer. As a pair differencing experiment, an important systematic that must be controlled is the differential beam response between the co-located, orthogonally polarized detectors. We generate per-detector far-field beam maps and the corresponding differential beam mismatch that is used to estimate the temperature-to-polarization leakage in our CMB maps and to give feedback on detector and optics fabrication. The differential beam parameters presented here were estimated using improved low-level beam map analysis techniques, including efficient removal of non-Gaussian noise as well as improved spatial masking. These techniques help minimize systematic uncertainty in the beam analysis, with the goal of constraining the bias on $r$ induced by temperature-to-polarization leakage to be subdominant to the statistical uncertainty. This is essential as we progress to higher detector counts in the next generation of CMB experiments., 8 pages, 3 figures. Accepted by the Journal of Low Temperature Physics (Proceedings of the 18th International Workshop on Low Temperature Detectors)

BICEP3 is a 520 mm aperture on-axis refracting telescope at the South Pole, which observes the polarization of the cosmic microwave background (CMB) at 95 GHz to search for the B-mode signal from inflationary gravitational waves. In addition to this main target, we have developed a low-elevation observation strategy to extend coverage of the Southern sky at the South Pole, where BICEP3 can quickly achieve degree-scale E-mode measurements over a large area. An interesting E-mode measurement is probing a potential polarization anomaly around the CMB Cold Spot. During the austral summer seasons of 2018-19 and 2019-20, BICEP3 observed the sky with a flat mirror to redirect the beams to various low elevation ranges. The preliminary data analysis shows degree-scale E-modes measured with high signal-to-noise ratio., 12 pages, 10 figures; Figure 7 shows the correct file

Branches of cosmic inflationary models, such as slow-roll inflation, predict a background of primordial gravitational waves that imprints a unique odd-parity B-mode pattern in the Cosmic Microwave Background (CMB) at amplitudes that are within experimental reach. The BICEP/Keck (BK) experiment targets this primordial signature, the amplitude of which is parameterized by the tensor-to-scalar ratio r, by observing the polarized microwave sky through the exceptionally clean and stable atmosphere at the South Pole. B-mode measurements require an instrument with exquisite sensitivity, tight control of systematics, and wide frequency coverage to disentangle the primordial signal from the Galactic foregrounds. BICEP Array represents the most recent stage of the BK program, and comprises four BICEP3-class receivers observing at 30/40, 95, 150 and 220/270 GHz. The 30/40 GHz receiver will be deployed at the South Pole during the 2019/2020 austral summer. After 3 full years of observations with 30,000+ detectors, BICEP Array will measure primordial gravitational waves to a precision $\sigma(r)$ between 0.002 and 0.004, depending on foreground complexity and the degree of lensing removal. In this paper we give an overview of the instrument, highlighting the design features in terms of cryogenics, magnetic shielding, detectors and readout architecture as well as reporting on the integration and tests that are ongoing with the first receiver at 30/40 GHz., Comment: 9 pages, 5 figures, presented at LTD18 in Milan (July 2019), accepted on JLTP (February 2020)

The BICEP/Keck (BK) experiment aims to detect the imprint of primordial gravitational waves in the Cosmic Microwave Background polarization, which would be direct evidence of the inflation theory. While the tensor-to-scalar ratio has been constrained to be r_0.05 < 0.06 at 95% c.l., further improvements on this upper limit are hindered by polarized Galactic foreground emissions and removal of gravitational lensing polarization. The 30/40 GHz receiver of the BICEP Array (BA) will deploy at the end of 2019 and will constrain the synchrotron foreground with unprecedented accuracy within the BK sky patch. We will show the design of the 30/40 GHz detectors and test results summarizing its performance. The low optical and atmospheric loading at these frequencies requires our TES detectors to have low saturation power in order to be photon-noise dominated. To realize the low thermal conductivity required from a 250 mK base temperature, we developed new bolometer leg designs. We will present the relevant measured detector parameters: G, Tc, Rn, Psat , and spectral bands, and noise spectra. We achieved a per bolometer NEP including all noise components of 2.07E-17 W/sqrt(Hz), including an anticipated photon noise level 1.54E-17 W/sqrt(Hz)., Accepted for publication in Journal of Low Temperature Physics

Advanced developments in handheld devices&rsquo, interactive 3D graphics capabilities, processing power, and cloud computing have provided great potential for handheld augmented reality (HAR) applications, which allow users to access digital information anytime, anywhere. Nevertheless, existing interaction methods are still confined to the touch display, device camera, and built-in sensors of these handheld devices, which suffer from obtrusive interactions with AR content. Wearable fabric-based interfaces promote subtle, natural, and eyes-free interactions which are needed when performing interactions in dynamic environments. Prior studies explored the possibilities of using fabric-based wearable interfaces for head-mounted AR display (HMD) devices. The interface metaphors of HMD AR devices are inadequate for handheld AR devices as a typical HAR application require users to use only one hand to perform interactions. In this paper, we aim to investigate the use of a fabric-based wearable device as an alternative interface option for performing interactions with HAR applications. We elicited user-preferred gestures which are socially acceptable and comfortable to use for HAR devices. We also derived an interaction vocabulary of the wrist and thumb-to-index touch gestures, and present broader design guidelines for fabric-based wearable interfaces for handheld augmented reality applications.

This work describes the fabrication of hierarchical 3D Nafion enhanced carbon aerogels (NECAGs) for sensing applications via a fast freeze drying method. Graphene oxide, multiwalled carbon nanotubes and Nafion were mixed and extruded into liquid nitrogen followed by the removal of ice crystals by freeze drying. The addition of Nafion enhanced the mechanical strength of NECAGs and effective control of the cellular morphology and pore size was achieved. The resultant NECAGs demonstrated high strength, low density, and high specific surface area and can achieve a modulus of 20 kPa, an electrical conductivity of 140 S m(-1), and a specific capacity of 136.8 F g(-1) after reduction. Therefore, NECAG monoliths performed well as a gas sensor and as a biosensor with high sensitivity and selectivity. The remarkable sensitivity of 8.52 × 10(3)μA mM(-1) cm(-2) was obtained in dopamine (DA) detection, which is two orders of magnitude better than the literature reported values using graphene aerogel electrodes made from a porous Ni template. These outstanding properties make the NECAG a promising electrode candidate for a wide range of applications. Further in-depth investigations are being undertaken to probe the structure-property relationship of NECAG monoliths prepared under various conditions.

We present results from an analysis of all data taken by the bicep2/Keck CMB polarization experiments up to and including the 2015 observing season. This includes the first Keck Array observations at 220 GHz and additional observations at 95 and 150 GHz. The Q and U maps reach depths of 5.2, 2.9, and 26 μKCMB arcmin at 95, 150, and 220 GHz, respectively, over an effective area of ≈400 square degrees. The 220 GHz maps achieve a signal to noise on polarized dust emission approximately equal to that of Planck at 353 GHz. We take auto and cross spectra between these maps and publicly available WMAP and Planck maps at frequencies from 23 to 353 GHz. We evaluate the joint likelihood of the spectra versus a multicomponent model of lensed-ΛCDM+r+dust+synchrotron+noise. The foreground model has seven parameters, and we impose priors on some of these using external information from Planck and WMAP derived from larger regions of sky. The model is shown to be an adequate description of the data at the current noise levels. The likelihood analysis yields the constraint r0.05

A low-cost optical sensor for monitoring the aquatic environment is presented, with the construction and design described in detail. The autonomous optical sensor is devised to be environmentally robust, easily deployable and simple to operate. It consists of a multi-wavelength light source with two photodiode detectors capable of measuring the transmission and side-scattering of the light in the detector head. This enables the sensor to give qualitative data on the changes in the optical opacity of the water. Laboratory tests to confirm colour and turbidity-related responses are described and the results given. The autonomous sensor underwent field deployments in an estuarine environment, and the results presented here show the sensors capacity to detect changes in opacity and colour relating to potential pollution events. The application of this low-cost optical sensor is in the area of environmental pollution alerts to support a water monitoring programme, where multiple such sensors could be deployed as part of a network.

In this work, we report the fabrication of gas sensors prepared by in situ polymerization of aniline on non-woven fabrics. It is anticipated that a thin coating of polyaniline film fabricated on porous fabric material would improve the performance of the polyaniline based gas sensor. The hypothesis is based on the recent improved technique that allows the fabrication of nanoparticle based polyaniline film, and the high gas permeability of the fabrics. Sensor fabrication parameters which included acidity of reaction media, precursor and reagent concentrations, and the number of modification cycle have been studied. The resulting gas sensors were found to be highly responsive to a range of volatile organic compounds (VOCs). This high sensitivity was also accompanied with fast response time (∼10 s). The order of sensitivity to VOCs was found to be ethanol > chloroform > toluene > acetone > ethyl acetate. Further, the sensor was three orders of magnitude more sensitive to ammonia than all organic vapours tested.

Precision measurements of cosmic microwave background (CMB) polarization require extreme control of instrumental systematics. In a companion paper we have presented cosmological constraints from observations with the BICEP2 and Keck Array experiments up to and including the 2015 observing season (BK15), resulting in the deepest CMB polarization maps to date and a statistical sensitivity to the tensor-to-scalar ratio of $\sigma(r) = 0.020$. In this work we characterize the beams and constrain potential systematic contamination from main beam shape mismatch at the three BK15 frequencies (95, 150, and 220 GHz). Far-field maps of 7,360 distinct beam patterns taken from 2010-2015 are used to measure differential beam parameters and predict the contribution of temperature-to-polarization leakage to the BK15 B-mode maps. In the multifrequency, multicomponent likelihood analysis that uses BK15, Planck, and WMAP maps to separate sky components, we find that adding this predicted leakage to simulations induces a bias of $\Delta r = 0.0027 \pm 0.0019$. Future results using higher-quality beam maps and improved techniques to detect such leakage in CMB data will substantially reduce this uncertainty, enabling the levels of systematics control needed for BICEP Array and other experiments that plan to definitively probe large-field inflation., Comment: 18 pages, 9 figures, 4 tables. Minor correction to Figure 2 and caption

An electrochemical synthesis method of reducing graphene oxide (GO) under constant potential is reported. Electrochemical technique offers control over reaction parameters such as the applied voltage, electrical current and reduction time; whereas the desired size and thickness of the film can be pre-determined by controlling the amount of precursor GO deposited on the electrode with defined shape and surface area. This synthesis technique produces high quality electrochemically reduced GO (ERGO) film with controllable size and thickness. Electrochemical symmetrical supercapacitors based on ERGO films achieved a specific capacitance of 128 F/g with an energy density of 17.8 Wh/kg operating within a potential window of 1.0 V in 1.0 M NaNO3. The supercapacitor was shown to be stable, retaining ca. 86% of the original specific capacitance after 3500 charge–discharge cycles. The results indicate that this simple synthesis technique for providing graphene-like materials has great potential in various applications such as energy storage.

With recent improvements in wireless sensor network hardware there has been a concurrent push to develop sensors that are suitable in terms of price and performance. In this paper a low-cost gas sensor is detailed, and significant improvements in sensor characteristics have been achieved compared to previously published results. A chemical sensor is presented based on the use of low-cost LEDs as both the light source and photodetector, coupled with a sensor slide coated with a pH sensitive colorimetric dye to create a simple gas sensor. Similar setups have been successfully used to detect both acetic acid and ammonia. The goal of this work was to optimise the system performance by integration of the sensing technique into a purposely deigned flowcell platform that holds the colorimetric slide and optical detector in position. The reproducibility of the sensor has been improved through this arrangement and careful control of deposited film thickness. The enhanced reproducibility between sensors opens the potential of calibration-free measurement, in that calibration of one sensor can be used to model the characteristics of all sensors in a particular batch.

Polyaniline and molybdenum oxide composite modified electrode (PANI–MoO 3 ) was prepared through immobilization of the oxide in the polymer matrix. The obtained composite was characterized by XPS and FTIR. Stability and electrocatalytic properties of the composite for the reduction of chlorate were investigated by using cyclic voltammetry and chronoamerometry. It was found that the electrocatalytic activity of MoO 3 towards the reduction of chlorate is improved by immobilization in PANI. The composite modified electrode showed a quick response time of 10 s to chlorate. Results of amperometric measurements at a working potential of 0.0 V vs. SCE showed that the composite modified electrode displayed linear amperometric responds to chlorate in a concentration range of 5 μM–10.0 mM with a lower detection limit (LOD) of 1.3 μM. The stability of MoO 3 was also improved through immobilization in PANI.

Composite film of polyaniline (PANI) and tungsten oxide (WO3) was electrodeposited by cyclic voltammetric technique from a solution of aniline and tungstic acid. The obtained WO3/PANI film displayed a significant enhancement of electrocatalytic activity for iodate reduction and a better stability than that of pure WO3 and PANI films. Result of amperometric experiment revealed a good linear relationship with concentration of IO3− from 20 to 500 μM, with a high sensitivity of 0.54 μA/μM and a detection limit of 2.7 μM for the determination of iodate. This composite film was also successfully applied in determination of iodate in commercial table salt.

Textile-based sensors offer an unobtrusive method of continually monitoring physiological parameters during daily activities. Chemical analysis of body fluids, noninvasively, is a novel and exciting area of personalized wearable healthcare systems. BIOTEX was an EU-funded project that aimed to develop textile sensors to measure physiological parameters and the chemical composition of body fluids, with a particular interest in sweat. A wearable sensing system has been developed that integrates a textile-based fluid handling system for sample collection and transport with a number of sensors including sodium, conductivity, and pH sensors. Sensors for sweat rate, ECG, respiration, and blood oxygenation were also developed. For the first time, it has been possible to monitor a number of physiological parameters together with sweat composition in real time. This has been carried out via a network of wearable sensors distributed around the body of a subject user. This has huge implications for the field of sports and human performance and opens a whole new field of research in the clinical setting.

Electrodeposition of polyaniline (PAni) was performed across a broad pH range from pH 0.0 to 14.0. PAni films were found to grow from strong acidic environments at much faster rate and appeared to adopt different growth patterns from those grown from higher pH media, thus producing PAni films with very different morphologies ranging from nanofibres to microsized tubules to flakes like structures. The various morphologies of the PAni films were results of homogeneous and heterogeneous nucleation during electrochemical polymerization. These phenomena occurred under specific conditions which could be induced by varying the pH of the reaction media. Characteristic IR absorptions of the films deposited from increasing pH environment indicated little differences in chemical structure of the polymers except for the film grown from pH 14.0. Cyclic voltammetry data also indicated different electron transfer efficiency as a result of different morphology adopted. All except for PAni films obtained from pH 2.0 to 4.0 gave high specific capacitance at around 450 F g −1 in 0.5 M H 2 SO 4 and in 1.0 M NaNO 3 (pH 1.0) solution using 1.0 mA cm −2 charging and discharging current density.

Worldwide, the demand for sensing devices that can conform with the requirements of large-scale wireless sensor network (WSN) deployments is rising exponentially. Typically, sensors should be very low cost, low power (essentially self-sustaining), yet very rugged and reliable. At present, functioning WSN deployments involve physical transducers only, such as thermistors, accelerometers, photodetectors, flow meters, to monitor quantities like temperature, movement, light level and liquid level/flow. Remote, widely distributed monitoring of molecular targets remains relatively unexplored, except in the case of targets that can be detected directly using 'non-contact' techniques like spectroscopy. This paper will address the issues inhibiting the close integration of chemical sensing with WSNs and suggest strategies based on fundamental materials science that may offer routes to new sensing surfaces that can switch between different modes of behaviour (e.g. active-passive, expand-contract).

In this paper, the oxidative degradation of 2, 4-dichlorophenoxyacetic acid (2, 4-D) using Mn2+/H2O2 reagent under UV irradiation was studied. The results show that 2, 4-D was degraded more completely in Mn2+/H2O2 solution than traditional Fenton solutions. The effects of the concentration of Mn2+, H2O2 and pH were also investigated. And under the optimal condition of \( c_{Mn^{2 + } } \) 1.48×10−4 mol/L, \( c_{H_2 O_2 } \) 8.99×10−5 mol/L and pH 3.38, the formation of ·OH was the most, both the decomposition rate of H2O2 and the degradation rate of 2, 4-D were the fastest. In addition, the photoreaction process was monitored using spin-trapping electron paramagnetic resonance (EPR), and the results indicated that the oxidative process was predominated mainly by the hydroxyl radical (·OH) gennerated in the system.

Sensors, which can be integrated into clothing and used to measure biochemical changes in body fluids, such as sweat, constitute a major advancement in the area of wearable sensors. Initial applications for such technology exist in personal health and sports performance monitoring. However, sample collection is a complicated matter as analysis must be done in real-time in order to obtain a useful examination of its composition. This work outlines the development of a textile-based fluid handling platform which uses a passive pump to gather sweat and move it through a pre-defined channel for analysis. The system is tested both in vitro and in vivo. In addition, a pH sensor, which depends on the use of a pH sensitive dye and paired emitter-detector LEDs to measure colour changes, has been developed. In vitro and on-body trials have shown that the sensor has the potential to record real-time variations in sweat during exercise.

Carbon dioxide gas concentration determination using infrared gas sensors combined with Bayesian regularizing neural networks is presented in this work. Infrared sensor with a measuring range of 0–5% was used to measure carbon dioxide gas concentration within the range 0–15000 ppm. Neural networks were employed to fulfill the non-linear output of the sensor. The Bayesian strategy was used to regularize the training of the back propagation neural network with a Levenberg–Marquardt (LM) algorithm. By Bayesian regularization (BR), the design of the network was adaptively achieved according to the complexity of the application. Levenberg–Marquardt algorithm under Bayesian regularization has better generalization capability, and is more stable than the classical method. The results showed that the Bayesian regulating neural network was a powerful tool for dealing with the infrared gas sensor which has a large non-linear measuring range and provide precise determination of carbon dioxide gas concentration. In this example, the optimal architecture of the network was one neuron in the input and output layer and two neurons in the hidden layer. The network model gave a relationship coefficient of 0.9996 between targets and outputs. The prediction recoveries were within 99.9–100.0%.

Nickel oxide (NiOx) and polyaniline (PAni) were electrocodeposited from NiSO4 and aniline through cyclic voltammetric scans to afford PAni–NiOx composite film at controlled pH environment. The electrochemical activities of the film were investigated by cyclic voltammetry in 0.1 M NaOH and 0.1 M H2SO4, respectively. Typical redox couples of PAni in 0.1 M H2SO4 appeared at approximately 0.2 and 0.4 V vs. saturated calomel electrode (SCE); Ni(II)/Ni(III) redox couple was observed at approximately 0.4 V vs. SCE in 0.1 M NaOH. The morphologies and elemental components of the films were inspected by scanning electron microscopy and energy dispersive X-ray diffraction. The stability of nickel oxide in the films was found to be enhanced against acidic environments. Electrochemical catalytic behavior of NiOx within the composite film was conserved and demonstrated by catalytic oxidation of methanol and ethanol.

In this paper, we present a low-cost, low-voltage and low-power polypyrrole-membrane microfluidic pump with two one-way push button check valves. This polymeric microfluidic pump is fabricated with a conductive polymer (polypyrrole) modified poly dimethylsiloxane (PDMS) membrane encased into a polymethylmethacrylate (PMMA) structure. The pumping action is induced by an electrochemical actuated PPy-PDMS membrane while check valves at the inlet and outlet control the flow direction in the respective pump phases. This pump is self-priming. Accurate control of the output flow rate can be obtained by changing the actuation frequency. With this pump, a maximum pumping rate of 52 μL/min was achieved using an input power of 55 mW operated at ±1.5 V.

Rapid developments in wireless communications are opening up opportunities for new ways to perform many types of analytical measurements that up to now have been restricted in scope due to the need to have access to centralised facilities. This paper will address both the potential for new applications and the challenges that currently inhibit more widespread integration of wireless communications with autonomous sensors and analytical devices. Key issues are identified and strategies for closer integration of analytical information and wireless communications systems discussed.

Silica gel-supported Fe(II) (SiOFe) was prepared and used for heterogeneous degradation of sulforhodamine B (SRB) and 2,4-dichlorophenol (DCP) under visible irradiation (λ > 420 nm) as an effective catalyst. UV-visible spectra, and infrared Spectrophotometry (IR), fluorescence, total organic carbon (TOC) and electron spin resonance (ESR) measurements were employed to analyze the photoreaction products. The results showed that SRB could be efficiently degraded by SiOFe/H2O2 system under visible irradiation with 100% decolorization and 72.3% TOC removal after 180 min illumination. The results of ESR and fluorescence measurements indicated that the oxidative process was predominated mainly by the hydroxyl radical (·OH) generated in the system.

A novel approach to autonomous chemical sensor regeneration is explored in this paper. It involves the movement of a sensor surface into measurement or regeneration zones using low powered conducting polymer actuators. The system demonstrated the feasibility of repeatedly cycling through a measurement–regeneration regime, which in principle allows remotely deployed chemical sensors to perform simple self-diagnostics. The sensor-actuator device is shown to repeatedly switch through 120 measurement–regeneration cycles. Detection of pH-dependent colour changes is demonstrated using LED-based colorimetry and remotely deployed video cameras.

In this paper we discuss the challenges and opportunities afforded by surface-based photoswitchable chemical sensors. We focus on spiropyrans as it is a well-studied system that can be photonically switched between two states, only one of which exhibits ion-binding behaviour. Surface immobilization and protection within a polymer matrix is identified as a route that can successfully address the need for a localized hydrophobic environment in which a user can maintain control over the spiropyran-merocyanine equilibrium and at the same time improve photo-fatigue resistance. Furthermore, we discuss the excellent potential of light emitting diodes as light sources and detectors for photoswitching between the states of spiropyran and measurement of bound species. A simple, low-cost, low-power experimental setup provides spatial and temporal control of surface illumination and surface binding. This, coupled with low irradiance, is shown to generate significant improvement in fatigue resistance of spiropyrans-modified films, and may prove to be an important step towards the realization of chemical sensors that can be deployed in large-scale wireless chemical sensor networks.

The use of a novel inexpensive photometric device, a paired emitter-detector diode (PEDD) has been applied to the colorimetric determination of phosphate using the malachite green spectrophotometric method. The novel miniaturized flow detector applied within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based detector. The optical flow cell was constructed from two LEDs, whereby one is the light source and the second is the light detector, with the LED light source forward biased and the LED detector reversed biased. The photocurrent generated by the LED light source discharges the junction capacitance of the detector diode from 5 V (logic 1) to 1.7 V (logic 0) and the time taken for this process to occur is measured using a simple timer circuit. The malachite green (MG) method employed for phosphate determination is based on the formation of a green molybdophosphoric acid complex, the intensity of which is directly related to phosphate concentration. Optimum analytical parameters such as reaction kinetics, reagent to sample concentration ratio and emitter wavelength intensity were investigated for the spectrophotometric method. Linear calibration plots that obeyed the Beer-Lambert law were obtained for phosphate in the range of 0.02-2 microM. The dynamic range, sensitivity and limits of detection are reported.

The development of smart nanotextiles has the potential to revolutionize the functionality of our clothing and the fabrics in our surroundings. Nanoscale manipulation results in new functionalities for intelligent textiles, including self-cleaning, sensing, actuating, and communicating. This is made possible by such developments as new materials, fibers, and finishings; inherently conducting polymers; carbon nanotubes; and antimicrobial nanocoatings. These additional functionalities have numerous applications, encompassing healthcare, sports, military applications, and fashion. The wearer and the surrounding environment may be monitored in an innocuous manner, giving continuous updates of individual health status or environmental hazards. More generally, smart textiles become a critical part of the emerging area of body sensor networks incorporating sensing, actuation, control, and wireless data transmission. This article reviews current research in nanotechnology application to textiles, from fiber manipulation and development to end uses of smart nanotextiles.

This paper describes the development of a wireless chemical sensor network (WCSN) and an environmental sensing chamber (ESC) within which this WCSN was tested. The WCSN used in this work takes advantage of recent advances in low power wireless communication platforms and novel light emitting diode (LED) based chemical sensing techniques. Plumes of acetic acid were employed for testing and were detected by LED based colorimetric acid responsive chemical sensors. Wireless sensor nodes were positioned in fixed locations within the chamber and responses to plumes of acetic acid were monitored. Preliminary test data show that sensor response time and magnitude are related to sensor position and plume profile, and by operating the sensors collectively in a WCSN it was possible to track chemical plumes in real-time as they moved through the chamber. We envisage that it will be possible to use chemical sensors arranged in a WCSN such as this to map and predict chemical plume dynamics.

There is much interest from the fisheries industry in developing rapid methods to evaluate real-time freshness of fish and seafood products. Emphasis is on the ones that would reflect and account for the products history and their storage conditions from “harvest-to-home”. The development of a “smart packaging” that monitors the microbial breakdown products in the headspace of packaged fish is described. When fish spoils it releases a variety of basic volatile amines which are detectable with appropriate pH indicating sensors. These are prepared by entrapping within a polymer matrix a pH sensitive dye that responds, through visible color changes to the spoilage volatile compounds that contribute to a quantity known as total volatile basic nitrogen (TVB-N). Laboratory trials on fresh fish filets showed that the sensor accurately tracks the increase in amines concentration in the package headspace. The response was also found to correlate to changing microbial populations (total viable count or TVC and Pseudomonas spp.). In addition, leaching of the dye was assessed over time to assess the suitability of the sensor formulation for food packaging application.

A low-power, high sensitivity, very low-cost light emitting diode (LED)-based device developed for low-cost sensor networks was modified with bromocresol green membrane to work as a solid-state pH sensor. In this approach, a reverse-biased LED functioning as a photodiode is coupled with a second LED configured in conventional emission mode. A simple timer circuit measures how long (in microsecond) it takes for the photocurrent generated on the detector LED to discharge its capacitance from logic 1 (+5 V) to logic 0 (+1.7 V). The entire instrument provides an inherently digital output of light intensity measurements for a few cents. A light dependent resistor (LDR) modified with similar sensor membrane was also used as a comparison method. Both the LED sensor and the LDR sensor responded to various pH buffer solutions in a similar way to obtain sigmoidal curves expected of the dye. The pKa value obtained for the sensors was found to agree with the literature value.

A low-cost chemical sensor comprising surface-mount light-emitting diodes (LEDs) has been developed for colorimetric gas detection. The device consists of a pair of LEDs connected to a simple PIC microcontroller circuit and in the most basic form, requires the use of only two input-output (I/O) pins on the chip. The key features of this sensor are the use of a LED rather than a photodiode for light detection and an all-digital light detection protocol that leads to a reduction in cost and power consumption by avoiding the need for an analog-to-digital converter. The surface-mount diodes employed are more compact than standard LEDs and are more amenable to coating by solid-state sensor films. Results from sensors employing a chemochromic ammonia sensitive film are presented, and the detection of this target is demonstrated in the parts-per-million range. The configuration is applicable to a wide range of colorimetric gas sensing materials

A transmittance mode optical device based on using a reverse biased light emitting diode (LED) as light detector has been developed for colorimetric analysis. This new optical device was validated with bromocresol green dye for absorbance measurements before being employed for detecting cadmium(II) and lead(II) in water. Results show that the performance of this LED-based device is comparable to much more expensive bench top UV–vis instruments, but with the advantages of being low cost, low power and simple to operate.

A low-power, high sensitivity, very low-cost light emitting diode (LED)-based device for intensity-based light measurements is described. In this approach, a reverse-biased LED functioning as a photodiode is coupled with a second LED configured in conventional emission mode. A simple timer circuit measures how long (in microsecond) it takes for the photocurrent generated on the detector LED to discharge its capacitance from logic 1 (+5 V) to logic 0 (+1.7 V). The entire instrument provides an inherently digital output of light intensity measurements for a few cents. This light intensity dependent discharge process has been applied to measuring concentrations of coloured solutions and a mathematical model developed based on the Beer–Lambert Law.

This project is focused on developing novel smart textiles based on conducting polymer coatings deposited on a foam substrate. This process renders the foam conductive, while retaining the tactile properties of the original material. The foam is a soft, porous and conductive solid, made by chemically oxidising pyrrole in the presence of a polyurethane foam. The 3-D structure of this material means it is sensitive to pressures exerted from all three dimensions, making it attractive for use in wearable sensors for sport and medical applications. A potential application under investigation is the development of a smart insole for patients with Diabetes Mellitus, who require constant monitoring of the pressure exerted underfoot during walking or standing in order to reduce the risk of damaging their feet due to excess pressure being applied. Future applications for this material may also lie in the area of wearable electronic components, whereby the material can be fabricated to produce resistors, capacitors, etc. The gas sensing capabilities of this material were also investigated. Results have shown that this smart fabric based chemical sensor offers higher selectivity towards ammonia over other volatile organic vapours.

A novel inexpensive optical-sensing technique has been developed for colorimetric flow analysis. This sensing system employs two LEDs whereby one is used as the light source and the other as a light detector. The LED used as light detector is reverse biased with a 5-V supply so that the photocurrent generated by the incident light discharges the capacitance. Direct digital output is provided by a simple timer circuit that measures the time taken for this discharge process from 5 V (logic 1) to 1.7 V (logic 0). This sensing concept has been applied in flow analysis by constructing an optical flow cell with a pair of LEDs. Calibration of the integrated optical flow cell using a dye resulted in a linear response that obeys the Beer–Lambert law. The flow rate, dynamic range, sensitivity and limits of detection were investigated. The system was also used for pH determination in the range of pH 2.5–6.8 using bromocresol green (BCG). The pKa of BCG was successfully determined by this technique.

A new compressible conducting material has been developed by coating polyurethane (PU) foam with inherently conducting polypyrrole (PPy). The optimised conditions for preparation of the conducting foam have been investigated. Evaluation of the conducting foam shows that a linear relationship exists between the conductance and the stress applied. Parameters such as sensitivity, dynamic range, repeatability of this pressure sensor are discussed. The use of this soft pressure sensor in a prototype breath monitor is also reported.

A non-reversible solid-state ammonia sensor based on formation of indophenol blue has been developed. A new optimised reaction conditions found for Berthelot’s reaction allow the sensor to respond to dissolved ammonia in ambient conditions at a much faster reaction rate than previously known. This solid-state colorimetric sensor reaches maximum colour intensity in ∼3 min at room temperature (∼20 °C) and responds linearly to ammonia between 1 and 10 ppm. A semi-automatic imaging system that consists of a black and white digital camera illuminated by red, green and blue LEDs was developed to measure the sensor responses.