Wireless sensors are devices in which sensing electronic transducers are spatially and galvanically separated from their associated readout/display components. The main benefits of wireless sensors, as compared to traditional tethered sensors, include the non-obtrusive nature of their installations, higher nodal densities, and lower installation costs without the need for extensive wiring.1–3 These attractive features of wireless sensors facilitate their development toward measurements of a wide range of physical, chemical, and biological parameters of interest. Examples of available wireless sensors include devices for sensing of pH, pressure, and temperature in medical, pharmaceutical, animal health, livestock condition, automotive, and other applications.4–7 Some implementations of wireless gas sensors can be already found in monitoring of analyte gases (e.g. carbon dioxide, water vapor, oxygen, combustibles) in relatively interference-free industrial and indoor environments.8,9 However, unobtrusive wireless gas sensors are urgently needed for many more diverse applications ranging from wearable sensors at the workplace, urban environment, and battlefield, to monitoring of containers with toxic industrial chemicals while in transit, to medical monitoring of hospitalized and in-house patients, to detection of food freshness in individual packages, and to distributed networked sensors over large areas (also known as wireless sensor networks, WSNs). Unfortunately, in these and numerous other practical applications, the available wireless gas sensors fall short of meeting emerging measurement needs in complex environments. In particular, existing wireless gas sensors cannot perform highly selective gas detection in the presence of high levels of interferences and cannot quantitate several components in gas mixtures. 1.1. Diversity Of Monitoring Needs Of Volatiles The monitoring of numerous gases of environmental, industrial, and homeland security concern is needed over the broad range of their regulated exposure concentrations. Figure 1 illustrates the relationships between several regulated exposure levels spanning several orders of magnitude of gas concentrations. Typical examples of concentrations of regulated exposure are presented in Table 110–14 for three groups of toxic volatiles such as volatile organic compounds (VOCs), toxic industrial chemicals (TICs), and chemical warfare agents (CWAs). These examples demonstrate the need for gas sensing capabilities with broad measurement dynamic ranges to cover 2 – 4 orders of magnitude in gas concentrations. Figure 1 Examples of regulated vapor-exposure limits established by different organizations: GPL: General Population Limit, established by USACHPPM – U.S. Army Center for Health Promotion and Preventative Medicine; PEL: Permissible Exposure Limit, established ... Table 1 Examples of regulated concentration levels (in ppm by volume) from three representative classes of toxic gases: VOCs, TICs, and CWAs.10–14 Additional needs for detection of volatiles originate from medical diagnostics, food safety, process monitoring, and other areas.15–17 In those applications, the types and levels of detected volatiles can provide the needed information for further control actions.

Wireless sensor networks that support the mobility of nodes are finding applications in different areas such as healthcare, elderly care, and rehabilitation from total knee and hip replacement. However, these application areas also require reliable and high throughput networks. Considering the high fluctuation of link quality during mobility, protocols supporting mobile wireless sensor nodes should be rigorously tested to ensure that they produce predictable outcomes. In this paper we present a wireless sensor network testbed for carrying out repeated and reproducible experiments, independent of the application or protocol types which should be tested. The testbed consists of, among others, a server side control station and a client side traffic flow controller which coordinate interand intra-experiment activities. We fully implemented the testbed for the TinyOS and TelosB platforms. We employed Diddyborg robots for emulating different types of movement in indoor and outdoor environments. The paper includes also an extensive evaluation of the testbed and the performance of two mobility-aware MAC protocols. Received on 17 November 2016; accepted on 6 July 2017; published on 21 December 2017

Wireless sensor networks that support the mobility of nodes are finding applications in different areas such as healthcare, elderly care, and rehabilitation from total knee and hip replacement. However, these application areas also require reliable and high throughput networks. Considering the high fluctuation of link quality during mobility, protocols supporting mobile wireless sensor nodes should be rigorously tested to ensure that they produce predictable outcomes. In this paper we present a wireless sensor network testbed for carrying out repeated and reproducible experiments, independent of the application or protocol types which should be tested. The testbed consists of, among others, a server side control station and a client side traffic flow controller which coordinate inter- and intra-experiment activities. We fully implemented the testbed for the TinyOS and TelosB platforms. We employed Diddyborg robots for emulating different types of movements in indoor and outdoor environments. The paper includes also an extensive evaluation of the testbed.

We report on the development and application of an aqueous sensor network (ASN). Designed for operation in lakes or drinking water reservoirs, the immersed ASN nodes are secured in place at a controlled depth by use of anchors with a node to node separation distance of ≤ 20 m. The individual nodes are integrated with various types of sensors enabling measurement of both physical and chemical analyte parameters. Node operation is overseen by programmable microcontrollers; the software on the microcontrollers is structured in a modular format so it can adapt to different types of sensors without extensive reprogramming. Node-to-node communication is achieved using timed bursts to avoid interference from unwanted signal reflections arising from the impedance mismatch at the water-air and water-land interface. We report on the application of the ASN for monitoring temperature and pH throughout a small pool. As desired the individual nodes of the ASN can be integrated with suitable chemical/biological sensors to detect down stream effluents from a source, or to ensure water reservoir quality.

We developed a simple and cost-effective fabrication technique to construct a hydrogen nanosensor by decorating single-walled carbon nanotubes with Pd nanoparticles. By varying the sensor's synthesis conditions (e.g., Pd electrodeposition charge, deposition potential, and initial baseline resistance of the SWNT network), the sensing performance was optimized. The optimized sensor showed excellent sensing properties toward hydrogen (ΔR/R of 0.42%/ppm) with a lower detection limit of 100 ppm and a linear response up to 1000 ppm. The response time decreased from tens of minutes to a few minutes with increasing hydrogen concentration at room temperature. The sensor's recovery time improved under humid air conditions compared to dry air conditions.

Titanium dioxide (TiO2) nanotubes were fabricated by anodisation of titanium foil in 0.15 M ammonium fluoride in an aqueous solution of glycerol (90 % v/v). Electropolymerisation of pyrrole and deposition of gold nanoparticles on to the TiO2 nanotube array electrode were carried out by cyclic voltammetry (CV). Electrochemical characterization of the sensor was performed by CV and electrochemical impedance spectroscopy. The morphology of the electrode was studied after every step of modification using field emission scanning electron microscope and atomic force microscope. The sensor was tested for AA and other biomolecules in phosphate buffered saline solution of pH 7 using CV, differential pulse voltammetry and amperometry. The sensor exhibited very high sensitivity of 63.912 μA mM−1 cm−2 and excellent selectivity to ascorbic acid (AA) in the presence of other biomolecules such as uric acid, dopamine, glucose and para-acetaminophen. It also showed very good linearity (R = 0.9995) over a wide range (1 μM–5 mM) of detection. The sensor was tested for AA in lemon and found its concentration to be 339 mg ml−1.

TiO2 nanotube arrays with remarkable visible photoluminescence were prepared by high magnetic field annealing in air at 450 °C due to the involvement of oxygen vacancies (OVs). A field with the intensities of 0, 2, 4, 6, and 8 T were applied in the annealing processing, along the directions set at 0°, 50°, and 90° from the surface normal of the substrate. The results demonstrated that the density of oxygen vacancies in TiO2 nanotubes can be controlled by varying the intensity and direction of the magnetic field. The mechanism for the effect of the high magnetic field has been investigated. This study opens an effective way to control the oxygen vacancies in nanomaterials to improve their performance.

This study compared the responses of Pd-functionalized and pristine titanate (TiO2) nanotube arrays to ethanol with those to acetone to determine the effects of functionalization of TiO2 nanotubes with Pd nanoparticles on the sensitivity and selectivity. The responses of pristine and Pd-functionalized TiO2 nanotube arrays to ethanol gas at 200 °C were ∼2877% and ∼21,253%, respectively. On the other hand, the responses of pristine and Pd-functionalized TiO2 nanotube arrays to acetone gas at 250 °C were ∼1636% and 8746% respectively. In the case of ethanol sensing, the response and recovery times of Pd-functionalized TiO2 nanotubes (10.2 and 7.1 s) were obviously shorter than those of pristine TiO2 nanotubes (14.3 and 8.8 s), respectively. In contrast, in the case of acetone sensing the response and recovery times of Pd-functionalized TiO2 nanotubes (42.5 and 19.7 s) were almost the same as those of pristine TiO2 nanotubes (47.2 and 17.9 s). TiO2 nanotube arrays showed the strongest response to ethanol and Pd functionalization was the most effective in improving the response of TiO2 nanotubes to ethanol among six different types of gases: ethanol, acetone, CO, H2, NH3 and NO2. The origin of the superior sensing properties of Pd-functionalized TiO2 nanotubes toward ethanol to acetone is also discussed.

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 are still a lot of open questions in the field of mobile ad hoc networks (MANETs) and sensor networks. If a topology incurs a large interference, either many communication signals sent by nodes will collide, or the network may experience a serious delay at delivering the data for some nodes, and even consume more energy. So, we reach the conclusion that interference imposes a potential negative impact on the performance of wireless networks. In the last few years, researchers actively explored topology control approaches for such networks. The motivation of topology control (TC) is to maintain the connectivity of the network, reduce the node degree and thereby reduce the interference, and reduce power consumption in the sensor nodes. Some literatures have pointed out that a node can interfere with another node even if it is beyond its communication range. To improve the network performance, designing topology control algorithms with consideration of interference is imminent and necessary. Since, it leads to fewer collisions and packet retransmissions, which indirectly reduces the power consumption and extends the lifetime of the network. In this paper, we propose a new interference-aware connected dominating set-based (IACDS) topology construction algorithm, namely, IACDS algorithm, a simple, distributed, interference-aware and energy-efficient topology construction mechanism that finds a sub-optimal connected dominating set (CDS) to turn unnecessary nodes off while keeping the network connected and providing complete communication coverage with minimum interference. IACDS algorithm utilizes a weighted distance-energy-interference-based metric that permits the network operator to trade off the lengths of the branches (distance) for the robustness and durability of the topology (energy and interference).   Key words: Interference, mobile ad hoc networks (MANETs), topology control, connected dominating set (CDS), wireless sensor network (WSN), interference-aware connected dominating set-based (IACDS) algorithm

The advancement of wireless communications and integrated circuit technology has enabled the development of low-cost sensor networks. The sensor networks can be used for various application areas (disaster recovery, health, military, homeland security, environment, home, etc.). For each application area, there are different technical issues that researchers are currently resolving. However, many of them are trying to tackle the limitations of this field from a network perspective. Sometimes, the effectiveness of some proposed approaches must be complemented by the supports of hardware design. This article points out the possibilities of overcoming the same problem set from a device perspective by taking advantage of the merits of nanotechnologies. At the same time, open research issues and challenges are identified to spark new interests and developments in this field.

The advancement of wireless communications and integrated circuit technology has enabled the development of low-cost sensor networks. The sensor networks can be used for various application areas (disaster recovery, health, military, homeland security, environment, home, etc.). For each application area, there are different technical issues that researchers are currently resolving. However, many of them are trying to tackle the limitations of this field from a network perspective. Sometimes, the effectiveness of some proposed approaches must be complemented by the supports of hardware design. This article points out the possibilities of overcoming the same problem set from a device perspective by taking advantage of the merits of nanotechnologies. At the same time, open research issues and challenges are identified to spark new interests and developments in this field

Synthesis—particularly by electrochemical anodization-, growth mechanism and chemical sensing properties of pure, doped and mixed titania tubular arrays are reviewed. The first part deals on how anodization parameters affect the size, shape and morphology of titania nanotubes. In the second part fabrication of sensing devices based on titania nanotubes is presented, together with their most notable gas sensing performances. Doping largely improves conductivity and enhances gas sensing performances of TiO2 nanotubes.

Synthesis of Nb-containing titania nanotubular arrays at room temperature by electrochemical anodization is reported. Crystallization of pure and Nb-doped TiO(2) nanotubes was carried out by post-growth annealing at 400°C. The morphology of the tubes obtained was characterized by scanning electron microscopy (SEM). Crystal structure and composition of tubes were investigated by glancing incidence x-ray diffraction (GIXRD) and total reflection x-ray fluorescence (TXRF). For the first time gas sensing characteristics of Nb-doped TiO(2) nanotubes were investigated and compared to those of undoped nanotubes. The functional properties of nanotubular arrays towards CO, H(2), NO(2), ethanol and acetone were tested in a wide range of operating temperature. The introduction of Nb largely improves conductivity and enhances gas sensing performances of TiO(2) nanotubes.

Recent advances in optical sensors show promise for the development of new wide area monitoring and distributed optical network hydrogen detection systems. Optical hydrogen sensing technologies reviewed here are: 1) open path Raman scattering systems, 2) back scattering from chemically treated solid polymer matrix optical fiber sensor cladding; and 3) shlieren and shearing interferometry imaging. Ultrasonic sensors for hydrogen release detection are also reviewed. The development status of these technologies and their demonstrated results in sensor path length, low hydrogen concentration detection ability, and response times are described and compared to the corresponding status of hydrogen spot sensor network technologies.

Palladium (Pd) nanoparticles (5-20 nm) are used as the sensing layer on surface acoustic wave (SAW) devices for detecting H2. The interaction with hydrogen modifies the conductivity of the Pd nanoparticle film, producing measurable changes in acoustic wave propagation, which allows for the detection of this explosive gas. The nanoparticle-based SAW sensor responds rapidly and reversibly at room temperature.

Microelectromechanical systems (MEMS) are a foundation for a broad range of mechanical, chemical, optical, and biotech products (sensors, microstructures and actuators) fabricated as integrated circuits on (primarily) silicon wafers in a batch mode. Commercial MEMS products include pressure sensors, acceleration sensors, gyros, ink-jet nozzles, read-write head positioners in hard drives, and digital light processors (DLPs) in projectors and television sets. The first four decades of MEMS development created a US$8 billion market. During the next decade, the MEMS market is estimated to increase by US$32 billion. Based on the presented overview of emerging MEMS sensors and microstructures, such a magnitude of growth is definitely possible.

In this work, we present the preliminary results for a wireless electronic nose platform embedding local sensor fusion component for the analysis of gas mixture in the framework of indoor pollution monitoring. This approach allow for significant reduction of power consumption by exploiting sensor censorship algorithms i.e. avoiding the transmission of uninformative contents to data sink. At the same time local situation assessment capabilities will allow the mote to perform adaptive, local reaction strategies e.g. duty cycle modifications, actuation etc. Performance are encouraging both on discrimination and estimation problem, we believe that a significant performance enhancement can be obtained by using a tapped delay neural network architecture.

In this work we present the development and proof of concept testing of a protoype wireless e-nose (w-nose) architecture capable of mesh shaped networking. The proposed w-nose is based on a TelosB by Crossbow Inc. and custom, power aware, TinyOS based components for data gathering and local processing. Sensor nodes are equipped with a small array of nonconductive polymer/CB based chemiresistors operating at room temperature for VOCs indoor monitoring. A properly developed conditioning stage board connects the sensor array to the microcontroller ADC. A single w-nose has been tested in a controlled test chamber for terpenes discrimination, while networked motes operation have been demonstrated in ad-hoc small testing facilities for acetic acid spill detection.

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.