Advantages of Slow Sensing for Ambient Monitoring: A Practical Perspective.

Air pollution is a ubiquitous threat, affecting 99% of the global populace and causing millions of premature deaths annually. Monitoring ambient air quality is essential, aiding policymakers and environmental agencies in timely interventions. This study delves into the advantages of slower gas sensors over their ultrafast counterparts, with a keen focus on their practicality in real-world scenarios. Slow sensors offer accurate time-averaged exposure assessments, harmonizing with established regulatory benchmarks. Their heightened precision and reliability, complemented by their cost-effectiveness, render them eminently suitable for large-scale deployment. The slow sensing ensures compatibility with regulations, fostering robust risk management practices. In contrast, ultrafast sensors, while claiming rapid detection, despite touting swift detection capabilities, grapple with formidable challenges. The sensitivity of ultrafast sensors to uncontrolled atmospheric effects, fluctuations in pressure, rapid response times, and uniform gas dispersion poses significant hurdles to their reliability. Addressing these issues assumes paramount significance in upholding the integrity of air quality assessments.

A Survey on Current-Mode Interfaces for Bio Signals and Sensors.

In this study, a review of second-generation voltage conveyor (VCII) and current conveyor (CCII) circuits for the conditioning of bio signals and sensors is presented. The CCII is the most known current-mode active block, able to overcome some of the limitations of the classical operational amplifier, which provides an output current instead of a voltage. The VCII is nothing more than the dual of the CCII, and for this reason it enjoys almost all the properties of the CCII but also provides an easy-to-read voltage as an output signal. A broad set of solutions for relevant sensors and biosensors employed in biomedical applications is considered. This ranges from the widespread resistive and capacitive electrochemical biosensors now used in glucose and cholesterol meters and in oximetry to more specific sensors such as ISFETs, SiPMs, and ultrasonic sensors, which are finding increasing applications. This paper also discusses the main benefits of this current-mode approach over the classical voltage-mode approach in the realization of readout circuits that can be used as electronic interfaces for different types of biosensors, including higher circuit simplicity, better low-noise and/or high-speed performance, and lower signal distortion and power consumption.

Resistive-Based Micro-Kelvin Temperature Resolution for Ultra-Stable Space Experiments.

High precision temperature measurements are a transversal need in a wide area of physical experiments. Space-borne gravitational wave detectors are a particularly challenging case, requiring both high precision and high stability in temperature measurement. In this contribution, we present a design able to reach 1 µK/Hz in most of the measuring band down to 1 mHz, and reaching 20 µK/Hz at 0.1 mHz. The scheme is based on resistive sensors in a Wheatstone bridge configuration which is AC modulated to minimize the 1/f noise. As a part of our study, we include the design of a test bench able to guarantee the high stability environment required for measurements. We show experimental results characterising both the test bench and the read-out, and discuss potential noise sources that may limit our measurement.

Long-Range Detection of a Wirelessly Powered Resistive Transducer.

Wireless measurement of resistance variation is particularly desirable inside confined cavities where wire connection and battery replacement are undesirable. Compared to capacitive or inductive transducers, resistive transducers have better availability, whose resistance changes can be directly converted into detectable voltages by electric bridges. However, to wirelessly operate electric bridges on batteryless platforms, multistage circuits are required to convert dc signals into wireless signals, making the whole system hard to miniaturize without using complicated integrated circuits. Alternatively, resistive transducers can be incorporated into passive L C resonators for contactless characterization by the backscattering method. This design, however, is ineffective beyond the near field, and it requires complicated line shape analysis of resonators' frequency response curves. Here, we will significantly improve the remote detectability of a resistive transducer, by inductively coupling it with a parametric resonator. Upon activation by wireless pumping power with an external antenna, the parametric resonator can self-oscillate and emit strong oscillation signals. The temperature-induced resistance change is converted into linear frequency shifts of the oscillation signal that can be detected over large distance separations for up to 20-fold the sensor's own dimension. Every 0.1 °C of temperature change can be converted into 8 kHz of frequency shift that is approximately threefold larger than the linewidth of oscillation peak. This sensor maintains good linearity between 25 °C and 41 °C, providing enough range for physiological monitoring. In conclusion, we have fabricated a resistance-to-frequency converter for remote detection of resistance changes via a wirelessly powered parametric oscillator. Besides this proof-of-concept demonstration for temperature sensing, the general concept of resistance-to-frequency conversion will improve the remote detectability of a broad range of resistive transducers for physiological and environmental monitoring.

Characterization of Anticipatory Postural Adjustments in Lateral Stepping: Impact of Footwear and Lower Limb Preference.

Lateral stepping is a motor task that is widely used in everyday life to modify the base of support, change direction, and avoid obstacles. Anticipatory Postural Adjustments (APAs) are often analyzed to describe postural preparation prior to forward stepping, however, little is known about lateral stepping. The aim of the study is to characterize APAs preceding lateral steps and to investigate how these are affected by footwear and lower limb preference. Twenty-two healthy young participants performed a lateral step using both their preferred and non-preferred leg in both barefoot and shod conditions. APA spatiotemporal parameters (size, duration, and speed) along both the anteroposterior and mediolateral axes were obtained through force plate data. APAs preceding lateral stepping showed typical patterns both along the anteroposterior and mediolateral axis. RM-ANOVA highlighted a significant effect of footwear only on medio-lateral APAs amplitude (p = 0.008) and velocity (p = 0.037). No differences were found for the limb preference. APAs in lateral stepping presented consistent features in the sagittal component, regardless of limb/shoe factors. Interestingly, the study observed that footwear induced an increase in the medio-lateral APAs size and velocity, highlighting the importance of including this factor when studying lateral stepping.

Electrical Percolation Threshold and Size Effects in Polyvinylpyrrolidone-Oxidized Single-Wall Carbon Nanohorn Nanocomposite: The Impact for Relative Humidity Resistive Sensors Design.

This paper reports, for the first time, on the electrical percolation threshold in oxidized carbon nanohorns (CNHox)-polyvinylpyrrolidone (PVP) films. We demonstrate-starting from the design and synthesis of the layers-how these films can be used as sensing layers for resistive relative humidity sensors. The morphology and the composition of the sensing layers are investigated through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and RAMAN spectroscopy. For establishing the electrical percolation thresholds of CNHox in PVP, these nanocomposite thin films were deposited on interdigitated transducer (IDT) dual-comb structures. The IDTs were processed both on a rigid Si/SiO2 substrate with a spacing of 10 µm between metal digits, and a flexible substrate (polyimide) with a spacing of 100 µm. The percolation thresholds of CNHox in the PVP matrix were equal to (0.05-0.1) wt% and 3.5 wt% when performed on 10 µm-IDT and 100 µm-IDT, respectively. The latter value agreed well with the percolation threshold value of about 4 wt% predicted by the aspect ratio of CNHox. In contrast, the former value was more than an order of magnitude lower than expected. We explained the percolation threshold value of (0.05-0.1) wt% by the increased probability of forming continuous conductive paths at much lower CNHox concentrations when the gap between electrodes is below a specific limit. The change in the nanocomposite's longitudinal Young modulus, as a function of the concentration of oxidized carbon nanohorns in the polymer matrix, is also evaluated. Based on these results, we identified a new parameter (i.e., the inter-electrode spacing) affecting the electrical percolation threshold in micro-nano electronic devices. The electrical percolation threshold's critical role in the resistive relative-humidity sensors' design and functioning is clearly emphasized.

Strategic Design of Hemi-Isoindigo Polymer for a Highly Sensitive and Selective All-Printed Flexible Nitrogen Dioxide Chemiresistive Sensor.

The study has developed two hemi-isoindigo (HID)-based polymers for printed flexible resistor-type nitrogen oxide (NO2 ) sensors: poly[2-ethylhexyl 3-((3'",4'-bis(dodecyloxy)-3,4-dimethoxy-[2,2':5',2'"-terthiophen]-5-yl)methylene)-2-oxoindoline-1-carboxylate] (P1) and poly[2-ethylhexyl 2-oxo-3-((3,3'",4,4'-tetrakis(dodecyloxy)-[2,2':5',2'"-terthiophen]-5-yl)methylene)indoline-1-carboxylate] (P2). These polymers feature thermally removable carbamate side chains on the HID units, providing solubility and creating molecular cavities after thermal annealing. These cavities enhance NO2 diffusion, and the liberated unsubstituted amide ─C(═O)NH─ groups readily form robust double hydrogen bonds (DHB), as demonstrated by computer simulations. Furthermore, both polymers possess elevated highest occupied molecular orbital (HOMO) energy levels of -4.74 and -4.77 eV, making them highly susceptible to p-doping by NO2 . Gas sensors fabricated from P1 and P2 films, anneal under optimized conditions to partially remove carbamate side chains, exhibit remarkable sensitivities of +1400% ppm-1 and +3844% ppm-1 , and low detection limit (LOD) values of 514 ppb and 38.9 ppb toward NO2 , respectively. These sensors also demonstrate excellent selectivity for NO2 over other gases.

Highly Stretchable and Multimodal MXene/CNTs/TPU Flexible Resistive Sensor with Hierarchical Structure Inspired by Annual Ring for Hand Rehabilitation.

With the advent of the intelligent age and people's higher pursuit of health, wearable sensors with functions of health monitoring and assisting physical rehabilitation are increasingly favored by consumers. Wherein, highly stretchable flexible sensors show promising potential, but the unstable conductivity under large strains remains a great challenge to develop flexible wearable sensors with both a wide work range and strain insensitivity. Based on this, a MXene/CNTs/TPU flexible resistive sensor (MCT/FRS) with hierarchical structure inspired by the annual ring was proposed. Benefiting from the bioinspired structure with tightly warped inner layers and deformable spring structure outside, the MCT/FRSs enable stable sensing over a wide working range of up to 700% under the stretching mode, as well as superior durability (7500 cycles). It also possessed linear and adjustable piezoresistive properties under the compression mode. Finally, the sensor was not only successfully employed for monitoring various human movements but also was utilized to assist hand rehabilitation in patients with Guillain-Barré syndrome in both stretching and compression modes. This work provides promising and attractive solutions for flexible wearable devices and intelligent medical care.

A Multitasking Flexible Sensor via Reservoir Computing.

Natural disasters are reported globally, and one source of severe damage to cities is flooding caused by locally heavy rain. Sharing of local weather information can save lives. However, it is difficult to collect local weather information in real-time because such data collection requires bulky, expensive sensors. For local, real-time monitoring of heavy rain and wind, a sensor system should be simple and low-cost so that it can be attached to a variety of surfaces, including roofs, vehicles, and umbrellas. To develop simple, low-cost multitasking sensors located on nonplanar surfaces, a flexible rain sensor to monitor waterdrop volume and wind velocity is devised. To monitor both simultaneously, a laser-induced graphene-based superhydrophobic conductive film is introduced. Using the superhydrophobic surface, water dynamics are measured when waterdrops collide with the sensor surface, and obtained time-series data are processed using "reservoir computing" to extract the volume and velocity from a single sensor as multitasking electronics. As a proof-of-concept, it is shown that the sensor measures continuous, long-term volume and wind-change dynamics. The results demonstrate feasibility of multitasking electronics with reservoir computing to reduce sensor integration complexity with low power consumption for both sensor and signal processing.

Phthalocyanines and Porphyrins/Polyaniline Composites (PANI/CuPctBu and PANI/TPPH2) as Sensing Materials for Ammonia Detection.

We combined a conducting polymer, polyaniline (PANI), with an organic semiconducting macrocyclic (MCs) material. The macrocycles are the phthalocyanines and porphyrins used to tune the electrical properties of the PANI, which benefits from their ability to enhance sensor response. For this, we proceeded by a simple ultrasonically assisted reaction involving the two components, i.e., the PANI matrix and the MCs, to achieve the synthesis of the composite nanostructure PANI/MCs. The composite nanostructure has been characterized and deposited on interdigitated electrodes (IDEs) to construct resistive sensor devices. The isolated nanostructured composites present good electrical properties dominated by PANI electronic conductivity, and the characterization reveals that both components are present in the nanostructure. The experimental results obtained under gas exposures show that the composite nanostructures can be used as a sensing material with enhanced sensing properties. The sensing performance under different conditions, such as ambient humidity, and the sensor's operating temperature are also investigated. Sensing behavior in deficient humidity levels and their response at different temperatures revealed unusual behaviors that help to understand the sensing mechanism. Gas sensors based on PANI/MCs demonstrate significant stability over time, but this stability is highly reduced after experiments in lower humidity conditions and at high temperatures.

Reliability of multi-purpose offshore-facilities: Present status and future direction in Australia.

Sustainable use of the ocean for food and energy production is an emerging area of research in different countries around the world. This goal is pursued by the Australian aquaculture, offshore engineering and renewable energy industries, research organisations and the government through the "Blue Economy Cooperative Research Centre". To address the challenges of offshore food and energy production, leveraging the benefits of co-location, vertical integration, infrastructure and shared services, will be enabled through the development of novel Multi-Purpose Offshore-Platforms (MPOP). The structural integrity of the designed systems when being deployed in the harsh offshore environment is one of the main challenges in developing the MPOPs. Employing structural reliability analysis methods for assessing the structural safety of the novel aquaculture-MPOPs comes with different limitations. This review aims at shedding light on these limitations and discusses the current status and future directions for structural reliability analysis of a novel aquaculture-MPOP considering Australia's unique environment. To achieve this aim, challenges which exist at different stages of reliability assessment, from data collection and uncertainty quantification to load and structural modelling and reliability analysis implementation, are discussed. Furthermore, several solutions to these challenges are proposed based on the existing knowledge in other sectors, and particularly from the offshore oil and gas industry. Based on the identified gaps in the review process, potential areas for future research are introduced to enable a safer and more reliable operation of the MPOPs.

Response of Palladium and Carbon Nanotube Composite Films to Hydrogen Gas and Behavior of Conductive Carriers.

To develop a high-performance hydrogen gas sensor, we fabricated a composite film made of carbon nanotubes (CNTs) and palladium nanoparticles. Carbon nanotubes were spin-coated onto a glass substrate, and subsequently, palladium nanoparticles were sputtered onto this film. The response to hydrogen gas was measured during two seasons (summer and winter) using a vacuum chamber by introducing a hydrogen/argon gas mixture. There was a clear difference in the sensor response despite the temperature difference between summer and winter. In addition, since a clean chamber was used, fewer water molecules acted as a dopant, and the behavior of the CNT changed from p-type to n-type because of the dissociative adsorption of hydrogen. This phenomenon was confirmed as the Seebeck effect. Finally, the work functions of Pd, PdHx, and CNT were calculated by first-principle calculations. As predicted by previous studies, a decrease in work function due to hydrogen adsorption was confirmed; however, the electron transfer to CNT was not appropriate from the perspective of charge neutrality and was found to be localized at the Pd/CNT interface. It seems that the Seebeck effect causes the concentration of conductive carriers to change.

Efficient Multiaxial Shoulder-Motion Tracking Based on Flexible Resistive Sensors Applied to Exosuits.

This article describes the performance of a flexible resistive sensor network to track shoulder motion. This system monitors every gesture of the human shoulder in its range of motion except rotations around the longitudinal axis of the arm. In this regard, the design considers the movement of the glenohumeral, acromioclavicular, sternoclavicular, and scapulothoracic joints. The solution presented in this work considers several sensor configurations and compares its performance with a set of inertial measurement units (IMUs). These devices have been put together in a shoulder suit with Optitrack visual markers in order to be used as pose ground truth. Optimal configurations of flexible resistive sensors, in terms of accuracy requirements and number of sensors, have been obtained by applying principal component analysis techniques. The data provided by each configuration are then mapped onto the shoulder pose by using neural network algorithms. According to the results shown in this article, a set of flexible resistive sensors can be an adequate alternative to IMUs for multiaxial shoulder pose tracking in open spaces. Furthermore, the system presented can be easily embedded in fabric or wearable devices without obstructing the user's motion.

Tuning the Magnitude and the Polarity of the Piezoresistive Response of Polyaniline through Structural Control.

We demonstrate the tunability of both the polarity and the magnitude of the piezoresistive response of polyaniline that is template-synthesized on poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PANI-PAAMPSA, by altering the template molecular weight. Piezoresistivity is quantified by gauge factor, a unitless parameter that relates changes in electrical resistance to applied strain. The gauge factor of PANI-PAAMPSA decreases linearly and becomes negative with decreasing PAAMPSA molecular weight. The polarity of PANI-PAAMPSA's gauge factor is determined by macroscopic connectivity across thin films. PANI-PAAMPSA thin films comprise electrostatically stabilized particles whose size is determined at the onset of synthesis. An increase in the interparticle spacing with applied strain results in a positive gauge factor. The presence of PANI crystallites increases connectivity between particles; these samples instead exhibit a negative gauge factor whereby the resistance decreases with increasing strain. The tunability of the piezoresistive response of these conducting polymers allows their utilization in a broad range of flexible electronics applications, including thermo- and chemoresistive sensors and strain gauges.

Magnetic Susceptibility Study of Sub-Pico-emu Sample Using a Micromagnetometer: An Investigation through Bistable Spin-Crossover Materials.

A promising and original method to study the spin-transition in bistable spin-crossover (SCO) materials using a magnetoresistive multiring sensor and its self-generated magnetic field is reported. Qualitative and quantitative studies are carried out combining theoretical and experimental approaches. The results show that only a small part of matter dropped on the sensor surface is probed by the device. At a low bias-current range, the number of detected nanoparticles depends on the amplitude of the current. However, in agreement with the theoretical model, the stray voltage from the particles is proportional to the current squared. By changing both the bias current and the concentration of particle droplet, the thermal hysteresis of an ultrasmall volume, 1 × 10-4 mm3 , of SCO particles is measured. The local probe of the experimental setup allows a highest resolution of 4 × 10-14 emu to be reached, which is never achieved by experimental methods at room temperature.