A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

Breath tests cover the fraction of nitric oxide in expired gas (FENO), volatile organic compounds (VOCs), variables in exhaled breath condensate (EBC) and other measurements. For EBC and for FENO, official recommendations for standardised procedures are more than 10 years old and there is none for exhaled VOCs and particles. The aim of this document is to provide technical standards and recommendations for sample collection and analytic approaches and to highlight future research priorities in the field. For EBC and FENO, new developments and advances in technology have been evaluated in the current document. This report is not intended to provide clinical guidance on disease diagnosis and management. Clinicians and researchers with expertise in exhaled biomarkers were invited to participate. Published studies regarding methodology of breath tests were selected, discussed and evaluated in a consensus-based manner by the Task Force members. Recommendations for standardisation of sampling, analysing and reporting of data and suggestions for research to cover gaps in the evidence have been created and summarised. Application of breath biomarker measurement in a standardised manner will provide comparable results, thereby facilitating the potential use of these biomarkers in clinical practice.

/pdf/a-european-respiratory-society-technical-standard-exhaled-2pn4ecxild.pdf

A European respiratory society technical standard : exhaled biomarkers in lung disease

In this review, we describe technical developments in breath analysis and its applications in clinical diagnosis, monitoring disease state, and assessing environmental exposure. Breath tests have been successfully employed in clinical analyses for symptoms including lung disease, oxidative stress, gastrointestinal disease, metabolic disorders, and Helicobacter pylori infection.

Although gas chromatography has been used mainly for the analysis of volatile constituents in breath samples, other techniques (e.g., sensors and lasers) have also been used satisfactorily. The analytical results of breath analysis can be derived both qualitatively and quantitatively. However, evaluation of the data from different approaches remains insufficient because of the lack of standardized procedures and poor methods of validation. Further research is therefore required to expand the applicability of breath analysis in clinical diagnosis of diseases.

A review of breath analysis for diagnosis of human health

Breath acetone monitoring by portable Si:WO3 gas sensors

Since the ancient discovery of the 'sweet odor' in human breath gas, pursuits of the breath analysis-based disease diagnostics have never stopped. Actually, the 'smell' of the breath, as one of three key disease diagnostic techniques, has been used in Eastern-Medicine for more than three thousand years. With advancement of measuring technologies in sensitivity and selectivity, more specific breath gas species have been identified and established as a biomarker of a particular disease. Acetone is one of the breath gases and its concentration in exhaled breath can now be determined with high accuracy using various techniques and methods. With the worldwide prevalence of diabetes that is typically diagnosed through blood testing, human desire to achieve non-blood based diabetic diagnostics and monitoring has never been quenched. Questions, such as is breath acetone a biomarker of diabetes and how is the breath acetone related to the blood glucose (BG) level (the golden criterion currently used in clinic for diabetes diagnostic, monitoring, and management), remain to be answered. A majority of current research efforts in breath acetone measurements and its technology developments focus on addressing the first question. The effort to tackle the second question has begun recently. The earliest breath acetone measurement in clearly defined diabetic patients was reported more than 60 years ago. For more than a half-century, as reviewed in this paper, there have been more than 41 independent studies of breath acetone using various techniques and methods, and more than 3211 human subjects, including 1581 healthy people, 242 Type 1 diabetic patients, 384 Type 2 diabetic patients, 174 unspecified diabetic patients, and 830 non-diabetic patients or healthy subjects who are under various physiological conditions, have been used in the studies. The results of the breath acetone measurements collected in this review support that many conditions might cause changes to breath acetone concentrations; however, the results from the six independent studies using clearly-defined Type 1 and Type 2 diabetic patients unanimously support that an elevated mean breath acetone concentration exists in Type 1 diabetes. Note that there is some overlap between the ranges of breath acetone concentration in individual T1D patients and healthy subjects; this reminds one to be careful when using an acetone breath test on T1D diagnostics. Comparatively, it is too early to draw a general conclusion on the relationship between a breath acetone level and a BG level from the very limited data in the literature.

http://iopscience.iop.org/article/10.1088/1752-7155/7/3/037109/pdf

Is breath acetone a biomarker of diabetes? A historical review on breath acetone measurements.

This work describes a novel method of embedded damage detection within glass fiber–reinforced polymer composites. Damage detection is achieved by monitoring the spatially distributed electrical conductivity of a strain-sensitive multiwalled carbon nanotube thin film. First, thin films were spray-deposited directly upon glass fiber mats. Second, using electrical impedance tomography, the spatial conductivity distribution of the thin film was determined before and after damage-inducing events. The resolution of the sensor was determined by drilling progressively larger holes in the center of the composite specimens, and the corresponding electrical impedance tomography response was measured by recording the current–voltage data at the periphery of the monitored composite sample. In addition, the sensitivity to damage occurring at different locations in the composite was also investigated by comparing electrical impedance tomography spatial conductivity maps obtained for specimens with sets of holes drilled at different locations in the sensing area. Finally, the location and severity of damage from low-velocity impact events were detected using the electrical impedance tomography method. The work presented in this study indicates a paradigm shift in the available possibilities for structural health monitoring of fiber-reinforced polymer composites.

Detection of Spatially Distributed Damage in Fiber-Reinforced Polymer Composites.

Fiber-reinforced polymer (FRP) structures and components are highly susceptible to damage due to delamination, matrix cracking, inter-laminar fracture, and debonding, all of which have potential to cause catastrophic structural failure. While numerous sensing technologies have been developed and embedded in FRP composites for monitoring strain, they serve as defects and can promote damage formation and propagation. Thus, in this study, an alternative technique is proposed for in situ strain monitoring of FRP composites via layer-by-layer multi-walled carbon nanotube-polyelectrolyte thin films deposited directly upon glass fiber weaves. To date, these carbon nanotube-based thin films have been validated for their piezoresistivity. The objective of this study is to characterize the strain sensing performance of different thickness thin films deposited on glass fiber weaves and embedded in FRP specimens using time-domain two-point probe resistance and frequency-domain electrical impedance spectroscopy (EIS) measurements. From the experimental thin film electromechanical response, a new method for fitting using a cubic smoothing spline is implemented and is compared to linear least-squares fitting. The results show that the cubic spline fit is better suited for capturing the strain sensitivities (or gage factors) of these thin films within the time- and frequency-domains along with the variation of strain sensitivity with applied strain. The bulk resistance response is described by the DC resistance measurements, whereas the EIS measurements provide insight of the inter-nanotube response.

/pdf/in-situ-strain-monitoring-of-fiber-reinforced-polymers-using-2am3h71lzz.pdf

In situ strain monitoring of fiber-reinforced polymers using embedded piezoresistive nanocomposites

The need for structural health monitoring has become critical due to aging infrastructures, legacy airplanes, and continuous development of new structural technologies. Based on an updated structural design, there is a need for new structural health monitoring paradigms that can sense the presence, location, and severity with a single measurement. This paper focuses on the first step of this paradigm, consisting of applying a sprayed conductive carbon nanotube-polymer film upon glass fiber-reinforced polymer composite substrates. Electrical impedance tomography is performed to measure changes in conductivity within the conductive films because of damage. Simulated damage is a method for validation of this approach. Finally, electrical impedance tomography measurements are taken while the conductive films are subjected to tensile and compressive strain states. This demonstrates the ability of electrical impedance tomography for not only damage detection, but active structural monitoring as well. This paper acts as a first step toward moving the structural health monitoring paradigm toward large-scale deployable spatial sensing.

Spatial Sensing Using Electrical Impedance Tomography.

/pdf/spatial-sensing-using-electrical-impedance-tomography-2yce1fsg7t.pdf

Spatial Sensing Using Electrical Impedance Tomography

This work describes a novel method of embedded damage detection within glass fiber–reinforced polymer composites. Damage detection is achieved by monitoring the spatially distributed electrical con...

/pdf/detection-of-spatially-distributed-damage-in-fiber-2gycp6f7e6.pdf

Bryan R. Loyola

Papers

Detection of Spatially Distributed Damage in Fiber-Reinforced Polymer Composites.

In situ strain monitoring of fiber-reinforced polymers using embedded piezoresistive nanocomposites

Spatial Sensing Using Electrical Impedance Tomography.

Spatial Sensing Using Electrical Impedance Tomography

Detection of Spatially Distributed Damage in Fiber-Reinforced Polymer Composites