This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Introduction to the Finite Element Method

The kesterite-structured semiconductors Cu2ZnSnS4 and Cu2ZnSnSe4 are drawing considerable attention recently as the active layers in earth-abundant low-cost thin-film solar cells. The additional number of elements in these quaternary compounds, relative to binary and ternary semiconductors, results in increased flexibility in the material properties. Conversely, a large variety of intrinsic lattice defects can also be formed, which have important influence on their optical and electrical properties, and hence their photovoltaic performance. Experimental identification of these defects is currently limited due to poor sample quality. Here recent theoretical research on defect formation and ionization in kesterite materials is reviewed based on new systematic calculations, and compared with the better studied chalcopyrite materials CuGaSe2 and CuInSe2 . Four features are revealed and highlighted: (i) the strong phase-competition between the kesterites and the coexisting secondary compounds; (ii) the intrinsic p-type conductivity determined by the high population of acceptor CuZn antisites and Cu vacancies, and their dependence on the Cu/(Zn+Sn) and Zn/Sn ratio; (iii) the role of charge-compensated defect clusters such as [2CuZn +SnZn ], [VCu +ZnCu ] and [ZnSn +2ZnCu ] and their contribution to non-stoichiometry; (iv) the electron-trapping effect of the abundant [2CuZn +SnZn ] clusters, especially in Cu2ZnSnS4. The calculated properties explain the experimental observation that Cu poor and Zn rich conditions (Cu/(Zn+Sn) ≈ 0.8 and Zn/Sn ≈ 1.2) result in the highest solar cell efficiency, as well as suggesting an efficiency limitation in Cu2ZnSn(S,Se)4 cells when the S composition is high.

Classification of lattice defects in the kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 earth-abundant solar cell absorbers.

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...

Compound Copper Chalcogenide Nanocrystals

A biosensor can be defined as a compact analytical device or unit incorporating a biological or biologically derived sensitive recognition element immobilized on a physicochemical transducer to measure one or more analytes. Microfluidic systems, on the other hand, provide throughput processing, enhance transport for controlling the flow conditions, increase the mixing rate of different reagents, reduce sample and reagents volume (down to nanoliter), increase sensitivity of detection, and utilize the same platform for both sample preparation and detection. In view of these advantages, the integration of microfluidic and biosensor technologies provides the ability to merge chemical and biological components into a single platform and offers new opportunities for future biosensing applications including portability, disposability, real-time detection, unprecedented accuracies, and simultaneous analysis of different analytes in a single device. This review aims at representing advances and achievements in the field of microfluidic-based biosensing. The review also presents examples extracted from the literature to demonstrate the advantages of merging microfluidic and biosensing technologies and illustrate the versatility that such integration promises in the future biosensing for emerging areas of biological engineering, biomedical studies, point-of-care diagnostics, environmental monitoring, and precision agriculture.

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Microfluidics Integrated Biosensors: A Leading Technology towards Lab-on-a-Chip and Sensing Applications

Kesterite-based solar cells are attracting considerable attention in recent years, owing to the reduced toxicity and greater abundance of their constituent elements. In this brief review, we discuss the current status of this important technology by focusing on three key aspects of the device: (i) the interface between the kesterite absorber and the Mo back contact, (ii) the kesterite absorber bulk defects and grain boundaries and (iii) the interface between the kesterite absorber and the buffer layer. By identifying key issues to be addressed, we provide suggestions for their potential improvement and future research. Copyright © 2016 John Wiley & Sons, Ltd.

The current status and future prospects of kesterite solar cells: a brief review

Effect of sodium diffusion on the structural and electrical properties of Cu2ZnSnS4 thin films

Biosensors have gained immense acceptance in the field of medical diagnostics, besides environmental, food safety and biodefence applications due to its attributes of real-time and rapid response This synergistic combination of biotechnology and microelectronics comprises a biological recognition element coupled with a compatible transducer device Diabetes is a disease of major concern since the ratio of world population suffering from it is increasing at an alarming rate and therefore the need for development of accurate and stable glucose biosensors is evident There are many commercial glucose biosensors available yet some limitations need attention This review presents a detailed account of the polypyrrole based amperometric glucose biosensors The polymer polypyrrole is used extensively as a matrix for immobilization of glucose oxidase enzyme owing to its favourable features such as stability under ambient conditions, conductivity that allows it to be used as an electron relay, ability to be polymerized under neutral and aqueous mild conditions, and more The simple one-step electrodeposition on the electrode surface allows easy entrapment of the enzyme The review is structured into three categories (a) the first-stage biosensors: which report the studies from the inception of use of polypyrrole in glucose biosensors during which time the role of the polymer and the use of mediators was established This period saw extensive work by two separate groups of Schuhmann and Koopal who contributed a great deal in understanding the electron transfer pathways in polypyrrole based glucose biosensors, (b) the second-stage biosensors: which highlight the shift of polypyrrole from a conventional matrix to composite matrices with extensive use of mediators focused at improving the selectivity of response, and (c) third-stage biosensors: the remarkable properties of nanoparticles and carbon nanotubes and their outstanding ability to mediate electrontransfers have seen their indispensable use in conjugation with polypyrrole for development of glucose biosensors with improved sensitivity and stability characteristics which is accounted in the review, which thus traces the evolution of polypyrrole from a conventional matrix, to composites and thence to the form of nanotube arrays, with the objective of addressing the vital issue of diabetes management through the development of stable and reliable glucose biosensors

Polypyrrole based amperometric glucose biosensors

Constant current source is essential in Electrical Impedance Tomography (EIT) for injecting a sinusoidal constant current to the phantom boundary. In medical EIT the multifrequency scanning is desired for studying the wide range of tissue conductivity among different type of subjects. A multifrequency constant current source is developed for medical EIT and the boundary data of a practical phantom is studied. A sinusoidal constant crrent is injected to the phantom boundary at different frequency levels and the boundary potentials are measured. Results show that the developed current source efficiently generate constant current with minimal amount of noise at different frequency levels. Boundary data are successfully generated at four different frequencies and found suitable for image reconstruction study in multifrequecy EIT.

A multifrequency constant current source suitable for Electrical Impedance Tomography (EIT)

In this paper, we present the fabrication and characterization of molybdenum microheaters for high-temperature gas sensing applications. The surface morphology of dc magnetron sputtered molybdenum thin films was characterized by scanning electron microscopy and atomic force microscopy. The suspended membrane microheater consumed 104 mW to reach a maximum temperature of 800 °C and showed an absolute thermal resistance of 7.2 °C/mW. Thermal distribution patterns over the active heating area were recorded using FLIR camera. It showed a temperature gradient of 1.18 % from the center of the microheater to its periphery. The thermal and mechanical stabilities of the microheater were analyzed, and its membrane failure at higher operating temperatures was prevented. The microheater membrane deformation at different temperatures was characterized using optical profilometer, and its maximum value was found to be $16.25~\mu \text{m}$ at 800 °C. The microheater response to a pulse, continuous pulse train, and constant dc voltages was characterized. Its response and recovery times are in the order of 19 and 34 ms, respectively. It showed a stable temperature with a negligible resistance drift (0.96%) over a period of 600 h. The TiO2 thin film integrated molybdenum microhotplate-based MEMS gas sensor response for CO (5000 ppb) was measured at different operating temperatures (300 °C–700 °C).

Molybdenum Microheaters for MEMS-Based Gas Sensor Applications: Fabrication, Electro-Thermo-Mechanical and Response Characterization

Under an alternating electrical signal, biological tissues produce a complex electrical bioimpedance that is a function of tissue composition and applied signal frequencies. By studying the bioimpedance spectra of biological tissues over a wide range of frequencies, we can noninvasively probe the physiological properties of these tissues to detect possible pathological conditions. Electrical impedance spectroscopy can provide the spectra that are needed to calculate impedance parameters within a wide range of frequencies. Before impedance parameters can be calculated and tissue information extracted, impedance spectra should be processed and analyzed by a dedicated software program. National Instruments (NI) Inc. offers LabVIEW, a fast, portable, robust, user-friendly platform for designing data-analyzing software. We developed a LabVIEW-based electrical bioimpedance spectroscopic data interpreter (LEBISDI) to analyze the electrical impedance data for tissue characterization in medical, biomedical and biological applications. Here, we test, calibrate and evaluate the performance of LEBISDI on the impedance data obtained from simulation studies, electronic circuit element combinations as well as various biological tissues. We analyze the Nyquist plots obtained from the electrical impedance spectroscopy (EIS) measurements and compare the equivalent circuit parameters calculated by LEBISDI with the corresponding original circuit parameters to assess the accuracy of the program developed. Calibration studies show that LEBISDI accurately interpreted simulated and circuit-element data. Furthermore, results obtained from biological tissues show that LEBISDI successfully interpreted bioimpedance data and estimates of capacitance and resistance data. Finally, LEBISDI efficiently calculated and analyzed variation in bioimpedance parameters of different tissue compositions, health and temperatures. LEBISDI can also be used for human tissue impedance analysis for electrical impedance-based biopsy or cancer diagnosis.

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A LabVIEW-based electrical bioimpedance spectroscopic data interpreter (LEBISDI) for biological tissue impedance analysis and equivalent circuit modelling

Nagaraju Jampana

Papers

Effect of sodium diffusion on the structural and electrical properties of Cu2ZnSnS4 thin films

Polypyrrole based amperometric glucose biosensors

A multifrequency constant current source suitable for Electrical Impedance Tomography (EIT)

Molybdenum Microheaters for MEMS-Based Gas Sensor Applications: Fabrication, Electro-Thermo-Mechanical and Response Characterization

A LabVIEW-based electrical bioimpedance spectroscopic data interpreter (LEBISDI) for biological tissue impedance analysis and equivalent circuit modelling