A micromechanical biosensor with interdigitated capacitor readout

The growing demands of high-throughput, accurate and fast response biological or chemical sensors are driving the development of new detection technologies. This paper presents a micromechanical biosensor with capacitive read-out method. The proposed biosensor design consists of a fixed-fixed beam attached to an interdigitated capacitor. Implementation of the interdigitated capacitor design improves the sensitivity of the biosensor. The effects of the electrode thickness, length and the number of electrode fingers on the change of capacitance are investigated. The results show that the percentage change of capacitance is proportional to the number of the electrode fingers. Similarly, the increase in the length of the electrodes results in an increase in the percentage change of the capacitance. However, as the thickness of the electrode increases, the percentage change of the capacitance decreases.

RF techniques for lowering the actuation voltage of RF MEMS shunt capacitor switch for C-K band

Increasing the capacitance ratio in RF MEMS shunt capacitive switch will increase its RF performance but also raise its actuation voltage. To improve the RF performance of the switch without increasing its capacitance ratio, this paper explores two methods: reducing the LC resonance from the mm-wave into the X-band by using an inductive bridge, and using two short high impedance transmission lines at both ends of the CPW line. Accordingly, this paper presents the design and simulation of an electro-static low actuation voltage and a very high isolation multipurpose switch with a very large bandwidth. The simulation results are presented and discussed.

Determination of human body composition

This thesis deals with two electrical methods designed to enable rapid, safe and noninvasive measurement of body composition, both for clinical and community use. The first section provides a review of the literature related to measurement of body composition in humans and outlines the approach of the research project. The second section deals with established methods of determining body composition, the two most important being hydrostatic densitometry and deuterium oxide dilution. In this part of the report, a novel method for measuring lung volume by hydrogen dilution at the time of underwater weighing is described. The main findings of the thesis are contained in the third section which deals with the assessment of body opposition by electrical means. There are two components to this part of the study. The first involved the testing of a commercially available bioelectric impedance analyser (BIA) which measures impedance to a flow of current through the body. Studies on the reproducibility and reliability of measurements were performed. Results showed the importance of correct electrode placement and revealed that subjects can consume a light meal and a drink before being measured with the BIA without adversely affecting impedance readings. Results suggested, however, that subjects empty their bladders before measurements are made. Strong correlations were found between height 2/ resistance and measurements of total body water (r = 0.839) and fat-free weight derived from densitometry (r = 0.821), Moderate correlations (r = 0.6 to 0.7) were also found when height /resistance was related to fat-free weight derived from anthropometric measurements. The second and major consonant of the third section deals with the development of a method based on the absorption of energy from a weak electromagnetic field established in a capacitor or chamber large enough to accommodate an adult human subject. The method involves measurement of the effect of the body on the electromagnetic field, and is based on differential absorption of energy by body fat and fat-free tissues. Regression equations were developed for predicting the weight of fat and fat-free tissue in the body from measurement of electromagnetic field effects in a test capacitor and in a resonating chamber. The test capacitor comprised a large aluminum cylinder with a copper rod as a central conductor. The following equation was derived for the relationship of fat-free weight (FEW) based on body density, with measurements of change in resonant frequency (ΔfR), height (H) and weight (W) : FFW = -4.39 + 0.690 W + 19.9 H + 37.6 ΔfR In a study of 17 subjects, a value of 0.891 was found for R2, and S.E.E. was 1.63. The resonating chamber consisted of a large enclosed aluminium cylinder with a copper rod as a central conductor. The following equation was derived for the relationship of fat weight (FW) based on the mean of estimates from body density and total body water, with measurements of change in signal attenuation (ΔA), change in resonant frequency (ΔfR), and height (H) and weight (W) : FW = 73.48 + 0.291 (W/√(ΔA) - 49.2 H - 0.53 ΔfR In a study of 27 subjects, a value of 0.956 was found for R2, and S.E.E. was 1.97. In these equations, variables were measured in the following units : FEW, FW and W (kg), ΔfR (MHz) and H (m).

Design and simulation of a low voltage wide band RF MEMS switch

This paper presents design of an electrostatic wide band shunt capacitive coupling RF MEMS switch with low actuation voltage. The key factors of the RF MEMS switch design are the proper scattering parameters, low actuation voltage, and the cost of the fabrication process. An overview of the recent low actuation voltage RFMEMS switches has been presented. These designs still suffer from the complexity of process, lack of reliability, limitation of frequency band, and process cost. RF characteristics of a shunt RF MEMS switches are specified mostly by coupling capacitor in upstate position of the membrane Cu. This capacitor is in trade-off with actuation voltage. In this work, the capacitor is eliminated by using two short high impedance transmission lines, at the input and output of the switch. The simulation results demonstrate an improvement in the RF characteristic of the switch.

Electrochemical performance of polyaniline nanofibres and polyaniline/multi-walled carbon nanotube composite as an electrode material for aqueous redox supercapacitors

Polyaniline (PANI) nanofibres are synthesized by interfacial polymerization and their electrochemical performance is evaluated in an aqueous redox supercapacitor constituted as a two-electrode cell. The initial specific capacitance of the cell is 554 F g−1 at a constant current of 1.0 A g−1, but this value rapidly decreases on continuous cycling. In order to improve the cycleability of the supercapacitor, a composite of polyaniline with multi-walled carbon nanotubes (CNTs) is synthesized by in situ chemical polymerization. Its capacitive behaviour is evaluated in a similar cell configuration. A high initial specific capacitance of 606 F g−1 is obtained with good retention on cycling. In both supercapacitors, the effect of charging potential on cycling performances is investigated.

Carbon nanofibers with inter-bonded fibrous structure for supercapacitor application

In this study, we have improved carbon nanofiber interconnection by using two electrospinning methods: conventional electrospinning and side-by-side bicomponent electrospinning to produce polyvinylpyrrolidone (PVP)/polyacrylonitrile (PAN) blend nanofibers and PVP/PAN side-by-side bicomponent nanofibers respectively. Upon carbonization, the nanofibers showed inter-bonded morphologies. PVP here functioned to bind nanofibers during carbonization. The inter-boned fibrous morphology was highly affected by the PVP/PAN ratio and the electrospinning method. Carbon nanofibers prepared by the bicomponent electrospinning were found to have larger capacitances compared to those prepared by the conventional electrospinning. The influence of electrospinning method, PAN/PVP ratio on the crystallinity of carbon nanofibers, their surface morphology and capacitor performance were examined. The influence mechanism was elucidated as well.

An effective VAR planning to improve dynamic voltage profile of distribution networks with distributed wind generation

This paper proposes an effective VAR planning based on reactive power margin for the enhancement of dynamic voltage stability in distribution networks with distributed wind generation. The analysis is carried over a distribution test system representative of the Kumamoto area in Japan. The detailed mathematical modeling of the system is also presented. Firstly, this paper provides simulation results showing the effects of composite load on voltage dynamics in the distribution network through an accurate time-domain analysis. Then, a cost-effective combination of shunt capacitor bank and distribution static synchronous compensator (D-STATCOM) is selected to ensure fast voltage recovery after a sudden disturbance. The analysis shows that the proposed approach can reduce the size of compensating devices, which in turn, reduces the cost. It also reduces power loss of the system.

Voltage profile improvement for distributed wind generation using D-STATCOM

This paper presents the application of FACTS devices for the enhancement of dynamic voltage stability in distribution networks with distributed wind generation. The analysis is carried over a test distribution system representative of the Kumamoto area in Japan. The detailed mathematical modelling of the system is also presented. Firstly, this paper provides simulation results showing the effects of higher and lower penetration of distributed wind generation on the voltage dynamics in a faulted system. Then, a distribution static synchronous compensator (D-STATCOM) is used to improve the voltage profile of the system. This analysis shows that D-STATCOM has significant performance to improve the voltage dynamics of distribution system compared to shunt capacitor.

Gamma-irradiated carbon nanotube yarn as substrate for high-performance fiber supercapacitors

As an electrical double layer capacitor, dry-spun carbon nanotube yarn possesses relatively low specific capacitance. This can be significantly increased as a result of the pseudocapacitance of functional groups on the carbon nanotubes developed by oxidation using a gamma irradiation treatment in the presence of air. When coated with high-performance polyaniline nanowires, the gamma-irradiated carbon nanotube yarn acts as a high-strength reinforcement and a high-efficiency current collector in two-ply yarn supercapacitors for transporting charges generated along the long electrodes. The resulting supercapacitors demonstrate excellent electrochemical performance, cycle stability, and resistance to folding-unfolding that are required in wearable electronic textiles.

A highly conductive porous graphene electrode prepared via in situ reduction of graphene oxide using Cu nanoparticles for the fabrication of high performance supercapacitors

Herein, a new graphene/Cu nanoparticle composite was prepared via the in situ reduction of GO in the presence of Cu nanoparticles which was then utilized as a sacrificing template for the formation of flexible and porous graphene capacitor electrodes by the dissolution of the intercalated Cu nanoparticle in a mixed solution of FeCl3 and HCl. The porous RGO electrode was characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The as-prepared graphene/Cu nanoparticle composite and the pure graphene film after removal of Cu nanoparticles possessed high conductivity of 3.1 × 10³ S m^-1 and 436 S m^-1 respectively. The porous RGO can be used as the electrode for the fabrication of supercapacitors with high gravimetric specific capacitances up to 146 F g^-1, good rate capability and satisfactory electrochemical stability. This environmentally friendly and efficient approach to fabricating porous graphene nanostructures could have enormous potential applications in the field of energy storage and nanotechnology.

Nonlinear backstepping controller design for sharing active and reactive power in three-phase grid-connected photovoltaic systems

In this paper, a nonlinear backstepping controller is designed for three-phase grid-connected solar photovoltaic (PV) systems to share active and reactive power. A cascaded control structure is considered for the purpose of sharing appropriate amount of power. In this cascaded control structure, the dc-link voltage controller is designed for balancing the power flow within the system and the current controller is designed to shape the grid current into a pure sinusoidal waveform. In order to balance the power flow, it is always essential to maintain a constant voltage across the dc-link capacitor for which an incremental conductance (IC) method is used in this paper. This approach also ensures the operation of solar PV arrays at the maximum power point (MPP) under rapidly changing atmospheric conditions. The proposed current controller is designed to guarantee the current injection into the grid in such a way that the system operates at a power factor other than unity which is essential for sharing active and reactive power. The performance of the proposed backstepping approach is verified on a three-phase grid-connected PV system under different atmospheric conditions. Simulation results show the effectiveness of the proposed control scheme in terms of achieving desired control objectives.

Performance analysis of a grid-connected PV system in LV distribution network

Over the past decade, the growing demand of Grid-connected photo voltaic (GCPV) system has been increasing due to an extensive use of renewable energy technologies for sustainable power generation and distribution. High-penetrated GCPV systems enhance the operation of the network by improving the voltage levels and reducing the active power losses along the length of the feeder. This paper aims to investigate the voltage variations and Total Harmonic Distortion (THD) of a typical GCPV system modelled in Power system simulator, PSS SINCAL with the change of level of PV integrations in a Low Voltage (LV) distribution network. Five different case studies are considered to investigate the impact of PV integrations on LV nodes and the corresponding voltage variations and harmonics. In addition, this paper also explores and benchmarks the voltage improvement techniques by implementing On Load Tap Changer (OLTC) with respective to the main transformer and addition of Shunt Capacitor (SC) at appropriate node points in LV network,

Lithium-ion capacitors with 2D Nb2CTx (MXene) - carbon nanotube electrodes

There is a growing interest to hybrid energy storage devices, such as lithium-ion capacitors, in which battery-type electrodes are combined with capacitor-type ones. It is anticipated that the energy density (either gravimetric or volumetric) of lithium-ion capacitors is improved if pseudocapacitive or fast insertion materials are used instead of conventional activated carbon (AC) in the capacitor-type electrode. MXenes, a new family of two-dimensional transition metal carbides, demonstrate metallic conductivity and fast charge-discharge behavior that make them suitable for this application. In this study, we move beyond single electrodes, half-cell studies and demonstrate three types of hybrid cells using Nb2CTx-carbon nanotube (CNT) films. It is shown that lithiated graphite/Nb2CTx-CNT, Nb2CTx-CNT/LiFePO4 and lithiated Nb2CTx-CNT/Nb2CTx-CNT cells are all able to operate within 3 V voltage windows and deliver capacities of 43, 24 and 36 mAh/g (per total weight of two electrodes), respectively. Moreover, the polarity of the electrodes can be reversed in the symmetric Nb2CTx-CNT cells from providing a positive potential between 0 and 3 V to a negative one from -3 to 0 V. It is shown that the volumetric energy density (50-70 Wh/L) of our first-generation devices with MXene electrodes exceeds that of a lithium titanate/AC capacitor.