D.M.G. Preethichandra

A simple interface circuit to measure very small capacitance changes in capacitive sensors

This paper presents an easy-to-design interface circuit to measure very small-percentage capacitance variations in capacitive sensors, especially suitable for industrial measurements. A computer-controlled 24-bit A/D converter is employed to obtain a higher resolution. This interface circuit can be used with various types of capacitive sensors. The most interesting thing is, that the measurement results through this interface circuit are independent of the initial capacitance of the sensor. In addition, the double differential operating principle used here minimizes the error caused by coupling and stray capacitance of sensor probes. The operating principle of the designed interface circuit, the major assumptions made, test data, and possible future developments are discussed.

An Amperometric Glucose Biosensor With Enhanced Measurement Stability and Sensitivity Using an Artificially Porous Conducting Polymer

A conducting polymer [polypyrrole (PPy)]-based amperometric biosensor fabricated on a platinum-coated nanoporous alumina electrode has been described. This fabricating process introduced artificial porosity into the PPy film, and the template pore sizes were carefully chosen to match the size of the glucose oxidase (GOx) molecule. The PF6 --doped PPy film was synthesized with 0.05 M pyrrole and 0.1 M NaPF6 at a current density of 0.3 mA/cm2 for 90 s. Immobilization was done by physically adsorbing 5 muL of GOx on the nanoporous PPy film. Glutaraldehyde (0.1 wt.%, 5 muL) was used for cross-linking. The synthesized films were characterized by using an electrochemical technique and scanning electron microscopy (SEM). Amperometric responses were measured as a function of different concentrations of glucose at 0.4 V. Nanoporous electrodes lead to high enzyme loading, whereas the use of a cross-linking agent increased stability, sensitivity, reproducibility, repeatability, and shelf life.

Charge injection mechanism across the Au-poly(3-hexylthiophene-2,5-diyl) interface

The nature of charge injection has been investigated across the Au-poly(3-hexylthiophene-2,5-diyl) (P3HT) interface of two kinds: P3HT on Au (bottom contact) and Au on P3HT (top contact). The J-V characteristics of a Au(bottom)/P3HT/Au(top) sandwich cell are analyzed by using the Fowler–Nordheim model and the hole barrier height at the top and bottom contacts has been estimated. The top contact showed a higher barrier height in comparison to the bottom contact. The quenching of photoluminescence spectra and the disappearance of characteristic P3HT peaks from the absorption spectra for the top contact supports that the ionically sputtered gold atoms on the polymer give rise to greater density of interfacial trap sites than those at bottom interface.

Design of a smart indoor air quality monitoring wireless sensor network for assisted living

Wireless indoor air quality monitoring is the main objective of this research in order to provide real time information for assisted living. The indoor air quality measured in the built environment provides a continuous stream of information for seamless controlling of building automation systems, and provides a platform for informed decision making. Further, this low power sensor network design provides vital air quality information under emergency and hazardous conditions even without grid power for a reasonable time. The proposed system has carbon dioxide, carbon monoxide, propane and methane sensors. This prototype network was first built using a hardware platform available in the market with industrial grade gas sensors. The concept was verified with actual parameter measurements under different real life situations. The results reveal that the domestic indoor air quality may be extremely different compared to what is expected for a quality living environment.

SAW Sensor Network Fabricated on a Polyvinylidine Difluoride (PVDF) Substrate for Dynamic Surface Profile Sensing

A combination of two 2-D sensor networks is proposed as a dynamic surface profile sensor network for biomimicing applications. A surface acoustic wave device fabricated on a polyvinylidine difluoride substrate has been investigated as the elementary 1-D bending curvature sensor used in the network. The device was tested under an injected signal and it shows the variation in amplitude and phase angle of output signal with respect to the injected signal in response to the bending curvature. These dual outputs provide opportunity to make an intelligent sensor with self error limit determination capability. Finally, a network of such sensors is proposed as a dynamic surface profile sensor

Effect of Glucose Oxidase Immobilizing Techniques on Performances of Nano Scale Polypyrrole Glucose Biosensors

Characteristic dependency of nano scale polypyrrole (PPy) glucose biosensors, achieved by three different immobilizing techniques namely, coentrapment, physical adsorption and a two step method of coentrapment superimposed with physical adsorption is reported. Different enzyme loading and material properties resulted in varied immobilizing methods lead to dissimilarities in characteristics. In this study, Pt coated AnodiscTMs (0.2 µm) were used as electrodes to polymerize PPy at 0.3 mA cm-2 using a solution containing 0.05 M Pyrrole and 0.1 M NaPF6. The polymerization time was optimized to 90 s. In the coentrapment method, glucose oxidase (GOx) (1 mg ml-1) was added to the monomer solution while an aliquot of GOx (5 µl) was placed on the pre-polymerized electrode for physical adsorption. A combined procedure of these two techniques was used as the last immobilization technique. Physical adsorption method gave a sensitivity of 3 mA cm-2 M-1 and a linear range of 0.5–13 mM with a response time of a 3 s. Sensitivity in the case of coentrapment was 3.75 mA cm-2 M-1 while it showed a value of 4.45 mA cm-2 M-1 in two step immobilization thus giving 25 and 48% increases respectively. Response times of 9 and 8 s in latter cases reveal the possible repercussion taking place at enzyme immobilization in three dimensional (3-D) PPy matrix and the delay occur in glucose to reach the enzyme. Linear range of the two step method was extended up to 16 mM due to the reinforced enzyme loading.

Actual condition monitoring of engine oil through an intelligent multi-functional sensing approach

A multifunctional sensor is designed to measure viscosity, cleanness, temperature and capacitance of engine oils to make a clear decision on its condition. The simple structure helps easy fabrication and low cost while measuring four parameters by one sensor. The operation is described theoretically and is supported by experimental data.

Nano-Biosensor Development for Biomedical and Environmental Measurements

Nano biosensor development for biomedical and environmental measurements has been tried by research groups all over the world. Identifying and fabricating suitable nano-materials as enzyme immobilizing matrices to enhance characteristics of the sensor is the most important and difficult task of it. In this chapter we discuss about polypyrrole(PPy) nano-tube array grown on Alumina AnodiscTM to serve this purpose successfully.

A Multi-Functional Sensor for Liquid Characterization and Identification

Liquid identification according to their physical properties is a well known technique and different types of stand alone sensors are used to measure each of these parameters. However, in this paper we propose a single multi-functional sensor for the measurement of four parameters namely, temperature, viscosity, clarity and permittivity of a liquid. The operation of the proposed sensor is theoretically described and its performances are experimentally tested. This multi-functional sensor can be used to identify an unknown liquid for its maximum likelihood into a characterized zone of liquids maintained in a previously built database.

Bending Curve Modeling of Ionic Polymer Metal Composites in Soft Actuator Applications

Ionic polymer metal composites (IPMC) may be used to replace the electro-mechanical actuators in a vast variety of application areas ranging from biomedical devices to soft actuators and sensor systems in modern humanoid robotics. The excellent characteristics shown by IPMCs are highly influenced by their interrelated mechanical, electrical and chemical properties. However, this makes it complicated and difficult to understand the physics and predict their behavior. In order to utilize the full potentials towards advanced engineering, there is an increasing need to investigate their actuation mechanism and derive means of predicting the behavior. The object of this paper is to characterize and model the bending motion of the strip-type IPMC actuators using the theory on large deflections of beams. After deriving a mathematical model approximately accounting for mechanical, electrical, and chemical properties and geometric parameters of the actuator, the model has been experimentally verified for an actuator with the dimensions 25 mmtimes2.6 mmtimes0.44 mm. Theoretical and experimental results are presented to demonstrate that the model is effective enough to predict the displacement output of the strip type-IPMC actuator all along the edge of the actuator as a function of the applied voltage.