Asok Nath Basu

Studies on the propagation of light from a light-emitting diode through a glass tube and development of an optosensor for the continuous detection of liquid level

The authors develop a new technique for continuous measurement of liquid level by an optosensor. The objectives are (i) to study the propagation of light from a light-emitting diode (LED) through a glass tube and (ii) based on this principle, to develop a continuous liquid level sensor. The attenuation of light from an LED through a glass tube with distance has been investigated and an empirical relation for it has been established. The result is applied to the detection of water level. The sensor comprises a hollow glass tube with a combined LED- photodetector assembly (the optosensor) and a light reflector inside the tube. The reflector floats on the liquid surface, and light emitted from the LED is detected after reflection from it. The detected light intensity varies with the distance between the optosensor and the reflector. The position of the float changes with the variation of the liquid level. The present level sensor can detect a change of liquid level at distances up to 80 cm with an accuracy of the order of 0.5 mm.

Unified study of the different physical properties of amorphous polymers

Uptil now it has not been possible to explain the different physical properties of amorphous polymers using a model based on a single conceptual scheme. In this paper, a phenomenological model is proposed which tries to explain the mechanical, optical and thermal properties (both thermal conductivity and expansivity) of amorphous polymers. The model has similarities with the composite model, proposed by the present authors, which has proved to be successful in interpreting the different physical properties of semicrystalline polymers. The present model considers the bulk form of the polymer as an aggregate of microscopic units possessing intrinsic physical properties. On drawing, the development of anisotropy in different physical properties is supposed to be due to the development of preferred orientation of these units. The development of the preferred orientation has been estimated directly from birefringence data. The agreement between the calculated and experimental values of the elastic modulus, thermal conductivity and thermal expansivity of PVC, PMMA and PS is found to be reasonable good.

Mechanical properties of oriented fibres of semicrystalline polymers based upon orientation function from optical properties

The computation of the orientational averages is a great problem in the case of semicrystalline polymers. In a previous communication [1] it has been shown that sinθ=f(λ) sinθ′ describes the orientational changes satisfactorily for a certain class of polymers. In this paper some alternative deformation schemes are also discussed. It has been concluded that birefringence provides a useful guideline in the choice of a deformation scheme.

Effect of Temperature on Electro-Optical Characteristics of Silicon Based p-n Photodiode (VTB8440BH)

To get useful information about the carrier transport mechanism we first measure the current-voltage (I-V) characteristics of a silicon p-n photodiode (VTB8440BH) in the temperature range 350 − 110 K. All semilog I-V curves exhibit three successive linearly dependent regions along with their bias levels which are defined as I, II and III regions, respectively. Regions I and II with different slopes are used to determine the bias dependent ideality factors namely, n1 and n2. The variation of n1 and n2 with temperature shows that with lowering of temperature the tunneling probability gradually increases. Furthermore, these results are used to identify the paramount carrier at different bias levels. Secondly, to acquire knowledge of electron-hole generation rate we measure the variation of photocurrent in the same temperature range. Results show that photocurrent decreases slowly as temperature decreases from 350 to 239 K and it changes sharply below 239 K. The change of photocurrent with temperature is explained in terms of temperature dependence of carrier mobility, lifetime and optical generation rate. Finally, these results will be helpful for precision application of the optoelectronics device in both high and low temperature ambience.