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1

Performance Capabilities and Detection Efficiency of Vehicle Backup Proximity Sensors for Narrow Objects

Edirisinghe M., Dilhani Y.H.N., Kangara K.M.J.C.B.

International Letters of Chemistry, Physics and Astronomy

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2015

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Vol. 52

134--146

EN

This paper investigates performance capabilities and potential safety effectiveness of ultrasonic backup proximity sensors with special attention on cylindrical and cubical shaped narrow obstacles with the dimensions varies from 2.6 cm to 11.0 cm. The experiment was performed using a commercially available parking aid system consisting of two ultrasonic sensors, and a rear bumper model constructed in a laboratory environment together with a test surface divided into grids having cells of 6 cm x 6 cm. It can be observed that there are considerable differences in detection zone patterns when comparing observations for cylinders and cubes even for same dimensions. Using detection zone maps, it can be seen that, when the size of the test objects become smaller, there are large blind spot areas in the space between the sensors and also near the right and left edges of the rear bumper. In average, when reducing the obstacle dimensions from 11.0 cm to 2.6 cm, the detection efficiency changes from 62.6% to 33.1% for cylindrical objects and for cubical shaped objects it was 39.3% to 21.6%. Average detection efficiency is lower than 50% for objects less than 5 cm in dimension irrespective of the object geometry.

2

Design Methods of Lightning Protection Systems by Keeping Aesthetic View of Architecturally Complex Structures

Edirisinghe M., Rupasinghe D., Jinadasa C. P.

International Letters of Chemistry, Physics and Astronomy

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2015

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Vol. 52

126--133

EN

The primary focus of this study is to understand design methods of appropriate lightning protection systems (LPS) for architecturally complex structures without any harmful affect to its aesthetic view. Two sites selected for this study consisting of architecturally complex structures named ‘Kuruluduwa Suspension Foot Bridge’ located in Matara, Sri Lanka (6.05No/80.20Eo) and ‘National Planetarium Building’ located in Colombo, Sri Lanka (6.95No/79.85Eo). Average lightning flash density for these two locations were 2.5 flyr-1km-2 and 2.3 flyr-1km-2 respectively. Different design methods were used to identify the most suitable LPS, based on the area of protection afforded by each one. After analyzing those two sites, it was able to introduce proper LPS for both sites by keeping architectural design as it is with no change for its aesthetic view. This study shows possibility of achieving this challenging task even for already constructed structures with present LPS standards successfully. When designing the architectural part of the structure, the architect should concern both on the visual appearance and the LPS. Creating a miniature model of the structure would be another suggestion which could be used to find the actual visual impact of the design and as well as to validate the protection system.

3

Arrhenius Accelerated Life Test for Luminary Life of High Bright Light Emitting Diodes

Edirisinghe M., Rathnayake P.

International Letters of Chemistry, Physics and Astronomy

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2015

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Vol. 49

48--59

EN

The High Bright Light Emitting Diodes (HBLEDs) generally having long life but very often its actual life is different from vendor’s specification. Vendors do not specify the failure criteria for their products but it may vary from 50% to 70% light output maintenance. Further time to test such a quantity takes too long under normal conditions. Longer time consumption for evaluation of such a quantity may not useful in mass production process of HBLEDs. The present study describes the determination of the useful lifetime of 1-W HBLEDs using Arrhenius Accelerated Life Test Model with the modeling parameter as the junction temperature. Failure criterion was chosen as 70% light output maintenance while two stress levels were selected as 90 °C and 110 °C and as recommended by IES LM-80-08 standard. Furthermore, forward voltage of the HBLED was used to determine junction temperature of the diode which is a critical parameter for this study. Moreover, junction temperature of the HBLED recognized as the most critical factor for degrades the lifespan. The Arrhenius Model is based on the junction temperature and activation energy parameters. The activation energy and the scaling factor were found to be 1.31 eV and 6.86×10-17 hours respectively. HBLED junction temperature under room temperature (23 °C) was found to be 55.72 °C. Finally the 70% luminary life time of 1-W HBLEDs under these conditions was found to be 8,344 hours.

4

Nonlinear Load and RLC Pulse Shaping Surge Generator Models in Simulation Environment

Edirisinghe M.

International Letters of Chemistry, Physics and Astronomy

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2014

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Vol. 17, iss. 3

334--347

EN

The present study was performed in order to understand how a nonlinear load affects the characteristics of the RLC pulse shaping surge generator waveforms under simulation studies. The obtained results were compared when analytical equations were used as source models for both 1.2/50 s voltage & 8/20 s current impulses. Three circuit models; Capacitor Bank generator, Combination waveform generator and Schaffner generator were evaluated under nonlinear loads varied from 10Ω to 106 Ω for voltage impulses and for current impulses it was from 10-4 Ω to 1 Ω. As it can perceive from the analysis, delay time, rise time and FWHM remain unchanged throughout the tested impedance range when used model equations as generator sources. It was found that for voltage impulses, these values were 4.95 μs, 1.20 μs and 81.8 μs respectively. For current impulses, these values were 16.2 μs, 8.02 μs and 20.7 μs respectively. However results obtained for generator circuit models shows that delay time, rise time and FWHM deviated from above values up to maximum of 35.15 %, 106.67 % & 115.16 % respectively for voltage impulses. For current impulses these deviations were up to maximum of 79.63 %, 48.75 % & 39.61 % respectively. The deviations were due to influence caused by the nonlinear load to the generator circuit parameters and effective internal impedance.

5

Fine Structure Signatures in Ground Flashes as a Source for HF Radiation

Edirisinghe M., Cooray V.

International Letters of Chemistry, Physics and Astronomy

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2014

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Vol. 1

91-104

EN

Lighting radiation fields below 10 MHz are of considerable interest since these frequencies correspond to the natural resonance of structures with dimensions of a few meters to tens of meters. In this paper we present the fine structure signatures of sub-microsecond range pulses appeared at the leader phase and after the return stroke in negative ground flashes which act as a source for HF radiations at 10 MHz, 5 MHz and 3 MHz observed in Sri Lanka, in the tropics. Of the total sub-microsecond range pulses analyzed, 298 were due to positive field changes and 228 were due to negative field changes. The average rise time of those pulses for both polarities is 127 ns and it was found to be varying from 110-160 ns. The peak amplitude is in the range of 0.65-2.19 V/m. For the total 526 pulses analyzed for this study, the FWHM was between 190-310 ns with an arithmetic mean of 238 ns. Signatures of these pulses are similar to the leader like electric field pulses which acted as a strong source for HF radiations at 10 MHz, 5 MHz and 3 MHz. The initiation process of pulses reported in this study could be similar to the initiation process of leader like pulses.

6

Performance comparison of varistor models under high current derivative impulses

Edirisinghe M., Montańo R., Cooray V., Roman F.

International Letters of Chemistry, Physics and Astronomy

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2013

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Vol. 6

40-53

EN

Surge protective devices (SPD) testing procedures are mainly performed with standard current pulse types. However, none of these standard current waveforms reproduce the very fast rise time and the large peak current derivatives observed in subsequent return strokes. In the literature there are several mathematical models to represent metal oxide varistor that have been developed based on standard impulse conditions. These models are being used routinely in the analysis of the various electronic circuits under transient conditions. In this paper, a study was conducted to have a performance comparison between the two varistor models, simplified varistor model and Durbak's model, available in the literature under high current derivative impulses. The experiments and simulations were performed on disk type varistors with different diameter sizes, i.e., 20mm, 10mm, and 05mm with nominal operating voltage of 230 V. The Roman Generator developed at Uppsala University was used as the high current derivative impulse generator which can produce a peak current up to 1500 A with 10 ns rise time and its rate-of-rise is in the order of 1011 A/s. The results showed that for standard 8/20 ěs lightning impulses, simulation results of these models had a good agreement with the experimental data. However, these two models need to be improving in order to improve their performance under high current derivative impulses into the sub-microsecond range.