Air-gap effect and the importance of the electrodes on the sample in the lumped-capacitance method for dielectric measurements

1990 ◽  
Vol 25 (4) ◽  
pp. 638-641 ◽  
Author(s):  
A. Lian ◽  
W. Zhong
Keyword(s):  
Air Gap ◽  
Gap Effect ◽  
Dielectric Measurements ◽  
Capacitance Method

Enhancing benefits of bolus use through minimising the effect of air-gaps on dose distribution in photon beam radiotherapy

2020 ◽  
pp. 1-7
Author(s):  
Karim Bahhous ◽  
Mustapha Zerfaoui ◽  
Abdelaali Rahmouni ◽  
Naima El Khayati
Keyword(s):  
Dose Distribution ◽  
High Energy ◽  
Air Gap ◽  
Photon Beam ◽  
Gap Effect ◽  
Field Size ◽  
Patient Treatment ◽  
Source Surface ◽  
Air Gaps ◽  
Good Treatment Outcome

Abstract Introduction: Bolus material is frequently used on patient’s skin during radiation therapy to reduce or remove build-up effect for high-energy beams. However, the air-gaps formed between the bolus and the skin’s irregular surface reduce the accuracy of treatment planning. To achieve a good treatment outcome using bolus, experimental investigations are required to choose its thickness and to quantify the air-gap effect. Material and methods: Measurements for a 6 MV photon beam with a fixed source surface distance were carried out using the 31021 Semiflex 3D chamber into the water phantom. Firstly, the depth of maximum dose (R100) and the dose value at surface (Ds) were evaluated as a function of bolus thickness for some square fields. Secondly, to test the effect of the air-gaps ranged from 5 to 30 mm with a step of 5 mm between the bolus and the phantom surface, a water-equivalent RW3 (Goettingen White Water) slab form of 10 mm thickness was considered as a bolus. Results: We observed that the linear behaviour of R100 in terms of the bolus thickness makes the choice of this parameter more convenient depending on field size. In addition, increasing the air-gaps widens the penumbra and created electrons that have a greater probability to quit the radiation field borders before reaching the surface. The dose spread of the off-field area could have a significant influence on the patient treatment. Conclusion: Based on dose distribution comparisons between the measurements with and without air-gaps for the field size of 100 mm × 100 mm, it has been demonstrated that a maximum air-gap value lower than 5 mm would be desirable for an efficient use of the bolus technique.

scholarly journals Error Analysis of Clay-Rock Water Content Estimation with Broadband High-Frequency Electromagnetic Sensors—Air Gap Effect

Sensors ◽  
2016 ◽  
Vol 16 (4) ◽  
pp. 554 ◽  
Author(s):  
Thierry Bore ◽  
Norman Wagner ◽  
Sylvie Delepine Lesoille ◽  
Frederic Taillade ◽  
Gonzague Six ◽  
...  
Keyword(s):  
Error Analysis ◽  
Water Content ◽  
High Frequency ◽  
Air Gap ◽  
Gap Effect ◽  
Clay Rock ◽  
Electromagnetic Sensors

scholarly journals Short columns composed of concrete-filled steel tubes in a fire situation – Numerical model and the “air-gap” effect

2022 ◽  
Vol 15 (3) ◽  
Author(s):  
Fábio Masini Rodrigues ◽  
Armando Lopes Moreno Júnior ◽  
Jorge Munaiar Neto
Keyword(s):  
Numerical Model ◽  
Steel Tube ◽  
Air Gap ◽  
Gap Effect ◽  
Joint Analysis ◽  
Steel Tubes ◽  
Short Columns ◽  
Study Results ◽  
In Fire ◽  
Concrete Filled Steel Tubes

Abstract The increase in temperature reduces the strength of steel and concrete, in such a way that it is essential to verify concrete-filled steel tube columns in fire situations. Numerical simulations, with lower costs than laboratory tests, have great importance in checking resistance and defining simplified methods for design practice. However, peculiarities of the thermal and mechanical behavior of heated confined concrete and the air-gap effect (a phenomenon inherent to concrete-filled steel columns) must still be better understood. Therefore, this study presents the development of a numerical model performed in the ABAQUS software (Dassault Systemes SIMULIA Corp., 2014) for the thermomechanical analysis of short columns composed of circular and square concrete-filled steel tubes considering the air-gap effect. The air-gap phenomenon is presented and analyzed according to possibilities of implementation to the numerical model and, finally, the proposed numerical model is validated with experimental results presented in the literature. According to the study results, the numerical model can be used to define and adjust simplified methods for verification of composite columns in fire situation. The importance of considering the air-gap effect in numerical modeling was confirmed, taking into account that disregarding its effect may result in overestimated responses of the steel tube resistance in fire situations. Moreover, it was suggested thermomechanical joint analysis and the use of the explicit solver as a strategy to minimize processing time.

Air-Gap Effect on Single Axis Vibration of Electromagnetic Braking Using Eddy Current on Bearing Cage

2014 ◽  
Vol 663 ◽  
pp. 400-405
Author(s):  
Mohamad Zairi Baharom ◽  
Mohd Zaki Nuawi ◽  
Mohammad Syuhaimi Ab-Rahman ◽  
Gigih Priyandoko ◽  
Che Ku Eddy Nizwan ◽  
...  
Keyword(s):  
Eddy Current ◽  
Repulsive Force ◽  
Air Gap ◽  
Gap Effect ◽  
Brake Disc ◽  
Current Experiment ◽  
Test Rig ◽  
Braking System ◽  
Braking Torque ◽  
Structure Test

An electromagnetic braking system using eddy current experiment was conducted to study the behaviour of the system in terms of vibration. Brake disc used which is Al6061 has a displacement in z-axis direction which occurred because of the repulsive force generated on both sides of the disc as drag force from electromagnetic braking. This study aims to analyze the vibration behaviour when braking occurred in different initial speeds of DC motor and different air-gap cases. Smaller air-gap will produce high braking torque due to the increasing of magnetic field density. The higher the force generated, the vibration of the disc may illustrates different behaviour of the vibration in the structure. Test rig was developed using sensor of accelerometer and data acquisition of NI-DAQ with the use of Dasylab for the measurement and instrumentation purposes. Findings shows that the electromagnetic braking force generated in smaller air-gap between electromagnetic poles and rotating conductive disc during the braking using eddy current has damped the vibration occur in the structure of bearing cage.

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