Shiban Koul

Bio: Shiban Koul is an academic researcher from Indian Institute of Technology Delhi. The author has contributed to research in topics: Thermography & Microwave. The author has an hindex of 4, co-authored 6 publications receiving 24 citations.

Infrared thermography for electromagnetic field pattern recognition

Abstract: The visualization of electromagnetic field intensity can be easily achieved by infrared thermography using an absorption screen of carbon loaded polymers. The electromagnetic waves falling on the absorption screen increase its temperature which is monitored by an infrared camera. The measured temperature profile can further be correlated to the electric field intensity. Measurement of electromagnetic field distribution is typically done by a small scanning antenna and is a time consuming process. Furthermore the scanning antenna will itself disturb the measurement process which is not the case with an absorption screen, even if the screen is kept very near to the electromagnetic wave source. Therefore fields very near to the source can also be visualized and measured. Also the length of the scanning antenna depends on wavelength of electromagnetic field to be measured, therefore it is improper to apply it to measure various fields. In order to show the utility of the above technique, an example of a patch antenna operating at a frequency of 2.45 GHz is given. Initial experiments show good agreement between simulated and measured results.

Infrared thermography for determination of wavelength of microwave signals from interference pattern

Abstract: A technique for wavelength measurement of microwaves is demonstrated. The wavelength is obtained from an interference pattern monitored by an IR Camera. The data captured by the camera is stored in a computer attached to it. This data is then processed for wavelength calculation. In order to show the utility of the above technique, two cases are demonstrated: Case (1) Interference pattern of two patch antennas each radiating at 8 GHz. Case (2) Interference pattern from a single antenna, radiating at 12 Ghz, kept in front of a metallic sheet with two slits. The simulation is carried in CST Microwave Studio software. A good agreement between simulation and experimental results is seen.

Determination of Polarisation of Microwave Signals by Lock-in Infrared Thermography

Abstract: Detection of polarisation of microwave signals using infrared thermography is described in this paper. A metal grating consisting of parallel, equally spaced metallic strips is placed in between a microwave source (antenna) and a microwave absorption screen for permitting the determination of direction of electric field vector (polarisation). Very low frequency modulation of the microwave source is added to permit lock-in thermography which enhances thermal resolution.In case of linear polarisation when the metallic strips of the grating are parallel to the direction of electric field vector, the temperature rise on the screen as observed by an infrared camera, is minimum. On the other hand if the metallic strips are perpendicular to the electric field vector the temperature rise observed on the screen is maximum. The orientation of the grid is changed by rotating the grid about a central axis perpendicular to its plane. With each different orientation of the grid a change in temperature rise is o...

Dual- and Triple-Band Polarization Insensitive Ultrathin Conformal Metamaterial Absorbers With Wide Angular Stability

Abstract: This paper describes a dual-band electromagnetic (EM) absorber for Cand X-band applications. The proposed structure consists of two circular ring resonators that are modified to make the absorber compact. The proposed absorber is demonstrated to be conformal, insensitive to polarization and angle of oblique incidence of incoming EM wave. To the authors' knowledge, it is the thinnest absorber reported with a thickness of λ0 /142.65 at lowest frequency of absorption. The absorption bands with absorption peaks of about 97% and 99% are observed at center frequencies of 4.19 and 9.75 GHz, respectively. The absorption frequency bandwidth (more than 90% of peak absorption) at these frequencies is 665 and 860 MHz, respectively. The double-band absorber can be extended to work at three frequencies by simply adding another ring between the two modified circular rings of dual-band absorber. The modified structure has absorption bandwidth of 610, 670, and 570 MHz with absorption peaks of 97.50%, 96.50%, and 98.85% at resonant center frequencies 4.19, 6.64, and 9.95 GHz, respectively. The temperature profile of the proposed absorber is measured by using lock-in infrared thermography and a temperature increase of 1.5°C is observed at all the absorbing frequencies with transmitted RF power of 10 dBm. The experimental results agree well with the simulation results, and the proposed structure is insensitive for the transverse magnetic/transverse electric field polarization of incident waves and also the angle of incidence. It provides wide angular stability up to 45°. Along with a flat surface, the proposed absorbers are tested on a curved surface to exhibit its conformal nature.

Modeling and Performance Improvement of Fractional-Order Band-Pass Filter Using Fractional Elements

Abstract: Fractional-order circuits are the emerging area for analyzing the parametric response of the filters and its performance improvement can be analytically observed by using an optimization technique....

A Triple Band Polarization Insensitive Ultrathin Metamaterial Absorber for S- C- and X-Bands

Abstract: In this paper, design of a triple band ultrathin compact polarization insensitive metamaterial absorber for S-, Cand X-band applications is proposed. The proposed absorber consists of periodic arrangement of a modified triple circular slot ring resonator as unit cell printed on the top of a continuous metal backed FR-4 dielectric substrate. The proposed absorber is ultrathin having thickness of λ0/135.66 at the lowest absorption center frequency. The measured wide stable absorption bands of 0.40 GHz, 0.45 GHz and 0.47 GHz with absorption peaks of 97%, 96.45% and 98.20% at absorption center frequencies of 2.90 GHz, 4.18 GHz and 9.25 GHz respectively are observed. The temperature profile of absorber is measured by using lock in infrared thermography, and a temperature increase of 1◦C at absorbing frequency as compared to non-absorbing frequency is observed. The absorber is demonstrated to be polarization insensitive to TE and TM polarized angles of incidence of electromagnetic wave with wide angular stability up to 45◦. The absorber is fabricated and tested in an anechoic chamber. Experimental results agree well with measured ones.

Detection and characterization of defects in composite materials using thermography

Abstract: Composite materials are widely used in the transport industry, particularly aeronautics, due to their light weight and enhanced mechanical properties. On the downside, these new materials are less known and their behaviour are unpredictable greatly because of their anisotropic properties, being difficult to simulate and understand their behaviour. To overcome these aspects regular preventive maintenance operations are necessary. In order to avoid major problems, Non-Destructive Testing (NDT) are a solution to assure the safety without destroying the components. From the vast possibilities available, field image NDT have proved to be fast, precise and easy to interpret. Image technologies usually capture and measure some type of electromagnetic radiation to identify a discontinuity in the radiation pattern that changes due to a component abnormality. Since the natural radiation emitted by objects at the ambient temperature is in the infrared waveband, this is used to create a temperature image, particularly in the middle and far-infrared wavebands. Better results can be obtained when is used a stimulation source to induce a temperature variation, highlighting any defect that a component may have. Two different types of tests can be done with: single or periodic stimulation. When using single stimulation (transient tests), a pulse of energy is applied to the object and observed its recovery to the previous equilibrium state. On the other hand, when performing periodic tests (lock-in), the stimulation is modulated in several cycles, with the amplitude response and phase delay being analysed. This work aimed to develop a numeric model able to predict the result of an infrared thermal test in carbon fiber reinforced polymers with structural defects. This work is divided in three main parts: field tests, numeric simulation and model validation. Several different field tests were performed with various test samples to identify the settings that produced the best results and give the highest sensitivity to defects detection. These tests were performed using the above refereed techniques, transient and lock-in. During the lock-in tests, it was identified an imperfection in the modulated sinusoidal stimulation, which was quantified and corrected improving the overall results. The samples used in the laboratory testes where simulated using the finite element technique in Matlab R ©. This manner it was obtained an internal view of the heat flow inside the component and provided the temperature evolution at the surface of the specimen during an entire test. With the results obtained from the simulations, it is possible to estimate the thermal response obtained with a certain type of test and waveform. Finally, the model was validated with experimental tests, consisting of samples made of carbon fiber reinforced polymers poly-methyl-meth-acrylate. At the end of this document it is presented a short comparison between the two thermal techniques and shearography.