Deepak Kumar Ghodgaonkar

Bio: Deepak Kumar Ghodgaonkar is an academic researcher from Universiti Teknologi MARA. The author has contributed to research in topics: Microwave & Dielectric. The author has an hindex of 3, co-authored 7 publications receiving 25 citations.

A free-space method for measurement of complex permittivity of silicon wafers at microwave frequencies

Abstract: A non-destructive, non-contact technique has been developed to characterize p-type and n-type silicon semiconductor wafers at microwave frequencies. The measurement system consists of a pair of spot-focusing horn lens antennas, mode transitions, coaxial cables and a vector network analyser (VNA). In this paper, the free-space reflection and transmission coefficients, S/sub 11/ and S/sub 21/, for a normally incident plane wave, are measured for a silicon wafer sandwiched between two teflon plates which are quarter-wavelength at midband. The actual reflection and transmission coefficient, S/sub 11/ and S/sub 21/, of the silicon wafers are calculated from the measured S/sub 11/ and S/sub 21/ of the teflon plate-silicon wafer-teflon plate assembly in which the complex permittivity and thickness of the teflon plates are known. From the complex permittivity, the resistivity and conductivity can be obtained. Results are reported in the frequency range of 11-12.5 GHz. The values of the dielectric constant obtained were close to published values for silicon wafers.

Comparison of Reflection and Transmission Method and Metal Back Method Measurement of Dielectric properties of transformer oil using free space microwave measurement system in 8 - 12 GHz frequency range

Abstract: Nondestructive, non-contact and real time evaluation of dielectric properties of low-loss liquids is important for applications such as service-aged transformer oil, biomedical, remote sensing and design of radar absorbing material. Free-space methods (which are nondestructive and non-contact) were developed a measurement of dielectric properties of transformer oil at microwave frequencies. Transmission and Reflection method and Metal Back Method are developed for measurements using free space microwave measurement system (FSMM). FSMM system consists of spot focusing horn lens antennas, mode transitions, coaxial cables and vector network analyzer (VNA). Dielectric constants and loss factors were measured for new transformer oil. It is observed that metal-back method is suitable for dielectric measurement of transformer oil compared to Transmission and Reflection method.

Microwave nondestructive testing of coatings and paints using free-space microwave measurement system

Abstract: Microwave nondestructive testing (MNDT) techniques are applied to evaluate quality of anti-corrosive protective coatings and paints on metal surfaces. A free-space microwave measurement (FSMM) system is used for MNDT of protective coatings. The FSMM system consists of transmit and receive spot-focusing horn lens antennas, a vector network analyzer, mode transitions and a computer. Diffraction effects at the edges of the sample are minimized by using spot-focusing horn lens antennas. Errors due to multiple reflections between antennas are corrected by using free-space LRL (line, reflect, line) calibration technique. We have measured complex reflection coefficient of polyurethane based paint which is coated on brass plates.

A free-space measurement of complex permittivity of doped silicon wafers using transmission coefficient at microwave frequencies

Abstract: A contactless and non-destructive method is presented to characterize p-type and n-type silicon semiconductor wafers using a spot-focused free-space measurement system. In this method, the free-space reflection and transmission coefficients, S 11 and S 21 , are measured for silicon wafer sandwiched between two teflon plates which are quarter-wavelength at mid-band. The actual reflection and transmission coefficient, S 11 and S 21 of the silicon wafers are then calculated from the measured S 11 and S 21 by using ABCD matrix transformation in which the complex permittivity and thickness of the teflon plates are known. Complex permittivity are computed using only the transmission coefficient, S 21 . From the complex permittivity, the resistivity and conductivity can be obtained. Results are reported in the frequency range of 9–12.5 GHz. The dielectric constant obtained were close to published values for silicon wafers and the resistivities agree well with that measured by other conventional method.

Microwave non-destructive testing of coatings and paints using free space microwave measurement / Norhayati Hamzah ... [et al.]

Abstract: Microwave nondestructive testing (MNDT) techniques are applied to evaluate quality of anti-corrosive protective coatings and paints on metal surfaces. A tree-space microwave measurement (FSMM) system is used for MNDT of protective coatings. The FSMM system consists of transmit and receive spotfocusing horn lens antennas, a vector network analyzer, mode transitions and a computer. Diffraction effects at the edges of the sample are minimized by using spot-focusing horn lens antennas. Errors due to multiple reflections between antennas are corrected by using free-space LRL (line, reflect, line) calibration technique. We have measured complex reflection coefficient of polyurethane based paint which is coated on brass plates.

Liquid-based dielectric resonator antenna and its application for measuring liquid real permittivities

Abstract: In this study, a water-based rectangular dielectric resonator antenna is designed and analysed. The compactness of the antenna because of the high relative permittivity of water is demonstrated in both simulation and experiment. In addition, a dielectric resonator antenna-based technique is proposed for measuring liquid permittivities. The resonance frequencies of the antennas with fixed configurations are obtained from finite-element electromagnetic (EM) simulation for liquids with different permittivity values. An analytical model of liquid permittivity as a function of the antenna resonance frequency is then developed. Based on this predictive model, the measurement of the liquid real relative permittivity can be easily achieved by measuring the antenna resonance frequency. The measured permittivity values of distilled water and 10% glucose solution are in agreement with previous data in the literature, demonstrating the effectiveness of the proposed liquid permittivity measurement technique.

Microwave Nondestructive Testing for Defect Detection in Composites Based on K-Means Clustering Algorithm

Abstract: Composite such as Glass Fibre Reinforced Polymer (GFRP) is increasingly used as insulation in many industrial applications such as the steel pipelines in the oil and gas industry. Due to ageing and cyclic operation, many hidden defects exist under insulation, such as corrosion and delamination. If these defects are not promptly detected and restored, the growth of defects causes a catastrophic loss. Therefore, an effective inspection technique using non-destructive testing (NDT) to detect the underneath defect is required. The ability of microwave signals to penetrate and interact with the inner structure within composites makes them a promising candidate for composite inspection. In the case of GFRP, the random patterns cause permittivity variations that influence the propagation of the microwave signals, which results in a blurred spatial image making the assessment of the material’s state difficult. In this research, a novel microwave NDT technique is presented based on k-means unsupervised machine learning for defect detection in composites. At present, the defect evaluation using an unsupervised machine learning-based microwave NDT technique is not reported elsewhere. The unsupervised machine learning is employed to enhance the imaging efficiency and defect detection in GFRP. The technique is based on scanning the composite material with an open-ended rectangular waveguide operating from 18 to 26.5 GHz with 101 frequency points. The influence of the permittivity variations on the reflected coefficients due to the random patterns of GFRP is mitigated by measuring the mean of a set of the adjacent points at each operating frequency point using a small rectangular window. The measured data is converted to the time domain using a fast inverse Fourier transform (IFFT) to provide significant features and increase the signal resolution to 201-time steps. K-means algorithm is utilized to cluster the given features into the defect and defect-free regions in GFRP. The findings presented in this paper demonstrate the benefits of an unsupervised machine learning to detect a defect down to 1 mm, which is a considerable contribution over any existing defect inspection technique in composites.

Calibrated Layer-Stripping Technique for Level and Permittivity Measurement With UWB Radar in Metallic Tanks

Abstract: A method to measure liquid level and electrical properties based on ultra-wideband pulsed radar is developed in this paper. Current methods of material property measurement using free-space radar typically use computationally intensive frequency-domain analysis or finite time-domain methods. The method presented is modified from layer-stripping algorithms and includes several improvements over previous techniques, such as an antenna array that allows measurement in a metallic tank environment and a method of calibration that characterizes path-loss and near-field effects for accurate amplitude-distance prediction. The method presented here also estimates the material loss properties and uses accumulated power with noise compensation to predict reflected pulse power. The method extends the use of pulsed radar for liquid-level measurement in tanks to the evaluation of liquid permittivity and the estimation of liquid height in liquids consisting of multiple layers. The accuracy of the presented method is evaluated using a transmitting single antenna element, a four-element antenna array, and an eight-element antenna array for measurement in a metallic tank environment. Accuracy is improved with larger antenna arrays, but the calibration becomes more critical. The accuracy for varying layer heights and materials is investigated to demonstrate the method reliability.

Improving microwave absorption efficiency of asphalt mixture by enriching Fe3O4 on the surface of steel slag particles

Abstract: In order to improve microwave absorption which would be used for in situ repair of asphalt pavement, Fe3O4 was enriched on the surface of steel slag particles through an activated carbon-reduction method. The surface modified steel slags were then added into asphalt mixture to replace fine aggregates. The results showed that the microwave heating rate of modified steel slag was 84.3 °C/min. That was 34.1 and 65.1% higher than that of the control group of unmodified steel slag and fine basalt aggregate, respectively. Within the microwave frequency band of 2–4 GHz, the real part and imaginary part of the complex permittivity of the modified steel slag asphalt mixture (MSAM) increased by 6.4–12.5 and 4.7–13.7%, respectively, comparing those of the ordinary steel slag asphalt mixture (OSAM) and the ordinary basalt asphalt mixture (OBAM). Meanwhile, the real part and imaginary part of the complex permeability of the MSAM increased by 9.8–31.9% and over 6.2 times, respectively. Besides, the microwave heating rate of the MSAM increased by 44.2 and 82.1%, respectively, comparing those of the OSAM and the OBAM. Simulation indicated that after microwave heating for 15 min, the temperature within the OBAM ranged from 62.23 to 125.48 °C. Moreover, the temperature field distribution of numerical simulation was similar to that of the test results. Since microwave absorption was sharply enhanced in the asphalt pavement, it is expected to promote the microwave heating technology in the asphalt pavement.

Comparison of Metal-Backed Free-Space and Open-Ended Coaxial Probe Techniques for the Dielectric Characterization of Aeronautical Composites.

Abstract: The trend in the last few decades is that current unmanned aerial vehicles are completely made of composite materials rather than metallic, such as carbon-fiber or fiberglass composites. From the electromagnetic point of view, this fact forces engineers and scientists to assess how these materials may affect their radar response or their electronics in terms of electromagnetic compatibility. In order to evaluate this, electromagnetic characterization of different composite materials has become a need. Several techniques exist to perform this characterization, all of them based on the utilization of different sensors for measuring different parameters. In this paper, an implementation of the metal-backed free-space technique, based on the employment of antenna probes, is utilized for the characterization of composite materials that belong to an actual drone. Their extracted properties are compared with those given by a commercial solution, an open-ended coaxial probe (OECP). The discrepancies found between both techniques along with a further evaluation of the methodologies, including measurements with a split-cavity resonator, conclude that the implemented free-space technique provides more reliable results for this kind of composites than the OECP technique.