Smitha Puthucheri

An efficient use of waste material for development of cost-effective broadband radar wave absorber

Very few literatures are available on the utilization of natural waste composite materials for radar wave absorption. The main objective of this paper was to achieve good absorption with wide bandwidth corresponds to reflection loss (RL) ≤ −10 dB for less absorber layer thickness (≤2.0 mm) for a cost-effective production of radar wave absorber. In this study, mineral dust and beach sand-based waste composite material is critically analyzed for its application as broadband radar wave absorber in the frequency range of 8.2–12.4 GHz. A multilayer approach is applied for obtaining the good absorption, where thickness of different layers is optimized by genetic algorithm. The effective absorption bandwidth for two- and three-layer composite absorber is 3.5 and 2.8 GHz for the optimized thickness 1.9 and 1.8 mm, respectively. The two-layer absorber possesses measured RL of −27.20 dB at 10.8 GHz and for a three-layer absorber, RL reaches up to −32.58 dB at 11.2 GHz. The measured RL values agree quite well with the calculated ones, which show the effectiveness of absorber for various practical EM wave absorption applications.

Microwave absorption properties of FSS-impacted composites as a broadband microwave absorber

The development of a cost-effective microwave absorber with wide bandwidth corresponding to reflection loss (RL) ≤ −10 dB is still a very challenging task. A sugarcane bagasse-based agricultural waste composite has been analyzed for its elemental contents. The combination of elements is suitable for its possible usage as a cost-effective microwave absorbing material. Therefore, this composite has been subjected to morphological and electromagnetic studies to analyze its microwave absorbing behavior. The frequency dependent complex dielectric permittivity and complex magnetic permeability values were obtained using a transmission/reflection waveguide approach in the X-band. Furthermore, the effect of the Minkowski loop frequency selective surface (FSS) was studied over the absorption capability of the composite. It was found that the application of FSS leads to a reduction in thickness up to 2.9 mm and an enhancement in absorption bandwidth up to 3.6 GHz. The FSS patterned composite shows a remarkable performance with peak RL of −28.4 dB at 10.7 GHz and absorption bandwidth of 3.6 GHz.

Computation of effective dielectric constant and electric field in the human head: A preliminary study for electromagnetic wave effect

Every day human body getting exposed to electromagnetic (EM) radiation of various kinds and is becoming a serious health threat. Computation of adverse biological effects due to EM radiation in the multilayer human head model is a very challenging task because in multilayer model it is not easy to define exact width of the layer. Quantitative analysis of adverse biological effect is done by computing electric field (E-field), absorbed power density (APD), and specific absorption rate (SAR) in human head. Effective dielectric constant of multilayer model in a more accurate way is quite demanding because all the power absorption and heating effect depends upon the dielectric constant. Generally, researchers are using multilayer model to compute the E-field, APD, and SAR but it has lot of limitation and may not resemble the human head. Therefore, there is a need to develop such a model which resembles more to the actual human head. In this paper, a model is proposed which is having effective dielectric constant of human head to compute E-field, APD, and SAR. Simulation of equivalent human model and a multilayered sphere (Skin, Fat, Bone, Dura, CSF, and Brain tissue layers) of human head of radii 10.63 cm under a normally incident EM wave has been undertaken. A comparison has been drawn between both the models in terms of E-field, APD, and SAR under the condition of normal incidence EM wave. These results may be useful to know the effect of mobile phone radiation on human head.

Fractal frequency selective surface embedded broadband microwave absorber using disassembled waste printed circuit boards

The main aim of this study is to develop an cost effective microwave absorber that can provide wide absorption bandwidth (RL ≤ -10 dB) with less coating thickness (i.e., ≤ 2.0 mm). To achieve this, an electronic waste composite based microwave absorber blended with fractal frequency selective surface (FSS) is presented. The disassembled computer and mobile printed circuit boards (PCBs) based electronic waste composite is prepared by top-down nanofabrication approach. The measured complex dielectric permittivity and complex magnetic permeability values have been used for implementation of a double layer absorber in the range of 8.2 to 12.4 GHz. Further, a double layer absorber loaded with Minkowski fractal geometry based FSS is designed with the help of Ansoft HFSS. The developed absorber possesses a peak reflection loss (RL) value of -30.5 dB at 11.3 GHz for 1.9 mm absorber layer thickness. Such a performance permits the use of absorber for various practical electromagnetic applications in an efficient manner.

ANN-Based Two-Layer Absorber Design Using Fe–Al Hybrid Nano-Composites for Broad Bandwidth Microwave Absorption

In the current scenario, the foremost use of microwave absorbers, such as stealth applications and electromagnetic (EM) wave shielding, demands thin and broad bandwidth microwave absorber. In this paper, an attempt is made to fabricate a “cost-effective” composite material, which has good absorption properties, and furthermore, to reduce the coating thickness, the multi-layering approach has been adopted. Because of the excellent magneto-dielectric properties, Fe and Al metal powders were chosen. To see the effect of particle size over microwave absorption property of Fe-Al hybrid nano-composites, the composite was milled for 40 h with an interval of 5 h using the mechano-chemical route. The phase analysis, morphology, and magnetic studies have been carried out for prepared samples and correlated with EM wave properties. The permittivity and permeability values in the frequency range of 4-14 GHz were determined using coaxial reflection/transmission method, and reflection loss (RL) has also been computed. The broad bandwidth of 9.35 GHz (4.65-14 GHz) has been achieved for 40 h milled nano-composite (size ~40 nm) with a coating thickness of 3 mm. For the reduction in the coating thickness, the multi-layering approach has been applied, and an artificial neural network-based method has been proposed to predict each layer thickness and material sequence. The computed results of RL for two-layer absorber exhibit a reduction in the thickness from 3 to 1.96 mm.

Parametric analysis of frequency selective surfaces over radar absorbing nanocrystalline structures

A thin radar wave absorber with wide bandwidth corresponding to reflection loss (RL) ≤ -10.0 dB is still very challenging job for researchers till date. In this paper, design of Frequency Selective Surface (FSS) loaded over single layer absorber is carried out with the help of Ansoft HFSS simulation tool. Copper and cobalt doped barium hexaferrite nanoparticles are synthesized through sol-gel auto combustion route and correspondingly its phase and morphology analysis is carried out using X-ray diffraction (XRD) and Field emission scanning electron microscope (FESEM), respectively. The waveguide measurements are performed to measure the complex permittivity and permeability values in the frequency regime of 8.2 to 12.4 GHz. Further, critical analysis of different type of FSS structures has been carried out to study the absorption effect. It has been found that strongest RL value for Minkowski loop with level 2 approaches up to -41.0 dB at 10.3 GHz with wide bandwidth of 3.0 GHz, which shows the effectiveness of absorber for various applications.

Effect of magneto-dielectric nanocomposite on the SAR value of phantom model

The harmful effect of electromagnetic radiation on human body through the usage of mobile phones and other electronic equipments calls the attention of researchers to find out a remedy for the same. Thus in this study the interaction between human head model and electromagnetic field source is studied with and without shielding layer. EM wave source as a dipole antenna for GSM applications with the three layer human head model is studied using a computer simulation using CST Microwave Studio 2013. A solution for reducing Specific Absortion Rate (SAR) is addressed by the use of microwave absorber which in turn prepared through sol-gel mediated autocombustion method. Parametric analysis is introduced to optimize the dimension of the microwave absorber for shielding.

Electromagnetic wave absorption properties of conducting polymer-spinel ferrite composites

Electromagnetic interference (EMI) is an undesirable and uncontrolled off-shoot of tremendous growth of electronics and widespread use of transient power sources. A novel class of nanocomposites such as spinel ferrite-conducting polymer composite that possess unique combination of electrical, dielectric and magnetic properties can be significantly used for the suppression of electromagnetic interference. The spinel ferrite synthesis is carried out through sol-gel mediated auto-combustion method. Ferrimagnetic nanostructured spinel ferrites are mixed with conducting polymer for the enhancement of electromagnetic (EM) wave absorption with wide bandwidth of absorption along with the added advantage of flexibility, adhesive nature and light weight of the composite. Complex permittivity and permeability of the synthesized materials are calculated with the help of Vector Network Analyzer (VNA) in the frequency range 2-18 GHz and the corresponding reflection loss is computed. The polymeric matrix PANI shows 7 GHz broad bandwidth of absorption -10 dB. Composites of spinel ferrites with PANI enhances the EM wave absorption properties of both nickel ferrite and nickel zinc ferrite. Nickel zinc ferrite with PANI shows significant enhancement in absorption for C-band (4-8 GHz), whereas nickel ferrite with PANI shows better reflection loss in Ku-band (12-18 GHz). Nickel zinc ferrite-PANI gives -10 dB bandwidth of 8.5 GHz and nickel ferrite with PANI shows maximum reflection loss of -17.44 dB at frequency of 12.25 GHz with bandwidth of 3.68 GHz.