Mahesh P. Abegaonkar

A microwave microstrip ring resonator as a moisture sensor for biomaterials: application to wheat grains

A miniaturized, non-destructive sensor employing a microwave microstrip ring resonator (MRR, GHz, mean diameter 3.69 mm) was developed for estimating the moisture content of a single wheat ( Triticum aestivum L) grain. A single wheat grain with a known amount of moisture was placed on the MRR at two different orientations ( and ) with respect to the feedline. The resonance frequency , bandwidth (B) and quality factor of the MRR were calibrated against the moisture content. The measurements were made with a scalar network analyser. The sensor was studied in the normal useful moisture range of 11-32% (on a wet-weight basis), the actual moisture values being obtained by an oven-drying method. The orientation was more sensitive to moisture than was the orientation. The total changes in for a 21% change in moisture content for and 90 orientations were 235 and 150 MHz, respectively. The errors in moisture estimation with for and were % and %, respectively. The corresponding values with B and for orientation were % and %, respectively. The proposed sensor is more sensitive than a reported waveguide resonator and is easy to operate, for the microstrip offers an open structure, thereby facilitating easy loading and unloading of the samples.

Gain Enhancement of a CPW-Fed Monopole Antenna Using Polarization-Insensitive AMC Structure

A polarization-insensitive dual-band artificial magnetic conductor (AMC) structure is designed and experimentally verified. It consists of a planar array of annular ring-slot loaded rectangular patches. Details of the proposed structure and origin of the two bands is discussed. Through simulations and measurements, it is shown that the structure is insensitive to polarization of the incident wave. The tuning of the higher AMC band is demonstrated by varying the capacitance of the annular slot through its width variation. The designed AMC is used as a reflector for a wideband monopole patch antenna. It is shown experimentally at the antenna frequencies in the AMC band that the gain of the antenna improves by almost 10 dB and front-to-back ratio is improved by 15 dB.

Miniaturized nondestructive microwave sensor for chickpea moisture measurement

A miniaturized microstrip ring resonator (MRR) 1 in.×1 in. resonating at fro=10.27 GHz was used as a nondestructive moisture sensor for chickpea kernels (Cicer arietinum L.) for ease in loading and unloading. The change in the resonant frequency (Δfr) of the MRR is a measure of the amount of moisture in the overlaid kernel. The percentage of moisture (M) was varied from 0% (dry) to ∼50% (fully soaked) calculated on a wet weight basis. Δfr increased with M, although not linearly. Three regions were observed in the sensitivity curve. The first region extended from 0%–12%, the central region from 12%–43%, and the saturation region from 43%–50% in moisture content. In the central region the observed Δfr was 574 MHz, whereas in the first and third regions it was 44 and 55 MHz, respectively. The regions in the sensitivity curves indicate different dominant phenomena. A small scatter was observed in the first region, which increased with the increasing percent of moisture content.

FSS Properties of a Uniplanar EBG and Its Application in Directivity Enhancement of a Microstrip Antenna

In this letter, frequency selective surface (FSS) properties of a uniplanar electromagnetic band-gap (EBG) unit cell are studied. The unit cell consists of meander-line inductor and interdigital capacitors on one side of a substrate. Simulation results indicate that the unit cell exhibits passband characteristics centered at 10.04 GHz. FSS property of the structure is verified by measurement using X-band waveguides. The measured results show passband characteristics at 9.45 GHz. A 13 × 13 array of these unit cells (FSS screen) is used as a superstrate at a distance ≈ 0.5λ0 over a patch antenna operating at 10.8 GHz, offset from center frequency of the FSS passband. Directivity improvement of 6.95 dB is observed along 0° in the measurements of patch antenna with FSS superstrate as compared to the patch antenna without superstrate.

Low intensity microwave radiation induced oxidative stress, inflammatory response and DNA damage in rat brain.

Over the past decade people have been constantly exposed to microwave radiation mainly from wireless communication devices used in day to day life. Therefore, the concerns over potential adverse effects of microwave radiation on human health are increasing. Until now no study has been proposed to investigate the underlying causes of genotoxic effects induced by low intensity microwave exposure. Thus, the present study was undertaken to determine the influence of low intensity microwave radiation on oxidative stress, inflammatory response and DNA damage in rat brain. The study was carried out on 24 male Fischer 344 rats, randomly divided into four groups (n=6 in each group): group I consisted of sham exposed (control) rats, group II-IV consisted of rats exposed to microwave radiation at frequencies 900, 1800 and 2450 MHz, specific absorption rates (SARs) 0.59, 0.58 and 0.66 mW/kg, respectively in gigahertz transverse electromagnetic (GTEM) cell for 60 days (2h/day, 5 days/week). Rats were sacrificed and decapitated to isolate hippocampus at the end of the exposure duration. Low intensity microwave exposure resulted in a frequency dependent significant increase in oxidative stress markers viz. malondialdehyde (MDA), protein carbonyl (PCO) and catalase (CAT) in microwave exposed groups in comparison to sham exposed group (p<0.05). Whereas, levels of reduced glutathione (GSH) and superoxide dismutase (SOD) were found significantly decreased in microwave exposed groups (p<0.05). A significant increase in levels of pro-inflammatory cytokines (IL-2, IL-6, TNF-α, and IFN-γ) was observed in microwave exposed animal (p<0.05). Furthermore, significant DNA damage was also observed in microwave exposed groups as compared to their corresponding values in sham exposed group (p<0.05). In conclusion, the present study suggests that low intensity microwave radiation induces oxidative stress, inflammatory response and DNA damage in brain by exerting a frequency dependent effect. The study also indicates that increased oxidative stress and inflammatory response might be the factors involved in DNA damage following low intensity microwave exposure.

Detection of Low Level Microwave Radiation Induced Deoxyribonucleic Acid Damage Vis-à-vis Genotoxicity in Brain of Fischer Rats.

Background: Non-ionizing radiofrequency radiation has been increasingly used in industry, commerce, medicine and especially in mobile phone technology and has become a matter of serious concern in present time. Objective: The present study was designed to investigate the possible deoxyribonucleic acid (DNA) damaging effects of low-level microwave radiation in brain of Fischer rats. Materials and Methods: Experiments were performed on male Fischer rats exposed to microwave radiation for 30 days at three different frequencies: 900, 1800 and 2450 MHz. Animals were divided into 4 groups: Group I (Sham exposed): Animals not exposed to microwave radiation but kept under same conditions as that of other groups, Group II: Animals exposed to microwave radiation at frequency 900 MHz at specific absorption rate (SAR) 5.953 × 10–4 W/kg, Group III: Animals exposed to 1800 MHz at SAR 5.835 × 10–4 W/kg and Group IV: Animals exposed to 2450 MHz at SAR 6.672 × 10–4 W/kg. At the end of the exposure period animals were sacrificed immediately and DNA damage in brain tissue was assessed using alkaline comet assay. Results: In the present study, we demonstrated DNA damaging effects of low level microwave radiation in brain. Conclusion: We concluded that low SAR microwave radiation exposure at these frequencies may induce DNA strand breaks in brain tissue.

Switchable and Tunable Notch in Ultra-Wideband Filter Using Electromagnetic Bandgap Structure

A simple technique to reconfigure a notch filter employing a 1-D electromagnetic bandgap (EBG) structure, which is capacitively coupled to a microstrip line, is presented in this letter. The resonant nature of the EBG creates a notch in the transmission band. The notch filter is made reconfigurable/tunable by introducing an additional capacitive structure to change the size (geometry) of the EBG unit cell. The structure is connected or disconnected to the main structure (unit cell) by means of a PIN diode or varactor diode. Its application in notched-band ultra wideband (UWB) filter is demonstrated. A 450 MHz change in notch frequency is observed using PIN diode, and 340 MHz tuning range is observed using varactor diode.

Cognitive Impairment and Neurogenotoxic Effects in Rats Exposed to Low-Intensity Microwave Radiation

The health hazard of microwave radiation (MWR) has become a recent subject of interest as a result of the enormous increase in mobile phone usage. The present study aimed to investigate the effects of chronic low-intensity microwave exposure on cognitive function, heat shock protein 70 (HSP70), and DNA damage in rat brain. Experiments were performed on male Fischer rats exposed to MWR for 180 days at 3 different frequencies, namely, 900, 1800 MHz, and 2450 MHz. Animals were divided into 4 groups: group I: sham exposed; group II: exposed to MWR at 900 MHz, specific absorption rate (SAR) 5.953 × 10−4 W/kg; group III: exposed to 1800 MHz, SAR 5.835×10−4 W/kg; and group IV: exposed to 2450 MHz, SAR 6.672 × 10−4 W/kg. All the rats were tested for cognitive function at the end of the exposure period and were subsequently sacrificed to collect brain. Level of HSP70 was estimated by enzyme-linked immunotarget assay and DNA damage was assessed using alkaline comet assay in all the groups. The results showed declined cognitive function, elevated HSP70 level, and DNA damage in the brain of microwave-exposed animals. The results indicated that, chronic low-intensity microwave exposure in the frequency range of 900 to 2450 MHz may cause hazardous effects on the brain.

Microstrip ring resonator as a moisture sensor for wheat grains

Microwave resonant frequency and quality factor of a ring resonator are measured with a single wheat grain as an overlay on the ring and are found to vary with the moisture content independent of the weight of the kernel.

Dual port ASA for frequency switchable active antenna

This report presents the design of a dual-port dual-band annular slot antenna suitable for use in the feed-back path of an oscillator resulting in an active antenna configuration. The proposed antenna is designed to radiate and transmit equal amounts of power. The return loss of the proposed antenna is higher than that desired for one-port antenna application at the desired dual-band frequencies. The antenna is fabricated on one side of a Neltec substrate (εr=3.2 and thickness = 0.762 mm) and the microstrip feeding line is fabricated on the opposite side of the board. The antenna was designed to operate at WLAN bands centered at 2.4 and 5.2 GHz. The simulated and measured results show fairly good agreement. The measured return losses were found 20.5 dB at 2.4 GHz and 13.9 dB at 5.2GHz while simulated return losses were 9.36 dB at 2.4 GHz and 31.35 dB at 5.2 GHz. The radiation pattern is approximately omnidirectional at both frequencies in H-plane.