Aruldas Shobha Rekh

A circular ring-shaped metamaterial (CRM) absorber was designed to harvest radio frequency (RF) energy in the ultra-wideband (UWB) frequency band applications. The proposed metamaterial unit cell features a circular shaped structure, with rectangular strip lines connected in the form of a cross leaving a square shaped slot at center. The unit cell dimensions are 15×15×1.6 mm. The absorber was etched on a low cost FR4 substrate having a dielectric constant of 4.4. Ansys high frequency structure simulator (HFSS) software was used for simulation and the analysis were carried out for unit cell, 2×2, 3×3, and 4×4 array structures. The absorber parameters plotted are absorption characteristics and reflection characteristics. Also, the metamaterial parameters (μeff) and (εeff) are also retrieved from the absorber parameters and analyzed. From the analysis, the values (μeff) and (εeff) were found to be negative, leaving refractive index also negative (n<0), which proved the metamaterial property. The proposed CRM absorber showed good absorption characteristics of more than 80% and also metamaterial property in the entire UWB band (4-13 GHz). Hence the absorber proves to be a good candidate in powering low power sensors/microcontrollers for internet of things (IoT) applications.

Double Elliptical Micro-strip Patch Antenna (DEMPA) is developed out of Double Elliptical Patch (DEP) which is a recently proposed shape of patch. The use of DEP results in higher flexibility in design of patch antenna and thus promotes antenna miniaturisation. The present work is an attempt to demonstrate the miniaturisation of radiolocation antenna through the concept of Design Flexibility (DF). In this paper, optimised neural network model for synthesis of DEMPA has been developed for radiolocation applications for which the earmarked frequency band is 8.50 GHz – 10.50 GHz. With the help of synthesis model, for an arbitrary operational frequency of 9.85 GHz, radiolocation antennas with effective patch area ranging from 142 mm2 to 66 mm2 were designed by using DEPs. In this case, the percentage reduction in effective patch area was found to be 53.52%. It shows that double elliptical patches can be employed to develop miniaturised radiolocation antennas. One prototype antenna was fabricated and tested to demonstrate the efficacy of the methodology adopted. The fabricated antenna had resonance at 10.15 GHz with a reflection coefficient of -20.73dB and bandwidth of 3.106 GHz (from 7.458 GHz to 10.564 GHz). Its Fractional Bandwidth was 34.469%. Positive and reasonably good gain was maintained over the entire working band. At resonance, the peak gain was 4.22 dB.The measured characteristics of antenna were in close agreement with the simulated results. The methodology presented in this paper can also be applied to frequency bands for other wireless applications.

Wireless sensor networks (WSNs), one of the prominent areas of research, provide a key background framework for the Internet of things (IoT). The key components of WSNs are sensors/actuators, embedded controllers, and connectivity devices (wireless/wired) through which data/information is communicated. One major challenge is to provide incessant supply to these enormous smart connected devices, which are mainly battery operated. RF harvesting energy provides an encouraging and economically friendly solution to provide low power DC supply from the harvested RF energy sources such as Wi-Fi, GSM, radio/TV broadcasting stations, radar, and so on. Quite a few research studies are on-going in the development of RF energy harvesting (RFEH) systems, which pose various challenges as compact antenna design, wide bandwidth, and overall DC conversion efficiency. An overview of the different RFEH systems with the challenges in designing the antenna, rectifier design, and matching circuit design is reported to afford the readers/researchers a general framework for designing RFEH systems.

Micro-Strip Patch Antenna (MSPA) finds large scale applications in various fields of communication. Elliptical shaped patch antenna is a prominent category among MSPAs. Possibility of circular polarization and dual resonant frequencies makes the Elliptical Micro-strip Patch Antenna (EMPA) widely accepted in modern communication devices. The present work aims to identify the constraints in further advancements in the design of EMPA and propose a novel shape to overcome these constraints. Minimizing the patch area and increasing the number of degrees of freedom in design were found to be the challenges. To overcome these challenges, a newly shaped patch called ‘Double-Elliptical Patch (DEP)’ is proposed for designing ‘Double-Elliptical Micro-strip Patch Antenna (DEMPA)’. A double-ellipse is a combination of two half-ellipses either with the same minor axis and different semi-major axes or with the same major axis and different semi-minor axes. The DEP has an additional degree of freedom in design compared to elliptical patch, which leads to greater design flexibility. In the present work, a DEP with the same horizontal major axis and centrally given feed was designed using Ansoft HFSS software. The semi-minor axis of upper half-ellipse was varied by keeping the semi-minor axis of lower half-ellipse a constant. The radiation properties of DEMPA were found to be similar to that of corresponding EMPA and this was achieved with less patch area. The maximum percentage reduction in patch area was 10.714%. The DEMPA covered the entire frequency range of Ultra Wide Band (UWB).

Elliptical Micro-strip Patch Antenna (EMPA) has been emerged as a peculiar and significant category among the different shaped micro-strip patch antennas because of its circular polarization and dual-resonant frequency features with a single feed. Elliptical and its derived shapes such as semi-elliptical, half-elliptical, slotted-elliptical and elliptical ring are found to be particularly instrumental for bandwidth enhancement and these antennas find great applications in Ultra Wide Band (UWB) and Super Wide Band (SWB) communications. Compared to antennas with circular or rectangular shapes, the design of EMPA is a research area of high potential as there is higher flexibility in its design due to more degrees of freedom. The reported literature in the field of EMPA is very less and there is ample scope for new researchers to work on. This review paper is an attempt to summarize and critically assess the-state-of-the-art design techniques as reported in literature and understand their effects on performance of elliptical patch antenna for suggesting new research fronts in the field of EMPA.

In this paper, a new metamaterial absorber which comprises of a symmetrically E shaped split ring resonator patches at the top of the FR4 substrate of height 1.6mm for RF Energy Harvesting is proposed. The proposed design provides two absorption peak one at 5.8GHz with a maximum absorption of about 99% and other at 7.8GHz with a maximum absorption of about 92%. The absorption mechanism is investigated for the proposed metamaterial absorber. Also the polarization behavior of the absorber is also analyzed under various angles of incidence. The absorber has been tuned in such a way to have good broadband response in the UWB range.

The level crossing ADC generates digitized samples consisting of the magnitude of input signal and time interval between two consecutive level crossings when the input signal crosses the threshold level. This paper presents a new architecture of low power asynchronous adaptive threshold level crossing (LC) ADC suitable for wearable ECG sensors based on a novel algorithm for determining adaptive threshold. The adaptive threshold was determined by calculating the mean of maximum and minimum values of signal in a predetermined window. Polynomial interpolation was used to reconstruct the signal. A signal to noise distortion ratio of 57.50 dB and a mean square error (MSE) measure of 1.368*10⁻⁸ V² was achieved by the proposed algorithm for a 1 mV, 10 Hz input sinusoidal signal in MATLAB. The asynchronous adaptive threshold LC ADC operating from a supply voltage of 0.8 V occupied a layout area of 266.33*331.385 μm² when implemented in CADENCE virtuoso using 180 nm technology. The designed circuit consumes an average power of 367.6 nW for a 1mVpp, 10 Hz input sinusoidal signal when simulated in Virtuoso.

Greater design flexibility and newer miniaturization techniques are highly sought after by the commercial antenna industry and researchers. Micro-Strip Patch Antenna (MSPA) is finding huge applications in various fields of communication. In the present paper, the novel idea of Double-Elliptical Micro-strip Patch Antenna (DEMPA) is proposed for antenna miniaturization and higher design flexibility. Double-Elliptical Patch (DEP) is made as the combination of two half-elliptical patches having the same minor axis and different semi-major axes or the same major axis and different semi-minor axes. A DEP with different lengths of horizontally arranged semi-major axes and centrally given feed was considered here. The length of semi-major axis for right half-elliptical patch was varied while keeping the length of semi-major axis for left half-elliptical patch fixed. Design of DEMPA was carried out using Ansoft HFSS software, and the antenna has been fabricated and tested. The measured results were in good agreement with the simulated ones. The percentage reduction in effective patch area was found to be 8.33 for DEMPA compared to the corresponding elliptical patch antenna. The DEMPA covered the entire frequency range of Ultra Wide Band (UWB). With this novel shape, greater design flexibility along with miniaturization is achieved. The axial ratio analysis showed that the resulted antenna was of linear polarization.