Sajid Asif

A Compact CSRR-Enabled UWB Diversity Antenna

The purpose of this letter is to introduce a compact ultrawideband (UWB) diversity antenna with a very low envelope correlation coefficient (ECC). The design employs a hybrid isolation enhancing and miniaturization technique. The antenna consists of two counter facing monopoles, and is miniaturized by using not only inverted-L stubs but also a complementary split-ring resonator (CSRR) on the ground plane. The added components enhance isolation and enable tighter packing of the antennas. The result is a very compact multiple-input–multiple-output (MIMO) array with an overall size of 23

A Frequency-Reconfigurable Series-Fed Microstrip Patch Array With Interconnecting CRLH Transmission Lines

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Design and In Vivo Test of a Batteryless and Fully Wireless Implantable Asynchronous Pacing System

29 mm2 , which covers the entire UWB spectrum from 3 to 12 GHz, with mutual coupling lower than –15 dB. Moreover, the CSRR unit that acts as a resonator is applied for the first time to suppress the interference of RF currents flowing through the ground plane of this UWB-MIMO/diversity antenna. The performance of the fabricated prototype in terms of scattering parameters, broadside (peak) gain, radiation patterns, efficiency, and ECC is presented and discussed.

On using the electrical characteristics of graphene-based conductors for designing a conformal monopole on a transparent substrate

This letter presents the design of a frequency-reconfigurable series-fed microstrip patch array in which the elements are interconnected with composite right/left-handed transmission lines (CRLH-TLs). Reconfigurable CRLH-TLs are used instead of meandered microstrip lines to reduce the overall size of the array and provide two different zero-phase frequencies of operation for broadside radiation in both instances. p-i-n diodes were used to reconfigure the array by changing the electrical lengths of the patches and microstrip sections of the CRLH-TLs. The measurements were taken in an anechoic chamber to verify the simulation results. The array can be reconfigured to operate at 1.97 and 2.37 GHz.

On using graphene-based conductors as transmission lines for feed networks in printed antenna arrays

Goal: The aim of this study is to develop a novel fully wireless and batteryless technology for cardiac pacing. Methods: This technology uses radio frequency (RF) energy to power the implanted electrode in the heart. An implantable electrode antenna was designed for 1.2 GHz; then, it was tested in vitro and, subsequently, integrated with the rectifier and pacing circuit to make a complete electrode. The prototype implanted electrode was tested in vivo in an ovine subject, implanting it on the epicardial surface of the left ventricle. The RF energy, however, was transmitted to the implanted electrode using a horn antenna positioned 25 cm above the thorax of the sheep. Results: It was demonstrated that a small implanted electrode can capture and harvest enough safe recommended RF energy to achieve pacing. Electrocardiogram signals were recorded during the experiments, which demonstrated asynchronous pacing achieved at three different rates. Conclusion: These results show that the proposed method has a great potential to be used for stimulating the heart and provides pacing, without requiring any leads or batteries. It hence has the advantage of potentially lasting indefinitely and may never require replacement during the life of the patient. Significance: The proposed method brings forward transformational possibilities in wireless cardiac pacing, and also in powering up the implantable devices.

A 4 element compact Ultra-Wideband MIMO antenna array

Conformal antennas printed on thin flexible substrates typically use copper conductors for the radiating portion of the designs. This paper presents an alternative to using copper conductors. More particularly, a novel compact monopole on a thin transparent substrate with 25 μm thick flexible graphene-based conductors for the radiating portion of the design is presented. The design was modeled in a full-wave simulation tool, and a prototype was manufactured and measured in a full anechoic chamber. Overall, it was shown that the S-parameter simulations agreed well with measurements and that the electrical benefits of the flexible graphene-based conductors could be used to design a useful conformal monopole.

Radiation performance and Specific Absorption Rate (SAR) analysis of a compact dual band balanced antenna

The use of graphene-based conductors (GBC) as a transmission line (TL) is presented as a conventional TL possessing right-handed (RH) nature and its coupling characteristics are investigated. In order to verify and demonstrate the wave propagation of a GBC TL, a 120 mm long 50 Ω TL was fabricated and tested. Performance of the single GBC TL was then compared to the conventional microstrip TL, analyzing the matching and wave propagation results. To investigate the unwanted coupling that may occur in a feed network, a similar GBC and a conventional microstrip TL, as well as two parallel GBC TLs on the same substrates were separately manufactured and tested to complete the study. It is shown that GBC TLs support the wave propagation in a fashion similar to the microstrip TL with an attenuation of less then 3.0 dB up to 7 GHz. Also the measurements of the near-end coupling showed that the two parallel GBC TLs have fairly good isolation in the frequency band of 4.5 KHz to 8.5 GHz, whereas the far-end coupling exhibits similar properties to that of the parallel microstrip TLs with same distance between them. The results demonstrated that GBC TLs could hence be a potential candidate for the feed network for planar antenna arrays.

Main Lobe Control of a Beam Tilting Antenna Array Laid on a Deformable Surface

In this paper, a compact planar Ultra-Wideband (UWB) antenna array with 4 monopole radiators is presented. To enhance the isolation, polarization of nearly placed elements is exploited. The proposed MIMO antenna array is electrically small 50 × 39.8 mm2, printed on a low loss 1.524 mm thick Rogers TMM4 laminate with a dielectric constant of 4.5 and a loss tangent of 0.002. Simulation in HFSS and printed prototype results satisfy the return loss requirement of better than 10 dB and isolation better than 17 dB on the entire 2.5 to 12 GHz bandwidth. The calculated envelope correlation value of less than 0.03 and the compactness of the proposed antenna array makes it suitable for small portable handheld devices.

A model for 3D-printed microstrip transmission lines using conductive electrifi filament

This paper presents a compact dual-band dipole antenna with meander line radiating elements. The proposed antenna has a balanced structure with dimensions of 35×6×1.52 mm3, and mounted on a 36.2 × 100 mm2 floating ground plane. The balanced operation of the design is validated by incorporating a differential feed in the software simulation and a 180 ° hybrid junction is used for measurement with the network analyzer to verify the balanced concept of the prototype. Simulated and measured results of the S-parameters along with the de-tuning of the antenna in the presence of the human body shows good agreement. Moreover the proposed design is used as an exposure source to the simulated human head model. The human head is modeled as six layers in the Electromagnetic (EM) software HFSS to study the interaction between the proposed balanced antenna and the human head model. The Electric field (E-field) distribution in the six layers of the human head model is shown to estimate the penetration of the field when the antenna is placed at a distance of 7 mm from the proposed design. Also Local Specific Absorption Rates (SARs) and average SARs simulation results at 3.78 GHz and 4.29 GHz are shown. The SARs analysis showed that in all the six layers of the human head model, local SAR values are greater in fat and Cerebrospinal fluid (CSF) for both the frequencies while the average SAR values are not very high.

On using the electrical characteristics of carbon microfibers for designing a monopole antenna

The projection method (PM) is a simple and low-cost pattern recovery technique that already proved its effectiveness in retrieving the radiation properties of different types of arrays that change shape in time. However, when dealing with deformable beam-tilting arrays, this method requires to compute new compensating phase shifts every time that the main lobe is steered, since these shifts depend on both the deformation geometry and the steering angle. This tight requirement causes additional signal processing and complicates the prediction of the array behavior, especially if the deformation geometry is not a priori known: this can be an issue since the PM is mainly used for simple and low-cost systems. In this letter, we propose a simplification of this technique for beam-tilting arrays that requires only basic signal processing. In fact the phase shifts that we use are the sum of two components: one can be directly extracted from strain sensor data that measure surface deformation and the other one can be precomputed according to basic antenna theory. The effectiveness of our approach has been tested on two antennas: a 4 × 4 array (trough full-wave simulations and measurements) and on an 8 × 8 array (trough full-wave simulations) placed on a doubly wedge-shaped surface with a beam tilt up to 40 degrees.