Saikat Chandra Bakshi

In this invited paper, the New Technology Directions Committee (NTDC) of the IEEE Antennas and Propagation Society (AP-S) presents new and emerging research directions to commemorate the 70th anniversary of the IEEE Transactions on Antennas and Propagation . The NTDC consists of three Working Groups (WGs); members and collaborators of these groups provide their perspectives on topics related to WG themes in this paper. WG-1 focuses on advancement of materials and manufacturing processes for future antenna applications. WG-2 focuses on advances in communications, sensing and imaging. WG-3 focuses on maximizing the societal impact of wireless connectivity. The discussion in this paper ranges from additive manufacturing techniques and system integration to advanced communications and quantum-based sensing technologies. Numerous applications are explored and a perspective on the digital divide is offered.

The paper presents a novel LoRa-based IIoT system for monitoring the underground coal mine environment. Additionally, a new adaptive data rate algorithm for mesh network topology is proposed to optimize the data rate and maximize the coverage distance. Maximum coverage distance is achieved with a minimum number of repeaters. However, unlike previous works, the current work takes into account the power constraints in the underground coal mine environment, and most low-power consumption system is presented with an intelligent design approach. The implementation of the proposed adaptive data rate algorithm achieves 1.46 Kbps data rate at spreading factor 9, bandwidth 125 KHz, and transmitted power 11 dBm and extended the battery life of the deployed end nodes. The deployed end nodes achieved a maximum of 180 m under diffused line-of-sight condition at the roadway region of the operational mine. The relevant parameters are measured from the operational mine. Finally, the hardware is fabricated and the proposed system is validated in an operational underground coal mine.

We introduce a new metasurface-based wideband polarization converter with a switchable notch band. Unlike previous structures, the proposed structure utilizes the properties of p-i-n diodes to offer switchable functionalities between single/dual-frequency bands. Specifically, during the on- state of diodes, an incident linearly polarized (LP) plane wave of frequency range 4.87–11.41 GHz is converted into an orthogonally linearly polarized (OLP) wave. Conversely, when the p-i-n diodes are set in their off- state, the structure converts the LP plane wave into an OLP wave within two adjacent frequency bands (4.80–7.31 GHz and 9.82–11.43 GHz) separated by a notch region (7.44–7.55 GHz). The notch band is characterized by an LP-full reflection behavior that can be exploited for stealth antenna applications. The working principle of the proposed device and its physical mechanisms are discussed. Finally, a prototype is fabricated and measured and the experimental results confirm the effectiveness of the proposed structure.

We introduce a new concept of three states polarization converting metasurface (TS-PCM) based on p-i-n diodes. The proposed structure can offer three distinct wave manipulation functionalities: linear polarization to orthogonal linear polarization (LP-OLP), linear polarization to circular polarization (LP-CP), and linear polarization to full reflection (LP-FR) state. Unlike previous structures, the multiple conversion features are simultaneously achieved in different frequency ranges, depending on the operating state of diode (OFF or ON). In the OFF state of diodes, the LP incident electromagnetic wave is converted into a CP wave in the range 5.20–6.10 GHz, whereas full reflection is obtained at 2-3.66 GHz and 8.42–9.52 GHz band. In the ON state, the TS-PCM converts the LP incident waves into OLP waves in the range 3.77–6.20 GHz and LP waves into CP ones at 7.75–8.60 GHz. Finally, a sample prototype was fabricated and the experimental results were verified with the simulated ones.

This article introduces a multifunctional polarization insensitive frequency selective rasorber (MF-FSR) comprised of periodic metallic patterns printed on two dielectric substrates and separated by an air-spacer. The novelty of the proposed MF-FSR lies in its combined feature of mode switching and frequency tuning characteristics. This uniquely offers a real-time and multifunctional capability to switch from “rasorber mode (FSA-T)” into an “absorber with notch band (FSA-N)” mode where both modes support continuous tunability of their “transmission” or “notch” band. By controlling the reverse bias voltage of the embedded varactor, the transmission band in FSA-T mode can be tuned from 3.76 to 4.26 GHz with a very low insertion loss in the range of 0.62-0.95 dB. In complementary FSA-N mode, the notch band is also tunable from 4.17 to 4.71 GHz. Moreover, the same varactor set can control the tuning of transmission or the notch band depending upon MF-FSR's basic state of operation which is further independently controllable by the p-i-n diode. Equivalent circuit models are also thoroughly examined. Finally, a prototype is fabricated and experimentally tested, showing a good agreement with the predicted results.

A novel wide-angle and broadband rasorber is presented incorporating several advances. To broaden the bandwidth, we introduce a new type of frequency selective surface (FSS) in the bottom layer of the rasorber. This strategy increases the upper and lower absorption bandwidths while reducing the insertion loss at transmission window. Furthermore, a new top resistive layer is proposed via the loading of electric field coupled resonator elements on a cross-dipole structure. The proposed design offers both, an angularly stable performance and a thin structure that can be fabricated on a single dielectric substrate. To enable switchability, p-i-n diodes are employed and a reconfigurable rasorber/absorber is designed where a new concept of “lossy/lossless” top layer is investigated and established as the best choice among other switchable designs. Equivalent circuit models are constructed for both active and passive designs to provide physical insight into their operation. Finally, to enable deployment of the rasorber over curved geometries, these advances are incorporated into a conformal structure. Three separate prototypes are fabricated and good agreement is obtained between design predictions and experimental results.

In a recent article, Al-Badri et al. [J. Appl. Phys. 124, 105103 (2018)] proposed a new method to split a single perfect absorption peak into two separate absorption spectra by using vertical sliding of conjoined cut-wire-pairs (CCWPs).The highest tuning of absorption bands are reported at frequencies 3.242 GHz and 3.640 GHz with absorptivity of about 90%. This comment expresses some concerns about the simulation environment and absorption characteristics of such an approach. Moreover, it is shown that the actual absorption peak is around 40% while simulated with periodic boundary conditions.

In this paper a fully reconfigurable frequency selective rasorber (FR-FSR) is presented. To establish systematic design guidelines, initially the conditions for full reconfigurability are derived. Then a specific equivalent circuit model (ECM) is proposed which satisfies all the derived conditions. The circuit model is separately simulated to verify the proposed concept and further extensively analyzed to provide an in depth design methodology for all three modes of operation. The ECM is further synthesized into a simple planar structure to obtain the design of the rasorber. In the proposed rasorber, both layers are independently reconfigurable with PIN diodes embedded in the top layer and varactors in bottom layer, all symmetrically mounted to achieve polarization insensitivity. PIN and varactor diodes are independently operated to achieve the desired mode of operation with minimum insertion loss. A simple and efficient bias network is proposed in such a way that it does not affect the performance of the rasorber. The sample prototype is also fabricated and experimentally tested where a good agreement between simulated and measured result is obtained.