Ali Raza

This study presents a compact passive backward coupler (CPBC) designed for efficient nonreciprocal switching, leveraging nonlinear Schottky diodes, microstrip transmission lines (MTLs), and metamaterial-based interdigital capacitors (MICs). Operating passively at 2.43 GHz, the CPBC achieves high isolation between transmitter and receiver ports without requiring external biasing voltage. The switch comprises four ports: Input (Port-1), Output (Port-2), Backward coupling (Port-3), and Forward coupling (Port-4). At low power, the input signal is directed solely to the output port, ensuring no signal coupling, while at high power, the signal is rerouted to Port-3 for backward coupling. The switch incorporates 32 anti-parallel Schottky diodes to facilitate bidirectional signal flow. The proposed structure is simulated and fabricated to validate its performance, and the measurement results show strong agreement with the simulations. This design effectively enhances signal routing and isolation performance for passive switching applications and enables efficient communication and power management by allowing seamless switching between data transmission and reception using a single antenna.

This article presents a novel integrated multifunctional metamaterial system (MFMS) that combines wireless power transfer (WPT), sensing, and communication capabilities to enable soil moisture monitoring and data transmission for precision agriculture. The proposed system features a 16-unit cell (16-UC) array, with each unit cell comprising a microstrip interdigital capacitor (MIDC), coupled transmission lines (CTLs), and two nonlinear switches. The system is designed for multiple modes, including WPT, sensing, and communication. In WPT mode, when high-power signals are applied to port 3, the proposed MFMS directs the signal to port 1, where a rectifier is used to convert the received RF energy to dc voltage for storage in a supercapacitor or battery. In the sensing mode, it operates as a differential soil moisture sensor at low input power, offering dual outputs (ports 2 and 4) to enhance accuracy by reducing environmental interference. This soil moisture data can be transmitted to the user via a transmitter for decision-making. Operating across multiple frequency bands, this structure enhances the precision and accuracy of soil moisture sensing. To prove the concept, the proposed MFMS is simulated and fabricated, with the results showing good agreement between simulation and measurement. With its multifunctional architecture, the MFMS seamlessly transitions between energy harvesting and soil moisture sensing, eliminating the need for complex external modifications. This versatility capability enhances its suitability for autonomous and remote applications, including IoT-based sensor networks.

In this article, a compact dual-band soil moisture sensor (SMS) is presented for precision farming. The presented sensor operates at low resonance frequencies (500 and 900 MHz), allowing it to efficiently cover a substantial volume under test. This ensures cost-effectiveness by minimizing the number of sensors required for the farming area. The higher band is suitable for homogeneous soil, whereas the lower frequency can penetrate more deeply, allowing for in-depth analysis of soil. The proposed sensor consists of a modified patch along with two parasitic patches to achieve dual bands and a three-turn complementary spiral resonator (CSR-3) for miniaturization, with dimensions of $50 \times 50\,\mathbf{m}{{\mathbf{m}}^2}$. Three varactor diodes have been integrated across the CSR-3 to achieve frequency switching between the two frequency bands. A directional coupler (DiC) is utilized with the SMS to realize a dual-port structure and a 20 dB gain amplifier is also integrated at the input to compensate for DiC coupling and free space losses. The integration of sensor, DiC, and amplifier realizes a dual-band in situ monitoring system. The compact and planar geometry of the proposed structure, together with high sensitivity and low resonance frequencies, makes the design suitable for smart farming.

In this article, a joint sensing and communication system is presented for smart agriculture. The system integrates an ultra-compact soil moisture sensor (UCSMS) for precise sensing, along with a pattern reconfigurable antenna (PRA) for efficient transmission of information to the base station. A multiturn complementary spiral resonator (MCSR) is etched onto the ground plane of a microstrip transmission line to achieve miniaturization. The UCSMS operates at 180 MHz with a three-turn complementary spiral resonator (3-CSR), at 102 MHz with a four-turn complementary spiral resonator (4-CSR), and at 86 MHz with a five-turn complementary spiral resonator (5-CSR). Due to its low resonance frequency, the proposed UCSMS is insensitive to variations in the volume under test (VUT) of soil. A probe-fed circular patch antenna is designed in the wireless local area network (WLAN) band (2.45 GHz) with a maximum measured gain of 5.63 dBi. In addition, four varactor diodes are integrated across the slots on the bottom side of the substrate to achieve pattern reconfiguration. Six different radiation patterns have been achieved by using different bias conditions of the diodes. In the standby mode, PRA can serve as a means for wireless power transfer (WPT) or energy harvesting (EH) to store power in a battery. This stored power can then be utilized to bias the varactor diodes. The combination of UCSMS and PRA enables the realization of a joint sensing and communication system. The proposed system’s planar and simple geometry, along with its high sensitivity of 2.05%, makes it suitable for smart agriculture applications. Moreover, the sensor is adaptive and capable of measuring the permittivity of various material under test (MUT) within the range of 1–23.

Capacitive coupling wireless power transfer (CCWPT) is one of the pervasive methods to transfer power in the reactive near-field zone. In this paper, a flexible design methodology based on Binary Particle Swarm Optimization (BPSO) algorithm is proposed for a pixelated microstrip structure. The pixel configuration of each parallel plate (43×43 pixels) determines the frequency response of the system (S-parameters) and by changing this configuration, we can achieve the dedicated operating frequency (resonance frequency) and its related |S ₂₁ | value. Due to the large number of pixels, iterative optimization algorithm (BPSO) is the solution for designing a CCWPT system. However, the output of each iteration should be simulated in electromagnetic simulators (e.g., CST, HFSS, etc.), hence, the whole optimization process is time-consuming. This paper develops a rapid, agile and efficient method for designing two parallel pixelated microstrip plates of a CCWPT system based on deep neural networks. In the proposed method, CST-based BPSO algorithm is replaced with an AI-based method using ResNet-18. Advantages of the AI-based iterative method are automatic design process, more efficient, less time-consuming, less computational resource-consuming and less background EM knowledge requirements compared to the conventional techniques. Finally, the prototype of the proposed simulated structure is fabricated and measured. The simulation and measurement results validate the design procedure accuracy, using AI-based BPSO algorithm. The MAE (Mean Absolute Error) of prediction for the main resonance frequency and related |S ₂₁ | are 110 MHz and 0.18 dB, respectively and the whole design process is 3629 times faster than the CST-based BPSO algorithm.

In this paper, a compact multi-service antenna (MSA) is presented for sensing and communication using a reconfigurable complementary spiral resonator. A three turns complementary spiral resonator (3-CSR) is inserted in the ground plane of a modified patch antenna to create a miniaturized structure. Two Positive-Intrinsic-Negative (PIN) diodes (D1, D2) are also integrated with the 3-CSR to achieve frequency reconfiguration. The proposed structure operates in three different modes i.e., dual-band joint communication and sensing antenna (JCASA), dual-band antenna, and single-band antenna. The required mode can be selected by changing the state of the PIN diodes. In mode-1, the first band (0.95–0.97 GHz) of the antenna is dedicated to sensing by using frequency domain reflectometry (FDR), while the second band (1.53–1.56 GHz) is allocated to communication. The sensing ability of the proposed structure is utilized to measure soil moisture using FDR. Based on the frequency shift, permittivity of the soil is observed to measure soil moisture. In mode-2 and mode-3, the structure operates as a standard dual and single band antenna, respectively, with a maximum gain of 1.5 dBi at 1.55 GHz. The proposed planar structure, with its simple geometry and a high sensitivity of 1.7 %, is a suitable candidate for precision farming. The proposed structure is versatile and capable of being utilized as a single or dual-band antenna and also measuring permittivity of materials within the range of 1–20. Hence, it is adaptable to a range of applications.