This paper presents a comparative investigation of analog and digital optical wireless communication (OWC) through a water-filled polyvinyl chloride (PVC) pipe sealed at both ends with optically transparent PMMA windows using visible-light light-emitting diodes (LEDs) operating at four wavelengths: blue (475 nm), green (528 nm), yellow (583 nm), and red (625 nm). A unified experimental and simulation framework is developed to evaluate continuous (analog) and modulated (digital) transmission under varying water-filling conditions of 0%, 25%, 50%, 75%, and 100%. In the analog analysis, the received optical power is measured to quantify absorption, refraction, and scattering effects based on the Beer-Lambert model. For digital transmission, pseudo-random binary sequence (PRBS7) on-off keying (OOK) modulation is employed to assess signal-to-noise ratio (SNR), analytically estimated bit-error rate (BER), eye diagrams, and information-theoretic channel capacity upper bounds. The presented digital performance metrics are intended for relative trend analysis and physical interpretation, rather than demonstrating a fully optimized or practically deployable communication system. The results show that the 50% water-filled condition introduces the most severe impairment due to repeated air-water interface interactions, which cause additional Fresnel losses, angular redistribution, and enhanced multipath scattering. In contrast, fully submerged operation provides a more homogeneous propagation medium, leading to improved transmission behavior. Among the tested wavelengths, the red LED exhibits the highest relative robustness under the present baseline implementation. The reported digital metrics should be interpreted as comparative indicators for trend analysis and physical interpretation of channel-dependent degradation, rather than as evidence of reliable or optimized communication performance.

This paper presents the development of the world's first high-gain, all-photopolymer Bragg horn antennas explicitly designed for the WR-3.4 band (220-325 GHz), marking a groundbreaking advancement in terahertz (THz) antenna technology. Unlike conventional metallic horn antennas, which suffer from conductor losses and manufacturing complexity, this innovative design utilizes eco-friendly photopolymer materials and additive manufacturing, achieving a fractional bandwidth of 38.5% that fully covers the WR-3.4 band. The proposed antenna achieves a measured peak gain of 28.98 dBi at 300 GHz, with a return loss better than - 20dB across the band and a consistent half-power beamwidth (HPBW) of similar to 5 degrees, ensuring precise directivity and minimal sidelobe interference. By employing a novel horn-type adapter for seamless mode conversion from TE10 to the fundamental HE11 mode, the design significantly enhances coupling efficiency and reduces signal loss. Additionally, fabrication costs can be reduced by over 50% compared to traditional metallic designs, while maintaining repeatability and enabling rapid prototyping. As the first demonstration of photopolymer-based antennas achieving such high gains in the 220-325 GHz THz spectrum, this work establishes a new benchmark in THz antenna technology, providing an eco-friendly, cost-effective, and high-performance solution for high-speed communication, medical diagnostics, security imaging, and spectroscopy applications.

This paper presents an in-depth investigation of optical wireless communication through water-filled PVC pipelines using high-brightness light-emitting diodes (HB-LEDs) operating at visible wavelengths: 475 nm (blue), 528 nm (green), 583 nm (yellow), and 625 nm (red). Simulations were conducted in Ansys Zemax OpticStudio using ray-tracing techniques and Bidirectional Scattering Distribution Function (BSDF) models to evaluate the effects of surface roughness, interface reflection, and wavelength-dependent absorption. A custom experimental setup was developed using a 375 mm long, 50 mm diameter PVC pipe and a Thorlabs S121C photodiode sensor to validate the simulation. Optical power was measured under five water fill conditions (0%, 25%, 50%, 75%, and 100%). Results show that the greatest transmission loss occurs at the 50% water level, where multiphase scattering dominates, with experimental power decreasing to −11.82 dBm at 583 nm (yellow). Full immersion improves transmission, with recovered power levels up to −2.3 dBm at 475 nm (blue). Absorption coefficients were calculated using the Beer–Lambert Law, with peak values exceeding 0.09 cm⁻¹ at 50% fill. Simulation results aligned with experimental measurements within 1–2 dB, validating the model’s reliability. These findings support the development of adaptive gain control strategies and wavelength-optimized optical links for autonomous robotic inspection in submerged or semi-submerged pipeline environments.

This article presents an optical sensing technique for estimating water-fill levels and stratification states inside closed plastic pipelines using multiwavelength visible light. Four LEDs (475, 528, 583, and 625 nm) and a photodiode receiver with automatic gain control (AGC) are deployed across a PVC pipe section to monitor the effects of air-water stratification on signal attenuation and channel impulse response (CIR). The experimental results and ray-tracing simulations reveal wavelength-specific optical losses and CIR variations that correspond to fill ratios from 0% to 100%. Compared to conventional water-level sensors, which often rely on float mechanisms, capacitive probes, or ultrasonic pulses, this method enables contactless, inline assessment of water distribution in sealed, nontransparent geometries. Unlike prior optical approaches applied mainly to open tanks or homogeneous media, this work demonstrates that stratified layers in confined pipelines can be resolved through spectral and time-domain features. The system offers a compact and mechanically simple sensing alternative for embedded monitoring or mobile robotic inspection platforms.

In this article, a novel and innovative approach to characterize THz Bragg fibers using a horn-type adapter is presented, enabling a two-tier calibration method for a direct, efficient, and reliable way to measure THz Bragg fibers, including return loss (RL) and insertion loss (IL). The proposed approach is robust, accurate, and repeatable, making it suitable for designing and optimizing THz Bragg fibers and systems and enabling continued research and development. This study employs a calibration approach, utilizing short-short-load-thru (SSLT) and thru-reflect-line (TRL) calibrations. The horn-type adapter connects a standard WR-3.4 rectangular waveguide and a THz Bragg fiber, allowing the mode conversion from the TE10 mode in the rectangular waveguide to the HE11 mode in the Bragg fiber, with a middle stage of the TE11 mode in the tapered horn region. Additionally, the highly accurate measurement quality presented advantages compared to the existing THz measurement setups, for example, setup complexity, coupling efficiency, impedance adjustability, and less sensitivity to measurement environments, etc. The present approach shows advantages in experimental setup complexity, coupling efficiency, impedance adjustability, measurement repeatability, operator experience required, and setup tool cost compared to other existing THz measurement techniques.

This paper presents a state-of-the-art planar microwave sensor designed for highly precise alcohol characterization in aqueous solutions, with a primary focus on its application in COVID-19 disinfectants. Modified from the Jerusalem patch, the sensor operates at 5.58 GHz, achieving a unique balance between heightened sensitivity and cost-effectiveness. A tailor-made 3D-printed case minimizes errors, securely housing the sensor and feeding tube. The sensor effectively discriminates between ethanol and methanol, revealing a notable 16 MHz frequency gap. In COVID-19 applications, it maintains alcohol percentages at 65-75%, with 1% increments. The paper outlines a mathematical model extracting concentrations with the maximum error of only smaller than 1.81%, affirming the sensor's precision. Beyond technical prowess, the sensor's non-destructive nature, real-time monitoring applicability, and freedom from life-cycle limitations mark it as an innovative tool for checking the percentage of alcohol and types of alcohol before using it to kill the virus, contributing significantly to global efforts on disinfectant measurements with noninvasive nature and high precision. This modified Jerusalem sensor stands as a transformative solution, offering unprecedented advantages in design, operational capacity, and broader support for virus-killing applications.

This study presents insights into high-speed optical wireless communication (OWC) within plastic pipes, introducing a Gbps-capable alternative for challenging environments. Utilizing a 1W LED with five wavelengths, the experiment explores signal power, attenuation, and bandwidth characteristics. Notably, the blue LED achieves an unprecedented 58.64 MHz bandwidth, red and purple LEDs demonstrate novel bandwidths of approximately 25.23 MHz, and green and yellow LEDs exhibit unique bandwidths of 23.75 MHz and 9.62 MHz, respectively. The attenuation parameters for different wavelengths provide numerous insights, showcasing the novelty of this research and its potential applications in robot communication within plastic pipes. Concurrently, the paper introduces an approach to address the temperature impact on five distinct wavelength LEDs in OWC. By focusing on variations in LED bandwidth and optical power, an optimal heat sink design is proposed. This design achieves a remarkable minimum temperature of 27.06 degrees C and reduces the chip LED device's response time from 15 to 9 seconds. The significance lies in the novelty of the proposed heat sink, which incorporates variables such as fin thickness, height, air gap width, number of fins, and airflow rate, marking a substantial advancement in thermal management for OWC systems.

This paper introduces a Curved Hollow Substrate Integrated Waveguide (CHSIW) to address the growing demand for millimeter-wave applications, including communication, sensing, imaging, radar, and wireless power transfer systems. Leveraging advancements in integrated circuits and system-in-package (SiP) technology, the CHSIW tackles the challenges associated with hardware integration into curved structures. The design utilizes MultiJet Printing (MJP) for the M3 crystal dielectric substrate and a water laser cutter system for copper sheets, streamlining the fabrication process by eliminating complex via manufacturing steps through prefabricated through-hole vias. Operating in the frequency range of 21.7 GHz to 32 GHz, the CHSIW exhibits outstanding performance on curved surfaces, with measured average attenuation constants of 1.89 Np m-1 (16.42 dB m-1) and 1.95 Np m-1 (16.94 dB/m) for samples with radii of curvature of 166.8 mm and 125.1 mm, respectively. Beyond addressing technical challenges, the CHSIW presents a cost-effective and simplified fabrication process, positioning it as a breakthrough solution for diverse millimeter-wave applications, including future robotic and UAV communications. Furthermore, the proposed design and fabrication technique hold promise for the realization of conformal and free-form Hollow Substrate Integrated Waveguide (HSIW) devices in the future.

Wireless communication technology evolves to meet current needs, focusing on antenna size reduction for smaller, multi-frequency devices. This research introduces a novel approach to miniaturizing a multiband Electromagnetic Band Gap (EBG) reflector using a Double Interdigitated Coplanar Waveguide (DICPW) structure. The mushroom-patterned EBG unit cell, employing a double interdigital technique based on a Coplanar Waveguide (CPW), achieves a significantly slower wave on the transmission line. The unit cell size can be reduced from lambda/2 to lambda /8, allowing control over the second to fourth resonance frequencies. Engineered for a fundamental frequency of 1.8 GHz (LTE), the proposed EBG unit cell supports frequency ranges of 2.45 GHz (WLAN), 4.3 GHz (Altimeter), and 5.2 GHz (WLAN). Integrating this EBG reflector with a dipole antenna at the same frequency results in directional radiation patterns and gains of 8.29 dBi, 8.76 dBi, 8.55 dBi, and 8.22 dBi at resonance frequencies. The innovative reflector, with improved gain and compact dimensions, is relevant to cube satellite and wireless communication systems with versatile multiband frequency requirements.

This paper presents a multiband director based on the frequency selective surface (FSS) unit cell structure using the double layer with interdigital CPW (ICPW) technique. The unit cell consists of the front and the back. The front part has been designed using an ICPW technique based on a coplanar waveguide structure to enhance the capacitance between the transmission line and the semi-ground. The overall structural dimension of the unit cell can be designed to be smaller than the conventional range of λ/2 to λ/8, due to the influence of the slow wave effect on the capacitance of the structure. The back part is the inverted layer of the front, which alternates between substrate and copper. It is composed of a square loop resonator with a double meandering line. The capacitance generated by a double meander line enhances the capacitance in the front part, which influences the control of all resonant frequencies and increases the slow wave on the double-layer unit cell structure, resulting in a significantly reduced dimension. The resonance frequencies for the designs are 1.8 GHz (LTE), 3.7 GHz (Wi-MAX) and 5.2 GHz (WLAN), respectively. According to simulation results, the FSS can transmit all resonant frequencies. It has an overall dimension of 10.93 mm × 11.48 mm. In addition, the FSS unit cell has been arranged as a 7 × 7 array for use as a director. The dimensions are 73.48 mm × 77.38 mm. The FSS director will be evaluated utilizing an omnidirectional dipole antenna at the same resonant frequency as the FSS unit cell. According to both the simulated and measured outcomes, the impedance matching value is below -10 dB at the three resonant frequencies. The FSS director equipped with a dipole antenna exhibits bidirectional propagation characteristics across all resonant frequencies. The antenna gains for simulation are 3.45 dBi, 3.05 dBi, and 3.72 dBi, while the antenna gains for measurement are 3.05 dBi, 2.98 dBi, and 3.12 dBi. The findings indicate a high level of concurrence.