Search Results (5,163)

This paper proposes an automatic power and modulation control (APMC) circuit that can directly detect the degradation of vertical cavity surface emitting laser (VCSEL) diodes by utilizing a novel voltage sensing mechanism, thereby eliminating the need for costly external monitoring photodiodes. Notably, the proposed APMC architecture facilely observes the performance degradation by sampling the voltage values at the upper node of the VCSEL diode during both modulation on and off states. The APC loop can perceive a 25 mV voltage drop that corresponds to a 0.5 mA increase in the threshold current, providing a 4-bit digital switch signal. Thereafter, it is delivered to the VCSEL diode driver to initiate compensation of the bias current. In the AMC loop, a 50 mV voltage drop equivalent to a 1 mA reduction in the modulation current is similarly detected to produce another 4-bit digital code. The proposed APMC IC is designed by using a 180 nm CMOS process and consumes a total power of 18.2 mW from a single 3.3 V supply. Full article

To cost-effectively meet 6G latency requirements, concurrent upstream and direct inter-optical network unit (ONU) communication passive optical networks (PONs) based on flexible point-to-multipoint (P2MP) optical transceivers and intensity modulation and direct detection (IMDD) have been reported to enable direct communications among different ONUs within the same PON without passing data to the optical line terminal (OLT). However, the previously reported P2MP transceivers suffer from high DSP complexity for establishing ultra-dense connections. For such application scenarios, the PON’s remote nodes also have high inter-ONU signal power losses. To effectively solve these technical challenges, this paper experimentally showcases (a) new P2MP transceivers by utilizing parallel multi-channel aggregation/de-aggregation and advanced extended Gaussian function (EGF)-based orthogonal digital filter banks, along with (b) low inter-ONU signal power loss-remote nodes. By introducing these two techniques into a 27 km, >54.31 Gbit/s concurrent upstream and direct inter-ONU communication IMDD PON, comprehensive experimental explorations of the PON’s performances were undertaken for the first time. The remote node is capable of supporting 128 ONUs. The results show that the new P2MP transceivers lead to >75% (>40%) reductions in overall transmitter (receiver multi-channel de-aggregation) DSP complexity, and they can also equip the PONs with an enhanced capability of providing ultra-dense connections. The experimental results also show that the PON allows each ONU to flexibly change its upstream and inter-ONU communication channel count without considerably compromising its performance. Therefore, the PON outperforms those of previously reported works in terms of ensuring low DSP complexity, highly robust transmission performance, and enhanced capabilities of flexibly accommodating numerous applications with diverse requirements regarding traffic characteristics, thus making it suitable for ultra-dense connection application scenarios. Full article

Recently, frequency diverse array (FDA) systems have gained attention in target localization due to their time-varying and range-angle-dependent beam-focusing characteristics, which are different from those of conventional phased array (PA) systems. However, analysis of the received signal is challenging due to its time-varying nature. In this paper, an artificial intelligence (AI)-based multi-target localization system is proposed, which works with a simple multi-Tx (Transmitter) and single-Rx (Receiver) FDA system. The AI-based model can find the relationship between the locations of the targets and the received signal, since all the necessary information is contained in the time-varying reflected signal. With a simple multi-Tx, single-Rx model, the system can be implemented in the real world. It is verified that the proposed system can locate at least two targets simultaneously with reasonable performance. Full article

Transcorneal electrical stimulation (TES) is a promising treatment for several retinal degenerative diseases (RDDs). TES involves the application of a controlled electrical current to the anterior surface of the cornea, aimed at activating the retina and posterior ocular structures. Dawson–Trick–Litzkow (DTL) and ERG-JET electrodes are among the most widely used for TES. However, their continuous metallic surface design limits spatial resolution and the ability to perform selective ES. In this work, we present the development of a transcorneal electrical stimulation (TES) electrode that, unlike conventional electrodes, enables spatially selective TES. The proposed electrode design consists of an array of 20 independent microelectrodes distributed across the central and paracentral regions of the cornea. The fabrication process combines surface micromachining and flexible electronics technologies, employing only three structural materials: aluminum (Al), titanium (Ti), and polyimide (PI). This material selection is critical for achieving a simplified, reproducible, and low-cost fabrication process. The fabricated electrode was validated through electrical and electrochemical testing. The results show a relatively high electrical conductivity of Al/Ti structures, low electrochemical impedance values—ranging from 791 kΩ to 1.75 MΩ for the clinically relevant frequency range (11 to 30 Hz)—and a high charge storage capacity of 1437 mC/cm². The electrode capacity for electrical signal transmission was demonstrated through in vitro testing. Finally, the applicability of the TES electrode for electroretinogram (ERG) recording was evaluated by measuring its optical transmittance across the visible wavelength range. Full article

The rapid advancements in wireless technology and digital electronics have led to the widespread adoption of compact, intelligent devices in various aspects of daily life. These advanced systems possess the capability to sense environmental changes, process data, and communicate seamlessly within interconnected networks. Typically, such devices integrate low-power radio transmitters and multiple smart sensors, hence enabling efficient functionality across wide ranges of applications. Alongside these technological developments, the concept of the IoT has emerged as a transformative paradigm, facilitating the interconnection of uniquely identifiable devices through internet-based networks. This paper aims to provide a comprehensive exploration of sensor technologies, detailing their integral role within IoT frameworks and examining their impact on optimizing efficiency and service delivery in modern wireless communications systems. Also, it presents a thorough review of sensor technologies, current research trends, and the associated challenges in this evolving field, providing a detailed explanation of recent advancements and IoT-integrated sensor systems, with a particular emphasis on the fundamental architecture of sensors and their pivotal role in modern technological applications. It explores the core benefits of sensor technologies and delivers an in-depth classification of their fundamental types. Beyond reviewing existing developments, this study identifies key open research challenges and outlines prospective directions for future exploration, offering valuable insights for both academic researchers and industry professionals. Ultimately, this paper serves as an essential reference for understanding sensor technologies and their potential contributions to IoT-driven solutions. This study offers meaningful contributions to academic and industrial sectors, facilitating advancements in sensor innovation. Full article

Rapid and accurate bacterial detection is essential in medicine, the food industry, and environmental monitoring. This work presents the development of an optical sensor based on color changes in the culture medium that leverages the optical interaction of bacterial metabolic products. The proposed prototype operates on the principle of optical transmittance through mannitol salt agar (ASM), a selective medium for Staphylococcus aureus. As bacterial growth progresses, the medium undergoes changes in thickness and, primarily, color, which is optically measurable at specific wavelengths depending on the type of illumination provided by the simplified light-emitting diodes (LEDs). The sensor demonstrated the ability to detect bacterial growth in approximately 90–120 min, offering a significant reduction in detection time compared to traditional incubation methods. The system is characterized by its simplicity, sensitivity, low reagent consumption (up to 140 fewer reagents per test), and potential for real-time monitoring. These findings support the viability of the proposed sensor as an efficient alternative for early pathogen detection in both clinical and industrial applications. Finally, a proposal for simplifying the sensor in a system composed of a light-emitting diode and a light-dependent resistor is presented. Full article

A novel encoding method based on the orbital angular momentum (OAM) mode and radial mode of composite vortex beams is proposed. The superposition of two vortex beams generates 32 different types of composite vortex beams: one of them is a Laguerre–Gaussian (LG) beam with a fixed OAM mode and radial mode, and the other is a LG beam containing four radial modes (p = 0, 1, 2, 3) and eight OAM modes with the same interval (l = ±3, ±5, ±7, ±9). A specially designed composite fork-shaped grating (CFG) is utilized to generate the intensity array pattern, and the received composite vortex beam is diffracted into a Gaussian beam with the relevant coordinates. Based on the coordinates and the number of bright rings in the intensity pattern, the OAM modes and radial modes of the two vortex beams composing the superposition state are determined, and finally the received composite vortex beam is decoded into the initially propagated information sequence. The correctness and effectiveness of the proposed encoding are confirmed through the comparative analysis of the correlation of the optical fields at both the transmitter and receiver in the two scenarios of interval and non-interval encoding. The proposed encoding method can significantly improve the efficiency of information transmission and its resistance to interference, holding great potential for future applications in free-space optical communication. Full article

One of the keys to medical microwave tomography is understanding the sensitivity of transmit–receive signals to changes in the electromagnetic properties to be reconstructed. This information is embedded in the Jacobian matrix for traditional inverse problem approaches and is a function of transmitter–receiver design characteristics and associated signal radiation/detection patterns. Previous efforts focused primarily on the 2D imaging problem for which sensitivity maps were generated in a single plane. In this paper, we describe sensitivity maps for the full 3D problem for monopole transceivers and their implications for associated antenna array configurations, including imaging zone coverage and computational efficiency. Full article

In the present study, the reflection and transmission of radiation in submicron indium tin oxide (ITO) films deposited on a borosilicate glass substrate are experimentally investigated for a wide spectral range, including ultraviolet, visible, infrared and terahertz regions. Theoretical modeling of the spectra is performed using the transfer matrix method. The interaction of electromagnetic radiation with ITO is considered in the framework of the Drude model. The simulated spectra are in good agreement with the experimental ones. New non-destructive methods for determining the ITO film parameters (sheet resistivity, thickness, electron concentration and mobility) have been developed. They are based on a fitting procedure for reflectivity and/or transmittance spectra. Full article

Wireless power transfer (WPT) technology offers a convenient, efficient, and environmentally robust power supply solution for rack-and-pinion modules. For WPT systems in such modules where the transmitter coil is a long rail, increasing the transmitter coil turns to enhance mutual inductance leads to issues like high cost, low efficiency, and installation difficulties. This paper introduces a relay resonator to strengthen system coupling and proposes a three-coil design scheme employing a single-turn long rail as the transmitter coil. The proposed all-detuned LCC-S-S topology exhibits constant output voltage (CV) and zero phase angle (ZPA) input characteristics while accounting for all cross-mutual inductances and coil resistances. The frequency detuning level of the relay resonator critically governs the system’s power transfer efficiency and directly determines the operational mode of the rectifier—either continuous conduction mode (CCM) or discontinuous conduction mode (DCM). To maximize system efficiency, the optimal detuning frequency of the relay coil is selected under CCM operation. Through optimized design of the three-coil parameters, the final prototype achieves an output power of 106.743 W and an efficiency of 90.865% when integrated with a 1200 mm single-turn long-rail transmitter coil. Full article

In loop-powered 4–20 mA transmitter systems, sensors like temperature, pressure, flow, and gas sensors are chosen based on specific application requirements. These systems are widely adopted in high-precision measurement scenarios, including industrial automation, process control, and environmental monitoring. The transmitter requires a high-performance analog front end (AFE) for precise amplification and signal conditioning. This paper presents a low-noise instrumentation amplifier (IA) for high-precision transmitter front ends, featuring a Successive Approximation Register (SAR)-assisted offset calibration architecture. The proposed structure integrates a chopper current-feedback instrumentation amplifier (CFIA) with an automatic offset calibration loop (AOCL), significantly suppressing internal offset errors and enabling high-accuracy signal acquisition under stringent power and environmental temperature constraints. The designed amplifier provides four selectable gain settings, covering a range from ×32 to ×256. Fabricated in a 0.18 μm CMOS process, the CFIA operates at a 1.8 V supply voltage, consumes a static current of 182 μA, and achieves an input-referred noise as low as 20.28 nV/√Hz at 1 kHz, with a common-mode rejection ratio (CMRR) up to 122 dB and a power-supply rejection ratio (PSRR) up to 117 dB. Experimental results demonstrate that the proposed amplifier exhibits excellent performance in terms of input-referred noise, offset voltage, PSRR, and CMRR, making it well-suited for front-end detection in field instruments that require direct interfacing with measured media. Full article

The online rapid classification of multi-cultivar watermelon, including seedless and seeded types, has far-reaching significance for enhancing quality control in the watermelon industry. However, interference in one-dimensional spectra affects the high-accuracy classification of multi-cultivar watermelons with similar appearances. This study proposed an innovative method integrating Gramian Angular Field (GAF), feature fusion, and Squeeze-and-Excitation (SE)-guided convolutional neural networks (CNN) based on VIS-NIR transmittance spectroscopy. First, one-dimensional spectra of 163 seedless and 160 seeded watermelons were converted into two-dimensional Gramian Angular Summation Field (GASF) and Gramian Angular Difference Field (GADF) images. Subsequently, a dual-input CNN architecture was designed to fuse discriminative features from both GASF and GADF images. Feature visualization of high-weight channels of the input images in convolutional layer revealed distinct spectral features between seedless and seeded watermelons. With the fusion of distinguishing feature information, the developed CNN model achieved a classification accuracy of 95.1% on the prediction set, outperforming traditional models based on one-dimensional spectra. Remarkably, wavelength optimization through competitive adaptive reweighted sampling (CARS) reduced GAF image generation time to 55.19% of full-wavelength processing, while improving classification accuracy to 96.3%. A better generalization of the model was demonstrated using 17 seedless and 20 seeded watermelons from other origins, with a classification accuracy of 91.9%. These findings substantiated that GAF-enhanced feature fusion CNN can significantly improve the classification accuracy of multi-cultivar watermelons, casting innovative light on fruit quality based on VIS-NIR transmittance spectroscopy. Full article

The Internet of Things (IoT) has become an integral part of today’s smart and digitally connected world. IoT devices and technologies now connect almost every aspect of daily life, generating, storing, and analysing vast amounts of data. One important use of IoT is in utility management, where essential services such as water are supplied through IoT-enabled infrastructure to ensure fair, efficient, and sustainable delivery. The large volumes of data produced by water distribution networks must be safeguarded against manipulation, theft, and other malicious activities. Incidents such as the Queensland user data breach (2020–21), the Oldsmar water treatment plant attack (2021), and the Texas water system overflow (2024) show that attacks on water treatment plants, distribution networks, and supply infrastructure are common in Australia and worldwide, often due to inadequate security measures and limited technical resources. Lightweight cryptographic algorithms are particularly valuable in this context, as they are well-suited for resource-constrained hardware commonly used in IoT systems. This study focuses on the in-house developed ChaosFortress lightweight cryptographic algorithm, comparing its performance with other widely used lightweight cryptographic algorithms. The evaluation and comparative testing used an Arduino and a LoRa-based transmitter/receiver pair, along with the NIST Statistical Test Suite (STS). These tests assessed the performance of ChaosFortress against popular lightweight cryptographic algorithms, including ACORN, Ascon, ChaChaPoly, Speck, tinyAES, and tinyECC. ChaosFortress was equal in performance to the other algorithms in overall memory management but outperformed five of the six in execution speed. ChaosFortress achieved the quickest transmission time and topped the NIST STS results, highlighting its strong suitability for IoT applications. Full article

The present reported work deals with the preparation of an energy-efficient smart window based on liquid crystal (LC) using a polymer-dispersed liquid crystal (PDLC) technique. The smart window was prepared using an LC–polymer composite by mixing photopolymer NOA-71 into nematic liquid crystal (NLC) 4-cyano-4’-pentylbiphenyl (5CB). The liquid crystal cell was prepared, the LC–polymer composite was filled inside the cell, and voltage was applied after the exposure of ultraviolet (UV) light. Textural analysis was carried out, and microscope images were taken out with the variation in voltage. Optical measurements were also performed for the smart window based on the PDLC system. Threshold voltage and saturation voltages were measured to carry out the operating voltage analysis. Transmittance was measured as a function of wavelength at different voltages. An absorbance study was also performed, varying the voltage and wavelength. The change in the power of the laser beam passing through the prepared smart window as a function of voltage was also investigated. The working of a prepared smart window using liquid crystal and a photopolymer composite is also demonstrated in opaque and transparent states in the absence and presence of voltage. The output of the present investigation into a PDLC-based smart window can be useful in the applications of adaptive or light shutter devices and in aerospace technology, as it shows the dual nature of opaque and transparent states in the absence and presence of electric field. Full article

Smart windows based on liquid crystal (LC) have made significant advancements over the past decade. As critical mediators of outdoor light entering indoor spaces, these windows can dynamically and rapidly adjust their transmittance to adapt to changing environmental conditions, thereby enhancing living comfort. To further improve device performance, reduce energy consumption, and ensure greater safety for everyday use, scientists have recently focused on reducing driving voltage and enhancing contrast ratio, achieving notable progress in these areas. This article provides a concise overview of the fundamental principles and major applications of LC smart windows. It systematically reviews recent advancements over the past two years in improving these two key optical properties for variable transmittance LC smart windows, both internally and externally, and highlights the remaining challenges alongside potential future directions for development. Full article