Search Results (985)

We present a tunable diode-laser absorption spectroscopy (TDLAS) system operating at 1.5711 µm for CO₂ gas concentration measurements. The system can operate in either a traditional direct-mode (dTDLAS) sawtooth wavelength scan or a recently demonstrated wavelength-toggled single laser differential-absorption lidar (WTSL-DIAL) mode using precompensated current pulses. The use of such precompensated pulses offsets the slow thermal constants of the diode laser, leading to fast toggling between ON and OFF-resonance wavelengths. A short measurement time is indeed pivotal for atmospheric sensing, where ambient factors, such as turbulence or mechanical vibrations, would otherwise deteriorate sensitivity, precision and accuracy. Having a system able to operate in both modes allows us to benchmark the novel experimental procedure against the well-established dTDLAS method. The theory behind the new WTSL-DIAL method is also expanded to include the periodicity of the current modulation, fundamental for the calculation of the OFF-resonance wavelength. A two-detector scheme is chosen to suppress the influence of laser intensity fluctuations in time (1/f noise), and its performance is eventually benchmarked against a one-detector approach. The main difference between dTDLAS and WTSL-DIAL, in terms of signal processing, lies in the fact that while the former requires time-consuming data processing, which limits the maximum update rate of the instrument, the latter allows for computationally simpler and faster concentration readings. To compare other performance metrics, the update rate was kept at 2 kHz for both methods. To analyze the dTDLAS data, a four-parameter Lorentzian fit was performed, where the fitting function comprised the six main neighboring absorption lines centered around 1.5711 µm. Similarly, the spectral overlap between the same lines was considered when analyzing the WTSL-DIAL data in real time. Our investigation shows that, for the studied time intervals, the WTSL-DIAL approach is 3.65 ± 0.04 times more precise; however, the dTDLAS-derived CO₂ concentration measurements are less subject to systematic errors, in particular pressure-induced ones. The experimental results are accompanied by a thorough explanation and discussion of the models used, as well as their advantages and limitations. Full article

This study presents a simulation-based design of a silicon single-photon avalanche diode (SPAD) optimized for picosecond-resolved photon detection. Utilizing COMSOL Multiphysics, we implement a dead-space-aware impact ionization model to accurately capture history-dependent avalanche behavior. A guard ring structure and tailored doping profiles are introduced to improve electric field confinement and suppress edge breakdown. Simulation results show that the optimized device achieves a peak electric field of 7 × 10⁷ V/m, a stable gain slope of −0.414, and consistent avalanche triggering across bias voltages. Transient analysis further confirms sub-20 ps response time under −6.5 V bias, validated by a full-width at half-maximum (FWHM) of ~17.8 ps. Compared to conventional structures without guard rings, the proposed design exhibits enhanced breakdown localization, reduced gain sensitivity, and improved timing response. These results highlight the potential of the proposed SPAD for integration into next-generation quantum imaging, time-of-flight LiDAR, and high-speed optical communication systems. Full article

The energy deposition process for the main components of SIC Schottky diodes is simulated based on Geant4. Particle bombardment results were simulated under different angles, target materials and doping concentrations on the same target material for different light particles and heavy ions, and then the Linear Energy Transfer of SiC materials and external conditions that affect LET are obtained. The results show that the LET value of protons exhibits significant oscillations at low energy incidence, gradually decreasing exponentially after 10⁻¹ MeV. Alpha particles have a LET peak near 1 MeV, while beta particles show an exponential decrease. The LET values at low energy levels increase exponentially, while at high energy levels, the LET values show a similar linear relationship with energy. For different incident angles, the average LET value of protons in the low-level region gradually increases as the incident angle increases. The average LET value of protons in the remaining energy ranges is less affected by angle; the incident angle has no significant effect on the LET distribution of alpha particles within the full spectrum range. The results provide important references for understanding the energy deposition process and LET distribution of silicon carbide devices under single-particle interaction. Full article

With the rapid growth of unmanned aerial vehicles (UAVs) and IoT users, spectrum resources are becoming increasingly scarce, making cognitive radio (CR) technology a key approach to improving spectrum utilization. However, traditional antennas are difficult to meet the lightweight, compact, and low-drag requirements of small UAVs due to spatial constraints. This paper proposes a tri-mode frequency reconfigurable flexible antenna that can be conformally integrated onto UAV wing arms to enable CR dynamic frequency communication. The antenna uses a polyimide (PI) substrate and has compact dimensions of 31.4 × 58 × 0.05 mm³. A microstrip line-based frequency-selective network is designed, incorporating PIN and varactor diodes to realize three operation modes, dual-band (2.25~3.55 GHz, 5.6~6.75 GHz), single-band (3.35~5.3 GHz), and continuous tuning (4.3~6.1 GHz), covering WLAN, WiMAX, and 5G NR bands. Test results show that the antenna maintains stable performance under conformal conditions, with frequency shifts less than 4%, gain (3.65~4.77 dBi), and radiation efficiency between 67.2% and 82.9%. The tuning ratio reaches 38.8% in the continuous mode. This design offers a new solution for CR communication in compact UAV platforms and shows promising application potential. Full article

This work proposes a highly sensitive optical sensor system that compensates for joint fragility by combining a flexible organic light-emitting diode (FOLED) with a stretchable light guide, and its performance was systematically evaluated. The developed sensor, leveraging the high flexibility of OLEDs, was capable of detecting mechanical deformations in various positions and forms in real time and could distinguish up to seven independent signals without electromagnetic interference. Under repeated 50% tensile strain, the device sustained 130,000 cycles, and during the 75° bending test, all three configurations—single line, serpentine, and serpentine with bump—exhibited stable performance for a minimum of 80,000 cycles. The sensor system developed in this study holds promise for future applications in wearable electronics and robotics. Full article

This study presents a reconfigurable frequency-selective surface (R-FSS) designed to dynamically switch between WLAN, WiMAX, and sub-6 GHz band frequencies. The electronic switching mechanism of this R-FSS is controlled in real-time using PIN-diodes. Depending on the activation state of these diodes, the structure operates in three distinct modes. Among the three modes, one exhibits polarization-stable wideband suppression, whereas the other two demonstrate polarization selectivity by interchanging between the dual-narrow and single-wide stopband regimes under orthogonal polarizations. The design is described with an equivalent-circuit model, corroborated by full-wave electromagnetic simulations, and validated through measurements of a fabricated prototype. This reconfigurability allows the proposed structure to operate across WLAN, sub-6 GHz, and WiMAX frequency ranges either with two narrow stopbands or with a single-wide stopband, while providing polarization selectivity for frequency-selective applications. Full article

The nitrogen-vacancy (NV) center magnetic sensor, leveraging nitrogen-vacancy quantum effects, enables high-sensitivity magnetic field detection via optically detected magnetic resonance (ODMR). However, conventional single-point integrated devices suffer from limitations such as inefficient regional magnetic field detection and challenges in discerning the directional variations of dynamic magnetic fields. To address these issues, this study proposes an array- based architecture that innovatively substitutes the conventional 532 nm laser with quantum-dot light-emitting diodes (QLEDs). Capitalizing on the advantages of QLEDs—including compatibility with micro/nano-fabrication processes, wavelength tunability, and high luminance—a 2 × 2 monolithically integrated magnetometer array was developed. Each sensor unit achieves a magnetic sensitivity of below 26 nT·Hz^−1/2 and a measurable range of ±120 μT within the 1–10 Hz effective bandwidth. Experimental validation confirms the array’s ability to simultaneously resolve multi-regional magnetic fields and track dynamic field orientations while maintaining exceptional device uniformity. This advancement establishes a scalable framework for the design of large-scale magnetic sensing arrays, demonstrating significant potential for applications requiring spatially resolved and directionally sensitive magnetometry. Full article

A reconfigurable microwave absorber based on double-layer metasurface is proposed for wide microwave band applications spanning 3 to 14 GHz. The absorber consists of two layers with two-dimensional array of four-semi-circular and square-ring metasurface patches loaded impedance devices, two spacers composed of honeycomb materials, and a bottom copper substrate. In order to break through the limitation of single-layer absorbers at finite resonant frequencies, a special double-layered metasurface structure is adopted. The layer I of metasurface is designed with two resonant peaks near the X band and transmission performance in the C band. Simultaneously, the layer II of metasurface is designed with a resonant peak near the C band and reflection performance in the X band. To achieve a reconfigurable effect, impedance adjustable device, such as PIN diodes, are connected between patterned metasurface cells of layer I. The simulation results revealed that the double-layer metasurface absorber can not only achieve broadband absorption effect, with the reflection value below −10 dB from 3.1 to 14.2 GHz, but also adjust the electromagnetic absorption rate, with the reflection value below −20 dB covers a bandwidth of 6.6–9 GHz. The good agreement between simulation and measurement validates the proposed absorber. Full article

Sol–gel-processed zinc oxide (ZnO) and magnesium-doped zinc oxide (ZnMgO) are widely used in quantum dot light-emitting diodes (QLEDs) due to their excellent charge transport properties, ease of fabrication, and tunable film characteristics. In particular, the ZnMgO/ZnO bilayer structure has attracted considerable attention for its dual functionality: defect passivation by ZnMgO and efficient charge transport by ZnO. However, while the effects of resistive switching (RS) in individual ZnO and ZnMgO layers on the aging behavior of QLEDs have been studied, the RS characteristics of sol–gel-processed ZnMgO/ZnO bilayers remain largely unexplored. In this study, we systematically analyzed RS properties of an indium tin oxide (ITO)/ZnMgO/ZnO/aluminum (Al) device, demonstrating superior performance compared to devices with single layers of either ZnMgO or ZnO. We also investigated the shelf-aging characteristics of RS devices with single and bilayer structures, finding that the bilayer structure exhibited the least variation over time, thereby confirming its enhanced uniformity and reliability. Furthermore, based on basic current–voltage measurements, we estimated accuracy variations in MNIST pattern recognition using a two-layer perceptron model. These results not only identify a promising RS device architecture based on the sol–gel process but also offer valuable insights into the aging behavior of QLEDs incorporating ZnMgO/ZnO bilayers, ITO, and Al electrodes. Full article

The wide application of light emitting diodes (LEDs) in lighting systems has necessitated the inclusion of spectral tunability by using multi-color LED chips. Since the lighting requirement depends on the specific application, it is very important to have flexibility in terms of the driving conditions. While many applications use single or rather white color, some recent applications require multi-spectral lighting systems especially for agricultural or human-medical treatment applications. These systems are underexplored and pose specific challenges. In this paper, a mixture of red, green, blue, white (RGB-W) LED chips was used to develop a compact light engine specifically for agricultural applications. A computational study was performed to understand the optical distribution. Later, attention was turned into development of prototype light engines followed by experimental validation for both the thermal and optical characteristics. Each LED string was driven separately at different current levels enabling an option for obtaining an infinite number of colors for numerous applications. Each LED string on the developed light engine was driven at 300 mA, 500 mA, 700 mA, and 900 mA current levels, and the optical and thermal parameters were recorded simultaneously. A set of computational models and an experimental study were performed to understand the optical and thermal characteristics simultaneously. Full article

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

In this paper, we present an extremely compact eleven-state microwave filter with four concentric split-ring resonators (SRRs). Reconfigurability is achieved by switching off either single or multiple SRRs, thereby obtaining different triple-band, dual-band, and single-band configurations from the initial quad-band topology. Switches are placed on the vertical branches of SRRs in order to minimize the additional insertion loss. As switching elements, we first use traditional RF switches—PIN diodes—and then examine the integration of non-volatile RF switches—memristors—into filter design. Memristors’ ability to remember previous electrical states makes them a main building block for designing circuits that are both energy-efficient and adaptive, opening a new era in electronics and artificial intelligence. As RF memristors are not commercially available, PIN diodes are used for experimental filter verification. Afterwards, we compare the filter characteristics realized with PIN diodes and memristors to present capabilities of memristor technology. Memristors require no bias, and their parasitic effects are modeled with low resistance for the ON state and low capacitance for the OFF state. Measured performances of all obtained configurations are in good agreement with the simulations. The filter footprint area is 26 mm × 29 mm on DiClad substrate. Full article

Periodontal disease is a prevalent condition in companion animals. It is crucial to prevent the plaque and bacteria on tooth surfaces to avoid gingivitis and the more harmful periodontitis. The aim of the present study was to assess the impact of MLS laser treatment on the bacterial load by analyzing the gingival swabs of a total of 16 owned dogs with no history of dental disease that were selected from a cohort of patients admitted for plaque removal and dental hygiene procedures. Following each dental hygiene session, each dog received a single MLS laser therapy treatment (808–905 nm diode laser, frequency 36 Hz, and fluence 0.16 J/cm²). Swabs were collected from the two upper premolars before and after the laser treatment. These were submitted for mesophilic bacteria counts, and microbiological analysis was conducted on 10 positive cultures to evaluate the changes in the oral bacterial microbiota. MLS laser therapy statistically significantly reduced the mesophilic bacteria count by 1 log, with higher pre-laser treatment counts (n = 0.44; 5.77 ± 0.21 95%CI) in comparison to post-laser treatment counts (n = 0.73; 4.80 ± 0.346 95%CI). The MLS laser therapy was found to reduce the bacterial load in 80% of the subjects (p < 0.05). No significant differences pre- and post-laser treatment were observed in the bacteria species isolated from the microbiological cultures. MLS laser therapy appears to be a useful, non-invasive method for reducing the bacterial load in the treatment and prophylaxis of periodontal disease in dogs. Full article

The Planck constant is a fundamental parameter of nature that appears in the description of phenomena on a microscopic scale. Its origin is associated with an explanation of the distribution of the blackbody spectrum performed by Max Planck. This constant stands the basis for the definition of the International System of Units (SI), and, in particular, the new mass definition. This paper presents different methods for determining the Planck constant based on phenomena such as blackbody radiation, light diffraction through a single slit, the current–voltage characteristics of a light-emitting diode, the photoelectric phenomenon, and the hydrogen atom spectrum in the visible range. The Planck constant was measured using instruments in a stationary laboratory and via remote access. The influence of various factors on the accuracy of the measurements was determined, and the consistency of the obtained results with the accepted value of the Planck constant are examined and discussed. Full article

This study proposes an improved Black-Winged Kite Algorithm (SRQ-BKA) for accurate parameter identification of the photovoltaic (PV) double diode model (DDM). The proposed method integrates three key mechanisms: specular reflection learning (SRL) to improve initial population diversity, preventing premature convergence and enabling a more comprehensive exploration of the solution space for optimal parameters; soft rime search (SRS) to balance global exploration and local exploitation, ensuring efficient identification by dynamically adjusting the search focus; and quadratic interpolation (QI) to accelerate convergence by fine-tuning the search toward optimal parameters, enhancing accuracy and speeding up the identification process. The root mean square error (RMSE) is employed as the objective function to minimize the error between the measured and predicted I-V characteristics of the PV module. Experimental results demonstrate that the SRQ-BKA outperforms other algorithms, achieving a minimum RMSE of 0.00262 A for the DDM and exhibiting strong stability, as evidenced by an average RMSE of 0.00278 A across 1000 runs. The method also demonstrates excellent parameter identification accuracy for both the single diode model (SDM) and triple diode model (TDM), further validating its robustness and practical applicability. Full article