The introduction of LED light sources, which has led to significant energy savings, requires energy-saving power sources. The main attention of LED driver developers is paid to the search for pulsed sources, the work of which is based on the results of studies of dynamic processes occurring in the LED structure itself. To study the influence of current pulses on the electrophysical parameters of LEDs, the small perturbation method was used in this work. The results of measurements of the differential resistance and capacitance of LEDs for various stationary states are presented. They are the main quantities that control transient processes in electrical circuits and play an important role in the development of pulsed power sources. It is shown that the increase and decrease of the injection current and the light flux are well described by an exponential dependence, and the time constant of the kinetics of the light flux is much greater than the current, which is associated with the lifetime of the donor-acceptor pairs. It was established that at a forward bias voltage of ≥ 2.65 V and a pulse frequency of 1 kHz, the reactive component associated with the capacitance of the LED disappears in the relaxation current, which makes it an active energy consumer. Based on the results of the study of the kinetics of the light flux, the maximum pulse frequency of the LED driver was determined to be 100 kHz.
In this work, copper-based spinel oxides with the general formula CuCr2 – xCoxO4 (x = 0 and 0.6) were synthesized via a facile combustion method to investigate the effect of cobalt incorporation on their structural, morphological, optical, and photocatalytic properties. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS), and UV–visible diffuse reflectance spectroscopy (UV–DRS). XRD confirmed the formation of well-crystallized single-phase spinel structures for both CuCr2O4 and CuCr1.4 Co0.6O4, with nanoscale crystallite sizes, indicating that cobalt substitution preserved the spinel framework. SEM images revealed agglomerated nanosized grains with nearly spherical morphology, while EDS confirmed the homogeneous distribution of Cu, Cr, O, and Co. UV–DRS analysis showed a decrease in the optical band gap from 2.81 eV (CuCr2O4) to 2.65 eV (CuCr1.4 Co0.6O4), suggesting enhanced light absorption. The photocatalytic performance of the samples was evaluated under UV irradiation toward the degradation of methylene blue (MB) and 4-nitrophenol (4-NP). The doped CuCr1.4Co0.6O4 exhibited markedly superior photocatalytic activity, achieving complete MB degradation and 72.9 % conversion of 4-NP within 15 min, outperforming the undoped CuCr2O4. This enhancement is attributed to improved charge separation efficiency, reduced band gap energy, and smaller crystallite size resulting from cobalt incorporation.
Cadmium sulfide (CdS) nanoparticles doped with copper (Cd1 – xCuxS) are synthesized using a chemical co-precipitation method to investigate the effect of Cu incorporation on the structural and optical properties, with particular emphasis on bandgap modulation. X-ray diffraction (XRD) analysis confirms the formation of a single-phase hexagonal CdS crystal structure without any detectable secondary phases, indicating the successful incorporation of Cu into the host lattice. A gradual reduction in crystallite size from 3.73 nm to 2.89 nm is observed with increasing Cu concentration. A slight decrease in the lattice parameters and unit cell volume further supports the substitution of Cd2+ ions by the relatively smaller Cu2+ ions.Field Emission Scanning Electron Microscopy (FESEM) reveals nanostructured particles with moderate agglomeration, while Cu incorporation improves particle size uniformity. Energy Dispersive X-ray Analysis (EDAX) confirms the presence of Cd, S, and Cu elements and shows no evidence of impurity phases, verifying the successful incorporation of Cu into the CdS lattice. The optical properties are examined using UV-Visible spectroscopy, which shows a progressive blue shift in the absorption edge with increasing Cu content. The optical bandgap increases from 2.08 eV for pristine CdS to 2.15 eV and 2.16 eV for the Cu-doped compositions. This bandgap widening is attributed to the combined influence of quantum confinement arising from the reduced crystallite size and lattice distortion associated with Cu substitution. These findings demonstrate that Cu doping provides an effective approach for tuning the structural and optical properties of CdS nanoparticles, highlighting their potential for optoelectronic and photocatalytic applications.
This paper presents a frequency-reconfigurable microstrip patch antenna with a modified defect in the ground plane. Frequency reconfiguration is achieved using two PIN diodes embedded in the ground plane at the appropriate locations. A DC biasing network was incorporated to supply the PIN diodes. The effect of the DC biasing network on the performance of the resonance frequency of the antenna is also presented. By altering the states of the PIN diodes, the antenna can operate in three different modes with resonance in four different frequency bands at 2.42 GHz (Wi-Fi), 3.62 GHz (n-78), 5.55 GHz (5G Wi-Fi), and 6.2 GHz (n-96). The proposed antenna has a small size of 16 17 mm2 and is fabricated on a low-cost FR-4 substrate. A strong correlation between the simulation and measurement results of the reflection coefficient with |S11| ≤ – 10 dB was achieved across all three operating modes of the proposed design, confirming its validity. The miniature size of the antenna makes it useful for modern wireless equipment, where space is the main issue.
This work presents a compact snow-flex structured MIMO radiator for wireless sensor network applications. The designed structure is simulated on an FR-4 dielectric substrate material with an overall size of 80 mm 45 mm, making it suitable for compact wireless devices. It operates at a resonant frequency of 2.48 GHz covering 2.46 to 2.51 GHz, which supports the ISM band for WSN communication. The simulated S11 of − 32.90 dB confirms excellent impedance matching. The isolation among MIMO system is − 26.64 dB (S21), demonstrating effective suppression of mutual coupling. A spacing of 3 mm is maintained between two radiator elements to further reduce electromagnetic interference by offering improved isolation. The key MIMO performance metrics as Envelope type Correlation Coefficient (ECC), Diversity related Gain (DG), Channel related Capacity Loss (CCL) and Total Active type Reflection Coefficient (TARC) are thoroughly calculated and discussed. All MIMO parameters satisfy the standard requirements for reliable wireless communication systems. The results indicate strong diversity performance, low correlation, and high channel capacity. Hence, designed MIMO radiator is a promising candidate for compact and efficient WSN and ISM band wireless applications.
