Institute of Radiophysics and Electronics

The effect of substrate temperature and laser wavelength on the laser deposition of CdTe thin films has been studied. CdTe thin films synthesized on glass substrates have been studied using X-ray spectral microanalysis, X-ray diffraction and scanning electron microscopy. It has been shown that the ratio of elements in the CdTe thin films depends on both the substrate temperature and the laser wavelength. Specific features of the crystalline structure, phase composition and structural parameters of the synthesized CdTe films depending on the deposition process conditions (substrate temperature 100–400 °С, laser wavelength 600–1200 nm) have been revealed. Specifically, CdTe thin films deposited using laser radiation of wavelengths of 600 and 1200 nm have a cubic crystalline structure, while CdTe films obtained at a laser wavelength of 1064 nm have either a hexagonal structure or are a mixture of cubic and hexagonal phases, depending on the substrate temperature. At a low substrate temperature (100 °C) the films crystallize to a hexagonal structure, whereas at higher temperatures (200, 300 and 400 °C) the films are a polycrystalline mixture of cubic and hexagonal CdTe phases, growing predominantly along the [111]C direction. It has been shown that CdTe thin films on glass substrates have similar morphologies but different thicknesses, regardless of deposition conditions.

A compact and efficient rectenna operating in the 2.4 - 2.5 GHz Industrial, Scientific and Medical (ISM) band is proposed for RF energy harvesting applications. The receiving antenna is a slotted rectangular microstrip patch with an inset feed and a defected ground structure (DGS), designed on a lowcost FR4 substrate of 1.6 mm thickness. The antenna exhibits a compact footprint of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$24 \text{mm} \times 21 \text{mm}\left(0.20 \lambda_{0} \times 0.17 \lambda_{0}\right)$</tex> and achieves resonance at 2.47 GHz with a measured gain of 1.49 dBi and return loss below - 10 dB. For rectification, a voltagedoubler topology is implemented using an SMS7621 Schottky diode with an LC matching network optimized in ADS. The simulated rectifier circuit achieves a peak power conversion efficiency (PCE) of 60.18 % with a load resistance of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${2.7 \mathrm{k} {\Omega}}$</tex> and an input signal power of 5 dBm at 2.47 GHz. Comparative performance analysis with existing works confirms the superiority of the proposed rectenna in terms of compactness and efficiency, making it a suitable candidate for low-power biomedical and IoT applications. The antenna design is experimentally validated, while rectifier testing is deferred due to component unavailability.

We present a hybrid ML framework combining regression and classification for QoT prediction in coherent optical networks. Trained on realistic data, it enables accurate estimation and detection of inoperability causes across diverse topologies and configurations.

Emergency modes of network operation that occur during short circuits and due to improper operation of relay protection and automation devices can be the cause of the occurrence and development of ferroresonance processes, including in power transformers and reactors. When a ferroresonance occurs, the vibration of the magnetic core of the transformer or reactor and the harmonic distortions of the mains voltage and current increase instantaneously compared to the duration of the heating process of electrical equipment above the permissible temperature. Harmonic distortion of voltage and current can be caused by the nonlinear nature of the consumer’s load. Therefore, a rational way to detect the ferroresonance process in power transformers and reactors is to detect it through a change in the vibration level of the magnetic core. The article discusses a device for detecting the ferroresonance process in power transformers and reactors by measuring the vibration level of a magnetic core. A design of a device for detecting a ferroresonance process at high magnetic field strengths and elevated temperatures is proposed. The adopted technical solutions make it possible to reduce noise and interference in the information channel of the device by shielding the useful signal using thin-film metallization, reduce the heating of the sensitive element of the device by Foucault currents, and reduce remagnetization by eliminating massive metal assembly units and performing an inertial mass in the form of a package of metal sheets glued together with high electrical resistivity, using a piezoelectric plate and a magnetic platform made of materials with a high Curie temperature.

Doped (Ag + Fe) zinc targets were obtained: Zn/Ag/Fe (Zn96, Ag2, Fe 2%; Zn94, Ag2, Fe 4%; and Zn90, Ag2, Fe 8%). ZnO/Ag/Fe films with n- and p- type conductivity were obtained on glass substrates at room temperature using the method of DC-magnetron sputtering of Zn/Ag/Fe targets in a gas mixture of Ar : O2, in a vacuum of about 0.666 Pa. The structural, electrophysical, optical, and morphological characteristics of the obtained films were studied. The research was conducted using X-ray diffraction (XRD), atomic force microscopy, UV/VIS spectroscopy, and Hall measurements. The X-ray diffraction patterns of the ZnO/Ag/Fe films with n- and p-type conductivity showed characteristic reflections of interplanar distances on glass substrates along the crystallographic directions 100, 002, and 101. The transmittance of these films is about 85–95% in the wavelength range of 400–930 nm. The ZnO/Ag/Fe films with p-type conductivity have a concentration of free carriers on the order of 1018 cm–3. The ZnO/Ag/Fe films obtained at room temperature of the substrate can be used in the development of functional optoelectronic devices.

The results of the analysis of the energy consumption of the transmitting active phased antenna array (APAA) of a spacecraft of the low-orbit communication system (with broadband access or with direct access to cellular subscribers) have been presented. It has been shown that in order to reduce energy consumption by switching on (off) the emitters, depending on the beam deflection angle from the nadir, it is possible to achieve a significant reduction in the heat release of the spacecraft’s APAA. But this solution is feasible only if the APAA forms one “jumping” beam.

Single phase and highly transparent ZnO:Tb films with a Tb concentration from 0.41 at% up to 0.78 аt% were formed on glass and silicon substrates by sol-gel deposition. The influence of ultraviolet radiation on the structural and photoelectric characteristics of n-ZnO:Tb/n-Si structures has been studied. The appearance of a photoelectric effect under the influence of a bias voltage and UV radiation (405 and 278 nm) was established, with an increase in photo effect when irradiated with shorter wavelength UV radiation (278 nm). It was shown that the concentration of the Tb3+ dopant is the determining factor for increasing the UV photosensitivity of the structures. The experimentally established selective sensitivity of n-ZnO:Tb/n-Si structures to UV radiation with a wavelength of less than 405 nm demonstrates the possibility of their use in UV radiation detectors or sun-blind detectors.

In this work, Alamouti coded asymmetrically clipped optical orthogonal frequency division multiplexing technique is investigated in a multimode fiber (MMF) transmission. Analysis is carried out on asymmetrically clipped O-OFDM and MMF models. The proposed technique finds significant improvement of bit error rate and received signal to noise ratio compared to conventional optical OFDM technique in MMF transmission.