Radiotekhnika

Optimization of digital signature calculation and verification operations for the FIPS 205 standard. Part 3

I.D. Gorbenko, Ye.G. Kachko, M.V. Yesina, Ya.A. Derevianko — Thu, 30 Apr 2026 00:00:00 +0300

The FIPS205 standard is fully hash-based signature algorithm: its security does not rely on numerical problems (factorization, discrete logarithms) or algebraic structures (lattices, codes), but only on the standard properties of cryptographic hash functions, in particular keyed hashes and PRF constructions based on these hash functions. The main mathematical constructions of the standard are Merkle trees (hash trees), hypertrees (tree-of-trees constructions), and combinatorial multi-signatures that sign a set of small indices.

The advantages of building a digital signature scheme based on such components are post-quantum resistance based on conservative assumptions, statelessness, and small key sizes. However, computational complexity remains a weakness of the FIPS205 algorithm and the respective reference algorithm SPHINCS+. This is due to the mathematics used. Signature generation involves a large number of hash computations (FORS, dozens of WOTS chains, many hashes for trees). This process is slower than the mathematics of most signature schemes. However, as shown in previous work, this can be improved using optimization.

Previous articles have considered and proposed practical improvements in order to optimize the digital signature formation process for the FIPS 205 algorithm. Previous works have discussed the possibilities of increasing the performance of the FIPS 205 algorithm by eliminating common calculations, using a special input format for hash calculations, and parallel calculations by using threads. This work is a extension of previous works. It additionally increases the performance of algorithms for key generation, signature generation, and signature verification based on the FIPS 205 standard. The results obtained can be applied to any signature scheme similar to FIPS 205.

This paper considers the use of AVX commands for hash calculation using the example of SHA256 and SHA512 functions, as well as their use in the implementation of various algorithm schemes, namely one-time signature schemes, extended Merkle trees, hypertrees, and forests. The article compares the optimization results obtained by the authors of SPHINCS+ and this work in the context of using AVX commands. This work is of great importance, since virtually all modern processors are capable of executing AVX commands and are multi-core and multi-threaded.

The results show that by optimizing algorithms and using AVX, we got a significant speed boost for all operations. For key pair generation, we got a speed boost of 7.76–8.35 times for STORE mode and 2.5–3.93 times for FAST mode. Signature generation was accelerated by almost 10 times for STORE mode and 1.87–3.99 times for FAST mode, while signature verification was accelerated by at least 1.4 times for STORE mode and 27% for FAST mode.

The results obtained are quite promising and show that the use of parallel computing on multi-core processors significantly increases the performance of functions for WOTS, XMSS, and FORS schemes, as well as the functions that use them.

Basic aspects of the zero-knowledge concept: theoretical foundations, modern ZKP systems, and conceptual representation of zk-SNARK technology

V.I. Yesin, V.V. Vilihura — Thu, 30 Apr 2026 00:00:00 +0300

In the context of rapid and widespread digitalization of society, active implementation of new innovative technologies, and the growth of cyber threats, the issue of organizing effective cybersecurity for enterprises is becoming particularly important. To protect today's modern digital enterprise, you need a comprehensive strategy for secure access to your corporate resources anytime, anywhere, regardless of where they are located. By following Zero Trust Architecture (ZTA) principles, which call for least privilege access and continuous verification, businesses can effectively minimize their attack surface and limit potential losses from compromised accounts. However, existing access control and authentication mechanisms alone are not always sufficient to ensure complete protection of critical data, especially in scenarios where proof of access rights or actions is required without revealing content. In such cases, an effective addition to ZTA can be the use of Zero-Knowledge (ZK) concept, which allows confirming access rights or ownership (knowledge) of certain information without the need to disclose it, which significantly reduces the risks of leaks and unauthorized access. At the same time, representatives of businesses interested in the security of their systems are not yet fully aware of the advantages of this concept. The practical application of already known Zero-Knowledge Proof (ZKP) capabilities in various relevant areas that ensure security is being hampered, among other things, by a lack of awareness and insufficient theoretical training in this area among specialists responsible for security and communicating these capabilities (their potential) to the managers of relevant IT companies. In other words, there is currently a problem related to a lack of awareness about the zero-knowledge concept (its theoretical and practical significance) for making the right decision when building a security system for a corporate information system in modern conditions. This article is exactly aimed at solving this problem. The purpose of this work is to systematize the theoretical foundations and practical application of the zero-knowledge concept using simple and obvious examples in order to understand the potential of ZKP in solving problems of confidentiality/privacy and data verification. To this end, it outlined the main aspects of the zero-knowledge concept, including an analysis of the applicability of interactive and non-interactive approaches, an assessment of existing ZKP systems, and a conceptual representation of zk-SNARK technology based on the popular Groth16 scheme with mathematical justification. This contributes to a better understanding and future use of this dynamically developing and complex concept as one of the key mechanisms of modern cryptography, providing the ability to prove the correctness of calculations without disclosing the computational process or the initial data.

Uniformly robust threshold secret sharing scheme with maximum threshold and reduced complexity of share computation and secret reconstruction

A.M. Alekseychuk, M.I. Pokydko — Thu, 30 Apr 2026 00:00:00 +0300

A secret sharing scheme is a cryptographic protocol that enables a secret to be distributed among a prescribed set of participants in such a way that only certain (authorized) coalitions of participants are able to reconstruct the value of the secret by combining their components (shares of the secret). The collection of all authorized coalitions of participants is referred to as the access structure of the given secret sharing scheme. A scheme is called threshold if its access structure consists of all coalitions whose cardinality is bounded below by a fixed number, called the threshold.

This paper is devoted to the construction of a uniformly robust perfect threshold secret sharing scheme with the maximum threshold (equal to the number of participants), which is characterized by lower time complexity of share computation and secret reconstruction compared to a previously known analogous scheme. The robustness of a scheme means its unconditional security against attacks by dishonest participants who may substitute their own shares in order to distort the value of the secret during reconstruction. A secret sharing scheme is called uniformly robust if it remains secure against this attack regardless of the method used to select the set of secret keys from the collection of all elements that can potentially be distributed.

Interest in such secret sharing schemes is primarily motivated by the possibility of constructing perfect schemes for arbitrary access structures on their basis, which is acceptable for practical applications provided that each participant belongs to a not excessively large number of minimal authorized coalitions.

It is shown that the proposed secret sharing scheme is not inferior to the previously known one with respect to any efficiency metric, while significantly outperforming it in terms of the complexity of the secret sharing and reconstruction procedures. The proposed scheme is constructed on the basis of a random maximum-distance separable (MDS) code, which differs from the Reed–Solomon code underlying the construction of the previously known scheme. This feature makes it possible to reduce the computational complexity without increasing either the amount of data stored by the participants or the probability of successful share substitution by dishonest participants.

PQC CSIKE algorithm on noncyclic Edwards curves with simultaneous formation of two independent keys encapsulation

A.V. Bessalov — Thu, 30 Apr 2026 00:00:00 +0300

Using a 2-processor computer, parallel calculation of two different encapsulation keys in the original CSIKE algorithm with one public key instead of two in CSIDH is proposed. The conditions for its implementation on two classes of noncyclic Edwards curves are substantiated. The properties of quadratic and twisted supersingular Edwards curves that form quadratic ttwist pairs with order p+1≡0mod8 over the prime field Fp are considered. For every curve in these classes with parameter d, there exists an isomorphic curve with parameter d^-1. On a set of isomorphic curves, the second encapsulation key can be computed simultaneously with the first. For all isogenies of degrees 3, 5, 7, the parameters d of chains of isogenies of noncyclic supersingular Edwards curves on period T of chains of isogenies for p=839 is calculated. The simulation of the CSIKE scheme with Alice encrypting two independent keys encapsulation with Bob's public key, as well as the stage of decapsulation by Bob of these keys, is considered. The implementation of parallel computations provides almost perfect protection against side-channel attacks, because it is impossible to set the task of measuring the computation time of fragments of two different isogeny chains.

Methods for implementing post-quantum cryptography standards based on OCaml-oriented modular architecture

Y. Kotukh — Thu, 30 Apr 2026 00:00:00 +0300

The development of quantum computing introduces fundamental risks to modern cryptographic systems used for protecting network infrastructure and software platforms. Following the publication of post-quantum cryptography standards by the National Institute of Standards and Technology (NIST) in 2024, including ML-KEM (FIPS 203), ML-DSA (FIPS 204), and SLH-DSA (FIPS 205), the need for efficient software implementation of post-quantum primitives in high-assurance programming environments has emerged. This paper proposes a multilayer architecture for post-quantum cryptographic algorithm implementation using the OCaml module system and functor-based parameterization of cryptographic primitives.

The proposed architecture is based on separating the software stack into a type-safe OCaml API layer, an algebraic cryptographic logic layer, and a low-level constant-time primitive layer implemented via C interfaces. Special attention is given to the implementation of Number Theoretic Transform (NTT) operations, centered binomial distribution (CBD) sampling for ML-KEM and ML-DSA.

To ensure implementation quality, NIST KAT vectors were integrated, along with side-channel statistical analysis tools including dudect, Valgrind, and TIMECOP.

The proposed architecture aims to minimize the trusted computing base, isolate cryptographically sensitive arithmetic operations, and enable future formal verification via coq-of-ocaml. The approach establishes the foundation for an OCaml-oriented post-quantum cryptography ecosystem and can be used for developing high-assurance cryptographic software.

Research into electromagnetic compatibility in mobile communication networks with shared use of radio frequency spectrum

Y.Y. Kolyadenko, V.O. Badeyev — Thu, 30 Apr 2026 00:00:00 +0300

With the development of the IMT (International Mobile Telecommunications) family of technologies, methods for assessing the conditions of their electromagnetic compatibility with each other and with other radio electronic means (REM) are also being improved, which should mainly take into account the specific features of each technology. The use of radio frequencies according to the principle of technological neutrality requires the determination of some generalized criterion for EMC. In foreign practice, as a criterion in the WAPECS project, it was proposed to use the edge mask of the BEM block, which is the “regulatory” spectral mask in the spectrum block allocated to the operator. Refarming of the radio frequency spectrum requires the development of conditions for the joint functioning of networks of several standards in adjacent frequency bands within the same range. It is also necessary to consider options for sharing DC / DB (Dual Carrier / Dual Band) carrier frequencies when aggregating in UMTS.

The article analyzes the EMC during refarming using the criterion of energy equivalence. The analysis allows us to determine the conditions for maintaining the energy equivalence of the 5G LTE network in the frequency band of the corresponding width planned to create the LTE network during refarming, namely: calculate the allowable number of 5G transmitters at each LTE site when planning sectors and MIMO configurations on them; еstimate (if necessary) the limitation of the radiation power of the 5G transmitters.

The analysis results allow us to assess and plan the possible architecture of the 5G radio network being created in specific situations. For example, if for some conditions the allowable number of transmitters at the 5G site is calculated as insufficient, it can be increased by some reduction (limitation) of the radiation power of these transmitters, while maintaining energy equivalence.

Development and configuration of a physical model of the LTE system based on the use of SDR technology

Yu.S. Zhuga, V.A. Loshakov, M.V. Moskalets, S.O. Saburova — Thu, 30 Apr 2026 00:00:00 +0300

Development of a hardware and software stand based on the LimeSDR radio platform for the study of mobile communication systems, in particular LTE, is being considered, as well as the possibility of using it to work with other systems, such as 5G, radio monitoring, satellite communications and television. At the same time, most of the work of the SDR radio platform performed on a personal computer, which provides the necessary software configuration of the radio system. The stand was created based on the Department’s and external experience in using SDR technology when developing physical models of base stations for next-generation mobile communication networks, digital terrestrial and satellite television. For educational purposes, the stand can be utilized both autonomously and remotely using, for example, a departmental server. Given the Russian military aggression, which seriously affected Ukrainian education, creating threats to the life and health of participants in the educational process and causing the destruction of educational infrastructure, the possibility of creating remote laboratories became a response to these challenges, allowing continuing training under conditions of restrictions. It is shown that for educational and research purposes in the field of telecommunications, the use of the LimeSDR platform is promising due to its high technical characteristics, support for MIMO technology and relatively low price. The flexibility of such a platform allows you to simulate various scenarios of mobile network operation. This opens up wide opportunities in laboratory conditions or remotely to study and test new technologies and algorithms, which makes such a stand a useful tool in educational institutions and research institutions. A step-by-step instruction has been developed for creating a physical model of an LTE BS based on LimeSDR and a computer with the Ubuntu OS. A step-by-step instruction is provided for installing the necessary software, configuring it, and using it in practice. Further research may include expanding the platform's functionality through the implementation of MIMO, expanding the operating frequency range, and supporting new 5G and 6G standards.

Comparative analysis of the effectiveness of TinyML models for sensor data classification tasks on the ESP32 platform

D.O. Pohuliai, D.Yu. Holubnychyi, M.V. Yesina — Thu, 30 Apr 2026 00:00:00 +0300

The article addresses the problem of efficient analysis of continuous streams of sensor data in embedded systems with limited hardware resources. Traditionally, the processing of large volumes of data obtained from inertial sensors, such as gyroscopes and accelerometers, has been performed using powerful cloud computing platforms. However, this approach has several disadvantages, including data transmission latency, dependence on network infrastructure, and increased energy consumption. In this context, the use of Edge Artificial Intelligence technologies, particularly the TinyML concept, is becoming increasingly relevant, as it enables machine learning inference to be executed directly on microcontrollers.

The aim of this study is to conduct a comparative analysis of the efficiency of different neural network architectures for the task of spatial sensor data classification under resource-constrained conditions. The experimental part of the research was implemented on the ESP32-C3 microcontroller, which represents a typical modern energy-efficient platform widely used in Internet of Things systems. Within the study, four machine learning models were developed and evaluated: Shallow Dense, Deep Dense with Dropout regularization, a one-dimensional convolutional neural network (1D CNN), and a hybrid architecture combining different layer types.

The results of hardware profiling demonstrated that the 1D CNN model provides the best balance between classification accuracy, inference speed, and memory usage. Due to the ability of convolutional filters to effectively extract spatial-temporal features from sensor data sequences, this architecture achieved the highest validation accuracy. At the same time, the hybrid model also demonstrated high performance; however, its practical use appeared less efficient due to increased computational complexity and longer inference time.

Special attention in the study was paid to the analysis of the impact of model quantization on classification accuracy. Experimental results showed that applying 8-bit quantization (Int8) leads to significant accuracy degradation because spectral features obtained through the Fast Fourier Transform contain important fractional components. Their forced compression into an integer representation distorts the feature space and consequently reduces classification performance.

Additional analysis of hardware resource consumption confirmed that the use of models with 32-bit floating-point precision (Float32) is feasible even for microcontrollers such as the ESP32-C3. The required RAM and Flash memory remain relatively small, allowing the system to be integrated into more complex embedded solutions. The overall system response time, including signal processing and neural network inference, is approximately 64 ms, which satisfies the requirements of real-time systems.

The obtained results confirm the effectiveness of TinyML technologies for developing autonomous intelligent devices capable of performing complex sensor data analysis without relying on cloud computing resources. The proposed approach can be applied in motion recognition systems, wearable devices, robotics platforms, and other Internet of Things applications.

Method for correction morphodensitometric parameters of trabecular tissue of vertebrae based on CT reconstruction of a composite body phantom

S.O. Filimonov — Thu, 30 Apr 2026 00:00:00 +0300

The article presents the results of the development and validation of a method for quantitative assessment of human bone status by using phantom CT models of the vertebra to adapt routine CT examinations of the human spine to the needs of specialized densitometric analysis of vertebral bodies. A composite digital phantom of the vertebral body was developed, reflecting the trabecular architecture of the vertebral body, its cortical shell, and surrounding soft tissues. For the first time an algorithm for modeling systemic bone degradation as a process of simultaneous thinning of trabeculae and cortex was proposed. The "Global Reference Normalization" (GRN) method was implemented to minimize hardware-related errors. The "Error Crossover" effect was identified, and a linear correction formula was derived. The proposed approach brings the accuracy of clinical CT close to the level of micro-CT, creating new opportunities for the early diagnosis of osteoporosis.

Research into the impact of electromagnetic radiation on biosystems using the STM32F407VG microcontroller

V.V. Semenets — Thu, 30 Apr 2026 00:00:00 +0300

The article investigates the energy density as a normalized value for determining the system of protection of medical workers from microwave radiation, which allows expressing the intensities of electric, magnetic and electromagnetic fields in the same units of measurement (energy per unit volume). The results of measuring a field of complex configuration can be easily converted into equivalent energy densities of a plane wave field. Calculation formulas have been obtained that are suitable for analysis and protection from the influence of parasitic radiation of medical personnel who use complex microwave equipment in their work. Using the formulas for the directivity diagram of a slit in an infinite screen, it is also possible to approximately estimate the diagram in the plane of the normal axis of the waveguide for cases of a transverse slit in a narrow wall.

The developed monitoring system constantly monitors the magnetic field in real time and analyses its parameters. The system can warn in time about a possible malfunction, which allows the user to take timely preventive measures.

Analog sensors will convert the induction of the magnetic field into a voltage, the sign and magnitude of which will depend on the polarity and strength of the field.

Analysis of the state of theory and the technology of radio-acoustic atmospheric sounding systems

O.V. Kartashov, I.E. Kondrashov — Thu, 30 Apr 2026 00:00:00 +0300

Radio-Acoustic Sounding Systems (RASS) enable measurements of vertical profiles of key atmospheric parameters, including temperature, wind speed, and turbulence characteristics. However, the development of the method has faced considerable difficulties over several decades. Currently, the field of radio-acoustic atmospheric sounding is experiencing a long-term, systemic crisis that has been ongoing for almost two decades. This crisis is caused by the fact that commercially produced RASS systems provide temperature profiles with acceptable performance and have modern, representative digital interfaces for visualizing the sounding results, while their operational algorithms are proprietary and not described in detail in the literature. Industrial RASS systems are implicitly regarded by the scientific community as sufficiently advanced and therefore are not subjected to critical evaluation. Under these conditions, scientific research in this field has almost come to a standstill and has remained stagnant for the past twenty years. As a result, the state of science and technology in this field has been effectively frozen for two decades.

To address this situation and to revive research in the theory and practice of RASS, this paper provides a qualitative assessment of the current state of the field, analyzes existing sounding systems, evaluates their algorithmic support, and formulates the key tasks required to overcome the crisis. Methods for achieving these goals are also proposed.

The main current task is to improve the methods for measuring vertical profiles of meteorological parameters using RAZ systems, which are based on existing algorithms for processing useful informative signals and on methods for adapting the systems to external conditions.

Methods of forming acoustic jamming for counteraction means against unauthorized documentation of speech information

A.M. Oleynikov, P.M. Shkopotko — Thu, 30 Apr 2026 00:00:00 +0300

The article is devoted to solving the actual problem of protecting confidential speech information by analyzing and improving methods of forming acoustic interference. The aim of the work is to systematize methods of acoustic jamming formation and experimentally substantiate the effectiveness of spectrally balanced and adaptive methods for counteracting unauthorized recording. The article provides a comprehensive analysis of existing approaches, among which white noise, tonal, speech-like, and formant jammers are highlighted. Special attention is paid to the scientific and methodological aspects of jammer synchronization with the useful signal.

Based on software modeling in the Python environment using signal processing libraries, a comparative evaluation of the effectiveness of four types of jammers was conducted. Effectiveness was assessed using a complex of objective metrics: PESQ (Perceptual Evaluation of Speech Quality) and STOI (Short-Time Objective Intelligibility), which provided verified quantitative results. It has been experimentally established that the highest efficiency is provided by the proposed method of formant jamming, which ensures targeted masking of the most informative spectral components of speech. It is calculated that the formant jammer provides the lowest quality scores (PESQ) and intelligibility scores (STOI) compared to other types of jammers. The research on the dependence of the STOI intelligibility index on the distance between the jammer source and the recording device confirmed the critical influence of spatial conditions on information security. The results prove the feasibility of using intelligent jamming formation methods in modern active acoustic protection systems to increase their effectiveness.

Alignment of receiving and transmitting apertures in wireless laser power transfer systems

D.V. Sokirkaiev, A.A. Zarudny — Thu, 30 Apr 2026 00:00:00 +0300

The article investigates the problem of matching the aperture between the transmitting and receiving optical systems in wireless laser power transmission channels. The system efficiency criterion is defined as the ratio of received optical energy to transmitted power. A condition is formulated under which the beam radius in the receiver plane must be equal to or less than the aperture radius, which allows for maximum energy intake.

Models for single-component lens systems and two-component afocal collimator telescopes are considered, and an analysis of the optimal magnification factor of the collimator and its effect on reducing the beam diameter at the receiver is performed. It is shown that the use of afocal systems provides more effective aperture matching at long distances compared to simple lens designs.

Practical limitations of receiver design are discussed. It is emphasized that the presented model is idealized, since it does not take into account atmospheric effects (absorption, scattering, turbulence) that can significantly reduce the efficiency of the system at long distances.

M.A. Omarov

M.A. Omarov, R.I. Tsekhmistro, S.V. Shapovalov, V.V. Usik — Thu, 30 Apr 2026 00:00:00 +0300

The article describes the analysis of correlation dependencies between neighboring microphones in ring two-section gratings at distances corresponding to the near and intermediate zones. An algorithm is used in which each microphone is modeled by an isotropic emitter represented by a spherical wave function. The algorithm makes it possible to take into account the time delay of microphone signals, allows considering an arbitrary even and odd number of emitters located along the arc length both evenly and unevenly. Most of such tasks are based on estimating the position of the sound source based on signals received by microphones in the matrix, including cross-correlation methods.

The maximum correlation should correspond to the change in time of signals between microphones of interest in time.

The analysis of correlation dependencies showed the presence of the influence of microphone signals, which is consistent with the dependencies built on experimental dependencies.

Correlation fields and tabular results also indicate the possibility of obtaining an acceptable sound level with a smaller number of microphones involved. Analysis of correlation dependencies for different numbers of microphones on an array of distances corresponding to the middle and far zones contributes to the search for improvements in neural network algorithms.

Mathematical model of signals in acoustic UAV detection systems

S.O. Sheiko, E.A. Shafronenko, S.V. Shapovalov — Thu, 30 Apr 2026 00:00:00 +0300

A mathematical model of acoustic signals in unmanned aerial vehicle (UAV) detection systems is developed. The model takes into account the main factors of sound propagation in the atmosphere, including geometric spreading, frequency-dependent absorption, scattering on atmospheric inhomogeneities, meteorological conditions, and multipath propagation caused by ground reflections.

A signal model at the outputs of a microphone array is proposed, considering time delays, amplitude attenuation, and the presence of acoustic interference. The reflected signal is modeled using the image source method. Signal processing is performed in a sliding time window, which allows accounting for signal non-stationarity and the Doppler effect.

Numerical simulation is carried out using real acoustic recordings of a Mavic UAV and background noise generated by road traffic. The simulated signals are used to test a localization algorithm based on the time difference of arrival (TDOA) method.

The results confirm the adequacy of the proposed model and its applicability to UAV detection and localization tasks. It is shown that for a signal-to-noise ratio of 10–15 dB, the localization error does not exceed 10%, with the largest deviations observed in elevation angle estimation.

Magnetron generators with cold secondary emission cathodes, triggered by field cathodes

M.A. Kopot — Thu, 30 Apr 2026 00:00:00 +0300

As is well known, a magnetron is a generator of the microwave range. One of its most important operational characteristics is its durability. This is both a technical and economic characteristic. Therefore, increasing the service life of the device will always remain a relevant task, on a par with improving its technical characteristics. The article discusses existing designs, proposes new ones, and determines the direction of development in this area. Historically, all electron vacuum devices had a thermionic cathode. Magnetrons were no exception. However, the durability of a thermionic cathode is quite low due to its constant heating, i.e., it simply burns out. The next step was to propose the use of a secondary emission cathode (SEC) as the main cathode. Moreover, it was cold. This raised two questions. The first was the material from which to make the VEC, and the second was the need for a source of primary electrons to start secondary electron emission. The first question is still being resolved, but it is more technological in nature. The second question was initially solved simply by using the same thermionic cathode. Although the starting currents are not large, the disadvantage remained, namely the heating of the cathode. This approach increased durability by 2 to 4 times. The next step in development was the use of autoemission (field) cathodes as starting cathodes. The implementation of this approach required additional electrodes, and initially these electrodes were located in the interaction space. Along with the appearance of electrons, this approach also had disadvantages, which consisted in the unevenness of the electric and magnetic fields in the same interaction space. The next step was to move the additional electrodes outside the interaction space. This created some technological difficulties, since the geometric dimensions of the electrodes are quite small. It should be noted that in the latest proposed designs, the starting cathode is located on the VEC itself and uses the principle of superposition of electrostatic fields. In addition, such designs allow for automatic switching on/off of autoemission. This has a positive effect on the equalization of spatial charge density inhomogeneities. The use of autocathodes to start the main cathode has led to an increase in durability by 4-5 times compared to starting with a thermionic cathode. Further development in this area may be linked to the appearance of primary electrons due to the ionization of residual gases. To implement this approach, a modulator is needed to provide the necessary anode voltage pulses. Some problems associated with this approach are already apparent, although there are ways to solve them.

Analysis of the functional properties of a fiber-optic sensor for field monitoring of water quality

D.V. Stadnik, O.B. Halat — Thu, 30 Apr 2026 00:00:00 +0300

The article examines the design principles and numerical modeling results of a fiber-optic sensor intended for online field monitoring of turbidity and changes in the optical properties of water samples. The authors justify the choice of a D-shaped geometry for the sensitive segment of a single-mode quartz fiber (initial structure: core ≈ 9 μm, cladding 125 μm, polished section ≈ 20 mm long with a cladding thickness of ≈ 3 μm), which significantly enhances the interaction of the evanescent field with the surrounding medium. For the experimental scenario, an IR laser with a wavelength of λ ≈ 980 nm and an output power of 5 mW was used. In the proposed model, the refractive index of the external medium was varied, corresponding to changes in salinity C in the range of 5–100 g/L. The dependences of the critical angle θ, the penetration depth δ of the evanescent field, and the relative output power P on the parameter C were investigated. The simulation results showed that with increasing salinity C and, accordingly, the refractive index n₂, the critical angle θ increases, which gradually disrupts the conditions of total internal reflection and leads to a significant decrease in the output signal. In particular, in the range C ≈ 0–100 g/L the relative power P decreases by approximately three orders of magnitude, with the most intense attenuation occurring within 0–40 g/L. The penetration depth δ exhibits a non-monotonic dependence with a local maximum near C ≈ 30–40 g/L, which determines a narrow region of increased sensor sensitivity. The sensor is highly sensitive to local (near-surface) changes in the environment due to the small value of δ. This makes it effective for detecting local anomalies, but at the same time limits its capability when it is necessary to assess volumetric properties of water. The results of the study confirm the suitability of the D-shaped fiber-optic design for highly sensitive local monitoring of turbidity and salinity in freshwater and slightly saline water samples, as well as the possibility of tuning the sensor to the working range of environmental parameters. Practical implementation requires well-considered engineering solutions for calibration, temperature compensation, protection of the sensitive segment, and integration with hardware-software systems to ensure stable operation under field conditions.