Digital Synthesis Method Research Articles

The recent digital resources of websites Internet auctions as a research source for the circulation of the Prague groschen in Ukraine

The article was aimed at updating the content of digital and digitised numismatic data of the Ukrainian segment of the Internet, in particular the antiques auction website “Violity”, for searching, identifying, processing, grouping and researching information on the findings of Prague groschen in Ukraine in 2019-2024. The research methodology was based on an interdisciplinary approach that integrates the subject matter and tasks of specific research practices in numismatics and the history of monetary circulation with historical science methods, source studies and mathematics. In particular, the study used the digital data analysis and synthesis methods of numismatic sources, their quantitative content analysis, classification methods and source criticism. The study had shown that in the notional category of the Late Middle Ages treasures, Bohemian groschen thesauri occupy a leading position. There is a relatively significant number of offers of entire treasures of these coins, which are evenly distributed throughout the territory of the Prague groschen circulation in Ukraine. The digital data sample analysis by the criterion of “location” allowed obtaining conditionally reliable data on the number of new finds of Prague groschen in certain regions of Ukraine. The finds geographical distribution practically coincides with the area of the coinage type circulation in the Ukrainian lands in the 14th-15th centuries. The digital data sample content analysis by the issuer criterion showed the absolute predominance of coins minted by Wenceslas IV (1378-1419). The second largest group of coins is the coinage of Charles I (1346-1378), and the third is the issue of John I of Luxembourg (1310-1346). The finds selection of clipped Prague groschen based on the criterion of “location” indicated that they belonged to John I and Charles I and originated from Lviv and Khmelnytskyi regions within the historical regions of Galicia and Podillia. A small group consists of coins with countermarks of German cities, which are recorded exclusively on the coins of King Wenceslas IV (1378-1419). The practical significance of the study lies in the introduction of a group of digital data from the newest numismatic sources into scientific circulation, which allows to clarify the geography and chronology of the Prague groschen circulation in Ukraine in the 14th-15th centuries

Digitizing protocols into single reactors for the one-pot synthesis of nanomaterials

Digitizing protocols into single reactors for the one-pot synthesis of nanomaterials

A Microcontroller-based Liénard Oscillator

Van der Pol Equation is a special case of Liénard equations. Both oscillators have significant historical importance. There are lots of different circuit topologies for Van der Pol and Liénard oscillators. Such oscillators can be made using vacuum tubes, diodes, etc. Some oscillators are made using microcontrollers, which are cheap and easy-to-use devices. They provide accurate adjustability of the frequency and magnitude of the waveforms. Arduino Nano Klon V3.0 microcontroller is a commonly used microcontroller. In this study, to the best of our knowledge, for the first time in literature, a Liénard Oscillator has been made with the Direct digital synthesis (DDS) method using the Arduino Nano Klon V3.0 microcontroller and two DACs. The experimental results of the oscillator are given. The circuit is able to produce the state variables of the oscillator, the effect of quantization can be seen on the waveforms, and it is shown that it performs well. The two variable outputs of the system let its phase portrait be examined easily. Also, using a microcontroller helps to design the oscillator in mere a few days.

High efficiency 3-D printed microchannel polymer heat exchangers for air conditioning applications

The design, fabrication, and experimental characterization of a counterflow Micro-pin array Polymer Heat eXchanger (MPHX) for HVAC applications is described. The design consists of water flow through microscale pin array plates, and airflow paths in a counterflow direction through adjacent rectangular channels. When compared to a Finned Tube Heat eXchanger (FTHX), the water plates take the place of fins and the crossflow tube bank is eliminated. The MPHX is fabricated by 3 D printing using a digital light synthesis method. A correlation-based model is developed and used to explore the parametric space to arrive at a baseline MPHX core geometry. Mechanical and fluidic simulations are performed on the baseline geometry to further develop the design. A sub-scale MPHX with a nominal cross duct area of 10.1 cm × 20.3 cm is designed and fabricated. Its thermal performance over a range of air and water flow rates corresponding to heat capacity rate ratios in the range of 0.25–1 is investigated. Results show that the effectiveness varies from 0.65 to 0.95 corresponding to a of 1 to 0.25. The experimental data are used to validate a correlation-based thermo-fluidic model of the MPHX. The validated model is further used to compare the performance advantages of the MPHX design over a FTHX. For a given heat exchanger volume and thermo-fluidic conditions, the MPHX transfers 55% more thermal energy when compared to a FTHX at comparable air-side pressure drops.

A New Method to Detect and Track the Resonance Frequency of Piezoelectric Transducers in Ultrasonic Power Supplies

In this paper, a new method is developed to detect and track the resonance frequency of ultrasonic transducers. In order to have an acceptable performance of transducers, power supplies should be able to detect and track the resonance frequency. Different methods have been used for this purpose. In this research, the voltage of the transducer and the phase difference between the voltage and current are used to find the resonant frequency. The maximum voltage of a transducer is founded in a predefined frequency interval. Afterward, the minimum phase difference between the voltage and current is obtained in a smaller interval around it. The simultaneous use of the voltage and phase shift increases the accuracy and speed of the algorithm. Since the transducer's voltage variations are relatively large near the resonant frequency, it is a versatile parameter compared to the current used in other methods to indicate the resonance frequency. The algorithm is implemented within a microcontroller. An FPGA is used to generate accurate frequency using the Direct Digital Synthesis (DDS) method. The algorithm can detect the resonant frequency under free conditions. Applying force to transducers or emerging the transducer's head to the water changes the resonant frequency. The experimental tests showed that the algorithm could find and track the resonant frequency automatically under loading conditions.

Radar hybrid signal generators based on high-speed digital-to-analog converters

Wideband frequency synthesizers are used in many different applications, such as radars, telecommunications and others. Radar parameters are dependent on the synthesizers phase noise. A general flow-chart of a hybrid frequency synthesizer based on direct digital and direct analog synthesis methods that uses a high-speed digital-to-analog converter (DAC) in special operating modes to increase the operating frequency is presented in this paper. The noise characteristics of a hybrid synthesizer with a DAC operating in two modes are simulated.

Physical work principles of digital computational synthesizers of multiphase signals

Modern systems of radio engineering systems are very widely used in radar and radio communications. An important component of the work of radio systems is the creation of diagnostic equipment with high resolution, noise immunity, improved security and reliability, which become more accessible with the advent of digital computer frequency synthesizers. Digital computer synthesizers using the direct digital signal synthesis method are the main nodes of modern diagnostic equipment for radar and radio communication systems. The article considers a number of advantages of digital computing synthesizers, which include a wide range of synthesized frequencies, an extremely small step of the frequency grid, extremely fast frequency tuning speed, phase continuity during frequency tuning, low phase noise, a simple algorithm for generating complex signals, the possibility of independent amplitude control, phase and frequency of the synthesized signal. The principles of construction and structural and circuitry solutions of digital computational synthesizers based on the method of direct digital synthesis of frequencies and signals are given. The principle of constructing structures of digital multiphase signal synthesizers is proposed, in which the initial phases of the synthesized signals can be set in software. Structural diagrams of digital computational synthesizers based on digital code storage devices and with an M-shaped law of frequency variation which allow synthesizing signals with amplitude, frequency and phase modulation in the frequency range from 0.001 to 400 MHz are presented.

Digital type synthesis method of twin parallel mechanisms and several novel manipulators

In the area of parallel mechanisms, the disadvantage of small workspace restricts its application in practical engineering fields. To resolve this common defect of parallel mechanisms, a new type of twin parallel mechanism (TPM) with large workspace is developed by coupling two identical parallel mechanisms through sharing certain kinematic pairs. Moreover, the configuration principle of the TPM is systematically investigated, and the applicable degrees of freedom of the TPM are presented. In order to acquire the desired TPM rapidly and effectively, a new definition of the incidence matrix of the spatial branch chain is proposed, and the mapping relationship between the branch chain and the incidence matrix is established. Furthermore, the limb screw system and the limb constraint system are automatically calculated, and a digital synthesis method of the TPM is presented. Various new configurations of the symmetrical TPM with excellent workspace performance are constructed. The proposed method can be widely applied in the fields of robot joints, antenna base, and orientation-adjusting mechanisms.

Application high-speed digital-to-analog converters for direct digital synthesis of high-frequency radio signals

The main features of high-speed digital-to-analog converters designed for direct digital synthesis of radio frequency signals in the UHF and microwave ranges are presented. A block diagram of a digital signal generator based on high-speed DACS is proposed. These DACs are designed to create digital signal generators that work based on the direct digital synthesis method. The main specialized modes of operation of high-speed digital-to-analog converters that allow efficient use of extra components of the spectrum are studied. Images of the main frequency of synthesis occur when the signal is restored from digital to analog form. Special operating modes of high-speed DACS allow you to create broadband and ultra-wideband signals. The use of high-speed digital-to-analog converters in special modes of operation makes it possible to simplify the block diagrams of digital signal generator. The scheme is simplified by reducing the number of cascades of the output frequency multipliers.

Multi-Mode OAM Radio Waves: Generation, Angle of Arrival Estimation and Reception With UCAs

Orbital angular momentum (OAM) at radio frequency (RF) provides a novel approach of multiplexing a set of orthogonal modes on the same frequency channel to achieve high spectrum efficiencies. However, there are still big challenges in the multi-mode OAM generation, OAM antenna alignment and OAM signal reception. To solve these problems, we propose an overall scheme of the line-of-sight multi-carrier and multi-mode OAM (LoS MCMM-OAM) communication based on uniform circular arrays (UCAs). First, we verify that UCA can generate multi-mode OAM radio beam with both the RF analog synthesis method and the baseband digital synthesis method. Then, for the considered UCA-based LoS MCMM-OAM communication system, a distance and AoA estimation method is proposed based on the two-dimensional ESPRIT (2-D ESPRIT) algorithm. A salient feature of the proposed LoS MCMM-OAM and LoS MCMM-OAM-MIMO systems is that the channel matrices are completely characterized by three parameters, namely, the azimuth angle, the elevation angle and the distance, independent of the numbers of subcarriers and antennas, which significantly reduces the burden by avoiding estimating large channel matrices, as traditional MIMO-OFDM systems. After that, we propose an OAM reception scheme including the beam steering with the estimated AoA and the amplitude detection with the estimated distance. At last, the proposed methods are extended to the LoS MCMM-OAM-MIMO system equipped with uniform concentric circular arrays (UCCAs). Both mathematical analysis and simulation results validate that the proposed OAM reception scheme can eliminate the effect of the misalignment error of a practical OAM channel and approaches the performance of an ideally aligned OAM channel.

Low-noise hybrid frequency synthesizers based on direct digital and direct analog synthesis

The research of the possibility of using hybrid frequency synthesizers based on direct digital and direct analog methods of frequency synthesis as heterodynes of modern spectrum analyzers constructed according to the superheterodyne scheme is presented. The main advantages of such synthesizers over traditionally used heterodyne schemes based on direct digital and indirect frequency synthesis methods are shown. The requirements for the heterodynes of the first mixing stages of spectrum analyzers are presented. A block diagram of a wideband heterodyne generating a frequency range from 4000 MHz to 8000 MHz with a step not exceeding 1 Hz is proposed. Formulas for calculating the main frequency ratios in the structure of the heterodyne have been developed. A mathematical model of phase noise power spectral density (PSD) depending on the offset frequency from the carrier is developed. The noise characteristics of the proposed scheme are studied using the model. It is determined that at the output frequency of the heterodyne equal to 4521,4 MHz, the level of phase noise PSD is: minus 90 dBc/Hz at the offset frequency equal to 100 Hz; minus 140 dBc/Hz at the offset frequency equal to 100 kHz. It is shown that the hybrid synthesizer based on direct digital and direct analog synthesis methods has an advantage in the level of phase noise from 5 to 30 dB over the low-noise heterodynes of modern spectrum analyzers at frequencies above 1 kHz from the carrier. Additional advantages of the proposed scheme are a simple architecture, low power consumption and high frequency tuning speed due to the absence of phaselocked loops in the structure of the heterodyne.

Design of a Carrier Wave for Capacitive Transducer with Large Dynamic Range.

Capacitive transducers are widely used in fundamental physics experiments, seismology, Earth or planetary observations, and space scientific and technical applications because of their high precision, simple structure, and compatibility with various measurements. However, in real applications, there is a trade-off between their resolution and dynamic range. Therefore, this paper is aimed at enlarging the dynamic range while ensuring high resolution. In this paper, a noise analysis of a capacitive transducer is presented, which shows that the amplitude noise of the carrier wave is the main limiting factor. Hence, a new method of generating a carrier wave with lower-amplitude noise is proposed in the paper. Based on the experimental verification, it is found that the carrier wave produced through the new method performed significantly better than the typical digital carrier wave when they were compared in the same sensing circuit. With the carrier wave produced through the new method, the dynamic range of the capacitive transducer can reach 120.7 dB, which is 18.3 dB greater than for the typical direct digital synthesis (DDS) method. In addition, the resolution of the carrier wave is mainly limited by the voltage reference components.

Low-noise hybrid frequency synthesizers for 5G technology

This paper presents the results of structural design and analysis of the noise characteristics of a low-noise hybrid frequency synthesizer based on direct digital and indirect synthesis methods for using as a shaper of harmonic signals for fifth generation telecommunication systems transceivers. The hybrid synthesizer is based on a phase-locked loop (PLL) with DDS operating on fundamental frequency images. Due to this, the hybrid synthesizer generates a wide range of output frequencies with high frequency resolution, as well as a low level of phase noise and discrete side components of the spectrum of the output signal.

Novel Low-Complexity Low-Latency Orthogonal Frequency Division Multiplexing Transmitter

Traditional orthogonal frequency division multiplexing (OFDM) transmitter is implemented by exploiting inverse fast Fourier transform (IFFT), up-sampling, and low pass shaping filter (LPSF) modules, which occupy a large number of hardware resources and severely lower down the operation speed. To address these limitations, we propose a novel OFDM transmitter architecture, by which the aforementioned modules can be discarded and replaced with some simple switches. In the proposed architecture, direct digital synthesis (DDS) method is employed to generate digital sub-carriers and to transform OFDM data from frequency domain to time domain. Through some sophisticated simplifications, the proposed architecture can avoid using multipliers and remarkably save hardware resources. Finally, comparative experiments are carried out on field programmable gate array (FPGA) platform which demonstrates that our DDS-based architecture saves more than half of the hardware resources and doubles the achievable maximum frequency compared with traditional structure.

Features of direct digital synthesis applications for microwave excitation signal formation in quantum frequency standard on the atoms of cesium

Features of direct digital synthesis applications in quantum frequency standard on the atoms of cesium are considered. A new design of a frequency synthesizer based on direct digital synthesis method and magnetic field stabilization system are presented. Experimental research of frequency synthesizer showed improvement parameters of a microwave excitation signal, such as step frequency tuning, time frequency tuning, range of generating frequencies and spectral characteristics. Magnetic field stabilization system eliminates one of the most important perturbing factors affecting on long-term frequency stability. Experimental research of metrological characteristic of quantum frequency standard showed improvement long-term frequency stability by 15%.

In brief

PAGE 995 The use of long coherent integration times in CZT-based algorithms could have applications for GPS systems operating in weak signal environments. A down-sampling data operation introduced by researchers in China demonstrates that the same signal acquisition can be achieved with a lower carrier-to-noise ratio and reduced computational effort. PAGE 991 Researchers in the UK working with semiconductor-based terahertz emitters have observed that temperature dependent polarity reversal within the material is an intrinsic property. Terahertz emission from various emitters over a range of temperatures revealed the semiconductor's inversion is not influenced by metallic contact, and creates potential for these devices to compete with commercial antennas. Signal detection probability improves with extended coherent integration times. PAGE 1007 A novel design for a simpler, more flexible, high performance microstrip power-divider (PD) has been implemented and tested by researchers in China. The device is composed of two dual-mode filtering PDs lacking any additional matching network, and provides significant design utility and size reduction with applications in wireless communications systems. Spectrometer set up for temperature dependence measurement of metal emitters. PAGE 967 Researchers from China have developed a frequency calibration method for a crystal-less current-controlled ring oscillator utilising a serial data signal from another chip as a reference. This newly presented auto-correlation method outperforms similar literature designs in terms of calibration accuracy, power consumption, and circuit area. Measured and simulated performances of power-divider device channels. PAGE 969 A purely digital approach to ultra-narrow pulse control for use in the picosecond and gigahertz domains has been presented by researchers in China. The digital synthesis method converts pulse-width control to the relative delay control between two signals, and can be applied to ultra-wideband communication systems and pulse radar. Frequency histograms before and after chip signal calibration. Diagram of ideal and real sharpener edge signal outputs.

High-Precision Electrical Impedance Tomography Data Acquisition System for Brain Imaging

In electrical impedance tomography (EIT), it is difficult to obtain the intracranial impedance due to the highly resistive skull enclosing the brain. Therefore, a high-precision data acquisition system is required for brain EIT. In this paper, we used a high-precision digital synthesis method and a digital demodulation technique with high noise immunity to eliminate random errors. Moreover, we focused on two problems encountered during EIT data acquisition: 1) the shunt effect on the excitation current due to the distributed capacitance between electrodes and ground and 2) high common-mode voltages in the boundary measurements. We designed a new electrode interface to reduce the influence of the distributed capacitance and a programmable current source to accurately compensate for the excited current. We also proposed a new voltmeter circuit with improved CMRR. Overall, this EIT data acquisition system can produce a programmable current with SNR greater than 89 dB. It can also measure the voltage difference precisely with CMRR higher than 75 dB with a 1- $\text{k}\Omega $ impedance imbalance. The results on a calibration model show that this system has a high SNR of 83 dB and a low reciprocity error of 0.125%. In addition, EIT imaging results were acquired using a brain physical phantom. The system can detect small disturbances of 0.35% in volume (1.99% of the cross-sectional area) and 17% in resistivity. Experiments on healthy volunteers also suggest that small intracranial impedance variations due to temporary occlusion and reperfusion of the unilateral carotid artery may be monitored by the system.

A wideband digital polarization synthesis method

A novel wideband digital polarization synthesis method is presented here. The method is based on the definition of antenna polarization and both simulated and measured antenna patterns. A mathematical formulation is used to determine the synthesis coefficients. Any state of polarization (elliptical, circular, and linear) can be synthesized theoretically. Here, we mainly focus on the method for synthesizing linearly polarized antennas into circularly polarized antennas. There is no restriction regarding the array geometry or element patterns. The method can yield pure circularly polarized antenna patterns within the whole working band. The synthesized circularly polarized antennas are then used to receive circularly polarized signals. The method can provide more accurate polarized data for wideband solar radio observations and other systems that require accurate polarization measurements.

Novel Low-complexity OFDM Transmitter Without IFFT and Multiplier

Traditional orthogonal frequency division multiplexing (OFDM) transmitter is implemented by exploiting inverse fast Fourier transform (IFFT), up-sampling, and low pass shaping filter (LPSF) modules, which occupy a large number of hardware resources and severely lower down the operation speed. To address these limitations, we propose a novel OFDM transmitter architecture, by which the aforementioned modules can be discarded and replaced with some simple switches. In the proposed architecture, direct digital synthesis (DDS) method is employed to generate digital sub-carriers and to transform OFDM data from frequency domain to time domain. Through some sophisticated simplifications, the proposed architecture can avoid using multipliers and remarkably save hardware resources. Finally, comparative experiments are carried out on field programmable gate array (FPGA) platform which demonstrates that our DDS-based architecture saves more than half of the hardware resources and doubles the achievable maximum frequency compared with traditional structure.

Precise modulation of laser radiation by an acousto-optic modulator for stabilisation of the Nd : YAG laser on optical resonances in molecular iodine

A system of precise frequency modulation of laser radiation by an acousto-optic modulator, which makes it possible to stabilise the radiation power and simultaneously suppress the residual amplitude modulation to a level of of the total laser power at the third harmonic of modulation frequency , is presented. The use of this system for the optical frequency standard and application of digital signal synthesis and processing methods provided a level of frequency standard instability as small as for .