Dual-frequency Mode Research Articles

Photo-capacitance measurement in dual-frequency mode and its application to study of Pt/κ-Ga2O3 planar Schottky diode

In this study, a dual-frequency method for the impedance/admittance measurements on illuminated junctions has been critically analyzed as an appropriate methodological approach for the measure of the depletion capacitance, both under steady-state light and during on-off illumination cycles. A planar Pt/κ-Ga2O3 Schottky diode was used as a test structure. Then capacitance-voltage (C-V) measurements were carried out under various applied AC frequencies and monochromatic UV-C light (λ = 254 nm) and compared to dark values. Transient photo-capacitance (TPC) measurements were performed at fixed applied voltages and the same AC frequencies and illumination conditions as the C-V measurements.Thanks to capacitance-frequency (C-f) measurements, the device under test was preliminary demonstrated to be well represented, both in dark and under light, by the equivalent circuit required for the applicability of the dual-frequency approach. It must include a depletion capacitance, parallel leakage resistance, and a series resistance. Dual-frequency capacitance resulted comparable to the single frequency C-V and TPC data obtained in the high-frequency limit for series configuration measurements and those obtained at low frequency in measurements carried out in parallel configuration.The experimental conditions of reliable data acquisition were discussed leading to the interpretation of the results in terms of the presence of slow-response traps.

Experimental Study of Magnetron’s Power-Pulled Characteristic to Realize a Quasi-Dual-Frequency Microwave Output

This article presents experimental evidence demonstrating the feasibility of implementing a quasi-dual-frequency microwave signal generator using a 1 kW commercial magnetron. The injection-pulled magnetron may generate quasi-dual-frequency output with nearly identical amplitudes by injecting signal at specific powers and frequencies out of the Adler locking band. This generator offers the advantage of developing a large-power and tunable quasi-dual-frequency signal at low cost and with simple implementation. In the present study, a tunable quasi-dual-frequency signal with a frequency interval ranging from 0.48 MHz to 13.74 MHz is generated experimentally. Furthermore, the effects of anode voltage ripples on the dual-frequency outputs are experimentally investigated. An empirical relationship between the frequency interval and injection ratio is obtained and presented. In addition, neither the output power nor the efficiency of the magnetron in the dual-frequency mode decreases. This research is promising for improving microwave heating uniformity in large-scale industrial applications.

Boiling Histotripsy Using Dual-Frequency Protocol on Murine Breast Tumor Model and Promotes Immune Activation.

Histotripsy is an ultrasound-guided, noninvasive, nonthermal ablation therapy that can mechanically lyse target tissues. There have been no reports of enhanced histotripsy for large-volume triple-negative breast cancer (TNBC). This study aims to verify the ability of a novel approach of dual-frequency mode combined with two-stage millisecond-length ultrasound pulses (DF-TS) to accelerate the treatment of murine subcutaneous 4T1 tumors and determine immune changes after treatment. A custom-designed 1.1-/2.2-MHz two-element confocal-annular array was used to treat approximately 6-mm tumors under ultrasound guidance and real-time monitoring. Two-stage millisecond-length ultrasound pulses were used to generate approximate cuboid ablation volumes (diagonal 5-6 mm) within each tumor, with a dose of 100 pulses/point. Immune effects were characterized by changes of pro-inflammatory cytokine levels and infiltration levels of immune cells. In all targeted treatment areas, bubble cloud activity was visualized by ultrasound monitoring. The novel protocol resulted in elliptical and controllable sized lesions, reducing the number of scanning points, and was generally well tolerated. After treatment, tumor growth experienced a seven-day stagnation period, the survival period of mice was prolonged, and the levels of pro-inflammatory cytokines and immune cell infiltration increased. This study demonstrates that DF-TS boiling histotripsy (BH) has a noninvasive, efficient, and precise ablation ability for TNBC and potentially enhances immune responses.

Contributions of reactor geometry and ultrasound frequency on the efficiency of sonochemical reactor

An intermediate-scale reactor with 10L capacity and two transducers operating at 700 and 950 kHz frequencies was developed to study the scalability of the sonolytic destruction of Per and Polyfluoroalkyl substance (PFAS). The impact of frequency, height of liquid or power density, and transducer position on reactor performance was evaluated with the potassium iodide (KI) oxidation and calorimetric power. The dual frequency mode of operation has a synergistic effect based on the triiodide concentration, and calorimetric power. The triiodide concentration, and calorimetric power were higher in this mode compared to the combination of both frequencies operating individually. The sonochemical efficiency for an intermediate-scale reactor (10L) was similar that obtained from a bench-scale reactor (2L), showing the scalability of the sonolytic technology. The placement of the transducer at the bottom or side wall of the reactor had no significant impact on the sonochemical reactivity. The superposition of the ultrasonic field from the dual transducer mode (side and bottom) did not produce a synergistic effect compared to the single transducer mode (bottom or side). This can be attributed to a disturbance due to the interaction of ultrasonic fields of two frequencies from each transducer. With the encouraging results scaling up is in progress for site implementation.

Degradation of sulfamerazine using ultrasonic horn and pilot scale US reactor in combination with different oxidation approaches

The present study aimed at utilizing ultrasonic horn (USH) and ultrasonic reactor (USR) having provision for dual frequency operation for the successful and cost-effective degradation of sulfamerazine (SMZ). USH and USR were combined with UV, persulfate (PS), peroxymonosulfate (PMS), Fenton (Fe2+/H2O2) and Fenton like (Fe3+/H2O2) process in detailed investigation to establish the optimal loading for obtaining the improved degradation of SMZ quantified in terms of the synergistic index values. A mathematical model was also developed to explain the complex SMZ degradation kinetics for all the AOPs. Significantly higher SMZ degradation (>99 %) was achieved for various combined approaches as USH/PS, USH/PMS, USH/Fe2+/H2O2, USH/Fe3+/H2O2, USH/PS/UV, USH/PMS/UV, USH/Fe2+/H2O2/UV, and USH/Fe3+/H2O2/UV, demonstrating the significant role of SO4¯ and OH radicals in intensifying the oxidation of the SMZ molecules. The pilot scale study with USR also demonstrated effective SMZ degradation using combined AOPs with maximum removal as 94.14 % for USR (22 + 44 kHz)/Fe3+/H2O2/UV. The dual frequency mode of operation was observed to be more efficient than the single frequencies. The cost estimation study based on of cavitational yield revealed that the most cost-effective system was the USR (22 + 44 kHz)/Fe3+/H2O2/UV with a degradation cost of 0.57 ₹/L (0.0069 $/L).

Frequency-stabilized Faraday laser with 10−14 short-term instability for atomic clocks

In this Letter, stabilizing a Faraday laser frequency to the atomic transition is proposed and experimentally demonstrated, where the Faraday laser can work at single- or dual-frequency modes. High-resolution spectroscopy of a cesium atom induced by a Faraday laser is obtained. By stabilizing a Faraday laser with atomic spectroscopy, the frequency fluctuations of the Faraday laser are suppressed without the need of a high-cost Pound–Drever–Hall system. The fractional frequency Allan deviation of the residual error signal is 3 × 10−14/τ at the single-frequency mode. While at the dual-frequency mode, the linewidth of the beat-note spectra between the two modes of the Faraday laser after locking is narrowed to be 85 Hz, which is an order of magnitude better than the free-running linewidth. It can be used for microwave atomic clocks and may have the potential to be used in the application of optical microwave generation when the performance is further improved.

A Dual-Band Receiver Based on a Single Superconducting Hot Electron Bolometer Mixer for DATE5 Telescope

Simultaneous multi-frequency observations can be of great advantage when line ratios need to be accurately determined. Five meters Dome A Terahertz Explorer (DATE5) telescope is proposed with two observation bands: 0.85 THz band and 1.35 THz band. In this paper, we report on a dual-band receiver based on a single quasi-optical superconducting hot-electron bolometer mixer. This novel concept allows simultaneous observation of the two bands for DATE5 telescope. Our measurement results show that the dual-band HEB receiver can simultaneously resolve the line spectra in both frequency bands. In particular, an RF tone has been observed with in single and dual frequency mode and the heterodyne performance of the HEB mixer has been compared. Although there is a reduction of mixer conversion gain, the available observation time can be improved by decreasing the time for source pointing and double-beam switching. Whats more, compared with conventional broadband receiver system, this novel technique can achieve compact system and provide a system redundancy for unattended observation.

Switchable frequency terahertz vortex beam generator

Most of the reported vortex beam generators generate vortex beams at a fixed frequency, which limits the practical applications. Therefore, it is inevitable to explore a vortex beam generator, which can actively control the operating frequency. We propose a switchable frequency terahertz vortex beam metasurface, it is freely switchable under single-frequency mode and dual-frequency mode by changing the external temperature, the phase state of vanadium dioxide (VO<sub>2</sub>) is also changeable. External temperature changes will cause VO<sub>2</sub> to transform from insulating state to metallic state. Generally, VO<sub>2</sub> conductivity can increase by several orders of magnitude as operating temperature changes. By using the phase change property of VO<sub>2</sub>, we can obtain a metasurface with switchable operating frequencies. For operating at room temperature, the proposed metasurface behaves as a single-frequency terahertz vortex generator. When (left-handed circularly polarized, LCP) terahertz wave is vertically incident on the metasurface, it generates vortex beams with different topological charge numbers at a frequency of 1.1 THz, and the mode purity is above 85%. The simulation results show that the mode purity of the vortex beam with the topological charge <i>l</i> = 1 is 90%, and the mode purity is about 91.1% for the vortex beam with <i>l</i> = 2, and 85.4% for the vortex beam with <i>l</i> = 3. When the external temperature is of 68 ℃, the designed metasurface becomes a dual-frequency vortex beam generator. At this time, the operating frequencies of vortex beams with different topological charges (<i>l</i> = 1, 2, 3) are 0.7 and 1.23 THz, whose mode purities are both above 60%. That is to say, the corresponding mode purities at topological charge with<i> l</i> = 1 for two operating frequencies are 89.1% and 71.6%, respectively. The mode purities are 83.2% and 94.4% with topological charge <i>l</i> = 2, respectively. The mode purities are 62.4% and 68.2% with topological charge<i> l</i> = 3, respectively. Therefore, the proposed switchable frequency terahertz vortex generator provides a new design idea for working frequency modulation in wireless terahertz communication.

Синтез широкополосных дифференциальных фазовращателей на электромагнитно связанных линиях для многолучевых антенных решёток*

The work is devoted to the synthesis of differential phase shifters on electromagnetically coupled lines with a closed ring conductor. In comparison with the known phase shifters, the proposed structure is characterized by additional degrees of freedom in printed strip design and provides the possibility of designing multipath equidistant phased antenna arrays with operating frequency bands up to one and a half octaves, provided that the emitters of their antenna canvases are characterized by the same broadband, for example, printed logoperiodic emitters. With narrow-band emitters, the possibility of implementing a dual-frequency or multi-frequency mode of operation of a multipath antenna array opens up.

Approaching Global Instantaneous Precise Positioning with the Dual- and Triple-Frequency Multi-GNSS Decoupled Clock Model

Precise Point Positioning (PPP), as a global precise positioning technique, suffers from relatively long convergence times, hindering its ability to be the default precise positioning technique. Reducing the PPP convergence time is a must to reach global precise positions, and doing so in a few minutes to seconds can be achieved thanks to the additional frequencies that are being broadcast by the modernized GNSS constellations. Due to discrepancies in the number of signals broadcast by each satellite/constellation, it is necessary to have a model that can process a mix of signals, depending on availability, and perform ambiguity resolution (AR), a technique that proved necessary for rapid convergence. This manuscript does so by expanding the uncombined Decoupled Clock Model to process and fix ambiguities on up to three frequencies depending on availability for GPS, Galileo, and BeiDou. GLONASS is included as well, without carrier-phase ambiguity fixing. Results show the possibility of consistent quasi-instantaneous global precise positioning through an assessment of the algorithm on a network of global stations, as the 67th percentile solution converges below 10 cm horizontal error within 2 min, compared to 8 min with a triple-frequency solution, showing the importance of having a flexible PPP-AR model frequency-wise. In terms of individual datasets, 14% of datasets converge instantaneously when mixing dual- and triple-frequency measurements, compared to just 0.1% in that of dual-frequency mode without ambiguity resolution. Two kinematic car datasets were also processed, and it was shown that instantaneous centimetre-level positioning with a moving receiver is possible. These results are promising as they only rely on ultra-rapid global satellite products, allowing for instantaneous real-time precise positioning without the need for any local infrastructure or prior knowledge of the receiver’s environment.

An optimization study on quality promotion of heavy crude oil exposed ultrasonic waves and magnetic nanoparticles addition

This study aims to investigate a new method of combining ultrasonic waves with different frequencies and magnetic nanoparticles in reducing the asphaltene content and kinematic viscosity of heavy oil. In general, the experiments included irradiation of ultrasonic waves at single-frequency mode, dual-frequency mode, temperature optimization, and the combined effects of the ultrasonic waves and magnetic nanoparticles in a constant magnetic field. The results demonstrated that, the ultrasonic irradiation at an optimum time of 10 min and a constant temperature of 20 °C with a frequency of 25 kHz and a power of 840 W decreased the asphaltene content and kinematic viscosity of the heavy oil from 13.52% and 87.2 cSt to 7.6% and 65.7cSt, respectively. In the dual-frequency mode (25 kHz and 1.7 MHz), the both parameters reduced to 7.33٪ and 62.9cSt. Subsequently the temperature of 50 °C was selected as optimum temperature for the experiments. The experimental optimizations cleared that at the concentration of γ-Fe2O3 magnetic nanoparticles (0.4 wt%) and the dual- frequency, the both parameters were significantly declined (7.1 cSt and 5.01 wt% respectively). Distillation test, FT-IR, SARA analyses and API index have verified that the ultrasonic waves and the magnetic nanoparticles have effectively lightened the studied oil.

Space weather: risk factors for Global Navigation Satellite Systems

Extreme space weather events affect the stability and quality of the global navigation satellite systems (GNSS) of the second generation (GPS, GLONASS, Galileo, BeiDou/Compass) and GNSS augmentation. We review the theory about mechanisms behind the impact of geomagnetic storms, ionospheric irregularities, and powerful solar radio bursts on the GNSS user segment. We also summarize experimental observations of the space weather effects on GNSS performance in 2000–2020 to confirm the theory. We analyze the probability of failures in measurements of radio navigation parameters, decrease in positioning accuracy of GNSS users in dual-frequency mode and differential navigation mode (RTK), and in precise point positioning (PPP). Additionally, the review includes data on the occurrence of dangerous and extreme space weather phenomena and the possibility for predicting their impact on the GNSS user segment.
 
 The main conclusions of the review are as follows: 1) the positioning error in GNSS users may increase up to 10 times in various modes during extreme space weather events, as compared to the background level; 2) GNSS space and ground segments have been significantly modernized over the past decade, thus allowing a substantial increase in noise resistance of GNSS under powerful solar radio burst impacts; 3) there is a great possibility for increasing the tracking stability and accuracy of radio navigation parameters by introducing algorithms for adaptive lock loop tuning, taking into account the influence of space weather events; 4) at present, the urgent scientific and technical problem of modernizing GNSS by improving the scientific methodology, hardware and software for monitoring the system integrity and monitoring the availability of required navigation parameters, taking into account the impact of extreme space weather events, is still unresolved.

Космическая погода: факторы риска для глобальных навигационных спутниковых систем

Extreme space weather events affect the stability and quality of the global navigation satellite systems (GNSS) of the second generation (GPS, GLONASS, Galileo, BeiDou/Compass) and GNSS augmentation. We review the theory about mechanisms behind the impact of geomagnetic storms, ionospheric irregularities, and powerful solar radio bursts on the GNSS user segment. We also summarize experimental observations of the space weather effects on GNSS performance in 2000–2020 to confirm the theory. We analyze the probability of failures in measurements of radio navigation parameters, decrease in positioning accuracy of GNSS users in dual-frequency mode and differential navigation mode (RTK), and in precise point positioning (PPP). Additionally, the review includes data on the occurrence of dangerous and extreme space weather phenomena and the possibility for predicting their im- pact on the GNSS user segment. The main conclusions of the review are as follows: 1) the positioning error in GNSS users may increase up to 10 times in various modes during extreme space weather events, as compared to the background level; 2) GNSS space and ground segments have been significantly modernized over the past decade, thus allowing a substantial in- crease in noise resistance of GNSS under powerful solar radio burst impacts; 3) there is a great possibility for increasing the tracking stability and accuracy of radio navigation parameters by introducing algorithms for adaptive lock loop tuning, taking into account the influence of space weather events; 4) at present, the urgent scientific and technical problem of modernizing GNSS by improving the scientific methodology, hardware and software for monitoring the system integrity and monitoring the availability of required navigation parameters, taking into account the impact of extreme space weather events, is still unresolved.

New technique for calculating the ionospheric phase advance and dual frequency mode of measuring ionospheric TEC

The earlier developed alternative technique for calculating the ionospheric contribution into the full phase of the signal on the transionospheric paths of propagation, based on the perturbation theory in spherical co-ordinates with the spherically symmetric inhomogeneous zero-order approximation for the ionosphere, is further extended in order to apply it to the two-frequency mode of operation of GNSS. When doing this, the method itself is additionally validated and verified in the numerical experiment, where the reconstruction of the slant TEC calculated by the alternative technique for the two-frequency mode of operation is compared to that directly generated by the NeQuick model of the ionosphere.

Beat frequency measurement of the stabilized He-Ne laser 633 nm calibration in SNSU-BSN

In the metrology area, typical stabilized lasers are used as length primary standard. KIM-1, i.e. the iodine stabilized He-Ne laser in National Measurement Standards Laboratory-National Standardization Agency of Indonesia (SNSU-BSN) has been traceable to SI through CCL-K11 inter-laboratory comparison. The result was suitable for KIM-1 to be used as the length primary standard in SNSU-BSN. Beat frequency measurement has been applied in the optical frequency and wavelength calibration system for stabilized He-Ne laser 633 nm using KIM-1 as a reference standard. In the calibration replica, a dual-frequency mode (Agilent 5519B) took a role as DUT laser, which emits a pair of beams with a central wavelength of 632.991 354 nm in the vacuum with frequency difference 3.4 to 4.0 MHz and ±0.02 ppm stability for a typical lifetime. As a measurement result, the beat frequencies of the 1st and 2nd polarized beam of Agilent 5519B against KIM-1 are (121.33±0.06) MHz and (118.59±0.06) MHz.

Numerical study on dual-frequency ultrasonic enhancing cavitation effect based on bubble dynamic evolution.

Ultrasonic cavitation is a physical dynamic phenomenon of bubbles inflation, compression, and collapse in liquid. A dual-frequency ultrasonic cavitation dynamics model is established in this paper to investigate dynamic evolution of bubble under single and dual frequency ultrasonic modes. The variation of bubble radius, pressure, energy, temperature, and number of water vapor molecules inside the bubble in single and dual frequency ultrasonic modes are analyzed, respectively. The results show the oscillation of cavitation bubbles is more unstable and easier to collapse in dual-frequency ultrasound field than those in single-frequency ultrasound field. With the increase of the ultrasonic frequency, cavitation effect is weakened due to the shortage of oscillation period. Under the same ultrasonic power, the maximums of bubble radius, pressure, and water vapor molecules number inside the bubble in the dual-frequency mode are larger than those in the single-frequency mode. Under the ultrasonic excited by 50 kHz + 70 kHz, the maximum bubble radius and pressure can reach 36.061 μm and 2285.9 MPa, respectively, which are much larger than 18.183 μm, 730.61 MPa at 50 kHz and 14.576 μm, 332.25 MPa at 70 kHz. The calculation results of three different frequency combinations (30 kHz + 50 kHz, 40 kHz + 60 kHz and 50 kHz + 70 kHz) indicate dual-frequency ultrasound can significantly enhance the cavitation effect.

Precise Point Positioning Using Dual-Frequency GNSS Observations on Smartphone.

The update of the Android system and the emergence of the dual-frequency GNSS chips enable smartphones to acquire dual-frequency GNSS observations. In this paper, the GPS L1/L5 and Galileo E1/E5a dual-frequency PPP (precise point positioning) algorithm based on RTKLIB and GAMP was applied to analyze the positioning performance of the Xiaomi Mi 8 dual-frequency smartphone in static and kinematic modes. The results showed that in the static mode, the RMS position errors of the dual-frequency smartphone PPP solutions in the E, N, and U directions were 21.8 cm, 4.1 cm, and 11.0 cm, respectively, after convergence to 1 m within 102 min. The PPP of dual-frequency smartphone showed similar accuracy with geodetic receiver in single-frequency mode, while geodetic receiver in dual-frequency mode has higher accuracy. In the kinematic mode, the positioning track of the smartphone dual-frequency data had severe fluctuations, the positioning tracks derived from the smartphone and the geodetic receiver showed approximately difference of 3–5 m.

The characteristics of unsteady cavitation around a sphere

The unsteady cavitation typically includes three processes: the growth of cavitation, the instability and shedding of cavitation, and the collapse of cloud cavitation and the regeneration of attached cavitation. In this paper, the unsteady features of the cavitating flow past a sphere are investigated. A detached eddy simulation turbulence model and a transport equation cavitation model are used to model the cavitating flow. The numerical results give the unsteady process of cavitation at different cavitation numbers (0.36 < σ < 1.0), which cover the cavitation state from inception to supercavitation. When the cavitation number 0.8 < σ < 1.0, the flow instability belongs to the single frequency mode; when the cavitation number σ < 0.8, the flow instability becomes the dual-frequency mode. We analyzed the Strouhal (St) number based on the length of the cavitation and found that the St numbers are stable around 0.5 and 0.2 in the dual-frequency mode. In this mode, the high frequency corresponds to the frequency of the large-scale cavity shedding caused by repeated re-entrant jets. The low frequency, caused by the combination of wake flow and cavitation, is close to the natural frequency of the sphere. In addition, the cavity leading edge position and cavity morphology are analyzed in details. Some of the numerical results are compared with existing experimental data.

Effect of multimode ultrasound assisted extraction on the yield of crude polysaccharides from Lycium Barbarum (Goji)

Abstract The goals of this exploration were to find out the optimum conditions of ultrasound assisted extraction (UAE) of L. Barbarum crude polysaccharides. Furthermore, to research the impacts of three multi-frequency ultrasound assisted extraction modes on the yield of L. Barbarum crude polysaccharides. The results showed that by applying the traditional single-frequency UAE mode, the optimum extraction time was 30 min, extraction temperature of 60 °C, and solid/liquid ratio of 20 g/600 mL, at a power density of 300 W/L, and ultrasound frequency of 28 kHz. Secondly; a comparison was carried out between three UAE modes using the optimum extraction conditions obtained previously. The energy aggregation counter flow dual-frequency UAE mode gave the highest yield of 38.93% of crude polysaccharides. Followed by the Opposite-sit dual-frequency UAE mode and the energy aggregation counter flow single-frequency UAE mode with yields of 33.60%, and 26.38% of crude polysaccharides, respectively. As a result the ultrasound assisted extraction with dual-frequency mode is more effective for the extraction of L. Barbarum crude polysaccharides. Furthermore, the yield of crude polysaccharides increased by 73.41% using the dual-frequency ultrasound extraction compared to traditional hot water extraction.

Wireless Power Transfer System Based on Strapping Resonators

In this study, a kind of strapped resonator is proposed to deal with high power wireless power transfer (WPT) in microwave regimes. In many specific applications, such as high power microwave wireless power transfer system (WPT), a coil resonator is not suitable due to the frequency limitations. The high cost of the high-permittivity dielectric resonators also limits their application. As a high Q resonator, the strapped resonator is often used in the anode structure of a magnetron. The field distribution of π and π + 1 modes allow the system to operate in dual-frequency mode. Numerical simulation and experimental validation show that with a certain distance, the system provides power transfer efficiency of more than 80% and 70% at 630 MHz and 970 MHz, respectively. Compared to the system based on dielectric resonators, the proposed system has higher power capacity. The leakage and radiation loss of the system is also discussed using numerical methods.