Dual-frequency System Research Articles

Code-Carrier coherence monitoring for dual frequency SBAS

User differential range error (UDRE) is used to bound satellite clock and orbit errors in satellite-based augmentation system (SBAS). The code carrier incoherence (CCI) originated from satellite payload faults may degrade generated satellite corrections and corresponding UDRE/DFRE bounding. To ease the burden on UDRE caused by the CCI induced ranging error, a code carrier coherence (CCC) monitor is implemented. With SBAS evolving towards L1-L5 dual-frequency multi-constellation direction, ionosphere-free smoothing is preferred for both ground and airborne data processing, saving the great effort of bounding the ionosphere correction. Due to the more pronounced CCI fault in the L5 signal compared to the L1 signal, its impact on user positioning is magnified. It has been analyzed that the presence of satellite clock failure CCI fault does not undermine the accuracy of the generated satellite corrections. However, to enhance the system availability, the satellite clock failure should be considered and a dual-frequency CCC monitor is required to monitor the measurements from both frequencies, while excluding the effects of ionosphere delay. One solution is to add another L1-like monitor for monitoring the additional L5 signal. Since only ionosphere-free errors need to be bounded in the dual-frequency system, an ionosphere-free monitor is another choice. Furthermore, a chi-squared monitor is proposed combining of three ionosphere-free statistics to monitor both frequencies simultaneously. These options are compared on the protected fault space and the performance on the probability of missed detection. It is concluded that the chi-squared monitor is an optimal choice, which protects user against an arbitrary CCI fault space excluding the ones with the form of ionosphere anomalies, and at the same time, achieves lower probability of missed detection than other monitors with the same fault magnitude.

FSS Sandwiched Dual-Frequency Reflectarray for Mobile Communication Applications

Sandwiched frequency selective surface (FSS) is proposed as an additional reflection surface for a dual-frequency reflectarray system. The range of reflection phase for a reflectarray depends on the substrate thickness sensitively. Usually, a tradeoff between the smooth linear level and the wide reflection phase range is needed, especially for a dual-frequency system. By inserting an FSS between the ground plane and the reflecting element layer, a selective plane for the dual-frequency band is provided. For the higher frequency band, the FSS layer is a reflection plane. For the lower frequency band, it is transparent and the reflection plane is changed into the metal ground plane. A dual-band reflectarray with a scattering angle of 30 degrees is simulated and measured to validate this concept.

A fundamental study on the degradation of paracetamol under single- and dual-frequency ultrasound

The degradation of paracetamol, a widely found emerging pharmaceutical contaminant, was investigated under a wide range of single-frequency and dual-frequency ultrasonic irradiations. For single-frequency ultrasonic irradiation, plate transducers of 22, 98, 200, 300, 400, 500, 760, 850, 1000, and 2000 kHz were employed and for dual-frequency ultrasonic irradiation, the plate transducers were coupled with a 20 kHz ultrasonic horn in opposing configuration. The sonochemical activity was quantified using two dosimetry methods to measure the yield of HO• and H2O2 separately, as well as sonochemiluminescence measurement. Moreover, the severity of the bubble collapses as well as the spatial and size distribution of the cavitation bubbles were evaluated via sonoluminescence measurement. The paracetamol degradation rate was maximised at 850 kHz, in both single and dual-frequency ultrasonic irradiation. A synergistic index higher than 1 was observed for all degrading frequencies (200 – 1000 kHz) under dual-frequency ultrasound irradiation, showing the capability of dual-frequency system for enhancing pollutant degradation. A comparison of the results of degradation, dosimetry, and sonoluminescence intensity measurement revealed the stronger dependency of the degradation on the yield of HO• for both single and dual-frequency systems, which confirms degradation by HO• as the main removal mechanism. However, an enhanced degradation for frequencies higher than 500 kHz was observed despite a lower HO• yield, which could be attributed to the improved mass transfer of hydrophilic compounds at higher frequencies. The sonoluminescence intensity measurements showed that applying dual-frequency ultrasonic irradiation for 200 and 400 kHz made the bubbles larger and less uniform in size, with a portion of which not contributing to the yield of reactive oxidant species, whereas for the rest of the frequencies, dual-frequency ultrasound irradiation made the cavitation bubbles smaller and more uniform, resulting in a linear correlation between the overall sonoluminescence intensity and the yield of reactive oxidant species.

Dual frequency ultrasonic cavitation in various liquids: High-speed imaging and acoustic pressure measurements

Ultrasonic cavitation is used in various processes and applications, utilizing powerful shock waves and high-speed liquid jets generated by the collapsing bubbles. Typically, a single frequency source is used to produce the desired effects. However, optimization of the efficiency of ultrasound reactors is necessary to improve cavitation activity in specific applications such as for the exfoliation of two dimensional materials. This research takes the next step to investigate the effect of a dual frequency transducer system on the bubble dynamics, cavitation zone, pressure fields, acoustic spectra, and induced shock waves for four liquids with a range of physical properties. Using ultra-high-speed imaging and synchronized acoustic pressure measurements, the effect of ultrasonic dual frequencies on bubble dynamics was investigated. The addition of a high frequency transducer (1174 kHz) showed that the bubble fragments and satellite bubbles induced from a low frequency transducer (24 kHz) were able to extend their lifecycle and increase spatial distribution, thus, extending the boundaries of the cavitation zone. Furthermore, this combination of ultrasonic frequencies generated higher acoustic pressures (up to 180%) and enhanced the characteristic shock wave peak, indicating more bubble collapses and the generation of additional shock waves. The dual frequency system also enlarged the cavitation cloud size under the sonotrode. These observations specifically delineated the enhancement of cavitation activity using a dual frequency system pivotal for optimization of existing cavitation-based processing technologies.

Dual color, frequency, pulse duration and shape agile laser system for particle spectroscopy and manipulation.

A dual color, frequency and pulse duration agile laser system, capable of delivering laser pulses in arbitrary temporal profiles with ∼1 ns to ∼1 µs pulse duration, chirping rates of ∼27 MHz/ns with an achievable chirping range of several GHz across the pulse duration, and with energies ranging from a few nJ to hundreds of mJ per pulse has been developed. The flexibility and capability of this laser system provide a wide range of laser parameters that can be exploited to optimize operational conditions in various experiments ranging from laser diagnostics to spectroscopy and optical manipulation of matter. The developed system is successfully demonstrated to obtain coherent Rayleigh-Brillouin scattering (CRBS) in both single and dual color configuration, in an effort to expand the non-intrusive accessibility towards lower pressure regime for neutral gas and plasma diagnostics.

Dual-Frequency RF Impedance Matching Circuits for Semiconductor Plasma Etch Equipment

The change in electrode impedance of semiconductor equipment due to repetitive processes is a major issue that creates process drift. In the current plasma etch chamber with a dual-frequency power system, the high-powered radio frequency (RF) source contributes to the enhancement of the plasma density, and the low-frequency bias power at the bottom electrode is adopted to enhance the injected ion energy in the plasma. The impedance control of the top electrode in dual-frequency capacity coupled plasma limits the impedance matching capability of the RF matching system because it only considers the high-frequency RF source. To control the precise impedance in dual-frequency semiconductor equipment, independent impedance control is required for each frequency. In this study, the impedance corresponding to a specific frequency was independently controlled using L (inductor) and C (capacitor). A 60 MHz stop filter and VVC were used to control 2 MHz impedance at a specific point, and a 2 MHz stop filter and VVC were used to control 60 MHz impedance. In the case of 2 MHz impedance control, the 2 MHz impedance changed from 10.9−j893 to 0.3−j62 and the 60 MHz impedance did not change. When controlling the 60 MHz impedance, the 60 MHz impedance changed from 0.33 + j26.53 to 0.2 + j190 and the 2 MHz impedance did not change. The designed LC circuits cover the impedance of 60 and 2 MHz separately and are verified by the change in the capacitance of the vacuum variable capacitors implemented in the RF impedance matching system.

Implementation of comparative detection approaches for the accurate assessment of sediment thickness and sediment volume in the Passaúna Reservoir

Siltation has significant economic and social impacts as it directly reduces the useable amount of water in reservoirs. Giving a solution to the issue of sedimentation is a complicated task and maybe one of the most important engineering and environmental challenges of the 21st century. The deposited volume and the distribution pattern of the sediment are often unknown and not easy to assess. The sedimentation process is highly dynamic, initially due to the hydrological conditions of the incoming rivers, but also due to common internal phenomena like resuspension or density currents. Sediment remediation measures such as mechanical sediment removal or flushing are planned based on the sediment thickness distribution and the overall sediment volume/mass. Often, the sediment thickness is calculated through topographic differencing between the pre-impoundment reservoir lake bottom and the actual lake bottom. However, it is common that the previous depth distribution map is not available or in insufficient quality. In this regard, alternative measurement techniques have to be taken into consideration. In this study, we assessed the best possible approach depending on the characteristics of the sediment and of the reservoir. We combined three different acoustic systems (a multibeam, a sub-bottom profiler, and a single beam dual frequency system) with sediment coring and dynamic free fall penetrometer measurements for an improved assessment of sediment stock and sediment distribution in the Passaúna Reservoir. Our results showed that topographic differencing could not be applied, as the data for the pre-impoundment lake bottom was insufficiently accurate. The parametric sub-bottom profiler could detect the sediment thickness in high accuracy, but significant limitations were recorded in areas with high gas contents. The dual-frequency echosounder derived the sediment thickness with a normalized mean absolute error of 56% due to the high volumetric gas content in the sediment. The dynamic free-fall penetrometer showed satisfying results compared to the other systems. The normalized mean absolute error was 22%, and sediment thickness could be detected in areas with up to 1.8 m of sediment. Sediment coring is also a reliable technique for sediment thickness determination. However, the results showed that if only traditional coring devices are used (gravity corer), the limited penetration depth of the equipment combined with sampling disturbances often prevent a correct assessment of the sediment thickness. The overall results of this study can help for an improved decision-making regarding reservoir management. The accurate assessment of sediment volume and distribution can reduce costs for sediment removal and assist in having a precise overview of the reservoir lifetime.

Synchronization analysis of two eccentric rotors with double-frequency excitation considering sliding mode control

In petroleum exploitation industry, self-synchronous vibrating screen excited with dual-frequency cannot obtained an ideal synchronization motion state due to its own inherent coupling characteristics, which is unsuitable to separate cuttings from drilling fluid. Thus, for solving the above-mentioned problem, a controlled system of two eccentric rotors (ERs) actuated with double-frequency is proposed by considering sliding mode control (SMC) method. Firstly, motion differential equation in each direction is established according to physical model of the vibration system. Then, self-synchronous mechanism between high-frequency rotor and low-frequency rotor is gradually analyzed by small parameters method and Poincare–Lyapunov theory, and it is revealed that the self-synchronous vibration system cannot implement a stable phase difference on account of the existence of velocity error and phase error. Subsequently, combining the SMC algorithm with master-slave control (MSC) structure, tracking controllers of velocity error and phase error are systematically designed to control the synchronization state of the dual-frequency system. Finally, Runge–Kutta method is assigned to validate the reliability of theory and the stability of system. Comparing controlled synchronization with self-synchronization, the results demonstrate that the phase difference between the rotors can be accurately stabilized at zero by the proposed control strategy. Meanwhile, the designed control system has strong robustness to restrain the dynamic behavior of vibration system under parameter variations. This study will be helpful for the improvement of separation technology.

Multifrequency Phase-Shifted Control for Multiphase Multiload MCR WPT System to Achieve Targeted Power Distribution and High Misalignment Tolerance

With urgent market demand for multiload electronic applications, multiload magnetically coupled resonant (MCR) wireless power transfer (WPT) system has caused widespread concern. In the practical applications, multiload MCR WPT system should have the capability to realize targeted power distribution among loads and stable output power against misalignment of load. To achieve this goal, a multiphase multifrequency system with multiple loads is proposed in this article, where multi-phase structure of transmitting coils can enhance the misalignment tolerance, and multiple operating frequencies are beneficial to achieve multiload identification and targeted power distribution. For simplicity, this article mainly studies a two-phase dual-frequency system with two loads and proposes two phase-shifted control strategies. The equivalent circuit model of the system is established, and the output power in the open-loop system under two phase-shifted control methodologies are analyzed. According to that, the targeted power distribution strategy by adjusting the resonant frequency of the transmitter is implemented. Moreover, the closed-loop control schemes based on phase-shifted control methodologies are adopted to realize stable output power precisely against the misalignment of loads. Finally, a prototype of two-phase dual-frequency MCR WPT system with two loads is built in the laboratory. The experimental results prove the correctness of the theoretical analysis.

Exploring fusion-reactor physics with high-power electron cyclotron resonance heating on ASDEX Upgrade

The electron cyclotron resonance heating (ECRH) system of the ASDEX Upgrade tokomak has been upgraded over the last 15 years from a 2 MW, 2 s, 140 GHz system to an 8 MW, 10 s, dual frequency system (105/140 GHz). The power exceeds the L/H power threshold by at least a factor of two, even for high densities, and roughly equals the installed ion cyclotron range of frequencies power. The power of both wave heating systems together (>10 MW in the plasma) is about half of the available neutral beam injection (NBI) power, allowing significant variations of torque input, of the shape of the heating profile and of Qe/Qi, even at high heating power. For applications at a low magnetic field an X3-heating scheme is routinely in use. Such a scenario is now also forseen for ITER to study the first H-modes at one third of the full field. This versatile system allows one to address important issues fundamental to a fusion reactor: H-mode operation with dominant electron heating, accessing low collisionalities in full metal devices (also related to suppression of edge localized modes with resonant magnetic perturbations), influence of Te/Ti and rotational shear on transport, and dependence of impurity accumulation on heating profiles. Experiments on all these subjects have been carried out over the last few years and will be presented in this contribution. The adjustable localized current drive capability of ECRH allows dedicated variations of the shape of the q-profile and the study of their influence on non-inductive tokamak operation (so far at q95 > 5.3). The ultimate goal of these experiments is to use the experimental findings to refine theoretical models such that they allow a reliable design of operational schemes for reactor size devices. In this respect, recent studies comparing a quasi-linear approach (TGLF) with fully non-linear modeling (GENE) of non-inductive high-beta plasmas will be reported.

Assessment of the Superharmonic Response of Microbubble Contrast Agents for Acoustic Angiography as a Function of Microbubble Parameters

Acoustic angiography is a superharmonic contrast-enhanced ultrasound imaging technique that enables 3-D high-resolution microvascular visualization. This technique utilizes a dual-frequency imaging strategy, transmitting at a low frequency and receiving at a higher frequency, to detect high-frequency contrast agent signatures and separate them from tissue background. Prior studies have illustrated differences in microbubble scatter dependent on microbubble size and composition; however, most previously reported data have utilized a relatively narrow frequency bandwidth centered around the excitation frequency. To date, a comprehensive study of isolated microbubble superharmonic responses with a broadband dual-frequency system has not been performed. Here, the superharmonic signal production of 14 contrast agents with various gas cores, shell compositions, and bubble diameters at mechanical indices of 0.2 to 1.2 was evaluated using a transmit 4 MHz, receive 25 MHz configuration. Results indicate that perfluorocarbon cores or lipid shells with 18- or 20-carbon acyl chains produce more superharmonic signal than sulfur hexafluoride cores or lipid shells with 16-carbon acyl chains, respectively. As microbubble diameter increases from 1 to 4 µm, superharmonic generation decreases. In a comparison of two clinical agents, Definity and Optison, and one preclinical agent, Micromarker, Optison produced the least superharmonic signal. Overall, this work suggests that microbubbles around 1 μm in diameter with perfluorocarbon cores and longer-chained lipid shells perform best for superharmonic imaging at 4 MHz. Studies have found that microbubble superharmonic response follows trends different from those described in prior studies using a narrower frequency bandwidth centered around the excitation frequency. Future work will apply these results in vivo to optimize the sensitivity of acoustic angiography.

Wideband polarizers, switches and waveguide for overmoded corrugated transmission lines

Overmoded corrugated waveguide is efficient at transmitting power over a large frequency bandwidth. This operational flexibility becomes important in multi-frequency systems. For 50-mm diameter aluminum corrugated waveguide nominally designed for the ITER 170 GHz ECH system, the theoretical ohmic loss of the HE11mode is around 0.3e-3 dB/m. In a possible dual-frequency system at ITER, the theoretical loss in the same waveguide increases to a manageable 0.8e-3 dB/m at 104 GHz. As examples of other wideband components, General Atomics has built several pairs of 63.5-mm diameter waveguide polarizers for the TCV tokamak’s ECH transmission line that are designed to operate for 1 MW at frequencies ranging from 82.6 to 118 GHz. In addition, polarizers have been designed for ITER’s 50-mm diameter transmission line. A computer code that calculates both the required mirror rotation angles and the ohmic losses predicts that these polarizers will function effectively at both 170 GHz and 104 GHz. A new class of wideband waveguide switches with rotary actuators have been supplied for the 82.6–126 GHz transmission lines at TCV, further emphasizing the broadband capabilities of corrugated waveguide components.

Power allocation and range performance considerations for a dual-frequency EBPSK/MPPSK system

ABSTRACTExtended binary phase shift keying/M-ary position phase shift keying (EBPSK/MPPSK)-MODEM provides radar and communication functions on a single hardware platform with a single waveform. However, its range estimation accuracy is worse than continuous-wave (CW) radar because of the imbalance of power in two carrier frequencies. In this article, the power allocation method for dual-frequency EBPSK/MPPSK modulated systems is presented. The power of two signal transmitters is adequately allocated to ensure that the power in two carrier frequencies is equal. The power allocation ratios for two types of modulation systems are obtained. Moreover, considerations regarding the range of operation of the dual-frequency system are analysed. In addition to theoretical considerations, computer simulations are provided to illustrate the performance.

Tunable dual frequency optoelectronic oscillator with low intermodulation based on dual-parallel Mach-Zehnder modulator.

A tunable dual-frequency optoelectronic oscillator (OEO) based on dual-parallel Mach-Zehnder modulator (DPMZM) with low intermodulation is proposed and experimentally demonstrated. Two tunable electronic band-pass filters are used to select the oscillation modes of the two oscillating frequencies to achieve tunable dual-frequency OEO (TDF-OEO). Each of the two selected modes are modulated onto one sub-modulator of the DPMZM. By choosing proper bias conditions of the DPMZM, the intermodulation components generated by the dual-frequencies are suppressed. The tuning range of the TDF-OEO is from 1 GHz to 15 GHz in the experiment. We also discussed and experimentally demonstrated the tuning limitation of this dual frequency system.

Multifrequency Method for Measuring Properties of Shock Tube Produced Plasma

A novel multifrequency method is introduced in this paper for measuring the plasma produced by a $ \Phi 800$ -mm shock tube. The core of the measured object is a volume of relatively uniform plasma contained by the rectangular test section, and the dual-frequency or multifrequency configuration of the measuring system enables the coherent cancellation of measurement deviations. Based on the Lorentz model of plasma, the obvious correspondence exists between the plasma parameters and the transmittance variation with different frequencies of the electromagnetic wave; hence, the electron density $N_{e}$ and the collision frequency $\nu $ of the plasma could be retrieved according to the measured transmittance. A dual-frequency system is established as the verification of the proposed method. The measured values of the electron density by the proposed method are compared with those obtained by other means, and the results are in good agreement.

Acoustical scattering cross section of gas bubbles under dual-frequency acoustic excitation

The acoustical scattering cross section is a paramount parameter determining the scattering ability of cavitation bubbles when they are excited by the incident acoustic waves. This parameter is strongly related with many important applications of acoustic cavitation including facilitating the reaction of chemical process, boosting bubble sonoluminescence, and performing non-invasive therapy and drug delivery. In present paper, both the analytical and numerical solutions of acoustical scattering cross section of gas bubbles under dual-frequency excitation are obtained. The validity of the analytical solution is shown with demonstrating examples. The nonlinear characteristics (e.g., harmonics, subharmonics and ultraharmonics) of the scattering cross section curve under dual-frequency approach are investigated. Compared with single-frequency approach, the dual-frequency approach displays more resonances termed as “combination resonances” and could promote the acoustical scattering cross section significantly within a much broader range of bubble sizes due to the generation of more resonances. The influence of several paramount parameters (e.g., acoustic pressure amplitude, power allocations between two acoustic components, and the ratio of the frequencies) in the dual-frequency system on the predictions of scattering cross section has been discussed.

Multifrequency Inductive Power Transfer

This paper presents a generalized analysis of an inductive power transfer system where multiple frequencies are used to transfer power through the magnetic link. Specifically, we consider a system that amplifies both the fundamental and the third harmonic generated by a full-bridge inverter in order to transfer power to a receiver at both frequencies. The system is analyzed in a generalized manner, by looking at the transconductance function at the transmitter and the receiver for each of the harmonics. Using this approach, the emitted field strength, inverter losses, combined transmitter and receiver coil conduction losses, and VA ratings are compared to a reference single-frequency system. The analysis shows that the dual-frequency system can outperform the single-frequency equivalent for all metrics considered; however, in practice, a tradeoff between the performance criteria is necessary, since the optimal operation points for each criterion cannot be attained with a single design.

High efficiency coupling of radio frequency beams from the dual frequency gyrotron with a corrugated waveguide transmission system

High efficiency coupling of the millimeter-wave output of the dual-frequency gyrotron with the transmission line was demonstrated. The dual-frequency gyrotron was design to produce similar beam profiles for two operation frequencies (170 GHz and 137 GHz). Using two RF beam reflecting mirrors in a matching optics unit (MOU), which are designed to transform the beam profile of the gyrotron output to the fundamental waveguide mode (HE(11) mode) at 170 GHz, high efficiency coupling was demonstrated for two frequencies. The measured mode purity of HE(11) mode was 96% at 170 GHz and 94% at 137 GHz operations with the identical mirrors at the fixed mirror position and angle. The results indicate that the significantly simple dual frequency system is realized by the gyrotron designed to output the similar beam profiles at different frequency operation.

Dual-Frequency Technique for Assessment of Cardiopulmonary Effective RCS and Displacement

In this paper, a technique for the precise assessment of key parameters relating to cardiopulmonary activity is presented. Dual-frequency radar measurements are described with quantitative analyses of the return signal, in terms of intensity and phase modulation magnitude. The first parameter is a measure of the radar cross section of the portion of the torso surface that is moving due to respiration and heartbeat activity. It is defined as the cardiopulmonary effective radar cross section (ERCS). The second parameter corresponds to the maximum displacement of the torso surface in the direction of incidence. This paper presents the first reported dual frequency radar system for determining cardiopulmonary ERCS and displacement. A system calibration procedure using spherical targets is described and displacement measurement is validated for the dual-frequency system. Preliminary testing results consistently showed an ERCS that is larger for the back of the torso and smaller for the side compared to the front, while the respiration depth is smaller in the prone position than in supine.

CALIBRATION OF SPACEBORNE LINEARLY POLARIZED LOW FREQUENCY SAR USING POLARIMETRIC SELECTIVE RADAR CALIBRATORS

Spaceborne synthetic aperture radar (SAR) systems operating at lower frequencies, such as P-band, are signiflcantly afiected by Faraday rotation (FR) efiects. This paper presents a novel algorithm for measuring system errors (channel imbalance and cross-talk) in the presence of Faraday rotation for spaceborne polarimetric SAR data. It uses four polarimetric selective calibrators (four polarimetric active radar calibrators (PARCs) or possibly two PARCs and two gridded trihedrals). Theoretical analysis and simulations demonstrate that the optimized calibration scheme puts tight constraints on the accuracy of the associated Faraday rotation if the cross-talk is to be accurately measured. There are also strong constraints on the allowable signal-to-noise ratio and average polarimetric noise associated with the calibration devices. The analysis suggests that, unless the calibration sites are at the magnetic equator, independent measurements of total electron content (TEC) from a direct ground-satellite line-of-sight dual-frequency system are also needed.