Triple Frequency Research Articles

Multifrequency ultrasonic transducers based on dual vibration and harmonic mode

Multifrequency ultrasonic transducers have broad application prospects in the field of biomedical due to their high imaging resolution and detection depth. This paper proposed a design method of triple frequency single-element transducers by finite element method(FEM). The triple frequency transducers are based on contour mode, thickness mode and the third harmonic of thickness mode. Nine micro single element transducers with different widths and matching layers were fabricated and characterized to verify the design method. The traditional 30 MHz single frequency transducer and 2.3 MHz 1–3 piezoelectric composite transducer were used to compare with high frequency part and low frequency part of the triple frequency transducers, respectively. The pulse-echo characteristics of the triple frequency transducers have impressive low and middle frequency part. The high frequency part is similar with traditional transducer except the sensitivity is 0.5 times. The results certify the feasibility of a triple-Frequency transducer based on dual vibration and harmonic modes.

Modeling and assessment of multi-frequency GPS/BDS-2/BDS-3 kinematic precise point positioning based on vehicle-borne data

BeiDou Navigation Satellite System (BDS) has got the global service capability after the launch of the 55th BDS-3 satellite on June 23, 2020. Currently, BDS is operated based on both the second generation BDS (BDS-2, with 15 satellites transmitting triple frequency signals) and the third generation BDS (BDS-3, with 30 satellites providing services from five frequency signals). To make full use of BDS-2 + BDS-3 signals (B1I, B2I, B3I, B1C, and B2a), this paper introduces an undifferenced and uncombined Precise Point Positioning (PPP) model by using single/dual/triple frequencies BDS-2/BDS-3 data. Results illustrate that the Root Mean Square (RMS) values of BDS-3 PPP based on new signals are better than BDS-2 (B1I + B3I), but worse than BDS-3 (B1I + B3I). Generally, triple-frequency PPP is close to that of dual-frequency PPP, but it is improved significantly in the north, east and vertical components comparing with single-frequency PPP. Compared to the positioning accuracy of GPS + BDS-2 PPP, those of GPS + BDS-3 PPP are improved obviously, especially in the horizontal components. While using BDS-2 and BDS-3 together, the positioning performance of GPS + BDS-2 + BDS-3 is upgraded significantly in both horizontal and vertical directions. Moreover, the convergence time of BDS-3 (especially B1C + B2a) and BDS-2 + BDS-3 PPP are accelerated visibly comparing with that of BDS-2 PPP.

Triple-frequency meteor radar full wave scattering

Context. Radar scattering from meteor trails depends on several poorly constrained quantities, such as electron line density, q, initial trail radius, r0, and ambipolar diffusion coefficient, D. Aims. The goal is to apply a numerical model of full wave backscatter to triple frequency echo measurements to validate theory and constrain estimates of electron radial distribution, initial trail radius, and the ambipolar diffusion coefficient. Methods. A selection of 50 transversely polarized and 50 parallel polarized echoes with complete trajectory information were identified from simultaneous tri-frequency echoes recorded by the Canadian Meteor Orbit Radar. The amplitude-time profile of each echo was fit to our model using three different choices for the radial electron distribution assuming a Gaussian, parabolic-exponential, and 1-by-r2 electron line density model. The observations were manually fit by varying, q, r0, and D per model until all three synthetic echo-amplitude profiles at each frequency matched observation. Results. The Gaussian radial electron distribution was the most successful at fitting echo power profiles, followed by the 1∕r2. We were unable to fit any echoes using a profile where electron density varied from the trail axis as an exponential-parabolic distribution. While fewer than 5% of all examined echoes had self-consistent fits, the estimates of r0 and D as a function of height obtained were broadly similar to earlier studies, though with considerable scatter. Most meteor echoes are found to not be described well by the idealized full wave scattering model.

Triple Band Compact Monopole Antenna for Applications Like Bluetooth, WiMAX and WLAN

In this work, a novel triband antenna is developed for wireless local area network (WLAN), worldwide interoperability for microwave access (WiMAX), and Bluetooth application. The proposed antenna is printed on a low-cost FR-4 substrate and has an overall size of 25 mm × 40 mm × 1.6 mm. Coplanar waveguide (CPW) line with characteristic impedance of 50 Ω is used as feed for the designed antenna. A prototype of this antenna is fabricated and tested to validate the simulation results. The measured result shows that the antenna has the triple-band response with frequency bands that correspond to S11<−10 dB 2.36 − 3.17, 3.8 − 4.35, and 5.69 − 6.02 GHz. The measured gains of the antenna at resonant frequencies of 2.61, 4.115 and 5.85 GHz are 0.756, 0.925 and 1.589 dBi, respectively. Maximum decrement in measured gain is only 0.671 dB which is attributed to losses from connectors and cables. A novel approach, based on a combination of a cap-shaped ground plane and gap coupling technique in the form of an interdigital capacitor (IDC), is used to achieve the characteristic of triple frequency bands. Finally, the utility of the proposed antenna is checked with a four-element MIMO antenna.

Phase unwrapping method combining dual-frequency heterodyne with dual complementary phase encoding

Phase encoding and phase-shift profilometry are two commonly used 3D measurement techniques. However, the acquired phases in the techniques are subject to jump errors due to phase ambiguity and phase errors caused by multiple heterodyne. The phase-shifting profilometry also makes the selection of fringe period difficult. To overcome this problem and achieve high-precision measurement, a phase unwrapping method that combines dual-frequency heterodyne with double complementary phase encoding is proposed. First, two wrapped phases are obtained by two groups of sinusoidal fringes; the heterodyne phase is obtained after heterodyne processing, and the high-frequency phase is expanded by heterodyne phase. Second, the fringe levels are obtained using the complementary phase encoding fringes that are shifted by half an order, and then the absolute phase is obtained by selecting different phase coding levels according to different regions for the first phase unwrapping; Finally, the phase noise is removed by exploiting the difference between the phase slopes of adjacent pixels. Experimental results show that a system with the proposed method achieves an RMS error of 0.015 mm. In addition, the period of dual-frequency heterodyne synthesis does not need to cover the whole field of view, which breaks the limitation of frequency selection of the traditional dual-frequency heterodyne method and triple frequency heterodyne method, enabling high-precision measurement with higher frequency fringes. This method overcomes the limitations of the phase principal value error when using higher frequency fringes for high-precision measurement, improves the measurement effect of reflective objects, and effectively avoids the error caused by phase jump.

Dual polarized triple wideband circular microstrip antenna for GSM and satellite applications

Dual polarized triple frequency wideband design of circular microstrip antenna using the combination of slots and stub is proposed. This triple wideband response is explored by using a thinner substrate in the air suspended configuration that enables the input impedance matching at various higher order resonant modes together with the fundamental mode. Amongst different variations, modifications in terms of the slots and stubs degenerates and optimizes the spacing in between the fundamental and higher order modes, which leads to dual polarized wideband response. On air suspended FR4 substrate with thickness of 0.055λg, optimized single patch configuration yields dual polarized triple wideband response at 856, 1177, and 1783 MHz respectively giving frequency ratio of 1:1.37:2.0. It yields impedance bandwidth of 8.4%, 11.5%, and 11.4% at the three frequencies with respective broadside gain of 7.4, 6.5, and 3.5 dBi. The proposed configuration yields frequency and polarization agility satisfying the requirements of GSM850/navigation satellite/GSM 1800 applications.

Modeling and Performance Evaluation of Precise Positioning and Time-Frequency Transfer with Galileo Five-Frequency Observations

The present Global Navigation Satellite System (GNSS) can provide at least double-frequency observations, and especially the Galileo Navigation Satellite System (Galileo) can provide five-frequency observations for all constellation satellites. In this contribution, precision point positioning (PPP) models with Galileo E1, E5a, E5b, E5 and E6 frequency observations are established, including a dual-frequency (DF) ionospheric-free (IF) combination model, triple-frequency (TF) IF combination model, quad-frequency (QF) IF combination model, four five-frequency (FF) IF com-bination models and an FF uncombined (UC) model. The observation data of five stations for seven days are selected from the multi-GNSS experiment (MGEX) network, forming four time-frequency links ranging from 454.6 km to 5991.2 km. The positioning and time-frequency transfer performances of Galileo multi-frequency PPP are compared and evaluated using GBM (which denotes precise satellite orbit and clock bias products provided by Geo Forschung Zentrum (GFZ)), WUM (which denotes precise satellite orbit and clock bias products provided by Wuhan University (WHU)) and GRG (which denotes precise satellite orbit and clock bias products provided by the Centre National d’Etudes Spatiales (CNES)) precise products. The results show that the performances of the DF, TF, QF and FF PPP models are basically the same, the frequency stabilities of most links can reach sub10−16 level at 120,000 s, and the average three-dimensional (3D) root mean square (RMS) of position and average frequency stability (120,000 s) can reach 1.82 cm and 1.18 × 10−15, respectively. The differences of 3D RMS among all models are within 0.17 cm, and the differences in frequency stabilities (in 120,000 s) among all models are within 0.08 × 10−15. Using the GRG precise product, the solution performance is slightly better than that of the GBM or WUM precise product, the average 3D RMS values obtained using the WUM and GRG precise products are 1.85 cm and 1.77 cm, respectively, and the average frequency stabilities at 120,000 s can reach 1.13 × 10−15 and 1.06 × 10−15, respectively.

Polysaccharides from ginger stems and leaves: Effects of dual and triple frequency ultrasound assisted extraction on structural characteristics and biological activities

Dual- and triple-frequency ultrasonic processing features advantages such as uniform energy distribution and the ease of resonance within the extracted raw material, which attenuates the directional effect of single frequency ultrasonic treatment. In this study, the effects of dual-frequency and triple-frequency ultrasound extraction were evaluated based on the physicochemical properties, structural characteristics, and biological activities of polysaccharides from ginger stems and leaves (GSLPs). Triple-frequency ultrasound extraction was found to obtain higher polysaccharide yield (10.50 ± 0.20%) than dual-frequency ultrasound extraction (9.74 ± 0.30%). Moreover, the former possessed higher contents of total sugar, uronic acid, and sulfate radicals, but lower molecular weight. Both types of polysaccharides exhibited intact helical structure, similar thermal properties, and clumpy structures with porous surfaces. More importantly, the polysaccharides extracted by triple-frequency ultrasound extraction showed stronger antioxidant activity and better functional properties, while those extracted by dual-frequency extraction exhibited superior rheological properties due to larger molecular weight. The latter also demonstrated better glucose entrapment and α-glucosidase inhibitory activity. In conclusion, dual- and triple-frequency ultrasound treatment may enable a greater range of GSLP applications in functional foods.

Tunable C + L bands triple frequency spacing multi-wavelength Brillouin-erbium fiber laser

We propose and experimentally demonstrate a wide tuning range triple frequency spacing multi-wavelength Brillouin erbium fibre laser (MBEFL). The laser can be tuned in the C- and L-bands of the optical communication windows. At a Brillouin pump power of 3 dBm and 1480-nm pump power of 195 mW, the proposed MBEFL generates up to five triple spacing Brillouin Stokes lines that can be tuned over 60 nm (from 1535 to 1595 nm). A wide tuning range is achieved through the combined techniques of pre-amplification and a virtual mirror of stimulated Brillouin scattering in the laser cavity. The generated Brillouin Stokes lines exhibit good flatness and stability with minimal power fluctuation.

Optimized Triple-Band h-Shaped Slot Microstrip Antenna Array Based Wireless Mobile Charger

This paper proposes a novel design of a triple frequency band passive communication receiver for wireless chargers for smart wireless devices, wearables and other wireless devices powered with lithium-ion batteries. The design of this receiver includes triple frequency band h-shaped slot microstrip two-element antenna array; Radio Frequency (RF) matching circuit; and passive Voltage Doubler Rectifier (VDR) circuits. The said antenna design uses 900 MHz, 1800 MHz, and 2400 MHz frequency bands. This design aims to have comparatively similar charging rate as existing wireless chargers. Therefore, the proposed antenna is the major part of the design, because it should receive more power from the three RF signal sources to achieve target charging rate. Also, in the receiver design, a (Duroid 6010) substrate with a relative permittivity 10.7 is used. Such a receiver consists of an RF matching circuit, RF multistage VDR, and a DC load circuit that would produce a 3.7 V at the output. In order to minimize the power dissipation in the rectifier circuit and consequently increase efficiency, a zero bias Schottky diode is used. Finally, the simulation results indicated that the number of VDR stages and the value of load resistance are the two major factors affecting the output of the proposed wireless charger.

A novel wavelength modulation spectroscopy in TDLAS

We propose a novel wavelength modulation spectroscopy (WMS), which adds a triple frequency modulation current to the fundamental sinusoidal modulation current. By selecting theoretical optimum modulation indices, amplitude of the detected 2f improves 66% than that of the traditional wavelength modulation spectroscopy. Experimental results accord with theoretical expectation. Minimum detection limit obtained by the new modulation method develops 56.6% in open-path background. The transitions of CH4 at = 1.654 μm are selected to verify this method. Our method presents good application prospects and can be applied to sense of other gas molecules.

The Analysis and Design of Circular Microstrip Moisture Sensor for Rice Grains

Two proposed design is analysed for determining the rice grains at different frequencies as well as it will be worked on triple frequency. The circular microstrip moisture sensor is designed with slotted in the ground plane at 2.2GHz and get the good return loss -25dB. The other circular microstrip antenna moisture is designed without slotted in the ground plane with the good return loss at different frequencies i.e., 3GHz, 4.7GHz, 4.8GHz and return loss is -27dB, -15.5dB, -15dB. The coaxial feed is used in this design because this is easy to minimize the spurious radiation as well as direct contact to patch. The proposed design will be fabricated on FR4 substrate with the thickness 1.676, εr = 4.3, and the loss tangent tanδ = 0.001.The proposed design parameters of the ground is 30mm. The oven drying technique will be used to determine the moisture content and measured the proposed design with the help of vector network analyser.

Ice water content assessment in the single-, dual-, and triple-frequency radar scenarios

With the advent of the Global Precipitation Measurement (GPM) mission and the associated Ground Validation campaigns, there has been a strong development of studies related to dual-frequency and more recently to triple-frequency radar. In this context, one requirement is that at least one of the radar frequencies operates in the Rayleigh regime while the others have to ensure a measurable difference in reflectivities. A common radar coupling for triple frequency systems is the Ku-, Ka-, and W-band.Multi-frequency radars, in addition to the classic single-frequency reflectivity (SFR) measurement for each frequency, allow a further parameter, the dual-frequency ratio (DFR) defined as the ratio between two reflectivities at two frequencies. Referring to the same measurement volume, and for a fixed microphysical ice particle model, SFR and DFR allow to better constraint parameters of the particle size distribution, such as the mass-weighted mean diameter (Dm) and the normalized intercept parameter (Nw) when a normalized gamma distribution is assumed.This paper deals with various topics with the preliminary purpose of assessing the accuracy of the ice water content (IWC) estimate obtained using SFR and DFR methods to evaluate the improvements brought by the use of DFR. To pursue this goal, a simple microphysical model was used to choose the form of the SFR and DFR estimation algorithms and to evaluate their performances in a simulated framework.The most important aspect revealed by the study is that the cloud water content (CWC) plays a very important role both in the mass vs. diameter relationship as well as in the IWC estimation. The combined use of specific radar algorithms according to the different CWC values has shown notable improvements for the IWC estimation. Since CWC is not an operational measure, a substitute parameter was sought in the (DFRaou, DFRwoa) domain defined by the Ka- and Ku-band and by the W- and Ka-band measurements. This new parameter provides improvements similar to those obtained with the use of CWC.Data from the OLYMPEX field campaign that include an airborne triple-frequency radar at Ku-, Ka-, and W-band, as well as airborne measurements of in-situ bulk microphysics and meteorological parameters were used to validate the robustness of the methodology.

Mutual self-trapping of three pulses with multiple current frequencies based on compensation of the induced phase gratings at the middle frequency

We discuss a mutual self-trapping of the pulses with basic frequency and triple frequency under three-waves interaction in a medium with quadratic nonlinear response. This mode of their interaction is based on a compensation of the induced phase gratings at the middle frequency corresponding to the second harmonic. It leads to absence of the energy exchange between waves with basic and triple frequencies. As a result, the pulses propagate without changing their energies. In the frame-work of long pulse duration approximation we provide a theoretical analysis, from which the conditions on the pulses second-order dispersion are stated and under which the pulses shapes are stable. The stability analysis is provided both theoretically and numerically. We show that weak wave at doubled frequency plays a stabilization role in three-waves interaction under consideration. A presence of weak incident second harmonic wave does not destroy the self-trapping mode of the pulses propagation.The theoretical results are confirmed by computer simulation results which demonstrate the pulses propagation without energy exchange between waves at a distance equal several dispersion lengths.

PPPLib: An open-source software for precise point positioning using GPS, BeiDou, Galileo, GLONASS, and QZSS with multi-frequency observations

Precise Point Positioning Library (PPPLib) is a multi-GNSS data processing software designed to process multi-frequency data from GPS, BeiDou, Galileo, GLONASS, and QZSS. PPPLib is written in the C/C++ programming language. It can compile and run on both Linux and Windows operating systems. PPPLib mainly performs precise point positioning from single to triple frequency based on either ionospheric-free or uncombined observations. Moreover, it solves for abundant parameters, including position, tropospheric delay, ionospheric delay, and ambiguity information. Useful scripts and visualization tools are also provided for data download, batch processing, or solution presentation. We give a preliminary review, including positioning accuracy and convergence time of PPP using dual-frequency, ionospheric-free from single system to multi-GNSS, to show the working status of the current version of the software. In addition, the software also supports post-processing kinematic mode and INS/GNSS loosely coupled mode for kinematic positioning.

Numerical investigation of unsteady cavitation around a twisted hydrofoil

In this paper, the unsteady cavitating flow around a symmetrical twisted hydrofoil is investigated numerically. Cavitating flow characteristics are analyzed in terms of dynamical behaviors and temporal/spatial fluctuations of the cavities along the hydrofoil. At the midsection of the foil, sheet cavity firstly grows with nearly constant speed until the occurrence of the reverse flow at the closure line. During the reverse phase the flow moves upstream, and the sheet cavity keeps growing turbulently with low vapor content at the closure area. Fast Fourier Transform (FFT), Bispecturm and Dynamic Mode Decomposition (DMD) analyses show the existence of harmonics of the shedding frequency, of which the double and triple frequency are captured but only the fundamental frequency dominates the cavitating field. Pressure fluctuations around the hydrofoil and force coefficients are governed by the acceleration of vapor cavity. Application of Proper Orthogonal Decomposition (POD) displays the large-scale coherent structures among cavity shedding evolution. The sheet cavity growth, the main cavity shrinking and developing into a pair of root-like cavity structure and the sector cavity structure are captured by the first mode.

Моделирование ангармонических блоховских осцилляций: численные проблемы и нелинейные эффекты

The work presents robust and fast numerical method for calculation of complex-valued energies and wave functions of carriers in one-dimensional electrically biased periodic structures. Using this method optical transitions were studied in a superlattice (Bloch oscillations). Transition probabilities were shown to disobey linear dependence from applied field when it is large enough; in this case transitional with double and triple Bloch frequency can be more intensive than on single frequency. In a superlattice with a split miniband the same holds, with non-linearity being more pronounced in wider split case.

Ripple Analysis and Suppression Method Research of Direct Drive Permanent Magnet Synchronous Wind Turbine under Wind Shear

Wind shear is among the important sources of torque fluctuation on mechanical side and output power fluctuation on electromagnetic side and grid connection point, which frequency are triple turbine rotation frequency. With the increase in wind turbine single capacity and wind power integration scale, the power fluctuation caused by wind shear cannot be ignored. The paper takes a direct-drive permanent magnet synchronous wind turbine (PMSWT) as the research object. Firstly, the fluctuation transfer mechanism model is established; then, the current ripple is extracted by a notch filter to calculate the voltage control signal to suppress power fluctuation actively by the DC link capacitor which absorbs fluctuation energy. The simulation experiment shows that the suppression strategy is effective and reliable.

Vibration Reduction Strategy for Offshore Wind Turbines

The operational environment of offshore wind turbines is much more complex than that of onshore wind turbines. Facing the persistent wind and wave forces, offshore wind turbines are prone to vibration problems, which are not conducive to their long-term operation. Under this background, first, how the wave affects the vibration characteristics of offshore wind turbines is analyzed. Based on the existing wave and wave load models, we analytically show that there exist fluctuating components related to the hydrodynamic frequency in the aerodynamic load and aerodynamic torque of offshore wind turbines. Simulation results based on a GH Bladed platform further validates the analysis. Second, in order to reduce the joint impacts of the wave, wind shear and tower shadow on the wind turbine, a variable pitch control method is proposed. The integrated tower top vibration acceleration signal is superimposed on the collective pitch reference signal, then the triple frequency (3P) fluctuating component of the wind turbine output power and the azimuth angle of each blade are converted into the pitch angle adjustment signal of each blade, which is superimposed on the collective pitch signal for individual pitch control. The simulation results show that the proposed pitch control strategy can effectively smooth the fluctuation of blade root flap-wise load caused by wind and wave, and significantly reduce the fluctuation of aerodynamic torque and output power of offshore wind turbines.

A Wide Flat Triple Brillouin Frequency Spacing Multiwavelength Fiber Laser Assisted by Four Wave Mixing

In order to improve the triple frequency spacing operation, we introduce a simplified arrangement of multiwavelength Brillouin-erbium-ytterbium fiber laser that incorporates only a single amplifier source. The strong responses amongst the interacting waves in the 500 m highly nonlinear fiber help in forming wider multiwavelength bandwidth and self-flattening of the output spectra. A total of 146 Stokes lines within 3-dB span are produced with a channel spacing of 0.246 nm. These are completed when the Brillouin pump (BP) wavelength is set at 1533 nm, BP power at -12 dBm and erbium-ytterbium doped fiber amplifier at 950 mW. A quality optical signal-to-noise ratio of 46.2 dB estimation is realized along the 36 nm lasing bandwidth that starts at 1533 nm wavelength. As a result of efficient suppression of self-lasing modes, the tunability covers the entire C-band which is associated to the lowest attenuation regime. For this particular area of fiber lasers, the results confirm dramatic advancements in spectral flatness and Stokes lines count combination especially with the additional benefit of high stability at only 1.22 dB fluctuation.