Amplitude Compensation Research Articles

Speed Sensorless Control of Linear Ultrasonic Motors Based on Stator Vibration Amplitude Compensation

In some applications of linear ultrasonic motors (LUSMs), not installing speed/position sensors can reduce the size and cost of the system, changes in load will cause fluctuations in the speed of the LUSM. To eliminate the influence of load changes on speed, a speed sensorless control scheme based on stator vibration amplitude compensation (SSCBVC) is proposed. This scheme is implemented under the framework of the stator vibration amplitude-based speed control (VBSC) and frequency tracking. Based on the stator vibration amplitude-speed and the output force-speed curves of the LUSM, the relationship between the load changes and stator vibration amplitude (SVA) to be compensated is established, realizing a speed sensorless control of the LUSM under variable load conditions. The experimental results show that the maximum fluctuation of the speed is about 2.2% when the output force changes from 0 to 6 N with SSCBVC. This scheme can effectively reduce the influence of load changes on the speed of the LUSM without using speed/position sensors.

An unbiased carrier-phase anti-interference filter based on mirror frequency amplitude compensation

Anti-interference and high-precision measurement are two important indicators of the performance of a satellite navigation receiver. However, current receiver designs do not simultaneously satisfy these two criteria. While the carrier-phase ranging technique is necessary for high-precision receivers, frequency domain interference suppression (FDIS) results in tracking error biases for nonideal analog receiver channels. Importantly, as the FDIS filter is adaptive, the bias will vary with the jamming pattern, particularly when the frequency of interference varies. For precision navigation applications, this bias must be mitigated. Therefore, a new FDIS filter based on the mirror frequency amplitude compensation (MFAC) method is proposed in this paper. The amplitude at the symmetry position of the notch frequency is doubled in the MFAC method to mitigate this carrier-phase bias. The simulation results showed that the MFAC method can reduce the range of the carrier-phase bias by more than 60% for different interference bandwidths, which substantially exceeds that achieved using the conventional FDIS and calibration filter methods of 20 orders.

Angle‐domain imaging of relative impedance perturbation

ABSTRACTImpedance is a physical parameter that plays an important role in seismic data processing and interpretation. A relative impedance perturbation (the ratio of the impedance perturbation and the impedance for the background models) imaging method in depth domain based on the reflection wave equation is proposed. Under the small perturbation assumption, primary wave and high‐frequency approximation condition, a linear propagation equation of the primary reflection waves based on the relative impedance perturbation was first derived. On this basis, we further derived the imaging formula of the relative impedance perturbation using a linear inversion theory. Then, the source–receiver bidirectional illumination compensation was used to improve the image quality of the subsurface structures. The image result obtained by this method can be used to estimate the relative impedance perturbation. In the angle domain, the extracted near‐angle‐domain image gather with amplitude compensation can estimate the relative impedance perturbation, and the far‐angle image gather provides the estimation of the relative velocity perturbation (the ratio of the velocity perturbation and the background velocity). Finally, several numerical tests demonstrate the effectiveness of the method.

Q-Factor Estimation by Compensation of Amplitude Spectra in Synchrosqueezed Wavelet Domain

We propose a stable Q-estimation approach based on the compensation of amplitude spectra in the time-frequency domain after a synchrosqueezed wavelet transform (SSWT). SSWT employing a post-processing frequency reallocation method to the original representation of a continuous wavelet transform (CWT) for improving its readability provides the sharper time-frequency representation of a signal when compared with the other traditional time-frequency methods such as CWT or S-transform. For Q-estimation, we transform a seismic trace into the time-frequency domain using SSWT at first. Then, we derive the amplitude compensation in the SSWT domain. By searching the predetermined Q range, the comparison between the compensated amplitude spectrum and the reference one in the SSWT domain is carried out. The output optimized Q-factor estimation is evaluated by the minimum of the mean square error. For the robust and fast stabilization form of the amplitude compensation in the SSWT domain with noise amplification damping, the seismic pulse is truncated with a limited length and the obtained time-frequency maps using an SSWT are smoothed. The synthetic vertical seismic profiling data and the real stacked seismic data applications illustrate the effectiveness and the ability of the proposed method.

Simulation of the image rejection phase method

The paper considers the algorithmic possibility of the image rejection method. The main resulting characteristics of circuits implementing the above method are presented. The simulation model allows estimating the selectivity coefficient as a function of the phase and amplitude imbalance of the circuit branches. Mathematical and circuit simulations were conducted. The results of different modeling methods coincide, and the simulation results verify the possibility of implementing the image rejection method. On the basis of this model it is possible to provide a high level (at least 40 dB) of image rejection by amplitude and phase circuit imbalance compensation. The dependence of the noise level at the output of the image rejection circuit as a function of the circuit elements frequency characteristics is given. The results of this work could be used for further practical implementation of above mentioned method at the stage of selecting elements based on an analysis of their characteristics. The simulation model could be used to select required radioelements and to estimate image rejection level. It is possible to estimate the level of image channel suppression, the noise level and the signal-to-noise ratio at the output of the image rejection circuit by using the above mentioned mathematical models and characteristics of the selected elements for practical implementation of the circuit. The effect of the broadband phase shifters on the noise level is considered with the implementation of the above method as an example. It was shown that ensuring a high level of selectivity in order to minimize the noise level of the image channel is advisable only up to some values (about 25 dB). Further improvement of selectivity, for example, by minimizing the phase and amplitude balances, or mutual compensation of the mixer and phase shifter branch imbalances are necessary, if there are requirements for increasing the signal-to-noise ratio. It is shown that it is possible to ensure selectivity of up to 25 dB and a noise level reduction of 2.5-3 dB if the amplitude imbalance of the circuit is up to 1 dB, and the phase imbalance is up to 5 deg. in the required frequency band.

A modified mixed domain method for modeling acoustic wave propagation in strongly heterogeneous media.

In this paper, phase correction and amplitude compensation are introduced to a previously developed mixed domain method (MDM), which is only accurate for modeling wave propagation in weakly heterogeneous media. Multiple reflections are also incorporated with the one-way model to improve the accuracy. The resulting model is denoted as the modified mixed domain method (MMDM) and is numerically evaluated for its accuracy and efficiency using four distinct cases. It is found that the MMDM is significantly more accurate than the MDM for strongly heterogeneous media, especially when the phase aberrating layer is approximately perpendicular to the acoustic beam. Additionally, a convergence study suggests that the second-order reflection could be sufficient for cases involving high contrast inhomogeneities and large loss values (e.g., skulls). The method developed in this work could facilitate therapeutic ultrasound for treating brain-related diseases and disorders.

An implicit stabilization strategy for Q-compensated reverse time migration

Reverse time migration with [Formula: see text] compensation ([Formula: see text]-RTM) is an effective approach to enhance the resolution of seismic images because it retrieves the amplitude loss and phase distortion induced by the viscosity of media. According to the crosscorrelation imaging condition, [Formula: see text]-RTM requires compensation for the amplitude loss in the propagation paths of source and receiver wavefields, which can be realized by solving an amplitude-boosted wave equation. However, the amplitude-boosted simulations suffer from numerical instability due to the amplification of high-frequency noise. We have developed a robust stabilization strategy for [Formula: see text]-RTM by incorporating a time-variant filter into the amplitude-boosted wavefield extrapolation step. We modify the Fourier spectrum of the operator that controls the amplitude compensation to be time variant, and we add to the spectrum a stabilization factor. Doing so, we integrate the time-variant filter into the viscoacoustic wave propagator implicitly, and we avoid any explicit filtering operation in [Formula: see text]-RTM. We verify the robustness of this stabilized [Formula: see text]-RTM with two synthetic data examples. We also apply this technique to a field data set to demonstrate the imaging improvements compared to an acoustic RTM and a more traditional [Formula: see text]-RTM method.

An integrated broadband preprocessing method for towed-streamer seismic data

Broadband preprocessing has become widely used for marine towed-streamer seismic data. In the standard workflow, far-field source designature, receiver and source-side deghosting, and redatuming to mean sea level are applied in sequence, with amplitude compensation for background [Formula: see text] delayed until the imaging or postmigration stages. Thus, each step is likely to generate its own artifacts, quality checking can be time-consuming, and broadband data are only obtained late in this chained workflow. We have developed a unified method for broadband preprocessing — called integrated broadband preprocessing (IBP) — which enables the joint application of all the above listed steps early in the processing sequence. The amplitude, phase, and amplitude-variation-with-offset fidelity of IBP are demonstrated on pressure data from the shallow, deep, and slanted streamers. The integration allows greater sparsity to emerge in the representation of seismic data, conferring clear benefits over the sequential application. Moreover, time sparsity, full dimensionality, and early amplitude [Formula: see text] compensation all have an impact on broadband data quality, in terms of reduced ringing artifacts, improved wavelet integrity at large crossline angles, and fewer residual high-frequency multiples.

Transmission-based near-surface deconvolution

We have developed a new framework for performing surface-consistent amplitude balancing and deconvolution of the near-surface attenuation response. Both approaches rely on the early arrival waveform of a seismic recording, which corresponds to the refracted or, more generally speaking, to the transmitted energy from a seismic source. The method adapts standard surface-consistent amplitude compensation and deconvolution to the domain of refracted/transmitted waves. A sorting domain specific for refracted energy is extended to the analysis of amplitude ratios of each trace versus a reference average trace to identify amplitude residuals that are inverted for surface consistency. The residual values are either calculated as a single scalar value for each trace or as a function of frequency to build a surface-consistent deconvolution operator. The derived operators are then applied to the data to obtain scalar amplitude balancing or amplitude balancing with spectral shaping. The derivation of the operators around the transmitted early arrival waveforms allows for deterministically decoupling the near-surface attenuation response from the remaining seismic data. The developed method is fully automatic and does not require preprocessing of the data. As such, it qualifies as a standard preprocessing tool to be applied at the early stages of seismic processing. Applications of the developed method are provided for a case in a complex, structure-controlled wadi, for a seismic time-lapse [Formula: see text] land monitoring case, and for an exploration area with high dunes and sabkhas producing large frequency-dependent anomalous amplitude responses. The new development provides an effective tool to enable better reservoir characterization and monitoring with land seismic data.

Two-dimensional random access multiphoton spatial frequency modulated imaging.

Spatial frequency modulated imaging (SPIFI) enables the use of an extended excitation source for linear and nonlinear imaging with single element detection. To date, SPIFI has only been used with fixed excitation source geometries. Here, we explore the potential for the SPIFI method when a spatial light modulator (SLM) is used to program the excitation source, opening the door to a more versatile, random access imaging environment. In addition, an in-line, quantitative pulse compensation and measurement scheme is demonstrated using a new technique, spectral phase and amplitude retrieval and compensation (SPARC). This enables full characterization of the light exposure conditions at the focal plane of the random access imaging system, an important metric for optimizing, and reporting imaging conditions within specimens.

Circular Polarization Hologram Realized by Pancharatnam-Berry Phase in Microwave Frequency

Metasurfaces have shown great potential in controlling the propagation of electromagnetic waves, making them suitable for holographic beam-shaping elements. Using the principle of array synthesis, holograms have been realized in microwave frequency to manipulate electromagnetic waves to generate specific field patterns. However, current research is almost based on linear polarization and has little analysis on the circular polarization microwave hologram. Herein, we propose a circular polarization hologram realized by sub-wavelength units with self-adaptively phase profiles of electromagnetic waves. The full, continuous control of the phase is achieved by using a single structure unit based on the Pancharatnam-Berry phase. The inhomogeneity of wave-front is considered through amplitude and phase compensation which are essential to improve the quality of microwave hologram. The model achieves circular polarization hologram in microwave frequency and the clear field pattern is generated. The circular polarization hologram enriched the research field of microwave imaging, thus providing more inspirations for the development of various related techniques.

Echolocating bats exhibit differential amplitude compensation for noise interference at a sub-call level.

Flexible vocal production control enables sound communication in both favorable and unfavorable conditions. The Lombard effect, which describes a rise in call amplitude with increasing ambient noise, is a widely exploited strategy by vertebrates to cope with interfering noise. In humans, the Lombard effect influences the lexical stress through differential amplitude modulation at a sub-call syllable level, which so far has not been documented in animals. Here, we bridge this knowledge gap with two species of Hipposideros bats, which produce echolocation calls consisting of two functionally well-defined units: the constant-frequency (CF) and frequency-modulated (FM) components. We show that ambient noise induced a strong, but differential, Lombard effect in the CF and FM components of the echolocation calls. We further report that the differential amplitude compensation occurred only in the spectrally overlapping noise conditions, suggesting a functional role in releasing masking. Lastly, we show that both species of bats exhibited a robust Lombard effect in the spectrally non-overlapping noise conditions, which contrasts sharply with the existing evidence. Our data highlight echolocating bats as a potential mammalian model for understanding vocal production control.

Vortex SAR Imaging Method Based on OAM Beams Design

Vortex synthetic aperture radar (SAR), combination of the orbital angular momentum (OAM) beams and the stripmap SAR technology, is proposed to achieve higher azimuth resolution. Firstly, the imaging scenario and the echo model are established and derived. Secondly, the pre-processing approaches, including the amplitude compensation and the phase compensation, are developed by the design of the transmitted OAM beams. Then, an improved range-Doppler (RD) algorithm is proposed to acquire target's two dimensional (2D) profiles. Simulation results demonstrate the effectiveness of the proposed algorithm, and the influence factors of the azimuth resolution are analyzed as well. Compared with the conventional SAR, the proposed vortex SAR imaging method can achieve higher azimuth resolution with the same synthetic aperture length (SAL). This work can benefit the applications of OAM-carrying waves in radar realms as well as the development of high-resolution SAR imaging technique.

Methods to Improve the Long Distance Time-Varying Channel Transmission Performance of Expendable Profiler

To improve the transmission performance of XCTD channel, this paper proposes a method to measure directly and fit the channel transmission characteristics by using frequency sweeping method. Sinusoidal signals with a frequency range of 100 Hz to 10 kHz and an interval of 100 Hz are used to measure transmission characteristics of channels with lengths of 300 m, 800 m, 1300 m, and 1800 m. The correctness of the fitted channel characteristics by transmitting square wave, composite waves of different frequencies, and ASK modulation are verified. The results show that when the frequency of the signal is below 1500 Hz, the channel has very little effect on the signal. The signal compensated for amplitude and phase at the receiver is not as good as the uncompensated signal. Alternatively, when the signal frequency is above 1500 Hz, the channel distorts the signal. The quality of signal compensated for amplitude and phase at receiver is better than that of the uncompensated signal. Thus, we can select the appropriate frequency for XCTD system and the appropriate way to process the received signals. Signals below 1500 Hz can be directly used at the receiving end. Signals above 1500 Hz are used after amplitude and phase compensation at the receiving end.

Inversion-Based Time-Domain Inverse $Q$ -Filtering for Seismic Resolution Enhancement

Seismic wave will suffer from resolution loss during its propagation in subsurface media, which is caused by the earth filtering effect. Inverse Q-filtering (IQF) is an essential scheme for eliminating earth filtering effect and enhancing temporal resolution. In this letter, IQF is achieved by solving a time-domain inverse problem whose corresponding forward model is established based on the idea of seismic migration, i.e., extrapolating the unfiltered record (the detected signal if there is no earth filtering effect) from surface downward to each time–depth point and then adopting imaging condition to obtain the attenuated record. We express this migration-based forward model as a matrix-vector equation and construct the objective function of inversion-based time-domain IQF (ITIQF). Instead of adopting frequency-domain incomplete amplitude compensation operator for the purpose of antinoise, we propose three transform-domain sparse regularization strategies, including wavelet-based constraint, curvelet-based constraint, and double constraint (a combination of wavelet- and curvelet-based constraints). Solvers of these constrained ITIQF methods are provided according to convex optimization theory. We demonstrate the superior performance of ITIQF scheme via both synthetic and field data examples.

Generalized stable inverse Q filtering

The conventional stable inverse Q filtering method overcomes the instability of the inverse Q filtering and can effectively perform amplitude compensation and phase correction. However, its shortcoming is that it cannot solve the problem of excessive compensation for shallow seismic records and insufficient compensation for deep seismic records. The essence is that the compensation bandwidth and intensity of the amplitude compensation operator cannot be adjusted. We propose a generalized stable inverse Q filtering method. By introducing a parameter into the stable amplitude compensation operator based on stabilization factor, the method can flexibly and effectively handle the compensation intensity and frequency bandwidth to achieve high resolution and high signal-to-noise ratio seismic data. The test results of theoretical synthetic seismic data and real seismic data show that this method has unique value in frequency band selection of amplitude compensation according to the quality of seismic data, which can improve the resolution and get high signal-to-noise ratio seismic data.

A Super-Twisting Sliding-Mode Stator Flux Observer for Sensorless Direct Torque and Flux Control of IPMSM

The scheme based on direct torque and flux control (DTFC) as well as active flux is a good choice for the interior permanent magnet synchronous motor (IPMSM) sensorless control. The precision of the stator flux observation is essential for this scheme. However, the performance of traditional observers like pure integrator and the low-pass filter (LPF) is severely deteriorated by disturbances, especially dc offset. Recently, a sliding-mode stator flux observer (SMFO) was proposed to reduce the dc offset in the estimated stator flux. However, it cannot eliminate the dc offset totally and will cause the chattering problem. To solve these problems, a novel super-twisting sliding-mode stator flux observer (STSMFO) is proposed in this paper. Compared with SMFO, STSMFO can reduce the chattering and fully eliminate the dc offset without any amplitude and phase compensation. Then, the precision of the stator flux and rotor position can be greatly improved over a wide speed region. The detailed mathematical analysis has been given for comparing it with another three traditional observers. The numerical simulations and experimental testing with an IPMSM drive platform have been implemented to verify the capability of the proposed sensorless scheme.

Integrated microwave photonic phase shifter with full tunable phase shifting range (> 360°) and RF power equalization.

We report a novel microwave photonic phase and amplitude control structure based on a single microring resonator with a tunable Mach Zehnder interferometer reflective loop, which enables the realization of a continuously tunable microwave photonic phase shifter with enhanced phase tuning range while simultaneously compensating for the RF power variations. The complimentary tuning of the phase and amplitude presents a simplistic approach to resolve the inherent trade-off between maintaining a full RF phase shift while eliminating large RF power variations. Detailed simulations have been carried out to analyze the performance of the new structure as a microwave photonic phase shifter, where the reflective nature of the proposed configuration shows an effective doubling of the phase range while the amplitude compensation module provides a parallel control to potentially reduce the RF amplitude variations to virtually zero. The phase range enhancement, which is first verified experimentally with a passive only chip, demonstrates the capability to achieve a continuously tunable RF phase shift of 0-510° with an RF amplitude variation of 9 dB. Meanwhile, the amplitude compensation scheme is incorporated onto an active chip with a continuously tunable RF phase shift of 0-150°, where the RF power variations is shown to be reduced by 5 dB while maintaining a constant RF phase shift.

Spectral phase and amplitude retrieval and compensation technique for measurement of pulses.

In this Letter, an in-line, compact, and efficient quantitative pulse compensation and measurement scheme is demonstrated. This simple system can be readily deployed in multiphoton imaging systems and advanced manufacturing where multiphoton processes are exploited.

Online Identification Method of Induction Motor Parameters Based on Rotor Flux Linkage

High-performance control of induction motors is inseparable from accurate motor parameters. Online identification of parameters can provide accurate parameters for motor control in real time, so it is particularly important. In this paper, the traditional voltage flux observer is improved. The high-pass filter is connected in series with low-pass filter, and then the amplitude and phase compensation methods are used to obtain the improved voltage-type flux linkage observation method. The current-type flux linkage observation method is also introduced. Then the principle of the model reference adaptive system is studied. Combined with the super-stability theory, an algorithm for identifying the rotor time constant on-line is designed based on the rotor flux linkage. Through the combination of simulation and experiment, the observation effect of two flux linkage observation methods is verified on a 160kW motor. At the same time, the online identification algorithm of rotor time constant is studied under different speeds and different parameters. The results verify its accuracy and effectiveness.