Active Cancellation System Research Articles

Laser-cavity locking utilizing beam ellipticity: accessing the 10−7 instability scale relative to cavity linewidth

Frequency-stable lasers form the back bone of precision measurements in science and technology. Such lasers typically attain their stability through frequency locking to reference cavities. State-of-the-art locking performances to date had been achieved using frequency modulation based methods, complemented with active drift cancellation systems. We demonstrate an all passive, modulation-free laser-cavity locking technique (squash locking) that utilizes changes in spatial beam ellipticity for error signal generation, and a coherent polarization post-selection for noise resilience. By comparing two identically built proof-of-principle systems, we show a frequency locking instability of 5×10−7 relative to the cavity linewidth at 10 s averaging. The results surpass the demonstrated performances of methods engineered over the last five decades, potentially enabling an advancement in the precision control of lasers, while creating avenues for bridging the performance gaps between industrial grade lasers with scientific ones due to the afforded simplicity and scalability.

FPGA-Based Active Cancellation of the EMI of a Boost Power Factor Correction (PFC) by Injecting Modulated Sine Waves

Boost power factor corrections tend to be considerable sources of electromagnetic disturbances. To ensure the proper functionality of susceptible systems in the vicinity, the emissions must be reduced. Passive filters, as a conventional solution to reduce conducted emissions, usually suffer from their high volume, weight and costs. Active filters can help to mitigate this problem, but the known solutions are systematically limited by inherent time constants and signal propagation delays since they derive the cancellation signal directly from a measured quantity by a feedforward and/or feedback approach. To resolve this issue, each harmonic can be individually suppressed by an artificially synthesized sine wave that is synchronized to the disturbances. By adjusting the amplitudes and phases of the suppressing sine waves, bothersome time constants and delay times can be compensated. In this work, it is shown that the switching harmonics of a power factor correction can be interpreted as modulated sine waves. By modulating the suppressing sine waves simultaneously, a very high performance can be achieved for the active cancellation system. The hardware and the algorithm are described, optimum parameters for the algorithm are identified and an FPGA implementation is applied to a real PFC.

Simulation of active cancellation system based on N-order SSC algorithm

PurposeThe purpose of this paper is to introduce the theoretical basis of N-order spectral spreading-compressing (SSC) frequency shift interference algorithm and expand it to active cancellation. An active cancellation simulation and verification system based on N-order SSC algorithm is established and carried out; simultaneously, the absorbing material coating stealth simulation of two kinds of thickness is carried out to compare the stealth effect with active cancellation system.Design/methodology/approachThe active cancellation method based on N-order SSC algorithm is proposed based on theoretical formula derivation; the active cancellation simulation and verification system is established in MATLAB/Simulink. The full-size model is built by CATIA and meshed by hypermesh. The omnidirectional radar cross section (RCS) is calculated in cadFEKO, and the results are analyzed in postFEKO.FindingsThe simulations are implemented on a stealth fighter, and results show that after active cancellation, the peak of spectrum analyzer has reduced in all azimuths, the omnidirectional RCS has also decreased and the detection probability of almost all azimuths has dropped under 50 per cent. The absorbing material coating stealth simulations of two kinds of thickness are carried out, and results show that the stealth effect of active cancellation is much better than absorbing material coating.Practical implicationsAn active cancellation system based on SSC algorithm is proposed in this paper, and the effect of active cancellation is verified and compared with that of absorbing materials. A new method for the current active stealth is provided in this paper.Originality/valueActive cancellation simulation and verification system is established. RCS calculation module, signal-to-noise-ratio (SNR) calculation module and detection probability module are built to verify the effect of active cancellation system. Simultaneously, the absorbing material coating stealth simulation is carried out, and the stealth effect of absorbing material coating and active cancellation are compared and analyzed.

Active Cancellation Stealth Technology Analysis and Verification in Experiment

As a Radar Countermeasure technique, Active cancellation could further decrease the radar detection probability of a stealthy target in some interest directions accomplishing with some traditional stealth techniques. According to radar equation, the received power of radar from the scattering of the target is positively linearly relative to the Radar Cross Section (RCS) of the target. The traditional stealth techniques aim at reducing the RCS by shaping and materials, but the active methods center the parameters of radar wave. Practically, there are many difficulties such as the real time signal measurement, the accurate anti-signal production, etc. In this paper, a type of structure of active cancellation system is proposed, and verified by measurement results its technique indexes This paper designs, and. At last, a verification experiment system and the confirm our conclusions about active cancellation stealth technology.

An Active Suspension System for Mitigating Motion Sickness and Enabling Reading in a Car.

The advent of autonomous automobiles raises new challenges for maintaining passenger safety and comfort. The challenge addressed here is how to predict and mitigate motion sickness when passengers read in a moving vehicle. We utilized a car equipped with a commercial active suspension system developed for attenuating the transmission of road surface fluctuations to passengers. The system was used to reproduce, in a parked car, either the vibrations that would be experienced in a moving car equipped with a conventional suspension system (unmitigated ride) or the attenuated vibrations that would occur on the road with the active cancellation system engaged (mitigated ride). We evaluated the consequences of these two simulated ride conditions for reading performance, comfort, and evocation of motion sickness. Both ride conditions reduced the 0 to 0.8 Hz vibrations to below threshold for evoking motion sickness during passive exposure [corrected]. Only the mitigated ride condition attenuated frequencies in the 0.8 to 8 Hz band where visual suppression of the vestibulo-ocular reflex is known to break down, and this condition also reduced the motion sickness induced by reading and increased reading comprehension and comfort relative to the unmitigated ride. The palliative effects of 0.8 to 8 Hz attenuation are discussed in terms of the different mechanisms underlying motion sickness evoked by reading in a vehicle versus mere exposure to vehicle motion without reading. Implications for ISO-2631 standards for human exposure to vibration are also discussed.DiZio P, Ekchian J, Kaplan J, Ventura J, Graves W, Giovanardi M, Anderson Z, Lackner JR. An active suspension system for mitigating motion sickness and enabling reading in a car. Aerosp Med Hum Perform. 2018; 89(9):822-829.

ANITA-An active vibration cancellation system for scanning probe microscopy.

The high sensitivity of scanning probe microscopes poses a barrier to their use in noisy environments. Vibrational noise, whether from structural or acoustic sources, can manifest as relative motion between the probe tip and sample, which then appears in the probe position ("Z") feedback as it tries to cancel this motion. Here we describe an active cancellation process that nullifies the appearance of this vibration by adding a drive signal into the existing Z-feedback loop. The drive is digitally calculated from accelerometer-based vibration measurements. By transferring the vibration cancellation effort to this drive signal, vibration-created noise is significantly reduced. This inexpensive and easy solution requires no major instrumental modifications and is ideal for those looking to place their microscopes in noisier environments, coupled, for example, to active refrigeration systems (e.g., pulse tube cryocoolers) or other high-vibration instruments.

Simulation and verification of active cancellation system

In this paper, the expressions of active cancellation signal of the LFM and NLFM are introduced and a simulation model of active cancellation system based on Simulink is investigated. The generation of target echo signal and cancellation signal based on Simulink has been proposed in details. Active cancellation is combined with RCS calculation and detection probability calculation to further measure the effectiveness of the system. The simulation is carried out on a stealth unmanned reconnaissance aircraft RQ-170 and result shows that after active cancellation, the peak of spectrum analyzer has reduced in all azimuths; the omnidirectional RCS has also decreased; the detection probability of all azimuths has dropped under 50% which can be considered as undetectable target.

Simulation analysis of an active cancellation stealth system

Active cancellation stealth is a smart signal blanking method, that it has become an important developing direction on modern stealth technology. In order to further explore the active cancellation stealth technology, we are considering the detection and cancellation of receiving/transmitting antenna pattern is different. Put forward active cancellation system simulation structure diagram based on MATLAB/SIMULINK, where the phased array radar system as the modelling object, and established the active cancellation stealth system mathematical model based on digital radio frequency memory (DRFM) and the radar signal processing system of the coherent video simulation model, based on linear frequency modulation and radar coherent pulse signal simulation, verified the rationality and validity of the design, as the active cancellation stealth engineering technology laid the foundation.

Enhancing the power output of moving coil actuators by incorporating soft polymers

A novel design of an actuator coupled with a low-hardness silicone elastomer called “the gel surround” is presented. It means that the output power of a conventional moving coil-type actuator can be greatly enhanced by applying the novel mechanism of the gel surround. This device is termed a “gel-type transducer”. The transducer delivers a wide frequency range from 40Hz to 10,000Hz and is integrated into any solid surface with both optimized impedance matching and minimized wave collisions. This effect was demonstrated by the laser scanning measurement, DMA (dynamic mechanical analyzer) and acoustic test. Furthermore COMSOL multiphysics simulation software was used to calculate the force factor, BL, electrical force, Fe and the sound pressure level (SPL) of the transducer as well as vibrating modes of a panel that the transducer is attached. The results were verified by experiment. It was demonstrated that the gel-type transducer can be used as a micro-subwoofer speaker. Future work will involve developing an active vibration cancellation and energy harvesting system by applying the operating principle of the gel-type transducer.

Design, Simulation and Implementation of an Active Sound-Noise Cancellation System for Use in a Cockpit Intercommunication System

In this paper, an active noise control system for denoising the intercommunication signal of an airplane cockpit isproposed. Noise sources such as engines degrade the quality of the intercommunication signal, especially in the caseof the pilot and copilot headsets. A two-microphone active adaptive noise controller is designed by using an adaptiveFIR filter in an active structure. The designed system is simulated and also implemented in real environment usingreal speech signals, periodic noise and AWGN noise. Also, an FPGA-based hardware implementation utilizing a novelmethod is provided. The whole design is considered an FPGA hardware core with low resource utilizations which issuitable for HW/SW codesign and System-on-Programmable-Chip (SoPC) applications. The codes have been writtenby using the VHDL93 hardware description language, the XilKernel embedded operating system and a finite statemachine. The obtained results showed competent functionality and performance of the proposed system. This ICSnoise removal architecture can be used on any cargo, civil or fighter platform (such as C-130, IR-AN 140 and F5-F)and also in radar and electronic warfare (EW) systems (for clutter/interference compensation) with minimum hardwareor software changes.

Passive magnetic field cancellation device by multiple high-Tc superconducting coils

A passive magnetic field cancellation device (PMFCD) is designed. The PMFCD could automatically cancel the field as an active cancellation system did; however it requires no power sources and feedback systems. The capability of the PMFCD is based on the principle that a closed loop can resist flux variation and keep the flux constant inside. The closed loop in the PMFCD is formed by connecting two pairs of high temperature superconductor Helmholtz coils with different radii in series. More important thing is that the ratio of the radius and the turn number between the coils has to satisfy a number of conditions, with which 100% cancellation can be reached. Theoretical methods to obtain the turn number ratio and radius ratio are the major part of the paper. Numerical simulation was followed, aiming to evaluate field distribution under a cancellation state and correct the theoretical values.

Targeted Resonance Control in a TEM Cell

We investigate extending the upper frequency limit of an asymmetric ldquoCrawford-style'' transverse electromagnetic (TEM) cell with targeted resonance control. Focusing on the fundamental TE cavity resonance, an active feedback cancellation system is applied with the aim of reducing the resonant field amplitude without affecting the desired TEM mode. A half loop J-dot current probe is positioned with a vertical polarization on one wall of the TEM cell to measure the wall currents generated from the TE resonance. An identical probe is placed on the facing wall that is connected to the first through a negative feedback chain. The second loop's purpose is to excite a field that has the appropriate magnitude and phase to attenuate the TE resonance amplitude. Experimental application achieved a 17-dB reduction in the amplitude of the resonance field. The method is also outlined with respect to the TE resonance. This system is planned for full-scale implementation into a hybrid reverberation/TEM whole-aircraft electromagnetic vulnerability testing facility.

Speech emission control using active cancellation

We investigated on the possibility of an active cancellation system for unnecessary speech radiation control. Some examples of the intended application of this system are cellular speech cancellation and speech input for recognition-based dictation systems. Both of these applications do not require speech to be radiated into surrounding space, but only into the input microphone, and would benefit if global radiation is controlled. We first show that speech cancellation is possible with a secondary source placed in proximity to the mouth generating linear-predicted phase-inverted speech. However, the prediction must also cover the long delay associated with the acoustic to/from electric conversion, as well as A/D, D/A conversions, and all associated processing, which we found could go up to as long as 3 ms. By using LPC predicted samples recursively to predict further samples, we found that prediction with SNR of about 6 dB is possible, even with this long delay. The prediction coefficient update is suppressed during this recursion. Lowering the sampling frequency in order to lower the number of predicted samples at the cost of reduced bandwidth further enhances prediction accuracy. At a sampling frequency of 8 kHz, speech emission control of about 7 dB for female speech and 4 dB for male speech was found to be possible. Finally, we experimentally evaluated the proposed active speech control method. Predicted samples of recorded speech was first prepared off line. We then actually played out both the original and the predicted samples simultaneously from two loud speakers. It was found that (1) speech cancellation of up to about 10 dB is possible, but is highly speaker dependent, (2) secondary loud speaker should be oriented in the same direction as the primary source, i.e., the mouth. We plan to investigate further to improve prediction accuracy using prediction coefficient extrapolation. A prototype system implementation using DSPs is also planned.

Active cancellation of stray magnetic fields in a Bose-Einstein condensation experiment

A method of active field cancellation is described, which greatly reduces the stray magnetic field within the trap region of a Bose-Einstein condensation experiment. An array of six single-axis magnetic sensors is used to interpolate the field at the trap center, thus avoiding the impractical requirement of placing the sensor within the trap. The system actively suppresses all frequencies from dc to approximately 3000 Hz, and the performance is superior to conventional active Helmholtz cancellation systems. A method of reducing the field gradient, by driving the six Helmholtz coils independently, is also investigated.

Numerically stable fast convergence least-squares algorithms for multichannel active sound cancellation systems and sound deconvolution systems

In recent years, recursive least-squares (RLS) algorithms and fast-transversal-filters (FTF) algorithms have been introduced for multichannel active sound cancellation (ASC) systems and multichannel sound deconvolution (MSD) systems. It was reported that these algorithms can greatly improve the convergence speed of the ASC/MSD systems using adaptive FIR filters. However, numerical instability of the algorithms is an issue that needs to be resolved. In this paper, extensions of numerically stable realisations of RLS algorithms such as the inverse QR-RLS, the QR decomposition least-squares-lattice (QRD-LSL) and the symmetry preserving RLS algorithms are introduced for the specific problem of multichannel ASC/MSD. Multichannel versions of some of these algorithms have previously been published for prediction or identification systems, but not for control systems. The case of underdetermined ASC/MSD systems (i.e. systems with more actuators than error sensors) is also considered, to show that in these cases it may be required to use constrained algorithms in order to have numerical stability. Constrained algorithms for multichannel ASC/MSD systems are therefore introduced for two types of constraints: minimisation of the actuator signals power and minimization of the adaptive filters square coefficients. Simulation results are shown to verify the numerical stability of the algorithms introduced in the paper.

Active cancellation of rotor/stator interaction tones in turbofan engines

Rotor/stator-generated aerodynamic noise in turbofan engines, HVAC axial fans, and other turbomachinery is often dominated by blade passage harmonics produced by dipole sound sources. Radiation toward the inlet and exhaust depends upon the effective orientation of the dipole sources relative to the propagation angles of the excited modes. Absorption of this tonal noise using passive treatment is often compromised because of a lack of knowledge of the relative phases and amplitudes of the propagating modes. A modal-based active cancellation system has been developed for global suppression of rotor/stator interaction tones. Axially spaced annuli of controlled wall-mounted actuators are located immediately upstream and downstream of the hubs and tips of stator vanes. Wall-mounted error microphone arrays are located in the inlet nacelle and exhaust duct. Actuator drive vectors are determined in an adaptive-quadrature control algorithm that seeks to minimize total radiated noise. The concept was initially developed and tested on a 24-in. axial fan facility and then extended and demonstrated on the 48-in. Active Noise Control Fan facility at NASA Lewis Research Center. Simultaneous suppression of modes (4,0) and (4,1) of 8–17 dB toward the inlet and 3–11 dB toward the exhaust was achieved at the second blade-passage harmonic.

Active cancellation system of acoustic noise in MR imaging.

In this paper, we introduce a new neural-network architecture for reducing the acoustic noise level in magnetic resonance (MR) imaging processes. The proposed neural network (NN) consists of two cascaded time-delay NN's (TDNN's). This NN is used as the predictor of a feedback active noise control (ANC) system for reducing acoustic noises. Experimental results with real MR noises show that the proposed system achieved an average noise power attenuation of 18.75 dB, which compares favorably with previous studies. Preliminary results also show that with the proposed ANC system installed, acoustic MR noises are greatly attenuated while verbal communication during MRI sessions is not affected.

An active charge cancellation system for switched-capacitor sensor interface circuits

Interface circuits determine the performance of microsensors in diverse automotive, medical, and process-control applications. Microsensor systems for acceleration, rotation, pressure, and other signals most typically rely on capacitive displacement measurement in microstructures. Displacement sensitivity requirements are typically 0.1 pm with sensor capacitor values of 100 fF or less. Conventional architectures for capacitive displacement measurement have required bias control with either large value off-chip or large-area integrated resistive circuit components. Switched-capacitor measurement methods may provide a fully integrated solution with compact geometry but have been limited by severe charge injection error signals. The active charge cancellation system (ACCS), reported here, provides the first direct compensation of switched-capacitor charge-injection error at the measurement system input. The ACCS, implemented in a 0.8-/spl mu/m digital CMOS technology, uses a novel feedback network to directly cancel charge injection and reduce error by over two orders of magnitude without need for component matching.

An adaptive system for active cancellation of the acoustic field with an auxiliary identification channel

An adaptive system for active cancellation of a narrow-band random acoustic field with an auxiliary identification channel for modeling a time-dependent acoustic path is investigated. The stability criterion of the system is found. The active cancellation system proposed has been tested experimentally.

Integrated active vibration cancellation and machine diagnostic system

A machine analyzer is connected to an active vibration cancellation system in order to identify the operating status of the moving machinery while using a minimum of additional parts and taking advantage of signal processing already occurring in the active vibration cancellation system. A preferred embodiment employs a neural network pattern classifier in connection with detecting operating states such as cylinder misfires in an internal combustion engine.