Linear Amplitude Response Research Articles

Single acoustic vector sensor DOA enhanced by unsaturated bistable stochastic resonance with linear amplitude response constrained

Acoustic vector sensors (AVS) are increasingly utilized for remote target passive perception, but accurate direction-of-arrival (DOA) estimation remains a formidable challenge, particularly in the presence of heavy background noise. In this paper, we propose a novel DOA estimation method that utilizes complex acoustic intensity measurements (CAIM) and unsaturated bistable stochastic resonance with linear amplitude response constrained (LAR-UBSR). The proposed method aims to exploit the excellent denoising performance of stochastic resonance (SR) to enhance the accuracy of DOA estimation. The proposed LAR-UBSR method is based on the theoretical analysis of the signal pre-processing requirements of CAIM, which determines the linear amplitude response and fixed phase shift. LAR-UBSR achieves a stable phase shift and linear amplitude response by utilizing the unsaturated potential well and limited potential parameters adjustment method of SR. We analyze the amplitude response linearity of LAR-UBSR under different signal-to-noise ratios (SNRs) and a wide range of frequencies, demonstrating a larger linear amplitude response interval that meets the signal pre-processing requirements of CAIM. Numerical analysis and application verification show that the proposed DOA method outperforms existing methods, particularly under low SNR conditions. The results suggest the potential for high-accuracy DOA estimation using nonlinear signal processing strategies in the presence of heavy background noise.

Resilience in Multiplex Networks by Addition of Cross-Repulsive Links

A multiplex network of identical dynamical units becomes resilient against parameter perturbation by adding selective linear diffusive cross-coupling links. A parameter drift at any instant in one or multiple network nodes can destroy synchrony, causing failure and even collapse in the network performance. We introduced [PRE 95, 062204(2017)] a recovery strategy by selective addition of cross-coupling links to save synchrony in the network from the edge of failure due to parameter mismatch (small or large) in any nodes. This concept is extended to 2-layered multiplex networks when the emergent synchrony becomes resilient against a small or large parameter drifting. In addition, the stability of the synchronous state is enhanced from local stability to global stability of synchrony. By the addition of cross-coupling, the network revives complete synchrony in all the nodes except the perturbed nodes, which emerges into a type of generalized synchrony with all the unperturbed nodes. The generalized synchrony is manifested simply by a linear amplitude response in the state variable(s) of the perturbed node(s) by a scaling factor proportional to the mismatch. A set of systematic rules has been derived from the linear flow matrix of the dynamical system representing the nodes dynamics that helps find the connectivity matrix of the cross-coupling links. Lyapunov function stability condition is used to determine the cross-coupling link strength that, in turn, establishes global stability of synchrony of the multiplex network. We verify the efficacy of our proposed coupling scheme with analytical results and numerical simulations of two examples of multiplex networks. In the first example, we use non-local connectivity in each layer, with nodal dynamics of the FitzHugh-Nagumo neuron model.

Bistable stochastic resonance with linear amplitude response enhanced vector DOA estimation under low SNR conditions

Abstract This work demonstrates a superior vector DOA estimation results by linear amplitude response of stochastic resonance with bistable nonlinear model, especially under low SNR conditions. The pre-processing problem of classical intensity based vector DOA estimation method is theoretically analyzed with gain-phase uncertainties, which demonstrate a constraint of linear amplitude response with a certain phase shift for an unbiased estimate of the true azimuth. In this way, linear amplitude response stochastic resonance is parametric modeled with gain-phase constraint, and achieved by the matched stochastic resonance theory with a maximized output SNR and a steady phase lag of π/2. The linear relation between the input and the output amplitude is simulative analyzed under different SNR conditions, which reflect a good linearity with the input amplitude A0

Step-scan differential Fourier transform infrared photoacoustic spectroscopy (DFTIR-PAS): a spectral deconvolution method for weak absorber detection in the presence of strongly overlapping background absorptions.

The determination of small absorption coefficients of trace gases in the atmosphere constitutes a challenge for analytical air contaminant measurements, especially in the presence of strongly absorbing backgrounds. A step-scan differential Fourier transform infrared photoacoustic spectroscopy (DFTIR-PAS) method was developed to suppress the coherent external noise and spurious photoacoustic (PA) signals caused by strongly absorbing backgrounds. The infrared absorption spectra of acetylene (C2H2) and local air were used to verify the performance of the step-scan DFTIR-PAS method. A linear amplitude response to C2H2 concentrations from 100 to 5000ppmv was observed, leading to a theoretical detection limit of 5ppmv. The differential mode was capable of eliminating the coherent noise and dominant background gas signals, thereby revealing the presence of the otherwise hidden C2H2 weak absorption. Thus, the step-scan DFTIR-PAS modality was demonstrated to be an effective approach for monitoring weakly absorbing gases with absorption bands overlapped by strongly absorbing background species.

Step-scan T cell-based differential Fourier transform infrared photoacoustic spectroscopy (DFTIR-PAS) for detection of ambient air contaminants

A step-scan differential Fourier transform infrared photoacoustic spectroscopy (DFTIR-PAS) using a commercial FTIR spectrometer was developed theoretically and experimentally for air contaminant monitoring. The configuration comprises two identical, small-size and low-resonance-frequency T cells satisfying the conflicting requirements of low chopping frequency and limited space in the sample compartment. Carbon dioxide (CO2) IR absorption spectra were used to demonstrate the capability of the DFTIR-PAS method to detect ambient pollutants. A linear amplitude response to CO2 concentrations from 100 to 10,000 ppmv was observed, leading to a theoretical detection limit of 2 ppmv. The differential mode was able to suppress the coherent noise, thereby imparting the DFTIR-PAS method with a better signal-to-noise ratio and lower theoretical detection limit than the single mode. The results indicate that it is possible to use step-scan DFTIR-PAS with T cells as a quantitative method for high sensitivity analysis of ambient contaminants.

Step scan T-cell Fourier-transform infrared photoacoustic spectroscopy (FTIR-PAS) for detection of ambient air contaminants

The theory of T-cells and their application in Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) based on a commercial FTIR spectrometer are discussed. This work was undertaken with the view to develop portable compact instrumentation for monitoring air contaminants. A resonant T-cell was determined to be the most appropriate resonator in view of the requirement for the low frequency and the limited space available in the FTIR spectrometer sample compartment. A two dimensional analytical solution with a semi-empirical boundary condition was introduced for resonance frequency prediction. Carbon dioxide (CO2) gas was the chosen air contaminant. Linear amplitude response to CO2 concentrations from 1000 to 8000 ppmv was observed, leading to a theoretical detection limit of 4 ppmv. The FTIR-PA phase shift was correlated to varying relaxation times in a mixture of CO2 and nitrogen (N2) gases. The analytical solution showed excellent agreement with simulated and experimental data, providing a reliable means for estimating the resonance frequency of the system. The experimental results establish the feasibility of using step-scan T-cell FTIR-PAS for quantitative detection of ambient air pollutants.

Feather Vibration as a Stimulus for Sensing Incipient Separation in Falcon Diving Flight

Based on our preceding studies on the aerodynamics of a falcoperegrinus in diving flight along a vertical dam it is known that even when the body shape of the bird is rather streamlined in V-shape some feathers tips may elevate in certain regions of the body. These regions were identified in wind tunnel tests for typical diving flight conditions as regions of locally separated flow. A life-size model in V-shape of a falcoperegrinus with artificial feathers fixed along the body was studied in a wind tunnel to focus on the fluid-structure interaction of feathers located in this sector. The distal ends of the feathers show flow-induced vibrations at typical flight conditions which grow linear in amplitude with increasing angle of incidence until incipient separation. In light of the proven existence of vibration-sensitive mechanoreceptors in the follicles of secondary feathers in birds it is hypothesized that this linear amplitude response offers the bird to sense the angle of incidence during the diving flight using the vibration magnitude as sensory stimulus. Thus the bird in streamlined shape has still a good measure to control its attitude to be in the narrow window of safe angle of incidence. This might have implications also for other birds or technical applications of airfoil sensors regarding incipient separation detection.

Validation and characterization of the computerized laryngeal analyzer (CLA) technique.

The aim of this study was to investigate the response characteristics of the Computerized Laryngeal Analyzer (CLA) and the validity of the noninvasive CLA method to detect swallowing-induced laryngeal elevation correctly. Two healthy adults and two experimental models were used in the study. The CLA technique identified all swallowing events but was unable to discriminate between swallowing and other movements of the tongue or the neck. The computer program produced a derivated response to a square wave signal. Stepwise bending increments of the sensor displayed a linear amplitude response. The degree of laryngeal elevation could not be estimated with the CLA technique, and it was not possible to draw any reliable conclusions from the recordings as to whether the larynx was moving upward or downward.

Fast variable-amplitude cold gas thruster

A fast response variable amplitude cold gas thruster is described. A laboratory prototype comprised of a piezoelectric stack and an associated microprocessor-based programmable dc power source, a low-loss mechanical displacement amplifier, a high-pressure spring-loaded axial valve, an integral high-pressure valve seat; an expansion nozzle, and a high-pressure gas supply were constructed and tested. The device is designed to operate as a stand-alone unit with a dedicated onboard microcontroller system and onboard energy storage system. Minimum pulse-width resolution (base-to-base) was shown to be 0.98 ms, with a lag time of 0.37 ms relative to the initiation of the drive pulse. Linear amplitude response was achieved beyond a threshold drive voltage of 80 vdc and was maintained through the limit of testing at 240 vdc.

Photoresponses of a sensitive extraretinal photoreceptor in Aplysia.

1. The light-evoked membrane current, photo-current, of an extraretinal photo-receptor, the ventral photoresponsive neurone (v.p.n.), in the abdominal ganglion of Aplysia californica, was studied using the voltage clamp method. Flashes and steps of monochromatic light were used as stimuli. 2. Flashes of light 100 msec in duration elicit slowly developing outward currents which peak at 5--10 sec and then return to dark levels within 30--60 sec. 3. The peak of the action spectrum of v.p.n. is at 470 nm and is similar to the peak for R2, another photoresponsive extraretinal Aplysia neurone, and to the peak of absorption spectra of molluscan rhodopsins. V.p.n. also contains membrane-bound cytoplasmic pigmented granules similar to those found in R2, and these are thought to mediate the light response. 4. Photo-current is associated with an increase in membrane conductance. In normal sea water photo-current has a reversal potential at the K equilibrium potential, EK and the reversal potential has a Nernstian relationship with external K concentration. The current--voltage relationships for peak and steady-state photo-current are fitted by the same constant field equation; currents measured when voltage was changed in steps at peak photo-current also have a similar relationship with voltage. The results are similar when saturating or non-saturating light intensities were used. Thus it appears that the light-activated K+ conductance is neither time nor voltage dependent. 5. Minimally detectable responses occurred at flash photon densities of 10(12) photons cm-2 which is 10(-3) that for R2. This value is comparable to those reported for retinal photoreceptors of Pecten irradians, a scallop, and Salpa democratica, a pelagic tunicate, and is lower than values reported for extraretinal photoreceptors such as the pineal photoreceptors of Salmo gairdnerii irideus, the rainbow trout, and the caudal photoreceptor in the sixth abdominal ganglion of Procambarus clarkii, a crayfish. 6. V.p.n. has a linear amplitude response range for low intensities of light and a non-linear range that saturates at high intensities. In the accompanying paper the response wave form and its temperature dependence are interpreted according to a diffusion-based model.

Use of a hot wire anemometer as a particle velocity detector in standing sound waves

It has been determined experimentally that the hot wire anemometer can, with restrictions, be used as a linear-amplitude response particle velocity detector in a longitudinal mode standing sound wave. In the case of a straight filament proper orientation of both the hot wire and the velocity field are important. Maximum sensitivity is obtained for a horizontal hot wire in a vertically oriented particle velocity field, but the output of a hot wire inclined 45°/135° to vertical in a horizontal standing wave tube is phase sensitive to the sense of the particle velocity vector. High-pass filtering is required to remove low frequency nonlinear components of the repetitive driveup–free-decay amplitude modulation. Traverses of the particle velocity field near a 0.9525 cm diam sphere in a 5.08 cm i.d. cylindrical cavity are presented for both straight and curved hot wires.

Recent Advances in Pure-Fluid Acoustic Amplification

The rapidly expanding field of pure-fluid amplification (fluerics) has brought forth applications and requirements that are stressing the capabilities of the wall attachment and proportional-type amplifiers. The increasing necessity for greater bandwidth, improved signal-to-noise ratio, and increased dynamic range indicates that recent developments with pure-fluid acoustic amplification will become an important phase of this infant field. Several years ago, predictions were made that bandwidths of 10 kHz would probably never be realized with pure-fluid amplification. Today, 10-kHz bandwidths are possible with carrier techniques, and recent studies with hot gas jets indicate that bandwidths of 50 kHz are within the near realm of possibility. Past research on the characteristics of sound-sensitive jets, jet edgetones, and jet ringtones is now playing a significant rôle in the fluerics field. Sound-sensitive laminar jets have an inherent amplification of perhaps 105, depending on the noise level of the undisturbed flow. The natural signal compression that results from the saturation of the developed vortex flow is detrimental to linear amplitude response, but for certain applications this phenomenon is desired. Perhaps the greatest disadvantage for the application of sound-sensitive jets for acoustic amplification is the restricted operational Reynolds number and the power-handling capability. The lack of knowledge on vortex flows in the vicinity of irregular solid boundaries is one of the most important factors retarding advanced studies.