Improving single flyover noise prediction for subsonic aircraft

Current ICAO Doc 9911 provides the algorithm to calculate aircraft noise levels for any kind of airport flight scenario. The essential difference exists between the measured and calculated sound levels, especially for single flight noise events. Doc 9911 recommends using this method for equivalent sound levels L and noise indices L first of all. A number of national noise regulations still require for single noise event assessment. An article analyzes a number of reasons to explain the inaccuracy of noise event calculations. For example, the differences between calculated balanced flight parameters (thrust and velocity first of all) and supervised in real flights may influence the accuracy first of all. Statistical data was gathered to make more general view on these differences and some proposal to use them in calculations has being proved. Also, the assumptions of the ICAO Doc 9911 method may contribute to the inaccuracy of calculations. Among them are the homogeneous atmosphere for sound propagation, generalized for overall fleet noise directivity pattern, etc. Ground effect model defines the values for aircraft absent in operation currently. The first assumption provides a conflict with flight path calculations for varied atmosphere parameters with height over the surface.

Design and Optimization of Sensitivity Enhancement Package for MEMS-Based Thermal Acoustic Particle Velocity Sensor

In this paper, small-sized acoustic horns, the sensitivity enhancement package for the MEMS-based thermal acoustic particle velocity sensor, have been designed and optimized. Four kinds of acoustic horns, including tube horn, double cone horn, double paradox horn, and exponential horn, were analyzed through numerical calculation. Considering both the amplification factor and effective length of amplification zone, a small-sized double cone horn with middle tube is designed and further optimized. A three-wire thermal acoustic particle velocity sensor was fabricated and packaged in the 3D printed double cone tube (DCT) horn. Experiment results show that an amplification factor of 6.63 at 600 Hz and 6.93 at 1 kHz was achieved. A good 8-shape directivity pattern was also obtained for the optimized DCT horn with the lateral inhibition ratio of 50.3 dB. No additional noise was introduced, demonstrating the DCT horn’s potential in improving the sensitivity of acoustic particle velocity sensors.

An Inverse Microphone Array Method for the Estimation of a Rotating Source Directivity

Microphone arrays methods are useful for determining the location and magnitude of rotating acoustic sources. This work presents an approach to calculating a discrete directivity pattern of a rotating sound source using inverse microphone array methods. The proposed method is divided into three consecutive steps. Firstly, a virtual rotating array method that compensates for motion of the source is employed in order to calculate the cross-spectral matrix. Secondly, the source locations are determined by a covariance matrix fitting approach. Finally, the sound source directivity is calculated using the inverse method SODIX on a reduced focus grid. Experimental validation and synthetic data from a simulation are used for the verification of the method. For this purpose, a rotating parametric loudspeaker array with a controllable steering pattern is designed. Five different directivity patterns of the rotating source are compared. The proposed method compensates for source motion and is able to reconstruct the location as well the directivity pattern of the rotating beam source.

Binaural (pre)processing for contralateral sound field attenuation and improved speech-in-noise recognition

ABSTRACTUnderstanding speech presented in competition with other sound sources can be challenging. Here, we reason that this task can be facilitated by improving the signal-to-noise ratio (SNR) in either of the two ears and that in free-field listening scenarios, this can be achieved by attenuating contralateral sounds. We present a binaural (pre)processing algorithm that improves the SNR in the ear ipsilateral to the target sound source by linear subtraction of the weighted contralateral stimulus. Although the weight is regarded as a free parameter, we justify setting it equal to the ratio of ipsilateral to contralateral head-related transfer functions averaged over an appropriate azimuth range. The algorithm is implemented in the frequency domain and evaluated technically and experimentally for normal-hearing listeners in simulated free-field conditions. Results show that (1) it can substantially improve the SNR (up to 20 dB) and the short-term intelligibility metric in the ear ipsilateral to the target source, particularly for speech-like maskers; (2) it can improve speech reception thresholds for sentences in competition with speech-shaped noise by up to 8.5 dB in bilateral listening and 10.0 dB in unilateral listening; (3) it hardly affects sound-source localization; and (4) the improvements, and the algorithm’s directivity pattern depend on the weights. The algorithm accounts qualitatively for binaural unmasking for speech in competition with multiple maskers and for multiple target-masker spatial arrangements, an unexpected property that can inspire binaural intelligibility models.

Design and implementation of a jellyfish otolith-inspired MEMS vector hydrophone for low-frequency detection

Detecting low-frequency underwater acoustic signals can be a challenge for marine applications. Inspired by the notably strong response of the auditory organs of pectis jellyfish to ultralow frequencies, a kind of otolith-inspired vector hydrophone (OVH) is developed, enabled by hollow buoyant spheres atop cilia. Full parametric analysis is performed to optimize the cilium structure in order to balance the resonance frequency and sensitivity. After the structural parameters of the OVH are determined, the stress distributions of various vector hydrophones are simulated and analyzed. The shock resistance of the OVH is also investigated. Finally, the OVH is fabricated and calibrated. The receiving sensitivity of the OVH is measured to be as high as −202.1 dB@100 Hz (0 dB@1 V/μPa), and the average equivalent pressure sensitivity over the frequency range of interest of the OVH reaches −173.8 dB when the frequency ranges from 20 to 200 Hz. The 3 dB polar width of the directivity pattern for the OVH is measured as 87°. Moreover, the OVH is demonstrated to operate under 10 MPa hydrostatic pressure. These results show that the OVH is promising in low-frequency underwater acoustic detection.

Algorithm for determining the design of an unbalanced wave channel antenna with a given direction of maximum radiation in the vertical plane

An integral part of the communication system with unmanned aerial vehicles is the airborne antenna-feeder system. As a rule, a circular pattern is required in the horizontal plane. However, since omnidirectional antennas have a small gain, they switch to schemes of several directional switchable antennas. It is proposed to use an unbalanced antenna for such systems. Unbalanced antennas have limited substrate dimensions. The maximum gain is achieved not towards the horizon, but at some elevation angle. Proposes a design definition algorithm an unbalanced antenna wave channel with a given direction of maximum radiation. For example, a similar antenna is constructed using the algorithm. An antenna for operation in the frequency range of 2,3…2,7 GHz is taken as the initial data. The dimensions of the antenna elements are obtained from numerical experiments using an optimization module in CAD. A study of the directivity characteristics of an unbalanced wave channel of an antenna with a limited substrate and the dependence of the elevation angle of the maximum of the directivity pattern is carried out. The minimum size of the substrate at which the gain in the direction to the horizon stops growing is revealed. The range of values of the elevation angle of the maximum of the amplitude radiation pattern in the vertical plane is determined.

Performance characteristics of acoustic direction finders of localized broadband signal sources

In this paper, we substantiate main performance characteristics of the regression algorithm of a two-channel direction finder of localized sources of broadband signal against the background of interference distributed in space, invariant to radiated power and supply voltage. We analyze mutual statistical characteristics of broadband signals in a two-channel direction finder. Based on the method of canonical decomposition in complex form, we show the cross-correlation function of processes at the outputs of direction finder antennas when operating on a localized signal source against the background of interference distributed in space. For invariance of performance characteristics, we consider the application of sign transformation to signals and analyze the dependence of a cross-correlation function of the input signals after the sign transformation at different signal-to-noise ratios. We show the formation of a directivity pattern in a correlation direction finder with signal-to-noise ratio more than 1. For direction-finding of localized signal source, we substantiated a regression algorithm with discrete-analog signal processing, where sign processing based on standard digital hardware components is used. The invariance of the algorithm to supply voltage is shown by representing Boolean functions as expressions of conjunction, disjunction, and negation. The regression algorithm is substantiated in the time domain. We obtain the expressions for mean and variance of the calculated statistics for direction-finding of localized signal source against the background of interference distributed in space. We show the possibility of formation of a directivity pattern with completely suppressed side lobes. The algorithm functions at signalto-noise ratios up to 1. The algorithms can be used in passive acoustic and hydroacoustic direction finders, as well as direction finders with ultra-wideband signals with computer-based signal processing.

Генерация второй гармоники-суммарной частоты в тонком сферическом слое. II. Анализ диаграмм направленности

The solution to the problem of second harmonic–sum frequency generation by two coherent plane electromagnetic waves with elliptical polarizations and equal frequencies in a thin spherical layer is analyzed graphically. Asymmetries are introduced that quantitatively describe the shape of three-dimensional directivity patterns (spatial distribution of the power density of second harmonic–sum frequency radiation). Three-dimensional directivity patterns and asymmetries are analyzed for various combinations of the parameters: ratio of the complex amplitudes of the incident waves, angle between the wave vectors of the incident waves (the opening angle), ellipticities, orientations of polarization ellipses, spherical particle size. It is found that, at small particle sizes, each anisotropy type corresponds to its own individual directivity pattern. It is revealed that, for one of the anisotropy types, the shape of the directivity pattern almost does not change for nearly all possible ranges of the above parameters.