Application of Active Noise Control to Reduce Cabin Noise in Single Engine General Aviation Aircraft

The application of active noise control to reduce cabin noise in single engine, general aviation aircraft is investigated through the use of the \u27filtered x\u27 least mean square algorithm and a simple acoustic feedforward method to generate a reference signal is tested. The system is designed to utilize one reference signal and up to two feedback signals and two audio speakers. The feedforward system consists of a microphone placed in close proximity to the front windshield and isolated from the cabin noise. Cabin noise and reference signals are recorded during flight in a Cessna 172 Skyhawk, a Piper Cherokee 140 and a Piper Malibu Mirage. The recorded data is used in laboratory tests to evaluate the capability of the control system to reduce the cabin noise signal with the recorded reference signal. The reference signal was found to lack coherence with the cabin noise in most aircraft which limited the noise reductions. Alternative feedforward methods are investigated and an alternative reference signal is tested in a laboratory simulation. The results with the recorded data and the modified reference signal are detailed in each case

Innovative Concepts in Microwave Photonics

This paper reports the work carried by ITEAM researchers on novel concepts in the field of Microwave Photonics (MWP). It includes activities related to the general modelling of MWP systems, the use of novel multicore fibers and recent advances in the emergent and hot topic of integrated microwave photonics.Capmany Francoy, J.; Sales Maicas, S.; Gasulla Mestre, I.; Mora Almerich, J.; Lloret Soler, JA.; Sancho Durá, J. (2012). Innovative Concepts in Microwave Photonics. Waves. 4:43-58. http://hdl.handle.net/10251/57919S4358

Software-Defined Radio Demonstrators: An Example and Future Trends

Software-defined radio requires the combination of software-based signal processing and the enabling hardware components. In this paper, we present an overview of the criteria for such platforms and the current state of development and future trends in this area. This paper will also provide details of a high-performance flexible radio platform called the maynooth adaptable radio system (MARS) that was developed to explore the use of software-defined radio concepts in the provision of infrastructure elements in a telecommunications application, such as mobile phone basestations or multimedia broadcasters

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

A Computational Analysis of the Aerodynamics and Aeroacoustics of Jets with Fluid Injection

A detailed numerical analysis of fluidic injection as a tool to reduce noise emission is presented here. The noise reduction strategy, developed at the Pennsylvania State University, is based on injectors that blow air into the diverging section of the nozzle to emulate the effect of interior corrugation on the jet plume. The advantage is that the injection can be activated during takeoff and turned o_ during other phases of flight so that performance is not affected. Numerical simulations are performed on a military-style nozzle based on the GE F400-series engines, with a design Mach number of 1:65, for over-expanded jet conditions. The effectiveness of the fluidic injection as noise reduction technique is analyzed for heated and unheated jets. A high-order Large Eddy Simulation (LES) solver, developed originally at Purdue University, is used to analyze the flow-field and the acoustic field. New initial conditions and new boundary conditions are introduced. A set of Reynolds Averaged Navier-Stokes (RANS) simulations is used to set up the initial and boundary conditions for the LES runs. The numerical results are compared and validated with the outcome of experiments and RANS simulations performed at the Pennsylvania State University. The characteristics of unheated and heated jets are presented and compared. The higher temperatures do not modify the shock-cell structures, while they affect the jet development and the acoustic signature. The fluidic injection shows the potential of breaking down the shock-cells into smaller structures with lower strength, directly reducing the intensity of broadband shock associated noise. Moreover, the injectors are found to affect the development of the larger turbulent structures that generate the peak noise. For the cases tested the injectors reduce the peak noise by more than 1:5 dB for the unheated jet and by 3 dB for the heated jet, on the azimuthal plane in between two lines of injectors. The direction of maximum sound propagation moves from about 30_ to about 50_ as the jet gets heated. An analysis of the thrust changes due to activating the injectors is also presented for the heated and unheated jet conditions. The specific thrust is reduced by about 3% when the injectors are used

Development and Characterization of Infrared Broadband Open-Path Hydrocarbon Detectors for Chemical Species Tomography

Chemical species tomography (CST) is an emerging diagnostic technique for estimating the spatial distribution of a chemical species of interest. This thesis focuses on using CST to detect and map fugitive hydrocarbon emissions resulting from crude oil refinement, where current methods of detecting and measuring these emissions can be costly and inaccurate. This technique utilizes multiple optical paths to measure path-integrated concentrations over a flow field that are used in reconstructions to obtain an estimated discrete distribution. Prior CST work has made use of diode lasers, ultraviolet differential optical absorption spectrometers, or Fourier transform infrared spectrometers. This thesis pioneers the use of broadband infrared open path detectors for CST. A theoretical background is laid out with a discussion of the fundamentals of how E-M waves interact with gas molecules, which underlies the CST measurement principle. This is followed by an explanation of monochromatic tomography, which involves solving a rank-deficient problem through the context of a Bayesian problem with prior information. Broadband tomography is then developed on that foundation, requiring a transfer function to linearize the problem. Details of a design overview is presented for four open path broadband detector and emitter pairs that were fabricated for use in lab-scale tomography experiments. Focusing on the mid-infrared ro-vibrational band of hydrocarbons at approximately 3.3 µm, the pairs contain optical components suitable for operation at distances up to 10 m. These components include a thermal emitter, a collimating reflector, bandpass filter, focusing lens, and photovoltaic detector. The detector pairs were validated and transfer functions were built with a calibration process through a custom-built absorption cell with gaseous species of methane, propane, and ethylene. Using known concentrations of one species at a time, the transmittance of an optical pair was compared to an expected model that was constructed from spectral data compiled in the HITRAN or PNNL databases. Twelve tomography experiments followed, culminating in a final successful proof-of-concept tomographic reconstruction of a propane plume that was validated with flame ionization detector measurements

Spatial, Spectral, and Perceptual Nonlinear Noise Reduction for Hands-free Microphones in a Car

Speech enhancement in an automobile is a challenging problem because interference can come from engine noise, fans, music, wind, road noise, reverberation, echo, and passengers engaging in other conversations. Hands-free microphones make the situation worse because the strength of the desired speech signal reduces with increased distance between the microphone and talker. Automobile safety is improved when the driver can use a hands-free interface to phones and other devices instead of taking his eyes off the road. The demand for high quality hands-free communication in the automobile requires the introduction of more powerful algorithms. This thesis shows that a unique combination of five algorithms can achieve superior speech enhancement for a hands-free system when compared to beamforming or spectral subtraction alone. Several different designs were analyzed and tested before converging on the configuration that achieved the best results. Beamforming, voice activity detection, spectral subtraction, perceptual nonlinear weighting, and talker isolation via pitch tracking all work together in a complementary iterative manner to create a speech enhancement system capable of significantly enhancing real world speech signals. The following conclusions are supported by the simulation results using data recorded in a car and are in strong agreement with theory. Adaptive beamforming, like the Generalized Side-lobe Canceller (GSC), can be effectively used if the filters only adapt during silent data frames because too much of the desired speech is cancelled otherwise. Spectral subtraction removes stationary noise while perceptual weighting prevents the introduction of offensive audible noise artifacts. Talker isolation via pitch tracking can perform better when used after beamforming and spectral subtraction because of the higher accuracy obtained after initial noise removal. Iterating the algorithm once increases the accuracy of the Voice Activity Detection (VAD), which improves the overall performance of the algorithm. Placing the microphone(s) on the ceiling above the head and slightly forward of the desired talker appears to be the best location in an automobile based on the experiments performed in this thesis. Objective speech quality measures show that the algorithm removes a majority of the stationary noise in a hands-free environment of an automobile with relatively minimal speech distortion