Topic
Fundamental frequency
About: Fundamental frequency is a research topic. Over the lifetime, 8941 publications have been published within this topic receiving 131583 citations.
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TL;DR: A nonlinear transition metal dichalcogenide (TMD) hologram with high conversion efficiency and atomic thickness made of only single nanopatterned tungsten disulfide (WS2) monolayer is reported, for producing optical vortex beams and Airy beams as well as reconstructing complex holographic images at the second harmonic (SH) frequency.
Abstract: Nonlinear holography enables optical beam generation and holographic image reconstruction at new frequencies other than the excitation fundamental frequency, providing pathways toward unprecedented...
58 citations
TL;DR: In this article, a speech coding and decoding system is proposed, in which a timewise segment of an acoustic speech signal is represented by a frame of a data signal characterized by a fundamental frequency and spectral harmonics.
Abstract: In a speech coding and decoding system, in which a timewise segment of an acoustic speech signal is represented by a frame of a data signal characterized by a fundamental frequency and spectral harmonics, a current frame is reconstructed using a set of prediction signals based on the number of spectral harmonics for the current frame and a preceding frame and reconstructed signal parameters characterizing the preceding frame The number of spectral harmonics for the current and preceding frames are reconstructed from at least a pair of digitally encoded signals that are generated using error protection codes for all of their bits
57 citations
TL;DR: In this article, a theoretical analysis of the vibrations of thin rotating laminated cylindrical shells was carried out using Love's first approximation theory and it included the effects of initial hoop tension and the centrifugal and coriolis forces.
57 citations
TL;DR: In this paper, the authors examined the fundamental features of third-harmonic generation microscopy and applied them to the characterization of layered structures, and proposed a method for the determination of the layer's third-order susceptibility relative to the substrate.
Abstract: The fundamental features of third-harmonic generation microscopy are examined both theoretically and experimentally, and the technique is applied to the characterization of layered structures. Measurements and model calculations have been performed of the third-harmonic yield generated from homogeneous layers. Model calculations based on the paraxial approximation show good agreement with the experimental results, despite the conditions of high numerical aperture. The method proposed here allows for the determination of (i) the layer’s third-order susceptibility relative to that of the substrate, (ii) its index of refraction at the third-harmonic frequency relative to that at the fundamental frequency, and (iii) its thickness and for the identification of a gradient region between two adjacent layers.
57 citations
TL;DR: In this paper, a three-channel active control system is applied to an operational turbofan engine to reduce tonal noise produced by both the fan and the high-pressure compressor.
Abstract: A three-channel active control system is applied to an operational turbofan engine to reduce tonal noise produced by both the fan and the high-pressure compressor. The control approach is the feedforward filtered-x least-mean-square algorithm implemented on a digital signal processing board. Reference transducers mounted on the engine case provide blade passing and harmonics frequency information to the controller. Error information is provided by large area microphones placed in the acoustic far field. To minimize the error signal, the controller actuates loudspeakers mounted on the inlet to produce destructive interference. The sound pressure level of the fundamental tone of the fan was reduced using the three-channel controller by up to 16 dB over a +/- 30-deg angle about the engine axis. A single-channel controller could produce reduction over a +/- 15-deg angle. The experimental results show the control to be robust. Outside of the areas contolled, the levels of the tone actually increased due to the generation of radial modes by the control sources. Simultaneous control of two tones is achieved with parallel controllers. The fundamental and the first harmonic tones of the fan were controlled simultaneously with reductions of 12 and 5 dBA, respectively, measured on the engine axis. Simultaneous control was also demonstrated for the fan fundamental and the high-pressure compressor fundamental tones.
57 citations