63 results about "Acoustic holography" patented technology

The invention discloses a high-precision near-field acoustic holography algorithm adopting a weighted iteration equivalent source method, which is characterized in that a holographic plane H is arranged in a sound source near-field radiation area, and sound pressure PH on the holographic plane H is measured; an equivalent source plane Se is arranged at the side, which is away from the holographic plane H, of an object reconstruction plane T, and equivalent sources are arranged on the equivalent source plane Se; a relation between the sound pressure PH and each equivalent source is established by using a sound pressure transfer matrix between the equivalent source and the holographic plane H; and the source intensity Q of each equivalent source is solved by adopting a new iterative regularization algorithm with a posteriori weighted norm constraint penalty term, and then sound field data on the object reconstruction plane T is calculated by using the solved source intensity Q and the transfer matrix between the equivalent source and the object reconstruction plane T. According to the invention, the source intensity of each equivalent source is precisely solved by using the new iterative regularization algorithm with the posteriori weighted norm constraint penalty term, thereby avoiding source intensity energy leakage caused by a 2-norm penalty term in the Tikhonov regularization process. Compared with conventional equivalent source based near-field acoustic holography, a calculation result acquired by the method disclosed by the invention is more accurate.

The invention discloses a pressure speed method sound field separation method, a measured sound field is provided with a measuring surface S; a sound pressure sensor is adopted to measure the sound pressure on the measuring surface S, and a particle velocity sensor or a sound intensity probe is adopted to measure the particle speed on the measuring surface S; both sides of the measuring surface S are provided with the imaginary source surfaces S1 <*> and S2 <*> which are provided with the equivalent sources; the transfer relationship between the equivalent sources and the sound pressure and the particle speed on the measuring surface S is constructed; the separation of sound source radiation sound pressure and the particle speed of both sides on the measuring surface according to the transfer relationship is realized; the sound field separation is realized by measuring the speed relation of sound pressure and particle on each surface; and the equivalent source method is adopted as the sound field separation arithmetic, the calculation stability is good, the calculation precision is high, and the implement is simple. The method can be widely applicable to the near-field acoustic holography measurement in the environments of internal sound field or noisy sound, the sound intensity method sound source identification in the noisy environment, the material reflection coefficient measurement, and the separation of the scattering sound field.

A system and method for analyzing a sample is described. The system may include, for example, a light source and a scanning probe microscope probe. The light source may generate a coherent laser beam that is modulated by a waveform of a lower frequency. The modulated laser beam is absorbed by the sample causing thermally induced expansion and resulting in an excitation of acoustic waves. The probe is locally deployed near the sample and detects, in real time, perturbations in the excited acoustic waves to detect surface and buried structures of the sample.

A method of performing near-field acoustic holography comprises the following steps. Establishing (102) acoustic data representing a set of near-field acoustic holography measurements at a first set of positions. Extrapolating (204) acoustic data using a model-based extrapolation to obtain extrapolated acoustic data relating to a plurality of positions outside the aperture. Applying (108) a spatial frequency transform to the padded acoustic data to obtain data in a spatial frequency domain. Propagating (110) the Fourier transformed acoustic data. Applying (112) a regularization in a wavenumber domain. Performing (114) an inverse spatial frequency transform.

The invention discloses a full-frequency-domain identification method for a vibration noise source of a transformer, and relates to a noise source identification method. The method comprises the following steps that sound pressure signals of the vibration noise source of the transformer are collected and measured, and divided according to the frequency domain; an acoustic holography method is usedto reconstruct low-frequency signals and calculate the vibration speed in the normal direction of low-frequency noise; a wave beam formation method is used to reconstruct high-frequency signals and calculate the vibration speed in the normal direction of high-frequency noise; and the noise sound pressure signals in the full frequency domain and the vibration speed in the normal direction of noisein the full frequency domain are calculated to identify full-frequency-domain noise of the vibration noise source of the transformer. Wave-number-domain zero-fill extrapolation is carried out on low-frequency sound pressure signals obtained by measuring an acoustic holographic measurement side, a result after zero-fill extrapolation is used to carry out reconstruction, reeling errors and an edgeGibbs effect caused by large size of the transformer are overcome, and noise of the vibration noise source of the transformer is identified in the full frequency domain.

The invention relates to a system and method for detecting plant diseases based on near field acoustic holography technology. According to acoustic emission phenomena of plants and on the theoretical basis of the near field acoustic holography technology of a distributed source boundary point method, a cylindrical surface-spherical surface non-conformal-surface acoustic holography experiment model is established, and simulation experiments on single sound sources and double sound sources are respectively carried out. By changing of parameters, in the model, such as the holographic cylindrical surface radius, holographic measuring point number, and node number on reconstruction spherical surface, distance between fictive particular solution sources and nodes on the reconstruction spherical surface, and the like, feasible experimental parameters are obtained. Simulation results show that the method can accurately identify and locate the position of an acoustic emission source. On the basis of the experimental parameters, a signal acquisition acoustic holography experiment system which adopts DSP as a core is established, and data analysis and processing are carried out by an upper computer which adopts Labview as a software platform. The system and method for detecting plant diseases based on the near field acoustic holography technology adopt plant acoustic emission signals as important sensitive information to know the growth states and disease-affected situations of the plants, and through studies of the acoustic emission signals based on the near field acoustic holography technology of the distributed source boundary point method, the diseases can be timely discovered and identified, and a new way and the new method for the prevention and control and detection of the plant diseases is provided.