Nonlinear elastic imaging with two-frequency elastic pulse complexes

Abstract

Methods and instruments for suppression of multiple scattering noise and extraction of nonlinear scattering components with measurement or imaging of a region of an object with elastic waves, where at least two elastic wave pulse complexes are transmitted towards said region where said pulse complexes are composed of a high frequency (HF) and a low frequency (LF) pulse with the same or overlapping beam directions and where the HF pulse is so close to the LF pulse that it observes the modification of the object by the LF pulse at least for a part of the image depth. The frequency and / or amplitude and / or phase of said LF pulse relative to said HF pulse varies for each transmitted pulse complex in order to nonlinearly manipulate the object elasticity observed by the HF pulse along at least parts of its propagation, and where received HF signals are picked up by transducers from one or both of scattered and transmitted components of the transmitted HF pulses. Said received HF signals are processed to form measurement or image signals for display, and where in the process of forming said measurement or image signals said received HF signals are one or both of delay corrected with correction delay in the fast time (depth-time), and pulse distortion corrected in the fast time, and combined in slow time to form noise suppressed HF signals or nonlinear scattering HF signals that are used for further processing to form measurement or image signals. The methods are applicable to elastic waves where the material elasticity is nonlinear in relation to the material deformation.

Description

technical field [0001] The present invention relates to methods and apparatus for using nonlinear elasticity for measurement and imaging using elastic waves in materials, such as, but not limited to, medical ultrasonic imaging, ultrasonic non-destructive testing, subsea sonar applications, and geological applications. Background technique [0002] Nonlinear elasticity means that the elastic stiffness of a material changes as the material elastically deforms. For example, material volumetric compression stiffness increases with volumetric compression of the material, and volumetric compression wave propagation velocity subsequently increases. Similarly, volume expansion reduces the material volume compression stiffness, and the volume compression wave propagation velocity subsequently decreases. [0003] In solids, there is also shear deformation elasticity, which makes shear deformation waves in solids possible. Gases and liquids are fully shape-variable, and thus do not e...

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Problems solved by technology

[0005] Acoustic noise and wavefront aberrations caused by multiple scattering degrade image quality and create problems with nonlinear scattering signals and extraction of propagation and scattering parameters

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