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Beamforming

Beamforming. Wave-front. Beam axis. No Focusing. Wave-front. Wave-front. τ. τ. τ. Wave-front. Beam axis. τ. τ. τ. τ. τ. τ. τ. τ. Focal point. τ. Beam axis. Focal point. Steering & Focusing = Beamforming. Beam axis.

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Beamforming

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  1. Beamforming Wave-front Beam axis No Focusing Wave-front Wave-front τ τ τ Wave-front Beam axis τ τ τ τ τ τ τ τ Focal point τ Beam axis Focal point Steering & Focusing = Beamforming Beam axis Electronicallycontrolledbeamforming can be obtainedbyusingarray of transducerelements. Steering Focusing

  2. Beamformers PhasedArrayBeamforming SyntheticArrayBeamforming

  3. Beamforming Techniques • Full Phased Array • All array elements simultaneously activated for transmit and receive • Requires complex front-end electronics • Improved SNR, Proportional with N√N • Classical Synthetic Aperture • The same element is activated for transmit and receive • Simple front end • Poor SNR, Proporional with • Synthetic Phased Array • All array element pairs individually activated using multiple pulse-echo • Average SNR

  4. PSF Analysis • The PSF is derived for an N element linear array with length D • Far field and paraxial approximations are used • The chosen parameters for the plot are N=8 and d=1.5λ

  5. PSF for phased array imaging • PSF for synthetic array imaging • comparison

  6. Performance Measurement Imaging System h(r,θ,φ) Real image slice i(r,θ,φ) Resulted image slice o(r,θ,φ)=h(r,θ,φ) * i(r,θ,φ) • Imaging system can be modelled as illustrated, The inpur is real image of interested area • and the output is visualized image slice • If input is just a point the result will show the transfer function of imaging system, h(.) • This function characterizes the imaging sistem and is known as Point Spread Function • For a 2-dimensional Nx×Ny element array point spread function can be expressed as, • ,where A(nx,ny) defines the element distribution.

  7. Beam Axial Lateral Image Quality Factors B A C • Lateral Resolution • Pixel Resolution: Main lobe Width (A) • Contrast Resoluion: Side lobe level (C), Grating Lobe (B) • Axial Resolution • Affected by pulse bandwidth

  8. Image Quality • Temporal resolution • The ability of imaging moving objects, requiring faster slice reconstruction • SNR • Affected by beamforming technique and array element size

  9. 2 Way PSF • 1Way and 2Way PSFs • Co-array concept • TX array * RX array • Co array differences between PA and SA.

  10. EffectiveAperture (Coarray) 2-wayPoint Spread Function EffectiveAperture (Coarray)Function

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