Active apertura |
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The Active Aperture is the total probe active length A => Active aperture. g => Gap between two adjacent elements e=> Width of a single piezocomposite element, its typical value is ≤ λ/2. n => Number of elements. λ => Wavelength. p (pitch) => It is the elementary distance between the centers of two adjacent elements. W => Passive aperture is the element length or width. It determines the focal length on y-axis. Fmin – Fmax => Maximum and minimum focal depths. |
Near-field |
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The near field depends on the aperture size.
A => Active aperture. No => Near field. |
Beam width |
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The beam width depends on the focal depth and the active aperture size. zfoco => Focal depth. κBW => Constant that depends on width criteria: κBW => 1 (Rayleigh criteria) κBW => 1.22 (FWHM - Full Width at Half Maximum - criteria) κBW=> 1.33(Sparrow criteria) Δx => Lateral resolution is defined by the beam width. Δz => Axial resolution is given by
ΔT-20dB - Echo duration at a -20dB drop-off. V=> Sound velocity in the test material. |
Focus depth |
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For a given aperture (A), the focus length (L) DECREASES as the focal distance (zfoco) DECREASES.
The maximum focal distance (zfoco(MAX)) must be inside the near-field No.
A => Active aperture. V => Velocity of propagation. |
Dynamic Depth Focusing (DDF) |
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The DDF dynamically changes the focal distance as the signal returns to the phased array probe. It significantly increases the depth-of-field, resolution and SNR. |
Calculation of emitting focal law – angular sweep |
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DLE => Emission delay time. DLR => Reception delay time. θ => Steering direction. xi => Position of the element “i”. FE => Distance from the array centre to the emitting focal point in polar coordinates (RE,θ). FR1, FR2, FR3, ...=> Distance from the array centre to the reception focal point “n”. rin => Distance from the reception focal point “n” to the element “i” - round-time-of -flight VM=> Ultrasound velocity in the test material. |
Max. steering angle |
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Maximum steering angle depends on the element size
θSTmax => Maximum steeering angle at -6dB. e => Width of a single array element. λ => Wavelength. |
Grating lobes |
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Grating lobes are generated by sub-sampling across the probe elements. Grating lobe amplitude depends on pitch size, number of elements, frequency and bandwidth.
βGrating => Location of grating lobes. p => Pitch. λ => Wavelength. |