Ultrasound

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Near Field Calculation and Beam Divergence

Near field calculation and beam divergence are well known for conventional transducers. For a phased array probe, we need to treat the active and the passive axes separately. The passive axis is the axis that is not controlled by the phased array delay. This can be considered an unfocused rectangular element. The near field is

Digitization

A digitizer converts the echo waveforms returned by the ultrasonic transducer into digital information using an ADC. For applications that require well-shaped waveforms in the time-domain, a sample rate 10 times higher than the resonant frequency of the transducers is required. In these applications, a transducer that has a resonant frequency of 5 MHz requires

Reflector Plate Inspection

Ultrasonic inspection of certain composite materials can be difficult. In fact, highly dense composite materials produce noisy ultrasonic response to pulse-echo inspections. Also, through transmission techniques cannot always be implemented due to mechanical restrictions and limitations. The use of a reflector plate can be a valuable alternative. A complex shape composite component was inspected for

Effect of Rough Surfaces

The condition of the surface through which a sound beam enters a material affects ultrasonic measurements. Increased roughness reduces the transmitted energy of the sound beam and this, in turn, reduces the amplitude of the received signal, leading to difficultly in measuring the size of the discontinuity. The defect signal amplitude decreases with increases in

Porosities – Ultrasonic

Porosity is a known detrimental material condition that includes a plurality of voids in the composite material caused by trapped or evolved gases which may be caused by improper processing, such as improper curing of the composite material. The ultrasonic inspection of composite laminates takes advantage of the fact that porosity does not block ultrasound,

Sensitivity and Resolution

Sensitivity is the ability of an ultrasonic system to detect defects at a given depth in a test material. The greater the signal that is received from these reflectors, the more sensitive the transducer system. Axial resolution is the ability of an ultrasonic system to produce simultaneous and distinct responses from indications Iocated at nearly

Ultrasonic Data Displays

Ultrasonic data can be collected and displayed in a number of different formats. A scan can be shown as an RF, half waves (positive or negative) or a rectified signal. B-scan, C-scan and D-scan representations are important to facilitate visualization.

Attenuation

A sound wave that runs through a medium loses energy during various processes (scattering, absorption, and reflection). This is called attenuation. The intensity I of the wave follows the law of attenuation I= I0 exp(-us) where (I0) is the initial intensity, (s) is the path length in the medium, and (µ) is the attenuation coefficient.

Pulse Width

Phased Array Instrument uses square wave pulse to generate the pulse. The pulse voltage and pulse width are adjusted directly to provide precise control over pulse shape. Pulse width must be adjusted to match the probe frequency as for the formulae below: The width of the beam determines the lateral resolution. The length of the

Side Lobes and Grating Lobees

Since Phased arrays have discrete elements, equally spaced, they can experienced side and grating lobes. They are experienced when the element spacing is greater than a half wavelength (see details below). The spatial distortion effect causes some sidelobes to become substantially larger in amplitude, and approaching the level of the main lobe; these are called