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Advanced techniques
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CODEXCoDex:  Coded excitation for SNR improvement


In highly attenuating materials like carbon-fiber, glass-fiber and austenitic steel, defect detection reliability can be compromised by a low signal-to-noise ratio (SNR). In those scenarios, increasing the number of emitted pulses (burst excitation) can help increasing the signal amplitude. As counterpart, axial resolution is reduced due to the increased pulse duration.


This trade-off between SNR and resolution can be overcome by using Coded Excitation. A known digital pattern (code) is emitted, which increase propagated energy in the material when compared with a single pulse. On reception, the echo signals pass through a matched filter that recovers the original axial resolution while maintaining the SNR improvement.



Other applications like simultaneous emission at different angles or SAFT can benefit from Coded Excitation, and have been extensively covered in ultrasound research literature.


Figure 1 – Oscilloscope capture of a 13 bits Barker Code of -125V amplitude.


All the SITAU systems manufactured by DASEL include a proprietary circuit for coded excitation named CoDex. For each channel, user can program a different excitation code up to 16 bits length. Because it is hardware implemented, it works in real time with no acquisition rate reduction.

        Four pulses excitation                                16 bits Golaycodes excitation

CoDex 2

Figure 2 – Example of resolution improvement with Golay coded excitation.

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