Elsevier

Ultrasonics

Volume 119, February 2022, 106612
Ultrasonics

Enhancing the spectral signatures of ultrasonic fluidic transducer pulses for improved time-of-flight measurements

https://doi.org/10.1016/j.ultras.2021.106612Get rights and content
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open access

Highlights

  • New approach for air-coupled ultrasound generation based on fluidic transducers.

  • Fluidic transducers generate random angle-modulated ultrasound pulses for NDT.

  • Envelope removal singles out the pulses’ spectral signatures.

  • Mutual interference and self-interference of the pulses are reduced.

  • Fluidic transducers are applicable for multi-input, multi-output setups.

Abstract

Air-coupled ultrasonic (ACU) testing has proven to be a valuable method for increasing the speed in non-destructive ultrasonic testing and the investigation of sensitive specimens. A major obstacle to implementing ACU methods is the significant signal power loss at the air–specimen and transducer–air interfaces. The loss between transducer and air can be eliminated by using recently developed fluidic transducers. These transducers use pressurized air and a natural flow instability to generate high sound power signals. Due to this self-excited flow instability, the individual pulses are dissimilar in length, amplitude, and phase. These amplitude and angle modulated pulses offer the great opportunity to further increase the signal-to-noise ratio with pulse compression methods.

In practice, multi-input multi-output (MIMO) setups reduce the time required to scan the specimen surface, but demand high pulse discriminability. By applying envelope removal techniques to the individual pulses, the pulse discriminability is increased allowing only the remaining phase information to be targeted for analysis. Finally, semi-synthetic experiments are presented to verify the applicability of the envelope removal method and highlight the suitability of the fluidic transducer for MIMO setups.

Keywords

Air-coupled ultrasound
Fluidics
Signal processing
Pulse compression
MIMO
Hilbert transform

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