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.

空气耦合超声 (ACU) 检测已被证明是一种提高无损超声检测和敏感样品研究速度的有价值的方法。实施 ACU 方法的一个主要障碍是空气-样本和换能器-空气接口处的显着信号功率损耗。使用最近开发的流体换能器可以消除换能器和空气之间的损失。这些换能器使用压缩空气和自然流动的不稳定性来产生高声功率信号。由于这种自激流动不稳定性，单个脉冲的长度、幅度和相位都不相同。这些幅度和角度调制脉冲提供了利用脉冲压缩方法进一步提高信噪比的绝佳机会。

在实践中，多输入多输出 (MIMO) 设置减少了扫描样品表面所需的时间，但需要高脉冲辨别力。通过对单个脉冲应用包络去除技术，提高了脉冲辨别力，只允许将剩余的相位信息作为分析的目标。最后，介绍了半合成实验以验证包络去除方法的适用性，并突出了流体换能器对 MIMO 设置的适用性。