As it is well known, ultrasonic guided waves exist in layered media and propagate along the media interface. An important property of guided waves is dispersive and guided waves have multiple modes. And different mode of guided waves has different dispersion property.

How to make the dispersive guided waves being focused? This research uses ultrasonic phased array method to achieve focusing for guided waves, rather than previously used acoustic time reversal which is difficult to artificially control beam focusing.

Researchers from the State Key Laboratory of Acoustics of IACAS proposed the novel focusing method for highly dispersive guide waves.

The basic principle of this method is to design an excited source signal based on the dispersion property of guide waves for each array element. The purpose of it is that the guided waves generated by the designed source signals from all transducer array elements will arrive at a target simultaneously and focusing is realized.

The key of this method is to control the phase for each frequency component of the transmitted signal, that is, to transmit the slower components of the guided waves earlier than the faster components so that the guided waves with all frequency components will arrive at the target at the same time to achieve focusing. This focusing method can be considered as a generalized phased array focusing method.

Compared to the conventionally ultrasonic phased array method, the generalized phased array method can achieve ultrasonic guided wave focusing and scan the whole detection area. However, different from the conventional method is that the generalized method controls the excitation pulse (focused pulse), while the conventional method controls time delay.

The numerical simulation results show that the guided waves with different modes, different frequency components, and from different elements of the transducer array can all be focused at the target and focusing is achieved.

The research titled “Ultrasonic Guided Wave Focusing by a Generalized Phased Array” was published online: http://iopscience.iop.org/1674-1056/22/1/014302/ and also on the recently issued CHINESE PHYSICS B (Vol. 22, No. 1, Article Number: 014302, DOI: 10.1088/1674-1056/22/1/014302, JAN, 2013) and Acoustical Physics (Vol. 59, No. 1, Pages 97–102. 2013).

 

Contact:

ZHANG Bixing

Institute of Acoustics, Chinese Academy of Sciences

e-mail: zhbx@mail.ioa.ac.cn