Ultrasonic Sensor/Actuator

Despite the fact that omnidirectional shear-horizontal (SH) waves have recently received much attention, there is no systematic design method with which to develop the corresponding transducers with enhanced output and power concentration levels at a target frequency. Here, we propose a method which can be used to design an optimal annular-array magnetostrictive patch transducer (MPT) that fulfills the above-mentioned objectives. The proposed transducer consists of optimally configured multiple magnetostrictive patches, consistently placed permanent magnets, and toroid coils. For the design, the transducer output signals are theoretically predicted using Green's function of guided waves in a plate and the analysis results are then used to develop new high-power annular-array MPTs generating omnidirectional SH waves in a plate. The validity of the analysis and the effectiveness of the design method were confirmed with numerical simulations and pitch-catch wave experiments performed on an aluminum plate. In the experiments, the mode selectivity and omnidirectivity of the designed transducer were also checked. While the proposed method is mainly developed for MPTs, it should be equally useful for the design of similar annular-type piezoelectric and electromagnetic acoustic guided wave transducers. 

C.I. Park et al., Smart Mater. Struct., 8, 075005 (2019).

The use of a specific wave mode is critical in ultrasonic non-destructive evaluations but it is difficult to generate a specific mode, especially a higher mode at a frequency where there exist multiple wave modes. Here, we propose a compact omnidirectional shear-horizontal wave MPT (magnetostrictive patch transducer) having two annular magnetostrictive patches for the generation of a nearly pure SH1 (second shear-horizontal) mode in a plate for frequencies above the first cutoff frequency. While a common wavelength-matching approach would typically require the use of several patches and does not appear completely to eliminate unwanted omnidirectional wave modes, the proposed MPT, with only two annular patches, generates the desired SH1 mode predominantly with the unwanted SH0 (first shear-horizontal) mode nearly eliminated. For the design, the geometries of the annular patches are optimally configured to maximize the ratio of the SH1 mode to the SH0 mode. Numerical simulations and experiments confirm the effectiveness of the proposed bi-annular shear-horizontal wave MPT. Because the SH1 mode near the first cutoff frequency is highly dispersive, the developed transducer is expected to be critically useful in various applications, such as ultrasonic inspections of wall thinning.

C.I. Park et al., Ultrasonics, 99, 105958 (2019).