Wide range generation of the circumferential guided waves (C-GWs) propagating along the perimeter of a pipe has been carried out using a single shear wave sensor along with several tone-burst sources. The C-GWs are classified mainly into two propagation modes, circumferential shear horizontal (C-SH) and circumferential Lamb (C-Lamb) waves. The authors previously reported that a simple and selective generation of the two modes using a single shear wave sensor could be realized by changing the polarization direction of the sensor. When the polarization direction of the sensor is parallel or vertical to the axial direction of a pipe, either the C-SH or the C-Lamb wave is selectively generated. In this paper, a newly exploited signal processing method to obtain a wide-range time–frequency analysis for the C-GW is proposed using wavelet transformation along with various tone-burst signals swept in the required frequency range. Time–frequency analyses of the results for the C-SH and C-Lamb waves propagating along 30-mm outer diameter and 1-mm-thick aluminum pipe are shown in comparison with the theoretical dispersion relation of the propagation modes. Quantitative evaluations of this method are discussed based on the Reciprocity theorem and Fourier transformation.

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We have studied an anneal-less domain wall displacement detection (DWDD) disk of a land/groove recording on a deep groove substrate using a numerical aperture (NA) 0.65 objective lens and a blue laser diode (LD). The substrates were prepared using a stamper formed by reactive ion etching (RIE) and O2 plasma treatment to realize both steep side-wall angles and smooth surfaces on the substrates. In designing the groove shape, we have clarified three key factors: the groove edge shape, the groove depth and the land width. These factors affected the magnetic film discontinuity at the groove edge and the recording power margin on the land. We have achieved a recording density of 27 Gbit/in2 by optimizing the groove shape.