Fig. 1: Experimental results.
From: Tailored elastic surface to body wave Umklapp conversion
Snapshots in time of temporal–spatially filtered scans along top and bottom surfaces observing S conversion (a–c) and P conversion (d–f), filtered between 1.1–1.2 and 1.45–1.55 MHz, respectively, normalised to the maximum of displacement of the top surface (uz). Solid red lines show where graded array begins, with increasing rod height in the direction of wave propagation on the top surface. The reversed conversion is clear; the forward propagating surface wave on the top surface is reverse converted into the bulk and is seen to excite reversed propagating surface waves on the bottom surface. The measured angles of reversed conversion, −131.8∘ and −106.9∘ for S and P, respectively, match the predicted angles from Fig. 3, with the separate polarisations evident from the difference in excitation wavelength on the bottom surface, marked λS, λP. The experimental setup is shown g, as is a schematic of array geometry h detailing the rod diameter, t, periodicity a and grading through the changes in height of the nth rod, hn, as hn = h0 + nΔh. Fabrication details are given in the “Methods” section, with the array parameters given in Supplementary Table 1.
