where A stands for anti-symmetric modes and S
stands for symmetric modes. Subscripts 0, 1, 2, etc. indicate the order
of the Lamb mode [20]. At 3.5 MHz it is possible to generate 12
Lamb modes (see Fig. 2). The received signal is recorded digitally.
The sampling rate for the received signal is 100 MHz which is more
than 10 times the signal frequency. High Pass and Low Pass filters
were used to minimize noise.