Structural Health Monitoring with Piezoelectric Wafer Active Sensors, 2nd Edition

Figure 13.47 2-D circular ring array design: (a) schematic of the circular ring array; (b) beamforming at various angles with $d=0.5\lambda$, $r/d=10$, $M=64$; (c) beamforming with $M=2$ when the circular ring array is reduced to a classic dipole.

The beamforming ...