Fig. 12.

The effect of the elastic properties of the spikes and shell on the mode of vibration. Spikes vibrate around the apparently rigid base at the low frequencies of 111–140 MHz. At the intermediate frequencies of 387–513 MHZ, the spikes move in the radial direction, together with the vibrating shell. Finally, there is a complex interaction between the vibration of the flexible spike and shell at the high end of the frequency spectrum 1110–1225 MHz. Some vibration modes are on different planes.