Resonant sensor with two independent degenerate modes of vibration

resonant sensor for determining variations in structural property, characterized by a structure (2) mounted to be able to resonate, wherein the structure (2) a cyclically symmetrical configuration with two vibration modes degenerate independent common natural frequency, and means (24 , 26, 28, 30, 32, 34, 36, 38) for exciting the structure (2) to resonate according to said two degenerate modes, modifying regions (8, 12, 16, 20) of the structure (2) so that when variations occur in the structural properties of the modified regions (8, 12, 16, 20), the natural frequencies (f1, f2) of the two modes of vibration become different, the difference in frequency (Af) proportional the variation of structural properties.