Low resistance quartz resonators for automotive applications without spurious modes

The performance of one-port resonators is often affected by spurious transverse modes which, in particular around the fundamental antiresonance, are troublesome. We demonstrate that by employing the fundamental antisymmetric instead of the fundamental symmetric waveguide mode to carry the main acoustic resonance, a suppression of these spurious resonances is obtained. Since the approach requires no additional space, it is particularly useful in applications where the space on the device is very scarce. As an example, a one-port resonator on quartz supporting 8 transverse modes is investigated, The resonator exhibits undesired resonances just above the fundamental antiresonance. The recently presented 2D P-matrix simulator (Pocksteiner, N. et al., IEEE Ultrason. Symp. p.137-41, 2000) accurately describes this impedance characteristic. Employing the simulator, a suitable antisymmetric resonator configuration was derived which efficiently suppresses the spurious resonances. Insight into the role the transverse modes play in forming the resonator´s impedance characteristic is obtained by a decomposition of the resonator function into the contributions of the single transverse modes.