The cut-off spatial frequency is got higher at the cost of the loss of mid-spatial frequency, and the information got by the system are different in all directions.
The cut-offfrequency of improved inverter output filter can be set higher to ensure the bandwidth of control system and improve the waveform quality of inverter output voltage.
The results show that there exist attenuation in all propagation modes along viscoelastic cylindrical tube, and higher-order propagation modes haven't cut-offfrequency.