Visualization of acoustic mode conversion and power flow in suspended thin-film phononic device*

Acoustic wave plays a critical role in electromechanical devices, which are widely utilized in wireless communication and quantum information systems. Since conventional terminal-to-terminal measurement misses important local features of acoustic fields, a new characterization method with high spatial resolution of the acoustic profile is highly sought after. Using a transmission-mode microwave impedance microscope (T-MIM), we directly visualize the acoustic mode conversion and power flow in suspended thin-film phononic devices. Moreover, with fast Fourier transform (FFT) filtering, the forward and backward propagation can be separately analyzed and the propagation loss for both waves calculated. Our result shows that T-MIM can be used as advanced characterization method for acoustic platforms including filters, resonators, phononic crystals, and acoustic metamaterials.