Metal-Loaded Acoustically Actuated Piezoelectric Antenna and Its Radiation Efficiency Limit

A metal-loading (ML) method is proposed in this article to increase effective length, near-field magnitude, and radiation efficiency for an acoustically actuated piezoelectric antenna (PEA). A field-based circuit model (FBCM) method is utilized to characterize the metal-loaded PEA (MLPEA) by introducing antenna fields into piezoelectric equations and impedance analysis at boundary. Furthermore, current distribution within PE cylinder and on loaded metal rod is calculated by the finite element modeling (FEM) method and formulated with piecewise functions. Also, an antenna effective length is evaluated with different loaded metal lengths, and the effects of the loaded metal are analyzed on antenna near-fields and radiation efficiency. All the methods are validated by measurement of a demonstrated MLPEA on a precise testing vehicle with a frequency error of 0.05% and a near-field magnitude error of 0.97 dB. Finally, a maximum increase of 4.6 dB for near-field magnitude and that of ten times for radiation efficiency are obtained for PEA with a loaded metal length of 0.8 m. Different loss mechanisms in MLPEA are also analyzed, and the radiation efficiency limit for PEA, as estimated by FBCM, is much larger than that of metallic antenna when $ka$ is less than 0.1, leaving far more room for radiation efficiency elevation of PEA for state-of-the-art.