Electrically Small Piezocomposite Strain Antennas

Recent literature has explored the use of single-material piezoelectrics for impedance matching in electrically small strain antennas. Efficiency calculations have assumed that radiation resistance is the same as that of a small wire dipole. In this work, piezoelectric composites, or piezocomposites, are used for impedance matching electrically small antennas to increase the degrees of freedom in the design process. A methodology is proposed for impedance matching a piezocomposite strain antenna at the desired center frequency over the desired bandwidth via optimal choice of materials, volume fraction, and shape without the need for an external matching network. Furthermore, the radiation resistance for piezoelectric strain antennas is derived from Wheeler’s power factor and is shown to be much smaller than that of the similarly sized electric dipole antenna that was assumed in much of the literature. The radiated power and efficiency are expressed directly in terms of piezocomposite material properties and the dimensions of the antenna. The results from this investigation provide a model of the impedance matching capabilities and efficiency limits for the piezoelectric strain antenna, demonstrating fundamental limitations for VLF applications.