Model, Design, and Testing of an Electret-Based Portable Transmitter for Low-Frequency Applications

Submarine communication and geologic examination in deep earth are challenging because high-frequency electromagnetic (EM) waves with short wavelength can be blocked by soil and seawater, as a result, the low-frequency (LF) waves are preferred in these applications. However, the conventional LF transmitter facility requires size on the scale of the wavelength (here, >1 km), making portable transmitters extremely challenging. To greatly decrease the size of the conventional LF communication system, this article introduces a novel LF transmitter based on electret, which applies mechanical motion to accelerate the charges on the polymer electret and realize the high-efficiency generation of EM fields. Moreover, a magnetic field analytical model is established to analyze the influence of structure parameters, shapes, rotation frequency, and stacking mode on the EM signals' generation and propagation, in terms of not only distance but also orientation. Finally, an electret-based mechanically actuated transmitter prototype is built to verify the correctness and feasibility of the design.