(1) Rapid Reconstitution of Submarine Shore Very Low Frequency (VLF) Communications System

Very low frequency (VLF) signals are employed for submarine communications due to their long electromagnetic (EM) wavelengths and low attenuation in seawater. However, conventional VLF antennas have typical dimensions of miles long; even an electrically small conventional VLF antenna would have huge dimensions which makes it challenging for rapid reconstitution and coordinated response in the event of maintenance or emergent Casualty Reporting situations. For example, current fixed submarine broadcast system (FSBS) VLF Transmitter Cutler operating at 24 kHz with 1.8 megawatts input power spreads across 8 km^2 in area and consists of 26 arrays of metal tower with about 300 m in height. Besides, VLF broadcast communications are limited to a low data rate of about ~100 bits/sec and shore-to-submarine only. Therefore, there is a necessity for compact, mobile, easily deployable, high-data-rate VLF transmitter systems for communications with the Navy submarines for rapid reconstitution of the submarine shore VLF communication systems. The goal of this Phase I project is therefore to design and develop rapid-reconstitution, transportable, and lightweight VLF magnetoelectric (ME) mechanical antennas and transmitters to meet the Navy’s needs. Specifically, the proposed VLF transmitter based on ME mechanical antennas will meet and exceed the performance specifications of the FSBS VLF transmitter stations. The proposed research builds upon the demonstrated experience in compact VLF ME mechanical antennas fabricated using magnetostrictive Metglas and piezoelectric PZT (lead zirconate titanate). An array of 12 VLF ME antennas was demonstrated in a compact size of 60x10x3 cm^3 and input power consumption of ~10 W to result in a radiation magnetic (B) field intensity of 2 fT at 10 km distance. The ME antenna technology, first invented and patented by the principal investigators (PIs) in 2016, has now been matured for compact and mobile VLF transmitter applications.  In Phase I, we will: (1) design and fabricate an ME transmitter module, i.e. minimum viable product (MVP) for operation in 3-30 kHz frequency range with a maximum dimension of 60cm, (2) demonstrate its performance through measurements of radiation B fields and power consumption, (3) achieve radiation B field >1 fT at a distance of 100 km, and (4) initiate technology transition efforts for both military FSBS and private commercialization. Our partner, Lockheed Martin, will review Phase I progress and provide system-level specifications for the integration of the ME antennas communication system with the Navy submarine com systems.  Also, Winchester Technologies will work with the SBIR program management office (PMO) and focus on Navy product acquisition program opportunities for commercialization. In Phase II, the MVP demonstrated in Phase I will be further developed and scaled up into an operational prototype placed in standard shipping containers for communication over a distance >10,000 km.