Collaborative Research: Distributed Electro-Mechanical Transmitters for Adaptive and Power-Efficient Wireless Communications in RF-Denied Environments

在某些情况下，射频（RF）电磁波的传播变得不可行的，从而导致“RF拒绝”环境。例子包括地下和深水设施（矿井、避难所、储存区、隧道、潜艇、海底电缆等）。最近的事件突出了无线通信在这种环境中的重要性。一个突出的例子是2018年7月从泰国Tham Luang Nang Non洞穴营救出一支被困在地下超过两周的足球队。这种拒绝射频的环境基本上是由电磁波在导电介质（如地球或海水）内的短“趋肤深度”造成的，这导致了高衰减。幸运的是，皮肤深度随着频率的降低而增加，因此千赫范围内的极低频（ELF）无线电波可以在名义上拒绝射频的环境中穿透长距离。例如，海水的表层深度为7.1米，频率为1khz，如果能够有效地将极低频无线电波耦合到介质中，那么在合理的发射功率水平下，海底通信将达到约30米的深度。然而，传统的天线非常大，不可能在这个频率范围内部署，而电短天线的功率效率非常低。这个项目试图通过采用一种基于永磁体机械运动的极低频天线的全新方法来解决这个基本问题。拟议的研究将对射频拒绝环境中双向无线通信的可用性产生广泛影响。具体来说，它将使低数据速率无线链路能够使用便携、健壮、低功耗和低成本的设备建立起来。这种连接有望在水下或地下环境的传感和网络、近地表地球物理、大气科学、搜索和救援行动、采矿和石油和天然气勘探等领域得到广泛应用。便携式低功率极低频收发器的可用性将通过与地面建立双向低数据速率无线链路，立即实现在rf拒绝环境下的通信。虽然可以使用小型化和高灵敏度的极低频接收器，但极低频发射器（通常是偶极子或环形天线）是实现这种链路的关键障碍，因为它们物理上很大且耗电。因此，该项目侧重于小型化和节能的极低频发射机，使其能够在导电介质中的中短程（最多约1公里）无线链路上进行双向通信。特别是，拟议的研究将探索一种全新的全机械方法来设计ELF发射机，该方法有可能有效利用这一区域的EM频谱。这个项目的主要智力贡献集中在这个整体方法的不同方面。它们包括：i)提出了基于有线或无线网络同步的分布式全机械发射机的概念，并展示了它如何克服现有ELF发射机架构的关键限制；（ii）为使用具有显著机械惯性的系统设计节能无线通信创造理论基础，从而将衰落信道上信息传输的数学与机械装置的物理联系起来；iii)为网络高速机器的精确控制奠定了第一个理论基础，这有可能通过无缝建模复杂的3-D（维度）机器参数变化及其与高速机器振动和发射机网络内能量/功率波动的紧密耦合，极大地推进当前的艺术状态。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Propagation of radio frequency (RF) electromagnetic waves becomes infeasible in certain situations, thus resulting in "RF-denied" environments. Examples include underground and deep-water facilities (mines, shelters, storage areas, tunnels, submarines, undersea cables, etc.). Recent events have highlighted the importance of wireless communications with such environments. A prominent example is the July 2018 rescue of a soccer team from the Tham Luang Nang Non cave in Thailand after they had been trapped underground for over two weeks. Such RF-denied environments are fundamentally produced by the short "skin depth" of electromagnetic waves within conductive media such as earth or seawater, which results in high attenuation. Fortunately, the skin depth increases as the frequency decreases, so extremely low frequency (ELF) radio waves in the kHz range can penetrate long distances in nominally RF-denied environments. For example, the skin depth in sea water is 7.1 m at 1 kHz, which would allow undersea communications to depths of about 30 m with reasonable transmit power levels if one could effectively couple ELF radio waves into the medium. However, conventional antennas are extremely large and impossible to deploy in this frequency range, while electrically-short antennas have very poor power efficiency. This project seeks to solve this fundamental problem by adopting a radically new approach to ELF antennas that is based on the mechanical motion of permanent magnets. The proposed research will have a broad impact on the availability of bidirectional wireless communications in RF-denied environments. Specifically, it will enable low-data-rate wireless links to be established using portable, robust, low-power, and low-cost devices. Such links are expected to have a multitude of applications in fields such as sensing and networking in underwater or underground environments, near-surface geophysics, atmospheric science, search and rescue operations, mining, and oil and gas exploration.The availability of portable low-power ELF transceivers would immediately enable communications within RF-denied environments by enabling bidirectional low-data-rate wireless links with the surface. While miniaturized and highly-sensitive ELF receivers are available, ELF transmitters (typically dipole or loop antennas) are the key obstacles for realizing such links since they are physically large and power-hungry. Thus, this project focuses on miniaturized and power-efficient ELF transmitters that enable bidirectional communications over short- and medium-range (up to about 1 km) wireless links in conductive media. In particular, the proposed research will explore a fundamentally new all-mechanical approach to ELF transmitter design that has the potential to enable efficient use of this region of the EM spectrum. The major intellectual contributions of this project focus on different aspects of this overall approach. They include: i) Proposing the concept of distributed all-mechanical transmitters based on synchronization over either wired or wireless networks and showing how it overcomes the key limitations of existing ELF transmitter architectures; ii) Creating a theoretical basis for the design of power-efficient wireless communications using systems that have significant mechanical inertia, thus linking the mathematics of information transfer over fading channels to the physics of the mechanical devices; and iii) Laying the first theoretical groundwork for the precise control of networked high-speed machines, which has the potential to dramatically advance the current state of the art by seamlessly modeling complex 3-D (dimensional) machine parameter variations and their tight coupling with high-speed machine vibrations and energy/power fluctuations within the transmitter network.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.