Near-Field Technologies for Multifunction Wireless Connectivity: Recent principles and applications

Antenna and array technologies have been in constant evolution for more than 100 years for various purposes in wireless connectivity among distant devices and/or systems by radiating electromagnetic waves, usually operating in a far-field manner. With the proliferation of the Internet of Things (IoT) that started more than two decades ago, wireless devices are often required to transfer, share, read, and store their information over a short distance in a secure and efficient way, which may not fall into the category of far-field applications. However, the conventional theories and techniques for far-field applications cannot generally be applied directly to the development of short-range communication because the nature of the electromagnetic fields in the near-field (NF) region is quite different from those in the far-field region. Therefore, the NF theories were developed to accurately describe the phenomenon of waves in antenna NF regions and then yield novel and practical applications. This article encompasses the recently developed principles and applications of NF techniques for multifunction wireless connectivity, including NF coupling, imaging, and signal processing.