Office of Technology Transfer – University of Michigan

Unidirectional Near-Field Focusing

Technology #5980

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Anthony Grbic
Managed By
Joohee Kim
Licensing Specialist, Physical Sciences & Engineering 734.764.8202
Patent Protection
US Patent Pending 2016-0087458
US Patent Pending 2017-0038463
Near-Field Plates: Subdiffraction Focusing with Patterned Surfaces
Science 25 April 2008: Vol. 320 no. 5875 pp. 511-513 DOI: 10.1126/science.1154753, 2008

Researchers at the University of Michigan have developed a near-field plate that can form a unidirectional subwavelength near-field pattern with significantly reduced radiation into undesired directions. Near-field plates are used to generate extreme electromagnetic confinement. Typically, near-field plates are designed to form a prescribed subwavelength electromagnetic focal pattern when excited by a specific source. However, extant near-field plate designs exhibit pronounced radiation in directions other than the desired focal pattern, limiting their utility in practical applications.

Design Details

The near-field plate designed at the University of Michigan can form a unidirectional subwavelength near-field pattern, with significantly reduced radiation into undesired directions, e.g., back radiation. Unidirectionality is achieved via adjustment of the field amplitude at the focal plane of the near-field plate. The near-field plate can be used to significantly increase sensitivity and resolution of probing and imaging systems. Compared to competing technologies such as metamaterial superlenses, the design is superior due to its unidirectionality, support for the stipulation of the subwavelength near-field pattern, simplified fabrication, and improved performance. The unidirectional near-field plate also finds applications in wireless power transfer systems by controlling the radiation pattern. The unidirectional near-field plate significantly reduces the radiation into unwanted directions due to the transmitting loop. Compared to the heavy, expensive, lossy, and non-eco-friendly ferrite slabs that are commonly used in power transfer systems, the near-field plate-based design entails simple, low-cost, and eco-friendly fabrication. Overall, the design can form unidirectional near-field patterns with minimal effect on the efficiency of the wireless power transfer system.


  • Wireless power transfer devices
  • High-resolution, high-sensitivity imaging, probing, or sensing systems
  • Lithography systems
  • High density data storage devices
  • Biomedical targeting devices


  • Unidirectionality
  • Improved performance and efficiency
  • High resolution and sensitivity
  • Low-cost, simple, and eco-friendly fabrication