The Microbead: A 0.009 mm3 Implantable Wireless Neural Stimulator

Adam Khalifa, Yuxin Liu, Yasha Karimi, Qihong Wang, Adebayo Eisape, Milutin Stanaćević, Nitish Thakor, Zhenan Bao, Ralph Etienne-Cummings

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


Wirelessly powered implants are increasingly being developed to interface with neurons in the brain. They often rely on microelectrode arrays, which are limited by their ability to cover large cortical surface areas and long-term stability because of their physical size and rigid configuration. Yet some clinical and research applications prioritize a distributed neural interface over one that offers high channel count. One solution to make large scale, fully specifiable, electrical stimulation/recording possible, is to disconnect the electrodes from the base, so that they can be arbitrarily placed freely in the nervous system. In this work, a wirelessly powered stimulating implant is miniaturized using a novel electrode integration technique, and its implanted depth maximized using new optimization design methods for the transmitter and receiver coils. The stimulating device is implemented in a 130 nm CMOS technology with the following characteristics: 300 μm × 300 μm × 80 μm size; optimized two-coil inductive link; and integrated circuit, electrodes and coil. The wireless and stimulation capability of the implant is demonstrated in a conductive medium, as well as in-vivo. To the best of our knowledge, the fabricated free-floating miniaturized implant has the best depth-to-volume ratio making it an excellent tool for minimally-invasive distributed neural interface, and thus could eventually complement or replace the rigid arrays that are currently the state-of-the-art in brain set-ups.

Original languageEnglish (US)
Article number8822735
Pages (from-to)971-985
Number of pages15
JournalIEEE Transactions on Biomedical Circuits and Systems
Issue number5
StatePublished - Oct 2019


  • Free-floating implant
  • microelectrode design
  • miniaturization
  • neural stimulation
  • wireless power transfer

ASJC Scopus subject areas

  • Biomedical Engineering
  • Electrical and Electronic Engineering


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