The Microbead: A Highly Miniaturized Wirelessly Powered Implantable Neural Stimulating System

Adam Khalifa, Yasha Karimi, Qihong Wang, Sahithi Garikapati, Webert Montlouis, Milutin Stanacevic, Nitish V Thakor, Ralph Etienne-Cummings

Research output: Contribution to journalArticlepeer-review


An implant that can electrically stimulate neurons across different depths and regions of the brain currently does not exist as it poses a number of obstacles that need to be solved. In order to address the challenges, this paper presents the concept of “microbead,” a fully integrated wirelessly powered neural device that allows for spatially selective activation of neural tissue. The prototype chip is fabricated in 130-nm CMOS technology and currently measures 200 μm × 200 μm, which represents the smallest remotely powered stimulator to date. The system is validated experimentally in a rat by stimulating the sciatic nerve with 195-μs current pulses. To power the ultrasmall on-silicon coil, 36-dBm source power is provided to a highly optimized transmitter (Tx) coil at a coupling distance of 5 mm. In order to satisfy the strict power limit for safe use in human subjects, a pulsed powering scheme is implemented that enables a significant decrease in the average power emitted from the Tx.

Original languageEnglish (US)
JournalIEEE Transactions on Biomedical Circuits and Systems
StateAccepted/In press - Mar 14 2018


  • Miniaturization
  • neurostimulator
  • on-chip coil
  • specific absorption rate
  • wireless power transfer

ASJC Scopus subject areas

  • Biomedical Engineering
  • Electrical and Electronic Engineering


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