Harsh Bais, PhD



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  • Hasti Amiri, Kenneth L. Shepard, Colin Nuckolls, and Raúl Hernández Sánchez Single-Walled Carbon Nanotubes: Mimics of Biological Ion Channels NanoLetters DOI: DOI: 10.1021/acs.nanolett.6b04967

    Here we report on the ion conductance through individual, small diameter single-walled carbon nanotubes. We find that they are mimics of ion channels found in natural systems. We explore the factors governing the ion selectivity and permeation through single-walled carbon nanotubes by considering an electrostatic mechanism built around a simplified version of the Gouy−Chapman theory. We find that the single-walled carbon nanotubes preferentially transported cations and that the cation permeability is size-dependent. The ionic conductance increases as the absolute hydration enthalpy decreases for monovalent cations with similar solid-state radii, hydrated radii, and bulk mobility. Charge screening experiments using either the addition of cationic or anionic polymers, divalent metal cations, or changes in pH reveal the enormous impact of the negatively charged carboxylates at the entrance of the single-walled carbon nanotubes. These observations were modeled in the low-to-medium concentration range (0.1−2.0 M) by an electrostatic mechanism that mimics the behavior observed in many biological ion channel-forming proteins. Moreover, multi-ion conduction in the high concentration range (>2.0 M) further reinforces the similarity between single-walled carbon nanotubes and protein ion channels.

  • Eyal Aklimi, Student Member, IEEE, Daniel Piedra, Student Member, IEEE, Kevin Tien, Student Member, IEEE, Tomás Palacios, Member, IEEE, and Kenneth L. Shepard, Fellow, IEEE Hybrid CMOS/GaN 40-MHz Maximum 20-V Input DC–DC Multiphase Buck Converter. IEEE Journal of Solid-State Circuits.

    This paper presents a 40-MHz hybrid CMOS/GaN integrated multiphase dc–dc switched-inductor buck converter with a maximum 20-V input voltage. The half-bridge switches are realized using lateral AlGaN/GaN HEMTs, while the drivers and other circuitry are implemented in standard 180-nm CMOS. The interface between the CMOS and GaN dice is achieved through face-to-face bonding, reducing inductive parasitics for the connection to less than 15 pH. A capacitively coupled level shifter provides the gate drive for the high-side GaN switch using 5-V CMOS devices. The converter demonstrates 76% efficiency for 8:1 V conversion and over 60% efficiency for conversion ratios up to 16:1.

  • Jordan Thimot and Kenneth L. Shepard. Wirelessly powered implants. Nature Biomedical Engineering 1, 0051 (2017) | DOI: 10.1038/s41551-017-0051

    Phased-array antennas that conform to body surfaces efficiently transfer electromagnetic energy to miniaturized semiconductor devices implanted in pigs.