This paper presents a dual-factor authentication protocol and its low-power implementation for security of implantable medical devices (IMDs). The protocol incorporates traditional cryptographic first-factor authentication using Datagram Transport Layer Security -Pre-Shared Key (DTLS-PSK) followed by the user's touch-based voluntary second-factor authentication for enhanced security. With a low-power compact always-on wake-up timer and touch-based wake-up circuitry, our test chip consumes only 735 pW idle state power at 20.15 Hz and 2.5 V. The hardware accelerated dual-factor authentication unit consumes 8 µW at 660 kHz and 0.87 V. Our test chip was coupled with commercial Bluetooth Low Energy (BLE) transceiver, DC-DC converter, touch sensor and coin cell battery to demonstrate standalone implantable operation and also tested using in-vitro measurement setup.

We present the design, implementation, and evaluation of μmedIC, a fully-integrated wireless and batteryless micro-implanted sensor. The sensor powers up by harvesting energy from RF signals and communicates at near-zero power via backscatter. In contrast to prior designs which cannot operate across various in-body environments, our sensor can self-reconfigure to adapt to different tissues and channel conditions. This adaptation is made possible by two key innovations: a reprogrammable antenna that can tune its energy harvesting resonance to surrounding tissues, and a backscatter rate adaptation protocol that closes the feedback loop by tracking circuitlevel sensor hints. We built our design on millimeter-sized integrated chips and flexible antenna substrates, and tested it in environments that span both in-vitro (fluids) and ex-vivo (tissues) conditions. Our evaluation demonstrates μmedIC's ability to tune its energy harvesting resonance by more than 200 MHz (i.e., adapt to different tissues) and to scale its bitrate by an order of magnitude up to 6Mbps, allowing it to support higher data rate applications (such as streaming low-res images) without sacrificing availability. This rate adaptation also allows μmedIC to scale its energy consumption by an order of magnitude down to 350 nanoWatts. These capabilities pave way for a new generation of networked micro-implants that can adapt to complex and time-varying in-body environments. CCS CONCEPTS • Hardware → Full-custom circuits; • Computer systems organization → Sensor networks; • Applied computing → Life and medical sciences;

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High-precision analogue circuits suffer from the finite gain and nonlinearity of operational amplifiers (opamps). Correlated level shifting is one efficient technique that provides gain and swing enhancement for switched-capacitor circuits. Charge-compensated correlated level shifting is proposed, a modification for the correlated level shifting technique, that improves the efficiency of gain enhancement for single-stage opamps.

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