Jayant Charthad

A mm-Sized Implantable Medical Device (IMD) With Ultrasonic Power Transfer and a Hybrid Bi-Directional Data Link

A first proof-of-concept mm-sized implantable device using ultrasonic power transfer and a hybrid bi-directional data communication link is presented. Ultrasonic power transfer enables miniaturization of the implant and operation deep inside the body, while still achieving safe and high power levels (100 μW to a few mWs) required for most implant applications. The current implant prototype measures 4 mm ×7.8 mm and is comprised of a piezoelectric receiver, an IC designed in 65 nm CMOS process and an off-chip antenna. The IC can support a maximum DC load of 100 μW for an incident acoustic intensity that is ~ 5% of the FDA diagnostic limit. This demonstrates the feasibility of providing further higher available DC power, potentially opening up new implant applications. The proposed hybrid bi-directional data link consists of ultrasonic downlink and RF uplink. Falling edge of the ultrasound input is detected as downlink data. The implant transmits an ultra-wideband (UWB) pulse sequence as uplink data, demonstrating capability of implementing an energy-efficient M-ary PPM transmitter in the future.

A mm-sized implantable device with ultrasonic energy transfer and RF data uplink for high-power applications

A first proof-of-concept mm-sized implant based on ultrasonic power transfer and RF uplink data transmission is presented. The prototype consists of a 1 mm × 1 mm piezoelectric receiver, a 1 mm × 2 mm chip designed in 65 nm CMOS and a 2.5 mm × 2.5 mm off-chip antenna, and operates through 3 cm of chicken meat which emulates human tissue. The implant supports a DC load power of 100 μW allowing for high-power applications. It also transmits consecutive UWB pulse sequences activated by the ultrasonic downlink data path, demonstrating sufficient power for an Mary PPM transmitter in uplink.

System-Level Analysis of Far-Field Radio Frequency Power Delivery for mm-Sized Sensor Nodes

Millimeter-sized and low-cost sensor nodes can enable future applications of the Internet of Things (IoT), for which the number of sensors is projected to grow to a trillion within the next decades. RF far-field power transfer is a potential technique for wirelessly powering these sensors since it offers flexible configuration of sensor networks, beamforming capability and a large power transfer range compared to near-field approaches. However, system design for RF power transfer needs to be completely rethought to enable this new paradigm of a trillion IoT sensors. This paper, therefore, presents a comprehensive, system-level analysis strategy and a modular framework for investigating the fundamental efficiency components in an RF power transfer chain. Through this detailed analysis, it is demonstrated that the optimal frequency is primarily determined by the antenna size and the quality factors (Q) of components in the matching network. Millimeter-wave frequencies are shown to be optimal for powering mm-sized sensors for practical matching component Q values. An intuitive explanation of our results is also provided, along with insights for the design and practical implementation of RF power transfer systems for the IoT space.

Design of high-efficiency miniaturized ultrasonic receivers for powering medical implants with reconfigurable power levels

Miniaturized ultrasonic receivers are designed for high efficiency ultrasonic powering of implants. Several piezoelectric materials are investigated for their practicality in designing millimeter-sized ultrasonic receivers. Piezoelectric receivers were built from these materials and measurements were performed in order to characterize their impedance and efficiency. We show operation of the piezoelectric receivers in an inductive frequency band, near resonance, allowing for impedance matching to typical implant loads. Finally, adaptive matching and frequency tuning techniques are demonstrated showing high power matching efficiencies across variable implants loads.

Design of Tunable Ultrasonic Receivers for Efficient Powering of Implantable Medical Devices With Reconfigurable Power Loads

Miniaturized ultrasonic receivers are designed for efficient powering of implantable medical devices with reconfigurable power loads. Design parameters that affect the efficiency of these receivers under highly variable load conditions, including piezoelectric material, geometry, and operation frequency, are investigated. Measurements were performed to characterize electrical impedance and acoustic-to-electrical efficiency of ultrasonic receivers for off-resonance operation. Finally, we propose, analyze, and demonstrate adaptive matching and frequency tuning techniques using two different reconfigurable matching networks for typical implant loads from 10 μW to 1 mW. Both simulations and measurements show a significant increase in total implant efficiency (up to 50 percentage points) over this load power range when operating off-resonance with the proposed matching networks.

27.7 A 30.5mm 3 fully packaged implantable device with duplex ultrasonic data and power links achieving 95kb/s with −4 BER at 8.5cm depth

The next generation of implantable medical devices focuses on minimally invasive miniaturized solutions that operate reliably at large depths, provide duplex communication for closed-loop therapies, and enable multi-access for a network of implants to gather information or provide systemic interventions. Using ultrasound (US), power and data can be efficiently transferred through the body as its wavelength at MHz is comparable to a mm-sized receiver, resulting in improved focusing, coupling, and acoustic-to-electrical conversion efficiency. Furthermore, thanks to the low propagation loss (∼1dB/cm/MHz) and 7.2mW/mm2 safety limit, several mW of power is obtainable at the receiver, enabling high-power, complicated functionalities.

An ultrasonically powered implantable device for targeted drug delivery

A wirelessly powered implantable device is proposed for fully programmable and localized drug delivery. The implant is powered using an external ultrasonic transmitter and operates at <; 5% of the FDA diagnostic ultrasound intensity limit. Drug release is achieved through electrical stimulation of drug-loaded polypyrrole nanoparticles. A design methodology for the implant electronics is presented and experimentally demonstrated to be accurate in predicting the concentration of the released drug. To the best of our knowledge, this is the first ultrasonically powered implantable device platform for targeted drug delivery using electroresponsive polymers. The active area of the implant electronics is just 3 mm × 5 mm.

A miniaturized ultrasonically powered programmable optogenetic implant stimulator system

A fully programmable, wirelessly powered optogenetic stimulator system is demonstrated. Implantable devices, with integrated optical stimulators, are powered and controlled using a programmable external ultrasonic transmitter. A methodical analysis is performed to investigate obtainable optical available powers using a highly efficient ultrasonic link. Optical intensities and stimulation patterns practical for optogenetic applications are easily achieved with safe levels of ultrasound. To our knowledge, this is the first ultrasonically powered optogenetic stimulator. The active area of the implantable device measures just 15 mm2.

A high-precision 36 mm 3 programmable implantable pressure sensor with fully ultrasonic power-up and data link

This paper presents the first fully ultrasonic (US) high-precision implantable sensor with active US links for power-up, data downlink, and data uplink. The packaged implant measures just 1.7×2.6×8.1mm3 and includes a custom IC, piezoelectric devices (piezos) designed for data/power links, and a pressure transducer (PT). Characterization is performed at a large depth of 12 cm, in a phantom material, giving a >10× improvement over state-of-the-art in both the depth/volume and energy per sample figures of merit. The IC has a front-end and 10-bit ADC which achieves a pressure LSB of 0.78 mmHg and full-scale range of 800 mmHg, exceeding specifications required for various pressure monitoring applications. The sample rate is externally controlled, up to 1 kHz, through the downlink, allowing power optimization for various applications.

The power of sound: miniaturized medical implants with ultrasonic links

Miniaturized wirelessly powered implants capable of operating and communicating deep in the body are necessary for the next-generation of diagnostics and therapeutics. A major challenge in developing these minimally invasive implants is the tradeoff between device size, functionality, and operating depth. Here, we review two different wireless powering methods, inductive and ultrasonic power transfer, examine how to analyze their power transfer efficiency, and evaluate their potential for powering implantable medical devices. In particular, we show how ultrasonic wireless power transfer can address these challenges due to its safety, low attenuation, and millimeter wavelengths in the body. Finally, we demonstrate two ultrasonically powered implants capable of active power harvesting and bidirectional communication for closed-loop operation while functioning through multiple centimeters of tissue.