Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies

Thermoelectric Energy Harvesting
Harvesting heat from the human body is a promising approach to realizing self-powered wearables that run continuously without the need to charge or replace the batteries. Thermoelectric generators placed on the body can convert the small temperature difference between the body and the ambient to electricity.

New and improved flexible thermoelectric energy generator with insulating materials between legs and conductive material on top and bottom.
To power sophisticated wearables that can wirelessly transfer information from many sensors, the heat harvesting area on the body may have to be several inches square or larger, which is difficult to accomplish with rigid thermoelectric modules.

ASSIST has developed a flexible thermoelectric generator technology by encasing the semiconductor elements in a silicone elastomer. In these devices, low-resistivity, stretchable, self-healing liquid metal interconnects are used to connect the elements electrically in series. The flexible package incorporates novel elastomers that are developed to have lower (or higher) thermal conductivities to optimize the thermal management of the flexible package. ASSIST flexible thermoelectric generators provide the highest power levels reported to date.
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Inertial Energy Harvesting

ASSIST is developing devices that harvest energy from human motion. The approach has required a number of advances, including the fabrication of bimorph lead zirconatetitanate (PZT) thin films with a high figure-of-merit (FoM), development of a technique to produce thick PZT layers on nickel foils, and optimization of the mechanical system.

An energy harvesting system that captures power from body motions can help power a variety of body-worn sensors. We are currently pursuing wrist-worn harvesters to extend the battery life of ASSIST’s on-wrist health and environmental tracking systems.

The primary system we have developed harvests energy from swinging motions, such as that generated by the arm of a person walking. The system utilizes an arrangement of piezoelectric beams that are “plucked” by posts on an eccentric rotating mass. This strains the beams, generating a current.
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Radio Frequency (RF) Harvesting

ASSIST is developing systems that wirelessly power and charge wearable devices using radio frequency (RF) energy. One system harvests energy from ambient RF signals commonly available in peoples’ environments. Another system wirelessly transmits power from RF emitters integrated into everyday objects to receivers integrated into novel wearables.

These systems address the challenge of powering wearable devices when users are sedentary, which research indicates is the case ~ 8 hours per day for the average person. During these periods, there is little opportunity for harvesting power from body motions, but such sedentary periods provide a ready opportunity for passively charging or powering devices through wireless signals. Such solutions could be used to charge smart clothing through WiFi or power smart bandages through hospital beds.

Through this research, ASSIST is developing systems that provide high-efficiency far-field RF power harvesting and near-field RF power transfer. Areas of research include novel designs for high-performance on-textile antennas; power-efficient rectifying circuits; resonators for unobtrusive implementation into textiles and apparel; optimization of near-field structures for integration of smart health solutions (e.g. for smart wound healing monitoring bandages); and development of stand-alone resonant methods using voltage-controlled oscillators.
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Acoustic Power Transfer
Aortawatch – An ultrasound-enabled implantable device for monitoring patients after endovascular aneurysm repairs.

ASSIST is working with Centre for Research in Medical Devices (CÚRAM) and the Centre for Cancer Research and Cell Biology (CCRCB) at Queens University Belfast to develop novel externally-powered implants for continuous cardiac health monitoring. A particular device involves abdominal aortic aneurysm (AAA), which is a condition in which the aortic wall becomes enlarged, which can ultimately lead to rupturing of the artery, significant internal bleeding and death. Most aneurysms are currently treated by endovascular aneurysm repair (EVAR), by lining the aorta using a stent-graft. Monitoring the sealing of these grafts is essential to ensure no leaks are present.

We develop a system that is powered externally using ultrasound. The ultrasonic transducer that receives power is also used to measure the size of the aneurysm and to communicate the measurements to the outside. Such an implantable monitoring device that can be activated on demand or periodically, eliminates the need for the patient to come back to the hospital for imaging-based assessments and hence minimizes the radiation exposure to the patient.

Ultrasound is an attractive modality for transferring power to biomedical implants. Ultrasound is already widely accepted in medical diagnostic applications with intensities as high as 720 mW/cm2 as regulated by the FDA. A receiving ultrasonic transducer embedded in the implanted device can convert acoustic power to electrical power for use by the sensors and associated data processing circuitry. We implement the described device by using a capacitive micromachined ultrasonic transducer (CMUT) that is integrated with supporting circuits in a small implantable form factor.
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Energy Storage

ASSIST is developing high energy density electrochemical capacitors to support its energy harvesting and low-power sensing technologies.

Batteries are not suitable for the rapid charging and discharging required for the self-powered devices ASSIST is developing. Supercapacitors can be charged more quickly than batteries, providing high flexibility in operation. Our supercapacitors provide flexible energy storage to ensure continued operation during short-term spikes in power consumption or drops in energy harvesting.

Through this research, ASSIST is creating capacitors with high energy density, long cyclability, and low self-discharge rates. We are developing lithium ion capacitors, all-solid-state capacitors, and flexible pouch cells for testbed integration.
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Low Power Sensors:

Environmental Sensors

Physiological Sensors

Zero-Power Fluid Extraction for Biochemical Sensors

Biochemical Sensors

Implanted Sensors
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Low Power Electronics:

Systems-on-Chip

Radios

Antennas

Emerging Nanodevices and Architecture
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Smart Textiles:

Electronics Integration

Garment Design
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Emerging Materials:

Liquid Metals

Carbon Nanotubes
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Engineered Systems:

Wearable System for Health and Environmental Tracking

Wearable Self-Powered Adaptive Platform
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Data Management:

Data-Driven Signal Aggregation

AI-Driven Data Processing

Data Repository to Enable Algorithm Development