It all began with a moment of concern. Dr. Jiayang Li, an electrical engineer from the University of Bristol, witnessed his 89-year-old mentor, Peter Langois, nearly lose his balance. Despite his age, Peter remains intellectually sharp, actively contributing to research.
"I noticed he was wobbling on his feet, which made me realize how risky this situation was," Li reflects. "A fall could have dire consequences, especially for those living alone." This incident sparked an innovative idea: if semiconductor technology could track minute fluctuations in lung function, could it also monitor foot pressure? This thought process led to the creation of a groundbreaking prototype shoe that brings advanced gait analysis from clinical settings to everyday life.
Gravity's Challenge for the Elderly
For older adults, gravity can be a formidable foe. As individuals age, frailty increases significantly, making falls a leading cause of severe injuries. In the UK, over 220,000 emergency hospital visits annually result from falls among those over 65, costing the healthcare system more than £2.3 billion each year.
While gait analysis can predict fall risks, it typically requires expensive lab equipment and controlled environments. To truly safeguard individuals like Peter, technology must be integrated into their daily lives--specifically, in their footwear.
Dr. Li's innovative solution is a "lab-on-a-sole." This prototype features an insole equipped with 253 piezo-resistive sensors that alter their electrical resistance when pressure is applied. As the wearer walks, these sensors generate a detailed pressure map of the foot, capturing data 82 times per second.
This high frequency of data collection enables the system to differentiate between various walking phases, such as heel strikes and toe pushes.
Engineering Breakthroughs
While the concept of a smart shoe is not entirely new, creating one without a bulky battery has posed significant engineering challenges. The key issue is reading numerous sensors simultaneously without excessive power drain. Traditional methods often struggle with electrical noise and consume too much energy.
To tackle this, Li's team, in collaboration with University College London, redesigned the microchip architecture. Their custom integrated circuit utilizes a "unified excitation/readout" approach, allowing the chip to read data directly through the power line that activates the sensors. This innovation combines the signal transmission and reception into a single, efficient circuit.
The chip employs a "time-to-digital" conversion method, measuring the time taken for a signal to cross a threshold. This technique enhances resistance to noise and interference, crucial for a device constantly in motion.
Moreover, the chip features a "pre-saturation adaptive bias" system, dynamically adjusting current flow based on pressure applied. This means if the foot is barely touching the ground, the chip conserves energy, and when full weight is applied, it ramps up power for accurate readings. Overall, the chip consumes just 158 microwatts, allowing it to operate for about three months on a single charge.
Bringing Lab Technology to Everyday Life
With such low power requirements--averaging 0.62 microwatts per sensor--the system could potentially run off a smartwatch or smartphone battery.
"The aim was to make this detailed analysis accessible in daily life, moving healthcare from reactively treating injuries to proactively preventing them," Li emphasizes. The shoe processes data to create images of foot pressure points, assessing balance and fall risk, potentially alerting users before a fall occurs.
For Peter Langois, the inspiration for this technology, the project holds personal significance. "When I shared the concept with him, he was genuinely moved and hopeful that it could help many others," Li shares.
The team is now focused on scaling production. "This design could be mass-produced, revolutionizing the lives of older adults," Li states. They plan to conduct formal clinical evaluations to refine the technology and collaborate with partners for a scalable product.
The innovative shoe was recently showcased at the International Solid-State Circuits Conference (ISSCC) in San Francisco, where Li's research stood out as the only UK-led project.