Penn state researchers develop highly sensitive sensor for human-machine interaction

As we enter a world where human-machine interactions play an increasingly significant role, there is a growing demand for pressure sensors capable of analyzing and simulating human touch.

Engineers face a challenge in developing cost-effective sensors that possess high sensitivity, as these are essential for various applications such as detecting subtle pulses, operating robotic limbs, and creating ultrahigh-resolution scales. However, a team of researchers from Penn State and Hebei University of Technology in China has successfully developed a sensor that can fulfill all of these requirements.

The researchers aimed to create a sensor that exhibits exceptional sensitivity and reliable linearity across a wide range of applications. The sensor needed to have high pressure resolution and be capable of functioning effectively under significant pressure preloads.

“The sensor can detect a tiny pressure even when a large pressure is already being applied,” explained Huanyu “Larry” Cheng, who is the James L. Henderson Jr. Memorial Associate Professor of Engineering Science and Mechanics at Penn State and co-author of a paper published in Nature Communications documenting the research.

He further added, “An analogy I like to use is that it’s like detecting a fly on top of an elephant. It can measure the slightest change in pressure, just like our skin does with touch.”

Cheng was motivated to develop these sensors by a deeply personal experience: the birth of his second daughter.

Credit: Nature Communications (2023). DOI: 10.1038/s41467-023-38040-4

Cheng’s second daughter experienced a weight loss of 10% shortly after birth, prompting the doctor to advise Cheng to monitor her weight regularly. Cheng attempted to weigh the baby by first weighing himself on a standard home scale and then weighing himself while holding his daughter.

However, Cheng noticed that when he placed his daughter down, the weight change was not detected by the scale. This realization led him to understand that commercial scales were unable to detect changes in pressure.

After exploring various approaches, the researchers discovered that a pressure sensor comprising gradient micro-pyramidal structures and an ultrathin ionic layer could provide a promising solution. However, they encountered a challenge: as pressure increased, the high sensitivity of the microstructures decreased. Additionally, the random microstructures derived from natural objects resulted in unpredictable deformation and a limited linear range, affecting the accuracy of the readings.

To overcome these obstacles, the scientists developed microstructure patterns that increased the linear range without compromising sensitivity. They achieved this by designing flexible structures that could adapt to the varying pressure gradients encountered in real-world applications. The researchers employed a CO2 laser with a Gaussian beam to fabricate programmable structures like gradient pyramidal microstructures (GPM) for iontronic sensors, which are soft electronics capable of mimicking human skin’s perception functions.

This fabrication process offered cost and complexity reductions compared to the commonly used photolithography method for delicate microstructure patterns in sensors.

Cheng acknowledges the contribution of Ruoxi Yang, a graduate student in his lab and the study’s first author, who played a crucial role in finding this solution.

The optimized sensor exhibited rapid response and recovery times, as well as excellent repeatability. The team validated its performance by detecting subtle pulses, operating interactive robotic hands, and creating ultrahigh-resolution smart weight scales and chairs.

The researchers also observed that the proposed fabrication approaches and design toolkit could be extended to fine-tune the performance of pressure sensors for different applications, opening up possibilities for other iontronic sensors that employ ionic liquids, such as ultrathin ionic layers. These sensors could have diverse applications, including facilitating easier weighing of infants by parents.

The team also successfully detected pulses not only from the wrist but also from other distal vascular structures like the eyebrow and fingertip. Additionally, they demonstrated the potential for using these sensors in human-robot collaborative interactions and envisioned healthcare applications, such as assisting individuals with limb loss in controlling robotic limbs.

Cheng also highlighted other potential applications, such as measuring a person’s pulse in high-stress work scenarios like search-and-rescue operations or hazardous tasks on construction sites.

The researchers employed computer simulations and computer-aided design to explore ideas for these innovative sensors, acknowledging the complexity of finding optimal sensor solutions. Leveraging electronic assistance in the form of modeling and simulation is expected to advance future research and lead to even better sensor designs.

Source: Pennsylvania State University

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