(Nanowerk News) As we move into a world where human-machine interaction becomes more prominent, pressure sensors capable of analyzing and simulating human touch will likely grow in demand.
One of the challenges engineers face is the difficulty of building the highly sensitive, cost-effective types of sensors needed for applications such as detecting subtle pulses, operating robotic limbs, and building very high-resolution balances. However, the research team has developed a sensor capable of performing all of these tasks.
The researchers, from Penn State and Hebei University of Technology in China, wanted to create a highly sensitive, linear sensor that is reliable over a wide range of applications, has high pressure resolution, and is capable of working under large pressure preloads.
“The sensor can detect small pressure when large pressure has been applied,” says Huanyu “Larry” Cheng, James L. Henderson Jr. Memorial Associate Professor of Engineering Science and Mechanics at Penn State and co-author of a paper about the work published in Nature Communications (“High-sensitivity iontronic pressure sensor over an ultra-wide linear range activated by laser-induced gradient micro-pyramids”). “An analogy I like to use is like detecting a fly on an elephant. It can measure the slightest change in pressure, just like our skin does with touch.
Cheng was inspired to develop this sensor because of a very personal experience: the birth of his second daughter.
Princess Cheng lost 10% of her body weight soon after birth, so doctors asked her to weigh the baby every two days to monitor any additional weight loss or gain. Cheng tried to do this by weighing himself on a regular weight scale and then weighing himself holding his daughter to measure the baby’s weight.
“I noticed when I put my daughter in her blanket, when I’m not holding her anymore, you don’t see any change in weight,” said Cheng. “So we learned that trying to use a commercial balance didn’t work, it didn’t detect changes in pressure.
After trying various approaches, they found that using a pressure sensor consisting of a gradient micro-pyramid structure and an ultrathin ionic layer to provide a capacitive response was the most promising.
However, there are further problems they face. The high sensitivity of the microstructure decreases as the pressure increases, and the random microstructure forged from natural bodies results in uncontrolled deformation and a narrow linear range. In simple terms, when pressure is applied to the sensor, it will change the shape of the sensor and therefore change the contact area between the microstructures and lose the reading.
To address this challenge, scientists devised microstructural patterns that can increase linear range without compromising sensitivity — they essentially make them flexible, so they can still function within pressure gradients that exist in the real world. Their study explored the use of CO2 lasers with Gaussian beams to fabricate programmable structures such as gradient pyramidal microstructures (GPM) for iontronic sensors, which are soft electronics that can mimic the perceptual function of human skin. This process reduces the cost and complexity of the process compared to photolithography, a method commonly used to prepare fine microstructural patterns for sensors.
Cheng credits Ruoxi Yang, a graduate student in his lab and first author of the study, for driving this solution.
“Yang was a very bright student who came up with this idea to solve this sensor problem, which is really like a combination of lots of little pieces, intelligently engineered together,” said Cheng. design. But designing or optimizing structures is challenging, and he’s working with the laser systems we have in our lab to make that possible. He had worked really hard in the last few years and was able to explore all of these different parameters and was able to quickly sift through this entire parameter space to find and improve performance.”
These optimized sensors have fast response and excellent recovery times and repeatability, which the team tested by detecting subtle pulses, operating interactive robotic hands, and building ultra-high-resolution smart scales and weight chairs. The scientists also discovered that the proposed fabrication approach and design tools from this work can be leveraged to easily adapt the performance of pressure sensors to various target applications and open up opportunities to fabricate other iontronic sensors, the sensor range employing ionic liquids such as ultrathin. ionic layer. Along with enabling a future scale where it will be easier for parents to weigh their babies, these sensors also have other uses.
“We can also detect not only the pulse from the wrist but also from other distal vascular structures such as the eyebrows and fingertips,” said Cheng. “In addition, we coupled it with a control system to demonstrate that it might be used for human robotic interactional collaboration in the future. In addition, we envision other healthcare uses, such as someone who has lost a limb and this sensor could be part of a system to help them control robotic limbs.”
Cheng noted other potential uses, such as sensors to measure a person’s pulse during high-stress work situations such as search and rescue after earthquakes or performing difficult and dangerous tasks on construction sites.
The research team used computer simulations and computer-aided design to help them explore ideas for this new sensor, which Cheng noted was challenging work given all the possible sensor solutions. These electronic aids will continue to drive research forward.
“I think in the future it will be possible to further improve the model and be able to describe more complex systems and then we can definitely understand how to make even better sensors,” said Cheng.