The first hybrid-response flexible pressure sensor, which can grasp the pulse of humans, and will also create human touch for robots
In recent years, the research of flexible wearable devices in monitoring human biological signals has made great progress, and the use of flexible patches to monitor blood pressure and pulse anytime and anywhere is just around the corner. However, the existing wearable pressure sensor has a big problem: high sensitivity and wide working range cannot be achieved at the same time. Even a very slight pressure will greatly reduce the sensitivity of the sensor.
”The flexible pressure sensor track is very crowded. After 20 years of development, research has encountered bottlenecks because there is still no good way to solve the contradiction between pressure and sensitivity,” Lu Nanshu said.
Recently, the team led by Lu Nanshu has filled this gap by innovating the first hybrid sensor method in history. “This is the first sensor that uses a piezoresistive-pressure-capacitance hybrid response to withstand pressure without significantly reducing sensitivity.” She said.
Combining capacitance and resistance for the first time to balance the wide range of pressure and sensitivity
The “composite response” pressure sensor invented by Lu Nanshu’s research group was recently published in Advanced Materials.
Through the combination of a conductive porous microstructure and an ultra-thin insulating layer, researchers have discovered for the first time that the mixed response of distributed piezoresistors and piezo capacitors can enable flexible pressure sensors to have both high sensitivity and wide operating range. As small as the weight of a fruit fly (0.07pa), as large as the pressure generated by a person’s footsteps (125kPa), it can be sensitively sensed.
“Composite Response” Pressure Sensor
According to reports, the sensor is composed of a porous nanocomposite (PNC) with ultra-high porosity, an ultra-thin insulating layer and Au/PI electrodes. Among them, the porous nanocomposite material (PNC) is composed of Ecoflex silica gel doped with carbon nanotube (CNT).
Composite response pressure sensor HRPS application demonstration
The subject puts on a virtual reality (VR) helmet and generates a pre-pressure of 8kPa on the HRPS, and the temporal artery pulsation signal can still be clearly measured
To show how sensitive the sensor is to tiny pressure signals, the researchers measured a fruit fly weighing only 0.7 milligrams, the airflow blown by a blower 3 cm above the sensor, three successively falling water droplets, and the human carotid artery and temporalis. The pulse of the artery is beating.
Experimental results show that the “composite response” pressure sensor has an accurate and rapid response to the pressure of Drosophila’s own weight of only 0.07kPa, as well as the pressure caused by the tiny airflow and the dripping of water droplets, with a response time of only 94 milliseconds.
In terms of health monitoring, members of Lu Nanshu’s research group attached a soft, thin and light “composite response” pressure sensor to the subject’s carotid artery, which can clearly detect pulse fluctuations. The carotid artery and the frontotemporal artery are minute pulsations, and their measurement requires extremely high sensitivity of the equipment.
Even if additional pressure is applied to the sensor in advance, such as wearing a virtual reality helmet for the subject, and the “composite response” pressure sensor generates a pre-pressure of 8kPa, the temporal artery pulsation signal can still be clearly measured.
”This is the first time that the temporal artery pulsation signal has been noninvasively measured by a capacitive pressure sensor.” Lu Nanshu said.
In the measurement of high pressure, the “composite response” pressure sensor also shows good sensitivity. In the supplementary video of the paper, the team members attached a “composite response” pressure sensor to the sole of a subject weighing 80kg and measured the pressure generated by walking on a yoga mat. The maximum recorded value of the final measurement was 125kPa. This number is consistent with the pressure produced by walking on human feet measured by other previous studies.
This research mainly demonstrates the application of “composite response” pressure sensors in human health monitoring. In addition, Lu Nanshu has a more ambitious vision for the flexible sensors they have developed. She is studying how to wrap this flexible sensor on other soft objects (such as robotic hands) to make it sensitive to human skin. By simulating the real human touch, the robot has the ability to recognize objects through touch.
From electronic tattoos to electronic skins, how do people and machines approach each other?
In 2012, Lu Nanshu was selected in the global regional list of “35 Technological Innovations Under 35” by MIT Science and Technology Review for his invention of “electronic tattoo”.
Traditional smart wearable devices are large in size, inconvenient to carry, and have poor wearing comfort. “Electronic tattoos” have non-invasive, thin, and excellent deformability capabilities, and transmit various body information such as ECG, EMG, and EEG to mobile phones, computers and other terminals. This kind of disposable electronic patch has great market prospects in the fields of medical treatment or human-computer interaction, and is considered to be the “ultimate sensor form of wearable devices.”
Multi-layer, modular “electronic tattoo” can realize wireless charging and wireless data transmission
Lu Nanshu received a bachelor’s degree and a doctorate degree from Tsinghua University and Harvard University, respectively, and later worked as a Beckman postdoctoral researcher at the University of Illinois at Urbana-Champaign. Her research field involves the mechanics of flexible electronics, materials, manufacturing, and human body integration.
At the moment, Lu Nanshu constructs his own scientific research building from two aspects. One is electronic tattoos. The thin and soft characteristics enable them to fit human skin well, capture biological signals, and sense human vital signs. The human body is an analog biological signal system, while the machine and electronic world are digital. Therefore, if you want to realize human-computer interaction, people need to be “digitalized”, and “electronic tattoos” are considered to be one of the effective ways for humans to “digitize”.
Multi-layer, modular “electronic tattoo” can realize wireless charging and wireless data transmission
The other is the electronic skin. Through flexible pressure, temperature and other sensors, the soft robot has a sensitivity similar to human skin, giving it vivid touch, vision, hearing, taste and smell. The research published this time is a new type of hybrid corresponding electronic skin that broadens the pressure working range of the sensor and maintains tactile sensitivity.
Lu Nanshu’s ultimate goal is to be able to complete the closed loop of human-computer interaction: the human body is connected to the digital world through electronic tattoos, and the robot simulates the human perception environment through electronic skin. Therefore, her team has been focusing on “flexible bioelectronic systems” in the following four aspects: The
first is the study of flexible/stretchable junction structure mechanics. Such as the deformation mechanism of the passive and active (piezoelectric) meandering ribbon structures and the bending decoupling of the upper and lower layers due to the mismatch of the Young’s modulus between the layers of the multilayer flexible electrons.
The second is two-dimensional materials and nano-materials, including graphene electronic tattoos, the mechanism of nano-bubbles and nano-tents formed by two-dimensional materials, and PNC.
The third is the preparation process and transfer technology, including the “cutting-welding-sticking” process of wireless electronic tattoos and water-assisted transfer printing.
The fourth is the bio-electronic interface, including the conformal mechanism between the device and the uneven biological tissue surface, the conformal artificial retina inspired by paper cutting, and the stable and reusable dry bonding interface brought about by the surface pit array.
Human-computer interaction opens the era of smart elderly care
When asked about the application scenario that she is most looking forward to, Lu Nanshu said: “I personally prefer medical applications, especially elderly care.” When it comes to the issue of elderly care, she was a little moved and described it as “beyond reach”.
Lu Nanshu’s grandmother, grandfather, and grandmother are nearly a hundred years old, but she has been abroad for a long time, and affected by the epidemic, she cannot return to China to take care of her parents and the elderly at home at any time. The real-time monitoring of the elderly’s activities and health through electronic tattoos, and the use of robotic caregivers to make up for the huge gaps and elderly care problems in the market are the future Lu Nanshu is looking forward to. Yes. Making electronic skins for robots, giving them the gentleness and tactility comparable to those of enemies, will greatly alleviate this type of professional gap.” When asked about artificial intelligence replacing human jobs, Lu Nanshu said: “Humans Emotional communication is irreplaceable, but transactional work can be done.” The
Chinese Academy of Social Sciences Institute of Elderly Research estimates that the business opportunities in China’s elderly care market are about 4 trillion yuan, which is expected to increase to 13 trillion yuan by 2030. “The elderly care service industry not only highlights the characteristics of people’s livelihood, but also demonstrates its great appeal as a sunrise industry.”
Data from the 7th census shows that my country’s aging population over the age of 65 has reached 190 million, accounting for 13.5%. China is accelerating its entry into an aging society. The traditional old-age care model can no longer fully meet the current needs. It has become an inevitable trend to seek new diversified and composite governance solutions to solve the multi-level needs of the elderly through scientific and technological means. The research by Lu Nanshu and other researchers will be an indispensable vision for the future “smart elderly care” A small piece of the puzzle is missing.
