Researchers at Harvard University develop highly sensitive and flexible capacitive sensors
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[China Instrument Network Instrument R&D] Recently, researchers from Harvard University's Vis Bio-Inspired Engineering Institute and John Paulson School of Engineering and Applied Science have created a highly sensitive flexible capacitive sensor. It is composed of silicone and fabric, which can monitor the movement of the human body accurately and freely as the human body moves and bends.
Today, from heart rate monitors to virtual reality helmets, all kinds of wearable technology products have shown explosive growth and popularity in the consumer electronics market and research fields. However, in order to detect and transmit data, most of the electronic sensors used in these wearable devices are made of a hard, inflexible material, which not only limits the natural movement of the wearer, but also affects the accuracy of data collection.
The paper for this study was published in the latest issue of Advanced Materials Technology and became part of Harvard's Biodesign Laboratory Flexible Robot Toolkit.
The capacitive sensor consists of a thin layer of silicone (a poorly conductive material) sandwiched between two silver-plated, conductive fabrics (a highly conductive material).
This sensor records body motion by measuring changes in capacitance. The so-called capacitance, which is the ability to hold the charge, also refers to the electric field between the two electrodes.
Daniel Vogt, a research engineer and co-author of the Vis Research Institute, said: “When we pull the sensor at one end of the sensor and apply tension, the silicone layer becomes thinner and the conductive fabric layer will come closer. The capacitance of the sensor is changed in a way that is proportional to the applied tension. Therefore, we can measure how much the shape of the sensor has changed."
The superior performance of this hybrid sensor stems from its new manufacturing process. Through this manufacturing process, the fabric is connected to both ends of the silica gel core through another layer of liquid silica gel. This method allows silicone to fill the air gap in the fabric and mechanically lock it onto the silica gel, increasing the surface area used to disperse tension and storage capacitance.
This mixture of silica gel and fabric enhances the sensitivity to motion by making full use of the properties of these two materials. When pulled up, this strong, interlocking fabric fiber can help silica gel limit its degree of deformation; and when the pull force is reversed, silicone can help the fabric to restore its original shape. Finally, the soft filaments pass through the heat-seal tape and are permanently attached to the conductive fabric, allowing the electrical information from the sensor to be transmitted to the circuit without requiring a hard, cumbersome interface.
Experiment: The team evaluated the new sensor they designed by performing tensile tests. In the experiment, the researchers performed various measurements when the sensor was stretched by an electromechanical test device. In general, when the elastic material is stretched, its length increases, and its thickness and width decrease, so the total area of ​​the material does not change, that is, its capacitance remains unchanged. Surprisingly, the researchers found that when the sensor was stretched, the conductive area increased and the capacitance was greater than expected. Asli Atalay, the lead author of the paper and a postdoctoral researcher at the Vis Institute, said: "Silicon-based capacitive sensors have limited sensitivity due to the material's natural characteristics. However, after embedding silicone into conductive fabrics, it creates a matrix that can Prevents silica from shrinking laterally, which increases sensitivity to the bare silicone we tested."
This hybrid sensor can measure the increase in capacitance within 30 milliseconds of strain application and less than half a millimeter of physical change, effectively capturing human motion. To test this ability in the real world, researchers integrated them into a glove and measured finer hand and finger movements in real time. As the finger moves, the sensor can successfully detect changes in capacitance, indicating their relative position as a function of time.
Vanessa Sanchez, co-author of the SEAS Biodesign Laboratory's graduate student and thesis, explained: "The higher sensitivity of our sensors means that it has the ability to distinguish between more subtle movements, such as moving the finger slightly from one end to the other. Instead of simply opening the entire hand or clenching their fists."
Value: For the value of this innovative research, let's take a look at what the experts say. The author of the paper, the core faculty member of the Weiss Institute, and John L. Loeb, associate professor of engineering and applied sciences at SEAS, said: “We are very excited about this sensor. Because it is made of textiles, it is naturally suitable for integration into fabrics. , Become 'smart' robot clothing."
Ozgur Atalay, one of the co-authors of the thesis and a postdoctoral researcher at the Weiss Institute, said: "In addition, we have designed a unified mass production process that allows us to create custom-shaped sensors that share a common feature and that Quick manufacturing based on a given application."
Although this research is still in the proof of concept phase, the team is full of confidence in the future direction of this technology. Walsh said: “This research represents our growing interest in the use of fabric technology in robotic systems, and we see the broad prospects of 'sporting in outdoor environments', such as sportswear that can monitor physical activity, or The patient's flexible medical equipment is monitored at home. In addition, these sensors, combined with a fabric-based flexible brake, allow the new robotic system to truly imitate clothing.â€
(Original Title: New Flexible Capacitance Sensor: Can Accurately Monitor Subtle Body Movements!)