AsiaIndustrial NetNews: Researchers at the University of Glasgow in Scotland have designed a graphene-based transparent and flexible capacitive touch sensor that not only provides touch detection, but also has a pressure sensing function. Because it is transparent, the haptic sensing layer can be stacked on rigid or flexible solar photovoltaic (PV) cells to automatically supply power during operation.
20170329-dims-eskin researchers in Advanced Functional Materialsnal Materials) published the article “Energy-Autonomous, Flexible, and Transparent Tactile Skin” (Energy-Autonomous, Flexible, and Transparent Tactile Skin), revealing a seemingly simple but highly scalable new approach to innovative Capacitive pressure sensor.The researchers are confident that further extensions can beRobotProvides full tactile feedback with applications such as prosthetics.
The actual capacitive touch sensor consists of a single-layer graphene coplanar cross-capacitive (IDC) electrode on a PVC substrate (125 μm thick) connected to titanium/gold (Ti/Au; 10 nm/100 nm) deposited on the edge of the electrode ) contacts. A single layer of graphene is grafted onto a PVC substrate through a thermal lamination process (and copper foil initially grown on graphene) before the copper foil is etched out. Next, metal contacts are deposited on the edges of the graphene layer (using electron beam evaporation and shielding), and a computer-controlled plotter blade is used to pattern the graphene onto the intersecting electrodes.
Flexible and transparent graphene touch sensor with a thickness of only 125μm
The sensor is completed by a 25 μm thick polymer layer (PDMS) spin-coated on top of the graphene channel. The final layer not only serves as a deformable dielectric layer, but also encapsulates the component. The researchers tried a variety of different electrode patterns and ended up with a square curve that maximized capacitive response as well as a variety of pressures.
To characterize this new type of capacitive sensor, the researchers found that it has a stable response under various pressures; in contrast, traditional coplanar or layered structures can only sense the presence or absence of touch, but not the Sensing pressure. They also found that the pressure sensitivity can be mainly attributed to the change in the dielectric constant of PDMS upon compression (due to the porous structure of the polymer).
Interestingly, the tested sensor sensitivities show slight variations in the pressure range of 0 to 60 kPa, but remain in the same order of magnitude: 9.3 × 10-3 kPa-3 for 0 to 20 kPa; 4 for 20 to 60 kPa ．3×10-3kPa-1, the sensitivity when the pressure exceeds 60kPa is 7.7×10-3kPa-1.
To demonstrate the usability of the sensor in practical electronic skin (e-skin) applications, the research team integrated it at the middle and proximal phalanx of an advanced bionic hand, and designed and built it on a flexible polyamide through a simple read interface circuit. imide PCB, thereby converting the capacitance change of the graphene sensor into a voltage. They were able to demonstrate real-time pressure mapping, such as a bionic arm grasping a soft ball, and implement a real-time haptic feedback loop with a readout circuit that controls how well the hand grasps.
A bionic hand with haptic feedback captures a soft ball (left). And on the right, the color map of the capacitive sensor around the middle and proximal phalanx indicates read voltage modulation.Inset is a logic diagram for controlling gripping force (relative to sensor readings)
To achieve a self-powered solution, the researchers stacked transparent sensors on top of commercial amorphous silicon solar cells. The researchers confirmed that despite using a 39.6 × 22.9 mm2 battery in this experiment, which can supply 160 μW cm2 of power, the sensor consumed 31 W and 55 nW, respectively, during touch. The sensing layer consumes only ultra-low power – 20nWcm2, which is about 10 times less power than PV energy harvesting.
Stacking graphene transparent touch sensors on top of solar cells
The researchers concluded that large, transparent sensors using flexible and stretchable PV cell stacks not only provide a self-powered electronic skin, but could also help provide robotics power by storing excess electricity or for driving actuators. and other systems to improve efficiency. These sensors can also be used to develop functional apparel, including helmets, gloves and other applications from which useful pressure data can be collected.
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