Low-cost, interdigitated capacitive sensor using laser-written graphene foam for touch, proximity, and liquid level detection

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Abstract
Flexible capacitive sensors are gaining popularity in place of sophisticated optical sensing or bulky mechanical designs for specific applications such as proximity/gesture detection and liquid level sensing. So, here, we propose Laser Induced Graphene Foam (LIGF) based planar capacitive sensors, which are flexible, highly sensitive, energy-efficient, and cost-effective, making them accessible for various applications. The working of these sensors involves the interdigitated planar electrode configuration and the fringing effect, influencing capacitance when the permittivity or the electric charge of the surrounding medium changes. LIGF planar capacitive elements were produced on a commercially availed polymer polyimide by using direct laser writing technique employing a low-cost diode laser. The developed LIGF-based planar capacitive touch sensor showed an average touch response (|ΔC/Co|) of more than 49%; moreover, when used for proximity sensing, this sensor could detect the presence of human hand up to a maximum distance of 170 mm from the sensor surface. An extended design of the sensor has demonstrated liquid level sensing with an accuracy of 0.97 mm. As a result of its ability to sense dielectric materials, contactless operation, long-range sensing, cost-effectiveness, low-power consumption, and environmental friendliness, the LIGF electrode-based capacitive sensor can be incorporated into a variety of modern technology and devices.

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