The role of humidity sensors in different industries and field applications, such as agriculture, food monitoring, biomedical equipment, heating, and ventilation, is well known. However, most commercially available humidity sensors are based on polymers or electronic materials that are not degradable and thus contribute to electronic waste. Here, we report a low-cost, flexible, easy-to-fabricate, and eco-friendly parallel-plate capacitive humidity sensor for field applications. The sensor is fabricated from copper tape and tissue paper, where copper tape is used to create the plates of the capacitor, and tissue paper is used as a dielectric sensing layer. Along with the low cost, the high sensitivity, better response and recovery times, stability, and repeatability make this sensor unique. The sensor was tested for relative humidity (RH), ranging from 40% to 99%, and the capacitance varied linearly with RH from 240 pF to 720 pF, as measured by an Arduino. The response time of the sensor is ~1.5 s, and the recovery time is ~2.2 s. The experiment was performed 4–5 times on the same sensor, and repeatable results were achieved with an accuracy of ±0.1%. Furthermore, the sensor exhibits a stable response when tested at different temperatures. Due to the above advantages, the presented sensor can find ready applications in different areas.
An eco-friendly, biodegradable, flexible, and facile fabricated interdigital electrode-based capacitive humidity sensor with applications in health and medicine has been reported here. Several sensors use copper tape as electrodes on the polyethylene terephthalate (PET) substrate, with non-woven paper as the sensing layer. Two different configurations of sensors were tested, i.e., with and without pores in the PET substrate. The sensing performance of both sensors has been tested for relative humidity ranging from 35 to 100% at temperatures ranging from 20 to 50 °C. The capacitance of the sensor varies linearly in response to the change in humidity. The sensor with pores shows a response from 28 to 630 pF as the humidity varied from 35 to 100%, whereas the sensor without pores responded from 22 to 430 pF. The response and recovery times of the fabricated sensor are observed as ∼2.4, and ∼1.8 s, respectively, and the sensitivity is 9.67 pF/% RH. The sensors are tested multiple times, and repeatable results are achieved each time with an accuracy of ±0.22%. Further, the sensor's response is also stable for different ranges of temperatures. Finally, to demonstrate an application of the proposed sensor, it has been utilized to monitor respiration through nose and mouth breathing. The low-cost, stable, repeatable, and highly sensitive response makes our fabricated sensor a promising candidate for practical field applications.
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