Facile Pressure-Sensitive Capacitive Touch Keypad for a Green Intelligent Human-Machine Interface.

There is a great demand for human-machine interfaces (HMIs) in emerging electronics applications. However, commercially available plastic-based HMIs are primarily rigid, application-specific, and hard to recycle and dispose of due to their non-biodegradability. This results in electronic and plastic waste, potentially damaging the environment by ending up in landfills and water resources. This work presents a green, capacitive pressure-sensitive (CPS), touch sensor-based keypad as a disposable, wireless, and intelligent HMI to mitigate these problems. The CPS touch keypads were fabricated through a facile green fabrication process by direct writing of graphite-on-paper, using readily available materials such as paper and pencils, etc. The interdigitated capacitive (IDC) touch sensors were optimized by analyzing the number of electrode fingers, dimensions, and spacing between the electrode fingers. The CPS touch keypad was customized to wirelessly control a robotic arm's movements based on the touch input. A low-pressure touch allows slow-speed robotic arm movement for precision movements, and a high-pressure touch allows high-speed robotic arm movement to cover the large movements quickly. The green CPS touch keypad, as a disposable wireless HMI, has the potential to enforce a circular economy by mitigating electronic and plastic waste, which supports the vision of a sustainable and green world.

Garage-Fabricated, Ultrasensitive Capacitive Humidity Sensor Based on Tissue Paper.

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.

Paper-based facile capacitive touch arrays for wireless mouse cursor control pad.

Wireless devices have become extremely inexpensive and popular in recent years. The two most significant advantages of wireless devices over wired ones are convenience and flexibility. Considering this, a wireless mouse pad prototype for access has been developed in this study. A capacitive sensors-based mouse pad with basic operations and conventional features has been developed using sensing arrays on paper. A facile, do-it-yourself fabrication process was utilized to develop a cost-effective, thin, wearable, and cleanroom-free wireless mouse cursor control (MCC) pad. The ablation process was used to cut the traces of conductive tape and paste them onto the paper to develop the MCC pad. The pad was connected with Espressif Systems (ESP)32 to wirelessly control the cursor of mobile and laptop. The capacitive touch sensor array-based pad is easy to reproduce and recycle. This pad can contribute to future advancements in thin human-machine interfaces, soft robotics, and medical and healthcare applications.

Invisible touch sensors-based smart and disposable door locking system for security applications.

Nowadays, security is one of the living essentials, and there is a dire need for reliable, secure, and smarter locking systems. The stand-alone smart security systems are of great interest as they do not involve keys, cards, or unsecured communication in order to prevent carrying, loss, duplication, and hacking. Here, we report an invisible touch sensors-based smart door locking system (DLS). The passive transducer-based touch sensors are fabricated through a facile do-it-yourself (DIY) based fabrication process by pasting the hybrid geometry copper electrodes on cellulose paper. The employment of biodegradable, and non-toxic materials like paper and copper tape makes this configuration a good candidate for green electronics. For additional security, the keypad in the DLS is made invisible by covering it with paper and spray paint. One can only open the door by knowing the password as well as the location of each key on the sensor keypad. The system can efficiently recognize the exact pattern of passwords without any false values. Invisible touch sensors-based locking systems can easily contribute to the security applications in homes, banks, automobiles, apartments, lockers, and cabinets.

Fast Response Facile Fabricated IDE-Based Ultra-sensitive Humidity Sensor for Medical Applications.

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.