Ultrasensitive Capacitive Sensor Composed of Nanostructured Electrodes for Human–Machine Interface

Abstract

because the sensing information contains human behavior-related inputs to enable efficient communication, process control, and safety assurance. The technologies for behavior monitoring include cameras, [3] radar, [4] electromagnetic, [5] and capacitive sensing. Among the methods, capacitance sensing is unique in that both proximity and physical contact can be detected at a fraction of cost and power.Traditional capacitive sensors have been limited in flexibility, sensitivity, and proximity to serve HMI applications, including wearable devices. Recent progress has been made to incorporate nanostructures into the electrode design to offer flexible and stretchable functions. [6] A flexible capacitive sensor was fabricated by printing copper traces to form crossing junctions. [7] Silver-plated fiber electrodes in combination with silicone dielectric were fabricated for a motion-sensing band. [8] A flexible touch sensor was fabricated by printing a silver nano-ink onto a polyethylene terephthalate (PET) film. [9] The ionic liquid was enclosed into the silicone to create a flexible capacitive strain sensor. [10] On the other hand, various capacitive sensors were developed and commercialized as a touchscreen format for finger motion detection with contact. A conventional cylindrical capacitive sensor has a detection range proportional to the electrode diameter. For example, a 34 mm diameter electrode has a detection range of 40 mm. [11] Novel designs were made to improve the proximity range while reducing the electrode dimension. Selfcapacitive sensors were demonstrated to detect a human hand at 120 mm-distance but with a 100 mm-dimension. [12] Thermoplastic polyurethane-carbon nanotube (TPU-CNT) film sensors demonstrated a proximity detection range of 120 mm with a 60 mm dimension. [13] For capacitive sensors, larger capacitive electrodes offer higher sensitivity due to the larger characteristic length of an electric field. However, the large electrode reduces a spatial resolution, which is a challenge for delicate gesture recognition.This paper presents a capacitive sensor composed of a nanostructured electrode array. One capacitive electrode is composed of high aspect-ratio cellulose fibers embedded with multiwalled carbon nanotubes. The electrode array enlarges the capacitance with a reduced form factor. The capacitive sensing mechanism is analyzed by numerical analysis. The sensitivity of multiple Human-machine interface requires various sensors for communication, manufacturing and environmental control, and health and safety monitoring. Capacitive sensors have been used to detect touch, distance, geometry, electric property, and environmental parameters. However, highly sensitive proximity detection with a small form factor has always been a challenge. This paper presents a capacitive sensor composed of a nanostructured electrode array for contact and noncontact detection. In the sensor configuration, the nanostructured electrode is made of high aspect ratio cellulose fibers embedded with carbon nanotubes. The co...

Liquid level measurement using a single electrode capacitive sensor made of carbon nanotube-paper composite

“…The high aspect ratio structure and large surface area enhanced the fringing electric field, thus, the capacitive sensitivity. The CPC electrodes were fabricated using tensional fracture [38] and characterized in sample variability such as fabrication methods and sensing areas in our previous studies [39]. Therefore, in this paper, the fractured CPC was used as the single electrode to conduct all the expriments.…”

“…A single-electrode capacitive sensor was made of CPC as reported in previous research [38,39]. In short, the sensor was fabricated by trimming the CPC material into a 10 × 5 mm 2 rectangle.…”

Recent Progress of Tactile and Force Sensors for Human–Machine Interaction

“…The human can be seen as a conductor connecting to the ground, and when part of the human body, such as a finger, approximates the anode of a capacitive sensor, an equivalent capacitance is formed between the human body and the anode that is in parallel with the anode and cathode of the capacitive sensor, resulting in the increase of the total capacitance [ 51 ]. Based on that mechanism, capacitive sensors for contact and non-contact tactile sensing were proposed by Li et al [ 52 ], and a smart pad for proximity recognition was demonstrated.…”

“…Moreover, different tactile sensing mechanisms can be combined for multifunctional tactile sensing, e.g., a heterogeneous tactile sensor able to sense stretching, bending, and compression individually was proposed by combining optical, microfluidic, and piezoresistive sensing mechanisms [ 74 ]. In addition to touch tactile interaction, proximity interaction is regarded as a generalized form of tactile, and sensing mechanisms, including capacitive [ 52 ], nearby charge induction [ 75 ], optical fiber [ 71 ], and magnetic field sensing [ 73 ], are utilized to realize non-contact tactile HMIs. Typical tactile and force sensors for human–machine interaction developed recently are summarized in Table 1 .…”

Smart Contact Lenses for the New Era of IoT: Integrated Biosensors, Circuits, and Human–Machine Interface Systems

“…[22][23][24] By presenting the sensor information to users in a simple and user-friendly interface, the HMI system enables a good user experience. [25,26] In particular, in the context of the coronavirus disease 2019 (COVID-19) pandemic, the use of smart electronic technology to achieve real-time and wireless interactive sensing is necessary. [27][28][29] Smart contact lenses (SCLs) have been employed for monitoring information regarding the eyes, including physical information (e.g., pressure and temperature) and chemical information (e.g., glucose, protein, and pH).…”