Dual-Scale Porous Composite for Tactile Sensor with High Sensitivity over an Ultrawide Sensing Range.

Porous structures have been utilized in tactile sensors to improve sensitivity owing to their excellent deformability. Recently, tactile sensors using porous structures have been used in practical applications, such as bio-signal monitoring. However, highly sensitive responses are limited to the low-pressure range, and their sensitivity significantly decreases in a higher-pressure range. Several approaches for developing tactile sensors with high sensitivity overing a wide pressure range have been proposed; however, achieving high sensitivity and wide sensing range remains a crucial challenge. This report presents a carbon nanotube (CNT)-coated CNT-polydimethylsiloxane (PDMS) composite having dual-scale pores for tactile sensors with high sensitivity over a wide pressure range. The porous polymer frame formed with dense pores of dual sizes facilitates the closure of large and small pores at low and high pressures, respectively. This results in an apparent increase in the number of contact points between the CNT-CNT at the pores even under a wide pressure range. Furthermore, the piezoresistivity of the CNT-PDMS composite contributes to achieving a high sensitivity of the tactile sensor over a wide pressure range. Based on these mechanisms, various human movements over a broad pressure spectrum are monitored to investigate the practical usefulness of the sensor.

Recent Progress in Flexible Tactile Sensors for Human-Interactive Systems: From Sensors to Advanced Applications.

Flexible tactile sensors capable of measuring mechanical stimuli via physical contact have attracted significant attention in the field of human-interactive systems. The utilization of tactile information can complement vision and/or sound interaction and provide new functionalities. Recent advancements in micro/nanotechnology, material science, and information technology have resulted in the development of high-performance tactile sensors that reach and even surpass the tactile sensing ability of human skin. Here, important advances in flexible tactile sensors over recent years are summarized, from sensor designs to system-level applications. This review focuses on the representative strategies based on design and material configurations for improving key performance parameters including sensitivity, detection range/linearity, response time/hysteresis, spatial resolution/crosstalk, multidirectional force detection, and insensitivity to other stimuli. System-level integration for practical applications beyond conceptual prototypes and promising applications, such as artificial electronic skin for robotics and prosthetics, wearable controllers for electronics, and bidirectional communication tools, are also discussed. Finally, perspectives on issues regarding further advances are provided.

Large-Area, Crosstalk-Free, Flexible Tactile Sensor Matrix Pixelated by Mesh Layers.

Tactile sensor arrays have attracted considerable attention for their use in diverse applications, such as advanced robotics and interactive human-machine interfaces. However, conventional tactile sensor arrays suffer from electrical crosstalk caused by current leakages between the tactile cells. The approaches that have been proposed thus far to overcome this issue require complex rectifier circuits or a serial fabrication process. This article reports a flexible tactile sensor array fabricated through a batch process using a mesh. A carbon nanotube-polydimethylsiloxane composite is used to form an array of sensing cells in the mesh through a simple "dip-coating" process and is cured into a concave shape. The contact area between the electrode and the composite changes significantly under pressure, resulting in an excellent sensitivity (5.61 kPa-1) over a wide range of pressure up to 600 kPa. The mesh separates the composite into the arranged sensing cells to prevent the electrical connection between adjacent cells and simultaneously connects each cell mechanically. Additionally, the sensor shows superior durability compared with previously reported tactile sensors because the mesh acts as a support beam. Furthermore, the tactile sensor array is successfully utilized as a Braille reader via information processing based on machine learning.