We proposed a novel, low-cost, and universal tactile sensing technology for imaging pressure distribution using a tomographic approach with conductors. In particular, we focused on the fact that pressure is related to the contact resistance between two conductive objects. The sensor comprised driving and probing conductors, which were electromechanically coupled. The system solved an inverse problem for estimating electrical boundary conditions using the voltage sets from electrodes on the border of the probing conductor. The sensing system successfully estimated the pressure distribution, contact location (error rate: 5.68 $\pm$ 2.78 %), and local pressure (error in the range 0.0269 - 0.0509 N/mm $^2$ for a maximum pressure of 0.50 N/mm $^2$ ). Finally, tactile imaging by sheet- and finger-type sensors was demonstrated as practical applications of the developed sensor.

Cold sensations of varying intensities are perceived when human skin is subject to diverse environments. The accurate presentation of temperature changes is important to elicit immersive sensations in applications such as virtual reality. In this article, we developed a method to elicit intensity-adjustable non-contact cold sensations based on the vortex effect. We applied this effect to generate cold air at approximately 0 $^\circ$ C and varied the skin temperature over a wide range. The perception of different temperatures can be elicited by adjusting the volume flow rate of the cold air. Additionally, we introduced a cooling model to relate the changes in skin temperature to various parameters such as the cold air volume flow rate and distance from the cold air outlet to the skin. For validation, we conducted measurement experiments and found that our model can estimate the change in skin temperature with a root mean-square error of 0.16 $^\circ$ C. Furthermore, we evaluated the performance of a prototype in psychophysical cold discrimination experiments based on the discrimination threshold. Thus, cold sensations of varying intensities can be generated by varying the parameters. These cold sensations can be combined with images, sounds, and other stimuli to create an immersive and realistic artificial environment.

An important function for a tactile navigation system of a handheld tool, such as a surgical scalpel, is the spatial transparency of the device. This paper proposed a new tactile display that can augment touch sensation at the finger pulps without the need for a stimulator between the tool and the finger pulps. We utilized transcutaneous electrical nerve stimulation at the middle phalanx of a finger to separate the stimulated and the perceived areas. In order to verify the effects of the spatial transparency, the performances of grip force control were examined. The results indicated that the proposed display was effective in helping the user to maintain the stable control of the grip force when using a handheld tool.

Recent advancements in soft robots, human–machine interfaces, and wearable electronics have led to an increased demand for high-performance soft tactile sensors. Tomographic tactile sensor based on resistive coupling is a novel contact pressure imaging method that allows the use of an arbitrary conductive material in a detector. However, the influence of material properties on the sensing performance remains unclear, and the efficient and appropriate selection of materials is difficult. In this study, the relationship between the conductivity distribution of the material used as a detector and the sensing performance including sensitivity, force range, spatial resolution, and position accuracy is clarified to develop high-performance tomographic tactile sensors for specific purposes. The performance maps reveal that a material with a conductivity of approximately 0.2 S/m can serve as an effective detector for touch interactions involving a force range of several Newtons. Additionally, incorporating gradient conductivity in the cross section of the detector and multilayer conductive porous media with anisotropic conductive bonding can help expand the design flexibility for enhanced performance. Based on these findings, various tomographic tactile sensors for soft grippers, tangible input interfaces, flexible touch displays, and wearable electronics are demonstrated by using a conductive porous media.