On‐Skin Stimulation Devices for Haptic Feedback and Human–Machine Interfaces

Abstract

On‐skin electronics have been widely used in fields, such as wearable healthcare and human–machine interfaces due to their excellent performances and wearable comfort. Among them, on‐skin sensors for collecting signals have been greatly developed, while the stimulators that provide tactile feedback are difficult to achieve in terms of flexibility and stretchability due to their rather complicated structures. Achieving on‐skin stimulators with superior performances and outstanding wearability requires major advances in materials, fabrication, and structure design. The on‐skin stimulator needs to be soft with a lightweight and thin structure so that it can be laminated onto the skin with conformal contact for accurate feedback. Three stimulation modes, namely electrotactile, thermal, mechanotactile, and vibrotactile stimulation, are investigated. Among them, electrotactile stimulation is the characteristics of high resolution and quick response. Thermal stimulation can provide a unique heat sensation without crosstalk with other stimuli. Mechanotactile and vibrotactile stimulation can bring comfortable feedback to skin, showing great potential in wearable applications. This paper summarizes the working principles, materials, structures, and applications of these on‐skin stimulators, and compares their advantages with conventional rigid devices. At the end of this paper, the challenging issues and future prospects in this field are discussed.

Soft Sensors and Actuators for Wearable Human–Machine Interfaces

“…In addition, the electric shock delivered by these electrostimulators, which typically work in direct contact with the skin, can cause discomfort, pain, and even skin damage. 63 One potential solution is the development of self-powered electrostimulators that can generate their own electrical energy through user movement or other means. TENGs have emerged as a promising technology for self-powered electrostimulators, utilizing the contact and separation of materials with different electron affinities to generate electricity.…”

“…While the electrode designs of conventional electrostimulators have advanced to resemble the mechanical properties of skin, they still face limitations in terms of requiring rigid and bulky power supplies, which greatly limits device portability and user comport. In addition, the electric shock delivered by these electrostimulators, which typically work in direct contact with the skin, can cause discomfort, pain, and even skin damage . One potential solution is the development of self-powered electrostimulators that can generate their own electrical energy through user movement or other means.…”

“…Due to the increasing demand for more diversified experiences and sophisticated control in next generation HMIs, haptic human–machine interface (HHMI) based on physical/physiological actions, as well as tactile sensation and force feedback have recently received significant attention. ,,− Particularly, the use of touch sensation not only involves direct physical interaction but also evokes emotion, which can provide the intense physical and emotional experience in the application fields of robotics, metaverse, and user-interactive devices . As shown in Figure , the HHMI is composed of four sequential components: user input generation, sensor detection, system translation, and actuator feedback.…”

Soft Fiber/Textile Actuators: From Design Strategies to Diverse Applications

“…A wireless haptic feedback system in wearable applications were demonstrated by integrating a haptic actuator into the glove and working with another glove with a sensor array. Critical parameters of textile actuators, including the actuation mechanism, degrees of freedom, displacement magnitude, and bandwidth, are determinants of their efficacy in wearable devices and inform their design and development. , …”

“…Critical parameters of textile actuators, including the actuation mechanism, degrees of freedom, displacement magnitude, and bandwidth, are determinants of their efficacy in wearable devices and inform their design and development. 178,179 5.…”