## 5 Survey of Sensing Systems for Haptic Interface
As a result, SMA (shape memory alloys) actuators on a wristband worn by the user's remaining limb begin to softly compress their forearm ([PERSON] et al., 2018). The B: Ionic glove contains electro-fluidic sensor pads beneath each fingertip carrying a conducting liquid, a fluidic control system, and a vibratory elastic band applied to the forearm. When the pad is pushed, the conductive liquid is forced through silicone channels closing a couple of contacts. The authors also created a wearable tactile device that stimulates the user's upper limb mechanically (Figure 16). The squeeze armband shown in ([PERSON] et al., 2018) inspired the design of the tactile armband used in this work. [PERSON] et al. developed SoftMatter Computer (SMC) (SMC) ([PERSON] et al., 2018); it was manufactured in silicone and formed into a 3D-printed mold, employing an ionic-conductive medium represented by saltwater, which is cheap and non-toxic. Five channels within the SMC allow silicone tubes to fit into the device. Each channel contains two holes to insert copper contacts with an applied AC voltage for preventing the saltwater from electrolyzing. The armband can alleviate phantom limb discomfort and improve embodiment, promoting prosthetic device acceptance and lowering high rejection rates. The armband has the potential for more sophisticated computing and can rely on a variety of pressure points and strengths applied by prosthetic fingertips to the user's skin. Figure 15: Schematic of B: Ionic glove, constituted by pressure pads, which contain conductive fluid applied to the prosthesis’ fingertip, a battery-powered fluidic controller, and an armband equipped with SMA actuators, worn by the user’s remaining limb to softly squeeze their arm ([PERSON] et al., 2018). Tremors, a common movement disease, can have a negative impact on a person's life. There is a requirement for a biomechanical solution due to the many limitations of the present therapeutic techniques. Neurodegenerative illnesses such as Parkinson's, neurological disorders such as multiple sclerosis, brain traumas, or drug side effects have been reported to produce tremors. [122]. However, the tremor-reduction systems now on the market have several drawbacks. Therefore, it is clear that low-weight, less imposing orthoses are required to control hand tremors. It is possible to apply the jamming mechanism, suggested by [PERSON] et al. in [123], to develop such products for hand tremor inhibition. To determine the nature and features of tremor movements, an initial tremor motion evaluation was carried out [124]. As a result, the layer jamming mechanism was suggested as the stiffening approach for tremor reduction devices [125]. Figure 17 illustrates the damping process of this tremor reduction device integrated into a glove. Negative pressure triggers the layer jamming layer, consisting of a pile of paper sheets within a closed polyethylene housing. When negative pressure is applied to this housing, the air between the sheets is removed, increasing the frictional forces between them, withstanding flexion. The standard HMI solutions are self-occluding and unintuitive, as in vision- and voice-based systems. To achieve a seamless and more user-friendly HMI, e-skin technology can be applied. Creating an HMI that can enable extensive bidirectional user interaction  
Figure 16: Haptic armband constituted of five re-entrant hexagonal components obtained by 3D printing. The device is actuated by twisted SMA wires, and the Kapton tape serves as a heat-resistant barrier [119]. Figure 17: Schematic representation of the jamming elements’ positioning on the tremor suppression glove [125]. while still conforming to the human skin is difficult. As mentioned, an e-skin should include four crucial elements to function as an interactive two-way HMI: (1) touch sensors; (2) vibratory actuators; (3) strain sensors; and (4) other specific and sophisticated capabilities for healthcare applications, etc.