## 4 Current Issues and Challenges of Realising the Tactile Internet
### Challenges Related to Haptic Devices
#### 4.11.1.1. _Haptic Sensors_  
Haptic sensors are useful for detecting pressure for a delicate body, body control, and for the worst-case control scenario of <10 kPa, 10 kPa to 100 kPa and 325 kPa, recognisable to humans [84; 85]. There are different methods to measure pressure. The most famous methods are resistive and capacitive. In the resistive method, the material used is pressure sensitive and is used to create a sensor [86]. In the capacity method [84], the capacitance difference is noted using a dielectric material between two conducting plates. Then the difference in capacitance is then converted and digitised to measure pressure. The dielectric material used for capacitive haptic sensors is the elastomer polydimethylsiloxane (PDMS), famously called silicone. PDMS features include (i) excellent dielectric constant, (ii) low young's modulus, and (iii) very flexible placement of sensors. However, there are some different non-idealities in PDMS pressure strain sensors, thus making the structure complicated. The non-idealities include creep unwinding, hysteresis, and so on. Thus, the need to design the capacitive weight sensor is taken into account by considering all non-idealities of PDMS. Another vital parameter to consider in building the capacitive sensor is sensitivity. Sensitivity comes into play whenever there is a change in pressure. When the sensor's sensitivity is high, the sensing process, conversion time and the sensor's estimation scope are reduced because of saturation effects. Therefore, the trade-off is if the blend of the high and low sensitive sensor is considered, the fabrication process becomes more tedious and thus increases its fabrication cost. In addition, PDMS can also be modelled to adjust the sensitivity range of the sensor. Nevertheless, the model will also add complexity and cost to the fabrication. When it comes to designing the haptic framework, a commonly neglected factor in the literature is the placement of sensors. There are two ways in which haptic sensors can be fabricated: (1) single-element sensor and (2) multiple-element sensor arrays [87; 88; 89; 90; 91]. However, single-element and array sensors are commonly expensive. Therefore, these sensors must be placed in the detection zone to increase the coverage radius with the correct placement techniques. The increase in array size is directly proportional to the scanning rate of the number of sensors. Thus, the overall consumption of power and the time required for sensing are incremented. There will always be a trade-off between spatial resolution and the coverage area. Subsequently, the chances of collaborative design of the single-element and array sensors are more likely achievable. However, these designs could make the placement of sensors tedious. There is an advancement issue to investigate [90] about the conceivable arrangement to have various sensing circuit-handling sensors in different areas of the array sensor. Hence, finishing up construction of a haptic sensor for applications of the TI is not a straightforward process. There are many challenges that need to be resolved, including scanning time, placement of the sensors, spatial resolution and sensitivity. might result in a limitation or complete prevention of the movement. There is another dimension for the perception of the weight of the object [100]. The recent implementation of glove-based haptic displays includes kinaesthetic feedback often restricted by the region of working space. This happens due to the glove being linked to the user's arm, or the entire system being grounded, e.g., in [100]. In addition, ungrounded trails are carried out with a glove-based haptic display where the system algorithm makes gloves too heavy for further testing. Thus, this process is more time-consuming. From the examination discussed above, there is no fixed or a total solution for kinaesthetic feedback yet.