Page 12 - Read Online

Page 10 of 26 Jin et al. Soft Sci 2023;3:8 https://dx.doi.org/10.20517/ss.2022.34

Figure 6. Multi-modal tactile sensors: (A) centralized ionic receptor that can distinguish temperature and strain (reproduced with
[111]
permission . Copyright 2020, The American Association for the Advancement of Science); (B) four-layer stacked multifunctional
[116]
sensor capable of sensing temperature, pressure, and proximity (reproduced with permission . Copyright 2020, Springer Nature); (C)
[119]
distributed temperature and strain sensor array (reproduced with permission . Copyright 2014, American Chemical Society); (D)
[122]
hybrid electronic skin matrix with stacked and distributed layout (reproduced with permission . Copyright 2018, Springer Nature).
Centralized sensors: Centralized sensors can use one sensing unit to distinguish multi-modal
information [109,110] . As shown in Figure 6A, You et al. presented an ionic receptor with a simple electrode-
electrolyte-electrode structure . Through the ion relaxation dynamics analysis, temperature and strain can
[111]
be simultaneously detected without signal interference. Some similar works differentiate mechanical stimuli
such as pressure, bending, shearing, or stretching by analyzing the characteristics of the signals [112,113] . Other
centralized sensors collect mutually independent signals from different measuring elements stacked
together [114,115] . Seok et al. developed a four-layer multifunctional sensor capable of simultaneous sensing of
temperature, pressure, and proximity, and the outputs of each element are measured independently, as
shown in Figure 6B . The centralized sensors are generally used in single-point sensing for dexterous
[116]
manipulation and grasping due to their compact structure. But advanced decoupling algorithms need to be
[117]
considered to overcome the effects of signal crosstalk .
Distributed sensors: Distributed sensors utilize the planar sensing array to form a multi-modal
measurement network. In general, the sensing units are designed with different structures to measure
various tactile stimuli respectively . Figure 6C illustrates the distributed multi-modal sensor array
[118]
reported by Harada et al., in which the sensing elements of strain and temperature are distributed in
different areas and work independently . Besides, elements with identical structures are usually assembled
[119]
to decouple normal and shear forces [60,120] . In contrast to the centralized one, the distributed multi-modal
sensors are more suitable for electronic skins, which can cover the entire robotic body to create large-area
interaction networks. The crosstalk is reduced due to the intrinsic isolated arrangement of sensing elements,
while it is necessary to apply a high-frequency signal acquisition circuit to cope with abundant sensing
units.

Hybrid sensors: Hybrid sensor combines the stacked structure and distributed arrays to measure multi-
[121]
modal tactile signals . Kim et al. developed an ultrathin strain, pressure, and temperature sensing array