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Wei et al. Soft Sci 2023;3:17 https://dx.doi.org/10.20517/ss.2023.09 Page 9 of 38

MULTIMODAL SENSING
Functional fibers with stimulus-response capabilities are prepared through advanced fiber fabrication
techniques, and then multiple functional fibers are integrated into electronic textiles using textile-forming
methods to achieve multimodal sensing functions. Electronic textiles manufactured by textile-forming
methods have a vertical cross structure, a loop structure, and a non-woven fabric structure, which can
improve the sensing performance of the device. In addition, electronic textiles have the advantages of
softness and large areas, facilitating the integration of multiple sensing mechanisms to achieve multimodal
sensing. In this section, we focus on the multimodal sensing capabilities of electronic textiles, including
physical, physiological, chemical, and hybrid signals.

At present, researchers have investigated multiple ways of converting stimuli information into electrical
signals, and Figure 4 depicts six types of common sensing mechanisms. The capacitance sensing mechanism
is the use of the capacitance variations of dielectric materials between conductive electrodes to characterize
stimulus information [112-114] . Piezoresistive sensing mechanism refers to the change in the resistance of the
device under external mechanical stimuli [115-117] . The piezoelectric sensing mechanism relies on polarization
phenomena inside the material to represent stimulus information in the form of electricity generation [118-120] .
The triboelectric sensing mechanism uses contact electrification and electrostatic induction coupling effects
to convert mechanical stimuli into electrical output [34,121,122] . The electrochemical sensing mechanism is a
method to convert chemical stimuli signals into electrical signals via chemical reactions [123-125] .
Electromagnetism is a sensing mechanism that converts magnetic signals into electrical signals [126-128] .

Physical signal sensing
Sensors based on electronic textiles have been widely used to detect various physical signals. Physical signals
are converted into detectable electrical signals through various methods, including the triboelectric
[130]
[129]
effect , the piezoelectric effect , the thermal resistance effect , etc., to detect physical signals, such as
[131]
pressure [132-134] , strain [135,136] , temperature , humidity [138-140] , and more. Nowadays, the detection of electronic
[137]
textiles with a single signal can no longer meet the needs of accurate monitoring and advanced applications.
Therefore, people began to study multimodal electronic textiles that can simultaneously detect two or more
physical signals.
Multimodal electronic textiles for physical signals can be divided into two categories. One is to detect
different manifestations of the same type of signals (such as pressure and strain [141,142] ), and the other is to
detect different types of signals (such as temperature and strain ). According to the designed device
[143]
structure and sensing mechanism, it is very significant to utilize different methods to measure the same
physical signal. For example, we can choose methods such as triboelectric, piezoelectric, capacitive, and
piezoresistive effects to measure pressure and strain signals. We can also choose thermal resistance and
piezoresistance effect methods to measure temperature and strain signals. Triboelectric and piezoelectric
effects have the advantage of fast response time based on the acquisition and analysis of the output transient
voltage signal for dynamic information detection. For capacitance, piezoresistive and thermal resistance
effects have the advantage of high sensitivity and wide response range based on the acquisition and analysis
of continuous capacitance or resistance signals for static information detection.

TENG not only can convert mechanical signals into electrical signals when triboelectric fiber materials
contact and separate but also has the characteristics of being self-powered, which is a good choice for
mechanical sensors [63,144] . As shown in Figure 5A, the pressure-strain multimodal electronic fabric combined
with the triboelectric nanogenerator is presented . Cotton yarn and PA composite yarn are used as positive
[68]
and negative triboelectric materials, respectively, wherein PA yarn coated with high-conductivity silver is