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P. Dwivedi and M. K. Singha
Flexible wearable sensors and devices are also known as “electronics skin” or
“E-skin”. E-skins are used for continuous monitoring of human health in real time.
These e-skins are in general having very good flexibility, transparency, stretchability
and stability [9–11]. Since wearable sensors are in contact with skin, therefore these
devices/sensors must not be toxic. This type of sensor must have high flexibility and
they should not create any discomfortability to the human skin. Few examples of the
flexible sensors used in modern days are tactile pressure sensor, strain, temperature
sensor and sweat sensors. There are two types of wearable sensors: physical sensors
and chemical sensors.
13.2.1 Flexible Wearable Physical Sensors
Flexible wearable physical sensors are used to measure the physical activities and
detect any abnormalities in the body like temperature, heart rate, etc. [12]. These
types of sensors work on the stimulus of the body by changing them into electrical
signals. Various nanostructures are engineered or functional nanomaterials are used to
fabricate these types of devices. Mostly piezoresistivity, piezoelectricity, capacitance
and strain mechanisms are used to measure the signals [12, 13]. Strain sensors are
among the pioneers for measuring any deformation due to external stimuli in the
body. For example, if the heart rate increases, then signal from the strain/pressure
sensor also varies accordingly. But for continuous measurement of patients, it needs
to keep the tactile information. Few research groups have included memory function
in the wearable strain sensors [14–16]. According to their findings they have shown
that this data can be preserved for as little as one week to six months of time [14,
15]. Metal oxide thin films are used for making the flexible Random-access memory
(RAM) structures. Body temperature is an important parameter which describes
whether the human being is healthy or sick. If there is any increase in temperature
from normal human body temperature then it is referred to as fever. Traditionally
thermometers are used worldwide to measure the body temperature. As earlier we
have mentioned, this process of measuring temperature using a thermometer is not
continuous. Due to pandemic situations like COVID-19, or elderly people need to
measure the temperature continuously for their safety purposes. Pulse oximeter is
recently used to know the amount of oxygen in blood for COVID-19 infected person.
Traditionally it is small devices packaged in a hard plastic chamber where a soft part
of the skin like fingers is placed and then by the principle of optics, it measures the
oxygen in the blood levels. Recently a Japanese research group has used organic
polymer-based light-emitting diodes (LEDs) and organic photodetector to fabricate
the wearable pulse oximeter [17, 18].
P. Dwivedi and M. K. Singha
Flexible wearable sensors and devices are also known as “electronics skin” or
“E-skin”. E-skins are used for continuous monitoring of human health in real time.
These e-skins are in general having very good flexibility, transparency, stretchability
and stability [9–11]. Since wearable sensors are in contact with skin, therefore these
devices/sensors must not be toxic. This type of sensor must have high flexibility and
they should not create any discomfortability to the human skin. Few examples of the
flexible sensors used in modern days are tactile pressure sensor, strain, temperature
sensor and sweat sensors. There are two types of wearable sensors: physical sensors
and chemical sensors.
13.2.1 Flexible Wearable Physical Sensors
Flexible wearable physical sensors are used to measure the physical activities and
detect any abnormalities in the body like temperature, heart rate, etc. [12]. These
types of sensors work on the stimulus of the body by changing them into electrical
signals. Various nanostructures are engineered or functional nanomaterials are used to
fabricate these types of devices. Mostly piezoresistivity, piezoelectricity, capacitance
and strain mechanisms are used to measure the signals [12, 13]. Strain sensors are
among the pioneers for measuring any deformation due to external stimuli in the
body. For example, if the heart rate increases, then signal from the strain/pressure
sensor also varies accordingly. But for continuous measurement of patients, it needs
to keep the tactile information. Few research groups have included memory function
in the wearable strain sensors [14–16]. According to their findings they have shown
that this data can be preserved for as little as one week to six months of time [14,
15]. Metal oxide thin films are used for making the flexible Random-access memory
(RAM) structures. Body temperature is an important parameter which describes
whether the human being is healthy or sick. If there is any increase in temperature
from normal human body temperature then it is referred to as fever. Traditionally
thermometers are used worldwide to measure the body temperature. As earlier we
have mentioned, this process of measuring temperature using a thermometer is not
continuous. Due to pandemic situations like COVID-19, or elderly people need to
measure the temperature continuously for their safety purposes. Pulse oximeter is
recently used to know the amount of oxygen in blood for COVID-19 infected person.
Traditionally it is small devices packaged in a hard plastic chamber where a soft part
of the skin like fingers is placed and then by the principle of optics, it measures the
oxygen in the blood levels. Recently a Japanese research group has used organic
polymer-based light-emitting diodes (LEDs) and organic photodetector to fabricate
the wearable pulse oximeter [17, 18].