Owing to the superior mechanical property and excellent sensitivity,
this proposed microfiber coupler sensor would have tremendous potential
applications in wearable devices for monitoring ultraweak physiological
signals, slight human motions and subtle environmental perturbations. By
using PDMS as an encapsulation material, this microfiber coupler strain
sensor had been developed to be a biocompatible, flexible and durable
device, which could be easily and firmly attached to the human skin with
comfortable wearability. As shown in Figure 3 a, this flexible
microfiber coupler sensor could be directly attached to the skin of
human face, neck, wrist, finger, and ankle etc., for real-timely
detecting the breath, pulse,
gesture, and speech. Breathing is one of the prime functions fulfilled
by human, and it can have considerable effects on the morphology and on
the craniofacial and cervical functions, and is also closely related to
some respiratory diseases. This flexible microfiber coupler strain
sensor was mounted on facial masks to monitor strain induced by
respiratory motions, where inhalation and exhalation would bring about
air pressure changes inside the mask and deform the mask. Three
different respiration modes were detected and discriminated by virtues
of the distinguishable response patterns as shown in Figure 3b, where
0.2 ΔCR and 38 times/min for deep breath, 0.07 ΔCR and 23 times/min for
normal breath, 0.02 ΔCR and 17 times/min for shallow breath,
respectively. By detecting the mask deformation, the respiration
frequency, breathing depth and various breathing styles could be sensed
and detected, which would be helpful to discover and diagnose some
respiratory diseases.
Arterial
pulse is a significant
physiological signal for the clinical diagnosis of cardiovascular
diseases. The arterial pulse is evaluated for the contour of the pulse
wave and its volume, rate, and rhythm, the intensity of arterial pulse
signal is often too weak to be palpated or detected, especially at the
fingertip and ankle sites. This flexible microfiber coupler strain
sensor was attached to different body’s sites, such as the neck, wrist,
fingertip and ankle. By virtues of high sensitivity and low detection
limit of this flexible strain sensor, the pulse waveforms at all body’s
sites were precisely detected and recorded as shown in Figure 3c. The
pulse waveform details could be captured and recovered without
distortion, for example, the
pulse signals at neck, wrist, and
finger exhibited three peak characteristics, and the ankle only had two
peaks, which was exact in agreement with the pulse signal
characteristics at body’s different sites\cite{Fang_2021}.
The weak motions of human body could be effectively monitored by this
flexible microfiber coupler sensor, which would have broad application
prospects in human-machine interaction and phonation rehabilitation
training. Firstly, this flexible microfiber coupler sensor was attached
on the wrist site for the gesture recognition demonstration, where the
bending of fingers would drive the wrist to produce weak movements. As
shown in Figure 3d, bending and straightening of different fingers could
be clearly recognized and distinguished. Then, this flexible microfiber
coupler sensor was attached on the neck to monitor the tiny epidermis
and muscle movements during speech for phonation recognition. As shown
in Figure 3e. this sensor captured distinguishable and repeatable signal
patterns when the volunteer spoke some alphabet letters, S-C-U-T. It
could be found that the three enlarged detail view of letter “T”
waveforms were nearly the same, which indicated that this flexible
sensor would be more powerful for in situ real-time monitoring based on
further pattern recognition technique.