Instrumentation & Measurement Magazine 24-5 - 47

Fig. 6. Experimental setup and results for multiplexed POF smart textile.
spatial-parameters of the gait such as the stride/step length,
cadence and time of double support (i.e., the time at which
both feet are touching the ground during the gait). The system
can also estimate the GRF pattern during gait that can also indicate
the times of stance and swing phases. Fig. 5 also shows
the results reported for the smart carpet, where the system was
characterized by placing calibrated weights at predefined positions
on the carpet, and the system shows the capability of
detecting the force applied in different positions.
Subsequently, tests during gait are performed, where a
volunteer walks on the whole extent of the carpet and the
step length and GRF pattern are shown. It is noticeable that
the GRF pattern can be used to detect gait phases such as the
stance and swing phases [21]. Therefore, the embedment of
the multiplexed POF system in a textile resulted in a portable
system for gait analysis that can be employed outside a
clinical environment due to its portability and capability of
remote monitoring. These features enable its use in home activity
monitoring and remote monitoring of patients; such
technologies are well aligned with the requirements of Healthcare
4.0. Compared with commercially available technologies
such as piezoelectric ones presented in [22], the POF-smart carpet
does not employ additional cameras (or vision systems)
August 2021
as the one presented in [22], which is a high cost component
with the necessity for constant calibrations and careful positioning.
In addition, POF-smart carpet has higher scalability,
since the commercial systems using electronic technologies
are generally limited to a few steps with maximum lengths below
10 meters, whereas POFs can transmit optical signals to
several meters (about 100 m for optical signals in the visible
spectrum). The optical signal transmission capability of POF
leads to the possibility of developing POF-embedded smart
carpet with longer lengths and even integrating it in the area
of a whole room.
The evaluation of the multiplexed POF system embedded
in a wearable smart textile was evaluated in [10], where
the POF with the flexible LED belt system were embedded in
neoprene textile fabric. Such textile can be incorporated into
clothing or can be extended to be used as smart clothing. The
textile is shown in Fig. 6, where highly flexible POFs were
used so they did not influence the flexibility of the textile. In
addition, the system also has a low weight and low energy
consumption (an autonomy of 10 hours can be achieved if
commercially available 10000 mAh power banks are used).
The data from the 3-sensor array can be stored in a SD card or
sent wirelessly via Bluetooth connection, with an acquisition
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