IEEE Solid-States Circuits Magazine - Spring 2023 - 57

In terms of the safety of BCC and BCP
methods, the power level is well below
the IEEE standard.
and such RF waves have been already
coupled to our body. So far,
we have not utilized it-it just
shunts to the Earth ground through
the parasitic capacitance between
the body and the ground (CLKG) [5].
Figure 14(b) shows the spectrum of
the body-coupled RF energy (in blue)
compared to the air-coupled RF (in
gray, through a 1-m-long monopole
antenna), measured in an office environment.
It should be noted that,
of various RF/EM sources in such an
environment, the 50/60 Hz coupling
from the building's power network/
lighting and appliances dominates.
If we were to use an explicit antenna
to harvest the 50/60 Hz from
these " interferences, " the antenna size
would become unrealistically bulky.
In contrast, we can exploit the bodycoupled
characteristic as is [Figure
14(a)]. Using the same power
receiver as in BCP, we can harvest
microwatt-level power. [29] demonstrated
that we can power up and
operate a calculator from body-coupled
energy harvesting in an office
environment. To adapt to the large
load difference between BCP and
harvesting, we can introduce a dual-mode
buck-boost converter (DMBBC)
[31] so that the efficiency will
improve (Figure 13).
BANs and Safety
In terms of the safety of BCC and
BCP methods, the power level is
well below the IEEE standard. For
example, at 1.2-W power [29], the efield
across the human body will be
below 0.032 V/m, which is orders of
magnitude below the IEEE standard
(2.1 V/m under a controlled environment
and 0.701 V/m for the general
public) [29]. Even if we increase the
TX power by 10 times (for a greater
margin), the e-field across the body
is still well below the threshold. The
same can be said for the harvesting-even
without the body-coupled
energy harvesting, the body already
has the coupling to the environmental
EM wave (50/60 Hz, etc.), and
this is not considered a safety concern-the
body-coupled harvesting
shows a similar level of coupling.
Conclusion
We have viewed the BAN as an attractive
means for pervasive connectivity
and powering of nodes in/
around the human body. Up to now,
researchers have focused on communication
and powering methods
on/inside the body. With this in
mind, what are the remaining topics
yet to be explored, and where
are we heading? Looking forward,
one such topic is combining communication
and powering; having
both concurrently and seamlessly
would provide flexibility in forming
a BAN system. Another topic is
a heterogeneous BAN; once we have
the data collected by the on/insidethe-body
BAN technology, we would
like to send the data to a nearby
central node, such as a smartphone
or base station via off-body BAN.
For this, robust and seamless communication/powering
is also important,
and integrating the two
will lead to a true heterogeneous
BAN, opening the door to the " human
intranet " [2].
Acknowledgment
This work involved human subjects
or animals in its research. Approval
of all ethical and experimental
procedures and protocols was
granted by the National University
of Singapore's Institutional Review
Board under Application No. NUSIRB-2021-304,
and performed in line
with the Body-Area Network (BAN)
Transceiver Design for Communication
and Powering and Wearable
System declaration.
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