IEEE Solid-States Circuits Magazine - Fall 2020 - 45

Artificial Intelligence
In current practice, collecting biosignals from many patients for a certain amount of time faces multiple

0.4

Increasing
PO2

0.2
0

AFE Output (V)

0.6

0

25
50
Time (µs)

75

0.4

Increasing
PO2

0.2
0

100

0

25

50
75
Time (µs)

(a)

100

(b)

600

Data 1
Fit 1
Data 2
Fit 2

500
400
300

0
200
400
600
Oxygen Partial Pressure (mmHg)

Fall Time (µs)

70
Data 1
Fit 1
Data 2
Fit 2

60
50
40
30
20

0
200
400
600
Oxygen Partial Pressure (mmHg)

(c)

(d)

FIGURE 14:  The fluorescence-based O2 sensor response. Fluorescence decay transients for different O2 pressures (PO2) with (a) lower reflectance and (b) higher reflectance optical paths. The
(c) intensity and (d) lifetime measurements for different O2 concentrations for both cases [38].

75

Normal

70

Occlusion

Lifetime (t) [µs]

Past attempts at medical wearables/
implantables have been bulky, with
rigid PCBs embedded in silicon foam
or rubber housings [26], [50]. Medical
device designers should take advantage of new flexible PCB technology
and even flexible devices. Organic
devices, such as LEDs and PDs, have
been demonstrated to provide effective
FEs for medical sensors with improved
patient compliance [19], [28]. New
stretchable and flexible substrates will
also facilitate more comfortable and
reliable medical wearables [20]. One
of the significant problems is stability
with temperature and humidity, which
is mainly limited by the encapsulation
of the devices [19], [28]. Forming reliable connections between terminals
and flexible substrates is a significant
challenge and needs careful consideration [51]. Researchers at the Georgia Institute of Technology present
stretchable copper and gold traces and
flexible connectors that can interface
with traditional IC packages [46].
Truly flexible battery cells are an
emerging technology and not yet
widely available. There are small,
semirigid lithium polymer cells available, but they cannot withstand much
bending and movement. Additionally,
interfacing these batteries with a flexible substrate is a challenge, as with
most ridged components. Wireless
charging offers a possible solution

minimizes pulling and skin damage
through newly developed patch material that bonds to the skin using van
der Waals force. Microfluidic channels
further reduce the forces needed to
remove the patch [20].

0.6
AFE Output (V)

Next-Generation Materials

with stretchable printed antennas
and small, high-density capacitors
and compact power transmitters and
receivers [20], [21]. In addition to adhesives, materials, in general, that are
used to attach medical devices to the
body will play a key role in creating
comfortable and practical wearables/
implantables. Researchers at Northwestern University have presented a
stretchable and flexible substrate that

AFE Output (mV)

- edical devices are categorized as
m
class 1, 2, and 3 depending on the
amount of risk, with class 1 presenting the least danger. While it is
extremely important and necessary
to meet regulatory requirements for
safety and efficacy, designers should
keep in mind the basic needs of the
end user. The monitor should be easy
enough to use that it does not require
the intervention or interpretation
of medically trained personnel. It
should be comfortable to handle
and not cause any additional harm
and discomfort to the patient. Nextgeneration flexible electronics and
PCBs need to be explored to facilitate
more comfortable devices.

65
60
55
50
Normal

45
40
Ribbon
(a)

0

50

Occlusion
100
150
Sample Time (s)

200

(b)

FIGURE 15:  (a) The test setup for transcutaneous measurements. (b) Transcutaneous O2 measurement on the human body [22].

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IEEE Solid-States Circuits Magazine - Fall 2020

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