eeworldonline.com | designworldonline.com 4 • 2020 DESIGN WORLD — EE NETWORK 15There are still numerous challenges before printed batteries can
be widely commercialized. One problem is that currently there are only
a few printable active materials that can be used as inks. Additionally,
much work remains to be done in characterizing how battery inks behave
when patterned over top other inks. And though there has been a lot of
work done on the materials for the electrodes and electrolytes, current
collectors will likely need a similar amount of optimization.
Once the technology is ready, healthcare applications will likely
benefit greatly from super-thin 3D-printed batteries. Skin patches
using printed batteries are already commercial. Smart skin patches
use laminar batteries, often partially printed, combined with printed
electrode patterns to deliver drugs, cosmetics, and other chemicals
through the skin. Medical diagnostic devices will likely benefit as well.
Wireless sensor/network applications will also benefit. Here, the
trend is to combine energy harvesting with thin batteries to keep the
package size down. Similarly, new small batteries will be a boon to
battery-assisted passive RFID although coin-cells are the main power
sources now. Smart card apps are another application wherein several
thin-film battery technologies have been optimized for lamination into
cards, though the prices are probably too high for disposable uses.
High peak currents can reduce battery capacity and lifespan. High
in-rush currents can arise in dc-dc converters which tend to incorporate
a high amount of capacitance on the power input to avoid voltage drops
on the supply rails. When power is applied initially, the charging of these
capacitors can result in an in-rush current that can exceed the nominal
load current. If left unaddressed, this high current can cause the voltage
rails to fall out of regulation, perhaps making the system unstable or
putting it in an unpredictable state. There are various ways of limiting
in-rush current. For example, some BLE devices incorporate built-in
current limiters.
All in all, the review cycles for medical devices are justifiably long,
and it can be several years before they can hit the mainstream. But
these devices have game-changing potential for patient care, and it all
starts with finally cracking these longstanding design challenges.MEDICAL IoT
References
Dialog Semiconductor, http://www.dialog-semiconductor.comOne example of a platform used for
devising connected medical devices
is Dialog Semiconductor’s Smartbond
Bluetooth low energy 5.1 system-on-a-chip
DA14531, visible on the daughterboard
plugged into the dev kit motherboard.
The DA14531 is a small, low-power SoC for
beacon and tracker devices and is designed
to work with any type of (disposable)
battery, 3-V coin cell or 1.5-V alkaline
button cells, 1.4-V zinc-air cells or even
printed batteries. The DA14531 supports
dc-dc peak current control, allowing
operation with low capacity (e.g. <20 mAh)
batteries with high internal resistance. The
SoC supports 2.5-dBm output power and a
96.5-dBm link budget. Sleep current can be
as low as 700 nA while using a hibernation
mode with external wake up trigger. The
DA14531finds use in (disposable) smart
labels, beacons or trackers.