14 DESIGN WORLD — EE NETWORK 4 • 2020 eeworldonline.com | designworldonline.com
Super-small radio SoCs are being paired with innovative battery
technologies to bring inexpensive medical electronics online.The Internet of Things (IoT) has disrupted many industries
in short order. However, when it comes to adopting the IoT, themedical and pharmaceutical space has largely been held back.It’s not entirely surprising. The high level of regulation in the
medical fi eld and the (literal) life-or- death stakes of introducing new
technologies for patient care understandable lengthen development
cycles for new medical devices. But engineering roadblocks around
power, size and cost have been the biggest factors in making
widespread development and adoption prohibitive for disposable
connected medical devices.
There is a path forward, though, for developers who want to
devise IoT-based medical designs that meet the necessary size,
power and cost requirements.
One of the major roadblocks to developing disposable
connected medical devices is cost. It can be a prohibitively
expensive venture to create designs in a small form factor that
integrate a system-on-chip (SoC) and the necessary external
components for, say, measuring blood pressure or glucose levels or
inhaling medicine. That cost is driven up by the need for components
like two crystals rather than a single low-power version; four-layer
PCBs rather than cheaper and simpler two-layer boards; and costly
batteries. As long as the bill of materials (BOM) remains high and
the product isn’t miniaturized, mass market adoption of connected
medical devices will slow to a crawl.
In addition to BOM cost, medical designers often must contend
with power consumption problems. Medical disposable products
must last a long time. Shelf lives of 18 months up to several years are
not unusual, followed with a relatively short active life measured in
weeks to months. During its time on the shelf, battery capacity can
drop from both self-discharge and leakage current to the application
itself. Once active life starts, the battery may not have enough
capacity available to support it. Clearly, both patients and doctors
need IoT medical devices to be dependable – both to treat the
patient and also to provide the data necessary to ensure dosages
and tests happen correctly.Finally, there’s the disposability issue. The nature of disposable
medical devices is that they will only be used for anywhere between
14 days and two months. Given that short lifetime and their cost,
insurance companies are naturally reluctant to support them.
The answer to all these challenges lies in the battery and
specifi cally, in implementing disposable silver-oxide or printed
batteries. Recently both high-energy thin fi lm lithium batteries and
printed rechargeable zinc batteries have become commercially
available. But there are questions about whether or not these
technologies are ready for mass deployment.
The fabrication of batteries via 3D printing has several
advantages over conventional battery fabrication technologies. For
one thing, battery components may be printed directly on the PCB
holding the rest of the electronics. Thus there is the possibility of
eliminating assembly and packaging steps that discrete batteries
require. Additionally, the printing process can also conceivably
fabricate complex battery architectures that may be impractical via
other means. Printing methods can adjust the shape and thickness of
the electrodes and print solid-state electrolyte that is stable and safe.
Printed zinc batteries look promising. One such device from
Impact Energy uses a High Conductivity Polymer Electrolyte (HCPE)
that is stable, rechargeable, and does not need a sealed container.
Because the chemistry is based on zinc rather than lithium, it avoids
the safety issues associated with many lithium technologies In
additoin, lithium titanate (LTO) and lithium iron phosphate (LFP) are
commonly used anode and cathode materials in 3D-printed batteries,
but carbon nanomaterials are promising for use as electrodes as
well. Carbon nanotubes and carbon nanofi bers are widely used in
printing inks because of their high mechanical strength, high chemical
stability, large specifi c surface area, and excellent electrical and
thermal properties.
It also looks as though printed battery electrolytes will help
reduce fabrication costs as well. The electrolyte serves as catalyst
by promoting the movement of ions from the cathode to the anode
on charge and in reverse on discharge. Electrolyte material plays a
key role in electrochemical performance, cycle life, and safety of the
battery.INTERNET OF THINGS HANDBOOK
Developing connected
medical devices for the IoT
Adrie Van Meijeren, Low Power Connectivity • Dialog Semiconductor