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applied to the treatment of scoliosis,
by measuring how often and how
tightly braces are being worn by
patients, in a bid to overcome the
barriers that can impede progress.
A Body in Motion
As MEMS are manufactured
via the same techniques used
in conventional semiconductor
production,
some
integrated
device manufacturers are well
positioned to develop and supply
MEMS sensors. A presentation at
the Medical MEMS and Sensors
Conference 2017 (Santa Clara,
November, 2017) given be Analog
Devices’ Engineering Manager of
High Performance Sensors, Mark
da Silva PhD, entitled ‘Ultra Low
Power Implantable Inertial MEMS
Sensors’, shows the direction some
semiconductor manufacturers are
moving. Implantable inertial MEMS
sensors could be used to monitor
the movement of limbs in real-time,
while similar sensors implanted in
the back could be used for spinal
cord stimulation for the treatment
of pain.
Ultra
low
power
MEMS
accelerometers, such as the ADX362
series from Analog Devices, are
already available and being used in a
wide array of applications, including
hearing aids and home healthcare.
This 3-axis accelerometer can
measure both dynamic and static
acceleration (for detecting shock,
for example) and consumes just
10nA in sleep mode and as little as
270nA when in a motion triggered
mode. Because it doesn’t use under-
sampling, as some MEMS sensors
do, the sensor’s full bandwidth is
sampled for both 8-bit and 12-bit
output resolutions. This can be as
low as 1mg/LSB at a ±2 g range
and the family has a standard noise
level of 500μg/√Hz, which can
be further reduced to 175μg/√Hz
through a lower noise mode. As
shown in Figure 1, the ADXL362 also
integrates antialiasing filters and a
temperature sensor, as well as an
analogue-to-digital converter (ADC),
SPI interface and digital logic.
All of the features of the ADXL362
can be evaluated using the Arduino-
compatible
EVAL-ADXL362-ARDZ
shield, which features an LCD for
displaying the tilt and temperature
data provided by the sensor. The
board is also compatible with
Analog Devices’ EVAL-ADICUP360
development board, which includes
both Arduino and Pmod interfaces.
Taking sensor integration to a higher
level, the ICM-20948 from TDK
InvenSense isa9-axismotiontracking
device which integrates a 3-axis
gyroscope, 3-axis accelerometer
and 3-axis magnetometer with a
digital motion processor in a multi-
chip module measuring just 3mm x
3mm x 1mm. Each sensor features a
self-test mode, while the integrated
motion processor handles calibration
as well as the motion processing
algorithms, reducing the workload
on the host processor.
Under Pressure
As mentioned above, one of the
biggest applications for MEMS in
medical applications is pressure
sensors. They can be used in
ventilators to monitor respiration
rates, in dialysis equipment to
measure the inlet and outlet blood
pressure for flow regulation, and
even in eye surgery. MEMS pressure
sensors can be used for the detection
of oxygen, carbon dioxide, calcium,
potassium and glucose in blood, as
Sensors
Special Edition
Figure 1:
The ADXL362 from Analog Devices is an ultra-low power 3-axis ac-
celerometer ideal for healthcare applications
56 l New-Tech Magazine Europe