Tech Briefs Magazine - June 2022 - Sensor-20

Figure 5 shows the 3D-printed inhaler
clip-on containing the Sensirion flow
sensor SDP3x as well as a Bluetooth low
energy communications chip and a battery
power source. The inhaler housing
has not been altered.
The Bernoulli/Venturi effect explains
that the acceleration of the air flow entering
the inhaler caused by the patient
inhaling creates a negative pressure at
10
20
30
40
50
60
70
80
020
10
30
Time (days)
Figure 4. Peak inspired airflow (PIF), inhaled volume (IV) and airway resistance (RAW) monitored over
time, providing valuable feedback to the healthcare professional and the patient. (Image: Sensirion AG)
40
50
60
the inhaler top opening, around the cannister
and the opening of the attached
clip-on. The magnitude of the negative
pressure is directly related to the magnitude
of the flow rate of the air flow
through the inhaler to the patient and is
measured by the flow-sensor.
A more graphic way of understanding
the principal is to consider the flow
setup to be a by-pass main-pass system
PIF
BT
Beginning of
treatment
IVC
RAW
Int
Interruption of
treatment
1
2
3
4
5
6
7
8
(See Figure 6). As the patient inhales,
the negative pressure around the inhaler
opening draws a small amount of
clean ambient air through the by-pass
path of the sensor and into the mainpass
of the inhaler. By measuring the
by-pass airflow and knowing the by-pass/
main-pass ratio, which is provided by the
inhaler/clip-on geometry, the total
amount of airflow to the patient can be
determined.
A MEMS-Based Flow Sensor
There are many different methods of
measuring gas flow: mechanical volumetric,
float-type, differential pressure,
ultrasonic, Coriolis, magnetic inductive,
and thermal flow metering, to
name but a few. Metering techniques
without contact between gas and sensor
require relatively expensive technology
and are thus out of the question
for many applications. In the classic
differential pressure method, hysteresis
effects and membrane fatigue can
lead to drift problems and a lack of zero-point
accuracy as well as low flow
sensitivity because the mechanical deflection
of a sensor membrane over an
orifice is used to gauge the pressure
drop.
Sensirion SDP
air flow
inhaler
Measuring techniques based on thermal
principles are therefore a good
solution. In the simplest of these - the
hot-wire anemometer - gas flow is determined
via the rate of cooling of an
electrically heated wire with a temperature-dependent
resistance. Advanced
methods use a heating element and
two temperature sensors, which measure
the transport of heat through the
gas. Sensirion refers to the term " microthermal
flow sensors " because in
the MEMS-based flow chip solution
utilized in their SDP3x flow sensor series,
the sensor components are integrated
into a millimeter-scale silicon
microchip.
The calibrated inhaler airflow shows
excellent agreement in a lab setup
against a calibrated spirometer syringe
or against an external flow reference.
Outlook for Flow Measurement in
Smart Inhalers
Adding a diagnostic unit to the drug
Figure 6. Visualization of the air flows as a by-pass main-pass system. (Image: Sensirion AG)
20
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delivery device that the patient is already
familiar with is a powerful tool in
asthma and COPD disease management.
Improper inhalation technique
Sensor Technology, June 2022
ST Applications 0622_1.indd 20
Cov
ToC
5/18/22 2:14 PM
PIF / IVC
RAW
http://www.techbriefs.com http://info.hotims.com/82322-850

Tech Briefs Magazine - June 2022

Table of Contents for the Digital Edition of Tech Briefs Magazine - June 2022

Tech Briefs Magazine - June 2022 - Intro
Tech Briefs Magazine - June 2022 - Sponsor
Tech Briefs Magazine - June 2022 - Band1
Tech Briefs Magazine - June 2022 - Band2
Tech Briefs Magazine - June 2022 - Cov1
Tech Briefs Magazine - June 2022 - Cov2
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Tech Briefs Magazine - June 2022 - Cov3
Tech Briefs Magazine - June 2022 - Cov4
Tech Briefs Magazine - June 2022 - MD-Cov1
Tech Briefs Magazine - June 2022 - MD-Cov2
Tech Briefs Magazine - June 2022 - MD-1
Tech Briefs Magazine - June 2022 - MD-2
Tech Briefs Magazine - June 2022 - MD-3
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Tech Briefs Magazine - June 2022 - MD-24
Tech Briefs Magazine - June 2022 - MD-Cov3
Tech Briefs Magazine - June 2022 - MD-Cov4
Tech Briefs Magazine - June 2022 - Sensor-Cov1
Tech Briefs Magazine - June 2022 - Sensor-Cov2
Tech Briefs Magazine - June 2022 - Sensor-1
Tech Briefs Magazine - June 2022 - Sensor-2
Tech Briefs Magazine - June 2022 - Sensor-3
Tech Briefs Magazine - June 2022 - Sensor-4
Tech Briefs Magazine - June 2022 - Sensor-5
Tech Briefs Magazine - June 2022 - Sensor-6
Tech Briefs Magazine - June 2022 - Sensor-7
Tech Briefs Magazine - June 2022 - Sensor-8
Tech Briefs Magazine - June 2022 - Sensor-9
Tech Briefs Magazine - June 2022 - Sensor-10
Tech Briefs Magazine - June 2022 - Sensor-11
Tech Briefs Magazine - June 2022 - Sensor-12
Tech Briefs Magazine - June 2022 - Sensor-13
Tech Briefs Magazine - June 2022 - Sensor-14
Tech Briefs Magazine - June 2022 - Sensor-15
Tech Briefs Magazine - June 2022 - Sensor-16
Tech Briefs Magazine - June 2022 - Sensor-17
Tech Briefs Magazine - June 2022 - Sensor-18
Tech Briefs Magazine - June 2022 - Sensor-19
Tech Briefs Magazine - June 2022 - Sensor-20
Tech Briefs Magazine - June 2022 - Sensor-21
Tech Briefs Magazine - June 2022 - Sensor-22
Tech Briefs Magazine - June 2022 - Sensor-23
Tech Briefs Magazine - June 2022 - Sensor-24
Tech Briefs Magazine - June 2022 - Sensor-Cov3
Tech Briefs Magazine - June 2022 - Sensor-Cov4
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