Active vs Passive sensing: Is one better than the other?
The original article published on 15.11.2021, we updated it on
02.08.2023 with new information for better overview of the topic.
Defining Active and passive sensors
First, to simply define the difference between active and passive sensing, we
need to clarify the general rule that applies to the sensors of both types:
passive sensors do not need an external power connection,
neither do they contribute anything to provide measurements, whereas in the case
of active sensors it is quite the opposite – these require a
source of power to operate and act alongside some sort of transducers that will
create a stimul to be detected.
Both active and passive sensors are widely used in
remote sensing technologies, these are also famous for surviving unusually harsh
environments. Sensors can also be used in harsh environments and places that are
inaccessible to people.
To better understand these sensors, we will go through some types, operating
principles and general use cases of these.
Generally, active sensors emit energy (i.e LIDAR, RADAR,
InfraRed. etc.), and the distance of reflection from that energy (the
point where the energy returns) are essentially the appropriate measurements. Not all passive sensors create resistor
change, however, there are also the ones that have active components
generating voltage, frequency changes, voltage changes, pulse width
Examples would be:
Hall effect sensors;
The common issue with these is that there is almost always a need for an
extra el. circuit to create the necessary energy.
Active sensors commonly used in manufacturing and networking environments,
(monitoring of data centers, industrial machinery, etc.). Examples of
technologies that are based on active sensors are for example LiDAR, X-RAYs and others, however
one of the more interesting and widely used, however not as celebrated one would
be the Air Pressure
These are practically pressure sensors that generate electrical signals which
are proportional to the pressure. Some of the more common types are gauge,
vacuum, atmospheric pressure sensors.
These measure different variables in terms of the pressure sensing:
Absolute (zero) pressure: Also known as absolute vacuum. This is essentially a negative
gauge pressure. The sensors of this variable measure the pressure in comparison
Gauge pressure: these sensors on the other hand provide
pressure difference between the measured, and ambient pressures.
Differential pressure: is a bit unlike gauge or absolute
pressures, however, it can basically be defined as the difference between two
Atmospheric pressure: is produced by the atmosphere
surrounding the earth (up to altitude ~ 480km) Its value at sea level is
Similarly to an active sensing, passive sensing shall be examined through the
capacity of the sensors. Identification of the types of these sensors have to
come from the essential qualities they possess, which is that these sensors are
designed to react to natural emissions produced in the vicinity of their
This means that passive sensors need no additional powering as these do not
create a special field of energy, but rather respond to changes of physical
quantities within the spectrum of energy around them that is preexisting or
created independent from them.
The more famous example would be a digital camera sensor that receives the
light on it(as an image pickup device) and encodes a digital file(photo or
video), rather than the older, film cameras that had to go through the process
sensors are famous for their responsiveness to vibrations, light, radiation,
heat, magnetic field, etc. Some examples of the technologies and sensors used as
passive sensing systems are thermal, photography, electric field, seismic,
chemical magnetic field sensing devices.
Some passive components are capacitors, inductors, antennas, diodes, etc.,
however, we would like to showcase the MicroWire sensors, which
are the more novel types of sensors within this characteristic.
The MicroWire sensors are a magnetic, passive element, which are extremely
sensitive to Pressure, Temperature and Magnetic field directly, and many other
parameters indirectly (electric current, torque, flow, bending, etc.)
These devices provide the measurements in real-time through a magnetic field that is induced
within their vicinity. The resolution is high as can be, and due to the special
size, flexibility and compatibility, these can be placed into a variety of
materials and thus, find use in a variety of industries that require passive
Passive Sensors vs Active Sensors: which one should replace the other?
It is common knowledge that when choosing a sensor, be it active or passive,
the main aspects to consider are the fit to the necessary technical capacity,
the cost of integration and maintenance (this includes the potential necessity
to replace the whole system).
Currently, there is no one sensor that can cover all the needs from all the
various industries be it in robotics, composite monitoring or rechargeable
battery maintenance monitoring systems – there are different needs
that cannot be met with either passive or active sensors, as a combination of
both may be necessary, or depending on the exact use case, active or
passive may prove more useful sensing method.
If we were to compare the sensors to human biology a MicroWire sensor could
simulate our touch receptors located in the skin (detecting pressure and
temperature with high accuracy), and an image detection system like a photosensitive capacitor,
it would quickly become clear that the existence of one not only don't harm the
other, but the absence of one can make general obstacles for the overall system.
Thus a conclusion, active and passive sensing have their special use within the
array of applications special to them, and even within the types of these
sensors there are some that serve multiple purposes (MicroWire sensor), yet
an existence of another type of sensor may be necessary for an assembly of a
All in all, it is generally difficult to make a blank statement crowning
passive sensors as universally better than active ones. Depending on the
specific scenario, where a passive sensor may have advantages over an active
sensor is not going to describe the effectiveness of the measurement even
halfway. As the more important questions, which come earlier are, for
what to measure
what is the environment
what are the expected accuracies
what are the expected resolutions
what are the expected sensitivity levels
what are the space/size/weight limitations, and eventually
With a B2B sales & marketing background in INGO & Foreign Investments in government sectors, Tigran is now responsible for extensive industry research in RVmagnetics focused on marketing the company both in R&D and Business spaces. Tigran is up to date with trends in deep tech, sensors, and innovative startups in need of niche growth. He shares the knowledge with RVmagnetics communities via blogs, publications, and news releases, while also using his experience to Manage RVmagnetics' Key Partners' accounts.