Instrumentation & Measurement Magazine 24-6 - 47

Method
Examples
Table 1 - Comparison between HAR sensors
Advantages
Disadvantages
Vision-based
* Monitoring Camera
* RGB-D Camera (e.g., Kinect)
* unobtrusive
* good accuracy
* sensitive to occlusion
* sensitive to image resolution
* sensitive to ambient
illumination
* privacy issue
* moderate to high cost
* computationally complex
* requires line of sight
* Inertial Measurement Unit
(IMU): Accelerometer,
Gyroscope, Magnetometer
Wearable
* Microphone
* Heartrate Pulse Sensor
* Smartphone
* Electromyography Sensor
* Skin Temperature Sensor
Object-tagged
* Radio-Frequency Identification
(RFID)
* Proximity Sensor
* Piezoelectric Sensor
* Pyroelectric Infrared Sensor
(PIR)
Device-Free
* Infrared Array Sensor
* RFID, Wi-Fi, Microwave
Doppler Radar
* Ultrasonic sensors
Piezoelectric Sensor
A piezoelectric material is one that, when mechanically
stressed, emits an electric field and conversely is subject to mechanical
strain under electrical field. So, this feature makes it
possible to detect physical vibrations.
One of the most significant categories of human activity
recognition for well-being assessment is fall detection. Falls
are a major cause of injury among people with disabilities
and the elderly and may lead to severe physical injury [19].
Moreover, early fall detection and reporting can help improve
recovery. Besides, as the elderly population grows, demand
for fall detection systems is increasing. Utilizing piezoelectric
for fall detection could be a suitable solution. In [6], a piezoelectric-based
fall detection system with a sensor made of thin
film is proposed. The sensor is installed directly onto the concrete
and covered by a flooring solution. The environment is
divided into different zones and the collected data from each
zone are sent to the processing unit.
Smart flooring is another smart home health monitoring
device. An example system is proposed in [7], which distinguishes
between footsteps and other events such as jumping,
September 2021
* low cost
* usable for vital signs
acquisition
* good accuracy
* preserves privacy
* obtrusive: is attached or
carried by user
* battery-powered; power
consumption management is
needed
* sensor specific to a limited type
of activity
* preserves privacy
* unobtrusive
* good accuracy
* low sensitivity to static objects
* limited to activities related to
the tagged objects
* moderate to high cost
* computationally complex
* limited to activities performed
in front of tags
* better performance in complex
environments
* unobtrusive
* preserves privacy
* typically low cost
* sensitive to static objects
(adjustment might be needed
in different environments)
* could be sensitive to noise
interference
* accuracy could be low
* could be computationally
complex
sitting down on a chair, standing up on a chair and impact with
an object. Analyzing these events can help in health assessment
such as gait analysis by footstep patterns. This specific
system is implemented with a thin piezoelectric polymer film
suitable for installing under the flooring, which is suitable for
large area covering. Any activity that applies pressure to the
floor causes the piezoelectric sensor to produce an output proportional
to the amount of pressure. The outputs of all sensors
are transmitted by cables to the processing unit for analyzing
and determining the performed activity.
Pyroelectric Infrared Sensor (PIR)
PIR sensors are sensitive to infrared light (IR) which is radiated
from environmental objects. The amount of IR radiation can be
measured by the PIR. The human body is constantly emitting
IR radiation; therefore, human movements cause changes in
the radiation received by the sensor. In fact, the PIR sensor has
two slots with each reacting specially to the IR radiation. In the
idle state, both slots receive the same radiation and the output
voltage remains steady. In contrast, output voltage alters with
changes in incoming radiation. For this reason, PIR sensors are
IEEE Instrumentation & Measurement Magazine
47
Instrumentation & Measurement Magazine 24-6

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 24-6
