Example Experiment #7: Using a Radar to Measure Respiratory Rate
Developed by: Mingzhe Li and Yue Zhang, South University of Science and Technology of China
Acknowledgement: Dr. Wu Guang
Lab Exercise: Using a UWB Radar to Measure Respiratory Rate
Experiment Objectives:
The objectives of this lab are to：
1.
2.
3.
Use a radar to measure the distance and log the distance to a seated human.
Obtain the respiratory frequency of the human by using signal processing to convert the logged data into
frequency data.
Understand the principles of Fourier transform and radar.
Part I: Introduction
In this lab, we will use a Time Domain P410 UltraWideband radar (see Figure 1) and the MRM software package to
measure the precise distance between the radar and a seated human (the target). Measurement of this range will be
taken at a high rate.
This radar system uses two antennas. One is used to transmit the radar pulse and the other is used to capture the
signals reflected by human body. We will use the Time Domain P410 radar because of its small size (75x100mm),
high performance, low cost, low power consumption and advanced real-time monitoring capabilities.
Figure 1: The Time Domain P410 radar
The radar will continuously send out very short RF pulses. These pulses will be reflected by human body and the
returning echos will be captured by radar. Thus, the distance between radar and target human pit can be measured.
When the human is breathing, the distance will change and these changes in distance will be tracked and recorded
by MRM.
In Figure 2, MRM’s screen displays the strength of the returning signal as a function of time. The gray curve is the
raw radar data, the blue curve is the bandpassed radar return, the black curve is the motion filtered data, the red dots
show wall motion filtered data which is greater than a user defined threshold, and the vertical red line marks the
earliest measured return.
Lab Instructions: Experiment #7
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Example Experiment #7: Using a Radar to Measure Respiratory Rate
Developed by: Mingzhe Li and Yue Zhang, South University of Science and Technology of China
Acknowledgement: Dr. Wu Guang
Figure 2: Waveform displayed by MRM
The MRM software allows the user to log all of the radar scan data to a .csv file. This EXCEL compatible file
contains all of the data shown in Figure 2 including the distance from the radar to the target. The range to target is
the “First Detection” shown in Figure 2. We will then use MATLAB to do Fourier transform of the collected data.
The result before Fourier transform is shown in Figure 3.
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normalized y axis
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normalized x axis
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Figure 3: Changes of distance between radar and human target as a function of time
The respiration of human can be thought of as a harmonic vibration. The change in distance as a function of time
can be viewed as a sine wave. Because the respiratory rate changes slightly with time, the change in distance is
Lab Instructions: Experiment #7
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Example Experiment #7: Using a Radar to Measure Respiratory Rate
Developed by: Mingzhe Li and Yue Zhang, South University of Science and Technology of China
Acknowledgement: Dr. Wu Guang
effectively the sum of several sine waves. If we take the Fourier transform of the distance we can convert the rate of
changes in frequencies. The frequency with the largest amplitude would correspond to the typical rate of
respiration. The result of the Fourier transform is shown in Figure 4.
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frequency（ unit:Hz）
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Figure 4：Measured respiratory rate in frequency domain (Energy vs. Frequency) (The frequency with the
maximum energy corresponds to the frequency of breathing.
The mathematics that define the Fourier transform and inverse Fourier transformation is shown below.
Continuous Fourier transform：
Where f(t) is the signal in time domain and F(w) is the expression of f(t) in frequency domain.
Continuous Fourier inverse transformation：
Where F(w) is the signal in frequency domain and f(t) is the expression of F(w) in time domain.
Part II: Lab Experiment
Lab Instructions: Experiment #7
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Example Experiment #7: Using a Radar to Measure Respiratory Rate
Developed by: Mingzhe Li and Yue Zhang, South University of Science and Technology of China
Acknowledgement: Dr. Wu Guang
2.1
Required Equipment
Hardware: Laptop, one P410 with power supply, two UWB antennas, long (3m) USB cable, measuring
tape
Software: MRM GUI, MATLAB
2.2
Experimental Procedure
1)
Install MRM software in the computer. Follow the Quick StartGuide provided with the intaller to connect to
the P410 and exercise the commands. Familiarize yourself with the operation of the MRM software and P410.
2)
Insure that the only moving target visible to the radar is the target person. Ideally one would use directional
antennas and point the antennas at the target. This will guarantee that the only radar echoes received by the
radar will be from the target. However, the UWB antennas provided with the equipment are omni-directional.
These antennas will work, but you must insure that the target person if the ONLY moving object within range
of the target. Otherwise the radar will see both the person and the other moving object. For example, if the
target is 1.5 meters from the radar, then there can be no other moving objects within at least 1.5 meters of the
radar in ANY direction. This is illustrated in Figure 5.
Target (Standing)
Distance 2
Distance 1
Figure 5: Location of radar, target, computer with operator. Distance 2 > Distance 1
3)
The human target should sit in chair, remain still and breathe uniformly. Observe the changes in range on the
MRM computer screen and log the data. The longer you collect data the better the information. A minute or
two would be a reasonable amount of time to log data.
4)
Make a sketch of the set up. Use a measuring tape to measure the distance from the radar to the target.
Part 2.4 Lab Report
1) Provide your measured data.
2) Please submit a figure which shows how the distance between the radar and the target person changes with
time.
3) Please analyze the date you collected and plot data as signal strength vs frequency. Attach your MATLAB
code.
4) Please analyze the two pictures you provided. Explain their relationship using your knowledge of the Fourier
transform.
Lab Instructions: Experiment #7
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