Instrumentation & Measurement Magazine 25-2 - 16

Microwave Vibrometry: Noncontact
Vibration and Deformation
Measurement Using Radio Signals
Songxu Li, Yuyong Xiong, Gaoyang Wu, Zesheng Ren, Guang Meng, and Zhike Peng
V
ibration and deformation monitoring is essential for
condition monitoring and fault diagnosis in various
fields, such as structural health monitoring (SHM)
and equipment maintenance, in which effective vibration and
deformation measurement is highly desired. The accelerometer
is one of the most widely used vibration measurement
instruments in a contact manner. However, the accelerometer
has poor performance due to low-frequency response and
low displacement measurement accuracy. What is more, for
SHM of large structures, in which a great number of measuring
points need to be arranged, the sensor networking is high-cost
and time-consuming. Meanwhile, the added mass may affect
the inherent characteristics of light structures.
Regarding the shortcomings of contact sensors, many efforts
have been made in noncontact vibration and deformation
measurement, such as laser-based [1] and vision-based [2]
techniques. The laser Doppler vibrometer is based on the laser
Doppler effect and the optical heterodyne interference principle
to measure the vibration velocity of objects and has the
characteristics of non-invasiveness, high precision and high
response frequency. Nevertheless, it has obvious limitations
in multi-point and multi-scale deformation measurement.
The vision-based method processes image data of successive
frames and extracts the information of each pixel to realize the
full-field deformation measurement, requiring calibrations
in advance. In addition, the sophisticated image stream data
processing, poor real-time performance and relatively low
measurement accuracy restrict its applications.
In the past decades, microwave sensing technology has
made much progress, owing to the development of microwave
front-end architectures, integrated chips and signal processing
methods. In particular, the research on microwave sensing
such as remote sensing, microwave imaging and dielectric
characterization have attracted extensive attention and attained
outstanding achievements. Different from the above
research, micro-motion monitoring based on microwave radar
is first developed in the context of contactless viral signs monitoring
[3]-[5]. However, the radar-based vital signs detection
mainly focuses on the estimation of respiration and heartbeat
16
frequencies rather than accurate displacement measurement.
In recent years, the emerging vibration and deformation displacement
measurement technique using microwave radars
has attracted much interest, creating a novel approach termed
as microwave vibrometry.
Here, to illustrate the characteristics and advantages of microwave
vibrometry, we show the feature comparison with
commonly used vibration measurement technologies in Table
1. The microwave vibrometry method has obvious advantages
in low-frequency response, multi-scale, low power consumption
and environmental adaptability. In this paper, we review
recent works and advances in the technology of microwave vibrometry
and its applications. It starts with the fundamental
theory of micro-motion monitoring using radio signals. Then
the typical microwave vital signs monitoring is briefly introduced.
On this basis, the advances of microwave vibration and
deformation measurement and the case study of microwave
vibrometry are presented. The conclusions and future work
are summarized at the end.
System Overview and Working Principle
In microwave vibrometry, the microwave transceiver is usually
working with continuous-wave mode. Compared with
the superheterodyne receiver, the zero intermediate frequency
receiver has the characteristics of no image frequency interference,
simple structure and high sensitivity. Here, we focus
on presenting a microwave vibration measurement system
with high integration, low power consumption and low cost,
whose transceiver commonly adopts the zero-intermediate
frequency radar architecture.
Fig. 1 illustrates the block diagram of the quadrature continuous
wave (CW) Doppler radar. The microwave signal with
a constant carrier frequency is generated by the signal source.
After that, it is divided into two parts by the power divider:
one is emitted by the power amplifier and the transmitting
antenna; and the other is used as the local oscillator signal.
The echo signal is mixed with the local oscillator signal by the
mixer, and then the baseband signal is obtained through the
low-pass filter. It is a good choice that the orthogonal phaser is
IEEE Instrumentation & Measurement Magazine
1094-6969/22/$25.00©2022IEEE
April 2022
Instrumentation & Measurement Magazine 25-2

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