Application of Microwave Doppler Sensor for Remote Vibration Measurement

This article describes a novel application of the microwave Doppler sensor as a remote vibrometer. The sensor is used to measure the speed of a moving object. Consider a situation where the Doppler sensor is fixed in place and the object is also fixed but vibrates, such as a factory motor. When the vibration amplitude is less than a quarter of the carrier wave of the sensor, it outputs the vibration amplitude under certain conditions. When the sensor attached to a mechanical oscillator with frequency
${\mathrm {f}}_{{\mathrm {s}}}$
and known amplitude
${\delta {\mathrm {s}}}$
faces a target vibrating with frequency
${\mathrm {f}}_{{\mathrm {t}}}$
and amplitude
${\delta {\mathrm {x}}}$
, its output shows mixed frequency voltages. Assuming
$f_{{\mathrm {s}}}{\ne }f_{{\mathrm {t}}}$
, the mixed frequency voltage can be resolved into components by using either filters or the fast Fourier transform (FFT) algorithm. As the voltages
$V_{{\mathrm {s}}}$
and
$V$
are proportional to the known amplitude
${\delta {\mathrm {s}}}$
and the vibration amplitude
${\delta {\mathrm {x}}}$
, respectively, the vibration amplitude can be calculated using
${\delta {\mathrm {x}}}=(V/V_{{\mathrm {s}}}){\delta }{\mathrm {s}}$
, where
$V_{{\mathrm {s}}}$
and
$V$
are the amplitudes of the voltages with frequencies
${\mathrm {f}}_{{\mathrm {s}}}$
and
${\mathrm {f}}_{{\mathrm {t}}}$
, respectively. On conducting experiments by varying the distance between the sensor and an object vibrating at 18 Hz from 0.1 to 1 m, the average vibration amplitude was obtained to be
$508 \mu {\mathrm {m}} $
with an error of
$9 \mu {\mathrm {m}}$
.