Automatic Radar–Accelerometer Calibration for Structural Displacement
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Solution Overview
Problem
Existing methods for structural displacement measurement, such as LVDT, LDV, and radar-based systems, face challenges in accuracy, cost, and complexity, particularly when measuring displacements in challenging environments like bridges over rivers or seas, and manual calibration reduces accuracy and speed.
Innovation Solution
A method and system that utilizes a radar and an accelerometer installed directly on the structure to automatically calibrate and fuse measurements, using a finite impulse response (FIR) filter to enhance accuracy and address phase wrapping issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If radar sensor is installed at a fixed point other than the structure to be measured, then the radar can detect multiple targets on the structure, but manual target selection and initial calibration are required which reduces accuracy and speed of displacement estimation
Solution Approach 1:
The system automatically selects the best target and performs initial calibration without manual intervention. The processor autonomously processes radar signals, identifies suitable targets, and calculates conversion factors, enabling the system to serve itself rather than requiring user involvement in calibration procedures.
Solution Approach 2:
Manual mechanical target selection and calibration procedures are replaced with automated electronic signal processing. The system uses computational algorithms to automatically determine target positions, evaluate suitability, and calculate conversion factors, substituting human operations with automated digital processing.
2Measurement precision
If radar sensor is installed at a fixed point, then the radar can detect displacement in line-of-sight direction, but phase wrapping occurs when structural displacement exceeds radar wavelength resulting in inaccurate displacement estimation
Solution Approach 1:
An accelerometer is introduced as an intermediary device to provide auxiliary measurement data. The acceleration data from the accelerometer serves as a mediator to detect and correct phase wrapping in the radar displacement measurements, allowing the system to overcome the limitation of radar's fixed installation point and wavelength constraints.
Solution Approach 2:
The system merges radar-based displacement measurement with accelerometer-based acceleration measurement. By combining these two measurement sources and processing them together, the system achieves more accurate displacement estimation while avoiding phase wrapping errors, as the accelerometer data provides complementary information about the structure's motion.
3Ease of operation
If accelerometer is used to estimate displacement via double integration, then no fixed point is required for sensor installation, but low-frequency component is greatly amplified due to measurement noise
Solution Approach 1:
The system combines accelerometer measurements with radar measurements to compensate for the noise amplification problem. While the accelerometer provides installation flexibility, the radar measurements serve as a reference to correct the low-frequency noise issues, achieving both ease of installation and measurement accuracy through data fusion.
4Measurement precision
If LVDT is used to measure displacement, then high accuracy and reliability are achieved, but additional temporary structure is required and it is difficult to measure displacement of bridges built on rivers and seas
Solution Approach 1:
The patent replaces the mechanical LVDT system with a radar-based measurement system. Instead of using physical contact sensors that require temporary structures, the radar system uses electromagnetic waves to measure displacement remotely, eliminating the need for additional temporary structures and enabling measurement of bridges in challenging environments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the need for additional fixed points, automates initial calibration, and improves displacement estimation accuracy by fusing radar and accelerometer data, allowing continuous monitoring with reduced time and cost.
Implementation Method 1
the radar sensor transmits a frequency-modulated signal, receives the reflected signal from the object, and estimates the displacement in a direction of a line-of-sight from a time delay between the transmitted and received signals
Implementation Method 2
estimates the displacement in a direction of a line-of-sight from a time delay between the transmitted and received signals
Implementation Method 3
An accelerometer, a sensor that measures the acceleration, is installed on the structure, and the displacement may be easily estimated from the acceleration via double integration
Implementation Method 4
a finite impulse response (FIR) filter method has been proposed, however, these methods do not clearly distinguish between the structure displacement and the noise in the actual low-frequency band
Implementation Method 5
The LDV is a non-contact sensor that may measure the displacement of the structure using a phase difference of reflected laser light
Data Source
AI summary
A structural displacement estimation method is performed by a computer program running on a computing device, and the program is configured to cause a processor of the device to perform an automated initial calibration may collect measured values respectively from a radar and an accelerometer installed directly at a structure, automatically determine a best target among candidate targets detected by the radar, and automatically calculate a final conversion factor to convert from a displacement in a line-of-sight direction for the best target to a displacement in an actual vibration direction, and a structural displacement monitoring may improve an accuracy of the structural displacement by calculating a final displacement by fusing based on a FIR-filter a radar-based displacement obtained by applying the final conversion factor to a phase extracted from the radar measured value of the best target and an accelerometer-based displacement obtained by double integrating the accelerometer measured value.