Microwave Sensor Time Expansion for Interference Immunity
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Solution Overview
Problem
Conventional time domain reflectometry (TDR) systems face challenges with measurement accuracy due to interference and the need for expensive high-frequency A/D converters, as well as slow response times and interference immunity issues, particularly under electromagnetic interference (EMI) conditions.
Innovation Solution
The system employs a time-stretching method that distributes periodic interference by scrambling sampling times, allowing for improved measurement accuracy and robustness against interference without the need for shielding or adaptive filters, using a time base unit with a DDS and PLLs synchronized to a master clock for flexible and high-resolution frequency generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional time stretching with small frequency difference is used, then time expansion is achieved, but synchronization period becomes long and phase noise increases
Solution Approach 1:
The patent changes the frequency parameters by using a large frequency difference (e.g., 10 MHz instead of 10 Hz) between transmission and sampling frequencies. This parameter change achieves the same time expansion effect while reducing the synchronization period from 100 milliseconds to a much shorter duration, and simultaneously reduces phase noise by eliminating the need for PLL structures with small bandwidths.
2Measurement precision
If conventional time stretching with small frequency difference is used, then time expansion is achieved, but interference immunity deteriorates due to PLL phase noise
Solution Approach 1:
The patent changes the frequency parameters by using a large frequency difference between transmission and sampling frequencies. This eliminates the need for PLL structures with small bandwidths that generate excessive phase noise, thereby significantly improving interference immunity and measurement robustness under EMI conditions without sacrificing time expansion precision.
3Measurement precision
If high-frequency A/D converter is used to resolve pulse shape, then measurement precision is improved, but system cost increases disproportionately
Solution Approach 1:
The patent introduces time expansion as an intermediary process that converts the high-frequency pulse measurement problem into a lower-frequency sampling problem. By expanding the pulse in time domain through frequency offset between transmission and sampling, the measurement precision is improved while allowing the use of lower-cost, lower-frequency A/D converters instead of expensive high-frequency components.
4Measurement precision
If linear time shifting is used for time expansion, then time stretching is achieved, but response time is slow due to long synchronization period
Solution Approach 1:
The patent changes the frequency parameters by using a large frequency difference between transmission and sampling frequencies. This parameter change maintains the accuracy of time expansion while reducing the synchronization period, thereby improving the measurement response time and enabling faster measurements without sacrificing precision.
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 enhances measurement accuracy and interference immunity, enabling faster response times and reducing the need for costly shielding or filtering, while maintaining measurement precision and robustness against interference.
Implementation Method 1
a time base unit with a DDS and PLLs synchronized to a master clock for flexible and high-resolution frequency generation
Implementation Method 2
a time base unit with a DDS and PLLs synchronized to a master clock for flexible and high-resolution frequency generation
Implementation Method 3
the TDR measuring principle (time domain reflectometry) is often preferred. It is based on the determination of propagation times of an electromagnetic signal to determine the distance of a discontinuity
Implementation Method 4
The scattering unit is designed to scramble support points of the time-expanded signal with respect to the transmission signal
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The sensor has a transmitter and a receiver for transmitting and receiving a microwave signal. A controller determines distance of a boundary area based on operating time of signals reflected at the boundary area. The controller repeatedly transmits signal for obtaining a time-extended single receiving signal. The controller selects temporal shift with each repetition corresponding to a table or calculation specification so that a computation rule of support points (1-6), which are specified by a sampling time point, of the receiving signals are arbitrarily predefined. An independent claim is also included for a method for measuring a distance of a boundary area based on operating time of signals reflected at the boundary area.