Shielded Remote Inductive Resonator for EMI-Resistant Sensing
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Solution Overview
Problem
Remote inductive sensing systems face issues due to wire interconnects introducing line inductance and acting as antennas for RF interference, causing second resonance modes and EMI challenges, especially in environments with strong RF transmitters.
Innovation Solution
A shielded transmission line with a signal line and shield return line is used to couple the sensor inductor and resonator capacitor, along with an inductance-to-data converter that includes an operational transconductance amplifier and low pass filter to drive oscillations and filter out second resonance frequencies, enhancing EMI immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a two-wire interconnect is used to connect the remote sensor resonator to sensor electronics, then the sensor can be located remote from the electronics, but the wire interconnect introduces line inductance that creates a second resonance mode
Solution Approach 1:
The resonator capacitor is extracted from the remote sensor location and placed at the sensor electronics location. This separates the capacitive element from the inductive wire interconnect, eliminating the formation of a second series resonator and its associated resonance mode complexity.
Solution Approach 2:
The patent transitions from a distributed LC resonator (both L and C at remote location) to a configuration where the capacitor is relocated to the electronics side, effectively changing the spatial dimension of the resonator components and eliminating the problematic second resonance mode.
2Length of moving object
If a two-wire interconnect is used for remote sensing, then the sensor can operate remotely, but the wire interconnect acts as an antenna that emits and receives RF interference signals
Solution Approach 1:
A shielded cable is introduced as an intermediary between the remote sensor and electronics. The shielding acts as a barrier that blocks RF interference signals from coupling onto the signal lines, preventing the interconnect from acting as an antenna while still allowing remote operation.
3Device complexity
If the inductance of the interconnect is similar to the sensor inductor, then the second resonance mode frequency is close to the sensor resonator frequency, but this makes the second resonance mode challenging to distinguish and filter
Solution Approach 1:
By extracting the capacitor from the remote location and placing it at the electronics side, the patent eliminates the series resonator formed by the interconnect inductance and resonator capacitor. This removes the second resonance mode entirely from the system, eliminating the measurement precision problem of distinguishing between two close frequencies.
4Ease of operation
If the resonator capacitor is placed at the sensor location with the inductor, then a complete resonator is formed at the remote site, but the wire inductance in parallel with the capacitor creates a second series resonator
Solution Approach 1:
The capacitor is extracted from the remote sensor location and relocated to the sensor electronics location. This breaks the formation of the second series resonator that would otherwise be created by the parallel combination of wire inductance and resonator capacitor at the remote site.
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 configuration increases frequency separation between resonator and second resonance modes, allowing for effective filtering and reduced EMI sensitivity, enabling reliable operation in EMI environments without requiring higher inductance or quality factors.
Implementation Method 1
the IDC can drive oscillation signals to the sensor resonator over the signal line to cause the sensor resonator to oscillate in a resonance state, projecting from the sense inductor a magnetic sensing field
Implementation Method 2
the wire interconnect can act as an antenna that emits and receives RF interference signals (EMI)... the shielded transmission line includes a signal line and a shield return line
Implementation Method 3
a second resonance mode current loop is introduced by the interconnect inductances and resonator capacitor... A low pass filter is included in the positive feedback path to filter a second resonance frequency mode
Data Source
Figure 1A~2
Figure 3A
Figure 3B
AI summary
In described examples, an inductive sensing system (100) includes a sensor resonator (112) with a remote sense inductor (112L) coupled to a resonator capacitor (112C) over a shielded transmission line (115). The shielded transmission line (1 15) includes a signal line (114A) and a shield return line (114B). The sense inductor (112L) is connected at a sensing end between the signal line (114A) and the shield return line (114B). The resonator capacitor (112C) is connected at a terminal end (116A/B) to at least the signal line (114A). An inductance-to-data converter (IDC) (190) is connected at the terminal end (116A/B) of the shielded transmission line (115) to the signal line (114A) and the shield return line (114B). In operation, the IDC (190) drives oscillation signals to the sensor resonator (112) over the signal line (114A) to cause the sensor resonator (112) to oscillate in a resonance state, projecting from the sense inductor (112L) a magnetic sensing field, and converts measured changes in oscillation signals representing changes in resonance state into sensor response data corresponding to a sensed condition.