Eddy Current Drive Circuit Noise Shaping for Higher SNR

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Solution Overview

Problem

Existing non-destructive testing (NDT) probes, particularly eddy current probes, face challenges in reducing generator noise, which limits the signal-to-noise ratio (SNR) and affects the speed and accuracy of inspections.

Innovation Solution

The implementation of a noise shaping filter in the drive circuit of NDT probes, which includes a digital section with a direct digital synthesizer and a noise shaping filter, increases the SNR by displacing quantization noise to higher frequencies, thereby reducing noise in the drive signal and improving measurement accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If generator noise is reduced to increase SNR, then measurement precision is improved, but device complexity increases due to additional noise shaping filter components

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoiddrive circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces traditional analog noise filtering methods with a digital noise shaping filter implemented in the drive circuit. The digital filter uses quantization noise shaping to redirect noise energy to higher frequencies where it can be easily filtered, thereby improving SNR without requiring complex analog circuitry. This substitution of digital processing for analog filtering resolves the contradiction by achieving noise reduction through software/algorithms rather than additional physical components.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the frequency distribution parameters of quantization noise through noise shaping. By modifying the spectral characteristics of the noise (shaping it to have higher energy at frequencies above the band of interest), the system achieves effective noise reduction in the measurement band. This parameter transformation allows SNR improvement without adding complex hardware, as the noise characteristics are altered through digital signal processing.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If inspection speed is increased, then productivity is improved, but noise in the drive signal increases, reducing measurement precision

Engineering Contradiction:

Improveinspection speedVSAvoidsignal-to-noise ratio

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent applies noise shaping filtering in advance, before the eddy current measurement is performed. By pre-shaping the quantization noise spectrum in the drive signal, the system ensures that noise energy is already redirected to higher frequencies before the measurement process begins. This preliminary noise management allows for faster inspection speeds without compromising measurement precision, as the noise is already optimized before affecting the measurement.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces traditional approaches that would require slower scanning speeds to achieve adequate averaging and noise reduction with a digital noise shaping filter. This substitution enables maintained or increased inspection speeds while achieving superior noise performance through digital signal processing in the drive circuit rather than relying on mechanical scanning adjustments.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If differential probes are used to reduce generator noise, then measurement precision is improved, but device complexity and cost increase due to additional coils

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidprobe structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts and addresses the generator noise problem at the source - in the drive circuit's digital-to-analog converter - rather than attempting to reject it at the probe level. By applying noise shaping to the drive signal before it reaches the probe, the system eliminates the need for complex differential probe structures. This extraction of the noise management function to the drive circuit resolves the contradiction by achieving noise reduction without requiring additional probe coils or differential configurations.

Inventive Principle:

Principle #2Taking out (Extraction)

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 the SNR by 10 to 20 dB, allowing for faster and more accurate inspections by reducing noise and increasing productivity, making NDT probes more effective in applications where higher SNR is critical.

Implementation Method 1

use noise shaping to reduce generator noise, thereby increasing the SNR of the NDT/NDI measurement

Methodology Applied

Scientific EffectNoise shaping:

Implementation Method 2

displacing quantization noise to higher frequencies, thereby reducing noise in the drive signal

Methodology Applied

Scientific EffectQuantization noise:

Implementation Method 3

Eddy Current (EC) is a commonly used method for non-destructive testing and inspection (NDT/NDI)

Methodology Applied

Scientific EffectEddy current: Eddy Currents

Data Source

PatentUS10684258B2Eddy current inspection instrument with noise shaping filter

Publication Date: 2020.06.16 EVIDENT SCIENTIFIC INC

AI summary

Quantization noise in an oversampled eddy current digital drive circuit is reduced using a noise shaping filter.