Discrete Frequency Stir Electromagnetic Testing

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Solution Overview

Problem

Existing mode stir methods for electromagnetic testing of enclosures, such as mechanical and traditional frequency stirring, are time-intensive, complex, and limited in their ability to provide accurate statistical measurements of electromagnetic field characteristics due to equipment requirements and dynamic range limitations.

Innovation Solution

The discrete frequency stir (DFS) method involves exciting an enclosure with a short duration, continuous wave source whose frequency is stepped in small increments across a frequency range of interest, allowing for statistically independent measurements and simplified equipment setups, enabling accurate determination of average and peak field levels within electrically large enclosures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If mechanical mode stirring is used to randomize electromagnetic fields, then statistical uniformity of the field is achieved, but test time and equipment complexity increase

Engineering Contradiction:

Improvestatistical uniformity of electromagnetic fieldVSAvoidtest time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces the mechanical paddle wheel stirring system with an electronic frequency modulation approach. Instead of physically moving conductive paddles to randomize field modes, the system varies the excitation frequency over time to achieve the same statistical uniformity effect, thereby eliminating mechanical complexity and reducing test time.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the excitation frequency parameter dynamically over time rather than using static mechanical positioning. By sweeping the frequency across a bandwidth and holding it for measurement, then moving to the next frequency step, the system achieves mode randomization through parameter variation instead of mechanical motion.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If traditional frequency stirring with band-limited noise is used, then mode randomization is achieved, but equipment complexity and dynamic range limitations increase

Engineering Contradiction:

Improvemode randomization capabilityVSAvoidequipment setup complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the need for separate band-limited noise signal generation equipment. By using a single frequency synthesizer that can generate precise frequency-modulated signals, the system removes the complexity of having separate noise generators and filters while maintaining the frequency modulation functionality needed for mode randomization.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent makes the frequency synthesizer perform multiple functions: it generates the carrier signal, applies frequency modulation for randomization, and provides the excitation for the enclosure. This multi-functional approach replaces what would traditionally require separate dedicated equipment for noise generation and frequency modulation.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If mechanical paddle wheel stirring is used, then field randomization is achieved, but synchronization complexity and setup difficulty increase

Engineering Contradiction:

Improvefield randomization effectivenessVSAvoidsetup and synchronization difficulty

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent substitutes the mechanical synchronization requirements with electronic frequency control. Instead of needing to synchronize paddle wheel rotation with measurement sampling, the system uses electronically controlled frequency steps that can be independently timed with the measurement process, greatly simplifying the setup and operation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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

DFS method reduces test time and complexity, provides improved dynamic range, and allows for statistical analysis of field levels, offering faster and more effective mode stir testing compared to traditional methods.

Implementation Method 1

exciting the enclosure or cavity with a short duration, continuous wave, radiated source where the continuous wave frequency is stepped in small frequency steps

Methodology Applied

Scientific EffectElectromagnetic radiation: Electromagnetic Induction

Data Source

PatentUS7554339B2Electromagnetic testing of an enclosure or cavity using a discrete frequency stir method

Publication Date: 2009.06.30 THE BOEING CO

AI summary

The “discrete frequency stir” (DFS) method provides improved mode stir testing of electromagnetic characteristics of an enclosure/cavity. Adequate sampling of the electric field inside the enclosure/cavity is provided by electronic perturbation or “stirring” of the field with a short duration, continuous wave, radiated source where the wave frequency is stepped in small steps across a frequency range of interest. The frequency steps are selected to be at least slightly larger than the resonant mode bandwidth associated with the given enclosure/cavity in order to provide statistically independent measurements. A stirring bandwidth is selected to encompass a statistically significant number of these measurement samples while maintaining adequate frequency resolution. A statistical evaluation of the measured field is then performed over this stirring bandwidth. For example, the average field level at a given frequency is determined by averaging over the samples contained within the stirring bandwidth when centered on that frequency.