Lock-in Thermography for High-Resolution Heat Flow Analysis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current heat flow thermography methods have limited time and local resolution, making it difficult to effectively examine defects near the surface or in layered structures with high heat conductivity, as they are restricted by camera imaging frequencies and cannot capture fast thermal response signals.
Innovation Solution
The method involves using a lock-in frequency technology with relative time delays between image sequences and excitation periods, allowing for a virtual imaging frequency higher than the camera's maximum frequency, enabling high-resolution analysis of heat flow velocity transitions and layer structures without requiring camera frequency adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If camera imaging frequency is increased to capture fast thermal response signals, then time resolution is improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent applies periodic excitation at a lock-in frequency that is lower than the camera imaging frequency. By using periodic heating cycles and synchronizing image capture with these cycles, the system achieves enhanced time resolution through temporal correlation without requiring the camera to operate at extremely high frequencies. The periodic nature allows accumulation of thermal response data over multiple cycles, effectively improving measurement precision while keeping camera frequency requirements manageable.
2Measurement precision
If lock-in frequency is increased to examine defects near surface or in high heat conductivity layers, then detection capability is improved, but camera imaging frequency requirements become unachievable
Solution Approach 1:
The patent employs periodic excitation at a controlled lock-in frequency that is deliberately kept lower than the camera imaging frequency. This periodic approach allows the system to detect fast thermal responses from shallow defects or high heat conductivity layers by correlating thermal signals with the known excitation周期, achieving high detection precision without requiring prohibitively high camera frequencies.
Solution Approach 2:
The system uses lock-in detection methodology where the thermal response is correlated with the excitation signal phase and amplitude. This feedback-based approach allows extraction of weak thermal signals from fast-responding defects by comparing measured data with expected periodic responses, thereby improving defect detection capability without increasing camera frequency beyond practical limits.
3Measurement precision
If multiple image sequences are captured with relative time delays and combined, then virtual imaging frequency is increased beyond camera maximum frequency, but data processing complexity increases
Solution Approach 1:
The patent captures multiple image sequences synchronized with periodic excitation cycles, each sequence starting at a different phase delay. By combining these sequences according to their temporal relationships with the excitation cycles, the system creates a virtual high-frequency dataset. The periodic structure provides a framework for systematically organizing and processing the multi-sequence data, reducing processing complexity compared to arbitrary multi-sequence acquisition.
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 allows for non-destructive, high-resolution imaging of heat flow velocity transitions and layer structures, enabling flexible and rapid reconstruction of thermal material parameters, even in materials with high heat conductivity, improving defect detection and layer analysis.
Implementation Method 1
exciting the sample by means of periodic heat pulses from at least one excitation source
Implementation Method 2
capturing thermal image sequences of a thermal flow originating from the heat pulses by at least one infrared camera
Data Source
AI summary
Method for a non-destructive and image forming examination of a sample (1) by means of a heat flow thermography method where the examination consists of evaluating the presence of any gradients in heat flow velocity at respective depth distances from a surface of the sample (1), comprising exciting the sample (1) by means of periodic heat pulses P1 from at least one excitation source, and capturing thermal image sequences of a thermal flow originating from the heat pulses by at least one infrared camera (5), implementing relative time delays Δt between a starting point of imaging of the respective image sequences and a starting point of the periodic excitation, combining all captured image sequences to a resulting image sequence in which all images are arranged in a correct time sequence, and extracting from the resulting image sequence an indication of the existence and depth distance of a heat flow velocity transition from a surface of the sample. Exciting the sample (1) comprises applying heat pulses to the sample with a lock-in frequency equal to or higher than one fourth of the imaging frequency of the camera for exciting the sample (1), controlling an excitation period of the heat pulses during which the excitation of the sample (1) by means of the heat pulses takes place, and capturing thermal image sequences comprises capturing the plural image sequences during successive excitation periods of the heat pulses with the imaging frequency. The invention includes also a system for implementing the above method.