Transient Thermal Gradient Detection in Substrates

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Solution Overview

Problem

Historians face difficulties in detecting watermarks on historical documents due to the presence of ink or paint, which obscures the visibility of the watermark when illuminated with light.

Innovation Solution

A device utilizing electromagnetic radiation, specifically infrared radiation, with a fast shutter and high sensitivity uncooled thermal imaging detector to detect transient thermal gradients in low mass substrates, allowing for the identification of embedded features like watermarks before the substrate heats up.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If visible light is used to illuminate the substrate, then the watermark becomes visible when the paper is blank, but the watermark becomes difficult to see when the paper has been painted or written on

Engineering Contradiction:

Improvevisibility of watermarkVSAvoidobscuration by ink or paint

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the wavelength parameter from visible light to infrared radiation. Infrared radiation penetrates through ink and paint layers that block visible light, allowing the watermark to be detected despite the presence of obscuring materials on the substrate surface.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses infrared radiation as an intermediary that can penetrate through the ink and paint layer to reach the watermark. This intermediary radiation type bypasses the blocking effect of the obscuring materials, enabling detection of the watermark without direct visual contact.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If thermal imaging is used to detect watermarks, then the detection can penetrate through ink or paint, but the substrate heats up and the transient thermal gradient is lost

Engineering Contradiction:

Improvepenetration through ink or paintVSAvoidsubstrate heating

Core Design Contradiction:

Object-affected harmful factorsVSTemperature

Solution Approach 1:

The patent employs pulsed infrared radiation rather than continuous illumination. By delivering thermal energy in short pulses and detecting the transient thermal gradient during the cooling phase, the system captures the watermark signal before the substrate reaches thermal equilibrium, preserving the detection capability.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent detects the thermal gradient in the transient phase immediately after the pulse, before the substrate has a chance to heat up significantly. This preliminary detection action captures the thermal response at the critical moment when the watermark contrast is most pronounced, before thermal diffusion obscures the signal.

Inventive Principle:

Principle #10Preliminary action

3Speed

If a fast shutter is used to pulse the electromagnetic radiation, then the transient thermal gradient can be detected, but the device complexity increases

Engineering Contradiction:

Improveresponse timeVSAvoidshutter mechanism

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent employs a simple mechanical shutter that can be rapidly opened and closed. Rather than using complex electronic modulators or expensive high-speed shutters, the system uses a straightforward mechanical solution that achieves the required pulsing capability at a lower cost and with reduced complexity.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

Enables the detection of watermarks and other features on substrates, such as paper or parchment, even when obscured by ink or paint, by capturing differential thermal responses before significant heating occurs, making the technology affordable and effective for historical document analysis.

Implementation Method 1

an electromagnetic radiation source configured to emit source electromagnetic radiation

Methodology Applied

Scientific EffectInfrared radiation heating: Infrared Radiation

Implementation Method 2

a high sensitivity uncooled thermal imaging detector configured to detect electromagnetic radiation emitted by the substrate

Methodology Applied

Scientific EffectThermal radiation emission: Thermal Radiation

Implementation Method 3

detect electromagnetic radiation emitted by the substrate after source electromagnetic radiation strikes the substrate to detect the transient thermal gradient

Methodology Applied

Scientific EffectElectromagnetic to thermal energy conversion: Absorption (EM radiation)

Data Source

PatentUS11677890B2Apparatus for detecting a transient thermal gradient in a substrate

Publication Date: 2023.06.13 UNITED STATES OF AMERICA THE AS REPRESENTED BY THE SEC OF THE ARMY

AI summary

An apparatus detects a transient thermal gradient in a substrate. The apparatus is comprised of an electromagnetic radiation source configured to emit source electromagnetic radiation; a fast shutter configured to block the source electromagnetic radiation when closed, and open in response to a command to pulse the source electromagnetic radiation; a substrate support that supports a substrate disposed to emit a pulsed radiation from a back side of the substrate when the source electromagnetic radiation is pulsed through the substrate; and a detector configured to face the back side of the substrate. The detector is used to detect a transient thermal gradient in the pulsed radiation.