Terahertz Surface Refractive Index Measurement Before Full Cooling

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Solution Overview

Problem

Existing methods for determining the refractive index of partially cooled and non-hardened objects, such as plastic strands or plates, are inaccurate and not suitable for rapid, reliable measurement, particularly with handheld devices, leading to potential errors in geometric parameter determination.

Innovation Solution

The method involves emitting terahertz radiation at a known angle of incidence to the object's surface, accounting for surface properties and using Fresnel equations to determine the refractive index in the hardened surface region, and optionally using calibration with a known reflectivity or adjusting the transmitter and receiver to maximize reflected intensity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the refractive index is determined immediately after leaving the extrusion system when the object is still heated and not fully cooled, then rapid measurement is achieved, but measurement accuracy deteriorates due to viscous components affecting the refractive index

Engineering Contradiction:

Improvemeasurement speedVSAvoidrefractive index accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The measurement is segmented into two distinct approaches: measuring only the surface region (which is already hardened) versus measuring the entire cross-section (which includes viscous interior). By using surface-only measurement with terahertz radiation at oblique incidence, the patent isolates the hardened surface from the viscous interior, achieving both rapid measurement and accurate refractive index determination without waiting for complete cooling.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses the hardened surface region as an intermediary layer that provides accurate refractive index information. This surface acts as a mediator between the measurement system and the still-cooling interior, allowing the measurement to proceed rapidly while the interior continues to cool without affecting the measurement accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If the refractive index is determined later when the object has completely cooled and hardened, then measurement accuracy improves, but production time is lost

Engineering Contradiction:

Improverefractive index accuracyVSAvoidcooling time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent segments the object into surface region and interior region, measuring only the surface region that is already hardened. This allows measurement to proceed in parallel with the interior cooling process, eliminating the need to wait for complete cooling while maintaining measurement accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The surface region is already hardened in advance before the interior completes cooling. The patent utilizes this preliminary hardening of the surface to perform measurements immediately, rather than waiting for the entire object to cool, thus saving time without compromising accuracy.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If terahertz radiation is emitted at normal incidence to simplify measurement, then device complexity is reduced, but surface property influences cannot be properly accounted for

Engineering Contradiction:

Improvemeasurement setup simplicityVSAvoidrefractive index determination reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent changes the incidence angle parameter from normal incidence (0 degrees) to oblique incidence. This parameter change enables the measurement to account for surface properties and their influence on reflected radiation, improving reliability while maintaining manageable device complexity through the use of Fresnel equations for calculation.

Inventive Principle:

Principle #35Parameter changes

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 accurate and rapid determination of the refractive index in the hardened surface region, minimizing measurement errors due to viscous components and enabling precise geometric parameter assessment.

Implementation Method 1

The terahertz radiation reflected from the surface of the object is received

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

using Fresnel equations to determine the refractive index

Methodology Applied

Scientific EffectFresnel reflection: Fresnel Diffraction

Data Source

PatentUS12474264B2Method and device for determining the refractive index of a surface region of an object

Publication Date: 2025.11.18 SIKORA AG

AI summary

A method for determining a refractive index in a surface region of an object from a production system which has not cooled to an ambient temperature includes emitting terahertz radiation from a transmitter at an angle of incidence to the surface region of the object. The terahertz radiation is reflected from the surface region of the object and received by a receiver. The refractive index of the surface region of the object from a ratio of the emitted and reflected terahertz radiation is determined using an evaluator in communication with the transmitter and the receiver. The influence of surface properties of the object on a portion of the reflected terahertz radiation is taken into account when determining the refractive index.