Terahertz Caliper Sensor for Sheet Products
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Solution Overview
Problem
Current terahertz devices require knowledge of the product's index of refraction to measure absolute caliper, which is often unknown and varies with composition and material density, limiting their effectiveness in measuring multi-ply or multi-layer products.
Innovation Solution
A non-contact terahertz time-of-flight method using a sensor with a transparent material and reflective member to measure the distance of terahertz radiation reflections from the film's surfaces, allowing for independent calculation of caliper and basis weight without knowing the refractive index, employing a processor to analyze the arrival times of terahertz radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If terahertz sensors are used to measure caliper, then measurement capability is improved, but the requirement for knowing the index of refraction increases device complexity and limits applicability
Solution Approach 1:
The patent introduces a reference material (intermediary) with known properties placed in the measurement path. By comparing the time-of-flight of terahertz radiation through the reference material versus the product, the system calculates the product's caliper without requiring knowledge of the product's index of refraction. The reference material acts as a mediator that enables absolute measurements through relative comparison.
Solution Approach 2:
The patent changes the measurement approach from direct absolute measurement (requiring index of refraction) to differential measurement relative to a reference. By measuring the difference in time-of-flight between the reference material and the product, the system transforms the problem into one that does not require knowing the product's refractive index, thereby simplifying the measurement process.
2Measurement precision
If terahertz time-of-flight method is used, then absolute caliper measurement is achieved, but multi-ply and multi-layer product measurement capability is limited
Solution Approach 1:
The patent applies segmentation by analyzing individual reflections from each interface between layers in multi-ply and multi-layer products. The terahertz radiation generates distinct reflection signals at each material boundary, and the system processes these segmented signals separately to determine the thickness of each individual layer, enabling comprehensive measurement of complex layered structures.
Solution Approach 2:
The patent extends the measurement capability from single-layer to multi-layer products by analyzing the temporal dimension of reflected signals. Each layer produces a reflection at a different time, allowing the system to resolve thickness measurements in the time domain and map these to spatial thicknesses of individual layers within the multi-layer structure.
3Productivity
If infrared sensors are used, then on-line measurement is achieved, but penetration capability in heavy or opaque products is insufficient
Solution Approach 1:
The patent changes the electromagnetic parameter from infrared frequency to terahertz frequency. Terahertz radiation has different penetration characteristics compared to infrared, allowing it to penetrate heavy and opaque products more effectively while maintaining on-line measurement capability. This parameter change in the electromagnetic spectrum enables reliable measurements through materials that block infrared radiation.
4Measurement precision
If nuclear sensors are used, then basis weight measurement is achieved, but safety concerns and maintenance cost increase
Solution Approach 1:
The patent replaces nuclear sensing technology with terahertz electromagnetic radiation-based measurement. This substitution eliminates the safety hazards and high maintenance costs associated with nuclear sensors while achieving comparable or superior basis weight measurement capability through non-contact, non-ionizing radiation that is safer and requires less stringent maintenance protocols.
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 robust and accurate thickness measurements of moving films and webs, independent of product density, and basis weight determination, suitable for a wide range of materials including paper and plastics, with sub-micron accuracy and stability.
Implementation Method 1
time-of-flight measurements can be employed to calculate the absolute caliper of a moving film
Implementation Method 2
measuring the distance of the measurement gap... receiving terahertz radiation reflected from the interior surface of the layer of transparent material, the first exterior (top) side of the film, the second interior surface of the film, and the reflective surface
Implementation Method 3
providing a sensor device that includes a first scanner head having a layer of transparent material, which is transparent to terahertz
Data Source
AI summary
Time-of-flight measurements calculate the absolute caliper of a moving film independent of the film's index of refraction. A reflective fiber coupled terahertz gauge is mounted co-axially with a temperature stabilized Z-sensor positioned within a scanner head. The terahertz gauge monitors four reflections: (1) the reflection from a sensor window, (2, 3) the reflections from the top and bottom surfaces of the sheet product being measured, and (4) the reflection from a reflector that is placed behind the sheet. The Z-sensor monitors the distance between the reflector and the sensor window. The terahertz reflection delays together with the Z distance measurements allow extraction of the caliper. Since the time delay due to the sheet is a function of thickness and index of refraction, the basis weight of the sheet can be determined by using a calibration of the sensor relating basis weight of the product to time delay.