Foam density mapping via THz imaging.

Area of Science:

• Materials Science
• Non-destructive Testing
• Terahertz Imaging

Background:

• Plastic foams are essential in various industries, with properties heavily influenced by density.
• Current methods for density mapping in plastic foams lack standardization and efficiency.
• Accurate density control is crucial for optimizing foam performance and applications.

Purpose of the Study:

• To develop and validate a novel Terahertz (THz) time-of-flight imaging technique for mapping plastic foam density.
• To establish a reliable method for non-destructive, contactless, and rapid density assessment.
• To demonstrate the capability of THz imaging in revealing spatial density variations invisible to visual inspection.

Main Methods:

• Terahertz (THz) time-of-flight imaging in normal reflection mode was employed.
• A calibration curve was established by correlating refractive index with known densities of polypropylene foam samples (70-900 kg/m³).
• The THz imaging approach was validated against standard density measurements and X-ray microscopy for accuracy and spatial resolution.

Main Results:

• A linear relationship was identified between the effective refractive index and polypropylene foam density within the tested range.
• The THz method achieved high accuracy, with an absolute error below 10 kg/m³ and a 5% percentage error.
• Quantitative density maps were generated, revealing non-uniformities in samples and showing good agreement with X-ray microscopy data.

Conclusions:

• Terahertz (THz) time-of-flight imaging provides a fast, cost-effective, and non-destructive solution for plastic foam density mapping.
• The established calibration curve enables accurate quantitative assessment of density distribution.
• This technique holds significant potential for quality control and material characterization in the plastic foam industry.