What is the requirement for active thermography to produce thermal contrast?

Active thermography relies on an energy source to create a temperature variation in the materials being inspected. This energy source can be anything that induces heat, such as infrared lamps or ultrasound. When energy is applied, it raises the temperature of specific areas, allowing for the detection of anomalies or defects through thermal contrast. The induced heat creates the necessary temperature differentials that thermography measures, revealing issues within the material.

The concept of utilizing an energy source is central to active thermography, as it directly influences how effectively contrasts can be generated and observed. In contrast, relying solely on natural elements such as sunlight would not provide the controlled, consistent heating necessary for thorough examination, making the requirement for an active energy source critical to the process.