Uncooled Resistive Metal Foil Bolometers For Imaging With Radiofrequency Magnetic Fields

A set of experiments were conducted looking at how characteristics of loop elements in an array affect their detected induced current and subsequent Joule heating when located in a radio frequency magnetic field. These experiments included evaluations of the observed steady state temperature rise versus the radius of the loop, the location of the loop with respect to the RF source, and the effect on steady state temperature rise when other loops were brought into close proximity. Loop elements were then combined into a radially-symmetric, five-element array which was used to create a coarse magnetic image of a simple piece of aluminum sheet. After normalization, the temperature rise versus loop size results showed a direct linear relationship which enabled prediction of the lower element size threshold based on the properties of existing thermosensing layer materials used in other bolometer applications and the typical performance of analog measurement equipment. Offset sample test results show how the RF field varied linearly across a given plane perpendicular to the RF source transmission axis, increasing as the distance between the sample and one side of the Helmholtz coil is reduced. Separation distance test results also reveal the RF magnetic field cancellation effects due to mutual coupling as the separation between closed-loop elements are brought into close proximity. Lastly, the excellent agreement achieved between the captured image and the actual object show promise in creating an imaging system with significant resolution and contrast differentiation.