Design and construction of a small embeddable nuclear magnetic resonance sensor utilizing 3D-printed components

This paper presents the design and construction of a cost-effective embeddable nuclear magnetic resonance sensor using 3D printing to improve the construction process. The sensor comprises two 25.4 mm diameter x 3 mm thick neodymium-iron-boron disk magnets and an elliptical radio frequency coil. Magnetic field simulations were employed to determine the optimal separation between magnets, achieving a relatively homogeneous B₀ field of 180 mT at the center of the array. Custom 3D-printed parts ensured precise magnet alignment and facilitated coil fabrication. The sensor was encased within a Faraday cage constructed from a printed circuit board to mitigate external electromagnetic interference. A remote tuning circuit was developed to tune the coil to 7.66 MHz. Initial testing involved using an eraser sample to determine the required 90° and 180° pulse amplitudes and duration. The sensor's performance was further validated under immersion conditions in milk, yogurt, and fresh cement paste, using the Carr-Purcell-Meiboom-Gill technique. The signals obtained were processed by fitting the data to an exponential decay function to obtain the T₂ lifetimes and their corresponding signal intensities, and by Inverse Laplace Transformation to obtain the T₂ lifetime distribution. Results indicate the sensoŕs capability to detect variations in samples having different compositions.