Design of Inside-Out Magnetic Resonance Sensor Based on Coordinate Search Method

The application of inside-out magnetic resonance sensors has emerged as a focal point in soil moisture detection, offering a non-invasive approach crucial for evaluating soil physical structure. While existing inside-out magnetic resonance sensors with a unilateral structure can effectively measure the shallow soil layer, they fall short in assessing deeper soil layers (1–10 cm). However, the lack of optimal design and horizontal comparison among relevant sensors has impeded the widespread adoption of magnetic resonance sensors in soil moisture measurement. This paper addresses this gap by optimizing a magnetic resonance sensor with a dumbbell structure. The magnet structure is fine-tuned using a non-derivative optimization method, specifically the coordinate search, under practical engineering constraints to establish a uniform field in the region of interest. Employing the coordinate search method enhances the sensor’s relative signal-to-noise ratio (SNR) to its maximum. Artificial soil samples are then tested, and the T2 spectrum distribution reveals insights into water distribution characteristics across different pores.