Mini‐Birdcage Coil for Portable Nuclear Magnetic Resonance Spectroscopy: Design, Simulation, and Performance Analysis

ABSTRACT Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for molecular analysis, yet its widespread use is limited by the bulky size and high cost of conventional radio frequency (RF) coils, which restrict portability and accessibility in clinical and field applications. To address this challenge, we propose a miniature birdcage coil implemented on a flexible printed circuit board (F‐PCB) with a Flame Retardant‐4 (FR‐4) substrate. The compact design, with a thickness of only 0.25 mm, enables the development of portable and user‐friendly NMR spectrometers without compromising performance. The coil generates a highly homogeneous magnetic field with 95% uniformity across a wide range of Larmor frequencies and achieves a magnetic field strength of 327 μT. Unlike traditional fixed‐frequency coils, the proposed design incorporates a programmable band‐pass function controlled by variable capacitors and a microcontroller, allowing electronic tuning across 1–13 MHz without hardware modifications. Finite element method (FEM) simulations confirm the coil's ability to maintain field homogeneity and high signal‐to‐noise ratio (SNR) over diverse operating conditions. Compared to existing RF coil designs such as planar, Helmholtz, or conventional birdcage coils, the proposed mini‐birdcage coil offers superior portability, tunability, and uniform excitation, thereby enhancing NMR signal acquisition and broadening applicability. This advancement holds promise for medical, pharmaceutical, biological, and geological applications, enabling portable NMR systems that improve diagnostic capabilities and expand accessibility in resource‐limited environments.