<p>This research exhibits a simple and accurate method for monitoring of the magnetic field intensity using the integration of the acoustic wave device, enhanced by a phononic crystal (PnC) structure. The incorporation of PnCs into the platform significantly enhances the acoustic wave confinement and energy localization, thereby leading to an improvement in the sensor’s sensitivity. Meanwhile, the designed PnC consists of a distinct number of unit cells in which each one is composed of a versatile magneto-strictive material (Terfenol-D) besides poly methyl methacrylate (PMMA), thus, the designed PnC structure is configured as, [Terfenol/PMMA] ^N. The mainstay of the present study is mainly focused on the inclusion of Terfenol-D in the structural design, whose young’s modulus is highly sensitive to change in the magnetic field intensities, resulting in shifts in the bandgap width in phononic bandgap (PnBG). Therefore, the numerical investigations including the changes in the bandgap behavior and acoustic reflectance properties have been essentially introduced based on the well-known transfer matrix method. Additionally, the tunability of the PnBG due to the changes in the intensity of the applied external magnetic field represents the cornerstone of this study towards the monitoring of the minute variations of this magnetic field. To ensure optimal performance, all the structural and geometrical parameters are meticulously optimized. The simulation upshots revealed that the proposed magnetic field sensor achieves a sensitivity of 5650&#xa0;Hz/Oe, a figure of merit of 3.248 × 10⁻³, a detection limit of 914 × 10³, a sensor resolution of 5164 × 10⁶, and a signal to noise ratio of 0.142. With this superior performance, the designed sensor shows a great potential for magnetic field sensing applications compared to the existing alternatives.</p>