Underground wireless sensors seem to be the most promising technique applied in mine safety monitoring, agricultural automation, etc. However, traditional EM wave-based transmission technique suffers from large propagation loss in complicated underground scenarios. Recent studies show that metamaterial magnetic induction (MI) technique can provide a reliable transmission in hostile underground medium, but how to implement an artificial electromagnetic metamaterial is still a time-consuming project. In this article, we design an optimized metamaterial slab (M-slab) to improve the energy-flux density of M2I transceiver antenna in destination direction. The M2I transceiver antenna (combination of coil and M-slab) was modeled by COMSOL Multiphysics in earth, and induction voltage at receiver coil is used to measure the enhancement by installing M-slab; the optimal permeability value of the metamaterial is proven to be − 20 through simulations, and the optimal parameters of the metamaterial slab structure are fitted using back propagation neural network algorithm in MATLAB; the metamaterial slab structure is designed and verified by HFSS simulations; the induction voltage at receiver coil is measured by experiments while M-slab installed before transmitter coil or/and receiver coil with optimal coil-slab gap (3 mm). The experimental results show that the designed M-slab can evidently improve the receiving signal strength, achieving at least 15.3 dB enhancement in voltage while M-slab placed in both Tx and Rx coil compared to that of no M-slab within its 3dB bandwidth while the coil distance is 0.5 m.