1：Experimental Design and Method Selection:

The study involves fabricating U-SO-BTO and G-SO-BTO ceramics using cold pressing and sintering techniques, with a gradient distribution achieved by layering powder blends with increasing BTO content. The rationale is to compare electromagnetic wave absorption properties between uniform and gradient distributions.

2：Sample Selection and Data Sources:

Samples are prepared with varying BTO content (0-11 wt%) and thicknesses (6, 8, 10 mm for U-SO-BTO; layer thicknesses of 1.0, 1.5, 2.0 mm for G-SO-BTO). Data on electromagnetic reflectivity, microstructure, linear shrinkage, and flexural strength are collected.

3：0, 5, 0 mm for G-SO-BTO). Data on electromagnetic reflectivity, microstructure, linear shrinkage, and flexural strength are collected. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Materials include quartz (SiO2, 99.5 wt%, 100 mesh), calcium sulphate (CaSO4, 99.9 wt%, 800 mesh), talc (Mg3[Si4O10](OH)2, 99.5 wt%, 200 mesh), albite (NaAlSi3O8, 95.0 wt%, 400 mesh), microcline (KAlSi3O8, 95.0 wt%, 600 mesh), and BaTiO3 (BTO, 99.5 wt%, 0.5 μm). Equipment includes a planetary ball grinder, steel mould for pressing, sintering furnace, vector network analyzer (VNA, N5245A, Agilent, USA), scanning electron microscope (SEM, JSM–7610F, JEOL, Japan), energy dispersive X-ray spectrometer (EDS), and three-point bending test machine (WDW-50, Hensgrand Instrument Co., Ltd. Jinan, China).

4：5 wt%, 100 mesh), calcium sulphate (CaSO4, 9 wt%, 800 mesh), talc (Mg3[Si4O10](OH)2, 5 wt%, 200 mesh), albite (NaAlSi3O8, 0 wt%, 400 mesh), microcline (KAlSi3O8, 0 wt%, 600 mesh), and BaTiO3 (BTO, 5 wt%, 5 μm). Equipment includes a planetary ball grinder, steel mould for pressing, sintering furnace, vector network analyzer (VNA, N5245A, Agilent, USA), scanning electron microscope (SEM, JSM–7610F, JEOL, Japan), energy dispersive X-ray spectrometer (EDS), and three-point bending test machine (WDW-50, Hensgrand Instrument Co., Ltd. Jinan, China). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Powder blends are prepared by mixing and ball-milling. For G-SO-BTO, layers are spread sequentially with increasing BTO content, cold pressed at

5：4 MPa, and sintered at 1150°C for 2 hours. Samples are machined for testing:

large samples for electromagnetic reflectivity, small samples for SEM and flexural strength.

6：Data Analysis Methods:

Electromagnetic reflectivity is measured using VNA and NRL testing system in 8.0-18.0 GHz range. Microstructure is observed via SEM and EDS. Linear shrinkage and flexural strength are calculated and tested statistically.