Pembuatan dan karakterisasi Bi1-xYxFeO3/C, BiFe1-yZnyO3/C, dan Bi0.88Y0.12Fe1-yZnyO3/C sebagai absorber gelombang mikro pada frekuensi x band = Synthesis and characterization of Bi1-xYxFeO3/C, BiFe1-yZnyO3/C, and Bi0.88Y0.12Fe1-yZnyO3/C as microwave absorber at the x-band frequency