A rotor (1) with N poles, wherein N is an even integer, wherein said rotor (1) is devoid of permanent magnets comprising rare earth elements and comprises a cylindrical body (2) and a filling material (16). The cylindrical body (2) extends along a body axis (X) and—in a plane perpendicular to the body axis (X)—delimits N adjacent angular sectors (4, 6). Each angular sector (4, 6) delimits cylindrical cavities (8, 12, 14, 8′, 12′, 14′) which have curvilinear cross-sections, where concave surfaces (18, 20, 22, 18′, 20′, 22′) of said cylindrical cavities (8, 12, 14, 8′, 12′, 14′) are directed in the opposite direction to the body axis (X). The filling material (16) fills at least partly the cylindrical cavities (8, 12, 14, 8′, 12′, 14′) and comprises or consists of a polymer matrix. At least one angular sector (6) delimits cylindrical cavities (8′, 12′, 14′) with a first geometry (type A) and at least one second angular sector (4) delimits cylindrical cavities (8, 12, 14) with a second geometry (type B) different from said first geometry. The first angular sector (6) is arranged angularly alternating with the second angular sector (4).