ʻO kahi puʻupuʻu hollow inductor kahi mea inductor ʻaʻole pono ke kumu magnetic. Ke hilinaʻi nei ia i nā wiliwili coil a me ke ea i loko e hoʻokō i nā hopena inductance. Hōʻike kēia hoʻolālā i ka nalowale o ka hysteresis magnetic haʻahaʻa, kahi ākea ākea, a me ka linearity kiʻekiʻe, e hoʻohana nui ʻia i nā mea kamaʻilio, nā antenna RF, nā mea lapaʻau, a me nā mea hou aku.