The relationship of levitation force between individual discs and double-layer disc YBa₂Cu₃O_7-x superconductors

Two well-textured single-domain YBa₂Cu₃O_7-x (YBCO) thin disc samples (Φ30 × 7 mm), SI₁ and SI₂, were used to investigate the relationship of levitation force between individual YBCO discs and a double-layer disc sample, SD (formed by putting samples SI₁ and SI₂ coaxially together). The levitation forces for samples SI₁ and SI₂ are 18.1 and 17.8 N, respectively. The levitation force of the sample SD is 31.2 N, slightly less than the levitation force summation of the two individual samples; the difference factor is about 15.1%. The real difference factor is about 0.64% after we take into account the real distance between the pigment and each individual disc. The result is very attractive and useful for practical applications of levitation devices during the design and fabrication.