Rayleigh distance Rayleigh distance Rayleigh distance in optics is the axial distance from a radiating aperture to a point at which the path difference between the axial ray and an edge ray is λ / 4. An approximation of the Rayleigh Distance is formula_1, in which Z is the Rayleigh distance, D is the aperture of radiation, λ the wavelength. This approximation can be derived as follows. Consider a right angled triangle with sides adjacent formula_2, opposite formula_3and hypotenuse formula_4. According to Pythagorean theorem, formula_5. Rearranging, and simplifying formula_6 The constant termformula_7 can be neglected. In antenna applications, the Rayleigh distance is
What Is This Thing Called Love? (Alexander O'Neal song) What Is This Thing Called Love? (Alexander O'Neal song) "What Is This Thing Called Love?" is a song written by Jimmy Jam and Terry Lewis and recorded by American recording artist Alexander O'Neal. It is the second single from the singer's fourth solo album, "All True Man" (1991). The song's distinctive backing vocals were performed by Lisa Keith. Following the successful chart performances of the "All True Man" single "All True Man", "What Is This Thing Called Love?" was released as the album's second single. Alexander O'Neal's 19th hit single and it reached #53 in the UK Singles Chart. In