An ultra-thin Schroeder diffuser comprises a backing-plate, wherein the backing-plate is provided with 7×p rows and 7×q columns of unit cells, p and q are integers greater than or equal to 1, a side length of the unit cell is 0.48λ, a depth of the square unit cell is 0.04λ, the unit cell is provided with a square neck, a side length of the square neck is less than the side length of the unit cell, a depth of the neck is 0.01λ, λ is a wavelength of the diffuser corresponding to the design at a center frequency center f0, the neck widths w of different unit cells are different, and a distribution of the widths satisfies a certain sequence.
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