A new methodology termed as equivalent nanocircuit (EN) theory is briefly introduced, and its recent important progress in designing meta-material devices with peculiar characteristics in optical or infrared frequency domain is reviewed. Three representative EN-based designs of infrared window meta-materials, such as Butterworth filter, metalinsulator-metal absorber and design-simplified TCO-based super-flat absorber, are demonstrated. All these progresses clearly indicate that the EN theory

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... vides an inspiring advancement on the way of designing more complicated meta-devices.