Broadband metasurfaces loaded with non-Foster elements

Metasurfaces have been widely used to design low-profile antennas, thin absorbers, lenses etc. The operational frequency band of a metasurface is rather narrow due to its resonant nature. Loading metasurface unit cells with non-Foster elements allows for remarkable bandwidth extension. In this paper, design of a broadband metasurface to operate as an artificial magnetic conductor is considered. The main issues which influence the bandwidth extension such as implementation of the non-Foster load, minimization of conversion error of a negative impedance converter, and circuit stabilization are addressed.

Low-precision Logarithmic Number Systems

Logarithmic number systems (LNS) are used to represent real numbers in many applications using a constant base raised to a fixed-point exponent making its distribution exponential. This greatly simplifies hardware multiply, divide, and square root. LNS with base-2 is most common, but in this article, we show that for low-precision LNS the choice of base has a significant impact. We make four main contributions. First, LNS is not closed under addition and subtraction, so the result is approximate. We show that choosing a suitable base can manipulate the distribution to reduce the average error. Second, we show that low-precision LNS addition and subtraction can be implemented efficiently in logic rather than commonly used ROM lookup tables, the complexity of which can be reduced by an appropriate choice of base. A similar effect is shown where the result of arithmetic has greater precision than the input. Third, where input data from external sources is not expected to be in LNS, we can reduce the conversion error by selecting a LNS base to match the expected distribution of the input. Thus, there is no one base that gives the global optimum, and base selection is a trade-off between different factors. Fourth, we show that circuits realized in LNS require lower area and power consumption for short word lengths.

Study on Underwater Image Conversion Algorithm Based on Light Refraction Model

Aiming at the problem of image distortion caused by light refraction during underwater imaging, and the conversion error caused by existing image conversion algorithms due to neglecting the secondary refraction of light, an underwater image conversion algorithm based on the light refraction model is proposed in this paper. The algorithm firstly obtains the pixel information of the underwater image, then calculates the corresponding coordinate information of the pixel points in the equivalent air image through the mapping relationship, and finally obtains the equivalent air image through image interpolation. Experimental results shows, compared with the existing image conversion algorithms, the proposed algorithm reduces the average error of u direction from 2.289 5 to 1.213 3, which is a decrease of 47.01%. The average error of v direction is reduced from 3.252 5 to 1.526 3, which is a decrease of 53.07%. At the same time, the mean value of ranging error was reduced from 58.83 mm to 28.88 mm, a decrease of 50.91%。