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Benefitting from the low storage cost and high retrieval efficiency, hash learning has become a widely used retrieval technology to approximate nearest neighbors. Within it, the cross-modal medical hashing has attracted an increasing attention in facilitating efficiently clinical decision. However, there are still two main challenges in weak multi-manifold structure perseveration across multiple modalities and weak discriminability of hash code. Specifically, existing cross-modal hashing methods focus on pairwise relations within two modalities, and ignore underlying multi-manifold structures across over 2 modalities. Then, there is little consideration about discriminability, i.e., any pair of hash codes should be different. In this paper, we propose a novel hashing method named multi-manifold deep discriminative cross-modal hashing (MDDCH) for large-scale medical image retrieval. The key point is multi-modal manifold similarity which integrates multiple sub-manifolds defined on heterogeneous data to preserve correlation among instances, and it can be measured by three-step connection on corresponding hetero-manifold. Then, we propose discriminative item to make each hash code encoded by hash functions be different, which improves discriminative performance of hash code. Besides, we introduce Gaussian-binary Restricted Boltzmann Machine to directly output hash codes without using any continuous relaxation. Experiments on three benchmark datasets (AIBL, Brain and SPLP) show that our proposed MDDCH achieves comparative performance to recent state-of-the-art hashing methods. Additionally, diagnostic evaluation from professional physicians shows that all the retrieved medical images describe the same object and illness as the queried image. [ABSTRACT FROM AUTHOR]

Radar cross section (RCS) reduction in the working band of antennas, likely leading to radiation performance change or deterioration, is quite difficult for both antenna elements and arrays. Aimed at this problem, this article presents a novel design strategy of microstrip patch antennas with low in-band RCS. This strategy combines metasurface with antenna from the perspectives of both structure and electrical performance. To be specific, anisotropic metasurface is proposed to replace the conventional patch and behave as the radiating structure of the antenna directly, which does not increase the original antenna size. Through proper connection of the metasurface units, the novel antenna has the same radiation performance with conventional microstrip antenna but low in-band RCS for any polarized incidence. The radiation and scattering mechanism of the novel antenna is carefully elaborated, from which a frequency reconfigurable antenna is also derived by loading varactors. Furthermore, different design strategies of low in-band-RCS antenna element and array are clarified. On the basis of which, a $4 \times 4$ array is developed to achieve in-band-RCS reduction with radiation performance kept. Both numerical and experimental results are demonstrated, and the reasonably good agreements verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

In this letter, a low scattering microstrip antenna array has been designed and fabricated using a coding artificial magnetic conductor (AMC) ground. Two different AMC unit cells are designed first, and then they are combined to replace the conventional metallic ground of an antenna array. It is found that the radar cross section (RCS) of the novel antenna array is reduced in a wideband from 6 to 13.4 GHz for the broadband diffusion property of an AMC ground. The maximum RCS reduction of 17 and 16.65 dB can be obtained at 10 GHz for both polarizations. Moreover, the antenna radiation properties are hardly influenced owing to the antenna array and an AMC ground work at different frequencies. The measured results are in good agreement with the simulations, verifying the validity of the proposed design method. [ABSTRACT FROM AUTHOR]

A novel approach aimed at reducing the in-band radar cross section (RCS) of a waveguide slot array while maintaining its radiation performance is presented. Anisotropic metasurface is developed and applied to cover half of the antenna structure. The RCS reduction is based on the energy cancelation from the metasurface and the metal ground. Both simulated and measured results show that after loading the metasurface, the in-band RCS is sufficiently reduced for both copolarized and cross-polarized incident waves while the radiation performance is well retained. The proposed method is simple, low-cost, and easily fabricated, providing a new way for in-band RCS reduction of antenna array. [ABSTRACT FROM PUBLISHER]