Directional Degrees Of Freedom Research Articles

A pentad-displaced ULAs configuration with hole-free co-array and increased degrees of freedom for direction of arrival estimation

In the recent past, sparse arrays have received significant attention due to their inherent ability of offering increased degrees of freedom (DOFs) along with an enlarged array aperture, compared to uniform linear arrays (ULAs). These attributes are essential to improve the direction-of-arrival (DOA) estimation accuracy. Keeping in view, a new sparse array configuration based on pentad-displaced ULAs (Pdis-ULAs) structure is presented in this paper. The proposed geometry generally consists of five ULAs and a single element placed effectively. Both the intra-ULA sensor placement and the displacement between ULAs, are uniquely determined by analytical expressions. The configuration is also benefited with closed-form expression to calculate the number of DOFs. Compared to the existing sparse array designs, the proposed configuration achieves more DOFs and wider array aperture for a given number of sensors. Moreover, the Pdis-ULAs structure desirably produces a hole-free resulting co-array. Owing to these improvements, the proposed antenna array scheme can accurately resolve the DOAs of several sources and achieves superior DOA estimation performance in under-determined conditions. Numerical works are carried out to validate the effectiveness of the Pdis-ULAs configuration.

Uncovering the Superlattice Structure of Calcium Iridium Oxide at Phase Transition

Order parameter of non-magnetic phase transition at 105 K, which is called "hidden order", was revealed in spin-orbit coupled iridate Ca5Ir3O12. This discover of order parameter with rotational and directional degrees of freedom in atomic scale will lead to development of energy saving devices with a fast cross-correlated response.

Design And Analysis of the Sparse Array for DoA Estimation of Noncircular Signals

Recently, many sparse arrays have been proposed to increase the number of degrees of freedom for direction of arrival (DoA) estimation especially for circular signals. Though many practical signals are noncircular, still the properties of noncircularity are hardly exploited in the design of sparse linear arrays. A new array geometry for noncircular signals, which significantly increases the aperture of the virtual array, has been proposed in this paper. The structure is obtained by systematically placing the two uniform linear array (ULA) side by side. The proposed design provides the largest aperture virtual ULA (VULA) as compared to the existing array structures. The aperture of VULA and corresponding weight function are evaluated analytically. The closed-form expression of the Cramer–Rao bound, the minimum lower bound on the error in the DoA estimation, is also obtained for the proposed structure. The performance of the proposed array is studied by the exhaustive computer simulations.

Elastic waves with correlated directional and orbital angular momentum degrees of freedom

We introduce a formalism that enables the calculation of elastic wave functions supported by parallel arrays of coupled one-dimensional elastic waveguides. These wave functions are expressed as tensor products of a spinor part associated with directional degrees of freedom and an orbital angular momentum (OAM) part associated with the phase of the coupled waveguides. We demonstrate that one can construct wave functions as a superposition of these elastic waves, which cannot be written as a tensor product of a spinor part and an OAM part. These elastic wave functions are not separable in the tensor product Hilbert space of directional and OAM subspaces. We show that we can construct maximally nonseparable states that are similar to Bell states.

Pnictides as frustrated quantum antiferromagnets close to a quantum phase transition

We present a detailed description of the dynamics of the magnetic modes in the recently discovered superconducting pnictides using reliable self-consistent spin-wave theory and series expansion. Contrary to linear spin-wave theory, no gapless mode occurs at the N\'eel wave vector. We discuss the scenario that the static magnetic moment is strongly reduced by magnetic fluctuations arising from the vicinity to a quantum phase transition. Smoking gun experiments to verify this scenario are proposed and possible results are predicted. Intriguingly in this scenario, the structural transition at finite temperature would be driven by an Ising transition in directional degrees of freedom.