Do-Sik Yoo

Graded-lattice AAO photonic crystal heterostructure for high Q refractive index sensing

We present a low-cost and versatile optical sensor based on anodic aluminum oxide (AAO) graded-lattice photonic crystal heterostructure (PCH) template controlled by voltage pulse and electrolyte temperature. Designed PCH shows high Q factor up to ∼55 from the first order side band peak in the reflectance spectra and vivid color change due to infiltrated analytes. Highly linear refractive index sensitivity “dλ/dn” up to 441 nm RIU−1 could be obtained independent of analytes polarities. Superb perceptual colorimetric sensing performance was attained up to 0.01 according to CIELab tristimulus mapping analysis.

ATSC digital television signal detection with spectral correlation density

In this paper, we consider the problem of spectrum sensing for advanced television systems committee (ATSC) digital television (DTV) signal detection. To exploit the cyclostationarity of the ATSC DTV signals, we employ spectral correlation density (SCD) as the decision statistic and propose an optimal detection algorithm. The major difficulty is in obtaining the probability distribution functions of the SCD. To overcome the difficulty, we probabilistically model the pilot frequency location and employ Gaussian approximation for the SCD distribution. Then, we obtain a practically implementable detection algorithm that outperforms the industry leading systems by 2-3 dB. We also propose various techniques that greatly reduce the system complexity with performance degradation by only a few tenths of decibels. Finally, we show how robust the system is to the estimation errors of the noise power spectral density level and the probability distribution of the pilot frequency location.

Refractometric and colorimetric index sensing by a plasmon-coupled hybrid AAO nanotemplate

Facile optical sensors capable of measuring a small change in an analyte’s refractive index have been highlighted as the demand for environmental and Internet-of-Things (IoT) applications increases. In this work, we demonstrate a large-area refractive index sensor capable of refractometric and colorimetric sensing with a plasmon-coupled hybrid nanotemplate of anodic aluminum oxide (AAO). The nanotemplate enhances the figure-of-merit and sensitivity due to the coupled mode of the Fabry–Perot microcavity and metallic nanosurfaces. The increased mode confinement and interaction between AAO pores and analytes show highly modulated reflection spectra, which enable a refractive index sensitivity up to 348 nm per RIU and a figure-of-merit value up to 27.7. Also, the vivid color change induced from infiltrated analytes allows a colorimetric sensing performance up to RIU/ΔE ∼ 0.006 according to CIELab 1931 analysis. The key features of our device are simultaneous applications to superb dual (refractometric and colorimetric) sensing schemes by the plasmon-coupled hybrid AAO nanotemplate.

Regularly configured structures with polygonal prisms for three-dimensional auxetic behaviour

We report here structures, constructed with regular polygonal prisms, that exhibit negative Poisson’s ratios. In particular, we show how we can construct such a structure with regular n-gonal prism-shaped unit cells that are again built with regular n-gonal component prisms. First, we show that the only three possible values for n are 3, 4 and 6 and then discuss how we construct the unit cell again with regular n-gonal component prisms. Then, we derive Poisson’s ratio formula for each of the three structures and show, by analysis and numerical verification, that the structures possess negative Poisson’s ratio under certain geometric conditions.

A Low Complexity Subspace-Based DOA Estimation Algorithm with Uniform Linear Array Correlation Matrix Subsampling

We propose a low complexity subspace-based direction-of-arrival (DOA) estimation algorithm employing a direct signal space construction method (DSPCM) by subsampling the autocorrelation matrix of a uniform linear array (ULA). Three major contributions of this paper are as follows. First of all, we introduce the method of autocorrelation matrix subsampling which enables us to employ a low complexity algorithm based on a ULA without computationally complex eigenvalue decomposition or singular-value decomposition. Secondly, we introduce a signal vector separation method to improve the distinguishability among signal vectors, which can greatly improve the performance, particularly, in low signal-to-noise ratio (SNR) regime. Thirdly, we provide a root finding (RF) method in addition to a spectral search (SS) method as the angle finding scheme. Through simulations, we illustrate that the performance of the proposed scheme is reasonably close to computationally much more expensive MUSIC- (MUltiple SIgnal Classification-) based algorithms. Finally, we illustrate that the computational complexity of the proposed scheme is reduced, in comparison with those of MUSIC-based schemes, by a factor of , where is the number of sources and is the number of antenna elements.

Equivalent Complex Baseband Representations of Linear Time-Variant Systems and Signals

The usual analytic or complex baseband representations of linear systems and signals may not be valid unless certain conditions are satisfied. In this correspondence, we provide the necessary and sufficient conditions for the validity of complex baseband and analytic representations of linear time-variant (LTV) systems and signals. We also provide a simple sufficient condition applicable to many practical situations of interest.

Pseudo floating point representation for non-binary turbo decoder extrinsic information memory reduction

A method is presented that can substantially reduce the memory requirements of non-binary turbo decoders by efficient representation of the extrinsic information. In the case of the duo-binary turbo decoder employed by the IEEE 802.16e standard, the extrinsic information memory can be reduced by about 43%, which decreases the total decoder complexity by 18%. We also show that the proposed algorithm can be implemented by simple hardware architecture.