We propose a novel simple method for quantitative and qualitative finger-tapping assessment based on miniature inertial sensors (3D gyroscopes) placed on the thumb and index-finger. We propose a ...simplified description of the finger tapping by using a single angle, describing rotation around a dominant axis. The method was verified on twelve subjects, who performed various tapping tasks, mimicking impaired patterns. The obtained tapping angles were compared with results of a motion capture camera system, demonstrating excellent accuracy. The root-mean-square (RMS) error between the two sets of data is, on average, below 4°, and the intraclass correlation coefficient is, on average, greater than 0.972. Data obtained by the proposed method may be used together with scores from clinical tests to enable a better diagnostic. Along with hardware simplicity, this makes the proposed method a promising candidate for use in clinical practice. Furthermore, our definition of the tapping angle can be applied to all tapping assessment systems.
Higher Order Sparse Microwave Imaging of PEC Scatterers Stevanovic, Marija Nikolic; Crocco, Lorenzo; Djordjevic, Antonije R. ...
IEEE transactions on antennas and propagation,
2016-March, 2016-3-00, 20160301, Letnik:
64, Številka:
3
Journal Article
Recenzirano
In this paper, we present an innovative algorithm for sparse imaging of perfect electric conducting (PEC) targets. The algorithm is based on higher order sources or multipoles, rather than zero-order ...ones as in the standard sparse imaging. We demonstrate that, due to the directivity of higher order sources, the imaging capabilities of the algorithm are enhanced. Particular improvements are achieved when dealing with complex-shaped targets. As a matter of fact, through several illustrative examples, we show that the zero-order sources are more suitable for the reconstruction of the convex parts of target boundaries, whereas the higher order sources are more appropriate for the concave parts of the boundaries. Taking advantage of some analytical considerations in a canonical case, we devise a strategy to select the optimal orders to consider in the imaging procedure without needing any a priori information on the target.
We develop an algorithm for localizing and estimating electrically small targets using sparse processing framework and vector electric-field measurements. To model the sources of electromagnetic ...field, we use equivalent electric and magnetic dipoles, assuming that only a few of them are sufficient for accurate source representation. To find the locations and complex amplitudes of the equivalent dipoles, we apply the <inline-formula> <tex-math notation="LaTeX">l_{1} </tex-math></inline-formula> regularization, which mitigates the inherent ill-posedness of the inverse problem. The method includes a normalization scheme which harmonizes imbalances in the system matrix and, consequently, improves the numerical stability of the method. In addition, we develop an algorithm for finding the optimal value of the regularization coefficient, based on the L-curve approach. The performance of the algorithm has been extensively tested using experimental data collected over a wide frequency bandwidth.
Abstract A new data processing method is described for estimation of angles of leg segments, joint angles, and trajectories in the sagittal plane from data recorded by sensors units mounted at the ...lateral side of leg segments. Each sensor unit comprises a pair of three-dimensional accelerometers which send data wirelessly to a PC. The accelerometer signals comprise time-varying and temperature-dependent offset, which leads to drift and diverged signals after integration. The key features of the proposed method are to model the offset by a slowly varying function of time (a cubic spline polynomial) and evaluate the polynomial coefficients by nonlinear numerical simplex optimization with the goal to reduce the drift in processed signals (angles and movement displacements). The angles and trajectories estimated by our method were compared with angles measured by an optical motion capture system. The comparison shows that the errors for angles (rms) were below 4° and the errors in stride length were below 2%. The algorithm developed is applicable for real-time and off-line analysis of gait. The method does not need any adaptation with respect to gait velocity or individuality of gait.
An approach to singularity cancelation by a variable transformation of Green's function in 2-D case, having log(<inline-formula> <tex-math notation="LaTeX">R </tex-math></inline-formula>) ...singularity, is outlined. It is intended for the method of moments analysis of 2-D structures of both curvilinear and flat cross sections. If the transformation is used with Legendre or Chebyshev polynomials as entire-domain basis functions, all involved integrals can be calculated with high precision using Gauss-Legendre quadrature. The optimal parameter of the transformation, having the minimal number of integration samples needed to reach 14-digit precision, is provided. Error estimations are presented for calculated current distributions on strips up to 400 wavelengths wide, analyzed with up to 1500 entire-domain basis functions.
High-Gain Quad Array of Nonuniform Helical Antennas Dinkić, Jelena Lj; Olćan, Dragan I.; Djordjević, Antonije R. ...
International journal of antennas and propagation,
01/2019, Letnik:
2019
Journal Article
Recenzirano
Odprti dostop
We present a design of a high-gain quad array of nonuniform helical antennas. The design is obtained by optimization of a 3-D numerical model of four nonuniform helical antennas placed above a ground ...plane, including a model of a feeding network, utilizing the method of moments with higher-order basis functions. The gain of one optimal nonuniform helical antenna can be about 2.5 dB higher than the gain of a uniform helical antenna of the same axial length. Creating a 2×2 array further increases the gain up to about 6 dB. The resulting quad array fits into a box whose dimensions are 2.5×3.3×3.3 wavelengths, and the gain in the main radiating direction is about 20.5 dBi in the frequency range from 0.9 GHz to 1.1 GHz. The design is verified by measurements of a prototype of the quad array.
A novel high-precision model of a custom-made coaxial chamber used for broadband measurement of the relative complex permittivity at microwave frequencies is presented. The model is based on a ...surface integral-equation formulation of the method of moments tailored for bodies of revolution. All singular integrals encountered in the numerical analysis are calculated in a unified way with a novel integral transformation, which enables the precision of up to 12 significant digits using the 64-bit representation of real numbers. The dielectric parameters are estimated from the reflection-coefficient measurement of the chamber with a disk-shaped dielectric sample by comparison of the measured data with the high-precision numerical analysis of the chamber. The complete measurement procedure is illustrated and verified using samples of known dielectric properties.
Microwave networks with parameters that are periodic in the frequency domain are found in many RF subsystems, e.g., in radar and wireless communication devices. This paper analyses the impulse ...response (IR) of those microwave networks, obtained by applying the inverse Fourier transform to data limited to the basic passband only. Here, we refer to such an IR as a quasi-impulse response (QIR). We investigate mathematical relations between the QIR and the exact IR. Additionally, we theoretically and experimentally demonstrate the importance of considering the parasitic passbands of these microwave networks when calculating the IR. Our insight is that neglecting the parasitic passbands can lead to unforeseen EMC problems and security vulnerabilities because these passbands may be entrance points for interference. We believe these results to be particularly important when considering intentional electromagnetic attacks.
We propose a novel design of internal impedance matching networks for axial-mode helical antennas. This network comprises a single wire attached to the helix. One of the main challenges when ...designing an internal matching network is its strong electromagnetic coupling with the antenna. The matching network must hence be designed in the presence of the antenna, which slows down the design process. To overcome this problem, we formulate an equivalent thin-wire model of the complete helix, including the matching wire (matching network) and the dielectric support. This computationally low-demanding model can be analyzed extremely rapidly, yielding accurate results, which are in excellent agreement with alternative numerical solutions and measurements.
We exploit the sparseness of induced currents on the surfaces of obscured perfectly conducting (PEC) scatterers in developing a single-frequency imaging algorithm in 2-D space. We model the induced ...currents on the targets by a set of unknown filament currents to which we apply the surface-equivalence theorem. We use l_{1} regularization to promote the solutions with a small number of equivalent sources placed in the vicinity of scatterer surfaces. The restored equivalent sources accurately determine the illuminated portions of the scatterer contours. We compare the performance of the algorithm with that of linear sampling (LSM) and MUSIC. We verify the proposed algorithm on the equivalent 3-D experimental model.
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