Measurements Of Higher Harmonics Research Articles

Real-time control in single-phase power inverters

The analysis of usability of selected digital signal controllers (DSC) in off-grid power inverters is presented in this paper. The digital signal controller’s task was to control the H-bridge through dedicated driver for power MosFET transistors and measurement of higher harmonics. NexFET power transistors with small channel resistance and small FOM coefficient were used for this purpose. Regular modulation with symmetrical triangle carrier signal was used as a modulation method. The main aim was to show the capabilities of Delfino digital signal controllers in real-time control of the power inverter and analysis of the possible implementations of voltage and harmonic measurements. These measurements can be used for regulation of the output voltage and reduction of the total harmonic distortion.

Nonlinear shear wave interaction at a frictional interface: Energy dissipation and generation of harmonics

Analytical and numerical modeling of the nonlinear interaction of shear wave with a frictional interface is presented. The system studied is composed of two homogeneous and isotropic elastic solids, brought into frictional contact by remote normal compression. A shear wave, either time harmonic or a narrow band pulse, is incident normal to the interface and propagates through the contact. Two friction laws are considered and the influence on interface behavior is investigated: Coulomb’s law with a constant friction coefficient and a slip-weakening friction law which involves static and dynamic friction coefficients. The relationship between the nonlinear harmonics and the dissipated energy, and the dependence on the contact dynamics (friction law, sliding, and tangential stress) and on the normal contact stress are examined in detail. The analytical and numerical results indicate universal type laws for the amplitude of the higher harmonics and for the dissipated energy, properly non-dimensionalized in terms of the pre-stress, the friction coefficient and the incident amplitude. The results suggest that measurements of higher harmonics can be used to quantify friction and dissipation effects of a sliding interface.

High Harmonic Generation and Molecular Orbital Tomography in Multielectron Systems: Beyond the Single Active Electron Approximation

It was recently shown that the highest molecular orbital of N2 could be reconstructed from a series of high harmonic measurements. Existing theories of high harmonic generation and orbital tomographic imaging are based on the single active electron approximation that ignores essential quantum mechanical properties such as the indistinguishability of identical particles and the Pauli exclusion principle. We show that, when fully antisymmetrized multielectron wave functions and electronic relaxation in the cation are considered, molecular orbital tomography records the image of the Dyson orbital plus exchange contributions from inner shells. The mixing of contributions from more than one molecular orbital gives access to additional wave function information. By utilizing the exchange term, harmonic emission from a closed-shell 4-electron system can be interpreted as a complete Hartree-Fock wave function.

On measurements of the higher harmonics of transmembrane current

Measurements of higher harmonics of transmembrane current in bilayer lipid membranes from diphytanoyl phosphatidylcholine (DPhPC) in n-decane and n-tetradecane, caused by alternating voltage applied to the membrane, have been conducted. A universal relation between the amplitudes of harmonics was suggested and experimentally checked. This allowed one to calculate the coefficients of expansion of membrane capacity in series with even powers of membrane voltage and to compare the inhomogeneity of membranes from diphytanoyl phosphatidylcholine in n-decane and n-tetradecane with respect to thickness.

Anisotropic Flow at RHIC

We present the first measurement of directed flow ($v_1$) at the Relativistic Heavy Ion Collider (RHIC). $v_1$ is found to be consistent with zero at pseudorapidities $\eta$ from -1.2 to 1.2, then rises to the level of a couple of percent over the range $2.4 < |\eta| < 4$. The latter observation is similar to that from NA49 if the SPS rapidities are shifted by the difference in beam rapidity between RHIC and SPS. We studied the evolution of elliptic flow from p+p collisions through d+Au collision, and onto Au+Au collisions. Measurements of higher harmonics are presented and discussed.

Study of local nonlinear properties using a near-field microwave microscope

We have developed a near-field microwave microscope to locally apply microwave frequency currents and fields to superconductors, and dielectric substrates, and measure the locally generated 2nd and 3rd harmonic responses. We measure the local nonlinear response of a Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub y/ film grown on an MgO substrate, and observe a large response due to the enhanced current density near the edge. We also study the local nonlinear response of a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film grown on a bi-crystal SrTiO/sub 3/ (STO) substrate, and spatially identify the grain boundary through higher harmonic measurements. The spatial resolution is determined by the magnetic loop probe size. A scaling current density J/sub NL/ is extracted to quantify the magnitude of the nonlinearity of the superconductor. Preliminary results on the nonlinear properties of some commonly used substrates, e.g., MgO and STO, have also been obtained.

Characteristic measurements of higher harmonics generated in the SASE-FEL process

The nonlinear harmonic generation of self-amplified spontaneous emission (SASE) has been studied in the far-infrared region. Angular distributions of the second harmonic and the third harmonic as well as the fundamental of SASE have been measured. The third harmonic radiation is emitted on the electron beam axis, while the second harmonic radiation is emitted slightly off-axis in the horizontal direction. It seems that there is competition in development of radiation between the fundamental and the other higher harmonics.

Measurement of higher harmonics in periodic vibrations using phase-modulated TV holography with digital image processing

We separately measure the higher harmonics vibration patterns of a periodic vibrating object by using time-average TV holography and phase modulation. During measurements the frequency of the phase modulation is adjusted to each harmonic component while the excitation of the object is set low enough to record all components on the linear part of the fringe function. Using acoustical phase stepping and calibration of the fringe function, we compute the amplitude and phase distributions of the frequency component. We measure components up to the 65th harmonic by using square-wave excitation.

Non-linearity of the YBa 2 Cu 3 O 7-δ low field diamagnetic properties: Multi-harmonic analysis.

The a.c. magnetic susceptibility data on YBa2Cu3O7−δ has been extended by measurement of higher harmonics, up to fifth order for low bias d.c. field and temperatures above and below the onset of phase-coherence between superconducting grains. The influence of small parasitic fields in the even terms is assesed.

Phase measurements of higher harmonics with a full-wave phase meter for nondestructive inspection

Phase measurements of higher harmonics with a full-wave phase meter for nondestructive inspection

Measurement of higher harmonics with a lock-in amplifier. Phase-selective and other forms of sinusoidal, sawtooth, square wave, triangular wave, and white noise alternating current polarography

Measurement of higher harmonics with a lock-in amplifier. Phase-selective and other forms of sinusoidal, sawtooth, square wave, triangular wave, and white noise alternating current polarography