Second-harmonic Voltage Research Articles

Investigation of a Class-J Power Amplifier With a Nonlinear $C_{\rm out}$ for Optimized Operation

This paper presents the operation principle of Class-J power amplifiers (PAs) with linear and nonlinear output capacitors (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> s). The efficiency of a Class-J amplifier is enhanced by the nonlinear capacitance because of the harmonic generation from the nonlinear C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> , especially the second-harmonic voltage component. This harmonic voltage allows the reduction of the phase difference between the fundamental voltage and current components from 45° to less than 45° while maintaining a half-sinusoidal shape. Therefore, a Class-J amplifier with the nonlinear C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> can deliver larger output power and higher efficiency than with a linear C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> . As a further optimized structure of the Class-J amplifier, the saturated PA, a recently-reported amplifier in our group, is presented. The phase difference of the proposed PA is zero. Like the Class-J amplifier, the PA uses a nonlinear C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> to shape the voltage waveform with a purely resistive fundamental load impedance at the current source, which enhances the output power and efficiency. The PA is favorably compared to the Class-J amplifier in terms of the waveform, load impedance, output power, and efficiency. These operations are described using both the ideal and real models of the transistor in Agilent Advanced Design System. A highly efficient amplifier based on the saturated PA is designed by using a Cree GaN HEMT CGH40010 device at 2.14 GHz. It provides a power-added efficiency of 77.3% at a saturated power of 40.6 dBm (11.5 W).

Microwave spin-torque excitation in a template-synthesized nanomagnet

A microwave-compatible lithography-free process is shown to allow the electrical contact of a single nanometric spin valve grown by template synthesis. The complex spin dynamics of a single nanomagnet is revealed by resonant microwave current excitations, detected electrically in the ${V}_{\text{dc}}$ and second-harmonic voltages. The uniform modes are attributed to spin transfer torque effects, whereas the effect of oersted field may play a role in exciting the nonuniform modes.

Second-harmonic response and temperature differential resistivity of noncollinear spin valves

By means of a diffusive description of spin-dependent thermal and electrical transport using Pauli-spin matrices, we analyze the spin-dependent transport mechanisms that determine the voltage response of a metallic spin valve to an ac temperature oscillation under steady current and the second-harmonic voltage response to spin-torque induced oscillations of the magnetization of the layers. We show the extent to which both measurements are sensitive to the relaxation of the transverse spin moment. The simulations of these signals suggest an experimental protocol to characterize the decay of the spin-accumulation precession due to $s\text{\ensuremath{-}}d$ interaction in ferromagnets.

Measurement of the Nonlinear Coefficient of a Second-Higher Term in Lead Zirconate Titanate Piezoelectric Ceramics with Half-Surface Electrodes

Second-harmonic voltage between a pair of electrodes, appearing due to nonlinearity, was theoretically calculated in piezoelectric rectangular vibrators with a pair of half electrodes which were driven by a sinusoidal constant current having the resonance frequency of length-extensional ½λ-mode vibration. The theoretical calculation was performed using the electrical equivalent circuit of a piezoelectric rectangular vibrator. A material constant as a nonlinear coefficient of second-higher term can be derived by using an equation, as that obtained in the present paper, showing the relationship between the magnitude of second harmonic voltage and the nonlinear coefficient of second-higher term.

Low-field AC magnetization of granular high-Tc superconductors

We report the low-field AC magnetization of granular high-Tc superconductors with an anomalous structure, not previously observed. The M-H curve develops a lobe in addition to the main loops, showing intergranular losses. We attribute this to the possible presence of a second kind of weak-link network, connecting the grains along the applied field direction. This is a consequence of the finite geometry of the grains, bringing their demagnetization factor into play. This also explains the observed double-peak structure in the second-harmonic voltage with DC fields.

Longitudinal Tune Control in Synchrotrons

Dual RF systems that use fundamental and higherharmonic cavities can be used to control the longitudinal tune in synchrotrons. The equations of motion and the Hamiltonian are defined for particle motion using dual RF systems. An example is considered using a second-harmonic system--it is shown, that as /phi/ /SUB s/ is increased, a substantial gain in bucket area over a single RF system can be realized by proper relative phasing of the first- and second-harmonic voltages.

V-2 derivative measurements of the light-current-voltage characteristics of (Al,Ga)As double heterostructure lasers and comparison with the theory of an ideal laser

It appears that derivative techniques will become quite useful in the characterization of semiconductor lasers.1.2 In this paper, a simple modulation and detection scheme for applying derivative techniques to the investigation of stripe-geometry (A1,Ga)As double-heterostructure lasers is described. It is shown that modulating the current at constant modulation index (Ai/i = constant) allows the desired quantities i dV/di and i2d2V/di2 to be directly and sensitively obtained, in the same apparatus, at the first and second harmonics of the modulation frequency, respectively. Particularly strong indications of laser threshold and of other optoelectronic interactions in the laser are contained in the second-harmonic-voltage response. The same apparatus may be used to obtain derivatives of the light-current relation. These are found to sensitively reveal light-current nonlinearities which are believed due to filaments and other spatial inhomogeneities and instabilities. This paper also clarifies the signal responses expected with the derivative techniques by calculating the fundamental and second-harmonic voltages which would be observed in the case of an ideal laser driven with a component of its current sinusoidally modulated. The previously untreated, nonanalytic, lasing-threshold region is explicitly included and the results are exact for any modulation amplitude. The harmonic voltages are then related to the first and second voltage derivatives and to the parameters characterizing (A1,Ga)As doubleheterostructure lasers.

Fundamental and harmonic response voltages of a sinusoidally current-modulated ideal semiconductor laser

It appears that derivative techniques will become quite useful in the characterization of semiconductor lasers. This paper clarifies the signal responses expected with these techniques by calculating the fundamental and second-harmonic voltages which would be observed in the case of an ideal laser driven with a sinusoidally modulated current. The previously untreated nonanalytic lasing-threshold region is explicitly included and the results are exact for any modulation amplitude. The harmonic voltages are then related to the first and second voltage derivatives and to the parameters characterizing (Al,Ga)As double-heterostructure lasers.

Measurement of flux distribution in toroidal and multiaperture cores

Recently, magnetic devices utilizing a partial switching have been used in many fields. From a point of core design, a flux distribution must be known. It is possible to calculate them under some assumptions, but it is difficult to measure them experimentally. This paper describes a technique of determining a flux distribution in toroidal and multiaperture ferrite cores. The patterns of flux distribution are expressed by a flux of local zone. The flux level is determined by measuring a second-harmonic voltages induced in a pick up coil under an application of a small ac magnetic field (10 kHz) orthogonal to the plane of core. Small holes for sensing are drilled through the core, and the pick up coil encloses cross-sectional areas between each of the holes. It was found that a flux reversal boundary in a toroidal core travels from inner edge to outer edge when it is switched partially by a dc field, but a pulse field switching produces a complex flux distribution, and that in both cases, the flux reversal boundary is not sharp. By a similar method, the flux distribution in the transfluxor is shown for the "unblocked" and "blocked" state before and after the interrogation. The transfluxor in the unblocked state after the interrogration showed a "kidney shaped" pattern. Readout characteristics obtained from the measured flux distributions agree with those obtained by ordinary induced voltage methods. The accuracy of the readout flux is about 8.7 percent.

Characterization of Second-Harmonic Effects in IMPATT Diodes

We discuss characterization of the tuned-harmonic mode of operation in IMPATT oscillators, and introduce an equivalent circuit which incorporates the large-signal, “single-frequency” oscillator admittances at the fundamental and second-harmonic frequencies. Complete characterization of this mode is equivalent to specifying the behavior of each of the four elements of the equivalent circuit as functions of the oscillation state variables: fundamental voltage and frequency, second-harmonic voltage and relative phase. Using the approximate large-signal analysis of Blue,1 the values of the equivalent circuit elements are presented, as an example, for a 6-GHz IMPATT diode under a variety of oscillation conditions. This equivalent circuit is used to clarify the role played by the fundamental and second-harmonic, single-frequency oscillator admittances in the tuned-harmonic mode. Using an approximation to the equivalent circuit, we investigate the criteria for stable oscillation of the tuned-harmonic mode. It is found that the stability criteria are in general quite restrictive. For the same 6-GHz germanium diode, the range of stable phase is investigated, as a function of the RF parameters, for certain special cases. It is found to be possible to satisfy the stability criteria for the phase which gives an optimum enhancement of the fundamental power output if certain conditions on the external RF circuit are satisfied.

Cross-field effects in tape cores

A number of authors have discussed cross-field effects in papers dealing with nondestructive read-out of saturation flux levels <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,2</sup> or with modulation devices. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> In this paper, it will be shown that the average flux level in a square-loop material controls the amplitude of the second-harmonic voltage induced in a coil as a result of a sinusoidal field orthogonal to the axis of the coil and the direction of the flux. A theoretical discussion of the cross-field effect and the experimental results is presented, along with a brief consideration of this effect as an experimental tool and applied device.

Harmonic Generation in Low-Field Nuclear Induction

The generation of second harmonics has been observed in a low-field nuclear-induction experiment with nearly coincident, constant and alternating, magnetic fields. A pair of Helmholtz coils furnishes both a constant (H0) and an alternating (amplitude ηH0) magnetic field, and a second Helmholtz pair furnishes a constant, small magnitude (hH0) field perpendicular to the first pair. Steady-state solutions of the modified Bloch equations (relaxation to the instantaneous field) that utilize the indicated field configuration (obtained by both analytic and numerical methods) indicate first, the existence of resonance when ωR, the alternating field frequency, is a subharmonic of the gyromagnetic frequency ω0(≡γH0), and, second, relatively slow variation of the magnetic-moment components as functions of η. Analysis and experiment indicate saturation of the signal with increasing h. The nuclear sample, water with a heavy concentration of Cu(NO3)2·3H2O, about 3 cm in diameter, was closely surrounded by a 1000-turn pickup coil the output of which was fed to a narrowband wave analyzer tuned to 2ωR. With H0=6.11 G, η=2, and h=0.013, the predicted and observed second-harmonic (52 kc/sec) voltage was 0.1 μV (rms).