Nonlinear Voltage Response Research Articles

A non-dimensional time-domain lumped model for externally DC biased capacitive microphones with two electrodes

Microphones that utilize externally biased capacitive transduction (condenser microphones) are typically being modeled in lumped parameter networks where the mechanical, acoustical, and electrical elements are all represented as passive electronic circuit components. Those models have been shown to be insufficient to fully describe crucial aspects of this type of transducer, such as the pull-in phenomenon in which, after a certain distance and for a certain bias voltage, the moving electrode, typically a flexible membrane, attaches itself to the stationary. In this paper, we account for several non-linearities present in an extended simplified model of such a transducer in the time domain and identify the different factors related to its nonlinear response. We derive a time-domain non-linear non-dimensional system of equations for the coupled lumped model where we also take into account parasitic capacitances that are usually present and can significantly affect the overall electroacoustic performance as well as the fringing fields due to the nonhomogeneous electric field between the electrodes and nonlinearities related to damping due to the thin-film of air between the electrodes. We present the nondimensionalization method we used that allows for the identification of a novel set of nondimensional parameters that characterize the non-linear behavior of our system in the time-domain. A designer can use these parameters to optimize for linearity in the voltage response of the transducer. We post-process our time-domain solution to calculate the response to the fundamental excitation frequency and discuss the harmonic distortion. It is shown that coupling the electrical nonlinearities to the mechanical can significantly contribute to the nonlinear voltage response of the transducer. Our model agrees well with nonlinear measurements of analog microelectromechanical (MEMS) microphones for a set of physical values of the nondimensional parameters.

Doping induced modification in magnetism and magnetoelectric coupling at room temperature in Fe2Te(1-x)NbxO6

The polycrystalline Fe2TeO6 (FTO) and Fe2Te(1-x)NbxO6 [x = 0.5 (FTON5), x = 0.10 (FTON10)] is prepared via solid state reaction route. Comparative structural study is done by the Rietveld refinement of the powder X-ray diffraction data of all the prepared samples. We observe the presence of ferroelectricity in FTO via remanent polarization versus electric field (PE) hysteresis loop measurement with remanent polarization ∼4.85 nC/cm2. On application of 1.2 T external magnetic field, this observed remanent polarization changes 60% which confirms the presence of magnetoelectric (ME) coupling in the material. The magnetic field dependent PE loops also confirms the presence of ME coupling in both FTON5 and FTON10. In case of FTON10 the remanent polarization changes by 80% on application 1.2 T. The presence ME coupling is also observed through the nonlinear magnetoelectric voltage response on application of modulated DC magnetic field in both FTO and FTON5. This nonlinear voltage response changes to linear behavior for FTON10 due to Nb doping.

Nonlinear magnetoelectric effects at high magnetic field amplitudes in composite multiferroics

Magnetoelectric effects (ME) in ferromagnetic-ferroelectric layered composites arise due to magnetostriction and piezoelectric effect in the ferroic phases and are mediated by mechanical strain. The ME coupling strength in such composites could be measured by electrical response to an applied ac magnetic field h and a bias magnetic field H. The coupling, in general, is linear for small ac field amplitudes, but one expects nonlinear ME interactions for high field strengths since the dependence of magnetostriction λ on magnetic fields is nonlinear. Here we report on nonlinear voltage response of a composite of ferromagnetic Metglas and piezoelectric lanthanum gallium tantalate (langatate) subjected to an ac and a bias magnetic fields, resulting in the generation of voltages at harmonics of the frequency of h. The dependences of the ME voltage of the first four harmonics on the magnetic fields for H = 0–20 Oe and h = 0–50 Oe were measured. Up to a hundred harmonics were observed in the voltage versus frequency spectra and was indicative of high nonlinearity of the ME coupling in the multiferroic structure. It is shown that for h smaller than the saturation magnetic field HS for magnetostriction in the ferromagnetic layer, the amplitudes of the ME voltages are proportional to the derivatives of λ with respect to H and show a power-law dependence on the pumping field amplitude An(H) ~ λ(n)(H)hn. We discuss a procedure for estimating the amplitudes of the harmonics for large pumping fields h, on the order of HS. The nonlinear ME effects in the composites are of interest for application in signal processing devices and highly sensitive magnetic field sensors.

Overlap of the intrinsic and extrinsic magnetoelectric effects in BiFeO3-PbTiO3 compounds: Potentialities for magnetic-sensing applications

The potentialities of BiFeO3-PbTiO3 multiferroic compounds for magnetic-field sensing applications is investigated by characterizing the dynamical magnetoelectric response of La doped (0.6)BiFeO3-(0.4)PbTiO3 piezoceramics. The results are compared with those obtained in Nb doped (1 wt. %) PbZr0.53Ti0.47O3 (PZT-5A) piezoceramics and the observed non-linearity of the oscillating voltage response of (0.6)BiFeO3-(0.4)PbTiO3 piezoceramics is attributed to the overlapping of the intrinsic and extrinsic magnetoelectric effects that were successfully decoupled by analyzing the in-phase and out-of-phase voltage components relative to applied oscillating magnetic field. For an alternating cosine-like magnetic field of 0.32 Oe, at the piezoelectric resonance frequency (184.2 kHz), the alternating voltage response decreases from 7.77 mV, at −10 kOe, to 2.71 mV, at 1.8 kOe, to subsequently increases until 5.97 mV at 10 kOe. This non-linear voltage response, which can be easily converted into a linear signal by using the phase difference, can be used for static magnetic field sensing in a wide range of magnetic fields.

A model for torsion-stress effect on nonlinear magnetoimpedance in amorphous wires with negative magnetostriction

A model to describe the influence of torsional stress on nonlinear magnetoimpedance in amorphous wires with negative magnetostriction is proposed. The nonlinear voltage response is found in the framework of the low-frequency approximation taking into account the spatial distribution of the circular magnetic field and the magnetoelastic anisotropy induced by the torsional stress. It is demonstrated that the application of torsional stress results in an increase of the second harmonic amplitude in voltage due to a reinforcement of helical anisotropy in the wire. The second harmonic amplitude is analyzed as a function of external field, torsional stress and current amplitude. The ranges of torsional stress and current amplitude to achieve maximal field sensitivity of the second harmonic are found.

Effects of helical anisotropy on nonlinear voltage response in amorphous wires

The nonlinear voltage response in soft magnetic amorphous wires exciting by an alternating current is studied. The frequency spectrum of the voltage in the pick-up coil wound around the wire with a helical anisotropy is found in the framework of a model based on quasi-static Stoner−Wohlfarth magnetization reversal. The effect of a deviation of the anisotropy axis from the azimuthal direction on the field dependences of amplitudes of voltage harmonics is analyzed. It is shown that the field sensitivity of even harmonics increases with the anisotropy axis deviation angle. The current amplitude range to obtain a maximal field sensitivity of the second harmonic is found. The influence of the skin effect on the frequency spectrum of the pick-up coil voltage is discussed. The results obtained may be of importance for the development of sensors of a weak magnetic field.

Voltage response of current carrying Y–Ba–Cu–O tapes to alternating magnetic fields

We present a study of the alternating voltage generated in YBa2Cu3O7−δ (YBCO) tapes in response to sinusoidal magnetic fields applied perpendicular to the tapes. The alternating field induces a strongly nonlinear voltage response with various waveforms that drastically change upon changing the bias current, the bias magnetic field, and the amplitude and frequency of the alternating field. In particular, one observes transitions from waveforms including double peaks to waveforms including a single peak in one cycle of the alternating field. We attribute these effects to modulation of the vortex pinning energy by both the alternating magnetic field and the alternating current induced by it. Our model allows separation of these two contributions to the total response, thus revealing the dominating source of the nonlinear response and its accompanied steady component at different experimental conditions.

Quantum ratchets and quantum heat pumps

Quantum ratchets are Brownian motors in which the quantum dynamics of particles induces qualitatively new behavior. We review a series of experiments in which asymmetric semiconductor devices of sub-micron dimensions are used to study quantum ratchets for electrons. In rocked quantum-dot ratchets electron-wave interference is used to create a non-linear voltage response, leading to a ratchet effect. The direction of the net ratchet current in this type of device can be sensitively controlled by changing one of the following experimental variables: a small external magnetic field, the amplitude of the rocking force, or the Fermi energy. We also describe a tunneling ratchet in which the current direction depends on temperature. In our discussion of the tunneling ratchet we distinguish between three contributions to the non-linear current–voltage characteristics that lead to the ratchet effect: thermal excitation over energy barriers, tunneling through barriers, and wave reflection from barriers. Finally, we discuss the operation of adiabatically rocked tunneling ratchets as heat pumps.

NMDA receptor-mediated oscillatory properties: potential role in rhythm generation in the mammalian spinal cord.

Previous studies have demonstrated that (1) NMDA receptor activation occurs during locomotor network operation in lower and higher vertebrates and (2) NMDA induces active membrane properties that can be expressed as intrinsic voltage fluctuations in cells located in the spinal cord of lower vertebrates, as well as in neurons located in supraspinal regions of the mammalian nervous system. This paper reviews recent data showing that NMDA can induce similar inherent membrane potential behavior in synaptically isolated motoneurons and interneurons in the mammalian (in vitro neonatal rat) spinal cord. These TTX-resistant voltage fluctuations include rhythmic oscillations and plateau potentials, as well as low-frequency long-lasting voltage shifts (LLVSs). 5-HT facilitates the transformation of LLVSs into oscillatory events, and 5-HT receptor antagonists have the reverse effect. In the absence of TTX, locomotor-related rhythmic drive potentials in spinal cord neurons can display nonlinear voltage behavior compatible with NMDA receptor activation, although other voltage-activated conductances are not excluded. Suppression of the nonlinear voltage response associated with NMDA receptor activation, via removal of Mg2+, disrupts locomotor patterns of network activity. The potential role of NMDA receptor activation in the operation of mammalian locomotor networks is discussed in the context of these recent observations.

Nonlinear voltage response due to thermal noise of Josephson junction

The effects of thermal fluctuations on the Josephson effect in a junction with finite capacitance are studied in the framework of two variables Fokker-Planck equation of Brownian motion. A general analytic stationary solution is obtained. Comparison with experimental data of YBCO junctions as well as BSCCO single crystals is shown with satisfactory agreement.

CDW depinning under inhomogeneous conditions in the blue bronzes

We have studied the non-linear voltage response to current pulses in a segment of a blue bronze sample where the CDW is depinned when a dc current is flowing in a neighboring segment. As the dc current is increased, various voltage response waveforms are found: overshoot, sluggish, undershoot. These non-local properties are discussed in terms of nucleation of edge and screw phase dislocations between the two neighboring segments.

Depinning of the charge density wave in pure and non-stoichiometric blue bronzes A 0.30MoO 3 (A=K, Rb)

We report the observation of non-linear voltage response to unipolar current pulses in pure A 0.30MoO 3 (A=K, Rb) and non-stoichiometric Rb 0.28MoO 3 blue bronzes near threshold for depinning of the charge density wave. In both types of samples, the transient response waveforms involve overshoot at the leading edge and a tail at the trailing edge of the pulse whose time decays obey stretched exponential laws exp-(t/τ)β (O<β<1). The characteristic times are found to be approximately one order of magnitude larger in Rb 0.28MoO 3 than in pure samples. The results are discussed in terms of charge density wave phase dislocations coupled to point lattice defects.