Electronic Phase Shifter Research Articles

Phase shifting and the beating of complex waves

At the introductory level, the demonstration and analysis of sound beating is usuallylimited to the superposition of two purely sinusoidal waves with equal amplitudes and verysimilar frequencies. Under such conditions, an observer hears the periodic variation of theloudness of a sound with an unchanging timbre. On the other hand, when complex waveswith very similar frequencies are superimposed, each harmonic beats with a frequencyproportional to the frequency of the harmonic. Consequently, the resulting soundexhibits a subtle variation of timbre with time. This article extends the normalintroductory discussion of beating and explains why electronic phase shifters, devicesfamiliar to many musicians, can produce the sound of beating complex waves.

New Electrostatic Phase Plate for Phase-Contrast Transmission Electron Microscopy and Its Application for Wave-Function Reconstruction

A promising novel type of electrostatic phase plate for transmission electron microscopy (TEM) is presented. The phase plate consists of a single microcoaxial cable-like rod with its electrode exposed to the undiffracted electrons. The emerging field is used to shift the phase of the undiffracted electrons with respect to diffracted electrons. The design overcomes the drawback of the spatial frequency-blocking ring electrode of the Boersch phase plate. First, experimental phase-contrast images are presented for PbSe and Pt nanoparticles with clearly varying phase contrast, which depends on the applied voltage and resulting phase shift of the unscattered electrons. With the new phase-plate design, we show for the first time the reconstruction of an object wave function based on a series of only three experimental phase-contrast TEM images obtained with an electrostatic phase plate.

Electron diffraction with bound electrons: The structure sensitivity of Rydberg Fingerprint Spectroscopy

Rydberg Fingerprint Spectroscopy (RFS) has proven to be a powerful method to probe molecular structures, especially transient structures with large amounts of internal energy. The technique is related to electron diffraction in that the molecular structure sensitivity originates from the wavefunction phase shift of the probe electron induced by the charge distributions in the molecule. Exploiting the close relationship between the two techniques, we investigate the origin of the molecular structure sensitivity of RFS by introducing a molecular ion core model that is solved analytically using perturbation theory as well as numerically using a numerical-grid method. The dependence of the Rydberg electron energy on some molecular parameters is investigated and the effectiveness of the numerical-grid method in solving our one-electron Schrödinger equation is validated. A reasonable consistency between experimental and computed quantum defect values is shown for specific molecular ion core model parameters.

Method for testing the condition of a drive shaft of a rotary machine

A method for non-destructive testing of a drive shaft that is accessible by only one of its ends in longitudinal waves, using a multi-element annular ultrasonic transducer. Such a transducer consists of independent elements that can be excited by electrical pulses of the same frequency, but for which different electronic phase shifts will be applied, in the invention, to the pulses transmitted to the elements. Such an electronic phase shift allows the focussing or deflection of a final beam synthesized by all the elements constituting the transducer, the said final beam being concentrated to adopt a generally cylindrical shape with a cross-section that is far smaller than the cross-section of the shaft to be tested and is highly energetic over a long distance due to the waveguide effect created by the cylindrical geometry of the shaft.

Spin splitting in AlxGa1−xN/GaN quasiballistic quantum wires

We have observed beating Shubnikov–de Haas oscillations in Al0.18Ga0.82N/GaN [112¯0]-direction quantum wires grown on (0001) sapphire. The spin-splitting energy, (2.4±0.3) meV for 200 nm wire, was suppressed to (1.2±0.3) meV for 100 nm wire and smeared by the scattering from edge states and intersubbands. The spin splitting of Rashba effect can be used to control the differential phase shift of spin-polarized electrons when a gate bias is applied to a nanometer arm of quantum ring. Based on the results of spin-splitting for the [112¯0]-direction AlxGa1−xN/GaN nanowire, the spin splitting of one-dimensional electron system in AlGaN/GaN nanowire can be applied to a low-power consuming quantum-ring interferometer.

Development of new free-fall absolute gravimeters

The design and first results of two free-fall absolute gravimeters are reported: a stationary gravimeter is designed and can be used as a reference system and a portable gravimeter is aimed at field measurements.The determination of the acceleration due to gravity is done interferometrically in both instruments. The whole fringe signal is digitized by a high-speed analogue-to-digital converter, which is locked to a rubidium frequency standard. This fringe recording and processing is novel as compared with commercial free-fall gravimeters, which use an electronic zero-crossing discrimination. Advantages such as the application of a zero-phase-shifting digital filter to the digitized data are depicted. The portable gravimeter's mechanics deviate from the conventional type. Springs are used to accelerate and decelerate the carriage supporting the falling object.A detailed uncertainty budget is given for both gravimeters. The combined standard uncertainty for the portable and for the stationary gravimeter is estimated at 38.8 µGal and 16.6 µGal, respectively. The corresponding statistical uncertainties are 1.6 µGal (over one day of measurement) and 0.6 µGal (over one month of measurement).The different designs and dimensions of the new free-fall gravimeters can help to reveal unknown or so far underestimated systematic effects. The assessments of the uncertainties due to seismic noise and shock vibrations, and electronic phase shifts give validity to this assumption.

A periodic structure for electronic signals and demonstration of electronic lasing

A sequence of electronic phase shifters and partial reflectors/transmitters is shown to form a true periodic scattering structure for electronic signals, complete with stop bands, interference, and dispersion effects. An experimental demonstration at 1kHz is made with supporting theoretical results. As with conventional periodic media, sharp defect modes in the forbidden band arise when the periodicity is broken. When gain is added to the structure, a type of lasing action is observed that in almost every aspect is similar to conventional lasers.

Quantum Dot in the Pseudo-gap Sate with Spin–Orbit Interaction

We study the linear conductance in quantum dot with spin–orbit interaction coupled to Fermi liquid leads with a power-low density of states. The conductance at zero temperature is calculated as a function of the power exponent from the density of state ρ(ω)∼|ω−EF|r at the Fermi energy EF and the different energy rates. The phase shift of the conduction electrons is also r-dependent. The model can be used in the study of the quantum phase transition.

Plasmon resonances and electron phase shifts near Au nanospheres

Quantitative phase maps from Au and polystyrene nanospheres were obtained using the transport of intensity equation approach for phase retrieval in the electron microscope. These were compared to surface plasmon maps, as generated by electron energy loss spectroscopy. Large phase excursions were observed in the vacuum regions surrounding the Au nanospheres, yet not near adjacent polystyrene nanospheres. It is proposed that these phase excursions are associated with surface plasmon excitation. These results suggest that phase retrieval offers an alternative means for sensing and interpreting the optical response of nanostructured metals.

Inelastic effects in electron transport studied with wave packet propagation

A time-dependent approach is used to explore inelastic effects during electron transport through few-level systems. We study a tight-binding chain with one and two sites connected to vibrations. This simple but transparent model gives insight about inelastic effects, their meaning, and the approximations currently used to treat them. Our time-dependent approach allows us to trace back the time sequence of vibrational excitation and electronic interference, the vibrationally introduced time delay, and the electronic phase shift. We explore a full range of parameters going from weak to strong electron-vibration coupling, from tunneling to contact, and from one-vibration description to the need of including all vibrations for a correct description of inelastic effects in transport. We explore the validity of single-site resonant models as well as its extension to more sites via molecular orbitals and the conditions under which multiorbital and multivibrational descriptions cannot be simplified. We explain the physical meaning of the spectral features in the second derivative of the electron current with respect to the bias voltage. This permits us to nuance the meaning of the energy value of dips and peaks. Finally, we show that finite-band effects lead to electron backscattering off the molecular vibrations in the regime of high-conductance, although the drop in conductance at the vibrational threshold is rather due to the rapid variation of the vibronic density of states.

Electron holography study of the temperature variation of the magnetic order parameter within circularly chained nickel nanoparticle rings

The magnetic structure within circular chains composed of 30-nm-diameter, polymer-coated nickel particles was studied by electron holography. The magnetic flux closure due to dipolar coupling was confirmed at zero external magnetic field. Its long-range order parameter was determined from the magnitude of the electron phase shift, and it was found to decrease more rapidly than that of bulk nickel as a function of temperature. The results of Monte Carlo simulations indicated that the temperature variation of the order-parameter was explained in terms of weakened dipolar coupling field ascribed to the decay of the bulk magnetization and enhanced thermal fluctuations.

A Low Phase-Noise Voltage-Controlled SAW Oscillator With Surface Transverse Wave Resonator for SONET Application

A surface transverse wave (STW) resonator-based oscillator was developed in response to SONET OC-48 application. To meet the low jitter objective, a high-Q STW resonator was designed and fabricated in this study. The residual phase-noise measurement techniques are used to evaluate the feedback oscillator components, such as the loop amplifier, STW resonator, and electronic phase shifter, which can play important roles in determining the oscillator's output phase-noise spectrum. The oscillator's white phase-noise floor is -170dBc/Hz for carrier-offset frequency greater than 1 MHz. The oscillator's phase-noise level is -67dBc/Hz at a 100-Hz carrier offset. Both low close-in phase-noise and low white phase-noise floor makes the oscillator meet low jitter requirement. The electronic frequency tuning range exceeds plusmn200ppm. The oscillator provides 13.5 dBm of output power and consumes 65 mA from +5-V power supply

Generalized data-aided multi-symbol phase estimation for improving receiver sensitivity in direct-detection optical m-ary DPSK

We present a generalized framework of data-aided multi-symbol phase estimation (MSPE) for improving the receiver sensitivity of direct-detection optical m-ary differential phase-shift keying (DPSK) through the extraction of a more accurate phase reference. Derivations of the data-aided MSPE algorithms for quaternary DPSK (DQPSK), 8-ary DPSK, m-ary DPSK, and DPSK/ASK are provided. Simulations show that receiver sensitivity improvements of over 2 dB can be obtained with the data-aided MSPE, enabling the performances of direct-detection m-ary DPSK signals to approach those of coherent homodyne-detection without resorting to an optical local oscillator. Performance improvements in nonlinear transmission are briefly discussed, and an electronic nonlinear phase shift compensation scheme is introduced for DPSK/ASK. Also presented is a simple yet universal receiver platform for m-ary DPSK consisting of just one pair of optical I/Q demodulators and a digital signal processing unit.

Liquid crystal multi-mode lenses and axicons based on electronic phase shift control

We report on the principle of operation, construction and testing of a liquid crystal lens which is controlled by distributing voltages across the control electrodes, which are in turn controlled by adjusting the phase of the applied voltages. As well as (positive and negative) defocus, then lenses can be used to control tip/tilt, astigmatism, and to create variable axicons.

Current density imaging by pulsed conduction electron spin resonance

In analogy with Nuclear MRI, the ESR signal phase shift of conduction electrons moving in electrical currents along controlled magnetic field gradients can be used to generate spatial electronic current density maps. First two-dimensional images of the current density distribution in quasi-one-dimensional organic conductors are presented.

Kondo state of Co impurities at noble metal surfaces

We use scanning tunneling microscopy and spectroscopy to study the properties of magnetic Co adatoms on noble metal surfaces at 6 K. Due to spin-flip scattering of the substrate electrons at the impurity the many-body Kondo state forms. This state is characterized by an energy, the Kondo temperature TK. We measure TK of adatom systems and a resonant scattering phase shift locally and are thus able to discuss the coupling of the Co adatom to the metal electronic system. From the resonant scattering phase shift of the surface-state electrons scattering off a Co adatom on Ag(111), we find that the coupling to the surface state is rather weak. On the other hand, increasing the number of nearest neighbor substrate atoms increases the coupling of a Co adatom to the host metal and increases TK. This shows the dominant character of the coupling of the Co atom to the bulk states of the substrate crystal.

Quantum coherence in quantum dot—Aharonov–Bohm ring hybrid systems

We investigate coherent transport through hybrid systems of quantum dots and Aharonov–Bohm (AB) rings. Strong coherence over the entire system leads to the Fano effect, which originates from the interference and the phase shift caused by the discrete states in the dots. The high controllability of the system parameters reveals that the Fano effect in mesoscopic transport can be a powerful tool for detecting the phase shift of electrons. We apply it to detect electrostatic phase modulation and the phase shift in a quantum wire with a side-coupled dot. Finally, we provide an experimental answer to the problem of “neighboring in-phase Coulomb peaks”.

Accurate calculation of phase shifts for electron–He+ collisions

The Harris–Nesbet variational method has been considered for the calculation ofelectron collisions with He+ at low energy. Calculations have been donefor both singlet and triplet scattering. Very accurate results of phaseshift have been obtained, for the first time, for partial waves withLequal to up to six. The results of the present calculation are compared with thoseavailable in the literature that have been calculated by other research groupsemploying various numerical methods.

Observing the scattering phase shift of isolated Kondo impurities at surfaces

The spin-flip scattering at Co adatoms on Ag(111) leads to the formation of a Kondo resonance. We determined the energy-dependent scattering phase shift of electrons scattering off single magnetic adatoms. A scanning tunneling microscope operating at 6 K was used to determine the amplitude of the Friedel oscillations created in the local density of states of the Ag(111) surface state electrons by the Co adatoms. We find that the standing-wave pattern around Co adsorbates exhibits a minimum in amplitude near ${E}_{F}$ of width ${2k}_{B}{T}_{K},$ where ${T}_{K}=92 \mathrm{K}$ is the Kondo temperature of the system. The wave pattern amplitude as a function of energy can be explained by assuming an energy-dependent phase shift for the scattering process.

Are Ferroelectric Crystals Blaze-Gratings for Electrons?

By means of electron holography, phase shifts of electron waves due to domains in ferroelectric crystals can be observed. For interpretation in terms of strength and direction of the ferroelectric polarization, one has to evaluate the specific interactions. However, the mechanism producing this phase shift of electrons is not yet completely understood. We propose and analyze a simple model using only ferroelectric dipole fields, which essentially turns out an analogon of a blaze grating in light optics.