Standing-wave Operation Research Articles

Ring modulators with enhanced efficiency based on standing-wave operation on a field-matched, interdigitated p-n junction

We propose ring modulators based on interdigitated p-n junctions that exploit standing rather than traveling-wave resonant modes to improve modulation efficiency, insertion loss and speed. Matching the longitudinal nodes and antinodes of a standing-wave mode with high (contacts) and low (depletion regions) carrier density regions, respectively, simultaneously lowers loss and increases sensitivity significantly. This approach permits further to relax optical constraints on contacts placement and can lead to lower device capacitance. Such structures are well-matched to fabrication in advanced microelectronics CMOS processes. Device architectures that exploit this concept are presented along with their benefits and drawbacks. A temporal coupled mode theory model is used to investigate the static and dynamic response. We show that modulation efficiencies or loss Q factors up to 2 times higher than in previous traveling-wave geometries can be achieved leading to much larger extinction ratios. Finally, we discuss more complex doping geometries that can improve carrier dynamics for higher modulation speeds in this context.

Deflecting RF Structures with reduced level of aberrations for transformation of particle distributions in the bunch

Deflecting RF Structures find applications for the rotation of a bunch of charged particles. The application for transformation of the particle distributions in the bunch results in additional requirements on the quality of the field distribution, i. e. the minimization of aberrations. Referring to the previous methodical analysis, deflecting structures with a reduced level of aberrations are developed both for traveling wave and standing wave operation.

Separation of fine particles at different frequencies and HRTs using acoustic standing waves

The objective of this study was to evaluate the separation of fine particles using several frequencies and hydraulic retention times (HRTs) in an acoustic standing wave reactor without any separate cooling devices. The acoustic standing wave reactor consisted of sufficient space (over 100 mm) between the transducer and reflector, resulting in a slight increase in temperature. However, the increase in temperature did not affect the formation of standing waves and particle aggregations in our experiments. The results indicated that the turbidity removal efficiencies of fine kaolin particles, when using frequencies of 580 kHz, 1, and 2 MHz, increased with longer standing wave operation time. Especially, the turbidity removal efficiencies for 1 and 2 MHz were higher than that for 580 kHz because the wavelength (λ) of the 580 kHz wave was longer than that of the 1 and 2 MHz waves. Furthermore, the turbidity removal efficiency of kaolin in a continuous reactor improved with increasing hydraulic retention times (HRTs), and the reactor was more effective with 1 and 2 MHz used in parallel instead of 1 and 2 MHz used individually under the same HRT conditions with the entrance length (EL) having no adverse effect.

Symmetry breaking phenomena in vector-field lasers

Polarization and phase symmetry breaking phenomena have been studied on the basis of elaborated and experimentally tested mathematical models of gas class A lasers. It is shown that, polarization symmetry breaking appears in a single-mode linear laser: for stationary regime--at the transition from the isotropic to an anisotropic cavity and destruction of the laser modes degeneracy; for periodical regime--in the presence of a sinusoidal longitudinal magnetic field on the active medium. Spontaneous phase symmetry breaking occurs in a single-mode ring laser at the transition from the running-wave to a standing-wave operation. For periodical regime this phenomenon can be accompanied by the appearance of deterministic and noise-induced chaos.

Active Control of Self-Locking Torque of Traveling-Wave Ultrasonic Motors Using Standing-Wave Operation

This article presents a new approach to perform self-locking torque control of traveling-wave ultrasonic motors. It is to engage the motor under standing-wave operation. At that mode, the motor constantly alternates between a “lock” state and a “float” state at high frequency. The self-locking torque is thus reduced. The basic operating principle of the motor is discussed. Theoretical derivation demonstrates that the voltage amplitude can be used as the control variable to manipulate the self-locking torque. Simulation is performed using an equivalent circuit analysis. Experiments have shown consistent results with simulation, and confirm the effectiveness of the method.

On the Relative Merits of Travelling-Wave and Resonant Operation of Linacs

Discussion of the relative merits of so-called standing wave vis-a-vis travelling wave operation of linear accelerator waveguide is complicated by various considerations. In the first instance, standing wave should be distinguished from resonant operation. Standing wave operation is exactly the same as travelling wave, excepting that the waveguide is terminated by a total reflection of power instead of a matched load. It is probable that more accelerators are operated standing wave than travelling wave; formerly, medical and industrial accelerators were built with detuned or short-circuited terminations since there is no net energy gain (or loss) from the reflected wave. The only serious drawback to the scheme was that with long pulses the output power of an RF source is often determined by the VSWR of its load and that an RF window is possibly subjected to increased field stress, depending on its relative location with respect to the standing wave pattern. In resonant operation a length of slow wave structure is terminated, theoretically at reflection planes of symmetry; the discrete modes of resonance consist of two oppositely directed travelling wave ensembles, one of which will provide a space harmonic of an intended phase velocity.

A Small Diameter Standing Wave Linear Accelerator Structure

A compact, small diameter, standing-wave linear accelerator structure suitable for industrial and medical applications is presented. The novel structure utilizes a new type of coaxial cavity as the coupling cavity for ?/2 mode, standing-wave operation. This structure offers a significant reduction in overall diameter over the side-coupled, annular ring, and existing coaxial coupled structures, while maintaining a high shunt impedance and large nearest neighbor coupling (high group velocity). A prototype 4 MeV, 36 cm long, S-band accelerator incorporating the new structure has been built and tested. Theoretical accelerator design parameters, as well as experimental results, are presented.

Aerosol agglomeration in high-intensity acoustic fields

The acoustic agglomeration kernels in various regimes have been evaluated for various parameters, namely, aerosol concentration, median diameter, standard deviation, acoustic intensity, acoustic frequency, ambient temperature, and pressure. It is found that with the existence of the acoustically induced turbulence, turbulent inertial interaction is the dominant process for agglomeration of aerosol. A computer code has been developed to furnish a comparison of relative importance of the principal agglomeration mechanisms at different acoustic intensities and particulate emission mass loadings. Finally, an experimental investigation has been performed to verify the theory of aerosol deposition and agglomeration in high-intensity acoustic fields. Using a laboratory-scale transmissometer for the continuous light-opacity measurements, separate experimental runs have been directed to investigate the effects of acoustic intensity I, frequency f, and massloading M. In the operating range of I = 160–164 db, f = 500–2200 Hz, and M = 10–30 g/m 3, the experimental data show a fairly good agreement with the theoretical results. It is also revealed that, under the same operating conditions, the standing-wave operation is more effective than the traveling-wave operation.

Multimode standing-wave operation in high intensity gas laser theory: A new approach based on a matrix formalism

A recurrence relation for the Fourier coefficients of the population inversion density is derived, for a multimode, standing-wave configuration in a gas laser. A formal solution to this equation is given in terms of a continued fraction expansion for an infinite matrix.

Standing Wave Operation of Electron Linear Accelerators

Standing Wave Operation of Electron Linear Accelerators

Proposed Microwave Systems for Superconducting Radiofrequency Beam Separators

In this paper various aspects of the microwave system for RF beam separators using superconducting iris-loaded deflectors are discussed. This microwave system differs significantly from a conventional design. The differences stem mainly from the very high Q, the mandatory standing wave operation, and the lack of frequency adjustments by temperature changes. Successful operation of the separator depends on keeping two narrow bandwidth resonators (Δf ≈ 20 Hz) at the same frequency, fo ≈ 1.3 GHz, and in rigid phase relationship. Mechanical tuning of the deflectors must be provided in the form of a variable path length for a resonant ring or in the form of an adjustable short for a resonant cavity. The resonant deflector can be powered either from a common source or by using the deflector as frequency determining element in an oscillatory system. Both microwave systems are described and their relative merits are compared.