high-Q Operation Research Articles

Universal Frequency-Domain Analysis of N-Path Networks

N-path commutated capacitive networks provide a practical solution to implement highly sought on-chip high-Q filtering applications in which the use of lumped inductors is undesirable due to their significant footprints and low Q-factors. Recently, it has been also revealed that N-path networks can also exhibit other interesting functionalities, such as nonreciprocal phase-shifting and ultra-wideband true time delay, providing a path to miniaturization of various reciprocal and nonreciprocal devices. The analytical treatment of these networks, however, remains challenging, because their operation involves frequency mixing produced by the time modulation. In this article, we present a highly accurate frequency-domain approach for the analysis of N-path networks based on perturbation theory. Our method compares favorably to the state-of-the-art polyphase analysis by being much simpler mathematically, yet providing results essentially indistinguishable from numerical simulations, while offering physical insights into the N-path filter operation. We particularize the solution for the high-Q operation regime and obtain simple closed-form analytical expressions for harmonic transfer functions, scattering parameters and baseband impedance.

Perovskite nanowire lasers on low-refractive-index conductive substrate for high-Q and low-threshold operation

Abstract Over the last five years, inorganic lead halide perovskite nanowires have emerged as prospective candidates to supersede standard semiconductor analogs in advanced photonic designs and optoelectronic devices. In particular, CsPbX3 (X = Cl, Br, I) perovskite materials have great advantages over conventional semiconductors such as defect tolerance, highly efficient luminescence, and the ability to form regularly shaped nano- and microcavities from solution via fast crystallization. However, on the way of electrically pumped lasing, the perovskite nanowires grown on transparent conductive substrates usually suffer from strong undesirable light leakage increasing their threshold of lasing. Here, we report on the integration of CsPbBr3 nanowires with nanostructured indium tin oxide substrates possessing near-unity effective refractive index and high conductivity by using a simple wet chemical approach. Surface passivation of the substrates is found out to govern the regularity of the perovskite resonators’ shape. The nanowires show room-temperature lasing with ultrahigh quality factors (up to 7860) which are up to four times higher than that of similar structures on a flat indium tin oxide layer, resulting in more than twofold reduction of the lasing threshold for the nanostructured substrate. Numerical modeling of eigenmodes of the nanowires confirms the key role of low-refractive-index substrate for improved light confinement in the Fabry–Pérot cavity which results in superior laser performance.

Study on Magneto-Resistance Sensors for Low Magnetic Field Measurements

High-Q operation of a superconducting radio frequency cavity can reduce the power loss at the surface and is desirable for continuous-wave operation. To realize the high-Q operation, the surface resistance, which is a sum of the Barden-Cooper-Schrieffer resistance and residual resistance, needs to be reduced. The residual resistance has been found to originate primarily from the magnetic flux trapping in defects in the cavity during the cooling down process. A magnetometer called the “flux gate sensor” has been used to measure the ambient magnetic field; however, this is larger in comparison with the cavity and it is very expensive. Sensors based on the magneto-resistance effect, such as the Anisotropic-Magneto-Resistance (AMR) sensor, are smaller and much less expensive than a flux gate sensor. We examined the characteristics of the magneto-resistance sensors at room temperature and liquid nitrogen temperature. The results are reported in this paper.

Photonic crystal coupled cavities with increased beaming and free space coupling efficiency

We implement the band-folding approach in coupled photonic crystal L3 (three missing holes) nanocavities and demonstrate a dramatic beaming improvement compatible with high-Q operation. Directional laser effect is achieved. In addition, resonant free-space coupling to the symmetric and anti-symmetric hybrid modes of the photonic molecule is shown. We measure the coupling to each mode as a function of the spatial position of the laser spot, which can be used as a technique to probe the symmetry of coupled cavity modes.

A High-Q Terahertz Resonator for the Measurement of Electronic Properties of Conductors and Low-Loss Dielectrics

The successful engineering of sources and components in the terahertz (THz) regime benefits from good characterization of materials properties. Previous research reports have shown that calculations of material parameters that are valid at radio frequencies are no longer accurate at THz frequencies. A high-quality-factor quasi-optical hemispherical resonator operating between 300 GHz-1 THz has been designed and implemented for the measurement of electronic properties of conductors as well as low-loss dielectrics. This apparatus is the first quasi-optical resonator to achieve Q≈ 4×105 at frequencies greater than 400 GHz in the THz regime. It is also the first open resonator designed to measure effective conductivity at these frequencies. This paper discusses the techniques that enabled high-Q operation in the THz regime. It also includes measurements of silicon with different doping densities and conductors of various surface roughness values with comparison to theoretical predictions.

Comparative studies on magnetic flux relaxations of varied spherical toroids produced by co‐helicity merging

AbstractThe co‐helicity merging operations of compact toroid (CT) and spherical tokamak (ST) have been performed with external toroidal fields in the CT/ST merging device TS‐4. The low‐q (safety factor) CT merging as the compact RFP merging and the spheromak merging show the flux conversion from toroidal to poloidal in the course of the reconstruction of the Taylor force free state. The relaxation to the Taylor state proceeds through the following three states: (1) axisymmetric merging with increasing toroidal flux; (2) increase in the poloidal flux Ψ; and (3) relaxation to the Taylor state. The high‐q ST merging shows different relaxation process from those of the compact RFP and the spheromak mergings. Increases in Ψ were not clearly observed in the ST merging. The measured eigenvalues λ show that ST's, especially high‐q ST's, approach a unique intrinsic equilibrium state that has a λ proportional to Ψ with a longer lifetime than that of CT's. When external toroidal field is set in a certain range between the low‐q operation and the high‐q operation for ST's, an abnormal phenomenon was found in the ST formation, namely, a drastic decrease in the plasma lifetime. This phenomenon is characterized by very weak poloidal flux generations during the initial plasma production phase and the subsequent plasma separation phase when the plasma starts detaching from the flux core. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 7–15, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20069

同極性合体を用いて生成された各種球状トーラスの磁束緩和に関する比較研究

The co-helicity merging operations of compact toroid (CT) and spherical tokamak (ST) have been performed with external toroidal fields in the CT/ST merging device TS-4. The low-q (safety factor) CT merging as the compact RFP merging and the spheromak merging show the flux conversion from toroidal to poloidal in the course of the reconstruction of the Taylor force free state. The relaxation to the Taylor state proceeds through the following three states: (1) axisymmetric merging with increasing toroidal flux; (2) increase in the poloidal flux Ψ; and (3) relaxation to the Taylor state. The high-q ST merging shows different relaxation process from those of the compact RFP and the spheromak mergings. Increases in Ψ were not clearly observed in the ST merging. The measured eigenvalues λ show that ST's, especially high-q ST's, approach a unique intrinsic equilibrium state that has a λ proportional to Ψ with a longer lifetime than that of CT's. When external toroidal field is set in a certain range between the low-q operation and the high-q operation for ST's, an abnormal phenomenon was found in the ST formation, namely, a drastic decrease in the plasma lifetime. This phenomenon is characterized by very weak poloidal flux generations during the initial plasma production phase and the subsequent plasma separation phase when the plasma starts detaching from the flux core. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 7–15, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20069

Chaotic scattering in deformed optical microlasing cavities.

We consider a common class of dielectric optical microlasing cavities with quadrupolar deformations and address the question of the maximally allowed amount of deformation for both high-Q operation and a high degree of directionality of light emission. Our approach is to compute the probability for light rays to be trapped in the cavity by examining chaotic scattering dynamics in the classical phase space. We develop a dynamical criterion for high-Q operation and introduce a measure to quantify the directionality of the light emission. Our results suggest that high-Q and directionality can be achieved simultaneously in a wide range of the deformation parameter.

Self-assembled 3-D silicon microscanners with self-assembled electrostatic drives

Three-dimensional, electrostatically driven resonant torsion mirror microscanners are constructed by surface tension powered out-of-plane rotation of parts formed in bonded silicon-on-insulator. Simultaneous self-assembly of the fixed electrodes using a below-substrate limiter mechanism allows scanning perpendicular to the assembly axis, and direct drive allows high-Q operation.

Sealed-cavity resonant microbeam pressure sensor

A quasi-digital pressure sensor based on polysilicon resonant microbeams has been demonstrated. Pressure sensitivities of nearly 4000 counts per second per psi have been attained on a 10 psi device with a base frequency of 233 000 Hz. Short-term stability as low as 0.01 ppm of the base frequency is typical. The microbeams are fabricated with their own integral vacuum cavities, allowing high-Q operation in the differential pressure mode or in contact with liquids such as silicone oil. Design considerations include the effects of internal strain and lead to a push-pull layout configuration independent of microbeam strain or diaphragm thickness. Fabrication technology incorporates fine-grained polysilicon, surface micromachining, bulk micromachining, and reactive sealing. Packaging into precision avionics headers is being used for preliminary testing. Testing results indicate suitability for precision avionics, industrial, and commercial applications. Optical methods have been used to test resonant microbeam pressure sensors and verify the push-pull design methodology. Testing methods developed under this effort include electrostatic drive/piezoresistive sensing, optical drive/optical sensing, substrate piezoelectric drive/optical sensing, and electrostatic drive/laser vibrometer sensing. Wafer-level testing of 200 μm×46 μm×1.9 μm microbeams shows an average fundamental frequency of 553 150 and first overtone of 1 332 550 Hz. The standard deviations across the wafer are 0.15 and 0.10%, respectively. The internal strain and effective thickness can be determined with high resolution. Laser vibrometer measurements through the microbeam shell verify the fundamental frequency and reveal at least ten overtones up to 25 MHz.

Burning plasmas

The fraction of fusion reaction energy that is released in energetic charged ions, such as the alpha particles of the D-T reaction, can be thermalized within the reacting plasma and used to maintain its temperature. This mechanism facilitates the achievement of very high energy multiplication factors Q, but also raises a number of new issues of confinement physics. To ensure satisfactory reactor operation, three areas of energetic ion interaction need to be addressed: (1) single ion transport in imperfectly symmetric magnetic fields or turbulent background plasmas; (2) energetic ion driven (or stabilized) collective phenomena; (3) fusion heat driven collective phenomena. The first of these topics is already being explored in a number of tokamak experiments, and the second will begin to be addressed in the D-T burning phase of TFTR and JET. Exploration of the third topic calls for high-Q operation, which is a goal of proposed next generation plasma burning projects. Planning for future experiments must take into consideration the full range of plasma physics and engineering R&D areas that need to be addressed on the way to fusion power demonstration.

The high-density Z-pinch as a pulsed fusion neutron source for fusion nuclear technology and materials testing

The dense Z-pinch (DZP) is one of the earliest and simplest plasma heating and confinement schemes. Recent experimental advances based on plasma initiation from hair-like (10s μm in radius) solid hydrogen filaments have so far not encountered the usually devastating MHD instabilities that plagued early DZP experimenters. These encouraging results along with the debut of a number of proof-of principle, high-current (1–2 MA in 10–100 ns) experiments have prompted consideration of the DZP as a pulsed source of DT fusion neutrons of sufficient strength (SN ⩾ 1019 n/s) to provide uncollided neutron fluxes in excess ofIw= 5–10 MW/m2 over test volumes of 10–30 liters or greater. While this neutron source would be pulsed (100s ns pulse widths, 10–100 Hz pulse rate), giving flux time compressions in the range 105–106, its simplicity, near-term feasibility, low cost, high-Q operation, and relevance to fusion systems thatmay provide a pulsed commercial end-product, e.g., inertial confinement or the DZP itself, together create the impetus for preliminary consideration as a neutron source for fusion nuclear technology and materials testings. The results of a preliminary parametric systems study (focusing primarily on physics issues), conceptual design, and cost vs. performance analyses are presented. The DZP promises an inexpensive and efficient means to provide pulsed DT neutrons at an average rate in excess of 1019 n/s, with neutron currents Iw≲10 MW/m2 over volumes Vexp ⩾ 30 liter using single-pulse technologies that differ little from those being used in present-day experiments.

Surface-acoustic-wave resonators

The surface-acoustic-wave (SAW) resonator is the surface-wave equivalent of the crystal resonator now used extensively for stable frequency sources and filters. High-Q operation above 30 MHz, ruggedness, and small size characterize these devices. This paper reviews the current status of SAW resonator developments for the benefit of readers with interest or experience in either crystal resonators or SAW devices. Several typical device geometries are illustrated before providing a qualitative description of resonator operation. Some standard terminology and measurement procedures are proposed, based on similarities to crystal resonators but accounting also for some fundamental differences in loss and coupling mechanisms. Certain irreducible losses which limit the achievable Q of the intrinsic cavity are discussed. Applications are summarized with the aid of two filter examples. A variety of fabrication techniques are being used and none have been fully evaluated, especially with respect to reproducibility, tunability, and stability. Advances in theory, applications, and fabrication are occuring at a rapid rate in this exciting new area.