Showing papers on "Q factor published in 1993"

High-Q microwave acoustic resonators and filters

Abstract: The authors present recent experimental and modeling results for high-Q microwave acoustic resonators and filters for use in oscillators and other frequency control applications. Overmoded resonators have exhibited an FQ product greater than 1*10/sup 14/ Hz (e.g., Q=68,000 at 1.6 GHz) with a strong inductive response suitable for one-port and two-port oscillator feedback circuits. Ladder filters fabricated with overmoded resonators have loaded Qs greater than 40,000 with 76-kHz bandwidth at 1.6 GHz. Aluminum nitride films were used for transduction on Z-cut sapphire and lithium niobate substrates. >

Surface resistance measurements of HTS films by means of sapphire dielectric resonators

Abstract: A sapphire dielectric resonator with a copper cylindrical shield and two endplates replaced by high-temperature superconducting (HTS) layers was used for very accurate surface resistance measurements on laser-ablated YBCO films. A system using the TE/sub 011/ mode has a resonant frequency of about 18.1 GHz and parasitic-loss Q factor of about 120000. It allows 10 mm*10 mm samples to be measured with sensitivity of +or-30 mu Omega . Individual samples can be measured with somewhat lower accuracy. Using larger HTS samples, one can reduce parasitic losses of the system to an unsignificant level. The exact formulas presented for the resonant system allow for avoiding calibration procedures during the evaluation of the surface resistance. >

High performance direct coupled bandpass filters on coplanar waveguide

Abstract: This paper describes the design and performance of shunt inductively coupled bandpass filters implemented on an open coplanar waveguide. This new structure exhibits low radiation loss due to the removal of the capacitively coupled gaps encountered in end or edge coupled filters. Unloaded Qs greater than 540 have been achieved in unshielded single section resonators at 4 GHz on very thin substrates. These high Qs enable the design of filters with low insertion loss and good stopband rejection. Applications include low insertion loss, high and printed filters where no screening is required, low noise oscillators and superconducting filters. >

Thin-film HTS probe coils for magnetic-resonance imaging

Abstract: Several planar coil designs, with integral resonating capacitors, are reported using large-area sputtered YBCO films. One design utilizes a distributed interdigital capacitor, while a second exploits capacitive coupling of two films on opposite sides of a dielectric. Devices of the first design made on LaAlO/sub 3/ have achieved Q>10/sup 4/ at 18.5 MHz, possibly limited by the loss tangent of this substrate. Identical coils made with silver films have Q=10. With the second design, Q>10/sup 4/ was achieved at the even lower frequency of 5.7 MHz. >

A Q-enhanced active-RLC bandpass filter

Abstract: The passive elements R, L, and C are combined with an amplifier to realize a high-Q bandpass filter. Positive feedback is used to enhance the finite Q of the lossy integrated inductors, and design equations are given that take into account the finite gain and finite bandwidth of the amplifier. It is shown that a quality factor of 20 at 1 GHz is possible with 10-GHz transistors. Preliminary noise analysis indicates promising results. >

Ultrahigh Q-factor cryogenic sapphire resonator

Abstract: Measurements were made of the electrical quality factor in whispering gallery modes of a cylindrical, high purity single crystal sapphire dielectric resonator. A Q-factor of 8.3*10/sup 9/ at 1.6 K for a mode at 12.7 GHz is reported.

Approximate approach to the design of shielded dielectric disk resonators with whispering-gallery modes

Abstract: An analytical method is presented for calculating the resonant frequency and the Q-factor of shielded dielectric disk resonators excited in whispering-gallery modes. The method is based on a single-mode representation of electromagnetic fields in partial regions of the resonator. For high order modes with high degree of energy concentration in the dielectric this method gives a good agreement with experimental results obtained for different sapphire disks at both room temperature and cryogenic temperatures. >

Measurement of material properties with a tunable resonant cavity

Abstract: A tunable resonant cavity is used to measure the complex permittivity of dielectrics and the surface conductivity of metals with high precision. The analytical approximations, traditionally used in the cavity perturbation techniques, have been replaced with a rigorous numerical solution of the electromagnetic field distribution inside the rotationally symmetric cavity filled with inhomogeneous dielectrics. The measured values of the unloaded Q factor are compared with the numerically computed values over the tuning range. The least-squares data fitting procedure yields simultaneously the values of the loss tangent and the surface conductivity, and their standard deviations.

Improved microwave performance of Ag‐doped Y1Ba2Cu3O7−δ thin film microstrip resonators

Abstract: Microwave transmission properties of undoped and Ag‐doped laser ablated thin film Y1Ba2Cu3O7−δ microstrip resonators have been studied both on <100≳ MgO and <100≳ LaAlO3 substrates at X‐band frequencies. While the Q factor and microwave surface resistance, Rs, of undoped films showed better performance on LaAlO3 as compared to that on MgO, Ag‐doped films on LaAlO3 showed far greater improvement as reflected not only by a decrease in Rs but also by a total absence of its microwave power dependence up to 13 dBm at 77 K. These results are explained as due to the influence of Ag in increasing the grain size and grain alignment and thus, significantly decreasing the density of grain boundary weak links which are known to affect the microwave transmission in high temperature superconductor films.

Viscous energy dissipation in laterally oscillating planar microstructures: a theoretical and experimental study

Abstract: The authors investigate energy loss in an incompressible, viscous fluid layer that provides skin-friction damping for a laterally oscillating planar microstructure. The physical model for the viscous dissipation is based on Stokes-type fluid motion. In the theoretical analysis, the damping property of a fluid layer is characterized in terms of viscous energy dissipation, resulting in damping formulas for practical Q estimation. In the experimental study, surface-micromachined polysilicon resonators have been fabricated and tested under an electrostatic excitation in atmosphere. The estimated Q compares well with the Q measured for the test structures, as well as with the experimental Q reported by previous investigators. It is concluded that the Stokes-type damping model presents a more general damping treatment with better Q estimation, although discrepancies of 10 to 20% still remain between the estimated and measured Q. Possible sources of these discrepancies are discussed. The results of the study are applicable to damping design for microsensors and microactuators. >

Ultrahigh Q pendulum suspensions for gravitational wave detectors

Abstract: Pendulum suspensions for laser interferometer gravitational wave detectors need to have an extremely high Q factor to minimize Brownian motion noise. In this paper we analyze the limits to the Q factor of the compound pendulum. We show that the observed acoustic loss of niobium can allow pendulum Q factors of 1010 to be achieved. This should enable a 3 km terrestrial laser interferometer detector to achieve strain sensitivity of 10−22/√Hz at frequencies as low as 10 Hz. At cryogenic temperatures Q factors up to 1012 should be achievable.

Polysilicon hollow beam lateral resonators

Abstract: The first microfabrication of hollow polysilicon beams is reported. Arrays of lateral resonators are designed, processed, and tested with resonant frequencies from 8 kHz to 0.5 MHz. The quality factor as a function of pressure of the hollow beam resonators is compared with solid beam resonators, and values as high as 34000 are obtained in vacuum. The hollow beam resonators are verified with theory and compared to resonators with solid cross sections. >

Tests on a low-frequency inverted pendulum system

Abstract: The authors report the performance and mechanical properties of an inverted pendulum as a vibration isolator. The advantages of such a system for vibration isolation in an interferometric gravitational wave detector is demonstrated through modelling of the isolator's response. An experimental investigation using a prototype inverted pendulum was also performed where the behaviour of the stability, resonant frequency and Q factor with varying load mass was examined. The pendulum was also used as a seismometer to examine low-frequency seismic activity.

Closed loop tests of the NASA sapphire phase stabilizer

Abstract: A cryogenic sapphire phase stabilizer (SPS) has been developed to meet microwave oscillator phase noise requirements. The SPS uses a high-Q, X-band sapphire dielectric whispering-gallery mode resonator as a discriminator to stabilize a quartz crystal oscillator. At an untuned frequency of 7.9449 GHz with a loaded Q of 6 million, an "open loop" discriminator noise floor (referred to 100 MHz) of approximately S/sub phi/(f) = -110 dB/f/sup 3/(/Hz) was previously reported for offset frequencies from 1 Hz to 1 kHz. Precise tuning of the sapphire resonant frequency now allows implementation of simplified control loops together with suppressed-carrier phase sensing circuitry. These improvements make possible an ultralow-noise demonstration of closed-loop SPS performance. From 1 Hz to 1 kHz a comparison of the SPS with a quartz crystal reference oscillator of the highest quality showed only the noise of the reference oscillator. These results appear to represent the lowest phase noise in a closed-loop or active sapphire oscillator to date at temperatures achievable with liquid nitrogen (77 K or higher). >

Effects of spurious modes in resonant cavities

Abstract: General theory of two reactively coupled interacting resonant modes is presented in terms of normalized equivalent circuit parameters. For the first time analytical equations are derived that explain the effects on the mode frequencies, Q factors and couplings as a function of detuning for two coupled resonant modes. All equations are verified experimentally by observing a mode interaction while tuning a tunable sapphire-loaded superconducting cavity resonator. This work enables theoretical analysis of the effect of a spurious mode on an operational mode in a resonant cavity. The extent that the spurious mode can translate its inferior frequency stability and Q factor is investigated. The impact of utilizing a high-Q whispering gallery resonator with a high spurious mode density for low-noise signal generation is discussed.

High-Q TE stabilized sapphire microwave resonators for low noise applications

Abstract: Two low-noise high-Q sapphire loaded cavity (SLC) resonators, with unloaded Q values of 2 /spl times/ 10/sup 5/ and very low densities of spurious modes have been constructed. They were designed to operate at 0/spl deg/C with a center frequency of 10.000000 GHz. The cavity was cooled with a thermoelectric (TE) Peltier element and in practice achieved the required center frequency near 1/spl deg/C. The resonator has a measured frequency-temperature coefficient of -0.7 MHz/K and a Q-factor which is measured to be proportional to T/sup 2.5/. An upper limit to the SLC residual phase noise to L(100 Hz) = -147.5 dBc/Hz, L(1 kHz) = -155 dBc/Hz, and L(10 kHz) = -160 dBc/Hz has been measured. The authors have created a free running loop oscillator based on the SLC resonator and measured its frequency noise using the other as a discriminator. >

Oscillator circuit for use with high loss quartz resonator sensors

Abstract: The disclosure is directed to a Lever oscillator for use in high resistance resonator applications, especially for use with quartz resonator sensors. The oscillator is designed to operate over a wide dynamic range of resonator resistance due to damping of the resonator in mediums such as liquids. An oscillator design is presented that allows both frequency and loss (R m ) of the resonator to be determined over a wide dynamic range of resonator loss. The Lever oscillator uses negative feedback in a differential amplifier configuration to actively and variably divide (or leverage) the resonator impedance such that the oscillator can maintain the phase and gain of the loop over a wide range of resonator resistance.

Gaussian-beam open resonator with highly reflective circular coupling regions

Abstract: A high-Q open resonator with quasi-optical coupling regions is described. The resonator consists of a pair of spherical mirrors, on each of which a highly reflective, partially transparent circular region is fabricated with a diameter larger than several wavelengths. The signal is coupled in and out as a Gaussian beam by means of these regions. Both very weak coupling and very efficient mode conversion are simultaneously achieved. This results in a Q-factor over 2*10/sup 5/ and a high signal-to-noise ratio at 105.9 GHz. The Q-factor of the open resonator can be varied by rotating the output mirror to change the angle between the directions of the conducting stripes on the two mirrors. >

High temperature superconducting 8.45-GHz bandpass filter for the Deep Space Network

Abstract: A high-temperature superconducting (HTS) stripline 8.45-GHz bandpass filter, designed for the Deep Space Network, is presented. It has very low insertion loss, indicative of resonators with unloaded Q's greater than 10000. The performance of this filter shows that practical, high-Q multiresonator devices can be constructed using lanthanum aluminate substrates in a stripline configuration. The HTS films used in this filter were of the thallium barium calcium copper oxide (TBCCO) variety, deposited on a lanthanum aluminate substrate using laser ablation and postdeposition thermal processing. The HTS surface resistance of these TBCCO films is less than 0.5 m Omega at 10 GHz and facilitates the construction of planar HTS resonators with unloaded Q's greater than 10000 at 10 GHz. HTS planar circuits with these Q's are very useful in constructing narrow-bandwidth filters due to the resulting very low minimum insertion loss. >

Equivalent circuit for birdcage resonators

Abstract: We present an equivalent circuit analysis for both low pass and high pass birdcage resonators loaded with lossy samples. In a generalization of the method of Hoult and Lauterbur (J. Magn. Reson. 34, 425 (1979)), we also derive circuit component values by application of the laws of electrodynamics. Measured resonance spectra, quality factors, and feed point impedances in a test resonator are shown to be in agreement with those predicted by the proposed model.

Overmoded high Q resonators for microwave oscillators

Abstract: High-overtone bulk acoustic wave resonators operating in the 1-6 GHz range have been fabricated on sapphire, lithium niobate, dilithium tetraborate, and quartz substrates in an effort to obtain high-Q C-axis normal aluminum nitride films were used for transduction for all the substrates, yielding longitudinal modes. The resonators on Z-cut sapphire exhibited an unloaded fQ product in excess of 1 /spl times/ 10/sup 14/ at frequencies between 1.6 and 4.0 GHz. The resonators on Z-cut sapphire exhibited Qs as high as 68,000 at 1.6 GHz with highly inductive response. Lithium niobate exhibited a Q of 54,000 at 1.6 GHz. When used in combination with a mode-select filter these resonators would make good feedback elements for low phase noise oscillators where inherent high temperature stability is not necessary. >

Ultra-stable sapphire resonator-oscillator

Abstract: Preliminary measurements of the properties of cryogenic sapphire resonators with various concentrations of paramagnetic impurities are reported. These resonators are mounted in both copper and niobium shields. It is found that one can achieve extrema in the frequency-temperature function in the temperature range 5-18 K due to the compensating effects of the dielectric constant temperature dependence and the Curie law dependence on the susceptibility of the paramagnetic impurities. In samples where dominant paramagnetic impurity has a high ESR (electron spin resonance) unloaded resonator Q factors as high as 4*10/sup 9/ are observed. The increased Q factors coupled with reduced shield interactions should result in an improvement in frequency stability for an oscillator based around this resonator as compared to the best results achieved to date as the authors' laboratory (an Allan variance of 9*10/sup -15/). The preliminary measurement of the tilt sensitivity of the oscillator is reported to be a fractional frequency shift of 6.5*10/sup -12/ per degree. >

Field solution for a thin-film superconducting parallel-plate transmission line

Abstract: By using Bose statistics and the Gorter and Casimir model for a two-fluid model, London's equations, and the classical skin effect for the normal component of the current, a sinusoidal wave solution is found for a superconducting transmission line. This solution gives expressions for the phase velocity and attenuation coefficient which are used to compare the behaviour of a wave in LTS's and HTS's and to investigate the value of the Q -factor of a parallel-plate resonator. The computed values of the Q -factor are compared with measured data in the literature.

High Q microwave acoustic resonators and filters

Abstract: The authors present recent experimental and modeling results for high-Q microwave acoustic resonators and filters for use in oscillators and other frequency control applications. Overmoded resonators have exhibited an FQ product greater than 1*10/sup 14/ Hz (e.g. Q=68000 at 1.6 GHz) with a strong inductive response suitable for one-port and two-port oscillator feedback circuits. Ladder filters fabricated with overmoded resonators have loaded Qs greater than 40000 with 76-kHz bandwidth at 1.6 GHz. Aluminum nitride films were used for transduction on Z-cut sapphire substrates. >

An uncooled microwave oscillator with 1-million effective Q-factor

Abstract: Calculations reveal the possibility of 10-15 dB flicker phase noise reduction in a bridge-type oscillator. A super-low phase noise S-band bipolar transistor oscillator based on a shielded sapphire disc dielectric resonator (SDDR) used as a filtering circulator bridge is considered. With shielding sizes optimized, the SDDR Q/sub /spl phi//- factor was /spl les/3 /spl times/ 10/sup 5/ at room temperature. An effective (loaded) oscillator Q-factor of greater than 3 /spl times/ Q/sub /spl phi//, i.e., of about 1 million, was realized. >

Tactical BVA quartz resonator performance

Abstract: The author considers the performance of tactical BVA quartz resonators, specifically their measured frequency stability. Data are presented demonstrating the resonators' ability to survive harsh environmental conditions. Test results suggest that an oscillator using a tactical BVA resonator could be developed that would have very high frequency stability, be relatively small, and have low mass. The tactical resonators evaluated are 10-MHz, third overtone, SC (stress-compensated) cut devices housed in HC-40 enclosures. The Q of the resonators tested was between 1.2 and 1.3 million. >

Analysis of superconducting transmission-line structures for passive microwave device applications

Abstract: A full-wave spectral-domain volume-integral-equation technique is used to calculate the complex propagation constant, the complex characteristic impedance, and the current distribution for Nb and YBa/sub 2/Cu/sub 3/O/sub 7-x/ microstrip lines and coplanar waveguides with superconducting ground planes. Measurements of resonant frequency and quality factor are performed on Nb microstrip and coplanar waveguide resonators, and the results are compared with numerical calculations. The power-handling capability of various superconducting transmission-line structures is calculated. Results of phase noise measurements on Nb microstrip resonators suggest that phase noise may be related to the current distribution in the structure. >

Narrow bandwidth long wavelength resonant cavity photodiodes

Abstract: Resonant cavity photodetectors at 1.53μm are demonstrated using the epitaxial liftoff technique to position an epilayer structure between two metallic mirrors. The epilayer consists of a pin structure with quantum wells placed strategically at the antinodes of the fabricated cavity. The quality factor of the 1.16μm long cavity is 59 corresponding to mirror reflectivies of 94 and 90%.

A new method of determining the equivalent circuit parameters of piezoelectric resonators and analysis of the piezoelectric loading effect

Abstract: An inductive method of piezoelectric resonance detection is applied to the determination of equivalent circuit parameters of piezoelectric resonators. Using this method one can measure the resonance frequency and mechanical Q-factor of a resonator directly as well as their dependences on the electrical impedance which is connected to the resonator. From the equivalent circuit analysis the changes in resonance frequency and Q-factor due to the piezoelectric loading effects are determined. Measurements on two typical commercial piezoelectric resonators, an AT-cut quartz crystal and a PZT ceramic resonator, are in good agreement with the analysis. >