Microwave Loss Research Articles

Microwave Quenching in DC-Biased Coplanar Waveguide Based on <inline-formula> <tex-math notation="LaTeX">${YBa}_{2}{Cu}_{3}{O}_{7-\delta}$</tex-math> </inline-formula> Thin Film

In this paper, we report on the results of features in the discovered effect of a strong change in the microwave losses (quenching) in HTS-based coplanar waveguide (CPW) at certain values of the input power $P_{in}$ and direct current (DC) $I_{dc}$. Two waveguides were studied: CPW-150 and CPW-75, fabricated of epitaxial 150 nm and 75 nm YBCO films. The insertion loss of CPW, $IL = 10 lg (P_{out} / P_{in})$, was measured versus both the operating temperature and the bias DC current $I_{dc}$ when a fixed level of the input X-band pulsed MW signal $P_{in}$ was applied. Here $P_{out}$ is the power measured at the CPW output. A pulse duration ${\tau}_i$ was 5 ${\mu}s$ with pulse repetition period T = 40 ${\mu}s$. Experiments showed a noticeable difference in specific values of $I^*= I_{dc}$ corresponding to the $P_{in}$ dependent quenching phenomenon in CPW-150 and CPW-75. With a weak input signal the difference in behavior of CPWs is anticipated, i.e., quenching occurs at a lower current for thinner film. For $P_{in}>1W$ the situation is opposite, i.e., quenching for CPW-150 takes place at a lower $I^*$. This is explained by stronger microwave heating of CPW-150.

Impact of hydrogen forming gas annealing on microwave properties of Ba(Zn1/3Ta2/3)O3 dielectric ceramics

The effect of H2forming gas annealing on the microwave properties of [Formula: see text] (BZT) dielectric ceramics has been studied. The structural, microwave, DC electrical and optical properties were analyzed by experiment results. With elevated temperature annealing, the microwave loss of BZT was increased. This trend correlated with high DC conductivity of annealed samples, as well as dampened phonons found in Raman spectra. These evidences, together, prove that the enhancement of oxygen vacancy defects induced by oxygen deficient sintering environment is one of the main extrinsic root causes for the high microwave loss in practical ceramic materials.

Effects of nonequilibrium quasiparticles in a thin-film superconducting microwave resonator under optical illumination

We have illuminated a thin-film superconducting Al lumped-element microwave resonator with 780 nm light and observed the resonator quality factor and resonance frequency as a function of illumination and microwave power in the 20 to 300 mK temperature range. The optically induced microwave loss increases with increasing illumination but decreases with increasing microwave power. Although this behavior may suggest the presence of optically activated two-level systems, we find that the loss is better explained by the presence of nonequilibrium quasiparticles generated by the illumination and excited by the microwave drive. We model the system by assuming that the illumination creates an effective source of phonons with energy higher than double the superconducting gap and solve the coupled quasiparticle-phonon rate equations. We fit the simulation results to our measurements and find good agreement with the observed dependence of the resonator quality factor and frequency shift on temperature, microwave power, and optical illumination. Examination of the model reveals approaches to reducing optically induced loss and improving the relaxation time of superconducting quantum devices.

Микроволновые потери в слабопоглощающих алмазоподобных материалах при 1 К < T < 300 К. Феноменологическое моделирование

Микроволновые потери в слабопоглощающих алмазоподобных материалах при 1 К < T < 300 К. Феноменологическое моделирование

Measurement of dielectric loss tangent at cryogenic temperature using superconducting film resonator

We demonstrate that the superconducting film resonator can be used to accurately and quantitatively measure the microwave dielectric loss tangent of a variety of materials. Compared to traditional dielectric resonator loaded metal cavity method, it has advantage of small sample size (~2–3 orders of magnitude smaller than the old method), and much higher sensitivity to measure small loss tangent values as small as 10−5 at around 7 GHz band at cryogenic temperatures. This method can be utilized widely in study of mechanism of microwave loss at cryogenic temperature range, which is extremely important in superconducting microwave application areas, such as novel super quantum computers.

Controllable-permittivity and low-loss of Ba0.5Sr0.5TiO3/MgO composites prepared by citrate gel derived core-shell powders

Core-shell Ba0.5Sr0.5TiO3(BST)/MgO nano-composites have been synthesized by using an oleic acid modified citrate gel in situ process. The nano-composites exhibit a spherical microstructure consisting of large amounts of small particles with average sizes of 50-100 nm, which results in high F center levels in the composite ceramics. Interestingly, microwave permittivity of the composite can be reduced significantly with increasing volume fraction of MgO, while microwave loss and tunability remain almost unchanged, which is in good agreement with the results of the columnar model.

Preparation of Low Microwave Loss YIG Thin Films by Pulsed Laser Deposition

Y3Fe5O12 thin films with thickness 10 $10~{\rm nm} \le t \le 1440$ nm were grown on Gd3Ga5O12 (111) substrates by pulsed laser deposition. The X-ray diffraction experiments confirmed the films are pure yttrium iron garnet (YIG) phase with preferred (111) orientation. The magnetic and microwave properties were studied as a function of film thickness by the dc magnetization and ferromagnetic resonance (FMR) measurements. The FMR linewidth ( $\Delta H$ ) was found to decrease with the increase in film thickness $10~{\rm nm} \le t \le 45$ nm), attaining a minimum value of $\Delta H_{\bot }=5$ Oe and $\Delta H_{\mathrm {\vert \vert }}=6$ Oe, for perpendicular and parallel resonance, and then rising with further increase in thickness. Acid etching experiments were performed to understand the mechanism contributing to $\Delta H$ . The increase in $\Delta H$ with thickness ( $t > 45$ nm) may be explained in terms of extrinsic mechanisms, such as inhomogeneities present at the surface of the films. However, the decrease in $\Delta H$ with thickness ( $t nm) is believed to be due to the surface anisotropy effect. The films showed low coercivity values in the range of $\sim 1.5$ –7 Oe, which is an indicator of good quality YIG films.

Effect of ferroelectric substrate on carrier mobility in graphene field-effect transistors

Effect of LiNbO3 ferroelectric substrate on the carrier mobility in top gated graphene field-effect transistors (G-FETs) is demonstrated. It is shown that, at the same residual concentration of the charge carriers, the mobility in the G-FETs on the LiNbO3 substrate is higher than that on the SiO2/Si substrate. The effect is associated with reduction of Coulomb scattering via screening the charged impurity field by the field induced in the ferroelectric substrate, but significant only for mobilities below 1000 cm2/V s. Raman spectra analysis and correlations established between mobility and microwave loss tangent of the Al2O3 gate dielectric indicate that the charged impurities are located predominantly at the gate dielectric and/or at the gate dielectric/graphene interface and are likely associated with oxygen vacancies.

Electromagnetic and microwave absorbing properties of the composites containing flaky FeSiAl powders mixed with MnO2 in 1–18 GHz

The flaky FeSiAl/ irregular shaped MnO2 composite with the different mass ratios were prepared by using a two-roll mixer and a vulcanizing machine. The morphologies of the composite absorbers were characterized by a scanning electron microscope. The microwave electromagnetic properties of the composites were measured using a vector network analyzer in the range of 1–18GHz. The effect of the mass ratio of FeSiAl/MnO2 on the microwave loss properties of the composites was investigated. The results show that the reflection loss (RL) values exceeding −20dB from 3.5 to 16.5GHz can be obtained for the flaky FeSiAl/MnO2 mass ratio of 1:1 from 1.5mm to 5mm. In addition, the FeSiAl/MnO2 composite with the FeSiAl/MnO2 mass ratio of 7:3 has −10dB bandwidth of 6.6GHz (from 11.4–18GHz) with a thickness of 1.5mm. It is found that the flaky FeSiAl/MnO2 composites can be potential microwave absorption materials.

Alternating current-driven microwave loss modulation in a fluxonic metamaterial

We introduce a fluxonic metamaterial on the basis of nanopatterned superconducting Nb microstrips and employ it for modulation and synthesis of quantized loss levels in the lower GHz range by a sine-wave quasistatic ac drive. The nanopatterns are uniaxial nanogrooves with identical and different slope steepness, which induce a pinning potential of the washboard type for Abrikosov vortices. For the fundamental matching field, when the location of vortex rows geometrically matches the nanogrooves, the following effects are observed: The forward transmission coefficient S21(f) of the microstrips can be controllably modulated within a range of about 3 dB by the ac. For the sample with symmetric grooves, depending on the choice of the operation point in the current-voltage curve, the shape and the duty cycle of the output signal can be tuned. For the sample with asymmetric grooves, depending on the ac amplitude, a sine-to-triangular or a sine-to-rectangular pulse shape conversion is observed. The possibility of synthesizing quantized loss levels by a serial connection of the two samples with different nanopatterns is exemplified and can be used for the development of multilevel excess-loss-based fluxonic devices.

Design and characterization of a W-band system for modulated DNP experiments

Magnetic-field and microwave-frequency modulated DNP experiments have been shown to yield improved enhancements over conventional DNP techniques, and even to shorten polarization build-up times. The resulting increase in signal-to-noise ratios can lead to significantly shorter acquisition times in signal-limited multi-dimensional NMR experiments and pave the way to the study of even smaller sample volumes. In this paper we describe the design and performance of a broadband system for microwave frequency- and amplitude-modulated DNP that has been engineered to minimize both microwave and thermal losses during operation at liquid helium temperatures. The system incorporates a flexible source that can generate arbitrary waveforms at 94GHz with a bandwidth greater than 1GHz, as well as a probe that efficiently transmits the millimeter waves from room temperature outside the magnet to a cryogenic environment inside the magnet. Using a thin-walled brass tube as an overmoded waveguide to transmit a hybrid HE11 mode, it is possible to limit the losses to 1dB across a 2GHz bandwidth. The loss is dominated by the presence of a quartz window used to isolate the waveguide pipe. This performance is comparable to systems with corrugated waveguide or quasi-optical components. The overall excitation bandwidth of the probe is seen to be primarily determined by the final antenna or resonator used to excite the sample and its coupling to the NMR RF coil. Understanding the instrumental limitations imposed on any modulation scheme is key to understanding the observed DNP results and potentially identifying the underlying mechanisms. We demonstrate the utility of our design with a set of triangular frequency-modulated DNP experiments.

Polyvinylidene fluoride/nanocrystalline iron composite materials for EMI shielding and absorption applications

The present paper reports, novel outcome comprising experimental results on electromagnetic interference (EMI) shielding and radar signal absorption characteristics of a polymer-metal composite (PMC) based on polyvinylidene fluoride (PVDF) dispersed with varying concentration of nanocrystalline iron (n-Fe). The PVDF/n-Fe composites, prepared using mechanical blending followed by hot-molding process at an optimum pressure and temperature, exhibited better filler dispersion. The relevant parameters, i.e.; microwave permittivity, permeability, shielding effectiveness (SE) and loss factors, has been calculated using scattering parameters measured in X-band (8.2–12.4 GHz) by waveguide method. The theoretical EMI SE has also been evaluated by transmission line model using measured material parameters as the input for meaningful comparison with the experimental results. Further, a theoretical analysis of single layer PMC is performed for the absorption by assuming that the absorbing structure is backed by perfect electrical conductor. The results so obtained, confirmed an improved shielding and absorption properties of PVDF/n-Fe composites vis-à-vis its counterpart reported in literature. The findings in this work, suggest potential futuristic applications of PMC in shielding and absorption of electromagnetic waves.

Microwave loss of DC sputtered NbTiN microstrip lines

Amorphous NbTiN is widely applied in superconducting electronic devices owing to its merits of wide energy gap, high Tc, and mitigated requirement in fabrication. Its highly disordered feature yields considerable kinetic inductance, making it an ideal material for parametric amplification. To build up the correspondence between the fabrication conditions and the desirable electrical performance, we designed, fabricated, and measured NbTiN microstrip resonators at microwave frequencies. The principal result is that the unloaded Q factor of the resonators does not depend on the film normal state resistivity, which largely depends on the sputtering pressure. This result is consistent with the dirty superconductor theories.

A Low-Voltage 35-GHz Silicon Photonic Modulator-Enabled 112-Gb/s Transmission System

We present a silicon photonic traveling-wave Mach–Zehnder modulator operating near 1550 nm with a 3-dB bandwidth of 35 GHz. A detailed analysis of traveling-wave electrode impedance, microwave loss, and phase velocity is presented. Small- and large-signal characterization of the device validates the design methodology. We further investigate the performance of the device in a short-reach transmission system. We report a successful 112-Gb/s transmission of four-level pulse amplitude modulation over 5 km of SMF using 2.2 ${\rm V}_{{\rm p} - {\rm p}} $ drive voltage. Digital signal processing is applied at the transmitter and receiver. 56-GBaud PAM-4 and 64-Gb/s PAM-2 transmission is demonstrated below a pre-FEC hard decision threshold of $4.4 \times 10^{-3}$ .

Microwave Losses in YBCO Coplanar Waveguide Resonators at Low Power and Millikelvin Range

We have investigated the temperature dependence of microwave losses in the low-power limit and millikelvin temperature range of a thin-film YBa2Cu3O7-x (YBCO) λ/2 coplanar waveguide resonator patterned on a (La0.3Sr0.7) (Al0.65Ta0.35)O3 (LSAT) substrate covered by a CeO2 seed layer. The unloaded quality factor is mainly governed by the surface resistance of the YBCO film and the dielectric losses caused by resonant absorption due to a bath of two-level fluctuators in the dielectrics. The value of the unloaded quality factor at 20 mK and low power, i.e., Q0∼2000, allows for the realization of YBCO microwave quantum circuits implementing biepitaxial grain-boundary Josephson junctions.

Theoretical Feasibility Demonstration for Over 100 GHz Electro-Optic Modulators With c-Axis Grown BaTiO <sub>3</sub> Crystal Thin-Films

Single-channel 100 GHz and higher bandwidth external optical modulators are dramatically demanded to realize the aggregate carrier data rate of 100 Tb/s per optic-fiber in next-generation optical networks, but the current technologies used in industrial systems have never shown any feasibility to reach such high-speed operations. In this study, the feasible potential of ultrahigh bandwidths higher than 100 GHz are theoretically demonstrated for waveguide electro-optic (EO) modulators with c-axis-oriented BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystal thin-films. As the three dominant factors of determining the bandwidths of EO modulators, the interaction length L, the absolute refractive difference of light-wave and microwave |N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> -N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> | determining the velocity mismatch, and the microwave loss coefficient are investigated to realize the ultrahigh bandwidths of over 100 GHz, where L is a weight factor of both the velocity mismatch and the microwave loss. Thus, in this process, the nonlinear EO modulation effects are taken into account to determine the L values with respect to the values of EO coefficient r <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">51</sub> under a given half-wave voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> . Then, the optimal tradeoff conditions for the over 100 GHz bandwidths are obtained with the consistent relations among the interaction length, the optical loss, the electrode gap, and the overlap integral of optical and electrical fields, the refractive index difference between the optical guidedmode and the microwave. As a result, for an industrial acceptable V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> of 5.0 V and a feasible absolute birefringence b <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eo</sub> of 0.005, at the EO coefficient r <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">51</sub> values of over 550 pm/V an optimal device in both optical rib waveguide and microwave electrode dimensions shows the illustrative results of over 100 GHz bandwidth in the believable simulations albeit both the velocity mismatch and the microwave loss are taken into account in simulations under a microwave impedance matching, which are all reachable in the real c-axis BaTiO3 crystal thin-film.

High-Frequency Dielectric Properties of Nanocomposite and Ceramic Titanates

A set of ferroelectric and related titanate ceramics and nanocomposites were prepared and their dielectric and electromagnetic properties were studied in a broad frequency range, including microwave, millimeter-wave and THz frequencies. Dielectric and conductivity spectra of the opal-matrix nanocomposites were typical for conductor-dielectric composites and could be described by Cole-Cole relaxations and Drude conductivity. The highest values of microwave dielectric permittivity, losses and conductivity were observed in the composite with Pr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> nanoparticles. Absorption properties of ceramic and some composite titanates were measured and estimated in the microwave range. Some of the studied compositions were found to be interesting for development of microwave absorbing or shielding materials.

Loss mechanism and microwave absorption properties of hierarchical NiCo2O4 nanomaterial

Understanding the loss mechanism of microwave absorption is of great significance for the design and fabrication of low-cost, high-efficient and light-weight microwave absorbing materials. In this study, the microwave absorption of a hierarchical NiCo2O4 nanomaterial synthesized via a hydrothermal method and a subsequent annealing process was investigated in detail. The effects of the annealing temperature on the phase evaluation and microwave absorption properties were also investigated to reveal the microwave loss mechanism of NiCo2O4 nanostructures. The results show that the Debye relaxation and superior electric conductivity of NiCo2O4 are beneficial to its excellent microwave absorption performance. This study will be useful for the fundamental understanding of microwave absorption in NiCo2O4 nanomaterial, and for the design of a novel microwave absorbent.

Dual cut-off direct current-tunable microwave low-pass filter on superconducting Nb microstrips with asymmetric nanogrooves

We present a dual cut-off, dc-tunable low-pass microwave filter on a superconducting Nb microstrip with uniaxial asymmetric nanogrooves. The frequency response of the device was measured in the range 300 KHz–14 GHz at different temperatures, magnetic fields, and dc values. The microwave loss is most effectively reduced when the Abrikosov vortex lattice spatially matches the underlying washboard pinning landscape. The forward transmission coefficient S21(f) of the microstrip has a dc-tunable cut-off frequency fd which notably changes under dc bias reversal, due to the two different slope steepnesses of the pinning landscape. The device's operation principle relies upon a crossover from the weakly dissipative response of vortices at low frequencies when they are driven over the grooves, to the strongly dissipative response at high frequencies when the vortices are oscillating within one groove. The filter's cut-off frequency is the vortex depinning frequency tunable by the dc bias as it diminishes the pinning effect induced by the nanopattern. The reported results unveil an advanced microwave functionality of superconducting films with asymmetric (ratchet) pinning landscapes and are relevant for tuning the microwave loss in superconducting planar transmission lines.

Structure, magnetic and microwave properties of indium-doped barium ferrite thick films prepared by tape casting

In this paper, pure and indium-doped barium ferrite (BaInxFe12-xO19, x = 0, 1) thick films were fabricated by tape casting. X-ray diffraction and scanning electron microscopy results show that these BaM thick films have highly c-axis oriented crystallographic texture. Magnetic measurements indicated that pure samples exhibit excellent properties with a saturate magnetization (4) of 3806G, a high squareness ratio (Mr/Ms) of 0·85. Ferromagnetic resonance measurements showed that the smallest ferromagnetic resonance line width is 383 Oe at 45 GHz. When indium was introduced, the hexagonal grains disappear, and the 4 is decreased to 3201G. The anisotropy field decreased from 15·9 to 12·2 kOe, and the smallest ferromagnetic resonance line width became 387 Oe at 30 GHz. These data meant that these thick films have high self-biased property and low microwave loss, which makes sure that these samples can be applied in self-biased microwave/millimeter wave devices such as filters, circulators and isolators.