Engineering the microwave to infrared noise photon flux for superconducting quantum systems

Electromagnetic filtering is essential for the coherent control, operation and readout of superconducting quantum circuits at milliKelvin temperatures. The suppression of spurious modes around transition frequencies of a few GHz is well understood and mainly achieved by on-chip and package considerations. Noise photons of higher frequencies – beyond the pair-breaking energies – cause decoherence and require spectral engineering before reaching the packaged quantum chip. The external wires that pass into the refrigerator and go down to the quantum circuit provide a direct path for these photons. This article contains quantitative analysis and experimental data for the noise photon flux through coaxial, filtered wiring. The attenuation of the coaxial cable at room temperature and the noise photon flux estimates for typical wiring configurations are provided. Compact cryogenic microwave low-pass filters with CR-110 and Esorb-230 absorptive dielectric fillings are presented along with experimental data at room and cryogenic temperatures up to 70 GHz. Filter cut-off frequencies between 1 to 10 GHz are set by the filter length, and the roll-off is material dependent. The relative dielectric permittivity and magnetic permeability for the Esorb-230 material in the pair-breaking frequency range of 75 to 110 GHz are measured, and the filter properties in this frequency range are calculated. The estimated dramatic suppression of the noise photon flux due to the filter proves its usefulness for experiments with superconducting quantum systems.

Quantitative signal subspace imaging

We develop and analyze a quantitative signal subspace imaging method for single-frequency array imaging. This method is an extension to MUSIC (multiple signal classification) which uses (i) the noise subspace to determine the location and support of targets, and (ii) the signal subspace to recover quantitative information about the targets. For point targets, we are able to recover the complex reflectivity and for an extended target under the Born approximation, we are able to recover a scalar quantity that is related to the product of the volume and relative dielectric permittivity of the target. Our resolution analysis for a point target demonstrates this method is capable of achieving exact recovery of the complex reflectivity at subwavelength resolution. Additionally, this resolution analysis shows that noise in the data effectively acts as a regularization to the imaging functional resulting in a method that is surprisingly more robust and effective with noise than without noise.

Highly Sensitive Flexible Pressure Sensors Enabled by Mixing of Silicone Elastomer With Ionic Liquid-Grafted Silicone Oil

Developing highly sensitive flexible pressure sensors has become crucially urgent due to the increased societal demand for wearable electronic devices capable of monitoring various human motions. The sensitivity of such sensors has been shown to be significantly enhanced by increasing the relative dielectric permittivity of the dielectric layers used in device construction via compositing with immiscible ionic conductors. Unfortunately, however, the elastomers employed for this purpose possess inhomogeneous morphologies, and thus suffer from poor long-term durability and unstable electrical response. In this study, we developed a novel, flexible, and highly sensitive pressure sensor using an elastomeric dielectric layer with particularly high permittivity and homogeneity due to the addition of synthesized ionic liquid-grafted silicone oil (denoted LMS-EIL). LMS-EIL possesses both a very high relative dielectric permittivity (9.6 × 105 at 10−1 Hz) and excellent compatibility with silicone elastomers due to the covalently connected structure of conductive ionic liquid (IL) and chloropropyl silicone oil. A silicone elastomer with a relative permittivity of 22 at 10−1 Hz, Young’s modulus of 0.78 MPa, and excellent homogeneity was prepared by incorporating 10 phr (parts per hundreds rubber) of LMS-EIL into an elastomer matrix. The sensitivity of the pressure sensor produced using this optimized silicone elastomer was 0.51 kPa−1, which is 100 times higher than that of the pristine elastomer. In addition, a high durability illustrated by 100 loading–unloading cycles and a rapid response and recovery time of approximately 60 ms were achieved. The excellent performance of this novel pressure sensor suggests significant potential for use in human interfaces, soft robotics, and electronic skin applications.

PMN-PSMNT ceramics fabricated using the twin-crystal mixed co-firing method

(1-w)[Pb(Mg1/3Nb2/3)0.67Ti0.33O3]-w[Pb1 − 1.5xSmx(Mg1/3Nb2/3)yTi1−yO3] ((1-w)PMN-wPSMN-PT) piezoelectric ceramics were prepared using the newly proposed twin-crystal mixed co-firing method in which two pre-sintered precursor powders were mixed and co-fired with designated ratios (w = 0.3, 0.4, 0.5, 0.6). X-ray diffraction results show that all the samples presented a pure perovskite structure. The grains were closely packed and the average size was ~ 5.18 µm from the observations of scanning electron microscopy images, giving the high density of ceramics to be 97.8% of the theoretical one. The piezoelectric, dielectric, and ferroelectric properties of the ceramic samples have been investigated systematically. It was found that the performance of ceramics was significantly enhanced when compared to the ceramics fabricated using the conventional one-step approach. Outstanding piezoelectric coefficient d33 of 1103 pC/N and relative dielectric permittivity εr of 9154 could be achieved for the ceramics with w = 0.5.

Investigation of Phase Formation and Electrical Properties of Fe-Doped PZT Ceramics

In this paper, some compositions described by the general formula Pb(ZrxTi1-x)0.99Fe0.01O3 have been considered and investigated. The compositions considered have been obtained by solid state reaction technique, where x corresponds to 0.42, 0.52 and 0.58. Sintering has been performed for 2 hours at temperatures between 1100oC and 1250oC. The influence of the sintering temperature on the microstructure and on the hysteresis loops of Fe3+ doped Pb(ZrxTi1-x)O3 system has been investigated. The crystallographic phase and microstucture of the sintered compositions have been studied in detail using X-ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM). The experimental results obtained by XRD have revealed that all the sintered samples have a perovskite structure. In order to correlate the behavior of the sintered materials to their microscopic structure, the domain structures have been defined by SEM. The dielectric properties, as relative dielectric permittivity (εr) and dielectric loss (tan δ) have been measured. The hysteresis loops at room temperature of all un-poled sintered compositions reveal a similar behaviour with “hard” PZT ceramics. The piezoelectric properties like electromechanical coupling factor (kp) have been investigated after polarization.

Gold-Nanoparticle-Deposited TiO2 Nanorod/Poly(Vinylidene Fluoride) Composites with Enhanced Dielectric Performance

Flexible dielectric polymer composites have been of great interest as embedded capacitor materials in the electronic industry. However, a polymer composite has a low relative dielectric permittivity (ε′ < 100), while its dielectric loss tangent is generally large (tanδ > 0.1). In this study, we fabricate a novel, high-permittivity polymer nanocomposite system with a low tanδ. The nanocomposite system comprises poly(vinylidene fluoride) (PVDF) co-filled with Au nanoparticles and semiconducting TiO2 nanorods (TNRs) that contain Ti3+ ions. To homogeneously disperse the conductive Au phase, the TNR surface was decorated with Au-NPs ~10–20 nm in size (Au-TNRs) using a modified Turkevich method. The polar β-PVDF phase was enhanced by the incorporation of the Au nanoparticles, partially contributing to the enhanced ε′ value. The introduction of the Au-TNRs in the PVDF matrix provided three-phase Au-TNR/PVDF nanocomposites with excellent dielectric properties (i.e., high ε′ ≈ 157 and low tanδ ≈ 0.05 at 1.8 vol% of Au and 47.4 vol% of TNRs). The ε′ of the three-phase Au-TNR/PVDF composite is ~2.4-times higher than that of the two-phase TNR/PVDF composite, clearly highlighting the primary contribution of the Au nanoparticles at similar filler loadings. The volume fraction dependence of ε′ is in close agreement with the effective medium percolation theory model. The significant enhancement in ε′ was primarily caused by interfacial polarization at the PVDF–conducting Au nanoparticle and PVDF–semiconducting TNR interfaces, as well as by the induced β-PVDF phase. A low tanδ was achieved due to the inhibited conducting pathway formed by direct Au nanoparticle contact.

Numerical Design and Experimental Validation of a Plastic 3D-Printed Waveguide Antenna for Shallow Object Microwave Imaging

Microwave imaging of shallow buried objects has been demonstrated with holographic radar for landmine detection, civil engineering and cultural heritage. A key component of this system is the antenna based on a truncated cylindrical waveguide with two feeds. This paper investigates for the first time a manufacturing technology based on the 3D printing of a volumetric cylindrical plastic antenna. The investigation of this manufacturing technology was motivated by the reduction in the antenna size and customization of the electromagnetic characteristics to the radio frequency electronics mounted on the robotic scanning system. The antenna that was designed using a simulator and filled with polylactic acid plastic material (relative dielectric permittivity Ɛr = 2.5) is compared to the metal antenna, both operating at around 2 GHz. The goal was to replicate the characteristics of the void core antenna to be able to provide the same quality/information of the microwave images of shallow buried objects. Finally, we compared the scan results of dielectric and metal targets both in the air and in natural soil. From the observation of some of the characteristics of the images, such as dynamics, morphology of the target, signal-to-noise ratio, and operating distance, we demonstrate that 3D printing for volumetric cylindrical waveguide antenna could be used to obtain compact and easily adaptable antennas for different applications in remote sensing.

Quantification of the Mechanized Ballast Cleaning Process Efficiency Using GPR Technology

Ground Penetrating Radar (GPR) has been used recently for diagnostics of the railway infrastructure, particularly the ballast layer. To overcome ballast fouling, mechanized ballast cleaning process, which increases track occupancy time and cost, is usually used. Hence it is of crucial significance to identify at which stage of track ballast life cycle, and level of fouling, ballast cleaning should be initiated. In the present study, a series of in situ GPR surveys on selected railway track sections in Czechia was performed to obtain railway granite ballast relative dielectric permittivity (RDP) values in several phases of railway track lifecycle. GPR data were collected in the form of B-scan, and time-domain analysis was used for post-processing. The results indicate (i) change of railway ballast RDP in time (long term); (ii) a dependency of ballast fouling level on RDP; and (iii) the RDP change during the ballast cleaning process, thus its efficiency. This research aimed to provide new perspectives into the decision-making process in initiating the mechanized ballast cleaning intervention based on the GPR-measured data.

Influence of graphene–carbon nanotubes and processing parameters on electrical and dielectric properties of polypropylene nanocomposites

In this study, the effect of carbon nanotubes (CNTs) and graphene nanosheets (GNs) on the microstructure, electrical conductivity and relative dielectric permittivity of polypropylene (PP) nanocomposites were investigated in relation to the melt compounding parameters. Although CNTs/GNs can significantly improve the conductivity and permittivity of PP nanocomposites, more significant results can be obtained by using optimal fabrication parameters. For optimal melt processing parameters using Taguchi optimization method, electrical conductivity and relative dielectric permittivity of about 3.08 × 10−5 S/m and 158.97 were achieved, whereas only about 1.34 × 10−11 S/m and 2.02 were measured for pure PP respectively. Therefore, this study showcased optimal melt compounding process parameters for the endless future research on PP-CNTs/GNs nanocomposites for various advanced engineering applications. This will also guide future research on the uniform use of melt fabrication parameters for proximity in comparison of results published on PP-CNTs/GNs nanocomposites.

On the Accurate Numerical Analysis of the Propagation Through Dielectric Frequency-Selective Surfaces Using a Vectorial Modal Method

In this work, we focus on the numerical analysis of the propagation of plane-waves in one-dimensional periodic lossy dielectric media, which constitute the building block of dielectric frequency-selective surfaces (DFSSs). To this end, a full-vectorial modal method was used, in which discontinuities of some components of the electromagnetic fields have to be evaluated, and we propose a numerical improvement in the evaluation of some integrals appearing in the developed formulation. Some confusion may exist in the evaluation of the cited integrals due to the discontinuous nature of the dielectric function and its transverse gradient. Therefore, some considerations are given in order to solve these integrals accurately for the general case of a relative dielectric permittivity function defined as a sum of lossy dielectric slabs. We particularize our study to a dielectric frequency-selective surface (DFSS), for which the periodic dielectric medium can be defined as constant functions inside an homogeneous region, whose contours define the discontinuities. Thus, the relative dielectric permittivity can be expressed in terms of the Heaviside or step function. In this way, the above-mentioned integrals can be correctly evaluated in the discontinuity, obtaining good results with the employed vectorial modal method for both the propagation constant and the electromagnetic fields obtained in the periodic dielectric medium constituting the DFSS. These results are compared with those obtained with a less accurate evaluation of the cited integrals, when an approximation made by other authors is used.