Vertical Transition Research Articles

Optical scatterings in layered systems

This paper presents a theoretical framework for exploring the optical properties of layered materials. The derived analytical formulas for reflectance and transmittance spectra incorporate vertical valence-state transitions and appropriate boundary conditions for finite-width bulk materials, integrated with the generalized tight-binding model to account for intrinsic interactions and external fields. The study reveals distinct structures in the spectra of multilayer graphene for different stacking layers at low energies (∼0.2–0.8[Formula: see text]eV), attributed to interband transitions at the K point. Furthermore, the high-energy part (≳5[Formula: see text]eV) highlights thickness-dependent plasmon effects characterized by unique resonance frequencies in the optical spectra. These features depend on the dimensionality, interlayer coupling, and electronic structure of the material. This work provides a deeper understanding of the optical properties of layered structures, facilitating their exploration and characterization for diverse applications.

A generalized rule for phase transition generated by additives in piezoelectric ceramics

The phase transition generated by additives has not been defined systematically in (1-x)Pb(Zr,Ti)O3-xPb(BI2+1/3Nb2/3)O3 (PZT-PBN, BI2+: Mg2+, Zn2+, and Ni2+, in this study). In order to define the phase transition of PZT-PBN, we identify the various phase transitions depending on the ionic site which an additive enters. The ionic site can be determined by the ionic size of a metal in an additive, and in the ABO3 of a perovskite structure, the phase transition is more significant when an additive enters the B site, compared to the A site. Until now, the phase transitions have mostly been described as the vertical or horizontal transitions in phase diagrams. However, in this study, we show that phase transitions actually occur in the diagonal direction. In particular, it is reported that a unique shift of morphotropic phase boundary (MPB) occurs, when the additive enters the BI2+ site in (1-x)Pb(Zr,Ti)O3-xPb(BI2+1/3Nb2/3)O3. The MPB shift is different from the normal phase transitions which are generally observed in PZT-based materials.

Facies association analysis of a Toarcian siliciclastic‑carbonate lacustrine system, Sichuan Basin, China

Globally, considerable coverage has been devoted to marine environment affected by the Jenkyns Event, but little attention has been given to lacustrine system. Here, siliciclastic‑carbonate samples of the Da'anzhai Member (J1dn) were examined for petrology and geochemistry in order to evaluate lithofacies characteristics, depositional processes and environmental changes of the palaeo-Sichuan lacustrine basin contemporaneous with the Jenkyns Event. Unique sedimentological and petrological features were used to identify five principal facies associations (FA) and depositional environments, including the distal delta front, accretionary bioclastic shoals, proximal bioclastic shoal ramp, distal bioclastic shoal ramp and (semi-)deep lacustrine environment. The vertical transitions of FA reveal that J1dn forms a complete lacustrine transgressive-regressive sedimentary system during the Toarcian, which can be further divided into 3 units in combination with standard gamma logging. The lower unit is characterised by frequent intermixing of multiple FA interpreted as frequent lake-level fluctuations. The middle unit is characterised by the deposition of clay-rich mudstone and the demise of bioclastic shoals interpreted as intensive lacustrine transgression that were at times affected by storm-induced waves or oscillatory currents coinciding with the initiation of the Jenkyns Event. The upper unit is characterised by the thicker and higher proportion of biogenic carbonate-rich lithofacies interpreted as the lake regression, contemporaneous with the end of the Jenkyns Event. Overall, clay-rich lithofacies from suspension settling, turbidity current or slumping triggered by storm events were deposited during a high relative lacustrine-level, accompanied by organic carbon-rich deposition and preservation. In contrast, carbonate-rich lithofacies were mainly controlled by biogenic carbonate sedimentation, associated with a low relative lacustrine-level unconducive to organic matter accumulation. Finally, the proposed depositional evolution model at the lake-level highstand stage and lowstand stage of the palaeo-Sichuan lacustrine basin provides new insights and understanding on the changing palaeolimnological history of the Toarcian lacustrine system.

Vertical take-off and hover to cruise transition for a hybrid UAV using model predictive controller and MPC allocation

PurposeDual-thrust hybrid unmanned aerial vehicle (UAV) technology offers a highly robust and efficient system that incorporates the take-off and landing capabilities of rotary-wing aircraft with the endurance capacities of fixed-wing aircraft. The purpose of this study is to model and control a hybrid UAV in three distinct flight modes: rotary-wing, fixed-wing and over-actuated model.Design/methodology/approachModel predictive control (MPC) along with linear models are applied to design controllers for the rotary-wing or vertical take-off and transition to the fixed-wing flight. The MPC algorithm is implemented with two approaches, first in its usual form and then in a new form with the help of tracking error variables as state variables.FindingsBecause the tracking error variables are more compatible with the cost function used in MPC, the results improve significantly. This is especially important for a safe and stable transition from rotary-wing to fixed-wing flight, which should be done quickly. The authors also propose a control allocation strategy with MPC algorithm to exploit the thrust and control inputs of both rotary-wing and fixed-wing systems for the transition phase. As the control system is over-actuated, the proposed algorithm distributes the control signal among the actuators better than the MPC alone. The numerical results show that the flight trajectory is also improved.Originality/valueThe research background is reviewed in the introduction section. The other sections are originally developed in this paper to the best of the authors’ knowledge.

A 194–214-GHz Single-Sideband Mixer With Vertical and Inline Transitions Suitable for Linear Array Applications

A 194–214-GHz Single-Sideband Mixer With Vertical and Inline Transitions Suitable for Linear Array Applications

Theoretical Study on the Spectroscopic Properties and Photodissociation Mechanism of Dibromocarbene.

Detailed calculations on the electronic states of dibromocarbene (CBr2) herein are presented. First, the spectroscopic properties of the electronic states including geometry parameters, harmonic vibrational frequencies and transition energies of the lowest electronic states of the neutral radical were calculated in detail using the internally contracted multireference configuration interaction methods including Davidson correction (icMRCI+Q) with correlation consistent basis sets of aug-cc-pVXZ (X = T, Q, 5). Second, as CBr2 including two Br atoms, the Spin-Orbit Coupling (SOC) effect on the spectroscopic parameters and the one-dimensional cuts of the potential energy surface (PESs) of the lowest three states were studied. The barrier to linearity and dissociation of the singlet state were discussed. Third, the one-dimensional cuts along with the vertical transition energy (VTE), the oscillator strength, and so on of the electronic states related to the several lowest dissociation limits of CBr2 were calculated at the icMRCI+Q/aug-cc-pVTZ level. Based on the computed results of the electronic states of the radical, the photodissociation mechanism in the UV region were discussed in detail. The ab initio calculations are compared with the previous theoretical and experimental data and are in good agreement. The present work will provide a comprehensive understanding on the electronic structures and dissociation dynamics for the electronic states of the CBr2 radical.

First-principles study of geometric and electronic structures, and optical transition energies of Mn4+ impurity ions: K2SiF6 as a prototype

In this study, we present the results of first-principles calculations conducted within the density functional theory to investigate the geometric and electronic structures of the ground 4A2 and excited 2E and 4T2 states, as well as the optical transition energies between these states, in the prototype system of K2SiF6:Mn4+. To achieve this, we employed a comprehensive evaluation of the five representative exchange-correlation functionals, enabling the development of a state-of-art calculation scheme that effectively describes the geometric and electronic structures of the excited 2E and 4T2 states. The calculated excitation, emission and zero-phonon line energies of the optical transitions between the ground 4A2 state and the excited 2E and 4T2 states demonstrate a better agreement with experimental results. However, we observed that the conventional and widely-used approach based on the analysis of the electronic density of states diagrams derived from the ground state calculations failed to accurately evaluate the vertical optical transition energies from the 4A2 ground state to the excited 2E and 4T2 states when compared to experimental data. The calculation technique developed in this study holds the potential for widespread application to other combinations of host materials and impurity ion, which is of great importance for future developments in the field of optical materials.

Vertical changes in water depth and environmental variables drove the antibiotics and antibiotic resistomes distribution, and microbial food web structures in the estuary and marine ecosystems

The influence of vertical changes in water depth on emerging pollutants distribution and microbial food web remains elusive. We investigated the influence of vertical transition in water depth on the environmental variables, antibiotics and antibiotic resistomes, and microbial community structures in estuary and marine ecosystems (0–50 m). Stepwise multiple linear regression model showed that among investigated environmental variables, change in water salinity was the most influential factor dictating the fluoroquinolone and macrolides concentrations, while dissolved oxygen and turbidity were the key influencers of sulfonamides and beta-lactam concentrations, respectively. Bacterial and eukaryotic diversity and niche breadth significantly increased with the increasing water depth. Ecosystem food web structure at the bottom depths was more stable than at the middle and surface depths. At the surface depth, the top 5 keystone genera were Cryothecomonas, Syndiniales, Achromobacter, Pseudopirsonia, and Karlodinium. Whereas Eugregarinorida, Neptuniibacter, Mychonastes, Novel_Apicomplexa_Class_1, Aplanochytrium and Dietzia, Halodaphnea, Luminiphilus, Aplanochytrium, Maullinia dominated the top 5 genera at the middle and the bottom depth, respectively. Absolute abundance of antibiotic resistance genes (ARGs) was drastically increased at the surface depth compared with the middle and bottom depths. Abundance of the top 10 ARGs and mobile genetic elements (MGEs) detected including tnpA-05, aadA2-03, mexF, aadA1, intI-1(clinic), qacEdelta1-02, aadA-02, qacEdelta1-01, cmlA1-01, and aadA-01 were amplified at the surface depth. This study demonstrated that ARGs abundance was disproportionate to bacterial diversity, and anthropogenic disturbances, confinement, MGEs, and ecosystem stability play primary roles in the fate of ARGs. The findings of this study also implicate that vertical changes in the water depth on environmental conditions can influence antibiotic concentrations and microbial community dramatically.

Tunable Interband Transitions in Twisted h-BN/Graphene Heterostructures.

In twisted h-BN/graphene heterostructures, the complex electronic properties of the fast-traveling electron gas in graphene are usually considered to be fully revealed. However, the randomly twisted heterostructures may also have unexpected transition behaviors, which may influence the device performance. Here, we study the twist-angle-dependent coupling effects of h-BN/graphene heterostructures using monochromatic electron energy loss spectroscopy. We find that the moiré potentials alter the band structure of graphene, resulting in a redshift of the intralayer transition at the M point, which becomes more pronounced up to 0.22eV with increasing twist angle. Furthermore, the twisting of the Brillouin zone of h-BN relative to the graphene M point leads to tunable vertical transition energies in the range of 5.1-5.6eV. Our findings indicate that twist-coupling effects of van der Waals heterostructures should be carefully considered in device fabrications, and the continuously tunable interband transitions through the twist angle can serve as a new degree of freedom to design optoelectrical devices.

Single and two-photo excited violet-blue fluorescence from aza [6]helicenes and the plannar precursors based-on indole, carbazole, and fluorene

Organic π-conjugated materials exhibiting violet-blue emissions are of great interest for diverse applications. Helicenes and stilbenes hold great potential as compounds capable of achieving violet-blue fluorescence. In this study, aza[6]helicenes THNI and DHNC, along with their planar precursors DFVHI and HHIVC, were successfully synthesized using indole, carbazole, and fluorene units as building blocks. The molecular structures were verified through the utilization of 1H and 13C nuclear magnetic resonance (NMR), high resolution mass spectroscopies (HRMS), and the crystal structure of THNI was further elucidated via X-ray analysis. The synthesized material exhibited exceptional thermal stability with a Td value of ≥350 °C. The HOMO and LUMO energy levels were determined through cyclic voltammetry analysis, while density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations at the B3LYP/6-31G(d) level were employed to investigate ground-state geometries and vertical electronic transitions. Optical properties were characterized using UV–vis absorption spectroscopy as well as single- and two-photon excited photoluminescence. The UV–vis absorption spectra indicate that helicenes possess superior light-harvesting capabilities compared to their planar precursors, owing to the former's higher molar extinction coefficients. These compounds exhibit violet-blue emissions in various solvents and solid-state films. In addition, aza[6]helicenes exhibit higher photoluminescence quantum yields (PLQYs) and shorter maximum emission peaks compared to their planar precursors. However, the maximum two-photon absorption (TPA) cross section (δ) values of aza[6]helicenes are lower than those of their planar counterparts. Therefore, THNI and DHNC may be promising candidates for violet-blue emitters in OLEDs due to their curved confined π-electron systems, high thermal and optical stability, and high PLQYs. Meanwhile, DFVHI and HHIVC exhibit potential as two-photon fluorescent probes for bioimaging.

High-Order Quasi-Elliptic-Type Wideband Bandpass Filter With Ultrabroad Input-Reflectionless Stopband Range

A two-layer wideband bandpass filter (BPF) with ultrabroad input-reflectionless stopband range is reported. It consists of a two-port-reflectionless high-order quasi-elliptic-type (QET) wideband BPF and two similar input-reflectionless low-pass filter (LPF) stages. The constituent 2-GHz BPF is shaped by two vertical transitions with shunt resistively terminated T-junctions, which are connected through a microstrip T-junction. It features a two-port-absorptive ninth-order in-band quasi-equiripple BPF response with two close-to-passband transmission zeros (TZs). The building LPF is made up of two in-series-cascaded input-reflectionless LPF units with their first TZs at 6 and 12 GHz, which results in an extended upper stopband beyond 18 GHz. Through this LPF-BPF-LPF approach, an extremely wide input-reflectionless stopband range with increased power attenuation levels in the overall BPF is attained. Its theoretical RF operational principles are detailed. Furthermore, for experimental validation purposes, a two-layer microstrip wideband BPF prototype is simulated, manufactured, and measured. It exhibits a minimum stopband power attenuation level of 29.57 dB, along with minimum input-power-matching levels of 10 and 6.7 dB from dc to 9.85 GHz and from dc to 20 GHz, respectively.

Vibrational, Rotational, and Electronic Spectroscopy for Possible Interstellar Detection of AlNH2 and HAlNH

We obtained accurate vibrational frequencies, rotational constants, and vertical transition energy for AlNH2(X1A1) and HAlNH(X1A′) isomers using ab initio calculations at various levels of theory. These two isomers are potential candidates for astronomical observation. AlNH2 and HAlNH are thermodynamically stable, with Al-NH2 and HAl-NH bond dissociation energies predicted to be 4.39 and 3.60 eV, respectively. The two isomers are characterized by sizable dipole moments of 1.211 and 3.64 D, respectively. The anharmonic frequencies and spectroscopic constants reported for the two isomers should facilitate their experimental differentiation. In addition, we evaluated the evolution of the low-lying electronic states along the stretching coordinates, as well as the absorption cross sections. AlNH2 absorbs strongly around 287, 249, and 200 nm, whereas the HAlNH absorption is centered around 370 and 233 nm.

Coupled Potential Energy Surfaces Strongly Impact the Lowest-Energy Spin-Flip Transition in Six-Coordinate Nickel(II) Complexes.

Luminescent complexes of earth-abundant first-row transition metals are of renewed, broad interest due to their spectroscopic and photochemical properties as well as emerging applications. New strong-field polypyridine ligands have led to six-coordinate 3d3 chromium(III) complexes with intense spin-flip luminescence in solution at room temperature. The ground and emissive states both arise from the (t2)3 electron configuration involving the dπ levels (O point group symmetry labels). Pseudoctahedral 3d8 nickel(II) complexes with such strong ligands are a priori also promising candidates for spin-flip luminescence. In contrast, the relevant electron configurations involve the dσ orbitals and (e)2 configurations. We have prepared the known nickel(II) complexes [Ni(terpy)2]2+, [Ni(phen)3]2+, and [Ni(ddpd)2]2+ as well as the novel complexes [Ni(dgpy)2]2+ and [Ni(tpe)2]2+ forming a series with increasing ligand field strengths (terpy = 2,2':6',2″-terpyridine; phen = 1,10-phenanthroline; ddpd = N,N'-dimethyl-N,N'-dipyridine-2-ylpyridine-2,6-diamine; dgpy = 2,6-diguanidylpyridine; tpe = 1,1,1-tris(pyrid-2-yl)ethane). The lowest-energy singlet and triplet excited states of these nickel(II) complexes are analyzed based on absorption spectra using ligand field theory and CASSCF-NEVPT2 calculations for vertical transition energies and a model based on coupled potential energy surfaces, leading to calculated absorption spectra in good agreement with the experimental data. No photoluminescence signal was observed in the wavelength ranges identified through the analyses of the absorption spectra. The models provide insight into key differences between the nickel(II) complexes and their strongly luminescent chromium(III) analogues.

Circular dichroism simulations of chiral buckybowls by means curvature analyses

A detailed understanding and interpretation of chiral properties of molecular systems, especially in condensed phase, often requires computational models that allow their structural and electronic features to be connected to the observed experimental spectra. The present paper is focused on modelling the circular dichroism spectra of chiral buckybowls, combining topological aspects and the density functional theory. For the first time Ball Pivoting Algorithm was proposed to hook up the chemical topology to the DFT through the surface reconstruction. Particularly, the gaussian curvature of a constructed probe set of corannulene and sumanene derivatives was used as discriminant parameter to benchmark a list of 10 functionals (B3LYP, B97D, M06-2X, HSEH1PBE, wB97XD, CAM-B3LYP, LC-wPBE, TPSSTPSS, mPW1PW91 and APFD). The latter provide to be noticeably accurate to reproduce the curvature effect of the considered molecules. A TD-DFT/BOMD mixed approach provided a comprehensive overview of the spectral chiral pattern prediction trends when multiple DFT functionals are scanned. The preliminary topological analysis efforts were then recompensed with the very precise computed CD spectra, again APFD confirmed as the leader functional, this time for TD-DFT vertical transition calculations. Therefore, we strongly recommend the use of the of dispersion embedded APFD functional coupled with the 6–311++G(2d,2p) basis set for the computation of the functionalized chiral buckybowls ECD spectra.© 2017 Elsevier Inc. All rights reserved.

Some Considerations about the Anodic Limit of Ionic Liquids Obtained by Means of DFT Calculations.

Ionic liquids are good candidates as the main component of safe electrolytes for high-energy lithium-ion batteries. The identification of a reliable algorithm to estimate the electrochemical stability of ionic liquids can greatly speed up the discovery of suitable anions able to sustain high potentials. In this work, we critically assess the linear dependence of the anodic limit from the HOMO level of 27 anions, whose performances have been experimentally investigated in the previous literature. A limited r Pearson's value of ≈0.7 is found even with the most computationally demanding DFT functionals. A different model considering vertical transitions in a vacuum between the charged state and the neutral molecule is also exploited. In this case, the best-performing functional (M08-HX) provides a Mean Squared Error (MSE) of 1.61 V2 on the 27 anions here considered. The ions which give the largest deviations are those with a large value of the solvation energy, and therefore, an empirical model that linearly combines the anodic limit calculated by vertical transitions in a vacuum and in a medium with a weight dependent on the solvation energy is proposed for the first time. This empirical method can decrease the MSE to 1.29 V2 but still provides an r Pearson's value of ≈0.72.

The Use of Regional Data Assimilation to Improve Numerical Simulations of Diurnal Characteristics of Precipitation during an Active Madden–Julian Oscillation Event over the Maritime Continent

This study examines the impact of regional data assimilation on diurnal characteristics of precipitation and winds over the Maritime Continent (MC) using a set of cloud-permitting-scale (~3 km) numerical simulations with the mesoscale community Weather Research and Forecasting (WRF) model and the NCEP Gridpoint Statistical Interpolation (GSI)-based ensemble-3DVAR hybrid data assimilation system. Numerical experiments focus on January 2018, when a well-defined, active Madden–Julian Oscillation (MJO) propagated through the MC region. Available conventional and satellite data are assimilated. Results show that simulated precipitation with data assimilation generally agrees better with satellite-derived rainfall than the control simulation without data assimilation. Simulations with data assimilation also reproduce the diurnal cycle of precipitation better, especially for the timing of the precipitation peak. Data assimilation modulates the overstrong (overweak) diurnal forcing over the land (ocean) in the control simulation. The vertical phase shift of the thermodynamic environment, associated with the timing of vertical motion transition along with low-level water vapor supplies, results in maximum precipitation occurring later, especially over land. To further demonstrate the impact of data assimilation, an additional experiment assimilates NASA Cyclone Global Navigation Satellite System (CYGNSS)-derived ocean surface winds. The results indicate that the assimilation of CYGNSS data exhibits an evident impact on the diurnal variation of surface variables and a similar shift in the diurnal cycle of precipitation. Overall, this study highlights the importance of regional data assimilation in improving the representation of precipitation over the MC, paving the way for a better understanding of the interactions of local diurnal convective precipitation cycles with MJO.

Spectroscopic characterization of [H, Cl, S, O] molecular system: Potential candidate for detection in Venus atmosphere.

Accurate spectroscopic parameters have been obtained for the identification of the [H, Cl, S, O] molecular system in the Venus atmosphere using computational methods. These calculations employed both standard and explicitly correlated coupled cluster techniques. All isomers possess C1 symmetry, with HOSCl being the most stable isomer. Only HOSCl and trigonal-HSOCl isomers are thermodynamically stable relative to the first dissociation limit HCl + SO. Fundamental modes of the lowest three isomers exhibit many anharmonic resonances, resulting in complex spectra. All isomers are found to be stable in the visible region as the calculation of vertical energy transition indicates. No electronic states were found to strongly absorb in the near UV-vis region.

Design of a High-Gain Hybrid Slot Antenna Array Based on Bulk Silicon MEMS Process for W-Band Applications

A W-band, high-gain, hybrid slot antenna array based on bulk silicon MEMS technology is proposed in this paper. The high-order-mode cavity is explored to excite the 2 × 2-slot basic unit, so as to reach the low-profile requirement of the bulk silicon MEMS process. To avoid the fragile structure of the large-scale antenna arrays based on the bulk silicon MEMS process, the ridge gap waveguide is employed to build the feed network for a large-scale array. A vertical transition between a rectangular waveguide and a ridge gap waveguide is designed to support the low-loss and low-cost assembling method between the radiation units and the feed network. An 8 × 8-slot hybrid antenna array is simulated and fabricated. The measured results show a relative bandwidth (VSWR < 2) of 8.1% with the first side-lobe level less than −11 dB over the frequency band of 91–97 GHz. A maximum gain of 26.1 dBi with the radiation efficiency of 65.2% is achieved. With high gain and high fabrication efficiency, the proposed hybrid slot antenna array would be valuable for W-band radar applications.

High-Order Quasi-Elliptic-Type Single-Ended and Balanced Wideband Bandpass Filters Using Microstrip-to-Microstrip Vertical Transitions

High-order single-ended and balanced wideband bandpass filters (BPFs) with quasi-elliptic-type (QET) responses are reported. Firstly, a fifth-order wideband BPF based on a two-layer microstrip-to-microstrip vertical transition with two shunt open-circuit-ended two-section microstrip stubs at the input and output ports, respectively, is designed. Compared to a typical third-order vertical transition, two more transmission poles (TPs) along with a pair of close-to-passband transmission zeros (TZs) are attained. Next, an application to design a ninth-order QET balanced wideband BPF using a vertical transition is carried out. Owing to the used slotline resonator, an intrinsic common-mode (CM) suppression capability is obtained for it. The RF operational and design principles of these BPF devices are detailed by means of their relevant transmission-line-(TL)-based equivalent circuits. For experimental-validation purposes, two microstrip prototypes corresponding to a 3-GHz fifth-order wideband BPF and a 2-GHz ninth-order balanced wideband BPF are developed and tested. The measured single-ended and balanced BPF circuits feature sharp-rejection QET responses with two close-to-passband TZs and stopband-power-attenuation levels above 27.3 dB and 43.66 dB, respectively. The measured CM suppression levels for the balanced BPF device are higher than 34.59 dB from DC to 5 GHz.

Planar Array of UWB Active Slot Antennas for Microwave Imaging of the Breast

A shielded planar array of active slot antennas is proposed for applications in the microwave imaging of the breast. The frequency band is from 3 to 8 GHz, where reflection loss better than 10 dB and interelement mutual coupling less than −20 dB are achieved. The center-to-center element spacing is 12 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times12$ </tex-math></inline-formula> mm. A low-noise amplifier (LNA) is integrated with each antenna element for use in a receiving configuration. A ground plane within the multilayer design separates the antenna array from the electronics array while providing shielding from the back and improving the power coupling into the tissue. The proposed structure resolves an outstanding problem in the design of large shielded antenna arrays for tissue imaging, namely, the interconnects between the array elements and the electronic circuits, which are separated by multiple dielectric layers and a grounded plane. The critical development is the new low-reflection triple-wire vertical transition that carries the signal from the antenna layer to the electronics layer while traversing through multiple layers of different permittivities and through openings in the ground plane. The design is verified by simulations and measurements. The passive and active designs are compared, illustrating the full utilization of the LNA gain. The performance of the proposed active array is also examined in imaging experiments with a compressed-breast phantom.