Jiaqi Liu

Jiaqi Liu
University of Liverpool | UoL · University of Liverpool Management School (ULMS)

About

90
Publications
2,724
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153
Citations
Citations since 2017
56 Research Items
142 Citations
20172018201920202021202220230102030
20172018201920202021202220230102030
20172018201920202021202220230102030
20172018201920202021202220230102030
Introduction
Skills and Expertise

Publications

Publications (90)
Article
The thin dielectric sheet (TDS) approximation-based theory of characteristic modes (TCM) is formulated for lossless thin dielectric coated conducting bodies. The proposed formulations are derived from the TDS-electric, magnetic, and combined field integral operators (TDS-EFIO, TDS-MFIO and TDS-CFIO). Similar to the cases of perfect electric conduct...
Article
An efficient solver based on volume-surface integral equation is proposed for the electromagnetic (EM) scattering of inhomogeneous medium targets with uncertain geometrical shapes and dielectric constants. On the one hand, the nonuniform ration B-spline surfaces can be used to constructed the uncertain geometrical shapes with a number of geometrica...
Article
Full-text available
An effective method for identifying inertia characteristics of cone-shaped space target based on deep learning is proposed. The inertia ratio is determined by the time-varying scattering fields from the cone-shaped targets. The multistatic method is introduced to reduce the evaluation time of time-varying scattering fields. The micro-Doppler spectr...
Preprint
Full-text available
Theory of characteristic modes (TCM) is applied to the design of a programmable flexible metasurface (PFMS) to achieve its multistate tunable microwave absorption. The designed metasurface consists of two layers. The first layer is a very thin polyimide (PI), on which unit cells consisting of two trapezoidal patches symmetrical along the central bi...
Preprint
Full-text available
An effective method for identifying inertia characteristics of cone-shaped space target based on deep learning is proposed. The inertia ratio is determined by the time-varying scattering fields from the cone-shaped targets. The multistatic method is introduced to reduce the evaluation time of time-varying scattering fields. The micro-Doppler spectr...
Article
A fast and accurate numerical method based on the theory of characteristic mode (TCM) is proposed for analyzing electromagnetic scattering from repetitive multiscale array structures. In order to overcome the low frequency breakdown problem when interacting at short distances between observation and source basis functions, the CMs are extracted fro...
Article
Full-text available
Design of ultra‐wideband (UWB) dual‐polarized magnetoelectric (ME) dipole antenna with compact size is presented. The proposed antenna consists of a double‐layer ME dipole, a pair of cross‐placed Γ‐shaped probes, and a box‐shaped reflector. Total size of the final design is 95 mm (0.87λ0) × 95 mm (0.87λ0) × 65 mm (0.6λ0). Both simulated and measure...
Article
Recently, total variation (TV) regularization has become a standard technique for image recovery. The mean squared error (MSE) of the reconstruction can be reliably estimated by Stein’s unbiased risk estimate (SURE). In this work, we develop two recursive evaluations of SURE, based on Chambolle’s projection method (CPM) for TV denoising and alterna...
Article
PSF (point spread function) estimation plays an important role in blind image deconvolution. It has been shown in our previous work that minimization of the Stein’s unbiased risk estimate (SURE) – unbiased estimate of mean squared error (MSE) – could yield an accurate PSF estimate. In this paper, we show that the PSF estimation error is upper bound...
Article
Full-text available
The compatible catalytic structure of NiCo2O4 was modified into multi-shelled hollow spheres by one-pot synthesis, followed by heat treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmet–Teller (BET) and N2 adsorption–desorption approaches were used for the characterization...
Article
Full-text available
Recently, total variation regularization has become a standard technique, and even a basic tool for image denoising and deconvolution. Generally, the recovery quality strongly depends on the regularization parameter. In this work, we develop a recursive evaluation of Stein’s unbiased risk estimate (SURE) for the parameter selection, based on specif...
Article
Alkali metal DC arc discharge has the characteristics of easy ionization, low power consumption, high plasma temperature and ionization degree, etc, which can be applied in aerospace vehicles in various ways. In this paper, we calculate the physical property parameters of lithium vapor, one of the major alkali metals, and analyze the discharge char...
Article
Point spread function (PSF) estimation plays an important role in blind image deconvolution. It has been shown that incorporating Wiener filter, minimization of the predicted Stein’s unbiased risk estimate (p-SURE)—unbiased estimate of predicted mean squared error—could yield an accurate PSF estimate. In this paper, we provide a theoretical analysi...
Article
In a scenario where a formation of flight vehicles tries to avoid the interception of a pursuer vehicle, it is very important for the formation to identify which member is being pursued by the pursuer. This paper proposes an identification model, which incorporates guidance parameter confidence measures and line-of-sight correlations to determine t...
Article
Full-text available
This paper addresses a pursuer tracking problem where the pursuer's acceleration is given by a proportional navigation (PN) guidance law with a time-varying navigation ratio which varies with the relative range between the pursuer and its target. Based on a motion model that exactly describes the relative motion and the PN guidance law, a novel fil...
Article
Compressed sensing (CS) for sparse backscattering field recovery from very limited measurements has received increasing attention among the radar imaging community. The chirp (i.e., linear frequency modulated, LFM) waveform, benefiting from large time-bandwidth product, is widely utilized in imaging radars, such as synthetic aperture radars (SAR) a...
Article
Micro-motion dynamics, such as rapid rotation, vibration and spinning motion, impose additional time-varying frequency modulation on the returned radar signals, which is known as the micro-Doppler (m-D) effect. Micro-Doppler frequency is considered as a stable and unique feature, where the uniqueness means that different micro-motions have distinct...
Article
In this paper, a framework for inverse synthetic aperture radars (ISAR) imaging with wideband V-FM waveforms is investigated, where the dual-channel compressed-sensing-based dechirping (CS-D) algorithms are applied to achieve high-resolution range profiles (HRRPs) of moving targets. The final HRRPs are reconstructed via the synthesis of the two HRR...
Article
Adaptive Kalman filtering was proposed to handle unknown prior statistics decades ago. The kernel idea of published mainstream works is to use residual-based adaptive estimation or its improved form to determine unknown noise levels to complete iteration equations inside Kalman filter. In this paper, innovative method of noise level estimation is p...
Conference Paper
Recently, total variation based image deconvolution has shown its superior performance. The restoration quality is generally sensitive to the value of regularization parameter. In this work, we develop a data-driven optimization scheme based on minimization of Stein's unbiased risk estimate (SURE)—statistically equivalent to mean squared error (MSE...
Conference Paper
In this paper, a novel and small sub-terahertz (THz) sheet beam extended interaction klystron (EIK) has been designed. With the help of a three-dimensional(3D) particle-in-cell(PIC) simulation, design and optimizing geometry of THz sheet beam EIK is performed. The interaction system consists of two dumbbell five-gap cavities, one is used for input...
Conference Paper
A modified augmented proportional navigation (MAPN) guidance law is proposed for the extra-atmospheric vehicle by using the adaptive extended Kalman filtering(AEKF) observer to estimate the target maneuver acceleration. The traditional Proportional Navigation (PN) guidance law has higher accuracy, in fact, it has been shown that PN is optimal solut...
Conference Paper
Sparse recovery via L1-penalized minimization can be typically solved by iteratively reweighted least squares (IRLS). The reconstruction quality is generally sensitive to the value of regularization parameter. In this wok, we propose a novel data-driven optimization scheme based on minimization of unbiased predictive risk estimate (UPRE). For a giv...
Conference Paper
We propose an image deconvolution algorithm when the data is contaminated by Poisson noise. By minimizing Stein's unbiased risk estimate (SURE), the SURE-LET method was firstly proposed to deal with Gaussian noise corruption. Our key contribution is to demonstrate that the SURE-LET algorithm is also applicable for Poisson noisy image and proposed a...
Conference Paper
We propose a variant of unbiased predictive risk estimate (UPRE) as a novel criterion for estimating a point spread function (PSF) from the degraded image only. Compared to the traditional unbiased estimates (e.g. UPRE and SURE), the key advantage of this variant is that it does not require the knowledge of noise variance. The PSF is obtained by mi...
Article
Considering blind image deconvolution as a statistical estimation problem, we propose an unbiased estimator of the prediction error – Mallows’ statistics CL – as a novel criterion for estimating a point spread function (PSF) from the degraded image only. The PSF is obtained by minimizing this new objective functional over a family of smoother filte...
Article
Point spread function (PSF) estimation plays an important role in blind image deconvolution. This paper proposes two novel criteria for parametric PSF estimation, based on Stein’s unbiased risk estimate (SURE), namely, prediction-SURE and its variant. We theoretically prove the SURE-type functionals incorporating exact (complementary) smoother filt...
Article
This paper concentrates on the problem of designing a three-dimensional nonlinear guidance law accounting for saturation nonlinearity and the dynamics of missile autopilot based on a command filtered backstepping (CFBS) scheme. In the design, the nonlinear kinematics of target–missile engagement is considered in the spherical coordinate system and...
Article
An active defense scheme in which a ballistic missile launches a defending missile to intercept the incoming intercepting missile is considered. Compared with traditional passive evasion strategies, the active defense scheme can greatly increase the ballistic missile’s survival rate. Different from many terminal guidance laws using the line-of-sigh...
Article
Iterative re-weighted least square (IRLS) algorithms for -minimization problems require to select proper value of regularization parameter, for which Stein’s unbiased risk estimate (SURE) – an unbiased estimate of prediction error – is often used as a criterion for this selection. In this paper, we propose a recursive SURE to estimate the predictio...
Conference Paper
Research on guidance law has begun to incorporate behavior information from non-cooperative target, and thus emphasized the importance and necessity of guidance law recognition. Recognition of guidance law on non-cooperative vehicle is highly supportive for pursued vehicle to conduct guidance law optimization, guidance law evaluation, and trajector...
Article
We propose a generalized cross validation (GCV) as a novel criterion for estimating a point spread function (PSF) from the degraded image only. The PSF is obtained by minimizing this new objective functional over a family of Wiener processings. Based on this estimated PSF, we then perform deconvolution using our recently developed SURE-LET algorith...
Conference Paper
This paper presents a model of RCS characteristic of non-uniform plasma sheltering disk target, by considering the absorption and refraction of electromagnetic wave, and combining graphic electromagnetic and ray tracking methods. The results show that: (1) RCS is reduced more than 10dB at wide-band frequency of electromagnetic wave, when the incide...
Conference Paper
In this paper, a higher-order shift operater (SO) FDTD scheme with second-order accuracy in time and fourth-order in space has been proposed to accurately model scattering of perfect electronic conductor coated with cloaking structures. Several different electromagnetic parameters of the cloaks are taken into account using SO-FDTD method. Numerical...
Conference Paper
Microwave tubes are vacuum electron devices used for the generation and amplification of radio frequencies in the microwave frequency range. Klystron is a kind of microwave tubes which is used in radar. A sheet-beam Extended Interaction Klystron (SBEIK) is an attractive MMW amplifier because of its high gain per unit length and compact configuratio...
Conference Paper
In this paper, a dispersive conformal FDTD method have been proposed to accurate model the interface between two adjacent dispersive mediums. The method is based on the technology of area average between two adjacent dispersive interfaces, which is different from existing dispersive conformal FDTD schemes which involve with the interface between fr...
Article
When multiple miniature vehicles with individual position and inter-vehicle distance measurement ability collaborate in a formation, navigation base can be established by data fusion in a decentralized and standalone scheme. A Composite Data Fusion (CDF) algorithm which combines Least Square Error and Kalman Filtering is proposed in this paper to b...
Article
We propose an unbiased estimator of the weighted mean squared error — Mallows’ statistics Cp — as a novel criterion for estimating a point spread function (PSF) from the degraded image only. The PSF is obtained by minimizing this new objective functional over a family of Wiener processings. Based on this estimated PSF, we then perform non-blind dec...
Conference Paper
In this paper, we consider blind deconvolution that consists of PSF (point spread function) estimation and non-blind deconvolution. It has been proved that blur-SURE - a modified version of SURE (Stein's unbiased risk estimate) - is a valid criterion for parametric PSF estimation. The key contribution of this work is to propose a fast algorithm for...
Conference Paper
On-Off thrusters have limitation both at minimum on-time and minimum off-time, so the output is nonlinear pulses. Use on-off thrusters to provide linear or near linear control force is a fundamental and important research topic. Existing previous works do not overcome the limitation of on-time and off-time constraints, so the output is only an appr...
Conference Paper
When multiple flying vehicles with bearing-only tracking collaborate in locating a target, observation data fusion is required to compensate the drift of navigation system, the noise from observation system, and the unknown maneuvering of target object. Kalman Filtering of nonlinear observation data needs a huge amount of computation, and will caus...
Conference Paper
When multiple miniature vehicles with inter-vehicle distance measurement ability collaborate in a formation, navigation base can be established without external assisting systems. Shared navigation data is fused to compensate the drift of navigation system and the noise from distance measurement. Existing algorithms like Least Squared Error (LSE) c...
Conference Paper
In this paper, the collisional absorption mechanism of electromagnetic wave in plasma of different types is studied with numerical methods. The collision frequency and electromagnetic wave which is made by RF discharge in the obturator or DC discharge around the opening space. The computation models are founded for calculating the absorption by the...
Conference Paper
When multiple flying vehicles collaborate in locating a target, their formation design is an important factor to the error of location. Based on the analyses of contribution that formation design made to the location error, Effective Observing Area is defined as a criterion to assess formation design. An evaluation method for formation design is th...
Conference Paper
During its flight, Spacecrafts need to maneuver its attitude across a number of predefined positions. The order to traverse these attitudes is a combinational optimization problem. In this article, fuel cost is estimated by analyzing the angular momentum change during attitude transitions. Based on this estimation, an optimization algorithm for bot...
Article
Large-angle attitude maneuver is common during the mission of spacecrafts, such as aligning to star to calibrate navigation system. Published works on attitude tracking always focus on optimizing the time and fuel cost, neglecting the smoothness requirement and angular speed limitations. In this paper, a nonlinear control algorithm is prompted for...
Article
A new method of aircraft low altitude penetration is proposed with temporal constraints that allow periods of high observability interspersed with periods of low observability as well as the way to develop in STAGE environment. The aircraft's RCS character is simplified into the "bow-tie" distribution, then the aircraft can dynamically adjust its h...

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