Large Effective Bandwidth Research Articles

Fabrication of core-shell Fe4N@C with sea-island structure by one-step nitriding method as efficient electromagnetic wave composite absorber

Porous structure design and magnetic-dielectric composite are effective ways to develop electromagnetic wave (EMW) absorbing materials with light-weight, thin-thickness, large effective absorption bandwidth (EAB), and strong reflection loss (RL). This article presents a simple one-step nitridation method for synthesizing Fe4N@C compounds with sea-island like and core-shell structures. The optimal RL value of Fe4N@C is up to -60.01dB, and the EAB (frequency range for RL< -10 dB) is 5GHz (11.1-16.1GHz) with a thickness of 1.9mm. The EAB reaches 5.5GHz (12.5-18GHz) when the matching thickness is 1.7mm. The multi-component design achieved excellent impedance matching properties. The carbon frame connects the core-shell particles to form a three-dimensional porous structure, providing multiple reflection losses. Therefore, this work provides a convenient way to design efficient and lightweight EMW absorbers with special structures.

Effect of magnetic-spring bi-stable nonlinear energy sink on vibration and damage reduction of concrete double-column piers: Experimental and numerical analysis

Concrete structures suffer from crack damage under heavy vibrations, caused by seismic loads. Passive vibration control devices can be used to reduce the damage. The most common device is the tuned-mass-damper (TMD), which is tuned to match the natural frequency of the primary structure. However, under prolonged vibration load, the natural frequency of the concrete structure decreases, reducing the TMD's effectiveness in mitigating vibrations and damage, as it can only target a fixed natural frequency. Therefore, this study will propose and implement the nonlinear energy sink (NES), which is a vibration control device that can adapt to changing frequency, resulting in a larger effective bandwidth than the TMD. As a concrete structure, the cast-in-place double-column piers is seismically loaded with a shaking table with and without NES to observe the vibration and damage-mitigating properties of the NES. More specifically, a magnetic bi-stable NES (MBNES) with a viscous fluid damper (VFD) is designed and built. The bi-stable restoring force allows for a larger bandwidth than conventional NESs, and the magnets and VFD allow for easy manufacturability. An optimization method is proposed to obtain optimal parameters, and the restoring force and damping of the experimentally designed MBNES are verified using the restoring force surface method. The proposed design, optimization and identification procedure are generic and can be applied to any (concrete) civil structure. Shaking table tests are used to verify the robust performance of MBNES under continuous changes in the natural frequency of concrete double-column piers. The experimental results show that the MBNES can effectively mitigate vibrations of the pier and, consequently, reduce the damage of the pier, slow down the decrease of the stiffness of the pier, reduce the curvature and shear deformation of the pier. Numerical analysis results show that MBNES can absorb the energy of the primary structure in a wide frequency bandwidth and has excellent robust performance compared to conventional devices.

Restricted growth of molybdenum carbide nanoparticles in hierarchically porous nitrogen-doped carbon matrix for boosting electromagnetic wave absorption performance

With the development of electronic science and technology, electromagnetic pollution is becoming increasingly serious, which urgent people to develop wave-absorbing materials with the features of “thin, light, strong and wide”. In this paper, restricted growth of molybdenum carbide nanoparticles in hierarchically porous nitrogen-doped carbon matrix (Mo2C/NC) was designed and prepared via a salt-assisted template route and carbonization process, whose morphology and the wave-absorbing properties are regulated by changing the content of Mo2C/NC nanoparticles. The honeycomb porous Mo2C/NC composites with large specific surface area and smooth surface can optimize the impedance matching and allow the entrance, multiple reflections and scattering of incident electromagnetic waves (EMW), which effective enhance the electromagnetic wave consumption. Meanwhile, the honeycomb cross-linked carbon matrix facilitates the construction of the conductive network and enhances its conductive loss. Furthermore, numerous Mo2C/NC nanoparticles dispersed restricted growth in carbon matrix induces interfacial polarization. In addition, the heteroatom nitrogen doping acts as dipole centers to induce dipole polarization under electromagnetic field. The uniquely designed Mo2C/NC absorbers show satisfactory EMW absorption behaviors of a minimum reflection loss (RLmin) of −61.53 dB at 1.5 mm and an effective absorption bandwidth (EAB) of 9.6 GHz at 3.5 mm. This work enriches the variety of EMW absorbers and offers the route to promote the EMW absorption performance, especially large effective absorption bandwidth.

Time-delay signature suppression of the chaotic signal in a semiconductor laser based on optoelectronic hybrid feedback.

An approach to generating chaotic signals with low time-delay signatures (TDSs) from a semiconductor laser (SCL) is proposed and demonstrated based on optoelectronic hybrid feedback. Through using a chirped fiber Bragg grating (CFBG) to provide distributed feedback, a chaotic signal with a low TDS is generated from the SCL. With the assistance of the nonlinear optoelectronic feedback provided by a microwave photonic link, the relaxation oscillation effect in the SCL is effectively suppressed, and the periodicity of the oscillation is greatly weakened. Hence, the TDS of the generated chaotic signal from the SCL is further suppressed, and the effective bandwidth is enlarged. Both simulation and experiment are carried out to verify the feasibility of the proposed scheme to suppress the TDS. In the experiment, a chaotic signal with a large effective bandwidth of 12.93 GHz, an extremely high permutation entropy (PE) of 0.9983, and a low TDS of 0.04, is generated by using a CFBG with a dispersion coefficient of 22.33 ps/nm. This TDS value is at the same level as that obtained by using the SCL-based scheme relying solely on distributed feedback in a CFBG with a dispersion coefficient of 2000 ps/nm.

Error performance analysis for chaotic pulse width position modulation in free space optical communication system

Abstract In this paper, a pulse time modulation method called chaotic pulse width position modulation (CPWPM) is studied for free space optical communication system. This is a digital modulation technique that combines pulse position modulation and pulse width modulation with chaos. In this scheme, the binary information is carried by both the position and width of the pulses, which are modulated by a chaotic signal. Hence, on a single pulse, two bits of information are encoded, which results in higher bit rates, better privacy, and larger effective bandwidth as compared to chaotic pulse position modulation (CPPM) and chaotic pulse width modulation (CPWM) techniques. Probability of error is investigated for different FSO scenarios, i.e., varying turbulence conditions and link lengths for CPWPM scheme. Finally, the performance of CPWPM-FSO system is compared with a commonly used differential chaos shift keying (DCSK) scheme. CPWPM-FSO system shows comparable results as DCSK-FSO system (for probability of error, P e = 10−4 average signal-to-noise ratio (SNR) required for DCSK and CPWPM scheme is 40 dB and 41 dB, respectively, for same length and system conditions), while data rate is doubled in latter, and this verifies the validity of using CPWPM in FSO communication system.

A Novel Two-Stage Timing Mismatch Calibration Technique for Time-Interleaved ADCs

This brief proposes a timing mismatch calibration for time-interleaved analog-to-digital converters (TI ADCs) with the novel parallel correlation derivative (PCD) technique and two-stage analog–digital hybrid compensation. The PCD technique could solve the frequency-relevant problem caused by low correlation derivative in the precise skew calculation. Besides, the compensation scheme with an analog coarse correction and then the all-digital fine correction is used to cover a larger normalized skew range and bandwidth with maintained calibration performance. Compared to previous works on timing mismatch calibration, this work has improved accuracy with a larger effective bandwidth and a larger skew calibration range. The technique is applied in a four-channel 14-bit 3 GS/s ADC model to verify its effectiveness. Simulation results show that it increases the SNDR and SFDR from 31.02 and 32.87 to 54.40 and 93.49 dB at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{f}_{\text{in}}$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$</tex-math> </inline-formula> 0.99 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{f}_{\textit{s}}$</tex-math> </inline-formula> and maintains good performance in the first three Nyquist bands.

Multi-interfacial TiO2/carbon fibers encapsulated with needle-like FeCo2O4 for excellent microwave absorption

The introduced heterojunction structures can effectively improve the interface polarization and microwave absorption ability. In this work, the titanium dioxide modified carbon fibers (TiO2/CNFs) covered with needle-like FeCo2O4 were synthesized by electrospinning process and sequential hydrothermal method. When the filling ratio in paraffin wax is only 1 wt%, the FeCo2O4/TiO2/CNFs composite demonstrates remarkable absorbing properties. The composite material displays low density (∼0.79 g/cm3) with optimal reflection loss (RL) of − 47.0 dB and a large effective absorption bandwidth (RL＜−10 dB) of 4.1 GHz (8.3–12.4 GHz). Density functional theory (DFT) calculations were performed to investigate the dielectric loss mechanism caused by interface polarization at the atomic level. The calculations revealed that the density of states (DOS) of the p orbitals near the Fermi level decreases significantly, caused by breaking of local microstructural symmetry and inducing additional electric dipoles at the interface of CNFs and needle-like FeCo2O4. Under an external electromagnetic field, the dipole oscillation strengthens the polarization loss. The dielectric loss mechanism caused by interface polarization is explored from the atomic level and it paves a new way for designing microwave absorbers. These findings pave the way for designing effective microwave absorbers.

Preparation of a Microwave-Absorbing UV Coating Using a BaFe12O19-Polypyrrole Nanocomposite Filler.

BaFe12O19-polypyrrolenanocomposites were prepared via the in situ chemical oxidative polymerization of pyrrole monomers in the presence of BaFe12O19 powder, with ammonium persulfate as an oxidant and sodium dodecyl benzene sulfonate as a dopant. X-ray diffraction measurements and Fourier-transform infrared spectroscopy indicated that there were no chemical interactions between BaFe12O19 and polypyrrole. In addition, scanning electron microscopy showed that the composites exhibited a core-shell structure. Subsequently, the prepared nanocomposite was used as a filler to prepare a coating suitable for ultraviolet curing. The performance of the coating was investigated by evaluating its hardness, adhesion, absorbance, and resistance to acids and alkalis. Importantly, the addition of BaFe12O19-polypyrrole nanocomposites not only improved the coating hardness and adhesion but also produced a coating with a good microwave absorption performance. The results suggested that BaFe12O19/PPy composite has a lower reflection loss peak and a larger effective bandwidth at the X band when the proportion of the absorbent sample is 5-7%, when the absorption performance is the best. The reflection loss is in the range of 8.88-10.92 GHz below -10 dB.

High laser performance of an Al3+ and Nd3+-codoping in sodium-borotellurite glass for NIR broadband laser application

The main spectroscopic properties of Nd3+ ions immersed in an oxide glass with composition 59B2O3–10TeO2–30Na2O–1Al2O3:1Nd2O3 (in mol%) has been studied by X-ray diffraction, EDS, SEM, luminescence, transmission, FTIR and Raman spectroscopies. Very high values of the main spectroscopic parameters of Nd3+ ions were determined from the Ωt intensity parameters according to Judd-Ofelt formalism. The 4F3/2 → 4I11/2 NIR transition at 1060 nm of Nd3+ ions is evaluated from the relevant laser parameters reporting a very high quantum efficiency (95%), large effective bandwidth (36 nm), high laser performance quality (9.19 × 10−24 cm2·s) and low saturation intensity (2.04 × 108 W/m2). The excellent non-linear properties of Nd3+ ions are attributed to a microcrystallization inside the glass induced by Al3+ and Nd3+-codoping and a high sodium concentration which intensified the ligand field strengths around Nd3+ ions. Such microcristallization is verified by the presence of several crystalline peaks observed in the FTIR and Raman spectra and identified as Al–O and Te–O linkage vibrations in α-Al2O3 and α-TeO2 phases. As a consequence, a significant reduction of free hydroxyls is appreciated at the midinfrared region in both spectra. Whereas the presence of graphite was detected in the Raman spectrum at 2450 and 2889 cm−1. The great centrosymmetric loss of the Nd3+-sites is indicated by a high value of the Ω2 parameter (36.98 × 10−20 cm2) and confirmed by matched vibrational modes displayed in the deconvoluted Raman and FTIR spectra from 370 to 1750 cm−1 according to the Mutual Exclusion Rule for non-centrosymmetric point groups. The X-ray pattern of the Nd3+-doped oxide glass shows three different amorphous phases generated by delocalized and localized 4f-electrons indicating coexistence of ionic and covalent oxide-metal bonds as characteristic of the invert glasses. However, the compositional parameters confirmed a preferentially covalent domain of oxide-metal bonds as well as presence of crystalline phase, being both structural characteristics consistent with the Judd-Ofelt, transmission, FTIR and Raman results. Finally, the radiative properties are compared with those reported for other Nd3+-activated aluminate glasses suggesting that Al3+ and Nd3+-codoped sodium-borotellurite glass has a great potential for NIR broadband laser application.

Core–shell-like nanocrystalline FeSiB/amorphous carbon composite powder with remarkable and tunable microwave absorption properties

Micron-sized Fe90Si7B3/carbon composite powder with 8–15 wt% C has been synthesized by ball milling. The powder possesses a core–shell-like structure, in which the Fe90Si7B3 core is composed of α-Fe nanocrystalline/amorphous dual phases, and the carbon shell is amorphous. The composites exhibit high permeability, matchable permittivity, and excellent microwave absorption properties including strong reflection loss of −54.8 dB at 12.7 GHz and large effective absorption bandwidth of 6.5 GHz with 1.9 mm in absorber thickness. The superior microwave absorption properties are benefited from the enhanced impedance matching and synergistic effect of strong magnetic and dielectric losses as contributed by the nature resonance and eddy current effect of the nanocrystalline Fe90Si7B3 core, and multiple polarizations and conduction loss between the Fe90Si7B3/carbon components, respectively. The microwave absorption performance can be tuned by changing carbon content and/or annealing. The Fe90Si7B3/carbon composites are promising as a new type of high-performance microwave absorbers.

4D Automotive Radar Sensing for Autonomous Vehicles: A Sparsity-Oriented Approach

We propose a high-resolution imaging radar system to enable high-fidelity four-dimensional (4D) sensing for autonomous driving, i.e., range, Doppler, azimuth, and elevation, through a joint sparsity design in frequency spectrum and array configurations. To accommodate a high number of automotive radars operating at the same frequency band while avoiding mutual interference, random sparse step-frequency waveform (RSSFW) is proposed to synthesize a large effective bandwidth to achieve high range resolution profiles. To mitigate high range sidelobes in RSSFW radars, optimal weights are designed to minimize the peak sidelobe level such that targets with a relatively small radar cross section are detectable without introducing high probability of false alarm. We extend the RSSFW concept to multi-input multi-output (MIMO) radar by applying phase codes along slow time to synthesize a two-dimensional (2D) sparse array with hundreds of virtual array elements to enable high-resolution direction finding in both azimuth and elevation. The 2D sparse array acts as a sub-Nyquist sampler of the corresponding uniform rectangular array (URA) with half-wavelength interelement spacing, and the corresponding URA response is recovered by completing a low-rank block Hankel matrix. Consequently, the high sidelobes in the azimuth and elevation spectra are greatly suppressed so that weak targets can be reliably detected. The proposed imaging radar provides point clouds with a resolution comparable to LiDAR but with a much lower cost. Numerical simulations are conducted to demonstrate the performance of the proposed 4D imaging radar system with joint sparsity in frequency spectrum and antenna arrays.

High temperature clarifier sulfate enhancing the infrared emission of Oxyfluorosilicate glass ceramics containing CaF2 nanocrystals

The laser glass at 2 μm plays an irreplaceable role in the military, communications, medical and environmental monitoring fields, but the dissolved water or hydroxyl group during the process of glass preparation has strong quenching effect on 2 μm infrared emission. Therefore, how to remove hydroxyl groups in the glass matrix is the key problem to improve the infrared luminescence intensity. In order to reduce hydroxyl content, the high temperature chemical clarifier sulfate is added into the raw material to prepare Tm3+ doped oxyfluorosilicate glass ceramics. The results show that a lot of gasses released during the decomposition of minor sulfate at high temperature will take away the hydroxyl group in the glass melt when the gas escapes, thus greatly enhancing the emission of Tm3+ close to 2 μm. XRD, TEM and Raman spectra show that the structure of the glass is not changed by the introduction of a small amount of sulfate ion. FTIR results reveal the hydroxyl content in the glass matrix is significantly reduced, which causes the enhancement of emission intensity. Our results reveal that the addition of 0.6 mol% CaSO4 instead of CaO in Tm3+/Yb3+ codoped oxyfluorosilicate glass ceramics containing CaF2 noncrystals are of best effective to remove OH− and these glass ceramics with large emission cross-section (0.712 × 10−20 cm2) and effective bandwidth (240 nm) present potential applications in optical amplifier close to 2 μm.

Activated carbon derived from mango leaves as an enhanced microwave absorbing material

Microwave absorbing materials have become an important component in electronics, communication, and modern warfare. The present study reports porous activated carbon derived from mango leaves biomass and by facile method of carbonization and activation. The porous activated carbon has the potential to become an efficient microwave absorbing material. The SEM and FESEM images clearly showed the porous structure which was further confirmed using BET analysis. The sample having 20 wt% loading of activated carbon in paraffin wax gave the Highest Reflection Loss (RLmax) of −23.26 dB at 17.68 GHz & 1.50 mm thickness. The maximum effective absorption band width (i.e. reflection loss < −10 dB) of 5.17 GHz was obtained at 1.75 mm thickness, which covered 86.16% of Ku band. The effective absorption bandwidth of 3.31 GHz was also obtained at 2.5 mm thickness which covered 82.75% of X band. This excellent microwave absorption property was obtained by high impedance matching and subsequent attenuation of microwave by dielectric loss facilitated by the porous structure. This work provides a new source of biomass which is abundant in nature and can be easily processed as an enhanced microwave absorbing material having large effective absorption bandwidth at less thickness and low filler loading.

Ethylenediamine-assisted hydrothermal synthesis of NiCo2O4 absorber with controlled morphology and excellent absorbing performance

In recent years, developing excellent electromagnetic wave (EMW) absorbers with small thickness and large bandwidth is an effective strategy to deal with the seriously EMW interferes in military and civil field. The morphology of absorbers has profound effects on their EMW absorption performance. Herein, ethylenediamine (EDA) was applied to EMW absorbing field as morphology control agent for the first time (as far as we know) for the synthesis of nickel cobaltate (NiCo2O4) absorber, and the effect of EDA content on the morphology and EMW absorbing performance was also investigated elaborately. As a bidentate ligand and structure-directing reagent, EDA controlled the morphology of NiCo2O4 by reducing the rate of nucleation and crystal growth through the complexation with metal ions, and adjusting the growth rate of different facets through the selective binding of amino to certain surfaces. The study found that the morphology of NiCo2O4 changed from three-dimensional urchin-like structures to two-dimensional nanosheets with the increase of EDA content, and meanwhile the dielectric loss property decreased, which led to decline in EMW attenuation properties. The urchin-like NiCo2O4 absorber at a molar ratio of 0.5 (EDA: metal ions) exhibited optimum absorption properties with a small thickness of 1.70 mm and large effective absorption bandwidth (EAB) of 5.81 GHz (12.19–18 GHz). The excellent EMW absorbing properties mainly originate from remarkable dipole polarization induced by oxygen vacancies and lattice defects, interface polarization stemming from the interfaces of NiCo2O4 fibers, and multiple reflections and scattering in its unique urchin-like structures. This work provides a simple method for absorber with controlled morphologies, and also expands the family members of Co-based ferrite with outstanding absorbing performance.

Realizing Maximum Microwave Absorption of Poly(3,4-ethylenedioxythiophene) with a Data-Driven Method

Large reflection loss (RL) and broad effective bandwidth (f10) are two of the most important parameters for microwave absorbing materials (MAM). In this manuscript, we report that a strong and bro...

Hierarchically porous carbon sheets/Co nanofibers derived from corncobs for enhanced microwave absorbing properties

In order to obtain a microwave absorbing material with strong absorption, broad bandwidth, and light weight, the hierarchically porous carbon sheets/Co nanofibers composites were prepared by using corncobs as precursors in this paper. The electromagnetic parameters of the C/Co composites can be well adjusted by changing the loading amount of Co nanofibers, and then an increased attenuation capability and impedance matching can be obtained. Benefiting from the hierarchically porous architectures and the optimized electromagnetic parameters, the C/Co0.4 absorber with a filler loading of only 20 wt% in paraffin possesses a minimum reflection loss of −64.50 dB at 13.76 GHz with a thickness of 2.60 mm, and a very large effective bandwidth of 8.40 GHz (9.6–18.0 GHz) at the thickness of 2.90 mm. The strong absorption, broad effective bandwidth and lightweight indicate that the C/Co composites can be employed as a high-performance microwave absorber.

Electrostatic self-assembly synthesis of ZnFe2O4 quantum dots (ZnFe2O4@C) and electromagnetic microwave absorption

Making effective usage of quantum size effect is a foregrounded strategy to design and fabricate excellent electromagnetic microwave absorption materials. In this research, ZnFe2O4 quantum dots were coated by hybrid amorphous carbon to form a sea islands structure by a facile electrostatic self-assembly synthetic technology. Simultaneously, the rejection of heterogeneous charges leads to the formation of quantum dots, by which the quantum size effects on dielectric and magnetic characteristic were investigated. Consequently, multiple hetero-interface and interfacial polarization was originated from polycrystalline feature of ZnFe2O4 with spinel and inverse spinel structures. In particular, the electromagnetic microwave absorption properties of ZnFe2O4 were greatly optimized, as the minimized reflection loss reached −40.68 dB at the frequency 11.44 GHz and thickness 2.5 mm, while the effective bandwidth corresponding was 3.66 GHz (from 9.87 to 13.52 GHz). The largest effective bandwidth was 4.16 GHz (from 8.08 to 12.24 GHz) with a thickness of 3 mm. It is suggested that high performance of microwave absorption of ZnFe2O4 quantum dots was well guided by the optimized impedance matching and attenuation constants.

Enhanced electromagnetic wave absorption of Ni–C core-shell nanoparticles by HCP-Ni phase

The strategy of phase control has been playing an important role in optimizing the electromagnetic wave (EMW) absorption properties. Here, Ni nanoparticles (NPs) with two phases, hexagonal close-packed Ni (HCP-Ni) and face-centered cubic (FCC-Ni), coated by C shells are synthesized by metal-organic chemical vapor deposition. The average size of the Ni nanocores and thickness of C shells are about 10 and 4 nm, respectively. After blended with paraffin wax at a mass ratio of 1:5, the Ni–C core–shell NPs exhibit excellent EMW absorption properties with an optimal reflection loss of −52.6 dB and a large effective bandwidth () of 9.3 GHz. The core–shell NPs annealed in vacuum to remove the metastable HCP-Ni exhibit degraded EMW absorption properties. Comparative analyses reveal that the HCP-Ni phase in the core–shell NPs can enhance the dielectric loss and thus improve the impedance matching, suggesting that phase control should be a practicable strategy for optimizing the properties of Ni-based EMW absorption materials.

Gram-scale synthesis, thermal stability, magnetic properties, and microwave absorption application of extremely small Co–C core–shell nanoparticles

Co–C core–shell nanoparticles have been synthesized in large quantity (in grams) by metal-organic chemical vapor deposition with analytical cobalt (III) acetylacetonate as precursor. Extremely small nanoparticles with an average core diameter of 3 nm and a shell thickness of 1–2 nm, and relatively large nanoparticles with an average core diameter of 23 nm and a shell thickness of 5–20 nm were obtained, depending on the deposition regions. The 3 nm Co nanocores are thermally stable up to 200 °C in air atmosphere, and do not exhibit visible structural and morphological changes after exposure to air at room temperature for 180 d. The extremely small core–shell nanoparticles exhibit typical superparamagnetic behaviors with a small coercivity of 5 Oe, while the relative large nanoparticles are a typical ferromagnetic material with a high coercivity of Oe. In the microwave absorption tests, a low reflection loss (RL) of −80.3 dB and large effective bandwidth (frequency range for dB) of 10.1 GHz are obtained in the nanoparticle-paraffin composites with appropriate layer thicknesses and particle contents. This suggests that the as-synthesized Co–C core–shell nanoparticles have a high potential as the microwave-absorbing materials.

Achieving Centimeter Accuracy Indoor Localization on WiFi Platforms: An Multi-Antenna Approach

Channel frequency response (CFR) is a fine-grained location-specific information in WiFi systems that can be utilized in indoor positioning systems (IPSs). However, CFR-based IPSs can hardly achieve an accuracy at the centimeter level due to the limited bandwidth in WiFi systems. To achieve such accuracy using WiFi devices, we propose an IPS that fully harnesses the spatial diversity in multiple-input-multiple-output WiFi systems, which leads to a much larger effective bandwidth than the bandwidth of a WiFi channel. The proposed IPS obtains CFRs associated with locations-of-interest on multiple antenna links during the training phase. In the positioning phase, the IPS captures instantaneous CFRs from a location to be estimated and compares it with the CFRs acquired in the training phase via the time-reversal resonating strength with residual synchronization errors compensated. Extensive experiment results in an office environment with a measurement resolution of 5 cm demonstrate that, with a single pair of WiFi devices and an effective bandwidth of 321 MHz, the proposed IPS achieves detection rates of 99.91% and 100% with false alarm rates of 1.81% and 1.65% under the line-of-sight (LOS) and non-LOS (NLOS) scenarios, respectively. Meanwhile, the proposed IPS is robust against environment dynamics. Moreover, experiment results with a measurement resolution of 0.5 cm demonstrate a localization accuracy of 1-2 cm in the NLOS scenario.