Inductive-capacitive Resonance Research Articles

Unveiling photon–photon coupling induced transparency and absorption

Abstract This study presents the theoretical foundations of an analogous electromagnetically induced transparency (EIT) and absorption (EIA) which we are referring as coupling induced transparency (CIT) and absorption (CIA) respectively, along with an exploration of the transition between these phenomena. We provide a concise phenomenological description with analytical expressions for transmission spectra and dispersion elucidating how the interplay of coherent and dissipative interactions in a coupled system results in the emergence of level repulsion and attraction, corresponding to CIT and CIA, respectively. This theory comprehensively captures both the phenomena while modelling the microstripline loaded resonators and their couplings systematically. The model is validated through numerical simulations using a hybrid system comprising a split ring resonator (SRR) and electric inductive-capacitive (ELC) resonator in planar geometry. We analyse two cases while keeping ELC parameters constant; one involving a dynamic adjustment of the SRR size with a fixed split gap, and the other entailing a varying gap while maintaining a constant SRR size. Notably, in the first case, the dispersion profile of the transmission signal demonstrates level repulsion, while the second case results in level attraction, effectively showcasing CIT and CIA, respectively. These simulated findings not only align with the theoretical model but also underscore the versatility of our approach. Subsequently, we expand our model to a more general case, demonstrating that a controlled transition from CIT to CIA is achievable by manipulating the dissipation rate of individual modes within the hybrid system, leading to either coherent or dissipative interactions between the modes. The results provide a pathway for designing hybrid systems that can control the group velocity of light, offering potential applications in the fields of optical switching and quantum information technology.

Thermal and electrical switchable wide-angle multi-band terahertz absorber.

Multi-band terahertz (THz) absorbers have recently gained attention due to their favorable application prospects in communication, imaging, detection, and other fields. However, many multi-band THz absorbers are tuned by a single method, which limits their tuning effect. To address this issue, we propose a multi-band THz absorber that can be co-modulated by thermal and electrical methods. Our proposed absorber uses vanadium dioxide (VO2) to achieve this co-modulation. When VO2 is insulating, the frequency of the absorbing peaks originating from the lateral Fabry-Pérot resonance mode can be changed by adjusting the VO2 width. When VO2 is a conductor, the quality factor of the absorbing peak based on the inductor-capacitor resonance mode can be tuned by adjusting the width of VO2. By varying the top dielectric layer thickness, the frequency of the absorbing peaks can be tuned over a wide range. For devices with two or three layers of graphene nanoribbons-dielectric stacks, a modulation effect similar to that of varying dielectric layer thickness in a single-layer graphene device can be achieved simply by applying a 1 eV Fermi energy to graphene nanoribbons in different layers. By combining thermal and electrical modulation, the two or three-layer stacked device can be dynamically switched between four or six absorbing states, and a wider range of dynamic peak frequency modulation can be realized. Furthermore, the performance of the absorber does not deteriorate significantly at an incident angle of up to 70°. Our proposed thermal-electrical switchable wide-angle multi-band THz absorber provides a reference for the design, fabrication, and application of high-performance THz absorbers in different fields.

Experimental observation of purely resistive effect in epsilon-near-zero transition metal perovskite

The epsilon-near-zero (ENZ) properties of nanomaterials provide a promising paradigm for the development of next-generation nanoscale electronic devices, especially in 6 G communication systems. However, realizing ENZ in the radio frequency (RF) domain remains a challenge due to the scarcity of materials. Here, a strategy is proposed to exploit the intrinsic excitation of polarons and delocalized electrons to modify the carrier dynamics in transition metal perovskite for tailored dielectric response in the RF domain. Polarons and delocalized electrons are introduced into the material through lattice distortion and exchange mechanisms between magnetic atoms, and are precisely governed. The tunable kHz-band ENZ is realized in La0.90Ba0.10CoO3 and described using the Debye-Drude model. Importantly, the purely resistive effect is experimentally observed under ENZ condition, manifesting as near-zero reactance and phase angle, which is attributed to the inductor-capacitor resonance through equivalent circuit analysis. These findings provide a new avenue for implementing ENZ at RF domain and identify transition metal perovskites as ENZ candidates.

Influence of Coupled Structural Parameters of Photoconductive Antennas on the Terahertz Narrowband Detection Performance of High Sensitivity and Frequency Selection

Narrowband terahertz (THz) detection plays a key role in biomedical imaging, biological applications, and security screening. Particularly rapid resolution of material differences based on spectral fingerprints or time‐resolved observation of the materials conformational state typically requires only the measurement of spectral information at a few selected frequencies. Here, a high‐performance resonance‐based coupled photoconductive antenna (PCA) was designed, which consists of a square split‐ring resonator (SRR) and an H‐shaped antenna. The incident THz wave energy can be effectively coupled in the gap of the H‐shaped antenna, and the coupling effect base on coupled harmonic oscillator model can be effectively strengthened. By decreasing the square SRR gap width HD, the relative position parameters of d and L3 between the square SRR and H‐shaped antenna can markedly improve the resonance frequency sensitivity with inductive–capacitive resonance. With the square SRR arm length L1 = L2 = L increased, the resonance frequency markedly shifted toward a lower frequency and the resonance sensitivity increased. The results prove that the THz frequency selection detection range of the coupled PCA can be designed to 0.1∼1.0 THz. Compared with the traditional H‐shaped photoconductive detection antenna, the detection resonance peak shifted the lower frequency and the maximum THz detection sensitivity increased by approximately two orders of magnitude at 0.2528 THz. The structure of the noncontact micrometer–coupled PCA is simple and easy to fabricate and integrate. Our findings may also help to advance the use of THz technology in rapid distinguish material properties.

High-performance direct terahertz modulator based on resonance mode transformation for high-speed wireless communication

The developing terahertz wireless communication demands higher performance modulators. In this Letter, a mechanism of resonance mode transformation for a high-speed terahertz direct amplitude modulator with rather low insertion loss and high modulation depth is presented. By embedding an H-shaped resonance structure, which consists of a fin-line and two flip-flopped GaAs Schottky diodes, into the E-wall of a waveguide, the fed terahertz waves are modulated by the inductive-capacitive (LC) resonance transformation of the structure. Based on this mechanism, a modulator working in the frequency band around 140 GHz is fabricated and packaged. Thanks to the LC resonance transformation, the presented modulator exhibits a low insertion loss of 1.8 dB at 138 GHz, a large modulation depth higher than 99% at 148 GHz, and high modulation speeds up to 30 Gbps at 146 GHz. Accordingly, the presented mechanism paves a promising route to develop high performance terahertz direct modulators, which is of great significance for terahertz high-speed wireless communication.

Single-layer near-zero refractive index metamaterial lens based on non-complete periodic arrays.

In this study, an electric inductive-capacitive (ELC) resonator with a refractive index of around 0.08+i0.08 at 5.8 GHz serves as the unit cell. Based on the ELC unit cell, together with the electromagnetic wave (EMW) single knife-edge diffraction model, a near-zero refractive index metamaterial (NZIM) lens with a non-complete periodic array and small dimension of 0.8λ0 2 is proposed to weaken the blocking of feed source radiation, and bring more significant gain enhancement compared to that with a complete periodic array. To demonstrate the proposed lens performance, the lens-loaded antenna formed by the proposed NZIM lens and a rectangular microstrip patch antenna (MPA) operating at the center frequency of 5.8GHz is provided. The measured results show that the relative bandwidth (RBW) of the lens-loaded antenna is 9.83% (5.51-6.08 GHz), which is expanded by 3.6 times contrasted with that of MPA (2.75%). Moreover, the average and maximum gains enhancement of 4.77 dB and 6.88 dB are obtained. Due to improving the radiation characteristic, this work can be used to drive the application of MPAs in wireless communication systems.

Reconfigurable beam-steerable leaky-wave antenna loaded with metamaterial apertures using liquid crystal-based delay lines.

An original liquid crystal (LC)-based substrate integrated waveguide (SIW) leaky-wave antenna is proposed. Inside the SIW, there is an embedded stripline sandwiched between an LC pool and another dielectric slab. The antenna couples the guided quasi-TEM mode into free space through a periodic set of complementary electric inductive-capacitive (cELC) resonators. Simulation results show that the antenna performs fixed-frequency continuous beam steering of 52° from backward -28° to forward 24° at 25.85 GHz. This relatively wide beam scan angle is achieved by tuning the LC permittivity through an applied quasi-DC bias voltage to the stripline. Simulation results show that the antenna has high realized gain through the entire scanning range (less than 1 dB degradation), relatively wide bandwidth, and good tolerance to frequency drift and fabrication errors.

Tuning symmetry-protected quasi bound state in the continuum using terahertz meta-atoms of rotational and reflectional symmetry.

Conventionally, a symmetry-protected quasi bound state of the continuum (BIC) becomes achievable by breaking the C2 symmetry of meta-atoms. Our work exhibits a novel approach to achieving dual band quasi-BIC by breaking the C2v symmetry into Cs symmetry. Also, we show that a single band quasi-BIC can be achieved by breaking the C2v symmetry into C2 symmetry. Our metasurface of C2v symmetry is composed of double gaps split ring resonator (DSRR), and it degrades to C2 symmetry when the double gaps are displaced in opposite directions. One band quasi-BIC can be observed occurring at around 0.36 and 0.61 THz respectively with the metasurface excited by x- and y-polarized terahertz radiation, respectively. A couple of dark dipole oscillator dominates the quasi-BIC at 0.36 THz, while a quadruple-like oscillator dominates the quasi-BIC at 0.61 THz. The damping ratio and coupling coefficients of the above single quasi-BIC are close to the orthogonal polarization of the incident terahertz wave. However, the metasurface of the DSRR array degrades down to Cs symmetry when the double gaps are displaced in the same directions. A dual band quasi-BIC (0.23 THz and 0.62 THz) is found to be sensitive to the y-polarized terahertz radiation. It is found that the inductive-capacitive (LC) resonance results in quasi-BIC at 0.23 THz, while a quadrupole-like oscillation results in quasi-BIC at 0.62 THz. The quasi-BIC at 0.62 THz has a higher coupling coefficient and lower damping ratio than quasi-BIC at 0.23 THz in a metasurface of Cs symmetry. The realization of the above locally symmetric breaking on the quasi-BIC of terahertz metasurfaces is helpful for the innovation of multi-band terahertz biosensors.

Ultra-sensitive passive wireless sensor exploiting high-order exceptional point for weakly coupling detection

Since the quantum concept of parity-time (PT) symmetry has been introduced into the conventional inductor–capacitor resonance, strategies based on exceptional points (EP) based strategies redefine our understanding of sensitivity limitation. This considerable enhancement of sensitivity originated in exploration of the non-Hermitian physics in photonics, acoustics and electronics, which exhibits a substantial application to the miniaturization of implanted electronic sensors in medicine field. By continuously accessing the EP, the spectral response of reader ∆ω follows a dependency of Δω ∼ κ 2/3 to a weakly coupling rate (|κ| ≈ 0), which may approach the theoretical limit of sensitivity in a second-order EP system. In this paper, we experimentally demonstrate a high-order (higher than second-order) PT symmetric system for weak coupling detection, in which a third-order EP can be employed to fulfill the sensitivity of Δω ∼ κ 1/2. Particularly, we introduce the incoming wave as an effective gain to balance the loss and obtain a pair of purely real eigenfrequencies. There are absence of imaginary parts despite corresponding real parts shifts dramatically by using a neutral resonator, without a broadening of the reflection spectrum so that maintaining a high resolution on the sensitivity. This work may reveal the physical mechanics of a small perturbation at a high-order EP and promote applications in implanted medicine devices.

Terahertz sensor based on a three-dimensional double I-type metamaterial integrated microfluidic channel.

Terahertz metamaterial sensors have received extensive attention in biosensing applications. However, sensitivity toward terahertz frequencies emitted by liquid samples remains challenging because of the strong absorption of terahertz waves by water. Here, we present a highly sensitive terahertz sensor based on a three-dimensional double I-type metamaterial integrated microfluidic channel. The designed sensor produces an inductive-capacitive (LC) resonance with a high quality factor of approximately 72, while demonstrating a maximum sensitivity of 832 GHz/RIU. Furthermore, we analyzed the relationship between the resonance frequency and ethanol concentration. These findings would promote the application of terahertz technology in label-free and rapid biomedical sensing as well as substance detection.

Detection of delamination defects inside carbon fiber reinforced plastic laminates by measuring eddy-current loss

Carbon fiber reinforced plastics are likely to experience delamination due to the heterogeneity and anisotropy of the materials. However, the through-thickness conductivity of CFRPs is low, resulting in a weak output signal and large amounts of noise interference of eddy current testing in the detection of delamination. Based on the eddy-current loss theory, a method is proposed to detect delamination inside CFRPs. The method consists of an absolute probe with an 8-shaped coil and a unique signal extraction technique using eddy-current loss. The 8-shaped coil of the proposed probe enables the probe to generate a sufficiently strong vertical eddy-current component at its geometric center. The eddy-current loss on CFRPs is extracted by the parallel inductor-capacitor resonance circuit and micro-power detection module. The experiments show that the sensitivity of the vertical 8-shaped probe to the delamination detection is higher than that of the circular and square probes. Compared with ECT, the proposed method by measuring eddy-current loss for delamination has a lower frequency and less noise. In addition, this paper further explores the application of the proposed method in automatic defect detection. The results show that the proposed method can be effectively applied to the automatic detection and visualization of delamination inside CFRPs.

Battery-free radio frequency wireless sensor for bacteria based on their degradation of gelatin-fatty acid composite films

Continuous and automated bacteria detection is pivotal for a myriad of biomedical, food safety and environmental applications. This work presents the fabrication of a prototype of a passive (battery-free) radio frequency sensor for wireless detection of bacteria. The sensing mechanism is based on the bacterial-induced (proteases and peptidases) degradation of glutaraldehyde (GTA) cross-linked gelatin-caprylic acid (CA) composite film. Proteolytic degradation of the film resulted in a decrease of its resistivity, a quantity that could be wirelessly monitored by coupling the film to a radio-frequency antenna (an inductor-capacitor resonator) and monitoring the frequency for which the transferred power between this antenna and another antenna connected to a Vector Network Analyzer (VNA) was maximized. We experimentally proved this concept by monitoring E.coli bacteria in aqueous medium and detected at 18.0 ± 2.8 h, 23.5 ± 0.7 h, 27.0 ± 2.8 h, 40.5 ± 3.5 h, 45.5 ± 0.7 h for the initial E.coli concentration of 3.2 × 108, 6.8 × 107, 2.3 × 106, 4.3 × 105, and 3.6 × 104 CFU/mL, respectively. Further, the E.coli induced degradation of the composite film was investigated by evaluating the thickness of the film by optical microscopy as well as morphology by scanning electron microscopy techniques.

A Harmonic-Tuned VCO With an Intrinsic-High-Q F23 Inductor in 65-nm CMOS

A harmonic-tuned (HT) voltage-controlled oscillator in a 65-nm CMOS process is demonstrated in this letter. The oscillation frequency and harmonics are tuned independently by two separated high- $Q$ resonators. A novel F23 inductor–capacitor resonator resonating at the second and third harmonics simultaneously is introduced. The proposed F23 inductor has a high-quality factor of 15 and 24 in common-mode (CM) and differential-mode (DM), respectively. The simulation results show that a 4.3-dB phase noise (PN) improvement is achieved in the thermal noise region due to the high- $Q$ HT method. Meanwhile, less harmonic currents are injected into the fundamental resonator due to the source-degeneration principle, hence decreasing the Groszkowski effect and suppressing the flicker noise. The measured PN is −117.5 dBc/Hz at the 1-MHz offset, and the tuning range is 12% from 6.80 to 7.66 GHz. The flicker noise corner is around 220 kHz and the figure-of-merit is 187.2 dBc/Hz. The power consumption is 5 mW under a 0.55-V supply.

High-efficiency cross-polarization conversion metamaterial using spiral split-ring resonators

We report on a high-efficiency cross-polarization conversion metamaterial design consisting of novel spiral split-ring resonators (SRRs). Numerical simulations on the resonant electric field and surface current distributions demonstrate that the cross-polarization response is attributed to the charge accumulation in the horizontal SRR gap. The dependencies of resonance frequency on the structural parameters of the SRR reveal that an inductive-capacitive resonance dominates the SRR. We further show that the polarization conversion efficiency can be significantly enhanced by integrating two orthogonal gratings, which enable a linear polarization wave to be rotated to its orthogonal direction with a high efficiency of ∼90%. These results offer a way to engineer novel high-performance metamaterial polarization devices.

Highly Stable Passive Wireless Sensor for Protease Activity Based on Fatty Acid-Coupled Gelatin Composite Films.

Proteases are often used as biomarkers of many pathologies as well as of microbial contamination and infection. Therefore, extensive efforts are devoted to the development of protease sensors. Some applications would benefit from wireless monitoring of proteolytic activity at minimal cost, e.g., sensors embedded in care products like wound dressings and diapers to track wound and urinary infections. Passive (batteryless) and chipless transponders stand out among wireless sensing technologies when low cost is a requirement. Here, we developed and extensively characterized a composite material that is biodegradable but still highly stable in aqueous media, whose proteolytic degradation could be used in these wireless transponders as a transduction mechanism of proteolytic activity. This composite material consisted of a cross-linked gelatin network with incorporated caprylic acid. The digestion of the composite when exposed to proteases results in a change of its resistivity, a quantity that can be wirelessly monitored by coupling the composite to an inductor–capacitor resonator, i.e., an antenna. We experimentally proved this wireless sensor concept by monitoring the presence of a variety of proteases in aqueous media. Moreover, we also showed that detection time follows a relationship with protease concentration, which enables quantification possibilities for practical applications.

Measurement and Error Analysis of Cu Film Thickness With Ta Barrier Layer on Wafer for CMP Application

Accurate thickness measurement of copper (Cu) film on silicon (Si)-based wafers is very important in the chemical mechanical polishing (CMP) process. For thickness measurement of Cu film, the eddy current method is widely adopted due to noncontact, high-efficiency, and high-accuracy characteristics. However, existing thickness measurements of Cu film ignore the effect of tantalum (Ta) barrier layer between Cu film and Si substrate, which makes the measurement result inaccurate. Therefore, it is necessary to investigate the effect of Ta barrier layer on thickness measurement of Cu film. In this article, an improved eddy current sensor system with a nanoscale resolution is proposed. It is based on the inductance–capacitance resonance principle and theoretical analysis is conducted. Several Si-based specimens with pure Cu film, pure Ta film, and Cu–Ta multilayer structure are prepared and measured. Experimental results show that there exists a balance thickness of Ta barrier layer as a threshold in Cu–Ta multilayer structure. When the thickness of Ta barrier layer is larger than the threshold, the measured thickness of Cu film increases with the increase of Ta barrier layer thickness. Conversely, the measured thickness of Cu film decreases when Ta barrier layer is thinner than the threshold. Then, a compensation method is presented, and the error of thickness measurement of Cu film is reduced to less than 6 nm.

A mutual coupled concentric crossed-Line split ring resonator (CCSRR) based epsilon negative (ENG) metamaterial for Tri-band microwave applications

A metamaterial design and its analysis based on an epsilon negative concentric crossed-line split ring resonator (CCSRR) have been presented in this paper. The CCSRR unit cell structure is the amendment of the typical concentric split ring resonator (CSRR). The inserted crossed line increases the electrical length of the presented CCSRR unit cell. The dimension of the proposed CCSRR unit cell is 10 × 10 × 1.575 mm3 and it is printed on the Rogers RT 5880 substrate material. The transmission frequency ranges from 6.33 GHz to 6.65 GHz, 10.42 GHz to 10.73 GHz, and 13.21 GHz to 13.42 GHz which covers the frequency bands of C, X, and Ku-band of microwave applications. A complete analysis of scattering parameters, effective medium parameters, mutual coupling effect as well as the unit cell characteristics with electromagnetic analysis have been performed in this study. The proposed CCSRR unit cell structure exhibits epsilon negative characteristics in the frequency ranges of 6.53 GHz to 6.96 GHz, 10.63 GHz to 10.91 GHz, and 13.37 GHz to 13.40 GHz. Experimental validation has also been performed by measuring the scattering parameters of the proposed CCSRR unit cell and its array structure. Furthermore, the capacitive coupling among the concentric split ring resonators within the 1 × 2 and 2 × 2 array structures have been studied which is based on the near field split gaps that lead to the fundamental inductive-capacitive resonances. Besides, the effective medium ratio 4.5 implies the effectiveness and compactness of the proposed CCSRR unit cell structure. The compactness, effective medium parameters, and effective medium ratio make the proposed CCSRR metamaterial appropriate for the microwave applications.

Storage and release of electromagnetic waves using a Fabry-Perot resonator that includes an optically tunable metamirror

We evaluate the transient response of an optically tunable meta-atom composed of an electric inductor-capacitor resonator that is loaded with a piece of high-resistivity silicon and perform a proof-of-concept experiment to demonstrate the storage and release of electromagnetic waves using this meta-atom in the microwave region. The transient time of the meta-atom immediately after commencing laser light illumination of the silicon in the meta-atom is found to be inversely proportional to the incident laser power. The transmittance of the meta-atom at the resonance frequency increases to ten times that obtained without laser illumination at 5.2 ns after the start of laser illumination for a laser power of 1600 mW, a laser spot size of 2 mm $\times$ 1 mm, and a laser wavelength of 447 nm. In contrast, the transient time after turning the laser light off is dependent on the carrier lifetime of silicon and is measured to be several tens of microseconds. Based on the results of evaluation of the transient response of the meta-atom, we propose a method for the storage and release of electromagnetic waves using a Fabry-Perot resonator that includes the meta-atom as one of its mirrors. The electromagnetic wave that is stored in the Fabry-Perot resonator for a few tens of nanoseconds is then successfully released by illuminating the silicon in the meta-atom with the laser light. It is also possible to use this method in the higher frequency region because metamaterials with semiconductor elements can even be used as active metamaterials in the optical region as long as their bandgap energy is higher than the signal photon energy.

Miniature power and data transceiver based on multimodal operation of a single photovoltaic device

Wireless bi-directional data telemetry and power delivery are demonstrated using a single photovoltaic (PV) cell. The same cell functions as a light-emitting diode (LED), a power transducer, and a reverse-biased photodiode. This is achieved through the use of a simple inductor-capacitor resonator, with the cell’s junction providing the circuit’s capacitive element. We show that pulsed illumination at the circuit’s resonance frequency results in active switching of the PV cell between the three operating modes. Using this approach we demonstrate backward data transmission in the form of optical pulses generated by the PV cell, as well as enhanced forward data transmission and power generation. This work demonstrates the principle of using a single PV cell as an optical data transceiver while simultaneously generating energy using only two circuit elements; an inductor and a PV cell. This approach benefits miniature wireless devices, such as medical implants, which operate within significant size, weight, and energy constraints.

Structure-based tunable metamaterials for electromagnetically induced transparency windows in low terahertz frequency

The electromagnetically induced transparency (EIT) metamaterials with active or passive modulation have been extensively studied and applied in slow-light devices, light on-off, and light storage. However, the preparation complexity and characterization difficulties of the EIT metamaterials limit their optoelectronic applications. Here, we have employed a structure-based tunable design to fulfill the passive modulation of EIT metamaterial. We propose a simple but effective EIT structural model composed of a cutting wire and two circular split rings. Through theoretical analysis and computational simulation, it is found that the localized surface plasma and the inductive-capacitive resonance mode coincidently contribute to the EIT effect, giving rise to a narrow transparency window. Moreover, the amplitude of the transparency peak gradually decreases at the same resonance frequency with the increment of the lateral distance between the wire and split ring, while it decreases proportionally with the increment of the radius of the split ring. Interestingly, when the radius continues to increase, the asymmetry of the EIT window aggravates and the second EIT broad transparency window appears, indicating the existence of another intriguing coupling mechanism. Our work unveils a simple and practical modulation strategy for EIT-based multifunctional optical devices and shed light on its potential application on the optical devices.