Interdigital Structure Research Articles

Ultra-Compact Low-Pass Spoof Surface Plasmon Polariton Filter Based on Interdigital Structure.

An ultra-compact low-pass spoof surface plasmon polariton (SSPP) filter based on an interdigital structure (IS) is designed. Simulated dispersion curves show that adding the interdigital structure in an SSPP unit effectively reduces its asymptotic frequency compared with traditional and T-shaped SSPP geometries, and the unit dimensions can be conversely reduced. Based on that, three IS-based SSPP units are, respectively, designed with different maximum intrinsic frequencies and similar asymptotic frequencies to constitute the matching and waveguide sections of the proposed filter, and the unit number in the waveguide section is adjusted to improve the out-of-band suppression. Simulation results illustrate the efficient transmission in the 0~5.66 GHz passband, excellent out-of-band suppression (over 24 dB) in the 5.95~12 GHz stopband and ultra-shape roll-off at 5.74 GHz of the proposed filter. Measurement results on a fabricated prototype validate the design, with a measured cut-off frequency of 5.53 GHz and an ultra-compact geometry of 0.5 × 0.16 λ02.

Design of High-Sensitivity Microfluidic Sensor Based on CSRR With Interdigital Structure

Design of High-Sensitivity Microfluidic Sensor Based on CSRR With Interdigital Structure

An Interdigital Microwave Sensor Based on Differential Structure for Dielectric Constant Characteristics Measurement.

In this work, a microwave resonator sensor with a unique configuration consisting of three resonators and two feedlines is proposed. This novel design aims to improve the performance and functionality of microwave resonator sensors for various applications. The frequency response of the sensor to materials with different dielectric constants is simulated. The results show that the most sensitive region of the sensor is located on the first interdigital structure, and placing the materials in other regions would enhance the linear correlation of its frequency response. The sensor also exhibits the ability to distinguish whether the same material has defects and the ability to qualitatively detect subtle changes in dielectric constant. Finally, the proposed sensor is fabricated and measured under the condition consistent with the simulation environment. The measured results are basically consistent with the simulation results, which confirms the potential of this sensor in detecting dielectric constants and resolving materials with defects, and the response of the sensor to the materials under test demonstrates its potential in measuring different thicknesses and loss tangents.

Timber moisture content evaluation using spiral capacitive structures

In this work a transducer based on spiral planar inter-digital capacitive structure is designed and implemented for timber moisture content measurement. The sensor capacitance measured at frequency 100 KHz is found to depend strongly on the material dielectric properties, which is found to increase with increasing moisture contents (MC). The moisture contents in the range from 0% to 82% for 5 different varieties of timber specimens are measured and the results presented. The measured capacitances increase with moisture contents with an exponential fitting, with a correlation coefficient better than 0.98 indicating good fit for all the timber varieties. The sensitivity of the technique varies with the specimen as well as its moisture content. The best sensitivity obtained is 0.01 pF/MC%. The performance of the technique in terms of relevant sensor parameters has been analysed and compared with existing techniques for the same measurement. Although several moisture measurement methods exist for timber, the present inter-digital capacitive technique has many advantages over them in terms of sensitivity, dynamic range, cost effectiveness, non-invasiveness, non-destructiveness and measurement speed.

High responsivity and multi-wavelength response photodetector based on single bandgap AlInN film by magnetron sputtering

The AlInN film with a band gap of 2.96 eV is prepared on glass by radio frequency magnetron sputtering. Photoluminescence spectra reveals that the emission band is originated from both the band-edge and some defect-related radiation. The interdigital AlInN photodetector based on metal−semiconductor−metal (MSM) structure exhibits photoresponse characteristics from ultraviolet to visible light. The defect energy level is responsible for the multi-wavelength response of the low-energy incident irradiation light. The photodetector exhibits the best performance under 660 nm illumination, with a responsivity of 102 A/W, an external quantum efficiency of 190% and a specific detectivity of 2.8 × 109 Jones. These three factors improve by 4–6 orders of magnitude compared to point electrodes. The AlInN MSM interdigital electrode structure provides a relatively promising candidate structure for achieving high-performance multi-wavelength photodetectors.

Dual-band frequency-selective rasorber with embedded interdigital capacitors

A dual-band dual-polarized FSR is proposed in this paper. The structure consists of two layers, a resistive layer and a lossless layer. The units of the resistive layer are designed based on the Jerusalem cross and absorbing waves are achieved by mounting resistors on the metal arms. the double-ring interdigital capacitor structures are embedded in the center of the cross to generate two parallel resonances, resulting in two transmissive windows. The lossless layer is designed for double bandpass by etching double square slots. The two layers transmit electromagnetic signals in two passbands and form absorbers outside the passbands to produce two absorption bands. The simulation results show that the reflection coefficient of the proposed FSR is under -10 dB from 2.96 to 10.31 GHz, and the fractional bandwidth is 110.8%, while the FSR has a stable performance within 40°. The equivalent circuit model of the FSR is also illustrated. Furthermore, the FSR is processed and the measurement results verify the design. The measurement results demonstrate that the insertion losses of the passbands are -0.35 dB and -0.2 dB at 5.91 GHz and 9.67 GHz.

Simulation Studies on the Design and Analysis of Interdigital and Fractal-Based Micro-Supercapacitors

Micro supercapacitors (MSC) are recently replacing traditional batteries in flexible and portable electronic devices owing to their outstanding features such as high power density and long cycle life. In-plane supercapacitors are usually built in an interdigital electrode (IDE) structure because of its fabrication simplicity and flexibility. This helps to reduce ion diffusion length and enables easy on-chip integration of the device. Recent researches show that by replacing the interdigital electrode structure with the new architecture technique of Fractal electrode design, the effective area of the electrode-electrolyte interface and capacitance can be increased. This work investigates the effect of the device architecture on the energy storage capacity of in-plane MSCs. IDE and Fractal-based electrodes are simulated using COMSOL Multiphysics and analyzed for performance using cyclic voltammetry, galvanic charge-discharge technique and electric field distribution. The results indicate that the device with fractal design has more areal capacitance than the traditional interdigital structure. The highest capacitance was achieved by the proposed Sierpinski Fractal electrode design which exhibited 85.59% more areal capacitance than the conventional IDE. This can be attributed to the significant increase in effective electrode area and the edging effect of the electric field in the sharp edges of fractal electrodes.

Optimal interdigitated electrode sensor design for biosensors using multi-objective particle-swarm optimization

<p>Interdigitated electrodes (IDEs) are commonly employed in biological cellular characterization techniques such as electrical cell-substrate impedance sensing (ECIS). Because of its simple production technique and low cost, interdigitated electrode sensor design is critical for practical impedance spectroscopy in the medical and pharmaceutical domains. The equivalent circuit of an IDE was modeled in this paper, it consisted of three primary components: double layer capacitance, C<sub>dl</sub>, solution capacitance, C<sub>Sol</sub>, and solution resistance, R<sub>Sol</sub>. One of the challenging optimization challenges is the geometric optimization of the interdigital electrode structure of a sensor. We employ metaheuristic techniques to identify the best answer to problems of this kind. multi-objective optimization of the IDE using multi-objective particle swarm optimization (MOPSO) was achieved to maximize the sensitivity of the electrode and minimize the Cut-off frequency. The optimal geometrical parameters determined during optimization are used to build the electrical equivalent circuit. The amplitude and phase of the impedance versus frequency analysis were calculated using EC-LAB® software, and the corresponding conductivity was determined.</p>

Sensitivity–Enhanced detection of acetone gas using MXene-Immobilized planar microwave sensor

This work presents the noncontact immobilization of Ti3C2Tx MXene on a planar microwave resonator sensor via a polyimide film to enhance the gas detection sensitivity, enabling the characterization of the part per million-level of acetone gas. Sandwiching a polyimide (PI) film confined an intense electromagnetic field between the resonator’s interdigital capacitor structure and the MXene layer, maintaining a significant interaction between the acetone gas molecules and the resonator’s EM field via the MXene layer. Therefore, contactless immobilization of the MXene layer enhanced the acetone gas detection sensitivity by 110% compared to the resonator gas sensor with MXene deposited directly on the resonator surface. As a proof of concept, two sensor prototypes were implemented using resonators with layers of PI film and MXene and resonators with MXene only and were applied to detect a wide range of acetone gas concentrations. Immobilizing the layers of PI film and MXene on the microwave resonator achieved a linear correlation between the resonant frequency and acetone gas concentration with high sensitivity (17.85 kHz/ppm, a fast response time (60 s), and recovery time (85 s).

Flexible, anisotropic strain sensor based on interdigital capacitance for multi-direction discrimination

The direction information of strain plays a pivotal role in practical applications such as soft robots and human-machine interfaces. However, most of the multi-directional strain sensors studied before are integrated devices, which accomplish the strain direction discrimination through the signal difference of independent sensing units when they are stretched, thus increasing the complexity of the detection system. In this article, a multi-directional flexible strain sensor based on an interdigital capacitance structure is reported. The structure enables opposite variation of the capacitance changes in the orthogonal direction because the device exhibits different structural deformation depending on the direction of strain, thus detecting multiple direction strain by a single device. This sensor is fabricated by a one-step transfer method, which takes advantage of the excellent electrical conductivity of silver nanowires and the extremely low surface adhesion of the release film. The strain range of this sensor can be up to 60%. The influence of the structural parameters of the sensor on the gauge factor (GF) is explored to optimize capacitance structure parameters. The device shows good stability dynamic response (0.1–1.0 Hz). When the angle of strain direction changes from 0° to 90°, the GF changes from 1.1 to -0.56. Furthermore, owing to the high sensitivity and excellent stability of the sensor, human motion such as the bending direction of the wrist, can be accurately detected by this sensor.

Planar on-chip micro-supercapacitors based on reduced graphene oxide and carbon nanotube by liquid–air interface self-assembly and photolithography

Recently, the development of miniaturized electronic devices has accelerated the demand for the rate capability of planar on-chip micro-supercapacitors (POMSs). The POMSs based on reduced graphene oxide and carbon nanotube (rGO/CNT) composite electrodes (rGO/CNT-POMSs) were manufactured in the work and detailed electrochemical tests of devices were carried out over a wide range of scanning rates (0.01–10000 V s−1). The rGO/CNT composite electrode films without binder were prepared on silicon substrates by a modified liquid–air interface self-assembly method and a hydroiodic acid reduction method. The electrodes were fabricated into interdigital structure with 50 μm width of electrode and gap of electrode by photolithography. Interdigital POMSs based on different electrodes were prepared by gold sputtering on the electrode lugs. The area capacitance of the rGO/CNT-POMSs was 28.62 μF cm−2. They also had 0.004 μWh cm−2 of energy density and 1.068 μW cm−2 of power density. In addition, the charge–discharge time constant of the device was only 5.6 μs, and the charge–discharge rate was very quick. After 10,000 cycles of charge–discharge, the capacitance retention rate was still above 88%. At the ultra-high scan rate of 10000 V s−1, the devices still worked well. Compared with the POMSs based on reduced graphene oxide electrodes (rGO-POMSs) and the POMSs based on carbon nanotube electrodes (CNT-POMSs), the introduction of the CNT significantly increased the area capacitance, energy density and power density of rGO/CNT-POMSs, and significantly shortened the charge–discharge time constant. This indicated that the rGO/CNT composite electrodes had a good application prospect in the micro-chip accumulator devices.

High Performance Multiple Passband Substrate Integrated Plasmonic Filters

We proposed a new variety of substrate integrated plasmonic filters (SIPFs) with multiple passband characteristics based on the concept of spoof surface plasmon polaritons (SSPPs). By etching a periodic interdigital structure array on the top metal layer of substrate integrated waveguide (SIW), we can achieve high-efficiency microwave SSPP transmission with an insertion loss of 1 dB in the passband of 7.4-12.5 GHz, and a high rejection level of 27 dB in the rejection bands. By introducing antisymmetric C-ring resonators (ASCRs) in the filter structure, the passband number and bandwidth of the filter can be flexibly manipulated. To validate the proposed design, four SSPP filters prototypes are fabricated and tested, showing good filtering performances with a high transmission coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}21\mathbf {&gt;}-$ </tex-math></inline-formula> 1 dB) and low reflection coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}11\,\,\mathbf { &lt; } - $ </tex-math></inline-formula> 12 dB) in their passbands, and a high rejection level over 15 dB between them. By changing the geometric parameters of ASCR, the number of passbands can be increased from 1 to 3, and the passband center frequency and bandwidth can be engineered accordingly. The proposed SSPP filters with good multiple passband characteristics may have great potential applications in microwave wireless integrated plasmonic circuits and communication systems.

A Compact Sixth-Order Common-Mode Noise Suppression Filter Based on 3-D Integration Technology

Based on three-dimensional (3-D) integration technology, a compact sixth-order common-mode noise suppression filter is proposed according to delay line theory. As the important parts of the filter, the on-chip inductors are established by through-silicon vias (TSVs) and the capacitors are realized by double layer interdigital structure. Compared with other relative literatures, the proposed filter has a minimized size of 0.29×0.32 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (0.0203 × 0.0224 λg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). And it can suppress the common-mode noise more than 10 dB from 3.8 to 8.6 GHz or more than 20 dB from 4.45 to 7.85 GHz. Meanwhile, the differential signal insertion loss is kept less than 3dB.

Dispersion engineering of spoof plasmonic metamaterials via interdigital capacitance structures.

This work presents an approach to realize the dispersion engineering of spoof plasmonic metamaterials with controllable cutoff frequencies. Interdigital capacitance structures are applied to construct the unit cells. Dispersion properties are firstly analyzed to investigate the effects of interdigital capacitance, and the influence of the geometrical parameters of the proposed unit cell on the cutoff frequencies is studied. Then, a spoof surface plasmon polariton (SSPP) transmission line (TL) is developed based on the proposed unit cell together with a smooth transition. The matching principles of the transition are explained by the dispersion curves and the normalized impedance of the corresponding matching unit cells. Finally, the transmission characteristics of the TL are simulated and measured to validate the feasibility of the proposed strategy. Both the lower and upper cutoff frequencies can be tuned jointly by the extra degrees of freedom provided by the interdigital capacitance structures. In comparison with designs based on a substrate-integrated waveguide (SIW), the proposed strategy can reduce the transversal dimension by a factor of two under the same conditions. This work can greatly accelerate the development of versatile microwave integrated circuits and systems based on spoof plasmonic metamaterials.

Paper-based wearable ultra-sensitive strain sensors for fitness monitoring

Emerging technologies that exhibit features of biodegradability and eco-friendliness are potential game changers. Paper is a cost-effective and easily available material that has proved itself a promising candidate for manufacturing strain sensors due to its easy integration into flexible electronics. In this work, an ultra-sensitive and highly stable strain sensor is presented. Easily available materials are used for sensors development and very easy and simple fabrication. The modified interdigital capacitor structure is fabricated on a simple printing paper, whereas copper tape is used as an electrode material. In the anticipated work, the milestones of high sensitivity, durability, and fast response time are achieved. The proposed flexible strain sensor is eco-friendly, bio-degradable, inexpensive, and responds well to applied strain. The proposed work exhibits a fast response time of 0.56 s. The high gauge factor value of 3040.26 and stability up to 5000 cycles. The proposed prototype has been also implemented on the human body for monitoring physical activities and fitness exercises. The proposed strain sensor is an outstandingly good option for assimilation into wearable systems like remote healthcare systems, electromechanical sensing, and human physical monitoring.

Modeling of dielectric resonator antenna array for retina photoreceptors

The retina encompasses several cone and rod photoreceptors at fovea region i.e., 90 million cells of rod photoreceptors and 4.5million cells of cone photoreceptors. The overall photoreceptors determine the vision of every human. An electromagnetic dielectric resonator antenna has been presented for retina photoreceptors in order to model them at fovea and its peripheral retina with the respected angular spectrum. Three coloring primary system of human eye (R, G, B) can be realized based on the model. Three miscellaneous models i.e., simple, graphene coated, and interdigital models have been presented in this paper. The nonlinear property of interdigital structures is one of the best advantages to use for creating the capacitor. The capacitance property helps improving the upper band of visible spectrum. The absorption of light for graphene as an energy harvesting material and its conversion into electrochemical signals is making it one of the best models. The mentioned three electromagnetic models of human photoreceptors have been expressed as a receiver antenna. The proposed electromagnetic models based on dielectric resonator antenna (DRA) are being analyzed for cones and rods photoreceptors of retina in the human eye by Finite Integral Method (FIM) utilized by CST MWS. The results show that the models are so fine for vision spectrum due to its localized near field enhancement property. The results indicate fine parameters of S11 (return loss below -10 dB) with invaluable resonants in a wide range of frequencies from 405 THz to 790 THz (vision spectrum), appropriate S21 (insertion loss 3-dB bandwidth), very good field distribution of electric and magnetic fields for flowing the power and electrochemical signals. Finally, mfERG clinical and experimental results validate the numeric results by the normalized output to input ratio of these models and it points out that these models can stimulate the electrochemical signals in photoreceptor cells for the best suiting of realizing the new retinal implants.

Ultra-wideband hybrid polarization conversion-absorption metasurface with a transmission window and narrow transition bands

This paper proposes an ultra-wideband hybrid polarization conversion-absorption (PCA) metasurface with a transmission band for radar cross section (RCS) reduction application. To achieve the in-band transmission of the incident wave and the out-of-band suppression of the scattering wave, the proposed metasurface is composed of a low-frequency PCA array, a high-frequency polarization conversion (PC) array, and a second-order frequency selective surface (FSS). The lumped resistors are used in the PCA array to generate the absorption characteristic, thus giving rise to the reduction of the co-polarization component of the scattering field and meanwhile the elimination of the high-frequency resonances. An interdigital structure is introduced into the PCA array to not only achieve a good transmission for a co-polarization component of the incoming wave but also result in an extra PC band for narrowing the transition band between the transmission window and the high-frequency PCA band. The orthogonal layout of the PCA array and the PC array is used to decrease the interaction between them, thus resulting in an ultra-wideband PCA band. The second-order FSS consisting of a stacked structure is designed to generate a good passband with the steep roll-off and the good out-of-band suppression. The proposed metasurface has an ultra-wideband PCA band, a good transmission band, and narrow transition bands. When the proposed metasurface is arranged into an array in a rotation way, the ultra-wideband RCS reduction performance can be obtained. Simulated and measured results are given to demonstrate a 10 dB RCS reduction band of 3.4–24.6 GHz with a −1 dB transmission band of 8.45–10 GHz.

A High-Temperature Superconducting Bandpass Dual-Mode Filter with Tunable Relative Bandwidth and Center Frequency.

This study proposes a high-temperature superconducting (HTS) bandpass filter with a continuously tunable bandwidth and center frequency. The proposed filter combines several gallium arsenide varactors and a dual-mode resonator (DMR). The even and odd modes of the DMR can be tuned simultaneously using a single bias voltage. The capacitive value of varactors in the circuit is tuned continuously under continuous voltage and frequency tunability. External couplings and the interstage can be realized using an interdigital coupling structure; a fixed capacitor is added to the feeder to improve its coupling strength. A low-insertion loss within the band is obtained using HTS technology. Additionally, the proposed filter is etched on a 0.5 mm-thick MgO substrate and combined with YBCO thin films for demonstration. For the as-fabricated device, the tuning frequency range of 1.22~1.34 GHz was 9.4%; the 3-dB fractional bandwidth was 12.95~17.39%, and the insertion loss was 2.28~3.59 dB. The simulation and experimental measurement results were highly consistent.

Design and analysis of novel DGS-loaded low-pass filter with wide stopband

Abstract This article deals with design and development of a novel 7th order low-pass filter with defected ground structures for S-band applications. The proposed LPF structure was comprised of dumbbell shaped interdigital defected ground structures and open stubs as series inductor and shunt capacitor in the pass band. In addition, an equivalent circuit model was derived and optimized to achieve a 3-dB cut off frequency about 4 GHz with a reflection coefficient of better than −20 dB. Moreover, proposed low-pass filter was manufactured on a Rogers RO4003C substrate with a dielectric constant of 3.38, the dissipation factor of 0.0027. The developed LPF has a very flat pass-band with a transmission coefficient less than −0.5 dB and the measured transmission coefficient better than −18 dB in the passband (DC-3.6 GHz). Meanwhile, the prototype has a 20 dB harmonic suppression level in the frequency range from 5.54 GHz up to 43.5 GHz. Furthermore, the measured peak to peak group delay variation was less than 170 ps in the passband. The proposed filter has a very compact size of 195.3 mm2.

High-performance hybrid graphene-perovskite photodetector based on organic nano carbon source-induced graphene interdigital electrode film on quartz substrate

Hybrid graphene interdigital electrode-perovskite structure has demonstrated high value in the photodetector (PD) due to high absorbance and carrier collection efficiency. However, direct pattern of graphene film on the dielectric substance still faces huge challenges. Especially, the involvement of multi-step transfer and high-energy etching process hamper its development.In this context, we propose an organic nano carbon source (ONCS). Direct pattern of graphene film on the quartz substrate (GFqtz) is attained by the calcination of patterned ONCS film for the first time, which is simply achieved by screen printing technology thanks to the gel state. The transformation mechanism from ONCS to GFqtz has been proposed. In detail, the ONCS in-situ react with the quartz substrate to induce the SiC nanocrystals layer during the calcination. Then, the graphene film composes of the non-ordered graphene crystal layer and the aligned graphene crystals layer. Finally, the perovskite PD are successfully constructed by the GFqtz interdigital electrode. Compared to the PD fabricated by the Au interdigital electrode, the GFqtz-perovskite PD present an ultra-low detective light power density (0.5 μW/cm2) at 1 V bias voltage. The maximum responsivity and defectivity (0.1 A/W) and D* (2.6 × 1011 Jones) of the GFqtz-perovskite PD demonstrate an order of magnitude higher than the Au-perovskite PD's value.