Capacitive Patches Research Articles

A compact half‐mode substrate integrated waveguide bandpass filter based on highly confined slow waves with loading capacitive patches

A compact half‐mode substrate integrated waveguide bandpass filter based on highly confined slow waves with loading capacitive patches

A broadband second-order bandpass frequency selective surface for microwave and millimeter wave application.

This paper presents a frequency selective surface (FSS) with a wideband second-order bandpass response in the dual-band of microwave and millimeter wave. The overall structure consists of three layers of metal pattern and two layers of thin dielectric substrate. The top and bottom metal layers have capacitive patches with integrated curled Jerusalem cross slot resonators, while the intermediate metal layer has an inductive grid structure with cross-shaped slot resonators. The incorporated slot resonators play a pivotal role in achieving the desired transmission poles or zeros, which enable a wideband second-order filtering response in the dual-band and a quick roll-off at the passband edges, increasing the efficacy of electromagnetic shielding. To fully investigate the structure's frequency response, an equivalent circuit model of the structure is created, spanning the complete frequency range of 5-50 GHz. Physical samples are created and measured to confirm the suggested approach's efficacy. The passband center frequencies of the FSS are found at f1 = 19.42 GHz and f2 = 42.78 GHz, and the - 3dB bandwidth is 4.34 GHz (17.25-21.59 GHz) and 8.54 GHz (38.51-47.05 GHz), respectively. The simulation results align well with the experimental data. The transmission response rapidly transitions from the passband to the stopband at the passband boundaries.

Compact high directivity branch‐line hybrid using distributed realization of lumped elements

AbstractThis letter presents a compact high directivity branch‐line hybrid. The proposed hybrid is designed using a symmetrical ‐shaped structure, which incorporates a symmetrical ‐equivalent circuit. The ‐structure comprises one series low‐impedance line and two shunt high‐impedance stubs. The low‐impedance line is realized using a ‐equivalent circuit consisting of two spiral inductors and one patch capacitor. A detailed analytical design procedure is developed. A prototype hybrid is fabricated on FR‐4 substrate and the measured ‐parameters are in close agreement with the simulated results. The proposed hybrid has a compact size with 54% area reduction compared to a conventional branch‐line hybrid. In addition, the hybrid achieves 43 dB directivity at its center frequency of 0.9 GHz.

Microwave Rotation Sensor Based on Reflection Phase in Transmission Lines Terminated With Lumped Resonators

A phase variation-based rotation sensor is presented in this article. The sensor is realized using a coplanar waveguide (CPW) terminated with a stepped impedance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit {LC}$ </tex-math></inline-formula> resonator. A circular dielectric slab is rotating above the resonator. Rotation of the slab modifies the overall capacitance and, thus, the input impedance of the resonator. This, in turn, modifies the phase of the reflection coefficient, which is translated to the rotation angle. The sensor’s linearity is eventually enhanced by tapering the width of the capacitive metallic patch along the rotation direction. The operation and sensing performance are studied in detail, using a circuit-based analysis and electromagnetic (EM) simulations. The designed sensor is capable of detecting the direction of rotation. A sensor prototype is fabricated and experimentally measured to prove the developed design and analysis procedure.

Thickness dependence of microwave dielectric tunability in Ba0·5Sr0·5TiO3 thin films deposited by pulsed laser deposition

In this study, the Ba 0·5 Sr 0·5 TiO 3 (BST) thin films with different thicknesses are fabricated on fused silica quartz substrate by using the pulsed laser deposition (PLD) technique. The deposition was done using a laser fluence of ∼2 J/cm 2 and the number of pulses was varied from 2500 to 20,000 to change the thickness of the thin films. X-ray diffraction (XRD) patterns and Raman spectrum were used for the phase confirmation. The FESEM technique was used to observe the microstructure of BST thin films and the average grain size was found to be 208, 255, 267, 300, and 393 nm for the BST thin films with thicknesses of 150, 300, 450, 600 and 1000 nm. The optical bandgap ( E g ) of all films was ∼3.54 eV. Dielectric properties of the BST thin films were measured not only in the low-frequency region (1 kHz-1 MHz) but also in the microwave frequency region (0.5 GHz-4 MHz). The microwave dielectric properties of the BST thin films were also measured as a function of voltage using the circular patch capacitor (CPC). The highest microwave tunability was found to be ∼55.5% for the BST thin film with a thickness of 300 nm. It was found that too small a film thickness where the polarizable dipoles are constrained by proximity to an amorphous substrate and thick films where the grains approach the size of that in bulk are not suitable for yielding high dielectric tunability.

A thin metallo-dielectric stacked metamaterial as “add-on” for magnetic field enhancement in clinical MRI

Magnetic resonance imaging (MRI) is a widely used clinical diagnostic tool, which is based on the principle of nuclear magnetic resonance of hydrogen atoms in human body. The Larmor frequency of precession of the hydrogen atoms is determined by the strength of static magnetic field ( B0) of MRI. A higher B0 can directly improve signal-to-noise ratio (SNR) of MRI. However, this method involves expensive hardware installation, which could have adverse effects of tissue-heating and make MRI unsafe for patients with medical implants. Hence, efforts have been made to increase the SNR of MRI without increasing B0. An effective solution in this direction would be to boost the radiofrequency (RF) magnetic fields emitted by the body part undergoing scan, particularly by using metamaterials. The higher the received RF signal strength, the greater the SNR of MRI. For a metamaterial to be used as an “add-on” in commercial scanners, its dimensions need to be designed appropriately so that it fits in the available gap between the transceiver coil and the human body. In this article, a 10-mm-thick metallo-dielectric metamaterial is designed by a stacking of alternate square-shaped capacitive patches and inductive apertures for enhancing the RF magnetic flux density and hence, the SNR of a 1.5 T MRI system. The inter-layer electromagnetic coupling in the stacked structure is deployed for spatial localization of magnetic fields at the resonant frequency (∼64 MHz) which is equal to the Larmor frequency of 1.5 T MRI. An equivalent circuit model, comprising a lumped-element third order bandpass filter, validated the transmissivity characteristics of the metamaterial obtained using full-wave simulations. Magnetic flux density enhancement by a factor of 55 is obtained when the metamaterial add-on is placed between a surface coil and a bio-model of human head.

Bioinspired construction of magnetic nano stirring rods with radially aligned dual mesopores and intrinsic rapid adsorption of palladium

Quick and precise recovery of palladium (Pd) from electronic waste remains a serious task, owing to the strong acid and complexity of chemical compounds in leachate. Here, bioinspired construction of magnetic nano stirring rod with radially aligned dual mesopores and abundant 8-aminoquinoline (MNSR-DM-AQ) is proposed for selective and rapid extraction of Pd(II) from highly acidic sample solutions. Benefit from the unique dual mesoporous (12.4 nm and 3.6 nm) and the stirring motion under an external magnetic field, MNSR-DM-AQ possesses enhanced adsorption capacity and kinetics, achieving 11.62 mg g−1 (97.2 % of the maximum adsorption capacity) in 15 min. Distribution coefficient (KD = 299.0 mL g−1), separation factor (α above 25.54) and concentration factor (CF = 230.2 mL g−1) reveal the excellent selectivity of MNSR-DM-AQ towards Pd(II) when comparing with the coexisting ions (Ca(II), Co(II), Cu(II), Fe(II), Mg(II), Ni(II), Pb(II), Zn(II)). The adsorption mechanisms of MNSR-DM-AQ are ion exchange and chelation due to a strong affinity between Pd(II) and N. Meanwhile, 96.82 % of the captured Pd(II) can be easily eluted within 15 min, and the adsorption capacity remains stable after five adsorption-desorption cycles. It is worthwhile to mention that MNSR-DM-AQ exhibits a high adsorption capacity of 8.39 mg g−1 from leachate of abandoned high-voltage patch capacitor, which is greatly desired in Pd(II) extraction from electronic waste.

Embroidered Textile Frequency-Splitting Sensor Based on Stepped-Impedance Resonators

This paper presents an embroidered textile frequency-splitting microwave sensor based on a pair of identical stepped-impedance resonators (SIRs) loading a microstrip transmission line. The sensor is implemented by means of conductive threads. The sensing region of the proposed structure is the capacitive square patch of one of the SIRs. If such region is kept unaltered, the structure is symmetric, and the frequency response (transmission coefficient) exhibits a single transmission zero. However, if symmetry is broken (e.g., through liquid absorption in the sensing region), the frequency response of the proposed sensor exhibits two transmission zeros (frequency splitting). The difference (in frequency and magnitude) between such zeros (or notches) is intimately related to the dielectric properties of the absorbed liquids to be sensed <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> detected. The proposed sensing structure is applied to the detection of deionized (DI) water absorption, and to the quantification of the number of DI water drops. The maximum measured sensitivity is found to be 2.70 MHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$/ \mu \text{l}$ </tex-math></inline-formula> and 0.03 dB <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$/ \mu \text{l}$ </tex-math></inline-formula> for the incremental frequency and incremental magnitude of the notches.

Microwave Resonance-Based Reflective Mode Displacement Sensor With Wide Dynamic Range

A wide dynamic range reflective mode displacement sensor is designed in this article based on the resonance frequency shift. The linearity of the sensor is enhanced using a tapered metallic patch that forms the capacitance of the sensor, leading to a better dynamic range. The sensor is designed using a coplanar waveguide (CPW) terminated with a series <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$RLC$ </tex-math></inline-formula> resonator with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R=50\,\,\Omega $ </tex-math></inline-formula> . A movable dielectric slab is placed above the capacitive patch of the resonator, where displacing the dielectric slab modifies the overall capacitance of the resonator causing a shift in the resonance frequency. The sensing principle is analyzed in detail, using an accurate circuit model and full-wave electromagnetic simulations. The proposed sensing method is capable of detecting the displacement direction. Furthermore, the sensing concept can be extended to a 2-D displacement sensor as well. The sensing approach and the design concept are verified through the fabrication and measurement of a sensor prototype.

Harmonic-Absorption Frequency Selective Rasorber Based on Non-Resonant FSS and Resistive-Sheet

In this article, we proposed a harmonic-absorbed frequency selective rasorber (HA-FSR). It consists of a non-resonant frequency selective surface (FSS) with inductive square loops, capacitive patches, and resistive sheet-based absorbers. The non-resonant FSS is of harmonic-suppression (HS) feature, which is free of spurious harmonic transmission bands up to three octaves of the main passband. We introduced resistive sheets on both sides of the HS-FSS to perform wideband absorption. Full-wave simulated and measured results both show that the proposed HA-FSR owns main passband with -3-dB bandwidth of 3 GHz at the X-band and -10-dB absorption band from 20 to 30 GHz. The frequency range of harmonic-absorption covers from around two to three octaves of the passband. The proposed HA-FSR can be applied in electromagnetic (EM) shielding and low-observable platforms.

Design investigation of mantle-cloak for a PEC cylindrical object under oblique incidence of TM and TE waves

In this paper, the possibility of cloaking a metallic cylinder is investigated for a wide range of angles of obliquely incidence TE and TM wave using the well-known mantle cloaking technique. Initially, the scattered field is formulated analytically using the circumferential waves in cylindrical coordinates. A full tensor is utilized for modeling the sheet impedance of an ideal metasurface wrapped around the cylinder to be cloaked. Then, a capacitive rectangular patch metasurface is designed and its parameters are optimized to suppress both the co- and cross-polarized components of the scattered fields. The analytical results are verified with those obtained using the full wave simulation investigation performed by CST Microwave Studio, and a very good agreement is observed between the obtained results.

In‐band radar cross‐section reduction of the slot array antennas by RAM‐based frequency selective surfaces

A method for reducing radar cross-section (RCS) of the slot array antenna by utilising the radar absorbing material, while preserving the radiation performance simultaneously, is proposed and discussed. The scheme is based on the implementation of the multilayer frequency selective surface-radar-absorbing material (RAM) capable of operation over a wide frequency band. The use of radar absorbing material on an antenna’s radiation screen causes a change in surface current, resulting in the radiation pattern of the antenna. Therefore, by designing the coating pattern of the radar absorbent material as a substrate and a capacitive patch as a unit cell on the antenna board, the reduction of 19 dB RCS at X-band and minimum antenna gain loss (3dB) is achieved. To demonstrate the proposed solution, a 30-cm diameter slot array antenna, which is considered as a test case, is coated by RAM and radar cross section reduction (RCSR) is dramatically accomplished over a frequency band ranging from 8 to 12 GHz. It is worth mentioning that the obtained RCSR at 9.4 GHz is as much as 19 dB. Subsequently, the proposed method can be a candidate for reduction of RCS in slot array antennas, considering the remarkable RCSR and acceptable effect on radiation characteristics.

A Systematic Study of Wearable Multi-Modal Capacitive Textile Patches

We present a study on wearable capacitive patches with engineered dielectrics to be used as a strain sensor and a piezoelectric sensor with multi-modal sensing capabilities. The patches consist of a parallel plate capacitive structure with highly (100%) stretchable textile electrodes and silicone or PDMS elastomers. The gauge factor of the capacitive strain sensor is enhanced two-fold with the inclusion of high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> Barium Titanate (BTO) nanoparticles dispersed in the silicone dielectric layer without sacrificing their excellent linearity or superb durability easily exceeding 2000 cycles. In addition to enhanced dielectric response, inclusion of BTO as well as other additives, namely PZT and PVDF-TrFE, in PDMS also induces piezoelectricity in the sensors at different weight ratios systematically studied by bending and vibrational tests. Corona poling of the piezo dielectrics improves their voltage output by at least two folds. Besides the piezoelectricity, tests on unpoled samples also uncovered evidence for triboelectricity in the nanocomposites. The proposed textile patches can simultaneously detect multiple stimuli such as strain, pressure, temperature, bending, vibration, and acoustic feedback. Deployed in appropriate locations and geometries, the patches can capture critical information on the type, strength, and duration between episodic movements and environmental factors, as demonstrated via a shoe-insert, elbow tracker, respiratory and heart-rate monitors. Accordingly, capacitive textile patches offer unique capabilities for multi-modal sensing in biomedical and robotic applications as well as overall system integration that are advantageous for sensor fusion and machine learning.

Tunable Microwave Device Fabrication on Low‐Temperature Crystallized Ba0.5Sr0.5TiO3 Thin Films by an Alternating Deposition and Laser Annealing Process

AbstractThis article demonstrates a method to fabricate crystalline Ba0.5Sr0.5TiO3 (BST) thin films at a lower temperature of ≈300 °C using an excimer laser by an alternating depositing and annealing process. Firstly, a BST thin film with a thickness of ≈120 nm is deposited at 300 °C (laser energy of ≈2 J cm−2) and subsequently laser annealed (66 mJ cm−2) at 300 °C. This process is repeated five times to obtain thicker device quality films. XRD patterns, TEM, Raman, and UV–Vis–NIR spectroscopy confirm that phase formation of BST thin films has taken place. The band edge value for BST thin films is observed to decrease systematically from 4.65 eV (amorphous, 300 °C) to 3.56 eV (5‐layers, crystalline, 300 °C). A varactor device with a Circular Patch Capacitor (CPC) structure is patterned on the five‐stage laser annealed BST thin films processed at 300 °C, which shows a microwave tunability of 34% at 1 GHz compared to conventionally deposited BST films (prepared at 700 °C). This study provides a way for fabricating ferroelectric thin film based tunable devices at low temperatures, making the process compatible with low melting substrates in flexible electronics and other situations where there is a temperature constraint.

A compact dual‐band superconducting filter with fine‐tuning coupling structure

A novel dual-mode optimized patch capacitor loaded T-type resonator is proposed for the design of a dual-band filter (DBF). The resonator has its lowest even- and odd-mode at the two expected passband frequencies and the first spurious mode far away from the passbands. For tuning of the two sets of coupling strengths for both passbands, open/shorted secondary coupling structures are introduced as a fine-tuning coupling structure to increase/decrease the primary coupling strength. A four-pole DBF with passbands centered at 2450 and 3500 MHz, respectively, is proposed and fabricated using the HTS material. The measured results of the filter indicate superior performance and good fitting with the simulation results. The return losses of both passbands and the insertion losses obtained by measurements are greater than 14 dB and less than 0.3 dB, respectively. The stopband rejection exceeds 50 dB up to 8.0 GHz.

Improved Sidelobe-Suppression Microstrip Patch Antenna Array by Uniform Feeding Networks

This article presents a design of a single-polarization, $4\times 4$ microstrip patch antenna array, operating at the $K_{a}$ -band. An integrated microstrip network with the aid of using feeding probes excites the antenna array. Simulation and measurement results show that the array operates in a wideband frequency range (return loss RL ≥ 15 dB) from 32 to 36.4 GHz with a low sidelobe level (SLL ≤ −15 dB). To obtain a wide bandwidth, each antenna is fed with a capacitive patch and enclosed by an integrated metallic cavity. Here, we show that an antenna array with an SLL could be achieved by mirroring and feeding the radiating elements with equal excitation. The design is also applicable to a dual-polarized antenna, as it does not only lower the sidelobe level but also improve the cross-polarization without increasing the circuit complexity. An antenna prototype has been realized with an experimental bandwidth better than 3 GHz and a sidelobe level of −15.6 dB. These excellent measured results prove that this method with a simple design approach is feasible for an antenna array with high suppression of sidelobe and cross-polarization.

Design of frequency selective rasorber with wide transmission/absorption bands

This paper presents a high-frequency transmissive frequency selective rasorber (FSR) with wideband transmission/ absorption properties. It is synthesized by placing a resistive sheet on top of a bandpass frequency selective surface (FSS) separated by an air spacer. The unit cell of resistive sheet comprises the resistor-loaded central tortuous Jerusalem cross. Its central tortuous cross, acting as a parallel LC resonator with a high inductance and a low capacitance, is utilized to realize a wide pass-band with low insertion loss by cutting off resistive sheet’s lossy path over a wide frequency band. The bandpass FSS adopts a triple-layer coupled structure, in which two layers of identical capacitive metallic patches are coupled through an intermediate inductive wire grid. A second-order pass-band with high selectivity is realized by this bandpass FSS. Simulation results show that the fractional bandwidth of the 1 dB transmission band and the 10 dB absorption band is 19.6% and 107.9%, respectively. Meanwhile, since its periodicity is only 8 mm, the proposed FSR also shows good angular and polarization stabilities. A good agreement between the measured and simulated results validates the proposed FSR design.

Auto-Resonant Tuning for Capacitive Power and Data Telemetry Using Flexible Patches

This brief proposes and demonstrates a reliable power and data transfer scheme for biomedical implants through a resonant capacitive link. Flexible, conformable, and biocompatible patches are adopted with an automatic resonant frequency calibration technique for the first time. A voltage feedback network, a Class- ${D}$ driver, and a custom algorithm have been developed for the low overhead calibration. An ex vivo chicken skin tissue-based experiment with 4 cm2 flexible, conformal capacitive patches demonstrated the method. Experimental results show that the power delivered to the load (PDL) of the link extends up to 150 mW and maximum power transfer efficiency (PTE) of the link is 54%. A simultaneous data transfer with a rate of up to 170 kbps alongside power transfer using 1.5 to 2 mm-thick biological skin tissue has been achieved.

Polarization-Insensitive Metasurface Lens for Efficient Generation of Convergent OAM Beams

A novel metasurface lens made of polarization-insensitive hexagonal units with honeycomb lattice is provided for generating orbital angular momentum beams. The unit is composed of multilayer capacitive hexagonal patches coupled through middle-layer inductive snowflake wire grids for a stable bandpass response. Due to the isotropy of the hexagonal unit and the honeycomb lattice of the cell arrangement, the proposed metasurfaces are polarization-insensitive, providing stable responses under different angles and polarizations of the incident electromagnetic wave.

A TM30-/TM40-Mode Pattern-Reconfigurable Microstrip Patch Antenna for Wide Beam Coverage

A novel two-state multi-lobe pattern-reconfigurable microstrip patch antenna (MPA) for wide beam coverage is proposed, where two states are realized by two higher modes, and a multi-lobe pattern is employed for each state. First, the equivalent transmission line model is used to analyze the input impedances of the dual-mode MPA. By adjusting sizes of the capacitive coupling patches and profile of the MPA, the frequency bands of TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> modes are controlled, yielding a band intersection. Second, by controlling the length of the radiating patch, the beam-level differences of TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> -mode and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> -mode patterns are reduced, respectively. Third, two parasitic patches are also loaded. As a result, the mode-gain difference between TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> modes is small, and all the beam overlap levels are higher than -3 dB. The measured results show that the 3 dB beam coverage of the MPA at 2.9 GHz ranges from -68° to +73° in the xoz plane, and its maximum gain is 7.0 dBi. Furthermore, the two-state pattern-reconfigurable MPA has a 3-lobe pattern pointing at {0°, ±37°} for the first state and a four-lobe pattern pointing at {±17°, ±58°} for the second state. The measured results are in good agreement with the simulated ones.