Antenna Electrode Research Articles

Complex Reflectivity Modulation Characteristics at Visible Wavelength Using Liquid Crystal on a Metasurface Device

Active metasurface device capable of complex modulation in the visible light range is demonstrated. To realize complex modulation, a liquid crystal (LC) of twisted nematic mode on a plasmonic antenna metasurface, where resonance wavelength is sensitive to its geometry and nearby optical environment, is integrated. For the LC process on the metasurface, the alignment characteristics of the material exposed to the LC on the metasurface are first identified and the polyimide alignment layer is omitted. The LC works in twisted nematic mode to enhance complex modulation characteristics. The complex reflectivity coefficient is measured while varying the voltage applied to both the antenna and metal electrode in the visible light region. Complex reflectivity into a doughnut shape with a small voltage variation of 3.1 V on the antenna electrode and 2.5 V on the metal electrode is successfully modulated. The largest complex modulation is achieved at a wavelength of 660 nm, with phase and reflectivity amplitude modulations of 0–2π radian in a doughnut shape and 0.3 and 0.6, respectively. So far true holographic experience is limited by high‐order overlapping and twin images. Through this approach, a technical method is suggested for overcoming such obstacles and accomplishing advanced holographic display.

Integrated Optical Waveguide Electric Field Sensors Based on Bismuth Germanate.

Bismuth germanate (Bi4Ge3O12, BGO) is a widely used optical sensing material with a high electro-optic coefficient, ideal for optical electric field sensors. Achieving high precision in electric field sensing requires fabricating optical waveguides on BGO. Traditional waveguide writing methods face challenges with this material. This study explores using femtosecond laser writing technology for preparing waveguides on BGO, leveraging ultrafast optical fields for superior material modification. Our experimental analysis shows that a cladding-type waveguide, written with a femtosecond laser at 200 kHz repetition frequency and 10.15 mW average power (pulse energy of 50.8 nJ), exhibits excellent light-guiding characteristics. Simulations of near-field optical intensity distribution and refractive index variations using the refractive index reconstruction method demonstrate that the refractive index modulation ensures single-mode transmission and effectively confines light to the core layer. In situ refractive index characterization confirms the feasibility of fabricating a waveguide with a refractive index reduction on BGO. The resulting waveguide has a loss per unit length of approximately 1.2 dB/cm, marking a successful fabrication. Additionally, we design an antenna electrode, analyze sensor performance indicators, and integrate a preparation process plan for the antenna electrode. This achievement establishes a solid experimental foundation for future studies on BGO crystal waveguides in electric field measurement applications.

Free-standing carbon nanotube film for high efficiency monopole antenna

A flexible radio-frequency (RF) antenna allows wearable smart devices to have various functionalities. To develop a high-performance RF antenna, an outstanding radiation efficiency should be achieved. Metallic films are commonly utilized in RF antenna electrodes owing to their high electrical conductivity, which is related to the radiation efficiency. However, their high density and low mechanical stability under deformed states, such as the folding of metallic films, hinder their use as flexible RF antenna electrodes. In this study, we fabricated a carbon-nanotube (CNT) film via the direct-spinning method for use in a flexible RF antenna electrode. The network structure of the CNT film endows it with a high electrical conductivity and allows it to be freestanding without a polymeric binder. The freestanding CNT film-based RF antenna attained a high radiation efficiency of 85.6%, commercially useable level, and its performance remained stable even under mechanical deformation, such as bending and folding. This high performance is attributed to the network structure of the CNT film composed of pure CNT bundles.

Array Integration and Far-Field Detection of Biocompatible Wireless LC Pressure Sensors.

In this paper, three configurations of LC (inductor-capacitor) pressure sensors are developed, namely series LC pressure sensors, compact LC pressure sensors, and far-field LC pressure sensor tags. The modified silk protein films have been chosen as substrates due to their good biocompatibility and air/water permeability, which is suitable for continuously pasting such substrates on skin. For series LC pressure sensors, conducting wire is used to connect the flexible capacitor and spiral inductor. It exhibits good cycling stability and high sensitivities, suitable for electronic skin. For compact LC pressure sensors, the spiral coil functions as inductor, antenna, and capacitor electrode simultaneously, minimizing the space cost and is suitable for array integration, while the sensitivities remain the same. By tailoring the turn of the spiral coil, the resonate frequency can be regulated continuously. An annular array of compact LC sensors with ten distinct resonate frequencies ranged from 400 to 1000MHz is developed to remotely monitor the press of number 0-9. Finally, far-field LC pressure sensor tags with elongated detection distances are developed in which each compact LC sensor acts as a filter. A wireless in-shoe plantar to detect the sole pressure distribution using the far-field LC sensor configuration is developed.

Full wave numerical analysis of wideband and high directive log spiralTHzphotoconductive antenna

AbstractThis study presents, for the first time, a novel design of ultra‐wideband (UWB), circularly polarized and highly directive log‐spiral THz photoconductive antenna. The proposed antenna is simulated in High Frequency Structure Simulator using gold as the antenna electrode material which is backed by a quartz substrate (εr= 3.78, tan δ = 0.0001) and hemispherical silicon‐based lens with a diameter of 140 μm. A comprehensive detailed parametric study of the antenna design parameters is performed in the frequency range of 1 to 6 THz for the optimal design of the developed antenna structure. The optimal antenna structure with integrated lens has UWB characteristics with −10 dB impedance bandwidth of 5 THz and 3 dB axial ratio bandwidth of around 4 THz. The observed directivity and half‐power beam width of the presented design varies in the range 5 to 12 dBi and 34° to 62°, respectively, for the frequency range of 1 to 4 THz. The wideband, high directivity as well as high‐efficiency (>50%) characteristics of the proposed design make it a favorable choice for the THz sensing and imaging applications.

Ecofriendly Catechol Lipid Bioresin for Low-Temperature Processed Electrode Patterns with Strong Durability.

We demonstrated catechol lipid-based bioresin, which is collected from lacquer trees, to produce conductive pastes that can be processed at low temperatures, which are highly adhesive and multidurable. Our conductive paste, which consists of catechol lipid-based urushiol resin and a multimodal mixture of silver fillers, exhibited stable dispersion with shear thinning properties. The urushiol lacquer induced spontaneous reduction of silver salt at the surface of the silver fillers, thereby contributing to lower the contact resistance between conductive fillers in the electrical conduction. Furthermore, the directional volume shrinkage of the urushiol lacquer matrix in a cross-linking reaction resulted in a highly ordered microstructure of the silver fillers with layer-by-layer stacking of the silver flakes. This structure contributed to the improvement of the electrical contact between fillers as well as excellent mechanical hardness, anti-scratch capability, and the long-term environmental stability of the conductive films. Conductive films based on the silver paste with urushiol lacquer exhibited low electrical resistivity below 4.4 × 10-5 Ω cm, 5B-class strong adhesion strength, and high hardness exceeding 200 MPa. Finally, we demonstrated the facile room-temperature processability and screen printability of the UL-Ag paste by fabricating a printed antenna and three-dimensional (3D) electrode assembly based on a plastic 3D block.

An Experimental Study on LT-GaAs Photoconductive Antenna Breakdown Mechanism

In this paper, an experimental study on the low-temperature-grown gallium arsenide (LT-GaAs) photoconductive antenna (PCA) breakdown mechanism is presented. A terahertz (THz) PCA is an important device for the THz wave generation. Due to that the typical LT-GaAs PCA breakdown scenarios, different trigger positions and different bias voltages, have been studied. Breakdown mechanism analysis has shown that when the trigger position was on the antenna electrode edge, the PCA breakdown was more probable to happen, because the electrode edge electric field was nearly 3 times greater than the electric field of the electrode center. Moreover, it has been shown that the thermal effect was the main cause of the LT-GaAs PCA breakdown. Last, the PCA lifetime has been calculated using the current waveform and the thermal effect analysis.

Study of Terahertz Antenna by Surface Wave Theory

In this paper, current pulse that propagates in Terahertz antenna was simulated as a propagated surface wave. The surface wave modes which propagate in electrode were studied. It was found that the current pulse propagates as a bulk electromagnetic wave in the antenna gap and that the current pulse propagates as a surface wave in the electrodes. Phase velocity and loss of each mode were investigated. The relation between thickness of the antenna electrode and optical properties of the substrate, such as absorption and refraction index, with surface wave characteristics was studied. After solving surface wave equation for the three-layer structure, dielectric-metal-dielectric, it was found that two surface wave modes, slow mode and fast mode are allowed to propagate in the electrode layer and that surface wave cannot propagate in the antenna gap region.

Effect of a DC external electric field on the properties of a nonuniform microwave discharge in hydrogen at reduced pressures

The effect of a dc external electrical field on the properties of a highly nonuniform electrode microwave discharge in hydrogen at a pressure of 1 Torr was studied using optical emission spectroscopy and selfconsistent two-dimensional simulations. It is shown that the negative voltage applied to the antenna electrode with respect to the grounded chamber increases the discharge radiation intensity, while the positive voltage does not affect the discharge properties. The simulation results agree well with the experimental data.

Wireless Tear Glucose Sensor

This paper presents a novel wireless tear glucose level sensor for diabetes patients. The miniaturized sensor can be worn non- invasively under the eye lid. It is composed of a chronoamperometric glucose sensor and an ASIC set with integrated potentiostat and transponder circuits. Wireless energy and data transmission according to the passive transponder standard ISO18000-3 is used to power and readout the sensor. A special coil shape enables high comfort for the patient. High integration level is achieved by a combination of antenna and sensor electrode wires. A complete demonstrator system including ASIC and sensor fabrication as well as assembly was manufactured and the function is demonstrated.

Piezoelectric components wirelessly driven by dipole antenna-like electric field generator

Abstract A new technique of transmitting electric energy wirelessly to piezoelectric components by using a dipole antenna-like electric field generator is explored. Two square size brass plate-shaped live and ground electrodes are used to form a dipole antenna-like electric field generator. When the dipole antenna-like electric field generator in electric resonance with an inductor, a maximum output power of 2.72 mW and an energy conversion efficiency of 0.0174% have been achieved wirelessly by the piezoelectric plate area of 40 mm 2 operating in the thickness vibration mode, placed at the center 4 mm away from the antenna plane with an optimum electrical load of 1365 Ω, resonant frequency of 782 kHz, 1 cm electrodes separation, 2500 cm 2 electrode area of dipole antenna-like structure, and input ac source power of 15.58 W applied to the series of dipole antenna-like structure and inductor. The theoretically calculated results have been validated by the experimental studies. It is seen that at the resonance frequency and optimum electrical load, the output power of the wirelessly driven piezoelectric component decreases with the size of piezoelectric component, distance of piezoelectric component from the electrode of antenna plane, but increases with the antenna electrode area.

Measurement of Terahertz Optical-Beat Frequency Using High-Order Harmonics of Microwave in a Photoconductive Device

A method for measuring frequencies of the terahertz (THz) radiation emitted by the antenna mounted on the photoconductive (PC) device is presented. Two laser beams with slightly different frequencies irradiate the PC device, producing a beat current of 1 THz in the photocurrent. A microwave signal is applied to the antenna electrode. The frequency of the THz wave is measured using the homodyne detection of the optical beat with the high-order harmonics of the microwave. It is being investigated that the high-order harmonics are produced by the PC device owing to its nonlinearity. Periodic peaks generated by the homodyne detection were observed in the photocurrent, as the microwave was swept from 16 to 20 GHz with a power of −40 dBm. Using the peak frequencies, the THz-wave frequency was determined to be GHz. The measurement error is estimated to be less than 0.43 GHz. The proposed method realizes a compact frequency meter in the THz region.

Characterization of in‐liquid plasma in a continuous liquid flow

In‐liquid plasma is a useful invention because its chemical reaction rate is several thousand times higher than those of conventional plasma techniques. However, in‐liquid plasma is not so familiar now because its fundamental characteristics remain unclear. We investigated characteristics of in‐liquid plasma in a continuous liquid flow to facilitate its application as a chemical decomposition or synthesis device. N‐dodecane is supplied by the pump and a stable liquid flow is set in the rectangular vessel. Because the flow velocity is insufficient, a nozzle is set 2 mm distant from the microwave electrode tip. The average flow velocity of n‐dodecane at the nozzle top is 0–19 m/s and the Reynolds number is as high as 1.2×104. A 2.45‐GHz microwave is introduced by a monopole antenna electrode inserted into a rectangular cavity resonator. In‐liquid plasma is generated and observed in the flowing cavitation bubbles generated from the ultrasonic horn tip. The vessel’s inner pressure is adjusted to 65–450 hPa. The temperature in the plasma reached 3600±300 K; it was almost independent of the flow velocity because the physical properties of the plasma are influenced only slightly by the acoustic cavitation stream.

H− ion beam extraction from a transformer coupled plasma source with triode extraction system

A continuous-mode H− ion source has been developed in SNU by using rf transformer coupled plasma source for long lifetime. Recently, its plasma confinement has been improved by modifying the main cusp magnet system that covers rf antenna and plasma electrode regions. The extraction system has also been upgraded to triode extraction system, where permanent magnets in dipole configuration are embedded in extraction electrode to provide additional magnetic field for filtering out fast electrons. Electrode shape, extraction hole size, and gap distance are optimized for high beam currents with low emittance by using PBGUNS code. With new configuration, H− beam currents of up to 1.67mA with 1.7kW, 13.56MHz rf power are extracted in a continuous mode. Low e∕H− ratios down to 8 are achieved by increasing total filtering field strength up to 190G.

Hollow cathode and hybrid plasma processing

Generation and features of the radio frequency (rf) hollow cathode discharge (HCD) and its transition into the hollow cathode arc (HCA) are described. Rf linear hollow cathodes for generation of plasma over large areas and suitable for further scale-up are presented. Examples of surface processing and coating by PVD, both by HCD and HCA, are given. The hybrid reactor, combining hollow cathode and microwave plasmas, integrates features of both and provides more options to control plasma characteristics and consequently properties of deposited films. The rf hollow cathodes can be operated in both, PVD and PE CVD regimes, depending on process parameters. These regimes can even be combined within one process. New concepts of fused hollow cathode (FHC), microwave antenna (MWA) and Hybrid hollow electrode activated discharge (H-HEAD) cold atmospheric plasma sources are introduced. The FHC with its modular concept can be used for gas conversion, cleaning and for surface treatment of temperature-sensitive materials at ambient atmosphere. The H-HEAD cold atmospheric plasma source, capable of generating plasma plumes more than 15 cm long, enables treatment of 3-d and complex geometry objects even at low gas flows.

Resonance Frequency Characteristics of Electric Field Sensor with Segmented Electrodes

An integrated electrooptical E-field sensor using a proton exchanged LiNbO 3 Mach-Zehnder (M-Z) interferometer with a combined antenna and modulation electrode structure is designed and fabricated. The experimental results show that the minimum detectable voltage is 2.5 mV at 900 MHz and 6 mA bias current of the laser diode. By comparing the measured frequencies with theoretical resonance ones over 1 MHz, it is found that the sensitivity variation is almost due to the resonance caused by the piezoelectric effect of the optical crystal substrate in the width direction.

An integrated electro‐optic E‐field sensor with segmented electrodes

AbstractAn integrated electro‐optical E‐field sensor using a proton‐exchanged LiNbO3 Mach–Zehnder (M–Z) interferometer with a combined antenna and modulator electrode structure is designed and fabricated to improve the sensitivity and bandwidth of the device. The experimental results show that the minimum detectable voltage is 0.22 mV at 900 MHz and the laser diode has a 5.6‐mA bias current. Variation of the sensitivity with the frequency is analyzed using the method of moments (MoM), and the calculated results basically agree with the measured results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 302–305, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11361

Observation of Terahertz Photon-Assisted Tunneling in Triple-Barrier Resonant Tunneling Diodes Integrated with Patch Antenna

Terahertz (THz) photon-assisted tunneling was observed in GaInAs/InAlAs triple-barrier resonant tunneling diodes (RTDs) integrated with patch antennas on InP substrates. The conduction loss of the antenna was reduced by a structure that consists of an Au-coated ground plane, an Au antenna electrode and a thick benzo-cyclo-butane layer as a dielectric between them. Large THz voltages were induced across the RTD with this structure by THz irradiation (frequency f=1.4–3.1 THz), e. g. , 122 mV at an incident power of 76 mW at f=1.4 THz. Current changes due to photon-assisted tunneling with photon absorption and emission were determined. The peak voltage of the current change shifts due to the multiphoton process with increasing incident power. The multiphoton process was remarkable at low irradiation frequency. These measurements were in reasonable agreement with theory.

Pulsed currents carried by whistlers. VII. Helicity and transport in heat pulses

In a uniform magnetoplasma (n≂1011 cm−3, kTe≥0.5 eV, B0≥15 G, 1 m × 2.5 m), electrons are heated locally and temporally by applying a short current pulse to a loop antenna or disk electrode. Electron magnetohydrodynamics characterize the experimental conditions. After the end of the applied current pulse and whistler wave transients, a current system driven by temperature gradients remains embedded in the plasma. The current system exhibits helicity. The associated electron drifts convect heat out of the flux tube. From diamagnetic field measurements, the decay of the electron temperature is obtained with high sensitivity (ΔkTe≂0.001 eV). The heat transport is inferred from the space–time dependence of the electron temperature. The temperature enhancement is confined to a channel whose length depends on heat input since the transport coefficients are temperature-dependent.

Frequency-Domain Electromagnetic Characteristics of a 26-Kilowatt Ammonia Arcjet

Abstract : Arcjet thrusters employ an arc discharge to heat propellant, which expands through a nozzle to produce thrust Spacecraft designers who desire to exploit the enhanced specific impulse of arcjets have expressed concern about the electromagnetic environment produced by the thrusters. Laboratory tests were performed to investigate the electromagnetic environment produced by a 26-kW ammonia arcjet in the frequency domain from dc to 10 GHz using antennas intended to characterize electric and magnetic fields. Results obtained with a 30-cm monopole antenna exposed to the arcjet plume correspond to those of similar ground tests at lower power. When the antenna was shielded from electrical contact with the plume by a Pyrex(R) cover, signal levels dropped sharply at all frequencies. With a covered 30-cm monopole antenna near the arcjet plume, arcjet-on signals exceeded ambient levels over the frequency range 10 kHz-5 MHz. The maximum signal level typically exceeded the ambient level of 40 dBumV/MHz by approximately 27 dBumV/MHz near 200 kHz. A likely explanation for The sharp reduction in signal level once the antenna electrode is covered is that electrons and ions from the plume are collected on the exposed antenna but not on the covered antenna. Signals on the shielded antenna may be interpreted as the result of propagating electric fields, but considerable uncertainty remains about the field source and the effects of the facility on the measurements. Although the electromagnetic fields produced by an arcjet operating as part of a satellite are probably lower than previously expected, these results raise new concerns about the character and Spacecraft compatibility of the plasma from an arcjet plume.