Radiation Efficiency Enhancement Research Articles

Gain Enhancement and Ground Plane Immunity of Mechanically Driven Thin‐Film Bulk Acoustic Resonator Magnetoelectric Antenna Arrays

AbstractCompact, conformal antennas with ground plane immunity and high gain are crucial to IoT, 5G, and biomedical applications. Conventional electrical antennas suffer large size, detuned impedance, and degraded gain and radiation efficiency on a ground plane as they operate on electromagnetic resonance and use electric dipole for radiation. Utilizing electromechanical resonance, magnetoelectric(ME) coupling, and magnetic dipole radiation in magnetostrictive/piezoelectric heterostructures, ME antennas exhibit ultra‐compact sizes comparable to acoustic wavelength and enhanced radiation performance on a ground plane. This study first utilizes parallel and series antenna array topology to achieve a profound gain and radiation efficiency enhancement without degrading impedance mismatch and quality factor of ME resonators. Notably, by increasing the array element number, 10 dBi gain enhancement is achieved in 3 × 3 thin‐film bulk acoustic resonator (FBAR) ME antenna array, reaching a peak antenna gain of −17.3 dBi. Unlike conventional antenna arrays, ME antenna arrays enhance radiation efficiency without affecting directivity, owing to ultra‐compact dimensions much less than one‐quarter of electromagnetic wavelength. Their ground plane immunity and 3 dB gain enhancement on ground planes with different shapes are also demonstrated. The demonstrated ME antenna arrays are outstanding platform‐independent ultra‐compact high‐gain conformal antenna candidates for wireless communication, wireless power transfer, and portable electronic and biomedical devices.

Enhancement of Radiation Efficiency for DUV-LEDs by AlN-Doped Silicone Layer Filled Chip-Side

Enhancement of Radiation Efficiency for DUV-LEDs by AlN-Doped Silicone Layer Filled Chip-Side

Compact Wearable Antenna with Metasurface for Millimeter-Wave Radar Applications.

Three metasurfaces (MTS) are designed to be combined with a series end-fed 1 × 10 array antenna with a modified Dolph-Chebyshev distribution for imaging applications in the millimeter frequency range, 24.05-24.25 GHz. A reduction in secondary lobes and an increase in FTBR can be achieved while preserving gain, radiation efficiency, SLL and size using an MTS-array combination. Moreover, as a result of each single-layer MTS-array combination, operation bandwidth is widened, with gain and radiation efficiency enhancement. The overall devices' size is 86.8 × 12 × 0.762 mm3. The envisioned application is collision avoidance in aid to visually impaired people at a medium-long distance.

Millimeter-Wave Patch Antennas With Ultralow Profile of 20 μm on Flexible Substrate

In applications of flexible communication electronics, the requirement for ultralow profile of antenna is gradually approaching a limit. In order to achieve a higher flexibility, it is necessitated to limit the vertical distance to 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> scale between the integrated antennas and the electrode ground (GND). Such a small Section height results in a severely reduced radiation efficiency and a narrowed bandwidth. In this article, the enhancement of radiation efficiency and bandwidth of a millimeter-wave (mmWave) patch antenna with 20 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> profile height are studied. On the metal GND, by properly opening two (or one) resonant slots with a width of 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , strong resonance coupling between the patch antenna and the slots can be induced, leading to a greatly enhanced radiation efficiency. Meanwhile, the spectra width of TM10 mode of the patch antenna can also be effectively broadened by the mode coupling, giving rise to a greatly improved radiation bandwidth. The physical mechanism and the sensitive factors to maximize bandwidth, antenna gain, and front-to-back ratio are discussed.

Radiation Efficiency Enhancement of Graphene Plasmonic Devices Using Matching Circuits

In the present work, the radiation properties of a graphene plasmonic patch antenna are investigated and enhanced in terms of efficiency, utilizing circuit-matching techniques. Initially, the reflection coefficient of graphene surface waves due to discontinuities is studied, while the power flow towards free-space is numerically extracted. This analysis indicates that the radiated power is increased for higher values of the chemical potential, although the surface wave is weakly confined and prone to degradation due to interference. For this reason, a graphene sheet that supports strongly confined surface waves is terminated via a matching layer, in order to enhance the radiating power. In particular, the matching layer consists of an appropriately selected larger chemical potential value, in order to minimize the reflection coefficient and boost the radiation performance. The numerical investigation of this setup validates the upgraded performance, since the radiating power is significantly increased. Then, a realistic setup that includes a graphene patch antenna is examined numerically, proving the augmentation of the radiation efficiency when the matching layer is utilized. Finally, the latter is designed with a graded increment in the chemical potential, and the computational analysis highlights the significant enhancement of the graphene plasmonic antenna gain towards the desired direction. Consequently, a more reliable framework for wireless communications between plasmonic devices at THz frequencies is established, which corresponds to the practical significance of the proposed methodology for improved radiation efficiency. All numerical results are extracted by means of an efficient modification of the Finite-Difference Time-Domain (FDTD) scheme, which models graphene accurately.

Radiation Efficiency Enhancement of Graphene THz Antennas Utilizing Metamaterial Substrates

The radiation efficiency improvement of graphene plasmonic antennas via synthesized substrates with metamaterial resonators is introduced in this letter. Graphene, represented as an ultrathin layer, can support highly confined surface waves of significantly decreased wavelength compared to the vacuum one. Although this concept yields more compact devices, its applicability to graphene antennas is limited, due to the degradation of radiation efficiency. Thus, the effect of a substrate material on the surface-wave wavelength is thoroughly examined, while radiators of larger dimensions and enhanced efficiency are designed for an epsilon-negative medium. Also, a novel realistic metamaterial substrate is developed for graphene terahertz (THz) antennas, successfully verifying all theoretical estimations. Numerical results are extracted via an accurate finite-difference time-domain algorithm that treats graphene as an efficient surface boundary condition.

Comparative study of X-ray treatment and photodynamic therapy by using 5-aminolevulinic acid conjugated gold nanoparticles in a melanoma cell line

Purpose: The most important challenges in photodynamic therapy (PDT) are related to the limited penetration of light and the low uptake of photosensitizers. In radiotherapy, they are correlated to radiation damage of normal tissues. Therefore, a targeted radio and photosensitizer can reduce the limitations of the mentioned methods. In this study, photosensitizing and radio-sensitizing effects of 5-aminolevulinic acid (5ALA)-conjugated GNPs were investigated. Materials and methods: First, cell toxicities of 5ALA, GNPs and a conjugate were assessed on Mel-Rm cell line. Then, the radio sensitizing effect of every agent was studied. Different experiments were designed in four separate groups, each group containing six subgroups receiving different radiation doses by using a superficial X-ray tube. Furthermore, the photosensitizing efficacy of the agents was evaluated after cells were irradiated by a He–Ne laser at four light doses in separate groups. Results: With regards to radio sensitivity assessments, there was no significant difference between different irradiation doses. The investigation on photosensitivity of 5ALA and a conjugate showed significant differences between the control (without illumination) and groups that received PDT in the presence of 5ALA and conjugate, wherein ED50 were estimated at 136.2 J/cm2 and 56.2 J/cm2, respectively. With regards to PDT experiments, the conjugate induces cell death more than twice in comparison with 5ALA. Conclusion: The conjugate does not cause any enhancement of radiation efficiency on MeL-Rm cell line. With regards to PDT, we found that the conjugate induced cell death at twice the rate when compared with 5ALA alone. Therefore, the conjugate can be an appropriate delivery agent for 5ALA and may also enhance the destruction of tumor cells. Finally, comparing the two types of treatment shows that PDT is a more efficient treatment for this cell line.

Radiation Enhancement Using Circular Split Ring Meta-Surface Mirror for a Small Patch Resonator

This paper investigate the radiation efficiency enhancement for a small square patch resonator with the integration of single layer circular split ring metasurface mirror (CSRMM) operating at 5.8 GHz using Transmission Line Matrix (TLM) method. The single layer CSRMM provide an appropriate reflection phase to act as a mirror and is able to enhance the resonator gain and efficiency. This work shows a linear phase response from 5.8 GHz to 5.9929 GHz that is sufficient for 50 Ω wireless communication system operation. A siginificant improvement of 0.391 to 0.741 dBi IEEE gain over the whole frequency range was demonstrated. The resonator has an initial radiation efficiency of 0.246 and incremented to 0.406 once CSRMM is inserted. The resonator small size configuration provides adequate space for mounting the mirror close to the resonator, making it more fitting for modern wireless devices.

Radiation efficiency enhancement using lumped inductors for dual-mode mobile phone

This letter proposes a radiation efficiency enhancement technique using a lumped inductor for a dual-mode mobile phone.Two planar inverted-F antennas (PIFAs) with a collinear arrangement are used for dual-mode operation at the CDMA band of 824–894 MHz and GSM band of 880–960 MHz. Each antenna is separately connected to a lumped inductor of 4.7 nH. The electric field is more confined on each inverted-F section at its operating band in this configuration and the coupling between PIFAs is less than −10 dB. The simulated and measured results show that radiation efficiency of the proposed antenna is improved by up to 33%. The radiation patterns are similar to those of a dipole antenna with slightly tilted main beam directions due to the PIFA placement. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1011–1013, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26735

Optical Modeling of Plasmonic Nanoparticles Enhanced Light Emission of Silicon Light-Emitting Diodes

Significant enhancement of radiative efficiency of thin-film silicon light-emitting diodes achieved by placing the active layer in close proximity to silver (Ag) nanoparticles has been observed. In this paper, optical properties including transmission, reflection, and absorption of a random assembly of Ag nanoparticles are theoretically investigated using the effective medium model. Furthermore, the influence of Ag nanoparticles on light emission of silicon light-emitting diodes is studied by an improved effective mode volume model we propose here. The normalized line shape of dipole oscillation is calculated directly using Lorentz–Drude model without using any approximation. Thus, it results in more accurate calculation of the enhanced Purcell factor in comparison with the conventional approach. We show that an enhancement of radiative efficiency of silicon light-emitting diodes can be achieved by localized surface plasmons on metal nanoparticles. The calculated result of optimal Ag nanoparticle size to enhance light emission of silicon light-emitting diodes at 900 nm wavelength is in very good agreement with those obtained from the experimental result. The model is useful for the design of metallic nanoparticles enhanced light emitters.

Plasmonic light-emission enhancement with isolated metal nanoparticles and their coupled arrays

We present a systematic study of the enhancement of radiative efficiency of light-emitting matter achieved by proximity to metal nanoparticles. Our goal is to ascertain the limits of the attainable enhancement. Two separate arrangements of metal nanoparticles are studied, namely isolated particles and an array of particles. The method of analysis is based on the effective mode volume theory. Using the example of an InGaN∕GaN quantum-well active region positioned in close proximity to Ag nanospheres, we obtain optimal parameters for the nanoparticles for maximum attainable enhancement. Our results show that while the enhancement due to isolated metal nanoparticles is significant, only modest enhancement can be achieved with an ordered array. We further conclude that a random assembly of isolated particles holds an advantage over the ordered arrays for light-emitting devices of finite area.