Radio Frequency Input Power Research Articles

Efficient Wireless Power Transfer System With a Miniaturized Quad-Band Implantable Antenna for Deep-Body Multitasking Implants

Passive operation and battery-charging of deep-body implants can be insured through wireless power transfer (WPT) technologies. However, the power transfer efficiency (PTE) is constrained by device miniaturization and implantation depth. This study proposes a complete WPT system consisting of a patterned WPT transmitter (Tx), an efficient rectifier, and an antenna integrated with the system. The WPT Tx had a size of 6 cm $\times$ 6 cm and was optimized to focus the power on the deep-tissue implants at 1470 MHz. The voltage doubler was optimized at 1470 MHz, had a small size of 5 mm $\times$ 10 mm, and exhibited a high radio frequency (RF)-to-direct current (dc) conversion efficiency of 90% at 2-dBm RF input power. Moreover, the implantable antenna occupies a small volume of 8.43 mm3 and supports quad-band operations: telemetry at 403 and 915 MHz, WPT at the midfield band of 1470 MHz, and control signaling at 2.4 GHz. First, the fabricated prototypes were measured individually in minced pork, in the American Society for Testing and Materials (ASTM) model, and in the saline-filled 3-D head phantom. While operating collectively as an integrated system, the PTE of the system was measured. Additionally, to enhance the PTE of the WPT system, a high-dielectric matching layer ( $\varepsilon _{r} = 78$ ) was used between the WPT Tx and the phantom. Furthermore, to demonstrate the PTE of the WPT system, the voltage doubler was integrated with the implantable antenna, encapsulated in a 3-D-printed capsule endoscope, and its PTE was measured in a saline solution and minced pork. Finally, the compliance of the WPT system with the human safety standards was analyzed and found that the system solely satisfied the safety limits. It is evident from the experimental results that the system can transfer 6.7-mW power to millimeter-sized implants located 5-cm deep in tissues.

A Compact Source–Load Agnostic Flexible Rectenna Topology for IoT Devices

This article presents a new compact lightweight radio frequency (RF) energy harvesting system. The system relies on a dual-tapered transmission line-based matching network that stretches the rectification capability of an integrated Schottky diode. This topology is demonstrated on a 2.4 GHz rigid harvesting system with a resulting power conversion efficiency that reaches up to 58% over 0 dBm input RF power. Its performance is compared with a reference rectifier that relies on a typical open circuit shunt-stub matching network. The rectifier along with a miniaturized monopole antenna is then tailored for a flexible substrate with a resulting efficiency around 50% at 0 dBm input power. The rectifier exhibits an almost flat efficiency over the 2.3–2.5 GHz frequency span despite wide load variations. The system is characterized in multiple bent configurations featuring high and stable performance. It is demonstrated that for different bent states, the proposed flexible harvester does not display large variations in harvested power. Thus, the presented rectenna demonstrates the remarkable combination of compactness, flexibility, and stability. Equipped with these features, such rectifier can be plugged into a variety of sensors, even on wearable surfaces, which makes it ideal for Internet of Things (IoT) applications.

Hybrid RF-Solar Energy Harvesting Systems Utilizing Transparent Multiport Micromeshed Antennas

The design of a hybrid radio frequency (RF) and solar energy harvesting (EH) system utilizing a transparent multiport antenna for indoor applications is described. The system incorporates an eight-port transparent antenna, operating in the unlicensed 2.4-GHz band, and is constructed from transparent copper micromeshed planar conductor. The antenna is integrated on the top surface of a solar cell with rectifiers positioned underneath to form a hybrid RF-solar indoor EH system. A key advantage of this approach is that the surface area of the solar cell is reused for the antenna saving space. Another novelty is the use of a multiport antenna for increasing the RF harvested energy. It is demonstrated that with a light intensity of 360 lux, the solar cell can obtain 1.68-mW power while the rectenna can achieve an additional 4.8%–45.8% harvested power when the incident RF input power density is varied from 13.30 to 52.96 mW/m2. The transparent antenna achieves 72.4% efficiency and is one of the highest reported results. In addition, the rectifiers obtain 53.2% RF-to-dc conversion efficiency for an RF input power of −10 dBm. These results demonstrate that the proposed RF-solar energy harvester can increase harvested energy and provide energy diversity.

Design of new power generating circuit for passive UHF RFID tag

In this paper, we propose a new power generating circuit for passive ultra high frequency (UHF) RFID tag. The proposed power generating circuit consists of a RF limiter, a high power efficiency and high sensitivity full wave radio frequency (RF) wave rectifier and a low-power regulator with NMOS diodes work like a DC-limiter. The design method proposed in this study use one low drop out (LDO) regulator to provide tow output stable supply voltages vdd1 of value 1V for the digital section supply, and vdd2 of value 0.5V for the analog front-end section power supply. The proposed power generating circuit is optimized in terms of power consumption of RFID tag system to have a high operating range under conditions of 50 Ohm antenna, -24 dBm input RF power, 900MHz and 1 M DC, with low power dissipation and 29.15% large power conversion efficiency. The power generating circuit was designed, simulated and layouted in Cadence using TSMC 180 nm technology. The final design occupies approximately 0.25mm<sup>2</sup>.

RF design and study of a 325 MHz 7 MeV APF IH-DTL for an injector of a proton medical accelerator

A compact interdigital H-mode drift-tube linac (IH-DTL) with the alternating-phase-focusing (APF) method, working at 325 MHz was designed for an injector of a proton medical accelerator. When fed in with a proper RF (radio frequency) power, the DTL cavity could establish the corresponding electromagnetic field to accelerate the “proton bunches” from an input energy of 3 MeV to an output energy of 7 MeV successfully, without any additional radial focusing elements. The gap-voltage distribution which was obtained from the CST® Microwave Studio software simulations of the axial electric field was compared with that from the beam dynamics, and the errors met the requirements within ± 5%. In this paper, the RF design procedure and key results of the APF IH-DTL, which include the main RF characteristics of the cavity, frequency sensitivities of the tuners, and coupling factor of the RF power input coupler are presented.

Optimizing Efficient Energy Transmission on a SWIPT Interference Channel Under Linear/Nonlinear EH Models

In this paper, we consider simultaneous wireless information and power transfer (SWIPT) in a multiple-input single-output interference channel (IC) system where the power-splitting (PS) receivers utilize linear/nonlinear energy-harvesting (EH) models. The functions that express the relationship between the input radio frequency power and the output direct current harvested energy of the EH circuits are usually assumed to be linear in recent SWIPT works, while the nonlinear function is suitable for practical data. In a SWIPT IC system, two important targets are sum harvested energy maximization and harvested energy efficiency maximization at the PS receiver, and they are investigated under linear/nonlinear EH models. Thus, some nonconvex resource allocation problems with the two targets and linear/nonlinear EH models are formulated to jointly optimize beamforming vectors at the transmitters and the PS ratios at the receivers. By exploiting a successive convex approximation method and a semidefinite relaxation (SDR) technique, iterative algorithms are proposed to obtain local optimal solutions. Interestingly, the optimal solution to the subproblem is proven to satisfy the rank-1 constraint of the SDR technique. Finally, numerical experiments illustrate effective performance from the proposed solutions, in comparison with some special schemes.

Fundamental experiments of radio‐frequency preionized inert gas plasma MHD electrical power generation

AbstractA seed‐free radio‐frequency (RF) preionized inert gas plasma MHD electrical power generation has been first demonstrated in fundamental experiments with a shock‐tunnel facility. An enthalpy extraction ratio of 2.6% was successfully obtained even under an inlet total temperature of 2200 K at which the power generation can be operated continuously. Since the RF input power required for the preionization tends to be increased for lower inlet total temperature, the reduction of the RF input power is needed for further improvement in the total performance.

Novel breeding approach for Japanese flounder using atmosphere and room temperature plasma mutagenesis tool

BackgroundArtificial induction of mutagenesis is effective for genetic resource innovation and breeding. However, the traditional mutation methods for fish breeding are not convenient or safe for daily use. Hence, development of a simple, safe and effective mutagenesis method with a high mutation rate and applicability to multiple fish species, is needed.ResultsWe reported the first successful mutagenesis in a marine aquaculture fish species, Japanese flounder, Paralichthys olivaceus, using a novel atmosphere and room temperature plasma (ARTP) mutagenesis tool. ARTP treatment time was optimized for the fertilized eggs and sperm, respectively. Eggs fertilized for 60 min were treated by ARTP with a radio-frequency power input of 120 W, and the ARTP treatment time was 25 min. Under an ARTP radio-frequency power input of 200 W, the optimal treatment time for sperm diluted with Ringer’s solution by 1:40 v/v was 10 min. The ARTP-treated group presented differences in morphological traits such as body height, total length among individuals at day 90 after hatching. Whole-genome sequencing was used to reveal the mutation features of ARTP-treated individuals collected at day 120 after hatching. In total, 69.25Gb clean data were obtained from three controls and eight randomly selected ARTP-treated individuals, revealing 240,722 to 322,978 SNPs and 82,149 to 86,798 InDels located in 17,394~18,457 and 12,907~13,333 genes, respectively. The average mutation rate reached 0.064% at the genome level. Gene ontology clustering indicated that genes associated with cell components, binding function, catalytic activity, cellular process, metabolic process and biological regulation processes had higher mutation rates.ConclusionsARTP mutagenesis is a useful method for breeding of fish species to accelerate the selection of economically important traits that would benefit the aquaculture industry, given the variety of mutations detected.

Electrical Characteristics of Capacitive Coupled Radio Frequency Discharges in Argon and Hydrogen

A symmetric radio frequency (RF) (13.56 MHz) electrode discharge system with different geometry has been investigated at low pressure. All electrical properties of symmetric capacitive RF discharge in pure argon (Ar) and pure hydrogen (H2) have been obtained from the current and voltage waveforms. Here, the changes of voltage and current were investigated according to external electrical discharge parameters. The electron densities of these discharges were measured with a single Langmuir probe. A homogeneous model of capacitive coupled RF (CCRF) discharge was used to determine the electrical properties of a parallel-plate RF discharge system and their dependences on the input RF power and gas pressure .

Diagnostic study and simulation of capacitive coupled RF plasma

Aiming at the discharge characteristics of radio frequency capacitively coupled (CCRF) plasma at moderate pressure and medium power, a one-dimensional plasma discharge model was established by using COMSOL software based on fluid model. The distribution law in plasma electron temperature and electron density were studied at the same pressure and different radio frequency input power with Ar gas as working gas. At the same time, a closed glass cavity and a flat plate electrode of the same size were designed and fabricated according to the simulation model. The effective current, voltage and emission spectrum of the discharge plasma were measured experimentally at different RF input power. The electron temperature and electron density of the plasma were calculated by the current-voltage relationship and the energy balance equation. The electron temperature and electron density of plasma were obtained by Boltzmann double-wire method. When the gas pressure was 250 Pa and the input power was 100~450 W, the plasma voltage and current showed a linear relationship. The electron density increased with the increase of the power, but the electron temperature did not change with the change of the power. At the same time, the accuracy of the experiment was further verified by simulation. In this paper, the discharge parameters of plasma at moderate pressure are preliminarily diagnosed by combining the equivalent circuit method, spectral method and numerical simulation method, and a combination of these three methods is proposed for experiment to make the experimental results more convincing and to provide a basis for further study of plasma characteristics.

Axial diagnosis of electron and negative ion behaviors in capacitively coupled O2-containing Ar plasma driven by 27.12 MHz

Capacitively coupled O2-containing Ar plasma driven by a radio frequency (RF) of 27.12 MHz has been investigated. The electron energy probability function (EEPF) was measured with a Langmuir probe. The electronegativity was measured with a laser-induced photodetachment (LIPD) technique in combination with a Langmuir probe. The probe measurement results show a transition of the EEPF from bi-Maxwellian to single-Maxwellian and finally to a Druyvesteyn distribution as RF input power or discharge pressure was increased. This transition indicates the evolution of the heating mode in the Ar plasma by changing the discharge conditions. Adding electronegative O2 gas into Ar plasma leads to the deviation of the EEPF from the pure Ar plasma case. This deviation becomes more serious at high pressure due to the inelastic collisions of electrons with oxygen molecules. Additionally, the addition of O2 not only lowers the electron density in the axial direction but also smoothens the electron density distribution close to the powered electrode in comparison to the linear electron density with the axis in the Ar plasma case. LIPD measurement results show that electronegativity in 5% O2-containing Ar plasma tends to be high as close to the powered electrode and to be a V-shaped distribution along the axis direction with the increase in the pressure. This behavior of the negative ion distribution may be caused by the combined effects of recombination of negative and positive ions and the pseudo-γ mode of negative ions with oxygen neutrals.

Dual-band aperture-coupled rectenna for radio frequency energy harvesting

The article presents a dual-band aperture-coupled rectenna for radio frequency (RF) energy harvesting at 2.45 and 5 GHz application. The rectenna consists of a dual-band π-shaped slot-etched aperture-coupled antenna, designed at the lower substrate of two FR4 substrate layers and a dual-band rectifier. The proposed antenna design also introduces the harmonic suppression of third- and higher order harmonics, ranging from 6 up to 10 GHz from the asymmetrical stubs design at the transmission feedline. The dual-band rectifier is designed to operate at 2.45 and 5 GHz frequency, successfully achieving high conversion efficiency at 68.83% and 49.90% with the optimum load resistor of value 700 Ω and 1.1 kΩ. The minimum DC voltage of 0.167 and 0.236 V with 0 dBm RF input power can be increased when greater RF power is being applied to it, increasing its flexibility to cater various low-power applications.

Argon and nitrogen plasma modified polypropylene: Surface characterization along with the optical emission results

This study focuses on the surface modifications of polypropylene using a capacitively coupled radio frequency gas discharge system. Improvements on the polymer surface properties are investigated for the case of argon and nitrogen plasmas at different radio frequency input power values. Higher number of reactions and their repetitions are expected by the charged particles at higher input power setting. On the other hand, the optical emission intensity does not change linearly with increasing RF input power. In addition to the optical emission spectroscopy, all chemical changes and formation of new functional groups are investigated using a Fourier transform infrared-attenuated total reflection spectrometer. Different reactions are observed for argon and nitrogen plasmas due to their ionization energies and their response to the polymer material. Changes in the surface morphologies are measured using a scanning electron microscope. Formed structures with different sizes and shapes are observed on the surfaces. Furthermore, it is observed that the originally hydrophobic type polypropylene surface is changed to a hydrophilic type after the plasma modification. Wettability of the surface is characterized by measuring the water contact angle. These changes due to the plasma exposure are discussed in detail for various discharge parameters.

Broadband lower-IF RF receiver based on microwave photonic mixer and Kramers-Kronig detection.

A broadband lower- intermediate-frequency (IF) radio frequency (RF) receiver with low cost and complexity based on a microwave photonic mixer and Kramers-Kronig (KK) detection is proposed and experimentally demonstrated. The feasibility of the proposed RF receiver is verified by comparing the error vector magnitude (EVM) performance of a down-converted IF signal with and without KK detection. EVM is measured as a function of IF carrier frequency, input local oscillator (LO) power, input RF power, and the coupling ratio between RF and LO paths. With KK detection, EVM can be improved by more than 9.5% when the IF carrier frequency is close to half of the signal bandwidth. This implies that a lower IF frequency can be down-converted with good EVM and that a low-speed photodetector and a low sampling rate analog to digital converter can be used for wideband RF signal reception.

Heat Transfer Characteristics of a Focused Surface Acoustic Wave (F-SAW) Device for Interfacial Droplet Jetting

In this study, we investigate the interfacial droplet jetting characteristics and thermal stability of a focused surface acoustic wave device (F-SAW). An F-SAW device capable of generating a 20 MHz surface acoustic wave by applying sufficient radio frequency power (2–19 W) on a 128°-rotated YX-cut piezoelectric lithium niobate substrate for interfacial droplet jetting is proposed. The interfacial droplet jetting characteristics were visualized by a shadowgraph method using a high-speed camera, and a heat transfer experiment was conducted using K-type thermocouples. The interfacial droplet jetting characteristics (jet angle and height) were analyzed for two different cases by applying a single interdigital transducer and two opposite interdigital transducers. Surface temperature variations were analyzed with radio frequency input power increases to evaluate the thermal stability of the F-SAW device in air and water environments. We demonstrate that the maximum temperature increase of the F-SAW device in the water was 1/20 of that in the air, owing to the very high convective heat transfer coefficient of the water, resulting in prevention of the performance degradation of the focused acoustic wave device.

Evaluation of Radio Resource Management Impact on RoF Signal Transmission for Downlink LTE

Analog radio-over-fiber (RoF) is a suitable technology for efficiently developing the cloud-RAN concept in fifth generation deployments based on long-term evolution advanced (LTE-A). Distortion and radiofrequency (RF) power amplifier gain should be taken into account in order to achieve the desired transmission power at the base station. Both mainly depend on several parameters that characterize the optical link, such as the RF input power and bias current. This paper analyzes the link performance due to variations on the traffic load as expected under real operation. In this paper, we show that it is possible in this scenario to adaptively choose the optimum RF input power to minimize the measured error vector magnitude and reduce the RF subsystem gain. Results show that this adaptation allows to relax the RF amplifier gain requirements up to 3-4 dB for medium load conditions.

Monolithic acoustic graphene transistors based on lithium niobate thin film

This paper introduces an on-chip acoustic graphene transistor based on lithium niobate thin film. The graphene transistor is embedded in a microelectromechanical systems (MEMS) acoustic wave device, and surface acoustic waves generated by the resonator induce a macroscopic current in the graphene due to the acousto-electric (AE) effect. The acoustic resonator and the graphene share the lithium niobate film, and a gate voltage is applied through the back side of the silicon substrate. The AE current induced by the Rayleigh and Sezawa modes was investigated, and the transistor outputs a larger current in the Rayleigh mode because of a larger coupling to velocity ratio. The output current increases linearly with the input radiofrequency power and can be effectively modulated by the gate voltage. The acoustic graphene transistor realized a five-fold enhancement in the output current at an optimum gate voltage, outperforming its counterpart with a DC input. The acoustic graphene transistor demonstrates a paradigm for more-than-Moore technology. By combining the benefits of MEMS and graphene circuits, it opens an avenue for various system-on-chip applications.

Design of a water-cooled tube for high-power and long-pulse radio frequency ion source

The radio frequency (RF) driven ion source is a promising solution to the neutral beam injectors of ITER and future fusion reactor. Because the demanded RF power is so high (>50 kW for one driver), a copper-made Faraday screen is installed inside the low dielectric tube to protect it against the plasma heat load. However, the Faraday screen may decrease the RF power transfer efficiency due to electromagnetic shielding and induced eddy current. Especially during the long-pulse experiments of plasma generation, the high heat load on the Faraday screen limits the increase of RF input power. Hence, a design of the water-cooled tube is proposed to avoid using the Faraday screen. The water-cooled tube should be able to suffer the plasma heat load by itself. Hence, the cooling circuit of the tube is designed and estimated through a fluid-thermal analysis. The water inlets with tangential injection direction are located inside the metal flanges. Such a design can induce a swirling flow around the tube, which can cause a more uniform temperature distribution and a lower peak temperature on the tube. In order to control the stress along the joints between the metal and the ceramic, the Kovar alloy (an iron-nickel constant expansion alloy) is chosen for the metal flanges, which has a similar thermal expansion coefficient with the ceramic. The thermo-structural analysis indicates a tolerable thermal stress on the ceramic layers of the designed tube under a uniform heat load of 30 kW.

Multiport Pixel Rectenna for Ambient RF Energy Harvesting

We describe the design of a multiport pixel rectenna for ambient radio-frequency (RF) energy harvesting consisting of an optimized triple-port pixel antenna and a triple-port rectifier with dc combining. The advantages of the multiport pixel approach include enhanced harvested RF power for a given area as well as a reduction in the antenna matching requirements. We formulate the design of the triple-port pixel antenna as a binary optimization problem with an objective function related to harvested RF power in the GSM-1800 band for specified power angular spectrums without the need for antenna matching components. The optimization of the triple-port pixel antenna is obtained by using successive exhaustive Boolean optimization. The design for the triple-port rectifier with dc combining is also provided and a prototype is demonstrated. The rectenna measurement demonstrates that the proposed triple-port pixel antenna has dc output power over double that of single-port-based antennas of similar size. The overall RF-to-dc efficiency of the multiport pixel rectenna is also evaluated and shown to be 19% when the total input RF power is −20 dBm. The effects of nonuniformity in the input RF power across antenna ports are also investigated.

Development of High-Density Radio Frequency Plasma Sources With Very Small Diameter for Propulsion

Radio frequency (RF) plasma sources, especially helicon ones, are very useful in many fields, because of the high-density (up to $\sim 10^{13}$ cm -3 ) and low electron temperature (from a few to several electronvolts) available, using an RF frequency range. Here, we develop and characterize very small-area (from 2-cm down to 0.1-0.3 cm in diameter) RF sources that are useful for a space propulsion system with an advanced concept of an electrodeless condition (no direct contact between the plasma and electrodes), leading to a longer operation lifetime. Measurements by using electrostatic probes as well as by a spectrometer based on the collisional radiative model in a small plasma region were employed to estimate the electron density $n_{\mathrm{ e}}$ and its temperature. Here, $n_{\mathrm{ e}}$ was measured as a function of the input RF power and RF excitation frequency, especially in a higher frequency range than the usual one of ~14 MHz, under the mirror magnetic-field configuration. The electron cyclotron resonance effect in the divergent field was examined under a weaker magnetic field with the RF frequency lower than those generally employed. The particle production efficiency, even in this small source, showed an excellent performance, based on classical diffusion discussions. In addition, applying these sources were applied to a space propulsion system with the concept of the m (azimuthal mode number) = 0 half-cycle acceleration, which was operated under all electrodeless conditions in both the plasma generation and electromagnetic acceleration phases.