Low Incident Power Research Articles

SiC whisker/AgNWs/TPU composite film with asymmetric structure for low‐reflection electromagnetic interference shielding

AbstractThe design and preparation of lightweight and flexible electromagnetic interference (EMI) shielding composites with high efficiency and low reflection are critical to the electronic field. First, silver nanowires (AgNWs) were vacuum filtered on the electrospun thermoplastic polyurethane (TPU) fibrous film. Then, by combining the adhesive with the electrospun silicon carbide nanowhisker (SiCnw) @TPU composite fibrous film, the asymmetric EMI shielding composite films with high electromagnetic shielding efficiency (EMI SE) and low incident power were obtained. The lower AgNWs‐TPU layer provides the primary EMI SE, and the upper SiCnw@TPU fibrous film is used for electromagnetic wave absorption. This unique asymmetric structure, the synergistic effect of SiCnw's particular absorbing function and the excellent conductivity of the AgNWs layer make the film show high overall SE (SET = 55.18 dB). In order to improve the absorption effect of the composite film, the number of layers of SiCnw@TPU was adjusted, resulting in a final reflection coefficient value as low as 0.55. This work proposes a new strategy for developing EMI shielding composite films with high efficiency and low reflection, serving as a reference.

Tailoring Sub‐Doppler Spectra of Thermal Atoms with a Dielectric Optical Metasurface Chip

AbstractCompact and robust structures to precisely control and acquire atomic spectra are increasingly important for the pursuit of widespread applications. Sub‐Doppler responses of thermal atoms are critical in constructing high‐precision devices and systems. In this study, a nanograting metasurface specifically is designed for atomic rubidium vapor and integrated it into a miniature vapor cell. Using the metasurface with built‐in multifunctional controls for light, pump‐probe atomic spectroscopy is established and sub‐Doppler responses are experimentally observed at low incident power. Moreover, the sub‐Doppler lineshape can be tailored by varying the incident polarization state. The spectrum transformation from absorption to transparency is observed. Using one of the sharp responses, laser stabilization with a stability of at 2 s can be achieved. This work reveals the effective control of atomic spectra with optical metasurface chips, which may have great potential for future developments in fundamental optics and novel optical applications.

Modeling of Schottky diode and optimal matching circuit design for low power RF energy harvesting

This work designs and implements a single-stage rectifier-based RF energy harvesting device. This device integrates a receiving antenna and a rectifying circuit to convert ambient electromagnetic energy into useful DC power efficiently. The rectenna is carefully engineered with an optimal matching circuit, achieving high efficiency with a return loss of less than −10 dB. The design uses a practical model of the Schottky diode, where both RF and DC characteristics are derived through extensive experimental measurements. The results from both experiments and simulations confirm the effectiveness of the design, showing its proficiency in efficient RF energy harvesting under low-power conditions. The antenna produced operates in the wifi band with a gain close to 4 dBi and a bandwidth of 100 MHz. With a load resistance of 1600 Ω, the proposed device achieves an impressive RF-to-DC conversion efficiency of approximately 52% at a low incident power of −5 dBm. These findings highlight the potential and reliability of rectenna systems for practical and efficient RF energy harvesting applications. The study significantly contributes to our understanding of rectenna-based energy harvesting, providing valuable insights for future design considerations and applications in low-power RF systems.

Morphology-dependent optical properties of a 3D CH3NH3PbBr3 based metal − organic framework

More recently, Metal–Organic Frameworks (MOFs) have displayed extensive promise in the fields of energy storage, solar cells, catalysis, super capacitors, and optoelectronic devices. This work investigates the nonlinear thermo-optical responses of CH3NH3PbBr3 (MAPbBr3) and mix MAPbBr3 with UiO-66-NH2 (MAPbBr3 + MOF) thin films using the Z-scan technique with different incident power of laser ranging from 10 mW to 50 mW. The results show that the third-order nonlinear optical coefficients of MAPbBr3 + MOF thin films were improved obviously than MAPbBr3 thin films. Furthermore, nonlinear optical properties of MAPbBr3 + MOF thin film is evaluated to be improved from 12.5 × 10-8 to 38.2 × 10-8 by decreasing the input power of laser from 50 mW to 10 mW. This treatment repeated for MAPbBr3 thin film, as well. Considering Kubelka-Munk equation, energy gap) Eg for the MAPbBr3 and MAPbBr3 + MOF thin films deposited on glass film is calculated to be 2.565 and 2.530 eV. Due to analyze the optical characterization of the synthesized samples, optical reflection, transmission and absorption were studied. Kramers-Kronig relations and the reflectance data were used for calculation of complex refractive index and dielectric constant. The transverse and the longitudinal optical phonon modes of MAPbBr3 and MAPbBr3 + MOF thin films locate at about 548 and 598 nm, and 590 and 640 nm, respectively. This research opens a new window for wide scale optoelectronic devices in Q-switching for the generation of pulsed lasers including MAPbBr3 with UiO-66-NH2 by detecting the remarkable nonlinear optical characteristics in lower incident power.

Ultrafast low-jitter optical response in high-temperature superconducting microwires

We report ultrafast optical response in high-Tc superconductor (YBa2Cu3O7−δ) based microwires operating at 76 K and we find a rise time ∼850 ps and a fall time ∼1250 ps and an upper limit of timing jitter of ∼100 ps, using twice the standard deviation of the fitted data. In our experiment, incident power is proven to be an important factor for a device jitter. At low incident power, a lower rate of hot-spot generation by a smaller number of absorbed photons results in a longer latency time to obtain the required number of hot-spots for superconductor-to-normal transition. The lower hot-spot generation rate also results in larger timing jitter of the device. Whereas, at high incident power, a higher hot-spot generation rate yields shorter latency and smaller timing jitter. These observations agree well with our statistical model. Enhancing the sensitivity of the current device can enable future high-Tc superconductor nanowire single photon detectors, toward the widespread use of ultrafast quantum technologies.

Wearable Rectenna With Integrated Miniaturized Feeding Slot and Rectifier Structure

A low-cost hybrid textile/PCB wearable rectenna is designed for smart on-body applications. It is an integration of a textile patch antenna and a highly efficient rectifier on a small PCB substrate, where the feeding aperture of the antenna is significantly miniaturized by exploiting an LC loading technique in order to have an effective integration with the rectifier. The feeding-rectifying circuitry is attached to the back of the antenna by normal sewing threads. The essential components are soldered on the small rigid PCB for a robust connection. The size of the rectenna is 0.817 × 0.817 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> while the rigid substrate area for the feeding-rectifying circuitry is only 0.278 × 0.147 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (3.4 cm × 1.8 cm) at 2.45 GHz. The intrinsic dielectric/conduction loss of textile feedlines, the loss of antenna-to-rectifier interconnectors, the loss of soldering or gluing on textiles, and the loss due to body absorption from typical large feeding slots are constitutively reduced. The soldering points and the consequent hard-to-be-characterized parasitic effects on textiles are avoided. The proposed integration approach reduces the cost and eases the rectenna design, fabrication, and integration. As a result, the power conversion efficiency (PCE) of the rectifier reaches up to 39.5% at -20 dBm input power level whilst the experimental rectenna prototype achieves the state-of-the-art PCE of 41% at an extremely low incident power density of 0.4 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The maximum PCE is 56% at the -5 dBm input power. Finally, the possibility of harvesting datalink energy from PC/mobile phones as power source for wearable electronics is investigated.

Analysis and Design of RF Energy-Harvesting Systems With Impedance-Aware Rectifier Sizing

Because of the interaction between the internal blocks of an RF energy harvesting (RFEH) system, sizing a rectifier only for high power conversion efficiency (PCE) is insufficient for improving global power harvesting efficiency (PHE). This brief analyzes and sizes the rectifier by taking its input and output impedances into account with a two-port model that combines the rectifier AC and DC characteristics. The AC characteristic in this model is used for impedance-aware rectifier sizing. We target a low input-impedance rectifier for better impedance matching between the receiver antenna and the rectifier. The DC characteristic describes the rectifier power loss allocation and estimates its maximum power point. A proposed parasitic-aware matching network sizing methodology predicts the PHE is finally limited by Ohmic loss in the matching network at a low incident power level. For overcoming this limitation, this brief also analyzes the impact of multiple rectifier stages on RFEH with a high peak-to-average power ratio (high-PAPR) incident waveform for improving the PHE. We design an RFEH prototype with a sized 28nm CMOS two-stage cross-coupled rectifier. Measurement results show sensitivity as low as −28.3 dBm with a peak PHE of 31.1% at −16.5 dBm 2.45-GHz high-PAPR incident power. It has sufficient high output impedance to prevent reverse leakage without the need for an additional self-gating circuit.

Nonreciprocal transmission in a nonlinear coupled heterostructure.

A nonlinear coupled heterostructure, metal-nonlinear-metal-insulator-metal, is proposed. The heterostructure is a non-Hermitian system that possesses reciprocal and nonreciprocal optical transmission characteristics. With low incident power, linear optical characteristic is observed whereas at high incident power, nonlinear optical characteristics is observed. Under the low incident power there is no nonlinear effect, the forward and backward transmission are reciprocal. With appropriate geometric parameters, for forward propagation two exceptional points where the reflection coefficients equal zero can be obtained simultaneously. With high power incident nonlinear effect becomes significant, leading to reciprocity broken and optical bistability observed. We investigated the behaviours of forward and backward transmission as well as the optical bistability under different incident powers using nonlinear coupled mode theory. There is excellent agreement between the simulation results and theoretical modelling. The theoretical study of proposed heterostructure shows it has several novel optical responses under different incident conditions. The proposed heterostructure is relatively simple to fabricate and therefore can be experimentally verified with ease. These unique optical characteristics allow more possibilities for the design of multifunctional devices.

Schottky barrier height modulation and photoconductivity in a vertical graphene/ReSe2 vdW p-n heterojunction barristor

A 3-terminal device with a tunable Schottky barrier controls the charge transport across a vertically stacked structure named “barristor”- one composed of a graphene/rhenium diselenide (ReSe2) p-n heterojunction to exploit the advantages of the high mobility of graphene with tunable ReSe2 for digital applications is reported herein. The CVD-graphene used to fabricate p-n heterojunction with ReSe2 is p-type doped by DUV irradiation in O2 atmosphere for 30 min. Density functional theory (DFT) calculations reveals highly anisotropic behavior of ReSe2, possessing bandgap of 1.17 eV. We demonstrate that the gate-controlled Schottky barrier can be utilized to modify carrier transport in graphene, resulting in tuning of the Schottky barrier height. Thus, by modulating the work function of the monolayered graphene via the back-gate voltages, the Schottky barrier height at the interface between the graphene and ReSe2 could be varied by up to 300 meV. A diode showed good rectification behavior with an ON/OFF current ratio of 102. Furthermore, the barristor exhibits good optoelectronic characteristics with a sensing range from visible (455 nm) to near IR (850 nm) and is capable of detecting low incident power density. The diode attained photoresponsivity and detectivity values of 42 AW-1 and 2.2 × 1012 Jones, respectively, and a rise time of 33.94 ms under 656 nm laser illumination. Our approach could aid the improved development of high-performance graphene-based heterojunction devices.

High-Performance Energy Selective Surface Based on the Double-Resonance Concept

In this article, a high-performance energy selective surface (ESS) is proposed based on a double-resonance concept, which has a nonlinear transmission response for high-power electromagnetic protection. With well-designed grid and cross patterns as well as properly chosen p-i-n diodes, bandpass and band-stop resonances are excited by the ESS at the same frequency under low and high incident power levels, respectively, resulting in low insertion loss (IL) and high shielding effectiveness (SE) of the ESS. Two samples of single-layer and double-layer ESSs operating at 3 GHz are designed to demonstrate the double-resonance concept. By utilizing a double-layer structure, a second-order band-stop resonance is produced to achieve a broader bandwidth with high SE in comparison with the single-layer ESS. Equivalent circuit models are employed to explain how the double resonances are produced and a wide bandwidth of high SE is obtained. Field circuit cosimulation is conducted to estimate the nonlinear performance of the ESS designs. Moreover, the ESS designs are measured in a rectangular waveguide setup. Good agreement is observed between the simulation and measurement. Simulated and measured results demonstrate that low IL less than 1 dB and high SE larger than 24 dB can be obtained under low and high incident power levels, respectively.

A Compact Rectenna With Flat-Top Angular Coverage for RF Energy Harvesting

The efficiency of rectifying antennas (rectennas) always suffers when the energy sources change with space and time and have low incident power density in the harvesting of radio frequency (RF) energy. This letter presents a novel rectenna design which consists of a receiving antenna array insensitive to the location of the energy source and a rectifier suitable for the low incident power conditions. The design of the receiving array is based on the method of maximum power transmission efficiency expressed in the form of quadratically constrained quadratic programing. The receiving antenna features a flat-top beam collection range whose angular coverage is adjustable depending on the applications. The SMS 7630 diode is selected and mounted on the rectifier for the enhancement of rectification efficiency when the incident power is low. To validate the design method, a six-element patch receiving array with less than half-wavelength interelement spacing and a rectifier operating at 5.8 GHz industrial, scientific, and medical (ISM) band are fabricated, and the overall rectification performance is tested. The measurement results indicate that the value of output dc voltage remains almost unchanged when the energy source moves within the range from –45° to +45° in the H -plane under the identical distance.

Optical limiting and speckle of low power continuous wave laser beams using nonlinear scattering in photorefractive Zr: LiNbO3 crystals

The optical limiting caused by nonlinear scattering in the photorefractive Zr-doped LiNbO3 crystals was studied for lower-power laser beams with wavelengths of 514.5 and 532 nm. The measurements of speckle evolution indicate that the samples with 0.625 ≤ [Zr] ≤ 1.25 mol% exhibit the very large gain factor for holographic amplification of noise gratings. Based on the direct measurements of the output power depending on the input one, we conclude that these samples behaved as hard optical limiters for the laser beams with a low incident power. Thus, these crystals find their potential application in the optical limiting devices.

A Self-Gating RF Energy Harvester for Wireless Power Transfer With High-PAPR Incident Waveform

In this article, we propose a self-gating radio frequency (RF) energy harvester (RFEH) for reaching a high-power harvesting efficiency (PHE) at a low incident RF power level with a high peak-to-average power ratio (high-PAPR) waveform. It includes a power switch between a cross-coupled rectifier and its supplied load to cut off the reverse leakage current in between the short power bursts. The power switch is dynamically controlled based on an indication of the ability of the RFEH to effectively charge the load at the instantaneous incident power level. This is achieved by comparing the load voltage with the open-circuit voltage of a replica rectifier. A comparator with optional proteresis (reversed hysteresis) is proposed for compensating its logic delay at the start and at the end of the short RF power bursts. As a result, the power switch is accurately turned on only during the power bursts. The self-gating RFEH was prototyped for 2.45-GHz wireless power transfer (WPT). It includes a cross-coupled rectifier with the proposed self-gating circuit fabricated in a 65-nm process, a discrete balun, a parasitic-aware-sized π matching network, and an off-the-shelf power management unit (PMU) with maximum power point tracking (MPPT). Measurement results show sensitivity as low as -26.7 dBm with a peak PHE of 32.3% at -14.1-dBm incident power. Compared with the state-of-the-art works, the proposed design significantly improves the RFEH performance at the target low average incident power.

Studies on backscattering noise in reflective coherent optical communication system

For the safety information transmission technology, here an improved high-security reflective coherent optical communication system is studied in this paper. The backscattering, mainly Rayleigh backscattering and stimulated Brillouin scattering, is analyzed to adversely affect the system performance. The results show that the sensitivity of the system can be as high as -36.3 dB m and the transmission distance is 83.2 km with a low incident power and a data rate of 10Gbps. In addition, under high incident power, the sensitivity of the system is -36.4 dB m and the transmission distance is 95.4 km. Therefore, we can reach the following conclusion that the reflective system can realize high-speed and long-distance communication. It can be applied to secure communication or some special fields.

High-Performance Optical Power Limiting Filters at Telecommunication Wavelengths: When Aza-BODIPY Dyes Bond to Sol–Gel Materials

An optical power limiter (OPL) device can change its optical properties depending on the input light intensity: it is ideally transparent at low incident power and presents a decrease in transmissi...

A miniaturized printed rectenna for wireless RF energy harvesting around 2.45 GHz

This paper presents the design of a highly compact printed rectenna for ambient RF energy harvesting around 2.45 GHz. Its antenna structure comprises a rectangular patch with two etched U-shaped slots fed by a symmetric 50 Ω coplanar line. In spite of compact size, it has been directly integrated with a rectifying circuit on the same substrate only at the expense of a 15% frequency shift. The proposed rectenna overall dimension is only 24.9 × 8.6 × 1.6 mm3, the smallest so far reported with comparable performance, which can be easily integrated with any device for energizing low-power wireless sensor networks. It was fabricated and experimentally characterized, achieving a reasonable agreement with the expected simulated results. Measured results indicate that, at the resonant frequency, the antenna part of the proposed rectenna provides a good matching level (<−25 dB) and has a 0.8 dBi peak gain as well as nearly symmetrical radiation properties (in both E- and H-planes). The measured RF-to-DC conversion efficiency (DC output voltage) of the proposed rectenna at a low incident power of −20 dBm is about 20% (97 mV) with a load resistance of 4.7 kΩ. A demonstration experiment of a LED driven by the rectenna was also presented.

Broadband supercontinuum generation based on filled structural photonic crystal fibers with low incident optical power

Highly nonlinear photonic crystal fibers (PCFs) can be used as a kind of new ways to realize the supercontinuum generation because of their highly nonlinear effects. Based on a type of material-filled method and structure, novel highly nonlinear PCFs are proposed to compare with the conventional highly nonlinear fiber for supercontinuum generation in this manuscript. The nonlinear coefficient and supercontinuum spectra varying with different parameters such as the hole-diameter, the hole-pitch and the refractive index of the filled material are investigated respectively and analyzed numerically. Even if lower incident optical power is used on the designed PCFs than that on the conventional fiber and the previous proposed PCFs, broadband supercontinuum can still be obtained easily from highly nonlinear effects. The results demonstrate that it is possible for this kind of novel PCFs to achieve the maximum 450 nm supercontinuum spectra, even though it is only 50-cm-long fiber and pumped by substantially lower incident optical power of 1.5 W near the wavelength of 1.55 µm.

A self-powered, flexible photodetector based on perovskite nanowires with Ni-Al electrodes

A flexible, self-powered, high-performance photodetector with the Ni/perovskite nanowires/Al structure has been fabricated successfully. CH3NH3PbI3 nanowires were synthesized by a simple spin-coating method at the appropriate temperature on a flexible substrate of polyimide (PI) film. The channel length between Ni-Al electrodes is about 15 μm. A built-in electric field has been established in the asymmetric device, which can effectively separate electron-hole pairs. The as-fabricated photodetector exhibited a high sensitivity from 405 nm to 808 nm. The external quantum efficiency (EQE) of the device is 33.7% at 405 nm with 0 V bias. Note that the device showed good performances of high sensitivity for detecting low incident power density. In addition, a responsivity of 0.227 A cm−2 was achieved under the incident light power of 1 × 10−8 W cm−2. The photodetector showed a high on/off ratio of 147, fast response speed of tens of microseconds, and excellent flexibility with a slight variation of photocurrent after bending test. These results create new opportunities for constructing low-cost, simple-process and high-performance photodetectors.

Novel L-Slot Matching Circuit Integrated with Circularly Polarized Rectenna for Wireless Energy Harvesting

Radio frequency (RF) power harvesting allows wireless power delivery concurrently to several remote RF devices. This manuscript presents the implementation of a compact, reliable, effective, and flexible energy harvesting (EH) rectenna design. It integrates a simple rectifier circuit with a circularly polarized one-sided slot dipole antenna at 2.45 GHz Industrial, Scientific, Medical (ISM) frequency band for wireless charging operation at low incident power densities, from 1 to 95 μ W/cm 2 . The rectenna structure is printed on a single layer, low cost, commercial FR4 substrate. The integration of the rectifier and antenna produces a low-profile and high performance circularly polarized rectenna. In order to maximize the system efficiency, the matching circuit introduced between the rectifier and antenna is optimized for a minimum number of discrete components and it is constructed using multiple of L-slot defects in the ground plane. For a given input power of − 6 dBm intercepted by the circularly polarized antenna with 3 dBi gain, the peak RF-DC (radio frequency-direct current) conversion efficiency is 59.5 % . The rectenna dimensions are 41 × 35.5 mm 2 . It is demonstrated that the output power from the proposed rectenna is higher than the other published designs with a similar antenna size under the same ambient condition. Thanks to its compact size, the proposed rectenna finds a range of potential applications for wireless energy charging.

High-DR CMOS Fluorescence Biosensor With Extended Counting ADC and Noise Cancellation

Accurately resolving small fluorescence power variations in presence of noise and high-background tissue autofluorescence from deep brain structures with a fiber photometry system requires highly linear and sensitive photo detectors. This paper presents a high-dynamic range (DR) CMOS biosensor fusing a low-noise photosensing front-end with a high-precision extended counting analog-to-digital converter (ADC) with noise cancellation to detect florescence neural signal fluctuations of very low incident power. The 7 MSBs are resolved by a first order continuous-time resettable $\Sigma \Delta $ ADC, whereas the residue voltage is quantized by a 10-bit single slope ADC for enabling wide-dynamic range and high-precision fluorescence sensing. The reset noise is canceled out by an embedded noise cancellation scheme which is subtracting the reset noise from the signal using a correlated double sampling scheme. Unlike other solutions, the biosensor has a short conversion time of $306.5~\mu \text{s}$ compared to a typical fluoresence sampling period of 10 ms, providing a very low duty cyle of 3%, which is a key to achieve low excitation source power consumption in this application to extend system autonomy, and to avoid photobleaching and phototoxicity in the tissue. The proposed optoelectronic biosensor is implemented in a 0.18- $\mu \text{m}$ CMOS technology, consuming $93~\mu \text{W}$ from a 3.3-V supply voltage while achieving a DR of 104 dB, a minimum detectable current of $1.3~\text {pA}_{\mathrm{ rms}}$ , and a chip area of 0.475 mm2. We present the measured performance of the biosensor using an optical experimental setup including a LED driver, a fiber optic, and a test board.