Direct Transmitter Research Articles

A Direct Digital Synthesis Transmitter for 5G Applications With Low-Resolution DACs

A Direct Digital Synthesis Transmitter for 5G Applications With Low-Resolution DACs

Research on driving technology of radio‐over‐fiber (ROF) compact optical transmitter module

AbstractIn response to the problems of communication capacity and spectrum resource constraints, radio over fiber (ROF) technology has gained widespread adoption, and the quality and performance of the optical transmitter module also directly affect the transmission of the link. This paper presents the design of a direct modulation optical transmitter module in the frequency band ranging from 2.6 kHz to 206.8 MHz using OPA690 broadband voltage feedback op‐amp. The module features a tunable bias voltage range from 0 to 5 V to accommodate different threshold voltages for modulation power supply. It offers a gain of 12 dB and a signal‐to‐noise ratio exceeding 50 dB while demonstrating excellent stability, high signal purity, good spectral response characteristics, and compact size advantages. Based on this design, we further optimized the system circuit by adding a fourth‐order Butterworth filter structure, reducing the lower cut‐off frequency to about 500 Hz, increasing the gain by 6 dB, reducing the return loss to −26.91 dB, and the module's signal‐to‐noise ratio exceeding 90 dB. This optimization scheme improves the stability and signal purity of the optical transmitter module and improves the spectral response characteristics. In this paper, Multisim is used to analyze and verify the proposed optical transmitter circuit. In addition, a complete link experiment was carried out using an optical receiving module designed in the same laboratory to verify the feasibility of our proposed module.

Optical discrimination of pathological red blood cells.

Fast diagnostic methods are crucial to reduce the burden on healthcare systems. Currently, detection of diabetes complications such as neuropathy requires time-consuming approaches to observe the correlated red blood cells (RBCs) morphological changes. To tackle this issue, an optical analysis of RBCs in air was conducted in the 250-2500 nm range. The distinct oscillations present in the scattered and direct transmittance spectra have been analyzed with both Mie theory and anomalous diffraction approximation. The results provide information about the swelling at the ends of RBCs and directly relate the optical data to RBCs morphology and deformability. Both models agree on a reduction in the size and deformability of RBCs in diabetic patients, thus opening the way to diabetes diagnosis and disease progression assessment.

Base‐assisted anionic polymerization of alkyl sorbates and subsequent ring‐closure without extreme dilution for synthesis of cyclic stereoregular poly(alkyl sorbates)

AbstractA typical base, lithium diisopropylamide (LDA) or lithium bis(trimethylsilyl)amide (LiHMDS), was found to initiate the anionic chain‐growth polymerization of ethyl sorbate (ES) in the presence of an aluminum Lewis acid, that is, methylaluminum bis(2,6‐di‐tert‐butyl‐4‐methylphenoxide) (MAD) and, after ES consumption, ring‐closure occurred without highly dilute conditions to give the cyclic poly(ES). The finding of ring closure was supported by matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) mass spectroscopy and direct transmittance electron microscope (TEM) observations, in which a series of spectral patterns separated by the mass of ES and cyclic objects with 7.4–25.9 nm rings were observed, respectively. The results indicated that instead of the use of an expensive N‐heterocyclic carbene (NHC), employing these commodity bases to initiate chain polymerization enabled us to fabricate the intended cyclic vinyl polymers without highly dilute conditions. Also, this polymerization proceeded even at −80°C to give threo (98%)‐disyndiotactic (91%) stereoregular poly(ES) in an excellent yield with narrow molecular weight distributions (Mn = 5.9 × 103–8.4 × 103, Mw/Mn = 1.14).

Analysis Of An Inductive Coupling Wireless Power Transfer System With a Finite Element Method For Charging Application Of Electric Vehicles

With the development of technology, Wireless Power Transfer (WPT) systems have also started to be used in charging applications of electric vehicles. The basic methods of WPT systems are based on power transmission systems with laser, microwave, magnetic induction and magnetic resonance. Factors such as the limited use of fossil fuels and environmental pollution have led researchers to see electric vehicles as a solution and to charge these vehicles with wireless systems. Most commercial applications of wireless power transmission are currently limited to close contact transmission distances. There are challenges in increasing coverage, routing transmissions and safely exploiting sufficiently strong electric fields. To provide power efficiently, highly directional transmitters must be applied. Otherwise, with an omnidirectional transmission, only a small part of the transmitted power will reach the receiver. In order to distribute power, especially over long distances, it is often necessary to resort to radiation transfer methods that tightly combine electric and magnetic fields. In this study, important studies on WPT systems were investigated and examined. Then, a WPT transformer is modeled with Finite Element Method based ANSYS-Maxwell-3D. The results obtained using the simulation method are presented in comparison with the research findings. Determining the efficiency of wireless power transfer used in electric vehicle charging applications is the expected result of the study.

Guiding acoustic waves via a gradient index meta-layer

In this work, we propose an efficient approach for controlling acoustic waves through guided mode conversion within a single meta-layer comprised of gradient index metamaterials. By harnessing the subwavelength localization characteristics of acoustic surface waves, the meta-layer can be properly shaped to accommodate arbitrary and prospective trajectories, thus enabling flexible guidance and routing of acoustic waves. Utilizing such a mode conversion mechanism, the acoustic directional transmitter and beam splitter have been devised and numerically demonstrated based on Archimedean spiral structures. These acoustic devices can exhibit a broadband response, achieving transmission efficiency exceeding 80% over a specific bandwidth that can be controlled by the geometry design. The proposed gradient index meta-layer may open new possibilities for acoustic wave manipulation, enabling some promising applications in noise control, information transmission, and energy harvesting.

Synthesis of Energy Efficiency-Enhanced Directional Modulation Transmitters

this article, we present new approaches to synthesize physical-layer secured directional modulation (DM) transmitters that can improve the overall energy efficiency of the system. This is achieved by creating orthogonal artificial noise (AN) that on one hand preserves signal waveforms only along desired spatial directions, and on the other hand reduces the peak to average power ratio (PAPR) of the transmitted signals. The PAPR-reduced signals become friendly to more efficient power amplifier (PA) modes (of operation), thus improving the energy consumption compared with conventional DM counterparts. In the proposed approach, reduced PAPR is achieved by applying power weighted orthogonal AN on transmitted symbols, so that the average power of signals in the RF chains is elevated, resulting in reduced PAPR. The enhancement of the total power efficiency of the transmitter, and the enhanced secrecy performance evaluated through bit error rate (BER) spatial distributions, are demonstrated through system level numerical simulation studies.

Distributed Localization of Target for MIMO Radar With Widely Separated Directional Transmitters and Omnidirectional Receivers

Conventional target localization algorithms for the multiple-input multiple-output (MIMO) radar with widely separated antennas are mainly based on the centralized localization framework, which suffer from huge burdens of computation and communication as well as robustness defect in complex environments. To overcome these issues, this paper first considers the MIMO radar with widely separated directional transmitters and omnidirectional receivers generating the bistatic range (BR) and angle of incidence (AOI) measurements for target localization, which is proven that the position of the target can be uniquely determined with one transmitter and one receiver. Then, the distributed localization framework using the hybrid BR and AOI measurements is developed, where each receiver acts as a fusion center extracting the BR and AOI measurements to perform the localization process, and the localization problem is formulated as solving a linear matrix equation. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">distributed constrained total least squares</i> (DCTLS) algorithm considering errors in both data matrix and observation vector is proposed for each receiver for target localization. The localization performance regarding the Cramér-Rao lower bound (CRLB) is derived for theoretical analysis. Numerical simulations are performed to validate the efficacy and superiority of the proposed DCTLS algorithm over other typical localization algorithms.

Photosynthetic and antioxidant‐related properties in blueberry under low‐ and high‐density covering material

AbstractCovering material is an important tool to reduce damage from extreme weather events, especially in horticultural species. However, physiological and biochemical responses to covering material are still limited in woody plants. Thus, this study aimed to evaluate covering material effects on photosynthetic and antioxidant performance in blueberry cv. Legacy to high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) covering treatments under field conditions during two consecutive seasons. Our results showed that net photosynthesis (Pn) was reduced in LDPE compared to uncovered treatment during the first season. Interestingly, Pn increased 10% in HDPE compared to uncovered and LDPE treatments. Stomatal conductance (gs) was not affected by covering material; meanwhile, the transpiration (E) only showed a 22% increment in LDPE. HDPE exhibited the highest chlorophyll a in the 2018/2019 season compared to the uncovering treatment, as well as chlorophyll b and chlorophyll a/b ratio, but during the 2017/2018 season. A tendency to decrease chlorophyll a level in uncovered plants and LDPE treatment was observed during the 2018/2019 season. Antioxidant activity showed no differences among covering materials. By contrast, phenols increased in LDPE treatment followed by control plants, showing HDPE treatment the lower values during 2018/2019. In conclusion, this study demonstrated that blueberry plants subjected to HDPE treatment showed better Pn and chlorophyll levels than uncovered and LDPE treatments, which could be associated with the diffuse transmittance in HDPE, whereas a high E and phenols were observed in LDPE, whereas intrinsic water use efficiency was lower, which is related to high direct transmittance in this covering material during the summer season.

A Wide-Dynamic Range (-40 °C to 180 °C) Active Wireless MEMS Temperature Sensor With 7m °C Sensitivity

We demonstrate a highly-accurate active wireless microelectromechanical (MEMS) temperature sensor with the largest reported dynamic range (-40°C to 180°C) among active MEMS temperature sensors. The sensor uses a 27.2 MHz high quality factor (Q > 3,200) AlN-on-Si thin-film piezoelectric-on-silicon (TPoS) MEMS resonator to enable highly accurate temperature sensing, with minimum sensitivity (S), better than 0.011 °C across this wide temperature range. The wireless sensor uses an innovative frequency shift keying (FSK) 900 MHz direct up-conversion transmitter. The transmitter uses frequency multipliers for up-conversion, obviating the need for a temperature-stable frequency reference clock, thereby preserving the temperature coefficient of frequency (TCF) of the resonator, and consequently the sensitivity of the sensor. The experimental results show a very high correlation (<0.03% error) between the TCF of the MEMS oscillator and that of the transmitter output signal, demonstrating the viability of the proposed direct up-conversion technique. A detailed analysis of the Allan variance for MEMS temperature sensors which can be used to design for a given minimum sensitivity, is also presented in the paper.

Investigation of the Optical Properties of Indium Tin Oxide Thin Films by Double Integration Sphere Combined with the Numerical IAD Method.

Transparent conductive electrodes have become essential components of numerous optoelectronic devices. However, their optical properties are typically characterized by the direct transmittance achieved by making use of spectrophotometers, avoiding an in-depth knowledge of the processes involved in radiation attenuation. A different procedure based on the Double Integration Sphere combined with the numerical Inverse Adding-Doubling (IAD) method is employed in this work to provide a comprehensive description of the physical processes limiting the light transmittance in commercial indium tin oxide (ITO) deposited on flexible PET samples, highlighting the noticeable contribution of light scattering on the total extinction of radiation. Moreover, harnessing their flexibility, the samples were subjected to different mechanical stresses to assess their impact on the material's optical and electrical properties.

Localization of Multiple Directional Transmitters in Cognitive Radio Context

Localization of transmitters has been gaining interest increasingly. Due to the emergence of directional transmitters in future technologies, localization in this manner is particularly considered. However, limited studies consider the localization of multiple directional transmitters. Our proposed system model describes multiple directional emitters by the means of a Uniform Linear Array (ULA). To localize these transmitters, we adapt the classical Direction of Arrival (DoA) localization techniques with our model. The localization accuracy is studied for multiple affecting parameters and compared to the theoretical limit of Cramer Rao Bound (CRB). The results show that a directional transmitter can be localized by the means of its high sidelobe effects. Root MUSIC outperforms other techniques in localizing the users.

Image Enhancement Technique Using Manchester Coding and RF Tripler for 1-bit Bandpass Delta Sigma Direct Digital RF Transmitter

Image Enhancement Technique Using Manchester Coding and RF Tripler for 1-bit Bandpass Delta Sigma Direct Digital RF Transmitter

Sun Glint Correction Based on BRDF Model for Improving the HY-1C/COCTS Clear-Sky Coverage

The Haiyang-1C (HY-1C) satellite was launched on September 7, 2018. The Chinese Ocean Color and Temperature Scanner (COCTS) onboard HY-1C has the capacity for ocean color and sea surface temperature (SST) observations. The sun glint reflected on sea surface can interfere with the radiance reaching the field of view of satellite sensor, leading to the higher reflectance that is misclassified as cloud and restrictions of satellite data availability. Due to the lack of ability to avoid sun glint, the bidirectional reflectance distribution function (BRDF) model is implemented in the sun glint correction of HY-1C/COCTS visible images. The atmospheric direct transmittance is calculated by aerosol optical depth (AOD) and Rayleigh optical depth (ROD). The comparisons before and after sun glint correction of visible images at different locations and different time are discussed and analyzed. The spectra are compared before and after the sun glint correction, and it has an obvious decrease in both radiance and reflectance. The performance of the BRDF model in low, moderate, and severe glint contaminations is compared. The results indicate that the BRDF model is useful in the sun glint correction of visible bands and leading to more HY-1C/COCTS clear-sky coverage, as consequence can be applied as the preprocessing in the cloud detection and SST retrieval to improve the clear-sky coverage.

Model to subtract contributions of scattered radiation from measured direct transmittance and specular reflectance by light diffusing materials.

The formalism of the Lorenz-Mie (LM) theory is used to estimate the contributions of radiation being scattered into the detector acceptance angle of spectrophotometers (with or without an integrating sphere) to the apparent direct transmittance and specular reflectance measurements. These contributions are subtracted from the measurements before doing the inversion to obtain the spectral variation of the scattering and absorption (S&A) coefficients of optically particulate liquid samples, decoupling the contribution to extinction from these two mechanisms. The method is applied to transmittance spectra of Pickering emulsions of dodecane oil (DO) and DO micelles with saturated dissolved Nile red dye, stabilized with anatase (T i O 2) in water. What we believe to be novel expressions are given to estimate the forward and backward average path-length parameters of propagating diffuse radiation from its equivalent quantities defined within the formalism of the LM theory and to relate these single particle average path-length parameters with the forward scattering ratio, asymmetry parameter, and higher-order coefficients in the expansion of the LM phase function. This novel approach makes it possible to avoid the underestimation of the S&A coefficients, which arises when the correction is not made by subtracting that contribution due to scattered radiation that is reaching the detectors from the directional reflectance and transmittance measurements.

Branch Growth, Leaf Canopies and Photosynthetic Responses of Zizyphus jujube cv. “Huizao” to Nutrient Addition in the Arid Areas of Northwest China

Jujube is one of the main tree species found in the arid areas of Xinjiang, China. However, the nutritional requirements of central leader jujube trees are not understood. Our aim was to explore the effects of different fertilization gradients on the growth, development, and canopy formation of jujube trees to provide a basis for efficient cultivation. We measured and compared various suitable indices of jujube trees under 16 different fertilization treatments, and we confirmed the treatments suitable for cultivation by correlation and principal component analyses. The jujube tree growth indices under different fertilization treatments significantly differed (p &lt; 0.05). The application of nitrogen fertilizer promoted the growth of branches and leaves. The soil and plant analyzer development value, light, and other traits significantly differed (p &lt; 0.05). The leaf area index and direct transmittance coefficient significantly differed (p &lt; 0.05). Compared with single-fertilizer application, mixed-fertilizer application significantly increased the leaf area index. Correlation analysis showed that the net photosynthetic rate of jujube leaves significantly correlated with the stomatal conductance, transpiration rate, and leaf SPAD content (p &lt; 0.01). We obtained three principal components with a cumulative variance contribution rate of 82.192%. The final ranking showed that the mixed treatment (N 460.77 g/tree, P2O5 460.77 g/tree, and K2O 588.23 g/tree) performed better. To ensure branch and leaf growth, this treatment promoted photosynthesis, enabling the growth and development of fruit trees.

Multi-scale fusion framework via retinex and transmittance optimization for underwater image enhancement

Low contrast, poor color saturation, and turbidity are common phenomena of underwater sensing scene images obtained in highly turbid oceans. To address these problems, we propose an underwater image enhancement method by combining Retinex and transmittance optimized multi-scale fusion framework. Firstly, the grayscale of R, G, and B channels are quantized to enhance the image contrast. Secondly, we utilize the Retinex color constancy to eliminate the negative effects of scene illumination and color distortion. Next, a dual transmittance underwater imaging model is built to estimate the background light, backscattering, and direct component transmittance, resulting in defogged images through an inverse solution. Finally, the three input images and corresponding weight maps are fused in a multi-scale framework to achieve high-quality, sharpened results. According to the experimental results and image quality evaluation index, the method combined multiple advantageous algorithms and improved the visual effect of images efficiently.

Light transmittance of mahogany wood treated with 20% hydrogen peroxide solution

There is an increased research interest in methods for transparent wood production and its use. Wood transparency could be achieved by its delignification followed by an impregnation process with polymers having proper optical properties. However, delignification processes are mainly time consuming and not environmentally friendly. The possibility of treating mahogany wood (Swietenia macrophylla King) with 20% hydrogen peroxide for 70, 100, 135, and 170 min at 103 °C is presented in this research. According to the treatment duration, lignin content decreased 40 to 94% relative to its initial content in the control samples, whilst the cell structure remained intact. Due to the light scatter effect, caused mainly by wood tissue structure, the direct optical transmittance of treated samples in the visible light spectrum (400 to 800 nm) was less than 40%. Simultaneously, the total optical transmittance of samples treated for 100 and 135 min reached values between 70 to 80% with high values of the haze at approximately 30 and 60%. Optical transmittance in the visible spectrum area of the samples treated for 170 min was from 45 to 80% and the haze from 25 to 45%.

Energy efficient time‐modulated OFDM directional modulation transmitters

AbstractIn this study, a reconfigurable power divider (RPD) enabled energy efficient direction modulation (DM) transmitter for orthogonal frequency division multiplexing (OFDM) modulated data transmission is proposed. The RPD can smartly select the output ports and operate as a power divider or a switch with appropriate control conditions. Hence, the RPD is able to recycle the energy in the ‘OFF’ state antennas, which is otherwise wasted in the conventional DM transmitter constructed using a fixed power divider and switches. It has been shown in a 4‐element array example that the newly proposed RPD‐based OFDM DM transmitter can provide 1.5–7.8 dB SNR gains (or in the other way, reducing power consumption by 1.5–7.8 dB) for different excitation strategies.

An optical and thermal analysis of translucent concrete considering its dynamic transmittance

Translucent concrete (TC) is promising to transmit daylight into buildings with high thermal performance and energy-saving potential. However, most of the existing studies on TC omit its dynamic transmittance. More research is required to analyze the impact of dynamic transmittance on the optical and thermal performance of TC walls, and to investigate how to take advantage of this distinctive feature so that the building energy-saving potential of TC walls can be fully exploited. In this study, an optical and thermal model of TC embedded with optical fibers (OFs) was developed considering the dynamic transmittance of TC under the influence of solar incidence angle. The model was validated with experimental data. By using the model, the effects of numerical aperture (NA), fiber volumetric ratio (FVR) and solar incident angle on TC were revealed. In addition, a kind of novel TC with inclined OFs was proposed to achieve improved climate-responsive transmittance, which can reduce the dependence on high NA OFs. It was found that in Changsha the direct radiation transmittance of an OF (NA = 0.51, tilt angle = 60°) embedded in TC walls can be controlled within 0.20 in summer, while it can increase up to 0.90 in winter. Though the inclusion of OFs imposes an adverse effect on the wall insulation, TC walls can reduce daily heat loss by about 9.14% and increase daily heat gain by about 51.66% in winter, contributing to energy conservation in buildings.