dB Level Research Articles

Design of a Quadband Doherty Power Amplifier With Large Power Back-Off Range

This paper proposes a technique which allows quadband impedance matching and impedance level shifting Doherty power amplifier (DPA) design. By using novel coupler networks with reactance and choosing appropriate complex load impedances, the quadband DPA can reach a power back-off range (OBO) of over 9 dB. In addition, the peak PA branch and the carrier PA branch use different coupler network parameters in order to satisfy different impedance requirements. To illustrate the design procedure a quadband DPA with 9 dB OBO operating in 0.5-0.7 GHz, 1.5-1.7 GHz, 2.5-2.7 GHz, and 3.5-3.7 GHz frequency ranges is designed, fabricated and tested. Measurements demonstrate that the DPA can deliver saturated output power between 43.1 dBm and 43.8 dBm in all four bands, with a drain efficiency ranging from 63.3% to 66.5%. Also, drain efficiency of from 42.2% to 52.3 % can be obtained at an OBO of 9 dB level. The DPA implemented here shows state-of-the-art performance for OBO under quad-band operation.

A novel design of compact broadband 4 × 4 Butler matrix-based beamforming antenna array for C-Band applications

In this paper, a compact broadband 4 × 4 Butler matrix (BM) as a feeding network for antenna array is presented and studied. The broadband performance of the BM occurs when it operates in the almost equal difference of phases and coupling throughout the operating band. The different components of the proposed design such as branch-line coupler, crossover, and Schiffman line phase shifter are designed and optimized to be low loss and wideband. The total size of the BM is 37 mm × 47 mm, equal to 0.64λ0 × 0.81λ0 in design frequency at 5.2 GHz. The measurement bandwidth for fabricated structure on the FR4 substrate is 24 % achieved from return loss lower than −10 dB. The beam directions are measured at −15, −43.2, +43, and +15° at 5.2 GHz for each input port 1–4 excitation respectively with the gain value of 10.2 ± 0.2 dB and sidelobe levels of −8.2 ± 1.2 dB. The Final BM exposures phase errors of 3 ± 1.7° with the amplitude imbalance of less than ±1 dB over the operational band.

Different threshold levels of circulating total and free 25-hydroxyvitamin D for the diagnosis of vitamin D deficiency in obese adolescents.

The total serum 25-hydroxyvitamin D [25(OH)DT] level is lower in obese individuals than in their nonobese peers, despite similar bone turnover markers and bone mineral density. This study aimed to investigate whether the threshold level of 25(OH)D for the diagnosis of vitamin D deficiency (VDD) in obese adolescents was lower than that in controls and to compare 25(OH)DT, free [25(OH)DF] and bioavailable [25(OH)DB] vitamin D with VDBP levels in obese individuals and their controls. A total of 173 adolescents (90 obese individuals and 83 controls) aged 12-18 years were included in the study. The metabolic and anthropometric parameters of the participants were recorded, the 25(OH)DT, 25(OH)DF, and VDBP levels were measured, and the 25(OH)DB levels were calculated. The cutoff values for VDD were estimated according to the level of 25(OH)D below which parathyroid hormone begins to rise. The obese subjects had lower 25(OH)DT (12.1 ± 5.8 vs. 16.4 ± 9.3 ng/mL, p < 0.001), 25(OH)DF (12.6 ± 4.2 vs. 16.7 ± 7.6 pg/mL, p < 0.001), 25(OH)DB [4.8 (2.3) vs. 6.1 (5.2) ng/mL, p = 0.012], and VDBP [112.2 (51.3) vs. 121.9 (95.5) μg/mL, p < 0.001] levels than the controls. The cutoff values for 25(OH)DT and 25(OH)DF levels for VDD were lower in the obese group than in the control group (9.4 vs. 14.1 ng/mL; 12.2 vs. 16.8 pg/mL, respectively).Conclusion: The vitamin D cutoff values for the diagnosis of VDD were different in the obese and control groups. Using the same cutoff value for VDD may cause overtreatment in obese adolescents. What is Known: • Vitamin D deficiency is more prevalent in obese children than nonobese controls, despite the same bone turnover markers and bone mineral density • The cutoff value of vitamin D level for the diagnosis of VDD is based on the PTH elevation What is New: • In obese adolescents, total and free vitamin D cutoff value for the diagnosis of VDD was lower than nonobese peers • Using the same cutoff value for vitamin D deficiency in both obese and nonobese adolescents may cause overtreatment.

Coherent ultrabroad orbital angular momentum supercontinuum generation in an AsSe2-As2S5 microstructured fiber with all-normal dispersion

We design and simulate a hollow AsSe2-As2S5 microstructured fiber surrounded by air holes with nearly-zero flattened all-normal dispersion profile. Simulation results show that the coherent first-order orbital angular momentum (OAM1,1) supercontinuum (SC) spectrum extending from 1.3 to 11 μm at −40 dB level, which can be achieved by pumping a chirp-free hyperbolic secant pulse with 100 fs pulse duration and 20 kW peak power at the wavelength of 6 μm into an 11 mm proposed fiber. Due to the flexible controllability for chromatic dispersion of this fiber, several coherent SC spectra generated by different OAM modes are analyzed.

Wind Farm Noise—Modulation of the Amplitude

The operation of a wind turbine results in a series of pulses where there is a significant instantaneous increase in the amplitude of the pressure signal, dependent upon the wind speed at the turbine blades. The variations in the amplitude of the sound being emitted can be significant at receiver locations both as an audible and inaudible sound. The modulation of the A-weighted amplitude of the acoustic signature for wind turbines is often referred to as “amplitude modulation”. Criteria have been proposed in the UK to define “excessive amplitude modulation”. In a technical sense, the general descriptor for wind turbine amplitude modulation is incorrect. The correct term for the variation of the A-weighted level is modulation of the amplitude. The rate of the modulation of the dB(A) level occurs at the blade pass frequency, which is in the infrasound region. Turbines can exhibit amplitude modulation in the low frequency region. The differences between amplitude modulation and modulation of the amplitude occurring at an infrasound rate are discussed in the context for an environmental assessment of a wind farm with respect to permit conditions and a simplified method of assessment with respect to the Modulation Index.

Effect of violin sound exposure with pressure level variation to green mustard (Brassica juncea L.) growth and productivity

The objective of this research was to investigate effect of violin sound exposure to morphology characteristic and green mustard productivity. Experimental design used was completely randomized design with one treatment factor which was sound level. The sound level consisted of three levels, 70-75 dB, 80-85 dB and 90-95 dB. Total treatment combinations were 4 combinations. The object of this research was Tosokan variety of green mustard which are commonly available in market. The number of samples was considered as repetition. Result showed that violin sound at level 70-75 dB resulted the highest germination rate about 98% when compared to 80-85 dB and 90-95 dB levels. Violin music sound stimulation gave significant effect on plant morphological characteristics such as plant height, leaf area and plant and root length when compared to the control plants. Sound exposure at 70-75 dB sound level generally produced highest values for all morphological characteristics. Statistical analysis showed that sound exposure at 70-75 dB sound level produced highest productivity average weight, 22.5 grams per plant, while control plants produced an average weight only 15 grams per plant. The conclusion of this study was violin music stimulation resulted increased green mustard productivity, especially at low sound level.

Real-time cavitation control and monitoring for focused ultrasound blood-brain barrier opening via dB-based subject calibrated feedback controller

With proposed the dB-based subject calibrated feedback controller, we can achieve different levels of blood-brain barrier opening by adjusting the desired dB level.

Broadband mid-infrared supercontinuum generation in dispersion-engineered As2S3-silica nanospike waveguides pumped by 2.8 μm femtosecond laser

Broadband mid-infrared (IR) supercontinuum laser sources are essential for spectroscopy in the molecular fingerprint region. Here, we report generation of octave-spanning and coherent mid-IR supercontinua in As 2 S 3 -silica nanospike hybrid waveguides pumped by a custom-built 2.8 μm femtosecond fiber laser. The waveguides are formed by pressure-assisted melt-filling of molten As 2 S 3 into silica capillaries, allowing the dispersion and nonlinearity to be precisely tailored. Continuous coherent spectra spanning from 1.1 μm to 4.8 μm (30 dB level) are observed when the waveguide is designed so that 2.8 μm lies in the anomalous dispersion regime. Moreover, linearly tapered millimeter-scale As 2 S 3 -silica waveguides are fabricated and investigated for the first time, to the best of our knowledge, showing much broader supercontinua than uniform waveguides, with improved spectral coherence. The waveguides are demonstrated to be long-term stable and water-resistant due to the shielding of the As 2 S 3 by the fused silica sheath. They offer an alternative route to generating broadband mid-IR supercontinua, with applications in frequency metrology and molecular spectroscopy, especially in humid and aqueous environments.

An Efficient Conformal Stacked Antenna Array Design and 3D-Beamforming for UAV and Space Vehicle Communications.

In this paper, a new conformal array structure and beamforming technique are proposed to provide efficient communication performance for unmanned aerial vehicles (UAVs) and space vehicles. The proposed array is formed by conformally stacking cylindrical, conical, and concentric circular (CSC4) arrays which are all coaxially aligned with the same axis of the conformed body and with uniform interelement spacing. The array elements are then fed by a weighting vector that has an adaptive cosine tapered profile where the maximum amplitude coefficient is oriented with the mainlobe direction to improve the scanning capabilities of the array and increase the array effective area. In addition, for very large, conformed body structures such as space vehicles, a frontal mainlobe-oriented partial CSC4 array beamforming technique is proposed to efficiently utilize the large CSC4 structure, reduce the processing requirements for mainlobe electronic steering, and to provide very low sidelobe levels with reduced backlobe levels. Simulation results show that the proposed CSC4 design can provide wide scanning angles of up to angular range in the -direction with only change in the beamwidth, without increasing array size and with achievable sidelobe level of −45 dB and backlobe levels less than −10 dB.

A Wideband Differentially Fed Dual-Polarized Laminated Resonator Antenna

A wideband differentially fed dual-polarized laminated resonator antenna (LRA) is presented in this communication. Two differential pairs of L-probes are inserted into the LRA to excite degenerate dominant modes in LRA for dual-polarized operation. As a proof of concept, a prototype antenna centered at 5 GHz is designed, fabricated, and measured. The measured results agree well with the simulated ones. The experimental results show that the designed antenna achieves a wide bandwidth of 29% with differential reflection coefficient less than -10 dB. Moreover, it exhibits stable and symmetrical radiation patterns within the bandwidth. Benefiting from the differentially fed scheme, high port-to-port isolation better than 35 dB and low cross-polarization level less than -25 dB are achieved across the entire operating band. The proposed antenna is the first differentially fed dual-polarized LRA. Taking advantage of its planar structure integrated in the substrate, the proposed antenna is a promising candidate for future 5G wireless communications and antenna-in-package (AiP) solutions in millimeter-wave frequencies.

Tunable Mid-Infrared Dispersive Wave Generation of High-Efficiency and Broadband in a Suspended Thin-Film Lithium-Niobate-on-Insulator Waveguide

A suspended thin-film lithium-niobate-on-insulator nano-waveguide (NanoLN) is designed, and tunable mid-infrared dispersive wave generation of high-efficiency and broadband is numerically studied on this designed platform. By hollowing out the silicon dioxide substrate between the NanoLN core and silicon wafer, the loss issue induced by mode leaking at mid-infrared region is eliminated. The second zero-dispersion wavelength of the suspended NanoLN is tailored to locate around 2 μm wavelength, so that mode-locked fiber laser pump sources in this waveband can be conveniently leveraged to generate dispersive wave beyond 3 μm wavelength. We show that dispersive wave at 3.16 μm with high conversion efficiency up to 36.26% and bandwidth (at -10 dB level) of ~471 nm can be achieved at the pump pulse energy of 0.23 nJ. The central wavelength of the dispersive wave can be flexibly tuned up to 5 μm with a maximum -10 dB bandwidth of ~2 μm by lithographic control of the waveguide geometry, which is naturally at the expense of degraded conversion efficiency. Our results show the suspended NanoLN can provide a versatile chip-scale platform for cost-effective mid-infrared targetable, broadband, and coherent sources generation. Using fiber laser pump sources gives the advantages of compactness, free-maintenance, and long-term stability, which suit field applications.

Design Analysis and performance evaluation of 3D printed baffle path diverters in hydraulic noise suppressor

The pump in the hydraulic systems is the main source of noise in form of vibrations or pulsations while noise reduction is an important part of pump design still some ripples are produced by the pump termed as pulsations. Pulsations result in line vibrations which cause additional noise. How much ripple the pump produces cannot be changed, so other ways to an average of 50 dB(A) to 60 dB(A) level of noise is often considered to safe, although the noise levels resulting due to pulsations are seen to be in ranges as high as 130 t 0 150 dB(A) that result in hose and piping failures and also results in damage to components like seals and valves. Through the introduction of a compressible membrane in the path with additional baffles for muffling of the noise the proposed solution is in the form of hydraulic noise reducer that incorporates both the compressible membrane as well as the baffle path diverter. Objective of paper is carried out the performance evaluation of the hydraulic noise reducer with elastomer membrane for noise reduction mechanism in conjunction to baffle type path diverters to even out the fluid pulsations or ripple to minimal without much pressure drop across the device to achieve minim; pumping losses. The paper discusses the performance evaluation of the diverter. The has been tested to determine mass flow rate and pressure drop. Experimental has been manufactured and test has been conducted to evaluate reduction in noiselevelinwithandwithoutthe3-dprintedbaffle arrangement and comparison has been carried out.

Design of a Compact Planar Transmission Line for Miniaturized Rat-Race Coupler With Harmonics Suppression

This paper presents an elegant yet straightforward design procedure for a compact rat-race coupler (RRC) with an extended harmonic suppression. The coupler’s conventional λ/4 transmission lines (TLs) are replaced by a specialized TL that offers significant size reduction and harmonic elimination capabilities in the proposed approach. The design procedure is verified through the theoretical, circuit, and electromagnetic (EM) analyses, showing excellent agreement among different analyses and the measured results. The circuit and EM results show that the proposed TL replicates the same frequency behaviour of the conventional one at the design frequency of 1.8 GHz while enables harmonic suppression up to the 7th harmonic and a size reduction of 74%. According to the measured results, the RRC has a fractional bandwidth of 20%, with input insertion losses of around 0.2 dB and isolation level better than 35 dB. Furthermore, the total footprint of the proposed RRC is only 31.7 mm × 15.9 mm, corresponding to 0.28 λ × 0.14 λ, where λ is the guided wavelength at 1.8 GHz.

Mid-infrared supercontinuum generation in a low-loss germanium-on-silicon waveguide

We experimentally demonstrate supercontinuum (SC) generation in a germanium-on-silicon waveguide. This waveguide exhibits propagation loss between 1.2 dB/cm and 1.35 dB/cm in the 3.6 µm–4.5 µm spectral region for both transverse electric (TE) and transverse magnetic (TM) polarizations. By pumping the waveguide with ∼200 fs pulses at 4.6 µm wavelength, we generate a mid-infrared (IR) SC spanning nearly an octave from 3.39 µm to 6.02 µm at the −40 dB level. Through numerical analysis of the evolution of the SC, we attribute the current limit to further extension into the mid-IR mainly to free-carrier absorption.

Comparative Studies on the Effects of High Sound Levels on the Haematological Parameters and Antioxidant Levels of Wistar Albino Rats

This is a detailed experimental and comparative study evaluating the harmful effects of graded loud noise on hematological and antioxidant in Wistar albino rats. Wistar albino rats were divided into a control group (those kept away from the noise due to a generator set), groups 1 (exposed to varied, 85 - 105 db levels of loud noise from a generator) and groups 2 (exposed to less, 40 - 55 db levels of loud noise from generator set) and exposed to way off fumes from electrical generator sounds at different sound level for 8 hours each day for 28 days. The result indicated that activities and concentrations of the antioxidant enzymes: glutathione peroxidase, catalase and glutathione increased significantly (p < 0.05) when compared with the control group in group 1. There was also an increase in the concentrations of malondialdehyde and hematological parameters (RBC, WBC, PCV, hemoglobin, platelets) among the rats exposed to loud noise from a generator set in group 2, when compared to the control group.

An assessment of noise exposure and hearing health status among auto body workers in Kermanshah, Iran.

BACKGROUND:Unwanted sound is recognized as the most extensive source of contaminant in the workplace. Exposure to intense, continuous, and higher than 85 dB level noise can lead to noise-induced hearing loss. The aim of the present study was to determine the level of noise exposure and its impact on hearing health among auto body workers.MATERIALS AND METHODS:This descriptive-analytic study was conducted in 2020 to investigate the hearing health status of workers in auto body workshops. Sixty-one participants were randomly selected for audiometric testing. The equivalent sound level (Leq) of the workers was measured using a Casella CEL-320 noise dosimeter. Audiometric testing was performed using an AC40 audiometer. The mean hearing threshold levels (HTLs) of both ears were calculated for different frequencies. The results obtained were analyzed using SPSS v21.0 at a significance level of 95%.RESULTS:The participants had an average age of 35.5 ± 11.8 years and an average work experience of 16.5 ± 9.8 years. The mean Leq was 92.3 ± 4.7 dB. The mean HTLs for the right ear and left ear were 20, 15, 17.6, 19.2 dB, respectively with the right ear suffering more loss. A significant relationship was found between hearing loss in both ears (P < 0.001). The highest prevalence of hearing loss in both ears was observed at a frequency of 4 kHz. About 73.8% of the subjects had a normal HTL, 23.3% had mild hearing loss, and 3.3% had severe hearing loss. With increasing work experience, HTLs also increased significantly, particularly at 2–8 kHz.CONCLUSIONS:Chronic exposure to noise pollution threatens hearing health. Therefore, it is necessary to raise the level of awareness among workers in order to enable better hearing health protection and also to promote the use of hearing protection devices.

Numerical Simulation of the CS2-Filled Active Fiber With Flattened All-Normal Dispersion

A CS2-filled Er-doped fiber, which can provide high nonlinearity and gain, low and flat all-normal dispersion profile, low loss and single-mode operation in the wavelength range of 1500-2500 nm, is proposed and analyzed by numerical simulation. When the 1900-nm 0.1-ps initial pulse with a peak power of 30 kW is injected into the active fiber, the generated supercontinuum (SC) spectrum has a double-hump structure in the 1550-nm window and covers about 800-nm wavelength range spanning from 1400 to 2200 nm at -20 dB level. Furthermore, the 1550-nm pulse can be obtained synchronously with the 1900-nm initial pulse when the amplified pulse with a temporal double-peak shape is passed through a band-pass filter with its center wavelength at 1550 nm.

Effects of Different dB Sound Levels on The Plant Growth, Nutrient Elements Uptake and Essential Oil Yield of Mentha piperita

Common environmental stimuli detected by living things include light, temperature and a variety of chemical signals some of which are closely related to physical-mechanical stimuli. Sound is one of the physical signals affecting plant life and the mechanism whereby plants perceive and react to sound stimuli is not currently well known. Sound waves and therefore sonication, are a form of abiotic stress for plants. Mint (Mentha piperita) is an important crop that produces volatile oils which are used extensively in pharmaceutical and nutraceutical products. Mint plants (10-week-old) cv. Granada was planted in four different sound chambers and subjected to different sound conditions. The experiment was carried out for 30 days. In each chamber, spe- cific sound areas were formed by sending signals with different dB levels (95, 100 and 105 decibel (db)) together with the chosen reference value was 1000 Hertz (Hz). Plant height, stem diameter, number of leaves, fresh and dry root weights and fresh and dry foliage weights were examined to evaluate the effects of different applications. In addition to the morphological data, the plant nutrient elements and essential oil yields were analyzed. Based on the results, plant height varied between 20 and 43 cm and the essential oil yield ranged between 0.76 and 2.17 %. In our study, sound applications at different SPLs affected the growth and nutrient element intake in mint plants negatively; however, at 95 dB, essential oil yields were affected positively.

Noise reduction performance of a low energy façade-integrated mechanical ventilator

Acoustic comfort and indoor air quality are essential for the health and wellbeing of the occupants of the building. Thus, the façade must guarantee enough sound insulation and ventilation conditions. However, these aspects conflict because opening windows or using ventilation openings reduces the sound insulation of the envelope and allows the exterior noise entrance. To limit noise transmission into the building, ventilators use passive, active or hybrid noise control techniques. This work addresses the noise reduction performance of a mechanical ventilator for façades, evaluating the effect of different options of passive noise control strategies in the sound insulation of the proposed ventilator. In addition, the air change rate and energy consumption of the ventilator were also investigated. Three prototypes were fabricated and tested at an acoustic chamber, along with ventilation tests carried out in a room equipped with a blower door. CFD simulations were used to enhance the aeraulic geometry of the prototypes, prior to its fabrication. The acoustic experiments showed Dn,e,w values up to 55 dB and noise emission levels lower than 25 dB(A). The use of resistive sound absorbers proved to be more effective in mitigating noise than reactive absorbers, over the entire frequency range. The ventilation tests revealed air change rates of 3.7 h−1 at 50 Pa, while the ventilator’s annual energy consumption was 17.52 kWh. The results highlight the proposed device as a viable alternative for decentralised mechanical ventilation, capable of ensuring noise protection and satisfactory ventilation rates, under a sustainable perspective of minimum energy demand.

Wideband planar substrate integrated waveguide cavity-backed amended dumbbell–shaped slot antenna

In this article, a novel design of wideband planar substrate integrated waveguide (SIW) cavity-backed antenna (CBA) consisting of amended dumbbell-shaped slot and two cylindrical metal vias is developed. The simple dumbbell slot perturbs the current distribution of the both TE110 and TE210 cavity modes and generates the three independent modes (half-TE110, even-TE210, and odd-TE210) at distinct frequencies. When the two metallic vias are loaded at the middle portion of the SIW cavity and due to simultaneous excitation, two hybrid modes come close to each other. These hybrid modes serve to widen the fractional bandwidth upto 17.36%. The bandwidth is further extended by modifying the simple dumbbell slot. A specimen is fabricated to validate the amended dumbbell-shaped slot experimentally. The proposed antenna offers two resonances and exhibits a fractional bandwidth of 22.4% (2.25 GHz). The antenna renders measured peak gains of 6.45 dBi and 6.2 dBi at 9.2 GHz and 10.6 GHz, respectively. Furthermore, the proposed design shows the front-to-back-ratio 14 dB and cross-polar levels –28 dB and –37 dB maximum at both the measured frequencies. Those amicable characteristics, e.g., low-profile, low cross-polarization levels, unidirectional radiation pattern, and wide impedance bandwidth, make the proposed antenna appropriate for X-band applications.