3,487 research outputs found
A novel design for an RF MEMS resistive switch on PCB substrate
No full textCopyright @ 2008 Stimulation Action on MEM
CuInSe2/CdS thin film solar cells by r.f. sputtering
No full textCuInSe2/CdS thin film solar cells were prepared by rf sputtering on an Al-covered glass substrate. The Al layer, deposited using an electron gun, is crystalline with an average grain size of 100μ. The Mo bottom contact, the CuInSe2 and CdS films were sputtered in sequence in the same sputtering chamber without breaking the vacuum. The CdS film deposited at substrate temperature of 200°C has a resistivity of ≈1 Ωcm due to small amount of H added during the deposition which increases the S vacancies in the film. CuInSe2/CdS sputtered solar cells have an efficiency of ≈4-5%. A higher efficiency can be obtained by improving the structural and electro-optical properties of CuInSe2 thin films
Zinc Cadmium Sulphide (Zn0.15Cd0.85S) thin-films by rf sputtering in an Ar-H2 atmosphere
No full textFilms of the title compound were prepared by radio-frequency sputtering from a (Zn,Cd)S target in pure Ar and Ar-H atoms. At a substrate temperature of 200°, Zn0.15Cd0.85S films grown in an Ar-H atmosphere exhibit a resistivity of ≈3 orders of magnitude lower than that of films grown in pure Ar. This is attributed to the formation of S vacancies by H reaction with a small number of the S atoms during the film deposition. The film grown in the Ar-H atmosphere exhibits a transparency of almost 100% when corrected for reflection loss for wavelengths longer than that of the absorption edge; the forbidden gap obtained from the absorption spectrum is ≈ 2.53 eV. The films prepared by sputtering in an Ar-H atmosphere are suitable for windows in CuInSe2/(Zn,Cd)S solar cells
Large grain (112) oriented CuInSe2 thin films grown by R.F. sputtering
No full text(112) oriented CuInSe2 thin films with grain size larger than 30 microns have been grown by magnetron RF sputtering on a glass substrate covered by a crystalline thin metalic layer obtained by a novel method. The CuInSe2 targets have been prepared by melting Cu, In, and Se in a high-pressure furnace using B2O3 as an encapsulant. The structural and electro-optical properties of CuInSe2 films have been found to depend on substrate temperature, sputtering power, substrate bias, target stoichiometry, and deposition rate. CuInSe2/CdS solar cells prepared by flash-evaporating CdS on top of RF-sputtered CuInSe2 films have so far exhibited high photocurrents, close to 40 mA/cm2 at 100-mW/cm2 illumination, and a maximum efficiency close to 4 percent
Automated detection of prostate cancer using wavelet transform features of ultrasound RF time series
No full textThe aim of this research was to investigate the performance of wavelet transform based features of ultrasound radiofrequency (RF) time series for automated detection of prostate cancer tumors in transrectal ultrasound images. Sequential frames of RF echo signals from 35 extracted prostate specimens were recorded in parallel planes, while the ultrasound probe and the tissue were fixed in position in each imaging plane. The sequence of RF echo signal samples corresponding to a particular spot in tissue imaging plane constitutes one RF time series. Each region of interest (ROI) of ultrasound image was represented by three groups of features of its time series, namely, wavelet, spectral and fractal features. Wavelet transform approximation and detail sequences of each ROI were averaged and used as wavelet features. The average value of the normalized spectrum in four quarters of the frequency range along with the intercept and slope of a regression line fitted to the values of the spectrum versus normalized frequency plot formed six spectral features. Fractal dimension (FD) of the RF time series were computed based on the Higuchi's approach. A support vector machine (SVM) classifier was used to classify the ROIs. The results indicate that combining wavelet coefficient based features with previously proposed spectral and fractal features of RF time series data would increase the area under ROC curve from 93.1% to 95.0%, respectively. Furthermore, the accuracy, sensitivity, and specificity increases to 91.7%, 86.6%, and 94.7%, from 85.7%, 85.2%, and 86.1%, respectively, using only spectral and fractal features. [ABSTRACT FROM AUTHOR]Peer reviewedFinal article publishe
An RF-Powered DLL-Based 2.4-GHz Transmitter for Autonomous Wireless Sensor Nodes
No full textThis paper presents the system and circuit design of a compact radio frequency (RF)-powered 2.4-GHz CMOS transmitter (TX) to be used for autonomous wireless sensor nodes (WSNs). The proposed TX utilizes the received dedicated RF signal for both energy harvesting as well as frequency synthesis. A TX RF carrier is derived from the received RF signal by means of a delay locked loop and XOR-based frequency multiplier. The 50-Ω load is subsequently driven by a tuned switching RF power amplifier (PA) with 25% duty cycle input for high global efficiency. The design is fabricated in 40-nm CMOS technology and occupies a die area of 0.16 mm2. Experimental results show a rectifier with 36.83% peak efficiency and power management circuit with 120-nA current consumption that enables a low start-up power of -18.4 dBm. The TX outputs a continuous 2.44-GHz RF signal at -2.57 dBm with 36.5% PA drain efficiency and 23.9% global efficiency from a 915-MHz RF input and supports ON-OFF keying modulation.Accepted Author ManuscriptBio-Electronic
A Wideband 2x13-bit All-Digital I/Q RF-DAC
No full textThis paper presents a wideband 2 13-bit in-phase/quadrature-phase (I/Q) RF digital-to-analog converter-based all-digital modulator realized in 65-nm CMOS. The isolation between I and Q paths is guaranteed employing 25% duty-cycle differential quadrature clocks. With a 1.3-V supply and an on-chip power combiner, the digital I/Q transmitter provides more than 21-dBm RF output power within a frequency range of 1.36–2.51 GHz. The peak RF output power, overall system, and drain efficiencies of the modulator are 22.8 dBm, 34%, and 42%, respectively. The measured static noise floor is below 160 dBc/Hz. The digital I/Q RF modulator demonstrates an IQ image rejection and local oscillator leakage of 65 and 68 dBc, respectively. It could be linearized using either of the two digital predistortion (DPD) approaches: a memoryless polynomial or a lookup table. Its linearity is examined using single-carrier 4/16/64/256/1024 quadrature amplitude modulation (QAM), as well as multi-carrier 256-QAM orthogonal frequency-division multiplexing baseband signals while their related modulation bandwidth can be as high as 154 MHz. Employing DPD improves the third-order intermodulation product (IM3) by more than 25 dB, while the measured error vector magnitude for a “single-carrier 22-MHz 64-QAM” signal is better than 28 dB.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Bracelet+: Harvesting the Leaked RF Energy in VLC with Wearable Bracelet Antenna
No full textVisible Light Communication (VLC) is widely considered a promising technology for the coming 6G networks. Recent studies show that a VLC transmitter not only emits visible light signals but also leaks RF signals during the transmission. In this work, we devote effort to harvesting the free leaked RF energy from VLC transmissions. We observe that the surrounding objects could help a coil antenna harvest significantly more RF energy. Based on this observation, we propose our system Bracelet+, which involves the human body in the harvesting system to increase the harvested power. After careful analysis of the influence of the human body on the harvested power, we prototype the coil antenna as a bracelet that achieves both high harvested power and convenience for wearing. The average power of the RF energy harvested by our design is 10 larger than that of the conventional coil antenna, without causing any interference to the communication of VLC systems. The harvested power can reach up to micro-watts in our tested scenarios. Such a micro-watt level of harvested energy has the potential to power up ultra-low-power sensors such as temperature sensors and glucose sensors.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Embedded System
Expression and modulation of an NADPH oxidase in mammalian astrocytes
No full textAmyloid β peptides generate oxidative stress in hippocampal astrocytes through a mechanism sensitive to inhibitors of the NADPH oxidase [diphenylene iodonium (DPI) and apocynin]. Seeking evidence for the expression and function of the enzyme in primary hippocampal astrocytes, we confirmed the expression of the subunits of the phagocyte NADPH oxidase by Western blot analysis and by immunofluorescence and coexpression with the astrocyte-specific marker glial fibrillary acidic protein both in cultures and in vivo. Functional assays using lucigenin luminescence, dihydroethidine, or dicarboxyfluorescein fluorescence to measure the production of reactive oxygen species (ROS) demonstrated DPI and apocynin-sensitive ROS generation in response to the phorbol ester PMA and to raised [Ca2+]c after application of ionomycin or P2u receptor activation. Stimulation by PMA but not Ca2+ was inhibited by the protein kinase C (PKC) inhibitors staurosporine and hispidin. Responses were absent in transgenic mice lacking gp91phox. Expression of gp91phox and p67phox was increased in reactive astrocytes, which showed increased rates of both resting and stimulated ROS generation. NADPH oxidase activity was modulated by intracellular pH, suppressed by intracellular alkalinization, and enhanced by acidification. The protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone suppressed basal ROS generation but markedly increased PMA-stimulated ROS generation. This was independent of mitochondrial ROS production, because it was unaffected by mitochondrial depolarization with rotenone and oligomycin. Thus, the NADPH oxidase is expressed in astrocytes and is functional, activated by PKC and intracellular calcium, modulated by pHi, and upregulated by astrocyte activation. The astrocytic NADPH oxidase is likely to play important roles in CNS physiology and pathology
Single Channel RF Signal Recovery for Nyquist Folding Receiver
No full textThis paper presents a method for exploiting wideband spectral information of real-valued radio frequency (RF) signals using the Nyquist Folding Receiver architecture. A new system model based on a symmetric modulation matrix is introduced so that the frequency band of the real input signals can be estimated without in-phase and quadrature reception and processing. To recover the original frequency of the input RF signal, we use the parameter-free sparse learning via iterative minimization (SLIM) method. Finally, the proposed model and the success of the recovery algorithm are demonstrated with data collected from an experimental testbed.Accepted Author ManuscriptMicrowave Sensing, Signals & System
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