11,060 research outputs found
A novel design for an RF MEMS resistive switch on PCB substrate
No full textCopyright @ 2008 Stimulation Action on MEM
On the investigation of a reliable actuation control method for ohmic RF MEMS switches
No full textThis is a post-print version of the article. The official published version can be accessed from the link below - Copyright @ 2011 ElsevierEfficient control of RF MEMS switches is a very important issue as it is correlated to main failure mechanisms/modes such as the impact force and bouncing phenomena, which degrade their dynamic performance and longevity. This paper presents the control of specific ohmic RF MEMS switches under three different actuation modes, a tailored pulse optimization method based on Taguchi's technique (voltage mode actuation control), resistive damping (charge mode actuation control) and finally the Hybrid actuation mode, which is a combination of the tailored pulse, the resistive damping and Taguchi's optimization technique. Coventorware simulations indicate that under optimized Tailored pulse and Hybrid actuation modes, the impact velocity is reduced by around 90%, the initial impact force by around 75% and the maximum bouncing displacement during the release phase by around 95%, while the switching speed is increased by around 20% compared with the step pulse control mode. The resistive damping control mode is inappropriate for this type of switch and only partial improvement during the pull-down phase has been achieved. Finally, a comparison between Hybrid and optimized tailored modes shows that Hybrid actuation mode excels with better switching characteristics and most importantly offers immunity to manufacturing and operation tolerances
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
On the design of an Ohmic RF MEMS switch for reconfigurable microstrip antenna applications
No full textThis paper presents the analysis, design and simulation of a direct contact (dc) RF MEMS switch specified for reconfigurable microstrip array antennas. The proposed switch is indented to be built on PCB via a monolithic technology together with the antenna patches. The proposed switch will be used to allow antenna beamforming in the operating frequency range between 2GHz and 4GHz. This application requires a great number of these switches to be integrated with an array of microstrip patch elements. The proposed switch fulfills the switching characteristics as concerns the five requirements (loss, linearity, voltage/power handling, small size/power consumption, temperature), following a relatively simple design, which ensures reliability, robustness and high fabrication yiel
Design and fabrication of RF MEMS switch by CMOS process
No full textThis work investigates the fabrication of a RF (ratio frequency) MEMS (micro elector mechanical system) switch using the standard 0.35 μm 2P4M (double polysilicon four metal) CMOS (complementary metal oxide semiconductor) process and the post-process. The switch is a capacitive type, which is actuated by an electrostatic force. The structure of the switch consists of a CPW (coplanar waveguides) transmission lines and a suspended membrane. The CPW lines and the membrane are the metal layers of the CMOS process. The main advantage of the RF switch is only needed a simple post-process, which is compatible with the CMOS process. The post-process uses an etchant, silox vapox Ⅲ, to etch oxide layer to release the suspended membrane and springs. Experiment results show that the pull-in voltage of the switch is about 17 V. The insertion loss and return loss in the range of 10 to 40 GHz are -2.5 dB and -13 dB, respectively.補正完畢E
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Growth optimisation and laser processing of thin film phosphors for electroluminescent displays
No full textThis thesis presents results of a study of ZnS:Mn thin film phosphors used in Thin Film ELectroluminescent (TFEL) and Laterally Emitting TFEL (LETFEL) devices, examining techniques for phosphor growth optimisation and post deposition processing in order to strengthen development of novel TFEL devices. To achieve this, thin films of phosphor were deposited using RF magnetron sputtering to investigate the use of co-sputtering in order to optimise dopant concentration. 800 nm films of ZnS:Mn were simultaneously co-sputtered from ZnS and ZnS:Mn (1 wt.%) solid targets. The thin films were deposited at different manganese concentrations by varying the relative RF power applied to each target. The films were deposited directly onto 100 mm diameter (100) n-type silicon substrates, or onto a layer of 300 nm of Y2O3 to fabricate electroluminescent test devices. Luminescence from the phosphor films was characterised via photoluminescent excitation using a 337 nm pulsed N2 laser, with the photoluminescence (PL) optimum obtained at 0.38 ZnS:Mn power ratio. Electroluminescence (EL) from TFEL devices were excited by applying a sinusoidal waveform voltage at a frequency of 1 kHz with maximum luminance obtained at 0.36 ZnS:Mn power ratio
RF bias to suppress post-oxidation of mu c-Si:H films deposited by inductively-coupled plasma using a planar RF resonant antenna
No full textOne challenge for microcrystalline silicon (mu c-Si:H) deposition is to achieve high deposition rates while maintaining high quality films. In this work, an inductively-coupled plasma (ICP) is used to deposit mu c-Si:H on glass substrates by means of a novel planar resonant antenna at 13.56 MHz. No particle formation occurs in the low pressure (5 Pa) plasma, but the films suffer post-oxidation. By embedding a 5 MHz RF-biased substrate, films deposited simultaneously with and without RF bias are compared. It is shown that large area, low pressure (5 Pa), particle-free ICP deposition at 1 nm/s of mu c-Si:H films can be obtained without post-oxidation by means of a planar resonant antenna, provided that RF substrate bias is included for independent control of the ion energy. (C) 2017 Elsevier Ltd. All rights reserved.SP
The role of biofilms in otolaryngologic infections
No full textPURPOSE OF REVIEW: Bacterial biofilms have recently been shown to be important in diseases of the head and neck. Because the concept of biofilms is novel to most practitioners, it is important to gain a basic understanding of biofilms and to recognize that strategies developed to treat planktonic bacteria are ineffective against bacteria in a biofilm. RECENT FINDINGS: Bacteria preferentially exist in complex, surface-attached organizations known as biofilms. Bacteria in biofilms express a different set of genes than their planktonic counterparts and have markedly different phenotypes. Biofilm bacteria communicate with each other, and have mechanisms to diffuse nutrients and dispose of waste. Biofilms provide bacteria with distinct advantages, including antimicrobial resistance and protection from host defenses. Thus, bacteria exist in a far more complex fashion than previously thought and can best be thought of as "self-assembling multicellular communities." Although a focus on the planktonic form of bacteria has been useful in understanding acute infections, chronic infections are much better understood as biofilm illnesses. Biofilms have been shown to be involved in chronic otitis media, chronic tonsillitis, cholesteatoma, and device-associated infections. SUMMARY: Now that basic research has demonstrated that the vast majority of bacteria exist in biofilms, the biofilm concept of disease is beginning to spread throughout the clinical world. Understanding that many of the infections that affect structures of the head and neck are actually biofilm related is fundamental to developing rational strategies for treatment and prevention
A micromachined zipping variable capacitor
No full textMicro-electro-mechanical systems (MEMS) have become ubiquitous in recent years and are found in a wide range of consumer products. At present, MEMS technology for radio-frequency (RF) applications is maturing steadily, and significant improvements have been demonstrated over solid-state components.A wide range of RF MEMS varactors have been fabricated in the last fifteen years. Despite demonstrating tuning ranges and quality factors that far surpass solid-state varactors, certain challenges remain. Firstly, it is difficult to scale up capacitance values while preserving a small device footprint. Secondly, many highly-tunable MEMS varactors include complex designs or process flows.In this dissertation, a new micromachined zipping variable capacitor suitable for application at 0.1 to 5 GHz is reported. The varactor features a tapered cantilever that zips incrementally onto a dielectric surface when actuated electrostatically by a pulldown electrode. Shaping the cantilever using a width function allows stable actuation and continuous capacitance tuning. Compared to existing MEMS varactors, this device has a simple design that can be implemented using a straightforward process flow. In addition, the zipping varactor is particularly suited for incorporating a highpermittivity dielectric, allowing the capacitance values and tuning range to be scaled up. This is important for portable consumer electronics where a small device footprint is attractive.Three different modelling approaches have been developed for zipping varactor design. A repeatable fabrication process has also been developed for varactors with a silicon dioxide dielectric. In proof-of-concept devices, the highest continuous tuning range is 400% (24 to 121 fF) and the measured quality factors are 123 and 69 (0.1 and 0.7 pF capacitance, respectively) at 2 GHz. The varactors have a compact design and fit within an area of 500 by 100 µm
Post-process local porous silicon integration method for RF application
No full textThe interest of porous silicon (PSi) for RF applications has been widely demonstrated in many previous works. In most of them, PSi is integrated into the substrate during its fabrication (PRE-PSi) prior to a standard process (e.g. CMOS). Such PRE-PSi technology has major incompatibilities with foundry-level processes (mechanical instability during annealing, warp, bow, etc.). This paper presents an innovative technique of post device fabrication integration of porous silicon (POST-PSi) with the substrate to overcome these incompatibilities. Furthermore, the frontside is not involved in porous layer growth and therefore the integrity of the RF circuitry is not impacted by the POST-PSi process. Additionally, the novel technique allows for local porosification, enabling local pockets of high-quality RF PSisubstrate, beneath the RF devices of interest, to be embedded within a structurally stable silicon crystalline bulk. Similar to PRE-PSi, the POST-PSi substrates are produced by anodization starting from the most widespread highly doped milliohmcentimeter Si wafers. A comparison of the RF performances with various advanced trap-rich (TR) silicon-on-insulator (SOI) and PRE-PSi substrates are presented. In addition to its compatibility with standard microfabrication processes and stable final structure, POST-PSi provides characteristics of low losses, high isolation and very high linearity, unmatched by any other siliconbased substrate
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