A solution to the charging problems in capacitive micromachined ultrasonic transducers

We report on a capacitive micromachined ultrasonic transducer (CMUT) featuring isolation posts (PostCMUT) as a solution to the charging problems caused by device fabrication and operation. This design improves the device reliability. The PostCMUTs were fabricated using a newly developed process based on the wafer-bonding technique. Paired tests showed the superior reliability characteristics of the PostCMUT design compared to those of conventional CMUT designs. No deleterious effect of the new design was seen in preliminary ultrasonic tests or in process yield. PostCMUTs, a design that serves as a solution to the aforementioned reliability problem, constitutes a major contribution to CMUT commercialization.     

Analysis of coherence,strain, thermal vibration and preferred orientation in carbons by X-Ray diffraction

In ideal graphitic layers the inter-atomic (or inter-unit cell) distances l and the number of atoms (or unit cells) n(l) at a distance from any atom (or unit cell) chosen as origin may be represented by sets l and n(l) which define the structure. In the defective lattice theory presented here the structure of diffusely scattering (the so-called amorphous) carbons are likewise defined by the two sets, however n(l)'s are modified by a probability (coherence probability) function g(l) and l's are modified for dispersion (strain effects). It is shown that the coherence probability function can be determined from the atomic radial distribution curves without a priori knowledge of distortion and temperature diffuse scattering. Analytical expressions have been developed that permit analysis of distortion and temperature diffuse scattering from the observed profiles of the diffuse peaks and from the atomic radial distribution functions. In analyzing the distortion, Gauss', Gauchy's and Laplace's distributions are considered. It is demonstrated that distortion could be responsible for the diffuseness of the diffraction profiles of carbons to a greater extent than the coherence probability, the so-called domain or particle size effect. It is also shown that the integrated intensities, I(φ), of the (00l) reflections of anisotropic, e.g. pyrolytic, carbons are related to the angle φ that the diffraction vector makes with the pole of the sample by I(φ) = K exp (?p²sin²φ) in which K is the proportionality constant and p is the characteristic parameter of the sample. The equation has a reasonably sound physical basis and has been found to be applicable to samples having a wide range of preferred orientations.     

An Accurate Indoor RSSI Localization Algorithm Based on Active RFID System with Reference Tags

Radio frequency identification technologies are popular since their cost is very low and its data transmission based upon radio-wave communications. Where, the objects that are attached to tags are located using the reference tags. However, RSSI information suffers from the multipath propagation and anisotropic interference. So, the localization accuracy will be affected severely. Also, the multipath-propagation increases whenever the reference-tags increase, and so does for the cost, and signal interference. This paper presents a boundary virtual reference label algorithm for improving the indoor-efficiency by inserting some virtual reference tags on the boundary with establishing a linear regression model that eliminates unwanted tag information from the estimation procedure. The Results show that the localisation precision of the proposed approach has significantly increased, at least 78% without adding extra reference tags or radio frequency interference which represents a significant improvement over other algorithms .

     

Capacitive Micromachined Ultrasonic Transducers: Theory and Technology

Capacitive micromachined ultrasonic transducers (CMUTs), introduced about a decade ago, have been shown to be a good alternative to conventional piezoelectric transducers in various aspects, such as sensitivity, transduction efficiency, and bandwidth. In this paper, we discuss the principles of capacitive transducer operation that underlie these aspects. Many of the key features of capacitive ultrasonic transducers are enabled with micromachining technology. Micromachining allows us to miniaturize device dimensions and produce capacitive transducers that perform comparably to their piezoelectric counterparts. The fabrication process is described briefly, and the performance of the CMUT transducers is evaluated by demonstrating characterization results. It is shown that the transduction efficiency as defined by the electromechanical coupling coefficient can be close to unity with proper device design and operating voltage. It is also shown that CMUTs provide large bandwidth (123% fractional bandwidth) in immersion applications which translate into high temporal and axial resolution. Finally, the feasibility of using CMUTs is demonstrated by showing imaging examples in air and in immersion.     

Surface properties of impregnated and varnished Scots pine wood after accelerated weathering

In this study, the effect of accelerated weathering on the surface properties of Scots pine specimens impregnated with wolmanit‐CB, tanalith‐E, and adolit‐KD5 and coated with synthetic and polyurethane varnishes was investigated by measuring surface hardness, glossiness, and colour. Results showed that weathering caused an increase in the hardness of impregnated and varnished specimens, while it caused a decrease in the glossiness of specimens. Surfaces became rougher and darker after weathering in comparison with the initial surfaces of wood specimens. Positive values of the chromatic coordinates indicated that the wood surfaces changed from their original colour to a reddish and yellowish colour. The highest colour change was detected in the specimens coated with polyurethane varnish alone. Both copper‐based wood preservative treatment and varnish coating improved the surface properties of specimens in comparison with the surface properties observed on specimens coated with varnish alone.     

Design and implementation of a teleconferencing system using improved HEVC coding

Teleconferencing has become an indispensable element in any business system, because it offers the opportunity for collaborators to participate in a virtual group while remaining in divergent regions. Teleconferencing also increases productivity, minimizes travel expenses and saves travel time. This paper presents a reliable Teleconference system that utilizes an improved high-efficiency video codec (HEVC) H.265 technology with congestion control. The improvement is based on CU size decision and entropy coding, which provides an adequate approach to enhance the real-time video/IP technology in terms of improved video quality and increased compression ratio compared to the previous codec (H.264) and original HEVC.     

An early split and skip algorithm for fast intra CU selection in HEVC

The rapid development and increase of multimedia applications, as well as the demand for higher video-quality services at restricted resources such as storage capacity, transmission bandwidth and power consumption, has brought the urgent need for more efficient video compression techniques. The new video coding standard high efficiency video coding (HEVC) has a significant superiority over its predecessor advanced video coding (AVC). HEVC is reported to halve the bit rate with the same visual quality, or a better quality with the same bit rate when compared with AVC. Beside other improvements, HEVC significantly gets its power from the use of dynamic hierarchical quad-tree structure by partitioning the frames into smaller regions called coding units (CU), by means of a rate–distortion optimization process. However, this improvement yields to a dramatic increase of high computational complexity and increased encoding time, which primarily restricts its adaptation in real-time applications. In this paper, we proposed an early CU determination algorithm for fast encoder realization to reduce the encoding time which is the most important part of the standard standing for development. The experimental results show that the proposed algorithm has approximately 45 % encoding time saving with a 4.6 % bit-rate increment, on average.     

Speech enhancement based on undecimated wavelet packet-perceptual filterbanks and MMSE–STSA estimation in various noise environments

In this paper, we proposed a new speech enhancement system, which integrates a perceptual filterbank and minimum mean square error–short time spectral amplitude (MMSE–STSA) estimation, modified according to speech presence uncertainty. The perceptual filterbank was designed by adjusting undecimated wavelet packet decomposition (UWPD) tree, according to critical bands of psycho-acoustic model of human auditory system. The MMSE–STSA estimation (modified according to speech presence uncertainty) was used for estimation of speech in undecimated wavelet packet domain. The perceptual filterbank provides a good auditory representation (sufficient frequency resolution), good perceptual quality of speech and low computational load. The MMSE–STSA estimator is based on a priori SNR estimation. A priori SNR estimation, which is a key parameter in MMSE–STSA estimator, was performed by using “decision directed method.” The “decision directed method” provides a trade off between noise reduction and signal distortion when correctly tuned. The experiments were conducted for various noise types. The results of proposed method were compared with those of other popular methods, Wiener estimation and MMSE–log spectral amplitude (MMSE–LSA) estimation in frequency domain. To test the performance of the proposed speech enhancement system, three objective quality measurement tests (SNR, segSNR and Itakura–Saito distance (ISd)) were conducted for various noise types and SNRs. Experimental results and objective quality measurement test results proved the performance of proposed speech enhancement system. The proposed speech enhancement system provided sufficient noise reduction and good intelligibility and perceptual quality, without causing considerable signal distortion and musical background noise.     

Integration of 2D CMUT arrays with front-end electronics for volumetric ultrasound imaging

For three-dimensional (3D) ultrasound imaging, connecting elements of a two-dimensional (2D) transducer array to the imaging system's front-end electronics is a challenge because of the large number of array elements and the small element size. To compactly connect the transducer array with electronics, we flip-chip bond a 2D 16 x 16-element capacitive micromachined ultrasonic transducer (CMUT) array to a custom-designed integrated circuit (IC). Through-wafer interconnects are used to connect the CMUT elements on the top side of the array with flip-chip bond pads on the back side. The IC provides a 25-V pulser and a transimpedance preamplifier to each element of the array. For each of three characterized devices, the element yield is excellent (99 to 100% of the elements are functional). Center frequencies range from 2.6 MHz to 5.1 MHz. For pulse echo operation, the average - 6-dB fractional bandwidth is as high as 125%. Transmit pressures normalized to the face of the transducer are as high as 339 kPa and input-referred receiver noise is typically 1.2 to 2.1 mPa/pHz. The flip-chip bonded devices were used to acquire 3D synthetic aperture images of a wire-target phantom. Combining the transducer array and IC, as shown in this paper, allows for better utilization of large arrays, improves receive sensitivity, and may lead to new imaging techniques that depend on transducer arrays that are closely coupled to IC electronics.     

Drinking water denitrification by a membrane bio-reactor

Drinking water denitrification performance of a bench scale membrane bio-reactor (MBR) was investigated as function of hydraulic and biological parameters. The reactor was a stirred tank and operated both in batch and continuous mode. The mixed denitrifying culture used in the batch mode tests was derived from the mixed liquor of a wastewater treatment plant in Erzincan province in Turkey. But the culture used in the continuous mode tests was that obtained from the batch mode tests at the end of the denitrification process. The nitrate contaminated water treated was separated from the mixed liquor suspended solids (MLSS) containing active mixed denitrifying culture and other organic substances by a membrane of 0.2 microm average pore diameter. The results indicated that the use of a membrane module eliminated the need for additional post treatment processes for the removal of MLSS from the product water. Concentration of nitrite and that of MLSS in the membrane effluent was below the detectable limits. Optimum carbon to nitrogen (C/N) ratio was found to be 2.2 in batch mode tests. Depending on the process conditions, it was possible to obtain denitrification capacities based on the reactor effluent and membrane effluent up to 0.18kgm(-3)day(-1) and 2.44 kg m(-2) day2(-1) NO(3-)-N, respectively. The variation of the removal capacity with reactor dilution rate and membrane permeate flux was the same for two different degrees of [MLSS]0/[NO3-N]0 (mass) ratios of 25.15 and 49.33. The present MBR was able to produce a drinking water with NO(3-)-N concentration of less than 4 ppm from a water with NO3-N contamination level of 367 ppm equivalent to a NO(3-)-N load of 0.310 kgm(-3) day(-1). The results showed that MBR system used was able to offer NO(3-)-N removals of up to 98.5%. It was found that the membrane limiting permeate flux increased with increasing MLSS concentration.