DESIGN OF TEMPERATURE CONTROLLED QUARTZ CRYSTAL MICROBALANCE SYSTEM

In this study, the dual modulated quartz crystal microbalance (QCM) with heating and cooling control has been developed for the quantitative determination of biological molecules, as a biosensor. On the other hand, since, the Sauerbrey formula is misprinted in some publications, the correct form of formula is also discussed. The proposed QCM biosensor has three main parts, which are the oscillator circuit, temperature control circuit, and the differential frequency measurement unit. Colpitts oscillators with the buffer amplifier, microcontroller (PIC16F877) for the temperature control circuit and a peltier element were used for heating and cooling inside the developed system. Differential frequency measurement is a known technique to compensate environmental effects causing instability of crystals. For this reason, one of the crystals is implemented with oscillatory circuits, i.e., the detector; the other one is used as the reference. The designed system was tested between 8°C and 50°C and frequency shift versus temperature is observed at 0.5 ppm/°C over a given temperature range.     

Experimental Investigation of the Properties of Lime-Based Plaster-Containing PCM for Enhancing the Heat-Storage Capacity of Building Envelopes

Experimental analysis of a wide range of properties of a lightweight plaster which should enhance the heat-storage capacity of building envelopes is presented. The basic physical characteristics, namely, the bulk density, matrix density, total open porosity, and pore-size distribution are measured at first. Then, the compressive strength is determined for an assessment of mechanical performance of the plaster. The thermal conductivity and thermal diffusivity are studied using an impulse technique. Differential scanning calorimetry measurements are performed as well, in order to identify the temperature range and latent heat of the phase change and to determine the specific heat capacity as a function of temperature. Durability properties are assessed using the measurement of the water absorption coefficient and sorption and desorption isotherms. The experimental results indicate a good capability of the designed plaster to moderate effectively the interior climate of buildings.     

Structural features of a polypeptide carrier promoting secretion of a β-lactamase fusion protein in yeast

Escherichia coli β-lactamase was secreted into the culture medium of Saccharomyces cerevisiae in biologically active form, when fused to the C-terminus of the hsp150δ-carrier. The hsp150δ-carrier is an N-terminal fragment of the yeast hsp150 protein, having a signal peptide and consisting mostly of a 19 amino acid peptide repeated 11 times in tandem. Here we expressed the hsp150δ-carrier fragment alone in S. cerevisiae. Apparently due to a positional effect of the gene insertion, large amounts of the hsp150δ-carrier were synthesized. About half of the de novo synthesized carrier molecules were secreted into the culture medium, the rest remaining mostly in the pre-Golgi compartment. The extensively O-glycosylated carrier fragment was purified from the culture medium under non-denaturing conditions. Circular dichroism spectroscopy showed that it had no regular secondary structure. Nuclear magnetic resonance spectroscopy showed that a non-glycosylated synthetic peptide, the consensus sequence of the repetitive 19 amino acid peptide, also lacked secondary structure. The unstructured carrier polypeptide may facilitate proper folding and secretion of heterologous proteins attached to it.     

Digitally gain controlled linear high voltage amplifier for laboratory applications

The design of a digitally gain controlled high-voltage non-inverting bipolar linear amplifier is presented. This cost efficient and relatively simple circuit has stable operation range from dc to 90 kHz under the load of 10 kΩ and 39 pF. The amplifier can swing up to 360 V(pp) under these conditions and it has 2.5 μs rise time. The gain can be changed by the aid of JFETs. The amplifiers have been realized using a combination of operational amplifiers and high-voltage discrete bipolar junction transistors. The circuit details and performance characteristics are discussed.     

Radiation impedance of collapsed capacitive micromachined ultrasonic transducers

The radiation impedance of a capacitive micromachined ultrasonic transducer (CMUT) array is a critical parameter to achieve high performance. In this paper, we present a calculation of the radiation impedance of collapsed, clamped, circular CMUTs both analytically and using finite element method (FEM) simulations. First, we model the radiation impedance of a single collapsed CMUT cell analytically by expressing its velocity profile as a linear combination of special functions for which the generated pressures are known. For an array of collapsed CMUT cells, the mutual impedance between the cells is also taken into account. The radiation impedances for arrays of 7, 19, 37, and 61 circular collapsed CMUT cells for different contact radii are calculated both analytically and by FEM simulations. The radiation resistance of an array reaches a plateau and maintains this level for a wide frequency range. The variation of radiation reactance with respect to frequency indicates an inductance-like behavior in the same frequency range. We find that the peak radiation resistance value is reached at higher kd values in the collapsed case as compared with the uncollapsed case, where k is the wavenumber and d is the center-to-center distance between two neighboring CMUT cells.     

Design and construction of uniform glow discharge plasma system operating under atmospheric condition

The design of a uniform glow discharge plasma system operating without vacuum is presented. A full-bridge switching circuit was used to switch the transformers. The primary windings of transformers were connected in parallel, but in opposite phase to double the output voltage. Theoretically, 20 000 V(pp) was obtained. Rectangle copper electrodes were used, and placed parallel to each other. To prevent the spark production that is, to obtain uniformity, two 2 mm Teflon sheets were glued to the electrodes. However, it was observed that the operating frequency also affected the uniformity. For the system presented here, the frequency at which more uniformity was obtained was found to be 14 kHz.     

A Low Voltage Wide-Input-Range Bulk-Input CMOS OTA

The G_m-C technique is extensively used for continuous-time filtering applications because it results in tunable, wideband and compact designs. In this paper, an OTA architecture using a novel bulk-input differential pair without the use of a tail current source is proposed. Good CMRR is still achieved by using the gate terminal to control the total current in the differential pair, via the use of a dummy pair. The OTA also exhibits a wide differential input range and good G_m-tunability. For this design, two standard double-poly double-metal CMOS processes were investigated: a 0.8 m process having a nominal threshold voltage of around 0.7 V and a 0.35 m process having a nominal threshold voltage of 0.5 V. Simulation results are presented for both designs while test results are presented, for the OTA, implemented using the 0.8 m process, used in a second order cochlea low-pass filter.Ivan Grech received his B.Eng.(Hons.) degree in 1993 and M.Sc. in 1996 from the University of Malta. In 1994 he joined the Department of Microelectronics at the University of Malta where he is employed as a lecturer. He received the Ph.D. degree from the University of Surrey, U.K. in 2002. His research interest is in CMOS analog integrated circuit design.Joseph Micallef received his B.Sc. Eng(Hons.) degree in electronics engineering from the University of Malta in 1972, and M.Sc. and Ph.D. degrees in electrical engineering from the University of Surrey, U.K., in 1989 and 1993, respectively. From 1973 to 1981, he was with General Instruments, engaged in work on high voltage components and circuits and on IFTs. He moved to SGS-THOMSON Microelectronics in 1981 where he was involved with packaging of MOS ICs. In 1989, he joined the Faculty of Engineering at the University of Malta and is now lecturer in the Department of Microelectronics. His current research activities include analog integrated circuit design, as well as optical properties of III-V quantum well structures.George Azzopardi photo/biography not available upon publication.Carl J. Debono photo/biography not available upon publication.     

A highly linear and fully-integrated FMCW synthesizer for 60 GHz radar applications with 7 GHz bandwidth

A highly linear and fully-integrated frequency-modulated continuous-wave (FMCW) generator based on a fractional-N phase-locked loop (PLL) that is able to synthesize modulation schemes in 57–64 GHz range is proposed in this paper. The fractional-N PLL employs Colpitts voltage-controlled oscillator (VCO) at 60 GHz with 13.5% tuning range. Automatic amplitude and frequency calibrations are implemented to avoid drifts due to process, voltage and temperature variations and to set the center frequency of the VCO. Five-stage multi-modulus divider is used for division ratio switching, controlled by the sigma-delta (\(\Sigma \Delta\)) modulator MASH 1-1-1. The frequency sweep (chirp) bandwidth and duration are fully programmable via serial peripheral interface allowing up to 16 different chirps in complex modulation scheme. The PLL reference signal is 250 MHz provided by external low-noise signal generator which is also used for digital modules clock. The overall PLL phase noise is lower than ?80 dBc/Hz at 10 kHz offset and the chirp linearity is better than 0.01%. The complete FMCW synthesizer is implemented and verified as a stand-alone chip in a commercially available SiGe HBT 130 nm BiCMOS technology. The total chip area is \(2.04\,\text {mm}^2\), and the total power consumption is 280 mW.     

High-power CMUTs: design and experimental verification

Capacitive micromachined ultrasonic transducers (CMUTs) have great potential to compete with piezoelectric transducers in high-power applications. As the output pressures increase, nonlinearity of CMUT must be reconsidered and optimization is required to reduce harmonic distortions. In this paper, we describe a design approach in which uncollapsed CMUT array elements are sized so as to operate at the maximum radiation impedance and have gap heights such that the generated electrostatic force can sustain a plate displacement with full swing at the given drive amplitude. The proposed design enables high output pressures and low harmonic distortions at the output. An equivalent circuit model of the array is used that accurately simulates the uncollapsed mode of operation. The model facilities the design of CMUT parameters for high-pressure output, without the intensive need for computationally involved FEM tools. The optimized design requires a relatively thick plate compared with a conventional CMUT plate. Thus, we used a silicon wafer as the CMUT plate. The fabrication process involves an anodic bonding process for bonding the silicon plate with the glass substrate. To eliminate the bias voltage, which may cause charging problems, the CMUT array is driven with large continuous wave signals at half of the resonant frequency. The fabricated arrays are tested in an oil tank by applying a 125-V peak 5-cycle burst sinusoidal signal at 1.44 MHz. The applied voltage is increased until the plate is about to touch the bottom electrode to get the maximum peak displacement. The observed pressure is about 1.8 MPa with -28 dBc second harmonic at the surface of the array.     

不同施主掺杂对(Sr0. 3Ba0. 7) T iO 3 系热敏L PTC 电阻率的影响

本文研究了Nb2O5、Y2O3或Sb2O3不同施主掺杂对(Sr0.3Ba0.7)TiO3热敏陶瓷LPTCR的影响,并讨论了不同施主掺杂的不同半导体机理。发现在本实验条件下掺Nb的（Sr0.3Ba0.7)TiO3热敏陶瓷为缓变形LPTC,掺Sb和Y的（Sr0.3Ba0.7)TiO3热敏陶瓷为突变形LPTC,且掺Sb的LPTC线性度最好,线性温区较宽。