Extension of an absolute vector error correction technique to wideband, high-frequency measurements

The authors have previously demonstrated how a transmitter (Tx), a reciprocal transmitter/receiver (Tx/Rx) signal path and two unidirectional receiver (Rx) paths can be used together with short, open and load standards for the absolute vector error correction (AVEC) of a Tx/Rx module. Once calibrated, this Tx/Rx module can then provide accurate vector measurements of the signals that are flowing into and/or out of the test port. In order to simplify the analysis, the AVEC technique was applied to a simplified baseband circuit that did not include frequency conversion mixers in a previous paper. Now, in this paper the authors first show how the AVEC technique can be extended to the vector calibration of high-frequency receivers that involve frequency conversion mixers. The authors then show how to calibrate a system that allows for wideband absolute phase relationship measurements of periodic modulated signals, provided that the same local oscillator is employed for the two down-conversion receivers, and different radio frequencies and intermediate frequencies are employed in these receivers. This novel AVEC technique is one of the key concepts in the design of a wideband absolute vector signal measurement system, which overcomes the limitations of traditional measurement instruments by combining the features of vector signal analysers, spectrum analysers and vector network analysers.     

The effect of AM noise on correlation phase-noise measurements

We analyze the phase-noise measurement methods in which correlation and averaging is used to reject the background noise of the instrument. All the known methods make use of a mixer, used either as a saturated-phase detector or as a linear-synchronous detector. Unifortunately, AM noise is taken in through the power-to-dc-offset conversion mechanism that results from the mixer asymmetry. The measurement of some mixers indicates that the unwanted amplitude-to-voltage gain is of the order of 5-50 mV, which is 12-35 dB lower than the phase-to-voltage gain of the mixer. In addition, the trick of setting the mixer at a sweet point--off the quadrature condition--where the sensitivity to AM nulls, works only with microwave mixers. The HF-VHF mixers do not have this sweet point. Moreover, we prove that if the AM noise comes from the oscillator under test, it cannot be rejected by correlation. At least not with the schemes currently used. An example shows that at some critical frequencies the unwanted effect of AM noise is of the same order-if not greater--than the phase noise. Thus, experimental mistakes are around the corner.     

Feasibility of a Frequency-Multiplexed TES Read-Out Using Superconducting Tunnel Junctions

We describe a feasibility study of a frequency multiplexed read-out scheme for large number transition edge sensor arrays. The read-out makes use of frequency up- and down-conversion and RF-to-DC conversion with superconducting-isolator-superconducting tunnel junctions operating at GHz frequencies, in combination with an existing frequency multiplexed read-out at MHz frequencies. The read-out scheme can drastically reduce the wiring from room temperature to the cryogenic detectors, with a possibility to read-out and control as many as 30000 pixels over three coaxial lines within a bandwidth of 1 GHz.     

New vector signal measuring system, featuring wide bandwidth, large dynamic range and high accuracy

A new measurement system, with two receiver channels per measurement port, has been developed that provides absolute magnitude and absolute phase relationship measurements over wide bandwidths. Gain ranging is used at radio frequency to provide optimum noise performance and a swept yttrium iron garnet (YIG) preselector filter is used to avoid spurious signals. A new absolute vector error correction method is used to calibrate the measurement system in order to allow for absolute vector measurements, and it also removes the time-varying responses caused by the swept YIG preselector filters. A quasi-reciprocal mixer with a characterised non-reciprocal ratio is used to provide the absolute calibration standard. The two receiver channels can be adapted to a wide variety of applications, including wide bandwidth vector signal analyser measurements, mixer measurements and harmonic measurements. The two channels can also be used as an absolute calibrated transmitter/reflectometer.     

Superheterodyne Measurement of Microwave Attenuation at a 10-kHz Intermediate Frequency

The excellent relative frequency stability of the output of two microwave oscillators phase-locked to a common reference signal permits the use of an audio intermediate frequency in the superheterodyne measurement of microwave attenuation. The phase-lock feature also permits the measurement of microwave phase at the audio frequency. The choice of the audio instead of the more conventional 30-MHz intermediate frequency is made on the basis of the low cost and convenient operation, for similar accuracy, of an audio ratio transformer and audio phase shifter in comparison with a 30-MHz cutoff attenuator and 30-MHz phase shifter. A measurement system of this type has been operated at frequencies ranging from 2.5 to 18 GHz. The basic reference signal for phase lock is fed into harmonic mixers associated with the signal source and local oscillator. The outputs of the harmonic mixers go to phase discriminators that control the microwave oscillator frequencies. The precision of measurement at a signal frequency of 10 GHz varies from ±0.0002 dB for an attenuation step of 10 dB or less, to ±0.001 dB for a 50-dB step.     

The Effect of Magnesium Stearate Admixing in Different Types of Laboratory and Industrial Mixers on Tablet Crushing Strength

Abstract

It is generally known that hydrophobic lubricants such as magnesium stearate can have a strong negative effect on the binding properties of directly compressible filler-binders. It was found that the decrease in binding forces is not only dependent on the tablet ingredients and the lubricant concentration used, but especially on the mixing time and mixing procedure. Most studies were performed, however with small laboratory scale mixers. In order to evaluate the effect of magnesium stearate admixing in different types of laboratory-scale and industrial mixers, the decrease in crushing strength was measured for a test formulation during mixing with the lubricant in different mixers. The formula used consisted of 90% a-lactose monohydrate 100 mesh, 9.5% microcrystalline cellulose and 0.5% magnesium stearate. The mixers used were two laboratory scale mixers: a 2 litre Turbula mixer and a 13 litre cubic mixer and five production scale mixers: a 45 litre drum mixer, 90 litre, 200 litre and 900 litre planetary mixers and a 1.000 litre V-shaped mixer, respectively. For the test formulation used, it was found that the effect of lubricant admixing on tablet crushing strength was strongly dependent on type, size and rotation speed of the mixer used.

When operated at the same rotation speed, the decrease in crushing strength was much faster for the large industrial mixers than for the small laboratory mixers. These differences were explained by differences in shear forces during the mixing process and the efficiency of the mixing procedure.

For the industrial mixers the decrease of the tablet crushing strength as an effect of lubricant admixing was mainly determined by the rotation speed and only to a small extent by the type and size of the apparatus. Moreover no effect of load could be observed between the mutual industrial mixers used.

For a prediction of the effect of lubricant admixing on tablet crushing strength in large mixers, efficient laboratory mixers, operating at high rotation speeds can be used. For this purpose a 2 litre Turbula mixer is a valuable tool in preformulation work.     

The Effect of Magnesium Stearate Admixing in Different Types of Laboratory and Industrial Mixers on Tablet Crushing Strength

It is generally known that hydrophobic lubricants such as magnesium stearate can have a strong negative effect on the binding properties of directly compressible filler-binders. It was found that the decrease in binding forces is not only dependent on the tablet ingredients and the lubricant concentration used, but especially on the mixing time and mixing procedure. Most studies were performed, however with small laboratory scale mixers. In order to evaluate the effect of magnesium stearate admixing in different types of laboratory-scale and industrial mixers, the decrease in crushing strength was measured for a test formulation during mixing with the lubricant in different mixers. The formula used consisted of 90% a-lactose monohydrate 100 mesh, 9.5% microcrystalline cellulose and 0.5% magnesium stearate. The mixers used were two laboratory scale mixers: a 2 litre Turbula mixer and a 13 litre cubic mixer and five production scale mixers: a 45 litre drum mixer, 90 litre, 200 litre and 900 litre planetary mixers and a 1.000 litre V-shaped mixer, respectively. For the test formulation used, it was found that the effect of lubricant admixing on tablet crushing strength was strongly dependent on type, size and rotation speed of the mixer used.

When operated at the same rotation speed, the decrease in crushing strength was much faster for the large industrial mixers than for the small laboratory mixers. These differences were explained by differences in shear forces during the mixing process and the efficiency of the mixing procedure.

For the industrial mixers the decrease of the tablet crushing strength as an effect of lubricant admixing was mainly determined by the rotation speed and only to a small extent by the type and size of the apparatus. Moreover no effect of load could be observed between the mutual industrial mixers used.

For a prediction of the effect of lubricant admixing on tablet crushing strength in large mixers, efficient laboratory mixers, operating at high rotation speeds can be used. For this purpose a 2 litre Turbula mixer is a valuable tool in preformulation work.     

Investigation of electrical nonlinearity of HTS thin films as applied to realization of a microwave IC mixer

The nonlinear response of superconducting thin film bridges and transmission line sections at microwave frequencies has been investigated. A number of mixer prototypes have been designed and characterized. A model, based on analysis of experimental pulsedI-V characteristics, predicting results of mixing experiments, has been introduced and good agreement with the model has been obtained.     

Comparison of 24 GHz receiver front-ends using active and passive mixers in CMOS

This study compares the key parameters of two integrated receiver front-end architectures: low noise amplifier (LNA) with active mixer against LNA with passive mixer. The authors discuss the differences in the performance and their impact on system characteristics for radar applications. A low-IF down-conversion receiver implementation is considered. The results are compared in measurement for two 24 GHz receiver front-end chips realised in a 0.13 mm digital CMOS process. Both circuits have been characterised over automotive temperature range -40 to 125°C. The front-end with an active mixer offers lower LO power dependence and exhibits better temperature stability, whereas the front-end with a passive mixer has the advantage of better input-referred linearity and lower flicker noise.     

A simple method for the evaluation of microwave mixer diodes

A simple method is described for the evaluation of the various microwave mixer diodes which can be used in 9-GHz electron paramagnetic resonance (EPR) spectrometers using magnetic field modulation below 1 kHz. The advantage of this method over other methods is that it is optimized for EPR applications and determines the optimum operating conditions for each microwave diode. This method utilizes a microwave bridge with a reference arm with an attenuator to control the microwave bias power level, and a signal arm where the signal is attenuated, phase shifted, and modulated at the typical magnetic field modulation frequencies. The microwave power from the two arms is recombined and demodulated by the microwave diode. The output of the microwave diode is then recorded with various video loads, microwave bias power, and modulation frequencies. Measurements are performed to determine the effect of the preamplifier that followed the microwave diode on the signal-to-noise ratio (SNR). The recorded spectra are used to determine the SNR, the noise floor, and the 1/f corner frequency. Comparison of these factors for the different types of microwave diodes shows that some Schottky-barrier diodes have noise figures at 1 kHz that are as low as those for tunnel diodes     

Influence of chopper and mixer speeds and microwave power level during the high-shear granulation process on the final granule characteristics

Although microwave drying technology has been used extensively, detailed studies in the pharmaceutical field are necessary to model the different operational parameters involved in microwave drying in combination with the high-shear granulation processes. The implications of the chopper and the mixer speeds during the granulation step and the microwave power level during the drying step on the final granule characteristics were investigated. alpha-Lactose monohydrate and microcrystalline cellulose were granulated at three different mixer and chopper speeds in a laboratory-scale high-shear mixer (Mi-Mi-Pro) and dried at three microwave power levels. The dried granules were characterized by friability tests, particle size analysis, bulk and tapped density studies, and porosimetry. Neither the mixer speed nor the chopper speed had a significant influence on the granule friability, which was low for all batches produced. The selected materials and experimental conditions induced a very robust granulation process, but the granule size distribution was influenced by the microwave power level. The reciprocal relationship between the dust formation and the microwave power level was analyzed using a central composite factorial design. The amount of dust remained low in all batches, but it influenced some of the inherent density properties and the volume reduction behavior of the granulation mass. In almost all cases, the Carr index decreased slightly with increasing microwave power. The major granule characteristics were not changed when different mixer or chopper speeds were changed, although the mixer speed did alter the intragranular pore size distribution.     

Optimization of a microfluidic mixer for studying protein folding kinetics

We have applied an optimization method in conjunction with numerical simulations to minimize the mixing time of a microfluidic mixer developed for protein folding studies. The optimization method uses a semideterministic algorithm to find the global minimum of the mixing time by varying the mixer geometry and flow conditions. We describe the minimization problem and constraints and give a brief overview of the optimization algorithm. We present results of the optimization, including the optimized geometry and parameter sensitivities, and we demonstrate the improvement in mixing performance with experiments using microfabricated mixers. The dye-quenching experiments of the original and optimized mixer designs show respective mixing times of 7 and 4 mus, a 40% reduction. The new design also provides more uniform mixing across streamlines that enter the mixer. The optimized mixer is the fastest reported continuous flow mixer for protein folding.     

On Characterization of Continuous Mixing of Particulate Materials

The concept of heterogeneity in relation to axial mixing in continuous mixers is investigated. The state of the mixture along the axial direction can be described by an axial heterogeneity function. It is shown that this function can be decomposed into two independent components. The first component describes the fluctuations caused by the feeding system. The second component is the fluctuations due to the particulate nature of the material. In addition, the second component, or the random component, can be modeled as a band-limited Gaussian white noise. Moreover, the variogram function is shown to be a useful tool in determining the variance of the random component. A linear time-invariant (LTI) model is proposed for continuous mixers. This model also implies that the Danckwerts-Weinekötter formula is applicable for the variance reduction ratio (VRR). However, it is shown that the Danckwerts formula for VRR is more appropriate for determination of mixer efficiency.     

New methods for accurate water dosage in concrete central mix plants

Online mixer measurements appear as being essential to the improvement of concrete manufacturing methods, as imposed by new economical and environmental demands. However, the lack of a well-established calibration procedure contributes to the poor reputation sometimes given to these measurements. The original in situ method developed and evaluated herein requires installing a sampler, yet only slightly disturbs the production process. By using this calibration method the mixing power becomes a reliable online indication of concrete water content (measurement standard deviation of 2.85 l/m³). A procedure for improving the regularity of water content in truck mixers has been presented to illustrate the benefit of well-calibrated online water content measurements in batch concrete in a central mix plant. The correction algorithms proposed herein have the potential to be automated and may improve up to 5 times the water content regularity in the truck mixers.     

Effects of Mixer and Mixing Time on the Pharmaceutical Properties of Theophylline Tablets Containing Various Kinds of Lactose as Diluents

Effect of mixing time on the flowability, compressibility, tablet hardness and dissolution of theophylline tablets was investigated using two types of mixers, i.e., twin-shell and high-speed mixers. Theophylline, three kinds of lactose ($aL-monohydrate, β-anhydrate and spray-dried product), disintegrator and magnesium stearate were mixed, and tablets were compressed. While the particles mixed with magnesium stearate by the high speed mixer were coated with magnesium stearate, those mixed by the twin-shell mixer formed an ordered mixture. The dissolution differed depending on the mixing time and method.     

New density-independent calibration function for microwave sensingof moisture content in particulate materials

Microwave techniques have been considered for a long time for moisture sensing in many food processing and agriculture-related industries. They are suitable for on-line real-time monitoring and control. However, with particulate materials, bulk density fluctuations cause significant errors in moisture content determination. To overcome this shortcoming, density-independent calibration functions are needed. In this paper, a new approach is presented in which both bulk density and moisture content are determined directly from measured microwave dielectric properties. A simple relationship between bulk density and the dielectric properties is identified, and a new density-independent function for moisture content prediction, exclusively dependent on the dielectric properties of the material under test (ϵ', ϵ"), is proposed. The validity and applicability of this function are demonstrated with an extensive data set obtained from measurements on a granular material (wheat), over wide ranges of frequency (11-18 GHz), temperature (-1°C-42°C), moisture content (10.6%-19.2%, wet basis), and bulk density (0.72-0.88 g/cm³). Explicit calibration equations for moisture prediction at different frequencies and temperatures are provided. Although data obtained by a transmission microwave measurement technique were used, this new approach remains valid in general for other techniques, provided that ϵ' and ϵ" are determined accurately     

Scale-up feasibility in high-shear mixers: determination through statistical procedures

The wet granulation scale-up of a formulation exhibiting plastic deformation behavior under compression was examined. Through experimental factorial design, the effect of solution level, mixing time, and mixer speed on granulation properties was investigated. Measurements of mean particle size, tapped density, bulk density, Carr's index, coarse-to-fine ratio, cumulative percentage, and flow rate were taken and compared among granulations. In addition, comparisons were done on the hardness of tablets made from the formulations. It was shown that the characteristics of the granulations made under different conditions were highly reproducible. The excipient system of microcrystalline cellulose and pregel starch was shown to be a very robust formulation that is resistant to changes in the scaling-up process in high-shear mixers.     

New absolute vector error correction technique for a transmitter/receiver module

The authors demonstrate how a transmitter (Tx), a reciprocal transmitter/receiver (Tx/Rx) signal path and two unidirectional receiver (Rx) paths can be used together with short, open, and load standards for the absolute vector error correction (AVEC) of a Tx/Rx module. Once calibrated, this Tx/Rx module can then provide accurate vector measurements of the signals that are flowing into and/or out of the test port. This novel AVEC technique is one of the key concepts in the design of a wideband absolute vector signal measurement system, which overcomes the limitations of traditional measurement instruments by combining the features of vector signal analysers, spectrum analysers, and vector network analysers. The AVEC method is validated using numerical simulation data for a simplified baseband test circuit. The AVEC technique is then extended to the calibration of wideband, high-frequency Tx/Rx modules that involve frequency up/down conversion mixers in a follow-on paper     

Scale-up Feasibility in High-Shear Mixers: Determination Through Statistical Procedures

The wet granulation scale-up of a formulation exhibiting plastic deformation behavior under compression was examined. Through experimental factorial design, the effect of solution level, mixing time, and mixer speed on granulation properties was investigated. Measurements of mean particle size, tapped density, bulk density, Carr's index, coarse-to-fine ratio, cumulative percentage, and flow rate were taken and compared among granulations. In addition, comparisons were done on the hardness of tablets made from the formulations. It was shown that the characteristics of the granulations made under different conditions were highly reproducible. The excipient system of microcrystalline cellulose and pregel starch was shown to be a very robust formulation that is resistant to changes in the scaling-up process in high-shear mixers.     

Ultrafast microfluidic mixer and freeze-quenching device

The freeze-quenching technique is extremely useful for trapping meta-stable intermediates populated during fast chemical or biochemical reactions. The application of this technique, however, is limited by the long mixing time of conventional solution mixers and the slow freezing time of cryogenic fluids. To overcome these problems, we have designed and tested a novel microfluidic silicon mixer equipped with a new freeze-quenching device, with which reactions can be followed down to 50 micros. In the microfluidic silicon mixer, seven 10-microm-diameter vertical pillars are arranged perpendicular to the flow direction and in a staggered fashion in the 450-pL mixing chamber to enhance turbulent mixing. The mixed-solution jet, with a cross section of 10 microm x 100 microm, exits from the microfluidic silicon mixer with a linear flow velocity of 20 m/s. It instantaneously freezes on one of two rotating copper wheels maintained at 77 K and is subsequently ground into an ultrafine powder. The ultrafine frozen powder exhibits excellent spectral quality and high packing factor and can be readily transferred between spectroscopic observation cells. The microfluidic mixer was tested by the reaction between azide and myoglobin at pH 5.0. It was found that complete mixing was achieved within the mixing dead time of the mixer (20 micros), and the first observable point for this coupled device was determined to be 50 micros, which is approximately 2 orders of magnitude faster than commercially available instruments.