一种同时测量液体粘密度的传感器研究

液相环境下振荡的压电石英晶体传感器的谐振频率变化主要受液体性质和表面质量负载的影响。通过将一表面抛光和一表面有沟槽的石英晶体传感器置于测量池,前者在液体中的谐振频移反映了液体粘密度之积的变化,而两晶体的谐振频差则反映了液体的密度变化。从而使该装置可同时用于液体的粘度与密度的测量。实验结果表明,该装置具有简单、灵敏度高和线性关系好等优点。     

Composite torsional quartz transducer for shear ultrasonic measurements of aqueous liquids

A composite torsional quartz transducer has been developed for the shear ultrasonic measurements of aqueous solutions in the frequency range from 10 to 100 kHz. In order to prevent the electric interaction and low contact angle between the transducer and water, a torsional quartz crystal transducer is attached to a fused quartz rod whose surface is partly gilded by evaporation. The accuracy of +/-60 dyn/cm2 for the rigidity and +/-0.03 cP for the viscosity is attained by use of this transducer.     

Simultaneous detection of surface coverage and structure of krypton films on gold by helium atom diffraction and quartz crystal microbalance techniques

We describe a quartz crystal microbalance setup that can be operated at low temperatures in ultra high vacuum with gold electrode surfaces acting as substrate surface for helium diffraction measurements. By simultaneous measurement of helium specular reflection intensity from the electrode surface and resonance frequency shift of the crystal during film adsorption, helium diffraction data can be correlated to film thickness. In addition, effects of interfacial viscosity on the helium diffraction pattern could be observed. To this end, first, flat gold films on AT cut quartz crystals were prepared which yield high enough helium specular reflection intensity. Then the crystals were mounted in the helium diffractometer sample holder and driven by means of a frequency modulation driving setup. Different crystal geometries were tested to obtain the best quality factor and preliminary measurements were performed on Kr films on gold surfaces. While the crystal structure and coverage of krypton films as a function of substrate temperature could successfully be determined, no depinning effects could be observed.     

Resistive cooling circuits for charged particle traps using crystal resonators

The paper addresses a novel method to couple a signal from charged particles in a Penning trap to a high Q resonant circuit using a crystal resonator. Traditionally, the trap capacity is converted into a resonator by means of an inductance. The tuned circuit's Q factor is directly linked to the input impedance "seen" by the trapped particles at resonance frequency. This parallel resonance impedance is a measure of the efficiency of resistive cooling and thus it should be optimized. We propose here a commercially available crystal resonator since it exhibits a very high Q value and a parallel resonance impedance of several MΩ. The possibility to tune the parallel resonance frequency of the quartz results in filter behavior that allows covering a range of some tens of its 3dB bandwidth by means of tuning.     

Improved frequency/voltage converters for fast quartz crystal microbalance applications

The monitoring of frequency changes in fast quartz crystal microbalance (QCM) applications is a real challenge in today's instrumentation. In these applications, such as ac electrogravimetry, small frequency shifts, in the order of tens of hertz, around the resonance of the sensor can occur up to a frequency modulation of 1 kHz. These frequency changes have to be monitored very accurately both in magnitude and phase. Phase-locked loop techniques can be used for obtaining a high performance frequency/voltage converter which can provide reliable measurements. Sensitivity higher than 10 mVHz, for a frequency shift resolution of 0.1 Hz, with very low distortion in tracking both the magnitude and phase of the frequency variations around the resonance frequency of the sensor are required specifications. Moreover, the resonance frequency can vary in a broad frequency range from 5 to 10 MHz in typical QCM sensors, which introduces an additional difficulty. A new frequency-voltage conversion system based on a double tuning analog-digital phase-locked loop is proposed. The reported electronic characterization and experimental results obtained with conducting polymers prove its reliability for ac-electrogravimetry measurements and, in general, for fast QCM applications.     

新型液体中双调制式石英晶体传感器系统的研制

传统的调频式石英晶体传感器无法区分引起频率变化的两种不同负载效应，介绍一种新型液体中双调制式石英晶体传感器系统，讨论了传感器谐振电路、液体测头结构及采集系统的设计。实验表明，该传感器在液体中３个小时频率稳定度达到±５Ｈｚ，幅值达到±２．５ｍＶ，液体的高度对传感器输出基本没有影响。     

Quartz crystal microbalance based on torsional piezoelectric resonators

A quartz crystal microbalance (QCM) is described, which is based on a torsional resonator, rather than a conventional thickness-shear resonator. Typical applications are measurements of film thickness in the coating industry and monitoring of biofouling. The torsional QCM is about a factor of 100 less sensitive than the conventional QCM. On the other hand, it can probe film thicknesses in the range of hundreds of microns, which is impossible with the conventional QCM due to viscoelastic artifacts. Data acquisition and data analysis proceed in analogy to the conventional QCM. An indicator of the material's softness can be extracted from the bandwidth of the resonance. Within the small-load approximation, the frequency shift is independent of whether the sample is applied to the face or to the side of the cylinder. Details of the geometry matter if the viscoelastic properties of the sample are of interest.     

DESIGN OF A SIMPLE LOW-COST QUARTZ CRYSTAL MICROBALANCE SYSTEM

This article describes a simple design of a low-cost, real-time, and computerized quartz crystal microbalance system. The system measures resonance frequencies up to 6 MHz with a resolution of 1 Hz, i.e., it can monitor mass change in the range of nano-gram and thickness change in the range of micrometer. The designed system consists of three main parts: input circuitry, control, and counting parts. In the input circuitry, three separated input signals types are allowable: the first is direct TTL compatible, the second is analog signal, while the third is the signal that may come from the quartz crystal microbalance. The last two signals are converted to TTL signals using wave-shaping circuitry. The control part is interfaced with the status and control ports of the computer LPT1 parallel port. It consists of time base circuitry and different multiplexers to control data sending to computer according to the input signal under investigation. The counter consists of six binary counters in cascade and directly interfaced to the computer through the LPT1 data port; the transfer process was carried out by two different ways according to the measuring mode of the system. All parts were controlled by specially designed software. Finally, the frequency readings of the quartz crystal microbalance were found to be in good agreement with those of a frequency counter model GFC-8055G connected in parallel during an experiment performed to test the system.     

A new method for wideband characterization of resonator-based sensing platforms

A new approach to the electronic instrumentation for extracting data from resonator-based sensing devices (e.g., microelectromechanical, piezoelectric, electrochemical, and acoustic) is suggested and demonstrated here. Traditionally, oscillator-based circuitry is employed to monitor shift in the resonance frequency of the resonator. These circuits give a single point measurement at the frequency where the oscillation criterion is met. However, the resonator response itself is broadband and contains much more information than a single point measurement. Here, we present a method for the broadband characterization of a resonator using white noise as an excitation signal. The resonator is used in a two-port filter configuration, and the resonator output is subjected to frequency spectrum analysis. The result is a wideband spectral map analogous to the magnitude of the S21 parameters of a conventional filter. Compared to other sources for broadband excitation (e.g., frequency chirp, multisine, or narrow time domain pulse), the white noise source requires no design of the input signal and is readily available for very wide bandwidths (1 MHz-3 GHz). Moreover, it offers simplicity in circuit design as it does not require precise impedance matching; whereas such requirements are very strict for oscillator-based circuit systems, and can be difficult to fulfill. This results in a measurement system that does not require calibration, which is a significant advantage over oscillator circuits. Simulation results are first presented for verification of the proposed system, followed by measurement results with a prototype implementation. A 434 MHz surface acoustic wave (SAW) resonator and a 5 MHz quartz crystal microbalance (QCM) are measured using the proposed method, and the results are compared to measurements taken by a conventional bench-top network analyzer. Maximum relative differences in the measured resonance frequencies of the SAW and QCM resonators are 0.0004% and 0.002%, respectively. The ability to track a changing sensor response is demonstrated by inducing temperature variations and measuring resonance frequency simultaneously using the proposed technique in parallel with a network analyzer. The relative difference between the two measurements is about 5.53 ppm, highlighting the impressive accuracy of the proposed system. Using commercially available digital signal processors (DSPs), we believe that this technique can be implemented as a system-on-a-chip solution resulting in a very low cost, easy to use, portable, and customizable sensing system. In addition, given the simplicity of the signal and circuit design, and its immunity to other common interface concerns (injection locking, oscillator interference, and drift, etc.), this method is better suited to accommodating array-based systems.     

High-resolution Brillouin spectroscopy with angular dispersion-type Fabry-Perot interferometer and its application to a quartz crystal

Although the multichannel Brillouin spectroscopy with an angular dispersion-type Fabry-Perot interferometer (ADFPI) becomes a powerful tool for quick measurements, its resolution and contrast are not enough for the study of single crystals. A highly sensitive multichannel detector enables the ADFPI to use a solid etalon with high reflectivity (99.5%); hence, the high resolution and the high contrast of a spectrum are achieved. The finesse, the inverse of the resolution, reaches 100 with a 10 mm diameter of aperture size. The highest finesse of 140 is obtained by using a smaller diameter of 2 mm. The accuracy is examined by the measurement of a quartz crystal. The improvement in the resolution and contrast enables investigations of weak attenuation in a quartz crystal. The elastic anomaly of the alpha-beta transition of a quartz crystal is clearly observed both in sound velocity and attenuation. From the elastic constant c(11), the critical parameter K=0.76 is determined.     

Method of the viscosity measurement by means of the vibrating micro-/nano-mechanical resonators

Atomic force microscopes, micro-/nano-mechanical resonators and nanowires or carbon nanotube can detect even a small change of properties of fluids and therefore they are often considered to be the prospective ultrasensitive micro/nano viscometers. However, due to the complicated physics behind such devices, the interpretation of experimental data including the viscosity extraction is mostly performed based on some approximations or data fittings. In this paper, the complete analysis of the vibrating cylindrical micro-/nano-cantilever submerged in a viscous fluid is presented. Based on the obtained results a simple way of the viscosity extraction from the maximum vibrational amplitude (MVA), the bandwidth and the resonance frequency shift, is proposed. The simple formulas for the achievable accuracy of the viscosity sensing are given. These results can be used in future development of the ultrasensitive micro/nano viscometers integrated on micro systems or flow meters.     

Nuclear magnetic resonance apparatus for pulsed high magnetic fields

A nuclear magnetic resonance apparatus for experiments in pulsed high magnetic fields is described. The magnetic field pulses created together with various magnet coils determine the requirements such an apparatus has to fulfill to be operated successfully in pulsed fields. Independent of the chosen coil it is desirable to operate the entire experiment at the highest possible bandwidth such that a correspondingly large temporal fraction of the magnetic field pulse can be used to probe a given sample. Our apparatus offers a bandwidth of up to 20 MHz and has been tested successfully at the Hochfeld-Magnetlabor Dresden, even in a very fast dual coil magnet that has produced a peak field of 94.2 T. Using a medium-sized single coil with a significantly slower dependence, it is possible to perform advanced multi-pulse nuclear magnetic resonance experiments. As an example we discuss a Carr-Purcell spin echo sequence at a field of 62 T.     

Method, algorithm and device for estimation of components above the harmonic frequency range up to 9 kHz

The paper presents a method of estimation of frequency groups with 200 Hz bandwidth in the frequency range from the 50th harmonic up to 9 kHz. The method consists of the application of a fast Fourier transform (FFT) for wavelet coefficients after input signal decomposition and partial synthesis for chosen frequency bands. It enables the computational complexity of the algorithm to be reduced and also attenuates influence of the fundamental component and low-frequency harmonics, as required by IEC Standard 61000-4-7. The particulars of this method are shown and analysis for a chosen wavelet family is provided. Further, the algorithm and its implementation in real device for power quality monitoring is presented. Finally, the results of measurements of two testing signals are shown. The required attenuation of fundamental component and required accuracy was obtained.     

介质加载谐振腔的小型化氢脉泽的研究

原子储存泡技术是氢微波激射器(氢脉泽)的关键技术。传统的石英薄壁储存泡位于TE011模的空心圆柱谐振腔的中心。为了缩小氢脉泽谐振腔和原子储存泡的体积采用了蓝宝石加载谐振腔取代传统的腔泡结构,并将蓝宝石晶体的内壁作为原子储存泡,分析了脉泽工作状态的变化。为了消除蓝宝石加载腔的腔频率随温度的敏感变化(-60 k Hz/K)对脉泽自激振荡频率相对大的牵引效应,在蓝宝石加载谐振腔中再加载具有负介电常数温度系数的钛酸锶晶体,将腔频率温度系数近似地补偿到零。实现了采用介质加载谐振腔的氢脉泽的自激振荡,并通过锁相环实现氢脉泽对晶体振荡器的控制而形成稳定的频率源,短期稳定度指标在量级上达到了主动型氢原子钟(氢钟)的指标(1 000 s稳定度达1.5×10-14)。     

High-load, high-temperature deformation apparatus for synthetic and natural silicate melts

A unique high-load, high-temperature uniaxial press was developed to measure the rheology of silicate melts and magmatic suspensions at temperature up to 1050 degrees C. This new apparatus is designed to operate at constant stresses (up to 300 kN) or constant strain rates (approximately 10(-7) to 10(0) s(-1)) and further allows us to carry on experiments on samples with high viscosities (approximately 10(8) to 10(12) Pa s). The rheological instrument represents an advance in that it accommodates homogeneously heated samples (+/-2 degrees C) of voluminous sizes (up to 790 cm(3)) which permit the insertion of thermocouples to monitor temperature distribution evolutions during measurements. At last this setup allows for accurate measurements of viscosity of natural multiphase materials at strain rates and temperatures common to natural systems. The apparatus aspires to precisely (1) describe the onset of non-Newtonian behavior and its evolution with increasing strain rate until the point of rupture in the brittle regime, (2) constrain the effect of crystals and bubbles on the viscosity, and (3) record heating dissipated through viscous deformation. Here, we present a series of measurements on NIST standard material SRM 717a to calibrate the instrument. We couple the viscosity determined via Gent's equation with certified viscosity data of the standard material to calibrate this state-of-the-art apparatus. This work shows that we can resolve the viscosity of voluminous melt sample within 0.06 logarithmic unit and furthermore present the detection of minor viscous dissipation for a high-temperature, high strain rate experiment.     

The viscosity of dimethyl ether

Dimethyl ether (DME) has been recognised as an excellent fuel for diesel engines for over one decade now. Engines fuelled by DME emit virtually no particulate matter even at low NO_x levels. This is only possible in the case of diesel oil operation if expensive and efficient lowering particles and NO_x traps are installed.The most significant problem encountered when engines are fuelled with DME is that the injection equipment breaks down prematurely due to extensive wear. This tribology issue can be explained by the very low lubricity and viscosity of DME. Recently, laboratory methods have appeared capable of measuring these properties of DME. The development of this is rendered difficult because DME has to be pressurised to remain in the liquid state and it dissolves most of the commercially available elastomers.This paper deals fundamentally with the measurement of the viscosity of DME and extends the discussion to the difficulty of viscosity establishing of very thin fluids. The main issue here is that it is not easy to calibrate the viscometers in the very low viscosity range corresponding to about one-fifth of that of water. The result is that the low viscosity is measured at high Reynolds numbers so that the outcome has to be corrected by various factors. The validity of these can be discussed especially when they exceed a few percent of the apparent viscosity.The volatile fuel viscometer (VFVM) developed at DTU is presented. By enclosing a standard glass capillary viscometer in a glass tube it is possible to measure the viscosity of fluids at pressures below 15 bars. The kinematic viscosity of DME was established at 0.184 cSt @ 25 °C at the vapour pressure of the fluid at that temperature. The measurements were made at reasonable Reynolds numbers so the correction factors are negligible indicating a high accuracy of the method.Other pressurised viscometers have appeared since the development of the VFVM. These predict a 5–19% higher viscosity for DME than the VFVM. It seems that the causes for these differences are a too high Reynolds number and/or an influence of the gas used for pressurisation in these methods. The results of the VFVM are consolidated by measurements of the viscosities of propane and butane: these agree with the outcome of measurements using a quartz crystal microbalance (QCM) a method that is supposedly less sensible than the Reynolds number.     

Force measurement using an inductively coupled sensor

A low-compliance, high-bandwidth force sensor is described. The bending of a quartz plate is converted to an analog voltage by using a phase-locked loop to measure the change in frequency of two oscillators inductively coupled to the plate. The resolution of the sensor is approximately 10(-5) N, with a bandwidth of approximately 1 kHz.     

A broadband ferromagnetic resonance spectrometer to measure thin films up to 70 GHz

We report the development of a broadband ferromagnetic resonance (FMR) system operating in the frequency range from 10 MHz to 70 GHz using a closed-cycle He refrigeration system for measurements of thin films and micron/nano structures. The system is capable of carrying out measurements in frequency and field domain. Using two coplanar waveguides, it is capable of simultaneously measuring two samples in the out of plane and in plane FMR geometries. The system operates in the temperature range of 27-350 K and is sensitive to less than one atomic monolayer of a single crystal Fe film.     

Improved electronic interfaces for AT-cut quartz crystal microbalance sensors under variable damping and parallel capacitance conditions

A new configuration of automatic capacitance compensation (ACC) technique based on an oscillatorlike working interface, which permits the tracking of the series resonant frequency and the monitoring of the motional resistance and the parallel capacitance of a thickness-shear mode quartz crystal microbalance sensor, is introduced. The new configuration permits an easier calibration of the system which, in principle, improves the accuracy. Experimental results are reported with 9 and 10 MHz crystals in liquids with different parallel capacitances which demonstrate the effectiveness of the capacitance compensation. Some frequency deviations from the exact series resonant frequency, measured by an impedance analyzer, are explained by the specific nonideal behavior of the circuit components. A tentative approach is proposed to solve this problem that is also common to previous ACC systems.     

A new theoretical basis for the bandwidth method and optimal power ratios for the damping estimation

Using the well-known bandwidth formula and the half power bandwidth formula [R.E.D. Bishop, G.M.L. Gladwell, An investigation into the theory of resonance testing, Philosophical Transactions of the Royal Society of London A 255 (1963) 241–280], in particular, is the simplest way to estimate modal damping for engineers. By using the half power bandwidth formula, the damping factor is estimated to be approximately the half bandwidth at the half power points. One of the major limitations that restrict the use of this method is the coupling effect between closely spaced modes. In this paper, the dependence of the damping estimation accuracy on the selected power ratios is studied with both analytical and experimental data of frequency response functions. The results show that by selecting adequate power ratio values, the coupling effect can be minimized and the estimation accuracy can be significantly improved for closely spaced modes. A further improvement of accuracy can be obtained by applying the algorithm of mode isolation [H.P. Yin, D. Duhamel, Substraction technique and finite difference formulas for modal parameter estimation, Mechanical Systems and Signal Processing 18 (2004) 1497–1503; M.S. Allen, J.H. Ginsberg, A global, single-input-multi-output (SIMO) implementation of the algorithm of mode isolation and application to analytical and experimental data, Mechanical Systems and Signal Processing 20 (2006) 1090–1111]. Also an exact bandwidth formula in case of a single degree of freedom system is presented and the link between the exact formula and the classical approximated formula is indicated. The exact bandwidth formula provides a new theoretical basis of the bandwidth method for the damping estimation from frequency response functions.