Self-temperature-testing of the quartz resonant force sensor

Temperature characteristics of a quartz resonant force sensor are important features, which should be seriously considered in the sensor's practical application. This paper analyzes the temperature characteristics of a quartz resonant force sensor and presents a self-temperature-testing method for the sensor by analyzing the different temperature characteristics when the quartz resonator vibrates in its fundamental mode and in its third overtone mode. A beat frequency results from the resonator's fundamental and third overtone frequencies. Experimental result show that the sensor's operating temperature can be measured by making use of this beat frequency rather than applying a temperature sensor     

A wireless, remote query glucose biosensor based on a pH-sensitive polymer

This paper describes a wireless, remote query glucose biosensor using a ribbonlike, mass-sensitive magnetoelastic sensor as the transducer. The glucose biosensor is fabricated by first coating the magnetoelastic sensor with a pH-sensitive polymer and upon it a layer of glucose oxidase (GOx). The pH-responsive polymer swells or shrinks, thereby changing mass, respectively, in response to increasing or decreasing pH values. The GOx-catalyzed oxidation of glucose produces gluconic acid, inducing the pH-responsive polymer to shrink, which in turn decreases the polymer mass. In response to a time-varying magnetic field, a magnetoelastic sensor mechanically vibrates at a characteristic resonance frequency, the value of which inversely depends on sensor mass loading. As the magnetoelastic films are magnetostrictive, the vibrations launch magnetic flux that can be remotely detected using a pickup coil. Hence, changes in the resonance frequency of a passive magnetoelastic transducer are detected on a remote query basis, without the use of physical connections to the sensors.The sensitivity of the glucose biosensors decreases with increasing ionic strength; at physiological salt concentrations, 0.6 mmol/L of glucose can be measured. At glucose concentrations of 1-10 mmol/L, the biosensor response is reversible and linear, with the detection limit of 0.6 mmol/L corresponding to an error in resonance frequency determination of 20 Hz. Since no physical connections between the sensor and the monitoring instrument are required, this sensor can potentially be applied to in vivo and in situ measurement of glucose concentrations.     

Magnetometer Design for Measuring Ultralow DC Magnetic Fields Using YBa2Cu3O7−x Superconductors

In the present work we examined a special sensor design using a YBa₂Cu₃O_7?x superconductor as a sensing element for the detection of ultralow DC magnetic fields. The experimental results have shown that the sensor signal, which is the second harmonic signal generated by co-application of AC and DC fields to high-T _c superconductors, varies linearly with the applied DC field even in the ?0.5 Oe to 0.5 Oe range. The critical factors affecting the strength of the second harmonic signal, such as the frequency and amplitude of the AC field, the intergrain critical field H _c1J , and the minimum field required for penetration through the entire specimen H ^?, were optimized. In this way we could detect DC magnetic fields as low as 1 nT.     

Frequency-temperature compensation of piezoelectric resonators by electric DC bias field

Electromechanical resonators have been widely used in signal processing and frequency control applications. It has been found that the resonant frequency of most resonator devices is highly temperature dependent, as temperature variation leads to materials properties change as well as resonator dimension change, which result in the undesirable shift of the resonance frequency. In this paper, we present a new frequency tuning method in which direct current (DC) bias field is used to control the resonance frequency of the piezoelectric resonator that is subjected to ambient temperature variations. It has been found that, depending on the polarity, the application of a DC bias field can reduce or increase the resonance frequency of the resonator. The experimental results demonstrate that the DC bias field tuning can achieve fairly good temperature compensation within a certain temperature range, and that the mechanical Q factor of the resonator is quite stable under different DC bias fields.     

Magnetoelastic Sensor Studies on Amorphous Magnetic FeSiB Wire and the Application in Viscosity Measurement

In this work, possible use of FeSiB amorphous magnetic wire as a magnetoelastic sensor was investigated. As-received wire did not show any magnetoelastic change. But, the wire annealed in a furnace at 465 ^°C for various times showed good magnetoelastic change. A very large change in the resonance frequency of annealed FeSiB wire as a function of DC magnetic field was obtained. This large change was explained on the basis of the high value of magnetostriction of FeSiB wire and the increase in the rotational magnetization process. It was also found that resonance frequency of FeSiB wire changes when the wire was in a liquid with different viscosities.     

Measuring the mass of thin films and adsorbates using magnetoelastic techniques

Magnetoelastic sensor techniques have the unique characteristics of being able to wirelessly detect resonant frequency shifts of a magnetoelastic foil in response to differences in the foil mass. However, the mathematical expression that links the resonant frequency shift with the change in the mass of the magnetoelastic foil is rarely reported. Furthermore, this relationship is not easy to ascertain due to potential changes in the Young's modulus of the sensor upon a change in mass loading. In this paper, we have shown that adsorption of water vapor from the gas phase by magnetoelastic ribbons coated with a two layer porous thin film (SiO2/Pt-TiO2) induces large changes in the effective Young's modulus of the sensor. We also demonstrated that the change in Young's modulus upon mass loading can be eliminated from the relationship between mass loading and shifts in resonant frequency by using a technique that we refer to as the two different length sensor method (TDLS). This methodology permits the conversion of the magnetoelastic sensor into a microbalance. From data presented in this paper, we illustrate that the sensitivity for the same sensor can range between 214 Hz/mg for mass loadings of Au to 438 kHz/mg for acetone. In the case of water adsorption, frequency shifts varies from 20.0 kHz/mg when Deltam 相似文献   

Ferrite-Piezoelectric Multilayers for Magnetic Field Sensors

A magnetic field sensor based on magnetoelectric effects in a ferrite-piezoelectric layered sample is proposed. Such sensors are passive, provide direct conversion of magnetic fields into an electrical signal, and allow measurements of both ac and dc magnetic fields. A multilayer sample of nickel zinc ferrite-lead zirconate titanate has been used to characterize the sensor response to ac and dc fields, field orientations, frequency, and temperature. The sample shows a linear response for dc fields up to a maximum of 1750 Oe. The sensor output is temperature independent over 273–337 K, but is dependent on frequency of the ac excitation field. Operating at electromechanical resonance for the element enhances the sensor sensitivity by an order of magnitude. For ac magnetic field sensors, the output varies linearly with amplitude.     

The effect of annealing and gold deposition on the performance of magnetoelastic biosensors

Magnetoelastic materials have a mass-sensitive, characteristic, resonant frequency that make them an ideal choice for application as the platform for a biosensor. The biosensor is formed by immobilizing a bio-molecular recognition element directly onto the surface of the magnetoelastic material. When exposed to the analyte, this bio-molecular recognition element binds the target species (spore or bacteria of interest), thereby increasing the mass and decreasing the resonance frequency of the sensor. This change in characteristic resonance frequency can be determined by monitoring remotely the magnetic flux in response to an applied, time varying, magnetic field with a pick-up coil. However, the environmental stability and bioactivity of the biosensor platform material are very important to performance of the overall biosensor. This research investigates the effects of annealing and deposition of a gold layer on the environmental stability and detection sensitivity of a magnetoelastic biosensor platform. The results show that deposition of a gold layer by sputtering additionally improved bioreactivity while maintaining a balance of environmental stability and detection sensitivity. Two annealing steps in a vacuum oven, one before and one after gold deposition, can effectively increase the magnetoelastic platform's environmental stability, as well as the Q-factor of the resonance signal.     

Characterization of gas-phase adsorption on metal oxide thin films using a magnetoelastic resonance microbalance

In this study, a magnetoelastic resonance microbalance (MERM) was used to directly measure the gas-phase adsorption behavior of water vapor, isopropyl alcohol, and acetone on a sol-gel-derived titanium dioxide sensor coating. The nature of the MERM platform enables chemical measurements in situations in which wires or physical connections are undesired (or not possible) or in which sensor cost is a major issue. The underlying MERM technique (with an uncoated sensor) showed excellent day-to-day stability, a linear calibration over a 1 kHz change in frequency (or a 1.5-mg change in mass), and the ability to detect a mass change of 15 microg without any efforts at sensitivity optimization. The titanium dioxide coated sensor yielded excellent response to each of the analytes; however, the response did not follow a simple linear calibration function. A more complex calibration model or utilization of the coated sensor in a limited concentration range would be required for quantitative analysis. The process of applying the metal oxide coatings onto the magnetic substrate altered the structure of the thin film layer, resulting in a relatively loose packing of the porous primary titanium dioxide particles to create an open overall honeycomb structure, thereby affecting the adsorption behavior at high relative concentration.     

The Effect of Dy Doping on the Magnetic Behavior of YBCO Superconductors

The effect of dysprosium (Dy) doping on yttrium barium copper oxide (YBCO) prepared by conventional solid-state reaction method has been investigated by means of XRD, AC susceptibility, and DC magnetization measurements. AC susceptibility measurements for sintered YBCO pellets have been performed as a function of temperatures at constant frequency and AC field amplitude in the absence of a DC bias field. DC magnetization measurements were done at 5, 20, and 77 K upon zero field cooling (ZFC) process. The magnetization measurements showed a paramagnetic behavior existing at high magnetic fields. The magnetic field dependence of critical current density of the samples has been estimated from DC magnetization data. The partial Dy substitution for Y on YBCO superconductors improves the bulk critical current density at high magnetic fields and at high-temperature regions (higher than 20 K).     

A general expression of magnetic force for soft ferromagnetic plates in complex magnetic fields

The experiments of ferromagnetic plates in different magnetic environments exhibit two distinct phenomena, i.e. the magnetoelastic instability of a ferromagnetic plate in transverse magnetic fields, and the increase of natural frequency of a ferromagnetic plate with low susceptibility in an inplane magnetic field. Although these two typical phenomena can be predicted separately by two kinds of theoretical models in which the magnetic forces are formulated by totally different expressions, no theoretical model has been found to commonly describe them. This makes it difficult to predict theoretically magnetoelastic interaction of a ferromagnetic structure in complex magnetic environment. A variational principle, here, is proposed to establish the governing equations of magnetoelastic interaction for soft ferromagnetic thin plate structures under complex magnetic fields. The functional is chosen as the summation of the magnetic energy and the strain energy as well as the external work from applied magnetic fields. From manipulations of the variational principle, the governing equations of the magnetic field and mechanical deformation together with an expression of equivalent magnetic force exerted on the ferromagnetic plates are obtained. It is shown that this theoretical model can commonly characterize the experimental phenomena of the magnetoelastic interaction aforementioned.     

Quantification of multiple bioagents with wireless, remote-query magnetoelastic microsensors

This paper presents a micromagnetoelastic sensor array for simultaneously monitoring multiple biological agents. Magnetoelastic sensors, made of low-cost amorphous ferromagnetic ribbons, are analogous and complementary to piezoelectric acoustic wave sensors, which track parameters of interest via changes in resonance behavior. Magnetoelastic sensors are excited with magnetic ac fields, and, in turn, they generate magnetic fluxes that can be detected with a sensing coil from a distance. As a result, these sensors are highly attractive, not only due to their small size and low cost, but also because of their passive and wireless nature. Magnetoelastic sensors have been applied for monitoring pressure, temperature, liquid density, and viscosity, fluid How velocity and direction, and with chemical/biological responsive coatings that change mass or elasticity, various biological and chemical agents. In this paper, we report the fabrication and application of a six-sensor array for simultaneous measurement of Escherichia coli O157:H7, staphylococcal enterotoxin B, and ricin. In addition, the sensor array also monitors temperature and pH so the measurements are independent from these two parameters.     

Improving the Sensitivity of Superconductor-Based DC Magnetometer

In this study we report on some critical factors affecting the sensitivity of a magnetic field sensor whose working principle is based on a linear DC field dependence of the second harmonic of the AC response in polycrystalline type-II superconductors. DC-fields down to 2?nT in magnitude could be detected by finding optimal conditions. The optimal sensor design was determined by studying superconductor cores having different geometries and coil configurations. The optimal AC-field frequency, which is required for excitation of the specimen, was found to be 50?kHz. The second harmonic signal changes quite linearly with the DC-field up to 0.1?Oe.     

Temperature feedback control for improving the stability of a semiconductor-metal-oxide (SMO) gas sensor

Stability is a major concern of semiconductor-metal-oxide (SMO) gas sensors in practical applications, as they may cause false alarm problems. Ambient temperature is a major factor affecting the SMO gas sensor's stability. In this paper, we use a novel way to improve temperature stability of SMO (tin oxide) gas sensors by applying a temperature feedback control circuits which are compatible with our microelectromechanical systems sensor fabrication. A built-in platinum temperature sensor can precisely detect the sensor's working temperature. It provides feedback information to compensate the microheater's current to maintain the sensor's working temperature constant, regardless of ambient temperature change. Test results showed that, with this approach, significant improvement of stability has been achieved compared to SMO gas sensors without temperature compensation under the same ambient variation. The algorithm is realized through a hardware circuit, whose advantages include real time, large feedback gain, and low cost.     

Spatial Harmonic Expansion for Use With Magnetic Sensor Arrays

In order to reduce the effects of external magnetic fields on the accuracy of magnetic sensor measurements used for the reconstruction of ac electric currents flowing in massive parallel conductors, we use a spatial circular harmonic expansion of the magnetic scalar potential. Thanks to the linearity of the magnetic field problem with respect to the sources, we can then apply the least squares inversion and obtain the set of currents from the knowledge of the magnetic field data collected by the sensor array in the vicinity of the current carrying conductors. Furthermore, we can optimize the positions and the orientations of the magnetic sensors using D-optimality theory and particle swarm optimization.     

Brillouin Sensing Cable: Design and Experimental Validation

We report on the design and experimental validation of a distributed Brillouin-based optical fiber sensor embedded into concrete structures for temperature and strain measurement. A composite-made wave-like coating designed by finite-element analysis ensures the sensor is transferring optimally temperature and strain fields from the concrete to the optical fiber, where Brillouin scattering takes place. During all experiments, sensors have been interrogated with a commercially available Brillouin optical time-domain reflectometer unit. First, temperature sensitivity of the Brillouin frequency shift were evaluated in PANDA and SMF28 optical fibers, before wrapping them into the specific sheath for embedment into a 3 m-long reinforced concrete beam. Temperature measurements during concrete beam casting agreed with reference measurements, and showed the significant sensor coating influence. A month later, strain measurements performed during a four-point bending experiment showed promising results: linearity and reliability of measurements were demonstrated, under tensile as well as compressive loadings.     

Silicon made resonant microcantilever: Dependence of the chemical sensing performances on the sensitive coating thickness

A gas sensor based on the use of a resonating microcantilever has been realized by using a polymer sensitive coating. From the theoretical study of the microcantilever sensitivity, it has been deduced that the sensitivity is enhanced when the resonant frequency or the sensitive coating thickness are increased. The sensitive coating thickness influence has then been verified experimentally by using polyetherurethane (PEUT) as sensitive coating for ethanol detection. From these measurements, some drawbacks are shown: the coating thickness increase leads to a sensor response time increase and a frequency noise increase which worsens the limit of detection. Conclusions are then made about the sensitive coating optimization depending on application constraint considerations.     

A Resonant Micromachined Magnetic Field Sensor

The design, modeling, and simulation of a novel micromachined magnetic field sensor are discussed. The sensor uses an electrostatic resonator whose fundamental resonant frequency is modified by a Lorentz force generated from the interaction of the sensor structure and the present magnetic field. The sensor was fabricated in a standard bulk micromachining process without the need for any additional processing steps. Since the sensor does not employ any magnetic materials, it does not exhibit hysteresis. A comprehensive model of the sensor behavior is derived which encompasses the interactions of the involved physical domains. Validity of the modeling results was verified by finite-element simulations, and later, through experiments. The sensitivities of the fabricated sensors are in the range of 48-87 Hz/T, depending on sensor structure and dimensions. The design of the sensor allows for its fabrication in many standard microelectromechanical system processes and is compatible with CMOS processes. The theoretical minimum detectable signal with current devices is on the order of 217 nT. Methods to improve the sensitivity of the current sensors are suggested. A linear response to a wide range of magnetic fields makes this design suitable for applications where large fields need to be measured with high resolution.     

Magnetometry in dense coherent media

The rotation of the polarization direction of linearly polarized light produced by the nonlinear magneto-optic effect has been proposed as a sensitive measure of small magnetic fields. In this paper, the advantages of this technique in optically thick media for precision magnetometry are discussed. Results are presented for measurements of this rotation for resonant light in optically dense Rb vapour under various conditions, with and without buffer gas. The sensitivity of the measurements of small magnetic field is investigated as a function of laser frequency, laser power, beam diameter and atomic density for D ₁ line of ⁸⁷Rb.     

Influence of thermomagnetic treatment on the propagation velocity of magnetoelastic oscillations and the ΔE effect in disordered ferromagnetics

An investigation was made of the propagation velocity of magnetoelastic oscillations and the ΔE effect as a function of the magnetic annealing temperature and the external magnetic field in iron-based amorphous metal alloys. It is shown that this dependence is nonmonotonic. The extreme values of the propagation velocity of the magnetoelastic oscillations and the ΔE effect only coincide in a specific range of annealing temperatures. As the annealing temperature increases, the extreme values of the magnetoelastic characteristics shift toward larger magnetic fields. Pis’ma Zh. Tekh. Fiz. 24, 79–83 (August 26, 1998)