Mass Sensitivity Distribution Research Articles

MEMS Resonant Beam with Outstanding Uniformity of Sensitivity and Temperature Distribution for Accurate Gas Sensing and On-Chip TGA.

Micromechanical resonators have aroused growing interest as biological and chemical sensors, and microcantilever beams are the main research focus. Recently, a resonant microcantilever with an integrated heater has been applied in on-chip thermogravimetric analysis (TGA). However, there is a strong relationship between the mass sensitivity of a resonant microcantilever and the location of adsorbed masses. Different sampling positions will cause sensitivity differences, which will result in an inaccurate calculation of mass change. Herein, an integrated H-shaped resonant beam with uniform mass sensitivity and temperature distribution is proposed and developed to improve the accuracy of bio/chemical sensing and TGA applications. Experiments verified that the presented resonant beam possesses much better uniformity of sensitivity and temperature distribution compared with resonant microcantilevers. Gas-sensing and TGA experiments utilizing the integrated resonant beam were also carried out and exhibited good measurement accuracy.

Design and Analysis of a Novel Quartz Crystal Microbalance Utilizing Distributed Mass Loading Area for Improved Sensitivity

Quartz crystal microbalance (QCM) operates based on a shift in its resonant frequency due to addition of mass in its mass loading area. QCM has been widely used in detecting microgram level surface mass changes in both liquid and gas phases. The conventional QCM structure possesses a circular electrode configuration, which uniformly disperses the mass loading area across its surface. However, due to the energy trapping effect, the radial distribution of mass sensitivity is found to be unequal and diminished toward the edges of the electrode. In this article, the influence of the energy trapping effect is investigated to identify effective regions on the electrode contributing to the frequency shift. From this analysis, a novel topology is proposed by designing a unique distributed electrode configuration to effectively utilize the energy trapping effect and enhance the device mass sensitivity while utilizing smaller mass loading area. This proposed electrode configuration is contrasted with the conventional circular electrode and ring-dot electrode configurations based on their mass sensitivity and uniformity distribution. The conducted analysis revealed that the novel electrode topology attains a noticeably higher mass sensitivity and a comparable uniformity distribution in contrast to the conventional circular and ring-dot electrode configurations.

Design and Analysis of Quartz Crystal Microbalance with a New Ring-Shaped Interdigital Electrode.

In this paper, a new type of ring-shaped interdigital electrode is proposed to improve the accuracy and repeatability of quartz crystal microbalance. The influence of different types of single finger, dot finger, dot double-finger electrodes on mass sensitivity distribution as well as the optimal proportion of finger and gap width are obtained through multi-physical coupling simulation. The results show that the design criteria of interdigital electrodes will not change with the increase in the number of fingers. The gap width should obey the decrease order from central to edge and be about twice the width of finger. The width of the outermost finger and the radius of the middle dot electrode should be maintained at about 0.4 and 0.2 times of the total electrode radius. An experiment was carried out to verify that the quartz wafer with a dot double-finger electrode has high quality factors and less modal coupling, which can satisfy the engineering application well. As a conclusion, this study provides a design idea for the electrode to maintain a uniform distribution of quartz crystal microbalance mass sensitivity.

Advances in the Mass Sensitivity Distribution of Quartz Crystal Microbalances: A Review.

A quartz crystal microbalance (QCM) is a typical acoustic transducer that undergoes a frequency shift due to changes in the mass of its surface. Its high sensitivity, robustness, small size design, and digital output have led to its widespread development for application in the fields of chemistry, physics, biology, medicine, and surface science. Mass sensitivity is one of the vital parameters and forms the basis for quantitative analysis using QCMs. This review firstly introduces the importance, definition, calculation, and measuring method of the mass sensitivity and then focuses on reviewing the influence of electrode parameters (including electrode shape, electrode diameter, electrode thickness, electrode material, etc.) on the mass sensitivity distribution of QCMs. Finally, the effect of the operating frequency on the mass sensitivity of QCMs is also analyzed.

Analysis of the Uniformization of the QCM Mass Sensitivity Distribution through a Dot Multiring Electrode Structure.

In this paper, to improve the uniformity of the quartz crystal microbalance (QCM) mass sensitivity distribution, the effect of the size of dot ring electrode and dot double-ring electrode on the mass sensitivity distribution is analyzed theoretically from the perspective of the electrode width ratio, the width of the partially electroded region, and the electrode thickness. Within a certain range of electrode thickness, there is an optimum electrode width ratio to obtain a relatively uniform distribution. As long as the width of the partially electroded region is not too large or too small, it has no significant influence on the uniformity of the mass sensitivity of the optimum electrode size. The dot triple-ring electrode is proposed and the comparison of the uniformity between the three electrode structures indicates that more division of the electrode region can greatly improve the uniformity of the mass sensitivity distribution. This research provides a new direction for the uniformization of QCM mass sensitivity distribution.

Uniform Mass Sensitivity Distribution of Elliptically Designed Electrodes Based on a Quartz Crystal Microbalance.

Uniformization of mass sensitivity distribution is conducive to the application of the quartz crystal microbalance (QCM) in some fields. However, the sensitivity of the QCM sensor surface perpendicular to the displacement direction is higher that of the displacement direction in the mass sensitivity distribution of ring and double-ring QCMs, which leads to poor reproducibility of the sensor. Considering the effect of the electrode structure on the mass sensitivity distribution, we found that for ring- and double-ring-type QCMs, when the elliptical single ring and double-ring electrode structures are combined, an approximately uniform mass sensitivity can be obtained in all directions. Therefore, this study proposes the elliptical single-ring and elliptical double-ring electrode structure design. Through theoretical calculations and three-dimensional finite element analysis verification, a systematic investigation is carried out to quantify the effect of the ratio of the minor axis to the major axis of the elliptical electrode on the mass sensitivity distribution in different directions, and the optimal ratio is found to be 0.8. Comparing the mass sensitivity of the new type of electrodes and the original electrodes, the result shows that the mass sensitivity distribution of the elliptical double-ring electrode structure is more uniform. Hence, these specially designed electrodes are conducive to improving the repeatability.

Uniformization of QCM’s Mass Sensitivity Distribution by Optimizing its Metal Electrode Configurations

The quartz crystal microbalance (QCM) is an ultra-sensitive measuring device and has been commonly used in many specific applications. The mass sensitivity distribution curve of m-m type QCM (QCM with symmetrical electrode) is a Gaussian distribution. However, achieving highly accurate and repeatable measurements requires the uniform distribution of mass sensitivity. To improve the uniformity of QCM mass sensitivity while ensuring high absolute mass sensitivity, the double-ring electrode geometry is designed. This study improves the size design of the double-ring electrode, and reveals the rules for varying sensitivity and electrode parameters based on a mathematical model. Through analyzing the mass sensitivity distribution of different electrode structures of QCMs, the uniformity of the double-ring electrode QCM is proved. The effects of mass sensitivity distribution of QCM are studied using the finite element method (FEM) by the variation of the size of electrodes, and an optimal size of electrode was discovered. Our results show that the double-ring type QCM has better uniformity of the mass sensitivity distribution and it can maintain the high mass sensitivity when the size of the inner ring of the double-ring electrode is close to half of the size of the outer ring. Meanwhile, there is an optimal outer radius that enables us to obtain an ideal and desirable displacement distribution. The numerical simulation results provide design ideas for the physical design of the double-ring type QCM.

Uniformization of Mass Sensitivity Distribution of Silver Electrode QCM.

Quartz crystal microbalance (QCM) is a highly sensitive mass sensor and has been widely used in many fields. However, the nonuniform distribution of mass sensitivity will lead to poor reproducibility of QCM, which is not conducive to the application of QCM in some fields. Considering the effect of electrode shape, size, and material on mass sensitivity distribution, we found that for an AT-cut QCM with a fundamental frequency of 10 MHz, when the inner and outer diameters of silver ring electrode and the electrode loading factor are 2 and 5 mm and 0.0033, respectively, an approximately uniform mass sensitivity distribution can be obtained. The plating experiment in which rigid silver films were plated on the surface of electrode verified the uniformity. The uniform mass sensitivity distribution will make the application of QCM more convenient; the reproducibility can also be improved. This design of QCM will enrich QCM products and facilitate the application of QCM in various fields.

The Design of a Frame-Like ZnO FBAR Sensor for Achieving Uniform Mass Sensitivity Distributions.

In this paper, an infinite circular ZnO thin film bulk acoustic resonator (FBAR) with a frame-like electrode operating at the thickness-extensional (TE) mode is studied. Two-dimensional scalar differential equations established for the problem in the Cartesian coordinate system are successfully solved by transforming them into normal Bessel equations and modified Bessel equations in the cylindrical coordinate system. Resonant frequencies and vibration distributions are obtained for this frame-like FBAR sensor. A nearly uniform mass sensitivity distribution in the active area is achieved by designing proper electrode size and mass ratio of the driving electrode to the ZnO film. Numerical results show that compared with the reported ring electrode FBAR sensor, the novel frame-like electrode FBAR can achieve a maximum optimization ratio (up to 97.90%) on the uniformity of the mass sensitivity distribution in the active area under the same structural parameters, which is also higher than the optimization ratio 77.63% obtained by the reported double-ring electrode design. Moreover, the mechanism to achieve a very uniform mass sensitivity distribution in the active area by the frame-like electrode is explained in detail according to dispersion curves. Namely, when the resonant frequency of the FBAR sensor is close to the cut-off frequency of the active region in the dispersion curve, the mass sensitivity distribution is nearly uniform. These conclusions provide a theoretical guidance for the design and optimization of ZnO FBAR mass sensors with high performance.

QCM Mass Sensitivity Analysis Based on Finite Element Method

The quartz crystal microbalance (QCM) mass sensitivity distribution based on a finite element method (FEM) is described in this paper. QCMs can measure the micromass through the measurement of resonance frequency; hence, it is widely applied in surface science, electrochemistry, biomedical science, and so on. It has the advantage of simple structure, label-free analysis, low price, and real-time output. However, the QCM measurement has a problem of lack of uniformity. After theoretical calculation and simulation, it was found that this deficiency is closely related to mass sensitivity. The QCM mass sensitivity depends on the metal electrode size, thickness, and shape. We calculated the QCM mass sensitivity based on Sauerbrey's equation, Bessel equation, and energy trapping. Then, the mass sensitivity was simulated based on FEM. The simulation result shows that the QCM mass sensitivity distribution is an approximate Gaussian curve. This method can help to better understand the mass sensitivity distribution, and give useful information to improve uniform of mass sensitivity distribution.

Quartz Crystal Microbalance with Approximately Uniform Sensitivity Distribution

The nonuniformity of QCMs' mass sensitivity distribution is a disadvantage to practical applications. Through theoretical calculations, we found that common ring electrode QCMs could obtain approximately uniform sensitivity distribution by carefully selecting the inner and outer diameters and mass loading factor of the electrode. A series of experiments were carried out using 10 MHz ring electrode QCMs with an inner diameter of 2 mm, an outer diameter of 5 mm, and a loading factor R of 0.0044. The experimental results proved that its mass sensitivity distribution is approximately uniform. This special designed ring electrode QCMs is suitable and convenient for highly accurate measurements.

Research on the frequency stability of a bonded QCM for dew point measurement

A bonded structure of quartz crystal microbalance (QCM) based on finite element method to measure dew point is proposed. Adhesive joints of QCM have dominating impacts on QCM’s stability in a constant environment which is one of crucial problems in designing dew point sensors. Our main purpose is to seek an optimum bonding plan for keeping the frequency stability of dew point sensor. Considering that the QCM mass sensitivity distribution along the surface of the bonded QCM follows a Gaussian-type function, we use R-square as a standard to compare the frequency stability of the structure by changing material and dimension parameters of adhesive joints with the help of APDL language in ANSYS 15.0. At last, four QCMs bonding with various lengths of adhesive joints (L) are chosen for testing time and temperature drift, and the QCM with L less than 2 mm had better frequency stability revealed by partly simulation results.

The modified design of ring electrode quartz crystal resonator for uniform mass sensitivity distribution

The mass sensitivity distribution curve of quartz crystal resonators (QCRs) with common circular electrodes is bell-shaped; however, a uniform mass sensitivity distribution is expected for highly accurate and repeatable measuring results. Pioneers designed a ring electrode QCR with a bimodal distribution curve of mass sensitivity, and an obvious concavity is presented between two peak points for a fundamental operating frequency of 10 MHz. The concavity is an obstacle to uniform mass sensitivity distribution, so eliminating the concavity is the goal of this study; two methods-changing overtone order and designing electrode geometry-are proposed to do so. An analytical theory for sensitivity distribution is introduced in this paper first. Analysis results show that the fifth overtone of 10 MHz is desirable for eliminating the concavity but with a drawback of sacrificing absolute mass sensitivity. The method of designing the electrode geometry can overcome this drawback and dot-ring and double-ring electrode geometries are proposed. When electrode parameters were selected properly, the maximum difference of mass sensitivity between two peak points was reduced by about 42.21% for dot-ring electrode QCR and 77.63% for double-ring electrode QCR compared with that of ring electrode QCR.

Analysis and Improvement of the Mass Sensitivity for Piezoelectric Immunosensor

The objective of this study was to improve the low repeatability in quartz crystal microbalance (QCM) measurements. The constitutive equations for the thickness-shear vibrations of an AT-cut quartz crystal with surface electrodes were used to obtain the particle vibration displacement amplitude equation. Then the mass sensitivity of piezoelectric immunosensor was analyzed and the approach to improve low repeatability was proposed. A 10MHz modified-electrode AT-cut QCM with a maximum mass sensitivity of was designed to verify uniform mass sensitivity distribution in the fully electrode region. Analysis results show that in order to improve the accuracy in QCM immunosensor measurements, it is feasible to improve its mass sensitivity.

Derivation of hazardous doses for amphibians acutely exposed to ionising radiation

Derivation of effect benchmark values for each taxonomic group, which has been difficult due to lack of experimental effects data, is required for more adequate protection of the environment from ionising radiation. Estimation of effects doses from nuclear DNA mass and subsequent species sensitivity distribution (SSD) analysis were proposed as a method for such a derivation in acute irradiation situations for assumed nuclear accident scenarios. As a case study, 5% hazardous doses (HD 5s), at which only 5% of species are acutely affected at 50% or higher lethality, were estimated on a global scale. After nuclear DNA mass data were obtained from a database, 50% lethal doses (LD 50s) for 4.8 and 36% of the global Anura and Caudata species, respectively, were estimated by correlative equations between nuclear DNA mass and LD 50s. Differences between estimated and experimental LD 50s were within a factor of three. The HD 5s obtained by the SSD analysis of these estimated LD 50s data were 5.0 and 3.1 Gy for Anura and Caudata, respectively. This approach was also applied to the derivation of regional HD 5s. The respective HD 5s were 6.5 and 3.2 Gy for Anura and Caudata inhabiting Japan. This HD 5 value for the Japanese Anura was significantly higher than the global value, while Caudata had no significant difference in global and Japanese HD 5s. These results suggest that this approach is also useful for derivation of regional benchmark values, some of which are likely different from the global values.

Film Conductivity Controlled Variation of the Amplitude Distribution of High-temperature Resonators

ABSTRACTHigh-temperature measurements of the spatial distribution of the displacement characteristics of a thickness shear mode langasite (La3Ga5SiO14) resonator are obtained using a laser Doppler interferometer. Thereby, the resonator is excited in the fundamental mode and the third overtone. Further, the resonator is coated with a gas sensitive CeO2-x film which exceeds the metal electrode. In reducing atmospheres the conductivity of the film increases and induces an increase of the effective electrode area. This effect leads to a broadening of the mechanical displacement distribution. The latter depends strongly on the size of the excited part of the resonator which is determined by the effective size of the electrodes. The direct determination of the mechanical displacement at different oxygen partial pressures confirms a model as derived from the electrical impedance of resonator devices [1]. Further, information about the mass sensitivity distribution of resonators is obtained since the property is directly proportional to the amplitude.

Patterned Electrodes for Thickness Shear Mode Quartz Resonators to Achieve Uniform Mass Sensitivity Distribution

Development of an electrode-modified thickness shear mode (TSM) quartz resonator that is responsive to nanogram mass loadings, while exhibiting a mass sensitivity profile that is independent of material placement on the sensor platform, is the aim of this study. The resulting nanogram balance would greatly enhance the field of mass measurement and become useful in applications such as droplet gravimetry, the study of nonvolatile residue (NVR) contamination in solvents. A ring electrode design predicted by an analytical theory for sensitivity distribution to achieve the desired uniform mass sensitivity distribution is presented in this work. Using a microvalve capable of depositing nanogram droplets of a polymer solution, and a linear stepping stage for radial positioning of these droplets across the sensor platform, measurements of the mass sensitivity distributions were conducted and are presented. The measurements agree well with theory. Further improvements are possible and are identified to achieve better uniformity and to reduce the instability in the resonant frequency of these devices. Additionally, droplet gravimetric results for NVR in methanol droplets using the modified TSM devices are presented, which compare well with determinations made by evaporation of larger volumes of the stock solutions.

Patterned Electrodes for Thickness Shear Mode (TSM) quartz Resonators to Achieve Univorm Mass Sensitivity Distribution

not Available.

Scanning Electrochemical Microscopy in Combination with Piezoelectric Quartz Crystal Impedance Analysis for Studying the Growth and Electrochemistry as Well as Microetching of Poly(o-phenylenediamine) Thin Films

The combination of scanning electrochemical microscopy (SECM) with piezoelectric quartz crystal impedance (PQCI) analysis was proposed as a novel multiparameter method for investigating the cyclic voltammetric growth of poly(o-phenylenediamine) (PoPD) thin films at Au electrodes in aqueous solutions of various pH values and the potentiostatic microetching (localized degradation) of these films in 0.10 mol/L aqueous H2SO4 for comparative examinations on polymer porosity and stability. Two potential-sweep ranges, -0.4 to 0.9 (I) and 0 to 0.9 (II) V versus SCE, and four solutions, acidic (A, 0.20 mol/L H2SO4 + 0.10 mol/L Na2SO4; B, 0.10 mol/L H2SO4 + 0.20 mol/L Na2SO4), neutral (C, 0.10 mol/L PBS + 0.20 mol/L Na2SO4, pH 7.2), and alkaline (D, 0.20 mol/L NaOH + 0.20 mol/L Na2SO4) aqueous solutions, were selected for PoPD growth. The pH increase for the polymerization solution increased the molar percentage of polyaniline-like chains in PoPD, as quantified from the current peaks at approximately 0.6 V versus a saturated calomel electrode (SCE) for the oxidation of -NH2 groups in as-prepared PoPD (grown from solutions C and D) during their redox switching in 0.10 mol/L aqueous H2SO4 for the first time. The unusual PQCI responses observed at negative potentials (potential range I) in the first several potential cycles during the cyclic voltammetric growth of PoPD in acidic and neutral solutions have been reasonably explained as being due to the precipitation/dissolution of the poorly soluble phenazinehydrine charge-transfer complexes developed during redox switching of oligomers for the first time, which brought about much less compact PoPD films and their higher degradability than those grown in the same solution but over potential range II. SECM, scanning electron microscopy (SEM), and piezoelectric quartz crystal (PQC) frequency were used to estimate the sizes of etched microscale spots. In addition, the x-, y-, or z-axis movement of a Pt microelectrode of 25-mum diameter near the PQC electrode was found to influence negligibly the PQCI responses in 1.0 mol/L aqueous Na2SO4 containing K4Fe(CN)6 up to 0.10 mol/L, and a new protocol of dynamically electrodepositing silver microwires via the chemical-lens method was proposed for examining the local mass-sensitivity distribution on the PQC surface.

Integration of an electrochemical quartz crystal microbalance into a scanning electrochemical microscope for mechanistic studies of surface patterning reactions

The scanning electrochemical microscope (SECM) is used in combination with an electrochemical quartz crystal microbalance (EQCM) to investigate principle modes of tip-induced interactions. The focus is on the influence of acoustic waves and surface modifying processes on the resonant frequency. Considerable importance is attached to high frequency resolution and its enduring accuracy, especially with regard to mechanistic studies of microstructuring processes. A two-dimensional pattern of standing acoustic waves over the entire quartz crystal was monitored for the first time, revealing the anisotropic thickness–shear motion. In the vertical direction, we detected standing pressure waves caused by reflection at the plane apex of the very small tip, which caused frequency changes below 1 Hz. The mass sensitivity distribution of the 10 MHz quartz crystal was mapped two-dimensionally, and an anisotropy due to the orientation of the electrode tabs was found, corroborating published results. The measured mass sensitivity at the center provides a maximum mass resolution of 50 pg, which is sufficient to elucidate mechanistic sequences involved in microstructuring processes.