Mass Density Sensors Research Articles

Design and simulation of a plasmonic density nanosensor for polarizable gases.

In this paper, an optical method of measuring the mass density of polarizable gases is proposed using a plasmonic refractive index nano-sensor. Plasmonic sensors can detect very small changes in the refracting index of arbitrary dielectric materials. However, attributing them to a specific application needs more elaboration of the material's refractive index unit's (RIU) relation with the introduced application. In a gaseous medium, the optical properties of molecules are related to their dipole moment polarizability. Hence, the theoretical index-density relation of Lorentz-Lorenz is applied in the proposed sensing mechanism to interpret changes in the gas' refractive index and to changes in its density. The proposed plasmonic mass density sensor shows a sensitivity of 348.8nm/(gr/cm3) for methane gas in the visible light region. This sensor can be integrated with photonic circuits for gas sensing purposes.

Optomechanical Density Sensor for Sample Consumption of Dozens of Nano-Liters Based on Microbubble Microcavity

Benefiting from the bridgework between cavity optomechanics and optofluidics, microbubble resonators (MBRs) have attracted wide attention both in optomechanics sensing and fundamental research. In this work, we present a novel approach for achieving a fluid mass density sensor based on optomechanics in MBRs. The density responsivity can range from -1.27~-1.54 MHz/(g/ml) for 4 types of mechanical modes. The validation of responsivity is analyzed theoretically, and the calculations indicate that a shorter average radius of the shell can achieve higher responsivity. The density responsivity in a smaller sized and thicker MBR can reach -2.147 MHz/(g/ml). Due to the small volume of the MBRs, the sample consumption can be controlled to dozens of nano-liters, which can greatly reduce the cost of sensing expensive biological samples.

Higher-Order Models for Resonant Viscosity and Mass-Density Sensors.

Advanced fluid models relating viscosity and density to resonance frequency and quality factor of vibrating structures immersed in fluids are presented. The numerous established models which are ultimately all based on the same approximation are refined, such that the measurement range for viscosity can be extended. Based on the simple case of a vibrating cylinder and dimensional analysis, general models for arbitrary order of approximation are derived. Furthermore, methods for model parameter calibration and the inversion of the models to determine viscosity and/or density from measured resonance parameters are shown. One of the two presented fluid models is a viscosity-only model, where the parameters of it can be calibrated without knowledge of the fluid density. The models are demonstrated for a tuning fork-based commercial instrument, where maximum deviations between measured and reference viscosities of approximately ±0.5% in the viscosity range from 1.3 to 243 mPas could be achieved. It is demonstrated that these results show a clear improvement over the existing models.

Array of Microfluidic Beam Resonators for Density and Viscosity Analysis of Liquids

This paper reports on the design, fabrication, and evaluation of a mass density and viscosity sensor based on an array of polysilicon microbeam resonators integrated with 20 pL fluidic microchannels. When filled with water, resonators exhibit resonant frequencies close to 500 KHz and Q-factor values of 400 operating at atmospheric pressure and ambient temperature. Real-time measurements are highly reproducible and only require $250~\mu \text{L}$ of the sample fluid. The built-in interferometric readout enables automatic detection of the beams increasing the throughput analysis and reducing detection times. The frequency shift response shows a linear behavior in accordance with the density of evaluated solvents, organic solutions, and alcoholic drinks, reporting a mass responsivity of 7.4 Hz/pg. Also, the sensor is capable of measuring the viscosity of liquid phase samples with a resolution of 0.15 cP by tracking the Q-factor response of the sensor within a linear regime between 1 to 2.6 cP. This approach demonstrates the ability to identify in real-time changes of fluids in the liquid phase that could provide a valuable assessment for bioanalytical applications. [2016-0319]

Multi Parameter Flow Meter for On-Line Measurement of Gas Mixture Composition

In this paper we describe the development of a system and model to analyze the composition of gas mixtures up to four components. The system consists of a Coriolis mass flow sensor, density, pressure and thermal flow sensor. With this system it is possible to measure the viscosity, density, heat capacity and flow rate of the medium. In a next step the composition can be analyzed if the constituents of the mixture are known. This makes the approach universally applicable to all gasses as long as the number of components does not exceed the number of measured properties and as long as the properties are measured with a sufficient accuracy. We present measurements with binary and ternary gas mixtures, on compositions that range over an order of magnitude in value for the physical properties. Two platforms for analyses are presented. The first platform consists of sensors realized with MEMS fabrication technology. This approach allows for a system with a high level of integration. With this system we demonstrate a proof of principle for the analyses of binary mixtures with an accuracy of 10%. In the second platform we utilize more mature steel sensor technology to demonstrate the potential of this approach. We show that with this technique, binary mixtures can be measured within 1% and ternary gas mixtures within 3%.

Reduced order models for resonant viscosity and mass density sensors

A generalized reduced order model for resonant viscosity and mass density sensors is presented and experimentally verified. The reduced expressions for the resonance frequency and quality factor, respectively, are mathematically valid for in-plane oscillating plates, oscillating spheres and laterally oscillating cylinders. However, as shown for measurements obtained with a tuning fork resonator with rectangular cross-section, the model can also be applied for resonating structures, for which closed form solutions of the fluid structure interaction are not available. Benefits of the presented model are amongst others first, its simplicity, which requires no more than three calibration measurements for parameter identification and second, its general applicability for resonant mass density and viscosity sensors which furthermore facilitates the comparison of different resonant mass density and viscosity sensors in terms of sensitivity and measurement noise propagation.

Validity of Describing Resonant Viscosity and Mass Density Sensors by Linear 2nd Order Resonators

Resonant viscosity and mass density sensors are based on the determination of a mechanical oscillator's frequency response at a characteristic resonant mode upon immersion in a liquid. In many cases the sensors’ characteristics and sensitivities are demonstrated by showing the dependence of their quality factor Q and resonance frequency fr to viscosity η and mass density ρ. Commonly, the transfer function of a linear second order resonator is fit into the recorded frequency response to extract fr and Q, which are then related to the liquid's η and ρ. This approach is widespread in the field of resonant (viscosity and mass density) sensors and thus became a common procedure. However, as from a theoretic point of view, resonators which are interacting with a liquid do not yield linear second order functions, the applicability of this standard approach and its limits are investigated in this work.

Modeling and Experimental Investigation of Resonant Viscosity and Mass Density Sensors Considering their Cross-Sensitivity to Temperature

Abstract In this contribution we discuss a generalized, reduced order model for resonant viscosity and mass density sensors which considers also the devices’ cross sensitivities to temperature. The applicability of the model is substantiated by experimental results from measurements obtained with a circular steel tuning fork in various liquids and temperatures. Advantages of this model are its simplicity, its general applicability for resonant mass density and viscosity sensors which furthermore facilitates the comparison of different sensors.

A Spiral Spring Resonator for Mass Density and Viscosity Measurements

Abstract Most recently introduced viscosity and mass density sensors utilize vibrating resonant mechanical structures interacting with the sample fluid where the resonance frequency and the quality factor are affected by both, the fluid's viscosity and its mass density. Unlike singly clamped beams, straight, doubly clamped structures are advantageous when using electromagnetic excitation and read-out based on Lorentz forces which allow high excitation forces and read-out signals. However, classical straight beams such as bridges are subjected to high cross-sensitivities of their resonance frequencies to ambient temperature. To overcome high spurious temperature dependencies but to benefit from the straight doubly clamped approach, a spiral spring resonator applicable as viscosity and mass density sensor has been designed.

A Mass Density Sensor for Liquids Employing a Lamb Wave Device of ZnO-Film/Al-Foil Composite Structure

A Mass Density Sensor for Liquids Employing a Lamb Wave Device of ZnO-Film/Al-Foil Composite Structure