Cantilever Sensor Research Articles

Development of a MEMS-based Piezoresistive Cantilever Sensor for Lead (Pb(II)) Detection in Drinking Water

Development of a MEMS-based Piezoresistive Cantilever Sensor for Lead (Pb(II)) Detection in Drinking Water

Replicating Spectral Baseline for Unambiguous Frequency Locking in Resonant Sensors.

Electrothermal piezoresistive resonant cantilever sensors have been fabricated with embedded actuating (heating resistor) and sensing (piezo resistors) parts, with the latter configured in a Wheatstone bridge circuit. Due to the close spacing between these two elements, a direct thermal parasitic effect on the resonant sensor during the actuating-sensing process leads to asymmetric amplitude and reversing phase spectral responses. Such a condition affects the precise determination of the cantilever's resonant frequency, f0. Moreover, in the context of phase-locked loop-based (PLL) resonance tracking, a reversing phase spectral response hinders the resonance locking due to its ambiguity. In this work, a replica of the baseline spectral was applied to remove the thermal parasitic effect on the resonance spectra of the cantilever sensor, and its capability was simulated through mathematical analysis. This replica spectral was subtracted from the parasitized spectral using a particular calculation, resulting in optimized spectral responses. An assessment using cigarette smoke particles performed a desired spectral shifting into symmetrical amplitude shapes and monotonic phase transitions, subsequently allowing for real-time PLL-based frequency tracking.

Higher-order resonance of single-crystal diamond cantilever sensors toward high f‧Q products

MEMS resonant sensing devices require both HF (f) and low dissipation or high quality factor (Q) to ensure high sensitivity and high speed. In this study, we investigate the resonance properties and energy loss in the first three resonance modes, resulting in a significant increase in f‧Q product at higher orders. The third order resonance exhibits an approximately 15-fold increase in f‧Q product, while the Q factor remains nearly constant. Consequently, we achieved an ultrahigh f‧Q product exceeding 1012 Hz by higher-order resonances in single-crystal diamond cantilevers.

Precisely controlled batch-fabrication of highly sensitive co-resonant cantilever sensors from silicon-nitride

Dynamic-mode cantilever sensors are based on the principle of a one-side clamped beam being excited to oscillate at or close to its resonance frequency. An external interaction on the cantilever alters its oscillatory state, and this change can be detected and used for quantification of the external influence (e.g. a force or mass load). A very promising approach to significantly improve sensitivity without modifying the established laser-based oscillation transduction is the co-resonant coupling of a micro- and a nanocantilever. Thereby, each resonator is optimized for a specific purpose, i.e. the microcantilever for reliable oscillation detection and the nanocantilever for highest sensitivity through low rigidity and mass. To achieve the co-resonant state, the eigenfrequencies of micro- and nanocantilever need to be adjusted so that they differ by less than approximately 20%. This can either be realized by mass deposition or trimming of the nanocantilever, or by choice of dimensions. While the former is a manual and error-prone process, the latter would enable reproducible batch fabrication of coupled systems with predefined eigenfrequency matching states and therefore sensor properties. However, the approach is very challenging as it requires a precisely controlled fabrication process. Here, for the first time, such a process for batch fabrication of inherently geometrically eigenfrequency matched co-resonant cantilever structures is presented and characterized. It is based on conventional microfabrication techniques and the structures are made from 1 µm thick low-stress silicon nitride. They comprise the microcantilever and high aspect ratio nanocantilever (width 2 µm, thickness about 100 nm, lengths up to 80 µm) which are successfully realized with only minimal bending. An average yield of % of intact complete sensor structures per wafer is achieved. Desired geometric dimensions can be realized within ±1% variation for length and width of the microcantilever and nanocantilever length, ±10% and ±20% for the nanocantilever width and thickness, respectively, resulting in an average variation of its eigenfrequency by 11%. Furthermore, the dynamic oscillation properties are verified by vibration experiments in a scanning electron microscope. The developed process allows for the first time the batch fabrication of co-resonantly coupled systems with predefined properties and controlled matching states. This is an important step and crucial foundation for a broader applicability of the co-resonant approach for sensitivity enhancement of dynamic-mode cantilever sensors.

Effects of viscous dissipation and activation energy for the MHD Eyring-powell fluid flow with Darcy-Forchheimer and variable fluid properties

The study of flow, heat and mass transference of Eyring-Powell fluid flowing in the existence of micro cantilever sensor is useful to create enhancement in the field of non-Newtonian fluid. The Darcy-Forchheimer porosity medium is considered for the flow analysis. The impressions of thermal radiation, viscous dissipation, heat generation, activation energy, Soret and Dufour effects are taken here to investigate the transference analysis of heat and mass rate. The flow phenomena are inspected under the influence of variable fluid properties. The motivation arises to work in this type of study is due to their applications in various industries such as steam generators, chemical reactors, system of dying package beds, several cooling and heating process and treatment of various diseases. The flow equations are occurred in the form of PDEs and then we utilize suitable similarity transformations to convert them into ODEs. These ODEs are numerically solved by the numerical technique namely, ‘shooting method’. The result reveals that the fluid velocity upsurges due to Hartman number and fluid coefficient whereas opposite impact is illustrious due to porosity coefficient, inertia coefficient and viscosity parameter. The finding indicated that we can upturns the temperature within the flow system due to thermal radiation, thermal conduction coefficient, Eckert number, heat generation and Dufour number. The rate of mass transference enhances for higher inputs of heat conduction coefficient, activation energy and Soret number while reverse behavior is seen due to temperature difference coefficient.

Fabrication and performance of bidirectional cantilever sensor with conductive Thermoplastic Polyurethane porous foams

Cantilever sensors are widely used in many application areas due to their bidirectional sensing performances. In this paper, we propose a bidirectional cantilever sensor with asymmetric sandwich structure via the simple low-temperature template casting and freeze-drying methods. The high sensitivity TPU porous foams are embedded in the low sensitivity foams, which changes the conductivity and sensitivity of asymmetric sandwich structure in different bending direction. Here, direction of the deformation in the cantilever beam can be detected by the piezoresistive behaviors. The results of the experiments demonstrate the asymmetric sandwich structure cantilever sensor exhibits good flexibility, excellent stability, rapid response speed, and remarkable bidirectional sensing.

Unimorph based sensor modelling and rheological assessment of fluidic media using frequency response of improved sensor design

This work presents a hassle-free rheological assessment of fluidic media using the frequency response of a self-sensing and self-actuating piezoelectric cantilever sensor. Firstly, an analytical modelling approach for a unimorph-based cantilever sensor is derived and validated. Afterwards, the sensing performance of a rectangular cantilever sensor is improved by modifying its profile to a stepped shape. Frequency response parameters of the cantilever sensors are tracked in vacuum as well as in water, glycerin and varying concentration glycerin solution. These parameters are used to develop the calibration curves for the density and viscosity assessment of the water-glycerin solutions. The calculated density and viscosity utilizing the cantilever sensors are in good agreement with the respective values given by the standard instruments. This implies that the presented sensors can be successfully used for density and viscosity measurement of range 1000–1270 kg/m3 and 12.82–41.35 cP, respectively. The presented method is capable to simultaneously estimate the density and viscosity of the fluidic media without fully immersing the sensor in that media, which can tackle many operational troubles.

Microgravimetric Modeling-A New Method for Extracting Adsorption Parameters of Functionalized MIL-101(Cr).

As a volatile air pollutant, formaldehyde can enter people's living environment through interior decoration, furniture and paint, causing serious harm to human health. Therefore, it is necessary to develop a sensor for the real-time detection of formaldehyde in low concentrations. According to the chemical interaction between amino groups and formaldehyde, a MIL-101(Cr) aminated-material-based formaldehyde cantilever sensor was prepared, of which ethylenediamine- functionalized MIL-101(Cr) named ED-MIL-101(Cr)) showed the best gas sensing performance. Using quasi-in situ infrared spectroscopy, ED-MIL-101(Cr) was found bound to formaldehyde through a Schiff base. The adsorption enthalpy of formaldehyde-bound ED-MIL-101(Cr) was -52.6 kJ/mol, which corresponds to weak chemical adsorption, so the material showed good selectivity. In addition, ED-MIL-101(Cr) has the most active sites, so its response value to formaldehyde is larger and it takes longer to reach saturation adsorption than bare MIL-101(Cr). Through the research on the gas sensing performance of functionalized MIL-101(Cr) material, we found that it has a strong application potential in the field of formaldehyde monitoring, and the material performance can be quantitatively and accurately evaluated through combining calculation and experimentation for understanding the gas sensing mechanism.

A Rapid, Sensitive, and Specific Detection of Aggregated α-Synuclein by a Liposome-Immobilized Cantilever Sensor

A Rapid, Sensitive, and Specific Detection of Aggregated α-Synuclein by a Liposome-Immobilized Cantilever Sensor

Metal-Multilayered Nanomechanical Cantilever Sensor for Detection of Molecular Adsorption.

A metal-multilayered nanomechanical cantilever sensor was proposed to reduce the temperature effect for highly sensitive gas molecular detection. The multilayer structure of the sensor reduces the bimetallic effect, allowing for the detection of differences in molecular adsorption properties on various metal surfaces with higher sensitivity. Our results indicate that the sensor exhibits higher sensitivity to molecules with greater polarity under mixed conditions with nitrogen gas. We demonstrate that stress changes caused by differences in molecular adsorption on different metal surfaces can be detected and that this approach could be used to develop a gas sensor with selectivity for specific gas species.

Investigation of Unwanted Oscillations of Electrically Modulated Magnetoelectric Cantilever Sensors.

Magnetoelectric thin-film cantilevers consisting of strain-coupled magnetostrictive and piezoelectric layers are promising candidates for magnetic field measurements in biomedical applications. In this study, we investigate magnetoelectric cantilevers that are electrically excited and operated in a special mechanical mode with resonance frequencies above 500 kHz. In this particular mode, the cantilever bends in the short axis, forming a distinctive U-shape and exhibiting high-quality factors and a promising limit of detection of 70pT/Hz1/2 at 10 Hz. Despite this U mode, the sensors show a superimposed mechanical oscillation along the long axis. The induced local mechanical strain in the magnetostrictive layer results in magnetic domain activity. Due to this, the mechanical oscillation may cause additional magnetic noise, deteriorating the limit of detection of such sensors. We compare finite element method simulations with measurements of magnetoelectric cantilevers in order to understand the presence of oscillations. From this, we identify strategies for eliminating the external effects that affect sensor operation. Furthermore, we investigate the influence of different design parameters, in particular the cantilever length, material parameters and the type of clamping, on the amplitude of the undesired superimposed oscillations. We propose design guidelines to minimize the unwanted oscillations.

A comprehensive look at the current and future technologies suitable for at home detection and management of viruses and virus causing diseases, Part I: point of care detection technologies

Home-based point-of-care diagnostic systems have proved to be transformative in the containment of COVID-19 pandemic. They are likely to a critical role in similar pandemics of the future. Some of the systems developed in recent years were used to control the pandemic and many more such systems are at various stages of development and evaluation. Appropriate use of some of the technologies has been shown to yield desired results through early detection and control of the virus. These technologies also assisted attempts to confine people within restricted quarters. This paper takes an outside look at many attempts made around the globe to mold and adopt these technologies to help mitigate the impact of COVID-19 and other similar outbreaks of the future. In addition to some of the implemented technologies, this paper also looks at potential untapped technologies that have prospective applications in controlling pandemic situations. Among the detection technologies reviewed are electrochemical sensors, microfluidic sensors, droplet collection and detection systems, transmucosal-extraction and detection systems, bi-dimensional graphene sensors, bi-conjugate quantum dot sensors, silicon nanowire sensors, nano-bio hybrid material sensors, and nano-sized cantilever sensors.

Optical Fiber-Based Polymer Microcantilever for Chemical Sensing: A Through-Fiber Fabrication Scheme.

Fiber optics offer an emerging platform for chemical and biological sensors when engineered with appropriate materials. However, the large aspect ratio makes the optical fiber a rather challenging substrate for standard microfabrication techniques. In this work, the cleaved end of an optical fiber is used as a fabrication platform for cantilever sensors based on functional polymers. The through-fiber fabrication process is triggered by photo-initiated free-radical polymerization and results in a high-aspect-ratio polymer beam in a single step. The dynamic mode application of these cantilevers is first demonstrated in air. These cantilevers are then tuned for sensing applications, including humidity and chemical sensing based on molecularly imprinted polymers.

Beyond biology: alternative uses of cantilever-based technologies.

Micromechanical cantilever sensors are attracting a lot of attention because of the need for characterizing, detecting, and monitoring chemical and physical properties, as well as compounds at the nanoscale. The fields of application of micro-cantilever sensors span from biological and point-of-care, to military or industrial sectors. The purpose of this work focuses on thermal and mechanical characterization, environmental monitoring, and chemical detection, in order to provide a technical review of the most recent technical advances and applications, as well as the future prospective of micro-cantilever sensor research.

Two-Dimensional MoS2 for Resonant-Gravimetric Detection of Ppb-Level Formaldehyde

The development of formaldehyde (HCHO) gas sensors with high sensitivity, good selectivity, and fast response at room temperature is an important research topic. The resonant microcantilever, with high sensitivity, easy batch manufacturing, and integration, generates sensing signals based on the relationship between the frequency and the mass addition of the adsorbed molecules and shows good application potential in HCHO detection. Herein, we report two species of MoS2 nanosheets (NSs) with 1T and 2H phases as sensitive materials to construct high-performance HCHO resonant cantilever sensors. The 2H-MoS2 gas sensors show better sensitivity toward HCHO compared to the 1T-MoS2 gas sensor. Specifically, the 2H-MoS2 sensor displayed a high sensitivity (Hz) of 13.6-1 ppm HCHO at room temperature, with high selectivity, low limit of detection (10 ppb), and good humidity resistance. The effect of phase structures on the sensing performance was studied by in situ characterizations, thermodynamic analysis, and density functional theory calculations. The good sensing ability could be attributed to the abundant active sites induced by the surface defects, suitable adsorption strength, and the outstanding thermodynamic performance of the 2H-MoS2. The combination of two-dimensional (2D) nanosheet and microcantilever sensors provides a new direction for developing a high-performance room-temperature gas sensor in the future.

Non-coplanar misalignment optical waveguide cantilever sensor with a monotonic response in a large operation range.

This paper reports a non-coplanar misalignment optical waveguide cantilever sensor realizing a monotonic response with a large operation range. A 1×2 Y-branch optical power splitter cantilever structure was designed, and one of the branches was reduced in thickness at the end, as a non-coplanar structure with respect to another. The misalignment coupling of the two branches due to the thickness of one branch leads to a monotonic response of an optical waveguide cantilever sensor. The simulation results showed a monotonic response with a sensitivity of 6×10-4 n m -1 in a large operation range of -1 to 1µm.

Terahertz radiation detection with a cantilever-based photoacoustic sensor.

We report the photoacoustic (PA) response in the terahertz (THz) range by employing a detection process actuated with a silicon cantilever pressure sensor and a carbon-based radiation absorber. The detection relies on the mechanical response of the cantilever, when the volume of the carrier gas inside the PA cell expands with the heat produced by the radiation absorber. The detector interferometrically monitors the movement of the cantilever sensor to generate the PA signal. We selected the absorber material with the highest THz responsivity for detailed studies at 1.4 THz (214 µm wavelength). The observed responsivities of two different radiation absorbers are nearly the same at 1.4 THz and agree within 10% with responsivity values at 0.633 µm wavelength. The results demonstrate the potential of covering with a single PA detector a broad spectral range with approximately constant responsivity, large dynamic range, and high damage threshold.

Support compliance: A non-ignorable factor for cantilever sensors for MEMS application

Support compliance at the fixed end of cantilever beams has significant effects on the measured modulus of elasticity in bending (Eb) and accurate deflection response. Additional deflection caused by support compliance is an easily neglected but an inevitable factor, which results in the large errors of the measured Eb. An effective strategy to design cantilever sensors was proposed by enhancing the loading distance, which not only improve the sensitivity, but also weaken the support compliance effect. In a nutshell, the support compliance effect must be taken into accounted by engineers carefully to improve the accuracy of the measured Eb and deflection response for cantilever sensors which used in MEMS.

Molecular-resolution micro-resonant biosensor with adjustable natural frequency

Modern sensors are becoming increasingly small in size while their sensitivity requirements remain relatively strict, to the point that the processing technology and test technology are highly difficult and costly. This paper proposes a micro-resonant biosensor with adjustable natural frequency. A positive feedback signal with a phase difference of 180 degrees is used to reduce the equivalent mass of the resonator, yielding an ultrahigh resonant frequency. The biosensor is formed by a coating bovine blood solution on the surface of the resonator of a cantilever sensor. The instantaneous frequency equation of the biosensor is established using a coupling dynamic calculation. The changes in instantaneous frequency during hemoglobin oxygen absorption and deoxygenation, are then measured. The proposed millimeter micro-resonant biosensor system measures the molecular weight of a single oxygen molecule quality at 5.7619×10−23 g, only deviating by 8.306 % from the theoretical value. Finally, the potential of the micron scale sensor is deeply taped.

Analysis of MEMS cantilever sensor for sensing volatile organic compounds

Increased concentration of Volatile Organic Compound (VOC) in environment can cause severe health issues and create the ozone layer at ground level. The increased concentration of ozone at the ground level creates the smog which will affect the biodiversity of mother earth, environment and human health in many ways. Many researchers have persuaded the continuous research on miniaturized sensors to detect the VOC with high sensitivity and selectivity. This paper presents the design and fabrication of MEMS cantilever sensor to sense VOCs viz., acetone (C3H6O) and Isopropyl alcohol (C3H8O). Here, the metal oxide films of Poly-vinyl-pyrrolidone (PVP) and Amino-propyl-tri-ethoxy-silane (3-APTES) having 600 nm thickness is deposited on oxidized p-type Si surface by RF sputtering process. The cantilever structure of 128 μm length, 80 μm width and thickness 600 nm is designed having a sensor area of 10,240 μm 2 . With this design specification the sensor is simulated in COMSOL Multiphysics software. Then, the sensor is fabricated using surface micromachining technique. The detection of VOCs is carried out by omnicant instrument. Here, the detection sensitivity of PVP and 3-APTES towards Acetone and Isopropyl alcohol are analyzed. The experimental results show that, PVP coated sensor performs 39% increase in sensitivity as compared to 3-APTES coated sensor to detect acetone, and 3-APTES coating sensor exhibit 7.5% increase in sensitivity to detect Isopropyl alcohol as compared to PVP coated sensor. • The cantilever sensor is designed in COMSOL Multiphysics and fabricated using surface micromachine technique. Then the fabricated sensor is tested in the omnicant instrument. By this experimentation following results and conclusions are drawn. • The coating material PVP and 3 APTES is tested against acetone and Isopropyl alcohol. The sensitivity of PVP with acetone is found 39% greater than sensitivity of 3-APTES with acetone. The sensitivity of PVP with isopropyl alcohol is 7.5% greater than 3PATES with Isopropyl alcohol. • The sensitivity of cantilever sensor is directly proportional to length and inversely proportional to the thickness of the cantilever beam. • The sensitivity is directly proportional to thickness of coated material on the sensor surface. The metal oxide film PVP is the preferable coating material to detect VOC Acetone. 3-APTES is preferable coating material to detect the Iso propyl alcohol.