Towards Portable MEMS Oscillators for Sensing Nanoparticles.

This paper reports on the design, and implementation of piezoelectric-on-silicon MEMS resonators installed within a portable experimental setup for sensing nanoparticles in a laboratory environment. MEMS oscillators with a center frequency of approximately 5.999 MHz are employed for sensing 50 nm size-selected silver nanoparticles generated in the laboratory.

Parametric Amplifiers Based on Quantum Dots.

Josephson parametric amplifiers (JPAs) approaching quantum-limited noise performance have been instrumental in enabling high fidelity readout of superconducting qubits and, recently, semiconductor quantum dots (QDs). We propose that the quantum capacitance arising in electronic two-level systems (the dual of Josephson inductance) can provide an alternative dissipationless nonlinear element for parametric amplification. We experimentally demonstrate phase-sensitive parametric amplification using a QD-reservoir electron transition in a CMOS nanowire split-gate transistor embedded in a 1.

Mode-localized accelerometer in the nonlinear Duffing regime with 75 ng bias instability and 95 ng/√Hz noise floor.

Mode-localized sensors have attracted attention because of their high parametric sensitivity and first-order common-mode rejection to temperature drift. The high-fidelity detection of resonator amplitude is critical to determining the resolution of mode-localized sensors where the measured amplitude ratio in a system of coupled resonators represents the output metric. Operation at specific bifurcation points in a nonlinear regime can potentially improve the amplitude bias stability; however, the amplitude ratio scale factor to the input measurand in a nonlinear regime has not been fully investigated.

On Weakly Coupled Resonant MEMS Transducers Operating in the Modal Overlap Regime.

Miniaturized physical transducers based on weakly coupled resonators have previously demonstrated the twin benefits of high parametric sensitivity and the first-order common-mode rejection of environmental effects. Current approaches to sensing based on coupled resonator transducers employ strong coupling where the modal overlap of the responses is avoided. This strong coupling limits the sensitivity for such mode-localized sensors that utilize an amplitude ratio (AR) output metric as opposed to tracking resonant frequency shifts.

A vibrating beam MEMS accelerometer for gravity and seismic measurements.

This paper introduces a differential vibrating beam MEMS accelerometer demonstrating excellent long-term stability for applications in gravimetry and seismology. The MEMS gravimeter module demonstrates an output Allan deviation of 9 μGal for a 1000 s integration time, a noise floor of 100 μGal/√Hz, and measurement over the full ±1 g dynamic range (1 g = 9.81 ms).

Weakly Coupled Piezoelectric MEMS Resonators for Aerosol Sensing.

This paper successfully demonstrates the potential of weakly coupled piezoelectric MEMS (Micro-Electro-Mechanical Systems) gravimetric sensors for the detection of ultra-fine particulates. As a proof-of-principle, the detection of diesel soot particles of 100 nanometres or less is demonstrated. A practical monitoring context also exists for diesel soot particles originating from combustion engines, as they are of serious health concern.

Dynamic modulation of modal coupling in microelectromechanical gyroscopic ring resonators.

Understanding and controlling modal coupling in micro/nanomechanical devices is integral to the design of high-accuracy timing references and inertial sensors. However, insight into specific physical mechanisms underlying modal coupling, and the ability to tune such interactions is limited. Here, we demonstrate that tuneable mode coupling can be achieved in capacitive microelectromechanical devices with dynamic electrostatic fields enabling strong coupling between otherwise uncoupled modes.

Closed-Loop Characterization of Noise and Stability in a Mode-Localized Resonant MEMS Sensor.

This paper presents results from the closed-loop characterization of an electrically coupled mode-localized sensor topology including measurements of amplitude ratios over a long duration, stability, noise floor, and the bandwidth of operation. The sensitivity of the prototype sensor is estimated to be -5250 in the linear operation regime. An input-referred stability of 84 ppb with respect to normalized stiffness perturbations is achieved at 500 s.

Measuring Aerosol Phase Changes and Hygroscopicity with a Microresonator Mass Sensor.

The interaction between atmospheric aerosol particles and water vapor influences aerosol size, phase, and composition, parameters which critically influence their impacts in the atmosphere. Methods to accurately measure aerosol water uptake for a wide range of particle types are therefore merited. We present here a new method for characterizing aerosol hygroscopicity, an impaction stage containing a microelectromechanical systems (MEMS) microresonator.

Comparison of the specificity and affinity of surface immobilised Affimer binders using the quartz crystal microbalance.

To enable multiplexed protein analysis through the use of microarrays, reliable molecules capable of specifically binding to a protein of interest with high affinity are required. Further, this specificity and affinity must be retained upon immobilization to the microarray surface. This study investigates the performance of surface bound Affimer proteins, comparing the affinity and specificity of different binders for closely related immunoglobulin molecules using the quartz crystal microbalance with dissipation monitoring (QCM-D).

A microfluidic platform for trapping, releasing and super-resolution imaging of single cells.

A multi-layer device, combining hydrodynamic trapping with microfluidic valving techniques, has been developed for on-chip manipulation and imaging of single cells and particles. Such a device contains a flow layer with trapping channels to capture single particles or cells and a control layer with valve channels to selectively control the trap and release processes. Particles and cells have been successfully trapped and released using the proposed device.

Twenty-Eight Orders of Parametric Resonance in a Microelectromechanical Device for Multi-band Vibration Energy Harvesting.

This paper contends to be the first to report the experimental observation of up to 28 orders of parametric resonance, which has thus far only been envisioned in the theoretical realm. While theory has long predicted the onset of n orders of parametric resonance, previously reported experimental observations have been limited up to about the first 5 orders. This is due to the rapid narrowing nature of the frequency bandwidth of the higher instability intervals, making practical accessibility increasingly more difficult.

Acoustic biosensors.

Resonant and acoustic wave devices have been researched for several decades for application in the gravimetric sensing of a variety of biological and chemical analytes. These devices operate by coupling the measurand (e.g.

Dynamic monitoring of single cell lysis in an impedance-based microfluidic device.

A microfluidic device that is capable of trapping and sensing dynamic variations in the electrical properties of individual cells is demonstrated. The device is applied to the real-time recording of impedance measurements of mouse embryonic stem cells (mESCs) during the process of membrane lysis, with the resulting changes in the electrical properties of cells during this process being quantitatively tracked over time. It is observed that the impedance magnitude decreases dramatically after cell membrane lysis.

Single cell studies of mouse embryonic stem cell (mESC) differentiation by electrical impedance measurements in a microfluidic device.

Biological populations of cells show considerable cell-to-cell variability. Study of single cells and analysis of cell heterogeneity are considered to be critical in understanding biological processes such as stem cell differentiation and cancer development. Recent advances in lab-on-a-chip techniques have allowed single-cell capture in microfluidic channels with the possibility of precise environmental control and high throughput of experiments with minimal usage of samples and reagents.

Characterization of mechanical properties of materials using ultrasound broadband spectroscopy.

This article explores the characterization of homogenous materials (metals, alloys, glass and polymers) by a simple broadband ultrasonic interrogation method. The novelty lies in the use of ultrasound in a continuous way with very low input power (0 dBm or less) and analysis of the transmitted acoustic wave spectrum for material property characterization like speed of sound, density and dimensions of a material. Measurements were conducted on various thicknesses of samples immersed in liquid where continuous-wave, frequency swept ultrasonic energy was incident normal to the sample surface.

Investigating biomechanical noise in neuroblastoma cells using the quartz crystal microbalance.

Quantifying cellular behaviour by motility and morphology changes is increasingly important in formulating an understanding of fundamental physiological phenomena and cellular mechanisms of disease. However, cells are complex biological units, which often respond to external environmental factors by manifesting subtle responses that may be difficult to interpret using conventional biophysical measurements. This paper describes the adaptation of the quartz crystal microbalance (QCM) to monitor neuroblastoma cells undergoing environmental stress wherein the frequency stability of the device can be correlated to changes in cellular state.

Modeling nonlinearities in MEMS oscillators.

We present a mathematical model of a microelectromechanical system (MEMS) oscillator that integrates the nonlinearities of the MEMS resonator and the oscillator circuitry in a single numerical modeling environment. This is achieved by transforming the conventional nonlinear mechanical model into the electrical domain while simultaneously considering the prominent nonlinearities of the resonator. The proposed nonlinear electrical model is validated by comparing the simulated amplitude-frequency response with measurements on an open-loop electrically addressed flexural silicon MEMS resonator driven to large motional amplitudes.

Observation of locked phase dynamics and enhanced frequency stability in synchronized micromechanical oscillators.

Even though synchronization in autonomous systems has been observed for over three centuries, reports of systematic experimental studies on synchronized oscillators are limited. Here, we report on observations of internal synchronization in coupled silicon micromechanical oscillators associated with a reduction in the relative phase random walk that is modulated by the magnitude of the reactive coupling force between the oscillators. Additionally, for the first time, a significant improvement in the frequency stability of synchronized micromechanical oscillators is reported.

Electrical actuation and readout in a nanoelectromechanical resonator based on a laterally suspended zinc oxide nanowire.

In this paper, we present experimental results describing enhanced readout of the vibratory response of a doubly clamped zinc oxide (ZnO) nanowire employing a purely electrical actuation and detection scheme. The measured response suggests that the piezoelectric and semiconducting properties of ZnO effectively enhance the motional current for electromechanical transduction. For a doubly clamped ZnO nanowire resonator with radius ~10 nm and length ~1.

Probing biomolecular interaction forces using an anharmonic acoustic technique for selective detection of bacterial spores.

Receptor-based detection of pathogens often suffers from non-specific interactions, and as most detection techniques cannot distinguish between affinities of interactions, false positive responses remain a plaguing reality. Here, we report an anharmonic acoustic based method of detection that addresses the inherent weakness of current ligand dependant assays. Spores of Bacillus subtilis (Bacillus anthracis simulant) were immobilized on a thickness-shear mode AT-cut quartz crystal functionalized with anti-spore antibody and the sensor was driven by a pure sinusoidal oscillation at increasing amplitude.

Anharmonic surface interactions for biomolecular screening and characterization.

The acoustic response of conventional mechanical oscillators, such as a piezoelectric crystal, is predominantly harmonic at modest amplitudes. However, here, we observe from the electrical response that significant motional anharmonicity is introduced in the presence of attached analyte. Experiments were conducted with streptavidin-coated polystyrene microbeads of various sizes attached to a quartz crystal resonator via specific and nonspecific molecular tethers in liquid.

Transduction dependent optimization of electromechanical parameters for electrostatically actuated MEMS/NEMS resonators.

This paper demonstrates an accurate model to predict the overall effective mass in micro- and nanomechanical resonators with non-uniform deformation along the transduction area. The model is verified experimentally through parameter extraction on various types of resonators with an error less than 3% well within the bounds dictated by manufacturing tolerances. Based on the model, an optimization of transduction electrode designs is proposed for micro- and nanomechanical resonators vibrating in the fabrication plane.

Anharmonic interaction signals for acoustic detection of analyte.

The challenges with frequency-based acoustic detection systems in sensitive, selective, and reliable quantitative estimation of surface-bound analyte are well-known. These systems are traditionally used in their linear incarnations; i.e.

Differential amplification of structural perturbations in weakly coupled MEMS resonators.

Measuring shifts in eigenstates caused by vibration localization in an array of weakly coupled resonators offers 2 distinct advantages for sensor applications compared with the technique of simply measuring resonant frequency shifts: 1) orders of magnitude enhancement in parametric sensitivity; and 2) intrinsic common mode rejection. In this paper, we experimentally demonstrate the common mode rejection in weakly coupled MEMS resonators with significant potential implications for sensor applications. The vibration behavior is studied in pairs of nearly identical MEMS resonators that are electrically coupled and subjected to small perturbations in stiffness under different ambient pressure and temperature.