Razvan Ciocan

Electrical detection of oscillations in microcantilevers and nanocantilevers

Precise determination of the resonant frequency, phase, and quality factor in micromechanical and nanomechanical oscillators would permit, among other things, (i) the detection of trace amounts of adsorbed molecules through a shift in the resonant frequency, and (ii) pressure variations in the environment which affect the mechanical damping of the oscillator. The major difficulty in making these measurements in many cases is the ancillary equipment such as lasers or high magnetic fields that must be used. Being able to make precise measurements with a fully electrical actuation and detection method would greatly extend the usefulness of these oscillators. Detecting the oscillation through changes in the capacitance between the oscillator and a counter electrode is difficult because the static capacitance between them as well as the parasitic capacitance of the rest of the circuitry overwhelm the detection. We have found that the charge on a microcantilever or nanocantilever when driven by a nearby counter...

Model-based microwave image reconstruction: simulations and experiments.

We describe an integrated microwave imaging system that can provide spatial maps of dielectric properties of heterogeneous media with tomographically collected data. The hardware system (800-1200 MHz) was built based on a lock-in amplifier with 16 fixed antennas. The reconstruction algorithm was implemented using a Newton iterative method with combined Marquardt-Tikhonov regularizations. System performance was evaluated using heterogeneous media mimicking human breast tissue. Finite element method coupled with the Bayliss and Turkel radiation boundary conditions were applied to compute the electric field distribution in the heterogeneous media of interest. The results show that inclusions embedded in a 76-diameter background medium can be quantitatively reconstructed from both simulated and experimental data. Quantitative analysis of the microwave images obtained suggests that an inclusion of 14 mm in diameter is the smallest object that can be fully characterized presently using experimental data, while objects as small as 10 mm in diameter can be quantitatively resolved with simulated data.

Optimized numerical pharmacokinetics model for optical molecular probes based on diffusion coefficients in matrigel measured using fluorescence imaging

An original algorithm for measuring diffusion coefficients of optical molecular probes in matrigel from fluorescence data is introduced. The algorithm was developed in Fortran and linked to Graphic User Interface in LabVIEW software that also performs image acquisition and processing. The software models pharmacokinetics of optical molecular probes providing the best fit of experimental data. The paper offers an original way for estimating the diffusion path length through extracellular matrix (ECM) from the rate constants given by the model and from measured diffusion coefficients.

Transmission line matrix model for detection of local changes in permeability using a microwave technique

A three-dimensional transmission-line matrix model was developed to simulate the microwave detection of local changes in permeability. The technique can be used to map local nonuniformities in magnetization. Numerical modeling was carried out for frequencies that are commonly used in microwave nondestructive testing (0.8-1 GHz). A comparison between experimental and numerically generated curves is provided. This comparison validated the proposed numerical model.

Method of early failure detection for elastic diaphragms based on frequency analysis of the acoustic signal

A method of in-service early failure detection based on frequency analysis of the acoustic signal obtained from elastic diaphragms in air-driven pumps is described. A fully digital system for frequency analysis based on a personal computer was developed with a view to practical implementation of this method. The validity of the method was demonstrated by experiments performed under realistic in-plant conditions.

Application of transmission line matrix method to antenna synthesis

A transmission-line matrix (TLM) model was developed to generate field patterns for antenna arrays. The spatial resolution of the proposed model is better than a tenth of a wavelength. Numerical modeling was carried out at 20GHz. The excitation current for each element was computed using the Fourier Transform method. A good agreement was obtained between TLM generated patterns and the analytical results for the considered geometries.

A three-dimensional transmission line matrix model for ultrasonic imaging

A three dimensional numerical model for elastic wave propagation in multilayered structures is the subject of this paper. The model is based on the Transmission Line Matrix method (TLM) and has a three dimensional acoustic node as a key element. A full description of the numerical method implementation is provided. The numerical analysis was applied to structures with a relatively complicated geometry, similar to the geometries used in non-destructive testing and in medical imaging. The comparison between the experimental and numerical frequency response for a multi-layered cylindrical piece validates the proposed numerical model. An acoustic impedance profile similar to biological tissue was numerically modeled. The comparison between real and numerically generated signals shows good agreement between experiment and numerical analysis.

Method and system for air-driven pump monitoring based on frequency analysis of the acoustic signal

A method for early failure detection for elastic diaphragms during their operation is described in this paper. The method is based on frequency analysis of the acoustic signal obtained from an air-driven pump. A fully digital system for frequency analysis based on a personal computer was developed for practical implementation of this method. The system was tested in the laboratory and in plant conditions. In laboratory, diaphragms with different artificial flaws were mounted in the pump and the corresponding spectra recorded. The results helped to set the parameters for in-plant experiments. These experiments were between three and fourteen days. During this time the system performed acquisition and data processing at 10 second apart. Three in-plant experiments have shown that a failure initiation event can be detected from frequency behavior analysis for each test and that a subsequent failure occurs. All failures indicated by the system have been confirmed by visual inspection.

Transmission line matrix model for ultrasonic imaging

A transmission-line matrix (TLM) model was developed to simulate the ultrasound propagation in the multi-layer structures. The spatial resolution of the proposed model is better than tenth wavelength. The numerical modeling is carried-out for frequencies that are usually used in ultrasound imagery (3.5 - 25MHz). The acoustic impedance profile of multi-layer structures considered are similar to those found in nondestructive evaluation and in medical imaging. The structures modeled are: brazed joints, stomach and colon walls. Structures with artificial flaws are also modeled. A comparison between real images and numerical generated ones is provided for each considered structure. Both frequency and time domain responses are obtained from the structures under investigation. Both single and array transducer techniques are modeled and their performances are evaluated for the proposed structures. Different shapes for the incident pulse are considered in numerically generated images.