601 research outputs found
Motion-compensated prediction based algorithm for medical image sequence compression
Cataloged from PDF version of article.A method for irreversible compression of medical image sequences is described. The method relies on discrete cosine
transform and motion-compensated prediction to reduce intra- and inter-frame redundancies in medical image sequences.
Simulation examples are presented
High Power CMUTs: Design and experimental verification
Cataloged from PDF version of article.Capacitive micromachined ultrasonic transducers
(CMUTs) have great potential to compete with piezoelectric
transducers in high-power applications. As the output pressures
increase, nonlinearity of CMUT must be reconsidered
and optimization is required to reduce harmonic distortions.
In this paper, we describe a design approach in which uncollapsed
CMUT array elements are sized so as to operate at the
maximum radiation impedance and have gap heights such that
the generated electrostatic force can sustain a plate displacement
with full swing at the given drive amplitude. The proposed
design enables high output pressures and low harmonic
distortions at the output. An equivalent circuit model of the
array is used that accurately simulates the uncollapsed mode
of operation. The model facilities the design of CMUT parameters
for high-pressure output, without the intensive need
for computationally involved FEM tools. The optimized design
requires a relatively thick plate compared with a conventional
CMUT plate. Thus, we used a silicon wafer as the CMUT
plate. The fabrication process involves an anodic bonding process
for bonding the silicon plate with the glass substrate. To
eliminate the bias voltage, which may cause charging problems,
the CMUT array is driven with large continuous wave
signals at half of the resonant frequency. The fabricated arrays
are tested in an oil tank by applying a 125-V peak 5-cycle
burst sinusoidal signal at 1.44 MHz. The applied voltage is increased
until the plate is about to touch the bottom electrode
to get the maximum peak displacement. The observed pressure
is about 1.8 MPa with −28 dBc second harmonic at the
surface of the array
An improved lumped element nonlinear circuit model for a circular CMUT cell
Cataloged from PDF version of article.This paper describes a correction and an extension in the previously published large signal equivalent circuit model for a circular capacitive micromachined ultrasonic transducer (CMUT) cell. The force model is rederived so that the energy and power is preserved in the equivalent circuit model. The model is able to predict the entire behavior of CMUT until the membrane touches the substrate. Many intrinsic properties of the CMUT cell, such as the collapse condition, collapse voltage, the voltage-displacement interrelation and the force equilibrium before and after collapse voltage in the presence of external static force, are obtained as a direct consequence of the model. The small signal equivalent circuit for any bias condition is obtained from the large signal model. The model can be implemented in circuit simulation tools and model predictions are in excellent agreement with finite element method simulations. © 2012 IEEE
A novel equivalent circuit model for CMUTs
A nonlinear equivalent circuit for immersed transmitting capacitive micromachined ultrasonic transducers (CMUTs) is presented. The velocity profile across the CMUT surface maintains the same form over a wide frequency range. This property and the profile are used to model both the electromechanical conversion and the mechanical section. The model parameters are calculated considering the root mean square of the velocity distribution on the membrane surface as the through variable. The new model is compared with the FEM simulation results. The new model predicts the CMUT performance very accurately. ©2009 IEEE
Experimental characterization of capacitive micromachined ultrasonic transducers
In this paper, capacitive micromachined ultrasonic transducers are fabricated using a sacrificial surface micromachining process. A testing procedure has been established in order to measure the absolute transmit and receive sensitivity spectra of the fabricated devices. The experiments are performed in oil. Pulse-echo experiments are performed and the results are compared to the pitch-catch measurements using calibrated transducers. © 2007 IEEE
Nonlinear modeling of an immersed transmitting capacitive micromachined ultrasonic transducer for harmonic balance analysis.
Finite element method (FEM) is used for transient dynamic analysis of capacitive micromachined ultrasonic transducers (CMUT) and is particularly useful when the membranes are driven in the nonlinear regime. One major disadvantage of FEM is the excessive time required for simulation. Harmonic balance (HB) analysis, on the other hand, provides an accurate estimate of the steady-state response of nonlinear circuits very quickly. It is common to use Mason's equivalent circuit to model the mechanical section of CMUT. However, it is not appropriate to terminate Mason's mechanical LC section by a rigid piston's radiation impedance, especially for an immersed CMUT. We studied the membrane behavior using a transient FEM analysis and found out that for a wide range of harmonics around the series resonance, the membrane displacement can be modeled as a clamped radiator. We considered the root mean square of the velocity distribution on the membrane surface as the circuit variable rather than the average velocity. With this definition, the kinetic energy of the membrane mass is the same as that in the model. We derived the force and current equations for a clamped radiator and implemented them using a commercial HB simulator. We observed much better agreement between FEM and the proposed equivalent model, compared with the conventional model
Investigation of transition frequencies of two acoustically coupled bubbles using a direct numerical simulation technique
The theoretical results regarding the ``transition frequencies'' of two
acoustically interacting bubbles have been verified numerically. The theory
provided by Ida [Phys. Lett. A 297 (2002) 210] predicted the existence of three
transition frequencies per bubble, each of which has the phase difference of
between a bubble's pulsation and the external sound field, while
previous theories predicted only two natural frequencies which cause such phase
shifts. Namely, two of the three transition frequencies correspond to the
natural frequencies, while the remaining does not. In a subsequent paper [M.
Ida, Phys. Rev. E 67 (2003) 056617], it was shown theoretically that transition
frequencies other than the natural frequencies may cause the sign reversal of
the secondary Bjerknes force acting between pulsating bubbles. In the present
study, we employ a direct numerical simulation technique that uses the
compressible Navier-Stokes equations with a surface-tension term as the
governing equations to investigate the transition frequencies of two coupled
bubbles by observing their pulsation amplitudes and directions of translational
motion, both of which change as the driving frequency changes. The numerical
results reproduce the recent theoretical predictions, validating the existence
of the transition frequencies not corresponding to the natural frequency.Comment: 18 pages, 8 figures, in pres
Assessment of breast pathologies using nonlinear microscopy
Rapid intraoperative assessment of breast excision specimens is clinically important because up to 40% of patients undergoing breast-conserving cancer surgery require reexcision for positive or close margins. We demonstrate nonlinear microscopy (NLM) for the assessment of benign and malignant breast pathologies in fresh surgical specimens. A total of 179 specimens from 50 patients was imaged with NLM using rapid extrinsic nuclear staining with acridine orange and intrinsic second harmonic contrast generation from collagen. Imaging was performed on fresh, intact specimens without the need for fixation, embedding, and sectioning required for conventional histopathology. A visualization method to aid pathological interpretation is presented that maps NLM contrast from two-photon fluorescence and second harmonic signals to features closely resembling histopathology using hematoxylin and eosin staining. Mosaicking is used to overcome trade-offs between resolution and field of view, enabling imaging of subcellular features over square-centimeter specimens. After NLM examination, specimens were processed for standard paraffin-embedded histology using a protocol that coregistered histological sections to NLM images for paired assessment. Blinded NLM reading by three pathologists achieved 95.4% sensitivity and 93.3% specificity, compared with paraffin-embedded histology, for identifying invasive cancer and ductal carcinoma in situ versus benign breast tissue. Interobserver agreement was κ = 0.88 for NLM and κ = 0.89 for histology. These results show that NLM achieves high diagnostic accuracy, can be rapidly performed on unfixed specimens, and is a promising method for intraoperative margin assessment.National Institutes of Health (U.S.) (Grant R01-CA178636-01)National Institutes of Health (U.S.) (Grant R01-CA75289-16)United States. Air Force Office of Scientific Research (Grant FA9550-10-1-0551)United States. Air Force Office of Scientific Research (Grant FA9550-12-1-0499)National Institutes of Health (U.S.) (National Research Service Award Postdoctoral Fellowship F32-CA165484
Integrated Quantum Optical Phase Sensor
The quantum noise of light fundamentally limits optical phase sensors. A
semiclassical picture attributes this noise to the random arrival time of
photons from a coherent light source such as a laser. An engineered source of
squeezed states suppresses this noise and allows sensitivity beyond the
standard quantum limit (SQL) for phase detection. Advanced gravitational wave
detectors like LIGO have already incorporated such sources, and nascent efforts
in realizing quantum biological measurements have provided glimpses into new
capabilities emerging in quantum measurement. We need ways to engineer and use
quantum light within deployable quantum sensors that operate outside the
confines of a lab environment. Here we present a photonic integrated circuit
fabricated in thin-film lithium niobate that provides a path to meet these
requirements. We use the second-order nonlinearity to produce a squeezed state
at the same frequency as the pump light and realize circuit control and sensing
with electro-optics. Using a 26.2 milliwatts of optical power, we measure (2.7
0.2 ) squeezing and apply it to increase the signal-to-noise ratio of
phase measurement. We anticipate that on-chip photonic systems like this, which
operate with low power and integrate all of the needed functionality on a
single die, will open new opportunities for quantum optical sensing.Comment: 14 pages, 3+3 figure
Scaling and super-universality in the coarsening dynamics of the 3d random field Ising model
We study the coarsening dynamics of the three-dimensional random field Ising
model using Monte Carlo numerical simulations. We test the dynamic scaling and
super-scaling properties of global and local two-time observables. We treat in
parallel the three-dimensional Edward-Anderson spin-glass and we recall results
on Lennard-Jones mixtures and colloidal suspensions to highlight the common and
different out of equilibrium properties of these glassy systems.Comment: 18 pages, 21 figure
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