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At least 559 records · Page 31Linked to original sources
PubMed2001

A low-cost transmittance transducer for measurement of blood oxygen saturation in extracorporeal circuits.

Designs for a low-cost dual wavelength transducer based on light transmittance and a disposable cuvette for monitoring oxygen saturation (SO2) in extracorporeal arterial and venous blood are presented. The transducer utilizes red and infrared light-emitting diodes and a large photodiode; it is designed to attach to a flow-through cuvette modified from 3/8-in x3/8-in bypass-circuit connectors. A mock extracorporeal circulation system was assembled to evaluate operation of the transducer at a controlled blood SO2 and the relationship between light transmittance and hemodilution. SO2 was calculated based on multiple linear regression analyses. The results show a high correlation between the SO2 obtained with the equipment designed and values measured with commercial gasometric equipment in the range of 50% to 100% (r2 = 0.976, error <2%). The method presented allows continuous and real time measurement of whole blood SO2 with a low-cost transmittance transducer.

Animals↗
PubMed2001

Miniature heart cell force transducer system implemented in MEMS technology.

A fully submersible force transducer system for use with isolated heart cells has been implemented using microelectromechanical systems (MEMS) technology. By using integrated circuit fabrication techniques to make mechanical as well as electrical components, the entire low-mass transducer is only a few cubic millimeters in size and is of higher fidelity (approximately 100 nN and 13.3 kHz in solution) than previously available. When chemically activated, demembranated single cells attached to the device contract and slightly deform a strain gauge whose signal is converted to an amplified electrical output. When integrated with a video microscope, the system is capable of optical determination of contractile protein striation periodicity and simultaneous measurement of heart cell forces in the 100-nN to 50-microN range. The average measured maximal force was Fmax = 5.77 +/- 2.38 microN. Normalizing for the cell's cross-sectional area, Fmax/area was 14.7 +/- 7.7 mN/mm2. Oscillatory stiffness data at frequencies up to 1 kHz has also been recorded from relaxed and contracted cells. This novel MEMS force transducer system permits higher fidelity measurements from cardiac myocytes than available from standard macro-sized transducers.

Animals↗
PubMed2001

Parametric study of the peak negative acoustic pressure distribution within the image plane of a phased array transducer.

A study is presented in which the influence of pulse and transducer characteristics on the distribution of the peak negative acoustic pressure within the image plane of a phased array transducer is shown. First, the influence of the center frequency, the bandwidth of the transmitted pulse, the position of the focus point, and the properties of the phased array are investigated by computer simulation. These simulations show that both the maximal amplitude and the homogeneity of the distribution of the peak negative pressure within a sector image depend on these parameters. Most remarkably, they show that the maximal peak pressure does not necessarily occur on the geometrical symmetry axis of the array transducer but can occur at the outermost lateral lines of a sector image. Second, this effect is demonstrated experimentally by hydrophone measurements of the sound field produced by a standard, clinically used, 2.5-MHz phased array transducer. The experimental results agree well with the theoretical model. The relevance of this study for contrast echography and the safety measurements of ultrasound is discussed.

Acoustics↗
PubMed2002

Finite element analysis of underwater capacitor micromachined ultrasonic transducers.

A simple electro-mechanical equivalent circuit model is used to predict the behavior of capacitive micromachined ultrasonic transducers (cMUT). Most often, cMUTs are made in silicon and glass plates that are in the 0.5 mm to 1 mm range in thickness. The equivalent circuit model of the cMUT lacks important features such as coupling to the substrate and the ability to predict cross-talk between elements of an array of transducers. To overcome these deficiencies, a flnite element model of the cMUT is constructed using the commercial code ANSYS. Calculation results of the complex load impedance seen by single capacitor cells are presented, then followed by a calculation of the plane wave real load impedance seen by a parallel combination of many cells that are used to make a transducer. Cross-talk between 1-D array elements is found to be due to two main sources: coupling through a Stoneley wave propagating at the transducer-water interface and coupling through Lamb waves propagating in the substrate. To reduce the cross-talk level, the effect of structural variations of the substrate are investigated, which includes a change of its thickness and etched trenches or polymer walls between array elements.

Artifacts↗
PubMed2003

Design, development, and characteristics of an in-shoe triaxial pressure measurement transducer utilizing a single element of piezoelectric copolymer film.

In gait analysis, there is growing awareness of the need to simultaneously measure shear and vertical forces for the diagnosis and treatment assessment of pathological foot disorders. This is especially the case in the measurement of the forces between the plantar surface of the foot and the shoe. Although clinical awareness of the need to simultaneously measure shear and vertical forces under the foot has increased little has been done to provide the technology. This is mainly due to the difficulty in constructing devices capable of carrying out this task in the in-shoe environment. The aim of this paper is to describe the development and characteristics of a miniature triaxial transducer measuring 10 x 10 x 2.7 mm and a weight of only 2 g. This transducer is capable of simultaneously measuring three orthogonal forces under any location of the plantar surface of the foot utilizing a single element piezoelectric copolymer P(VDF-TrFE). Transducer sensitivity, linearity, hysteresis, cross-talk and temperature dependence is presented. As well as in-shoe force measurement, this triaxial transducer could have other biomedical and general engineering applications, e.g., prosthetic interface forces, handgrip forces, sport, robotics, etc.

Calibration↗
PubMed2002

Characterization of MEMS transducer performance using near-field scanning interferometry.

Sophisticated ultrasonic transducer microarrays based on micro-electro-mechanical-systems (MEMS) technologies are quickly becoming a reality. A current challenge for many researchers is characterizing the dynamic performance of these and other micro-mechanical devices. In this work, the performance characteristics of a MEMS ultrasonic transducer array were successfully measured using a scanning heterodyne interferometer system. The dynamic response of the entire transducer array was measured, and the results were compared with theoretical predictions. Individual elements were found to vibrate with Bessel-like displacement patterns, and they were resonant at approximately 4 MHz. The full array showed variations in peak out-of-plane displacement levels across the device of 16%, and isolated elements that were dramatically overresponsive and under-responsive. The measured variations across the array may have an undesirable impact on the performance of the transducer and its radiated field.

Elasticity↗
PubMed2003

Electrical characterization of coupled and uncoupled MEMS ultrasonic transducers.

We report electrical characterization of micromachined polysilicon capacitive diaphragms for use as ultrasonic transducers. Admittance measurements yield insight into the resonant behavior and also the damping resulting from ultrasonic radiation and frictional forces caused by the etch release holes. Unbonded transducers exhibit sharp resonances with Q values that increase with decreasing air pressure. We also report for the first time direct bonding of these transducers to solid surfaces. Transducers survive the bonding process and show distinctly different displacement in response to applied dc bias. Finally, a single-degree-of-freedom model is used to obtain insight into the various contributions to damping.

Acoustic Stimulation↗
PubMed2003

Toward virtual biopsy through an all fiber optic ultrasonic miniaturized transducer: a proposal.

The present generation of devices based on opto-acoustic and acousto-optic conversion lets us foresee the possibility of realizing complete miniaturized transmitting-receiving transducers, able to generate and detect wideband ultrasounds by laser light. In the present paper, a miniaturized ultrasonic transducer entirely based on fiber optic technology is proposed. Such a device springs from the conjunction between our research, which has produced a highly efficient fiber optic opto-acoustic source, with the results obtained by other researchers concerning the realization of an ultrasonic receiver based on optical interferometry. Making use of the thermo-elastic effect for ultrasound generation, a source of ultrasound can be obtained by coupling a fiber optic to pulsed laser, if a film capable of absorbing laser light is placed onto fiber end. Starting from these remarks, we propose an efficient opto-acoustic source, able to generate pressure pulses with amplitude of the order of 10(4) Pa and bandwidth extending up to 40 MHz and beyond by using graphite materials as absorbing film. This solution makes use of a low-power pulsed laser as optical source possible. An ultrasonic receiving element was realized placing a Fabry-Perot cavity over the tip of a fiber optic. The cavity thickness modulation induced by ultrasonic beam is detected by an interferometer optical technique. We have realized a prototype of a receiving device that exhibits a sensitivity comparable with that of piezoelectric devices (10-100 nV/Pa) and an almost flat bandwidth extending up to 20 MHz or more. The extreme miniaturization of the resulting ultrasonic transducer, together with its wide ultrasonic frequency bandwidth, is the first step toward ultrasonic tissue biopsy. In this paper, before discussing the problem of constructing a complete ultrasonic transducer composed by a transmitter and receiver, the results carried out in these fields during the last decade are reviewed.

Biopsy↗
PubMed2005

Design and fabrication of broadband graded ultrasonic transducers with rectangular kerfs.

Broadband ultrasound imaging is capable of achieving superior resolution in clinical applications. An effective and easy way of manufacturing broadband transducers is desired for these applications. In this work, a graded material in which the piezoelectric plate is mechanically graded with rectangular grooves is introduced. Finite element analysis (FEA) demonstrated that the graded piezoelectric material could achieve a broadband, time-domain response resulting from multiple resonant modes. Experimental tests were carried out to validate these theoretical results. Based upon the FEA designs, several single-element transducers were fabricated using either a nondiced ceramic or a diced, graded ceramics. A superior bandwidth of 92% was achieved by the graded transducer when compared to a bandwidth of 56% produced by the nondiced ceramic transducer at the expense of a reduced sensitivity.

Ceramics↗
PubMed2005

Acoustic coupling in capacitive microfabricated ultrasonic transducers: modeling and experiments.

In the design of low-frequency transducer arrays for active sonar systems, the acoustic interactions that occur between the transducer elements have received much attention. Because of these interactions, the acoustic loading on each transducer depends on its position in the array, and the radiated acoustic power may vary considerably from one element to another. Capacitive microfabricated ultrasonic transducers (CMUT) are made of a two-dimensional array of metallized micromembranes, all electrically connected in parallel, and driven into flexural motion by the electrostatic force produced by an applied voltage. The mechanical impedance of these membranes is typically much lower than the acoustic impedance of water. In our investigations of acoustic coupling in CMUTs, interaction effects between the membranes in immersion were observed, similar to those reported in sonar arrays. Because CMUTs have many promising applications in the field of medical ultrasound imaging, understanding of cross-coupling mechanisms and acoustic interaction effects is especially important for reducing cross-talk between array elements, which can produce artifacts and degrade image quality. In this paper, we report a finite-element study of acoustic interactions in CMUTs and experimental results obtained by laser interferometry measurements. The good agreement found between finite element modeling (FEM) results and optical displacement measurements demonstrates that acoustic interactions through the liquid represent a major source of cross coupling in CMUTs.

Acoustics↗
PubMed2005

Transducer for harmonic intravascular ultrasound imaging.

A recent study has shown the feasibility of tissue harmonic imaging (THI) using an intravascular ultrasound (IVUS) transducer. This correspondence describes the design, fabrication, and characterization of a THI-optimized piezoelectric transducer with oval aperture of 0.75 mm by 1 mm. The transducer operated at 20 MHz and 40 MHz, and was comprised of a single piezoelectric layer with additional passive layers. The Krimholtz-Leedom-Matthaei (KLM) model was used to iteratively find optimal material properties of the different layers. The transducer characterization showed -6 dB fractional bandwidths of 30% and 25%, and two-way insertion losses of -20 dB and -36 dB, respectively.

Catheterization↗
PubMed2006

Design of a multilayer transducer for acoustic bladder volume assessment.

Catheterization remains the "gold standard" for bladder volume assessment, but it is invasive and introduces the risk of infections and traumas. Therefore, noninvasive bladder volume measurement methods have gained interest. In a preceding study a new technique to measure the bladder volume on the basis of nonlinear ultrasound wave propagation was validated. This paper describes a first prototype of a dedicated multilayer transducer to implement this approach. It is composed of a PZT transducer for transmission and a PVDF layer for reception. Acoustical measurements in a water tank and phantom measurements showed that there is a relation between bladder volume and the harmonic contents of the echo obtained from a region of interest behind the bladder. Simulations with an equivalent transducer model on the basis of KLM-circuit modeling closely matched with the results from the acoustical measurements. The results demonstrated the feasibility of the multilayer transducer design for bladder volume assessment on the basis of nonlinear wave propagation.

Animals↗
PubMed2006

Electrostatic transducers for micromechanical resonators: free space and solid dielectric.

Three electrostatic transduction methods are analyzed for a micromechanical, longitudinal mode, beam resonator. The conventional parallel plate transducer placed at the location of maximum displacement is compared to two solid, dielectric transducers internal to the resonator. Although the solid dielectric offers higher permittivity than the free-space-filled transducers, the unfavorable locations of the internal transducers reduce or even remove the performance advantage of the higher permittivity.

Acoustics↗
PubMed2005

Power Doppler 'blanching' after the application of transducer pressure.

The aim of this study was to determine if transducer pressure modifies power Doppler assessments of rheumatoid arthritis synovium at the metacarpophalangeal joints and metatarsophalangeal joints. Five rheumatoid arthritis patients of varying degrees of 'disease activity' and damage were assessed with power Doppler ultrasound scanning of the dominant hand second to fifth metacarpophalangeal joints. Two rheumatoid arthritis patients had their dominant foot first to fifth metatarsophalangeal joints assessed with power Doppler ultrasound. Ultrasonography was performed with a high frequency transducer (14 MHz) with a colour mode frequency of 10 Mhz, and a standard colour box and gain. In the joint that showed the highest power Doppler signal, an image was made. A further image was taken after transducer pressure was applied. In all patients, there was increased flow to at least one joint. After pressure was applied, power Doppler signal intensity markedly reduced in all images and in some there was no recordable power Doppler signal. Increased transducer pressure can result in a marked reduction or obliteration in power Doppler signal. This power Doppler 'blanching' shows the need for further studies to evaluate sources of error and standardization before power Doppler ultrasound becomes a routine measure of 'disease activity' in rheumatoid arthritis.

Adult↗
PubMed1991

A comparison between fibreoptic and catheter-tip bridge strain gauge transducers for measurement of intrauterine pressure in labour.

A new fibreoptic pressure transducer was used to measure uterine activity in labour, and the results were compared with those obtained with the catheter-tip bridge strain gauge transducer. Readings were obtained from 8 patients in spontaneous labour, and a total of 565 contractions were analysed. When all contractions were analysed the coefficient of variation ranged from 11.24 to 42.74. In 2 patients with vast difference in pressure readings one of the catheters had slipped into the lower uterine segment, when these 2 cases were not considered the coefficient of variation ranged from 11.24 to 21.18. Even in the others there were transient periods lasting 5 to 15 minutes when the pressure difference was greater than 10 mmHg between the 2 catheters. When they were excluded from analysis, along with the 2 cases where one of the catheters was displaced, the coefficient of variation ranged from 9.30 to 16.05. The fibreoptic pressure transducer appears to be a safe, convenient and fairly accurate means of assessing uterine activity. But one must be aware that a catheter giving low readings compared with the initial period soon after insertion may be due to displacement of the transducer tip to the uterine lower segment.

Evaluation Studies as Topic↗
PubMedDate not supplied

New method to obtain ultrasonic angle independent Doppler color images using a sector transducer.

A new method based on the multiple beam procedure to obtain ultrasonic angle independent Doppler color (AIDC) images using Doppler color imaging with a sector transducer has been developed. The transducer was sequentially placed at three locations with different direction orientations to acquire velocity information for the same flow field. Equations have been derived and used to obtain the velocity amplitude and flow direction angle for each point in the flow field from the acquired velocity data and the known positions of the transducer. AIDC images then can be reconstructed. To evaluate the feasibility of this method, AIDC images using a sector transducer have been reconstructed for steady flow fields in a latex tube model and for blood flow in the abdominal aorta of normal human subjects. The quantitative results obtained using this method were in reasonably good agreement with those obtained from existing reference methods.

Aorta, Abdominal↗
PubMed2004

Miniature C-shaped transducers for chordae tendineae force measurements.

C-shaped strain gauge force transducers were designed to enable dynamic measurements of the tension of the individual mitral valve chordae tendineae during the cardiac cycle. The force transducers were constructed from a C-shaped brass ring with a diameter of 6 mm, width of 2 mm, thickness of 0.5 mm, and a mass of <80 mg. Miniature strain gauges elements were cemented onto the inner and outer side of the ring. The strain gauges were connected to thin Teflon wires and coupled in a Wheat-stone half-bridge circuit to a signal conditioner and amplifier. The transducer was coated with a resistive sealing ensuring electrical insulation as well as mechanical protection. Technical testings of sensitivity, linearity, noise level, and frequency response characteristics demonstrated that the transducers were suitable for dynamic chordal force measurements performed under in vitro and in vivo experimental conditions.

Animals↗
PubMed2000

Static and fatigue strength of a fixation device transducer for measuring anterior cruciate ligament graft tension.

To determine which exercises do not overload the graft-fixation complex during intensive rehabilitation from reconstructive surgery of the anterior cruciate ligament (ACL), it would be useful to measure ACL graft loads during rehabilitative activities in vivo in humans. A previous paper by Ventura et al. (1998) reported on the design of an implantable transducer integrated into a femoral fixation device and demonstrated that the transducer could be calibrated to measure graft loads to better than 10 percent full-scale error in cadaveric knees. By measuring both the static and fatigue strengths of the transducer, the purpose of the present study was to determine whether the transducer could be safely implanted in humans without risk of structural failure. Eight devices were loaded to failure statically. Additionally, seven devices were tested using the up-and-down method to estimate the median fatigue strength at a life of 225,000 cycles. The average ultimate strength was 1856 +/- 74 N and the median fatigue strength was 441 N at a life of 225,000 cycles. The maximum graft load during normal daily activities is estimated to be 500 N and the 225,000 cycle life corresponds to that of the average healthy individual during a 12-week period. Considering that patients who have had an ACL reconstruction are less ambulatory than normal immediately following surgery and that biologic incorporation of the graft should be well developed by 12 weeks thus decreasing the load transmitted to the fixation device, the FDT can be safely implanted in humans without undue risk of structural failure.

Activities of Daily Living↗