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At least 523 records · Page 29Linked to original sources
PubMed1999

Apparatus to measure simultaneously 14 isometric leg joint moments. Part 1: Design and calibration of six-axis transducers for the forces and moments at the ankle.

An apparatus has been developed for making isometric measurements of the joint moments corresponding to the 14 degrees of freedom of the legs, in postures ranging between sitting and near full extension. The apparatus is called the multi-moment chair system (MMCS) and is described in the companion paper. This paper describes the most critical components of the MMCS, which are the six-axis transducers for measuring the force and moment components on the plantar-flexion axis of each ankle while the feet are laced into fixed shoes. The transducers are made of steel bars, on which strain gauges are mounted, joined by clamps. The design of the transducer and methods of calibration and error estimation are described. The RMS errors are less than 2 N for the forces and 1 Nm for the moments, but these may be correlated. A method for error reduction that compensates for the finite compliance of the transducer does not reduce the measured errors.

Ankle Joint↗
PubMed1997

[Principle requirements for an electromechanical transducer for implantable hearing aids in inner ear hearing loss. I: Technical and audiologic aspects].

In order to overcome the disadvantages of hearing aids, a significant amount of research aimed at replacing them by implanted ossicular-coupled electronic hearing devices is being carried out. The technical and audiological demands on the electromechanical transducer of an implantable hearing aid for moderate to severe sensorineural hearing losses include high transmission quality of the equivalent sound-pressure level without significant linear or nonlinear distortion, and an energy balance suitable for implantation. Fundamental specifications for a transducer are a high spectral bandwidth of up to 10 kHz, an elongation amplitude of at least 100 nm within this range, a small ripple of the elongation frequence response of around +/- 3 dB, a total harmonic distortion (THD) of less than 0.5%, and a maximum electric power consumption of 0.1 mW. The demands on construction, such as hermetic sealing, biocompatibility, and biostability, are also discussed in detail. It appears that optimum transducer design is essentially a compromise between the physical requirements which are in part conflicting regardless of the transducer principle employed.

Cochlear Implants↗
PubMed2005

A comparison of external transducers and microtransducers in urodynamic studies of female patients.

The urodynamic catheter and its transducer play a significant role in the performance of good urodynamic studies. The fluid-filled (perfusion) catheter with its external strain gauge transducer and the microtransducer catheter with a transducer built directly into the catheter are the two most prevalent catheters used in urodynamic studies today. Either functions differently with regard to how pressures are measured during testing. Both are unique with regard to their requirements for handling and management during testing. Proper transducer calibration, maintenance of standardized reference levels, and attention to catheter zeroing procedures as outlined by the International Continence Society are vital to good study technique and quality testing results. When used in a manner consistent with the catheter's performance characteristics, study error is minimized and meaningful clinical data can be obtained.

Equipment Design↗
PubMed1975

Effect of transducer placement on echocardiographic measurement of left ventricular dimensions.

An echocardiogram from the left ventricle may be used to estimate left ventricular volume and rate of circumferential fiber shortening, to measure posterior wall and interventricular septal thickness and to evaluate the normality of septal motion. Extended application of this technique in this laboratory has emphasized the need for a more standardized means of transducer location and direction. The effect of placing the ultrasonic transducer in several intercostal spaces along the left sternal border was tested in 14 patients. Variability in the left ventricular dimension and the difference in this dimension from end-diastole to end-systole were greater than for duplicate measurements from the same interspace. A system has been developed for more consistent placement of the transducer in each patient, using intracardiac landmarks and observation of transducer orientation to record specific cardiac structures.

Adolescent↗
PubMed1993

A thin bite-force transducer with three-dimensional capabilities reveals a consistent change in bite-force direction during human jaw-muscle endurance tests.

The construction of a 2 mm-thick bite-force transducer, capable of measuring the magnitude and direction of a bite force in three dimensions, is described. The transducer is programmed to display the properties of a bite force on a computer monitor. A preliminary study was designed to test its performance. This took the form of endurance tests on three human subjects: the test was repeated on one subject. The direction of a sustained maximum incisal bite force was monitored while subjects clenched for as long as possible on the transducer. The initial bite force was directed about 10-15 degrees forward of the vertical. During the test the magnitude of the bite force was kept roughly constant but, for all four tests, its direction gradually changed until at the failure point it was nearly vertical. The consistency of the results suggests that the transducer is sufficiently accurate to be a useful tool for studying human jaw mechanics.

Acrylic Resins↗
PubMed1995

Factors affecting sensitivity of a transducer for measuring anterior cruciate ligament force.

In order to determine the measurements and calibration methods necessary to accurately measure in vivo forces in the anterior cruciate ligament (ACL) of the goat, an in vitro study was conducted to evaluate the effect of several factors that could influence the sensitivity of a transducer implanted within the ligament. Four factors were studied in six specimens: flexion angle [0 degrees, 10 degrees, 30 degrees, 50 degrees, and 70 degrees from full extension (FFE)]; tibial rotation (0 degrees and 10 degrees of internal rotation at 30 degrees, 50 degrees, and 70 degrees flexion FFE); loading rate (cycling frequencies of 0.2, 0.5, 1.0, and 2.0 Hz); and temperature (22 degrees C and 37 degrees C). Anteroposterior tibial displacements were applied to the specimens following tissue resection to isolate the ACL. The resultant ACL force magnitude was measured with a multi-component load cell, and transducer sensitivity was calculated as the slope of the output vs force curve in the linear response region. Transducer sensitivity varied with joint position in each specimen, but there was no consistent trend from specimen to specimen in how the sensitivity changed. As a result, there were no statistically significant mean differences (p > 0.05). There were no significant differences and little variation in sensitivity due to changes in either loading rate or tissue temperature, although the latter produced a voltage offset. The results show that the transducer output with zero force on the ligament must be determined in vivo, after which in vitro calibrations may be conducted at room temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

A new transducer system for direct motor unit force measurement.

A new transducer was developed for in situ measurement of the force vector in a complex muscle. The transducer measures the magnitude, and the line of action of a force in a single plane. The dynamic range of the transducer is 0-5 N. This range includes the small forces developed by an active motor unit and the relatively large passive force of a whole muscle. In this study we present the details of the transducer design and specifications, and describe its application in the measurement of motor unit forces of the rabbit masseter muscle.

Animals↗
PubMed1992

Development and validation of a new transducer for intradiscal pressure measurement.

Potentially damaging tensile stresses in the annulus fibrosus are directly related to the hydrostatic pressure in the centre of an intervertebral disc: the design and development of a miniature strain gauge pressure transducer is described for measuring such pressures. Static calibration tests in bulk liquid demonstrated that measurements made with the transducer were of sufficient accuracy and stability for in vitro and in vivo investigations of spinal mechanics, and a study of the dynamic behaviour of the transducer demonstrated that it had a frequency response suitable for in vitro and in vivo investigations. Tests within loaded cadaveric discs showed that the transducer could be used to make repeatable measurements which were free from significant artefacts, when the disc was subjected to forces of up to 4000 N and when deformed in full flexion/extension.

Adult↗
PubMed1982

An improved, ultrasonic auxotonic transducer for use with isolated tissues.

A new type of auxotonic transducer is described which utilises ultrasonic (40 KHz) radiation as an indirect means of detecting length changes in isolated tissues. The transducer is very sensitive to small changes in tissue length and is electrically stable with an adequate frequency response suitable for detecting changes in a wide range of isolated tissues. The transducer does not require an external bridge circuit or external amplification to provide a DC signal adequate to drive a pen recorder (0--1 mV). Applications of the transducer to pharmacological experiments are shown.

Animals↗
PubMed1986

The locations of peak pressures and peak intensities in finite amplitude beams from a pulsed focused transducer.

The effect of finite-amplitude distortion on the positions of peak pressures and peak intensities in beams generated in water by pulsed focused transducers has been investigated experimentally. The pulses generated by three single-element, circular, focused transducers with nominal frequencies of 2.25, 3.5, and 5.0 MHz have been investigated with pressures at the transducer P0 being varied over the range 10 kPa to 1.4 MPa. Measurements were made using a 9 micron thick polyvinylidene difluoride membrane hydrophone. In all cases the locations of peak pressures were not stationary as the field strength was altered. As P0 increased, the distance from the transducer to the positive peak initially increased, and then decreased. The distance to the negative, or decompression peak decreased monotonically with increasing P0. The location of peak pulse intensity integral was found to alter slightly with power, taking a position between the peak positive and negative pressures.

Calibration↗
PubMed1995

Monitoring of pulmonary arterial diastolic pressure through a right ventricular pressure transducer.

Pulmonary arterial diastolic pressure is an important parameter for hemodynamic monitoring in congestive heart failure. It is traditionally obtained through a pulmonary arterial catheter. If it could be obtained from a sensor in the right ventricle, chronic monitoring would be possible without the use of a pulmonary arterial catheter. This study is based on the hypothesis that pulmonary valve opening and pulmonary arterial diastolic pressure occur at the time of maximum positive rate of pressure development (dP/dt) in the right ventricle, when the pressures should be equal. Thus, right ventricular pressure at the time of maximum dP/dt (PAD index) should be a reasonable estimate of pulmonary arterial diastolic pressure. Eight patients with heart failure were catheterized and exposed to hemodynamic stress. Right ventricular and pulmonary arterial pressures were simultaneously recorded from a Millar (Houston, TX) catheter with two pressure transducers. The distal transducer was positioned in the bifurcation of the pulmonary artery and the proximal transducer was placed in the right ventricle. Pulmonary arterial diastolic pressure and PAD index were stored beat by beat on a bed-side computer. Acceptable recordings were obtained in all patients. Recordings from the individual patients showed a good covariation between PAD index and pulmonary arterial pressure during different hemodynamic manuevers, except during infusion of dobutamine, when the correlation was not as good. Pulmonary arterial diastolic pressure may be estimated from a transducer in the right ventricle, thus eliminating the need for a permanent pulmonary arterial catheter in an implantable hemodynamic monitoring system. Further studies are needed to verify the correlation on a long-term basis.

Aged↗
PubMed2007

Analysis of effective radiating area, power, intensity, and field characteristics of ultrasound transducers.

OBJECTIVE: To characterize the ultrasound fields produced by a cohort of transducers from a single manufacturer via hydrophone and Schlieren technology. DESIGN: Descriptive study. SETTING: Measurement laboratory. PARTICIPANTS: Seven same-model ultrasound transducers from a single manufacturer. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Effective radiating area (ERA), total power, spatial average intensity (SAI), beam nonuniformity ratio (BNR), and Schlieren beam widths at 1.0 and 3.3 MHz. RESULTS: Values for ERA (1.0 MHz range, 3.62-4.38 cm(2); 3.3 MHz range, 3.74-4.76 cm(2)), total power (1.0 MHz range, 5.0-5.6 W; 3.3 MHz range, 4.7-5.7 W), SAI (1.0 MHz range, 1.2-1.4 W/cm(2); 3.3 MHz range, 1.0-1.5 W/cm(2)), and BNR (1.0 MHz range, 2.79-5.85; 3.3 MHz range, 2.51-4.56) fell within manufacturer's specifications and U.S. Food and Drug Administration (FDA) regulations. Schlieren analysis showed significantly larger beam widths at 3.3 MHz compared with 1.0 MHz and a large degree of variability in the ultrasound fields generated by the different transducers. There were no significant correlations between beam widths and ERA values. CONCLUSIONS: ERA and total power values in a test cohort exist within a range that met FDA regulations. Individual variability in ERA and total power resulted in 50% variability in SAI. This variability may help explain previous reports of heating differences between transducers.

Acoustics↗
PubMed2004

Estimation of some transducer parameters in a broadband piezoelectric transmitter by using an artificial intelligence technique.

An estimation procedure to efficiently find approximate values of internal parameters in ultrasonic transducers intended for broadband operation would be a valuable tool to discover internal construction data. This information is necessary in the modelling and simulation of acoustic and electrical behaviour related to ultrasonic systems containing commercial transducers. There is not a general solution for this generic problem of parameter estimation in the case of broadband piezoelectric probes. In this paper, this general problem is briefly analysed for broadband conditions. The viability of application in this field of an artificial intelligence technique supported on the modelling of the transducer internal components is studied. A genetic algorithm (GA) procedure is presented and applied to the estimation of different parameters, related to two transducers which are working as pulsed transmitters. The efficiency of this GA technique is studied, considering the influence of the number and variation range of the estimated parameters. Estimation results are experimentally ratified.

Algorithms↗
PubMed2006

High frequency broadband PZT thick film ultrasonic transducers for medical imaging applications.

A modified sol-gel method is used to prepare PZT thick film on Pt-coated silicon substrate. A new method of vacuum filling sol-gel precursor solution is introduced to improve film quality. The effects of the filling on PZT thick film structure and ferroelectric properties are discussed. The fabrication of a high frequency transducer with the PZT film as the actuating layer is described. The performance of the transducer is measured and results show that the transducer backed by E-Solder without a matching layer has a center frequency of 103 MHz and a bandwidth of 70%. Beam profile measurements show that the transducer has an axial resolution of 9.2 microm and a lateral resolution of 33 microm.

Electromagnetic Phenomena↗
PubMed1998

Micropipet-based pico force transducer: in depth analysis and experimental verification.

Measurements of forces in the piconewton range are very important for the study of molecular adhesion and mechanics. Recently, a micropipet-based force transducer for this type of experiment was presented (E. Evans, K. Ritchie, and R. Merkel, 1995, Biophys. J., 68:2580-2587). In the present article we give a detailed mechanical analysis of this transducer, including nonlinear effects. An analytical expression for the transducer stiffness at small elongations is given. Using magnetic tweezers (F. Ziemann, J. Rädler, and E. Sackmann, 1994, Biophys. J., 66:2210-2216), we were able to determine the force displacement relation of this transducer experimentally. Forces from approximately 10 pN to 500 pN were applied. Theoretical predictions and experimental results coincide remarkably well.

Biomechanical Phenomena↗
PubMed1997

A low profile human tendon force transducer: the influence of tendon thickness on calibration.

An in vitro calibration method for human tendon force transducers using tendon thickness to predict the calibration factor has been previously proposed (An et al., 1990, J. Biomechanics 23, 1269-1271). However, changes in the calibration factor due to changing tendon geometry during repeated tendon loading are unknown. A new, low-profile transducer design that measures tendon thickness in the transducer, in situ, is developed. An empirical model estimating the transducer's calibration factor is developed using data from in vitro tension testing of 12 fresh frozen human finger flexor tendons. Each tendon is preseated with ten loading cycles before data collection. Using tendon thickness, the model predicts the measured calibration factor to within 0-15% (average 6%). During repeated loading of an in vitro tendon, the calibration factor changes 15% over the first ten cycles (0-50 N) due to the observed changing tendon thickness. After the first ten loading cycles the variability of the calibration factor is reduced to less than 1% for the next three loading cycles. Hence this new, modified in vitro calibration procedure with tendon preseating reduces the cycle-to-cycle variability caused by the associated change in the tendon thickness.

Calibration↗
PubMed2002

Interdigital transducer analysis using equivalent PSpice model.

Interdigital transducers generating surface acoustic waves have found numerous applications. The present paper deals with an equivalent model of a single interdigital transducer as well as an SAW filter complying with the PSpice programme for the analysis of electronic systems. The suggested model makes it possible to take into account such effects as interelectrode reflections, losses along the acoustic path and the electromagnetic coupling between the transducers. The obtained results of the analysis of an interdigital transducer comply with the results obtained basing on an admittance model and delta-function model. The final aim is to model an SAW oscillator.

Acoustics↗
PubMed2002

Simulations of circular 2D phase-array ultrasonic imaging transducers.

Theoretical simulations of the pulse-echo beam forming of two-dimensional (2D) circular planar phase-array ultrasound transducers were conducted for the optimization of the effective architectures. These results were compared with equivalent linearly reticulated 2D phase-array transducer configurations. It is predicted that ultrasound imagers based on circular 2D phase-array transducers will out perform the other architectures for several medical applications. This study was motivated by the recent demonstration of micromachining of high-density circular as well as linear reticulated 2D phase-array transducers, to achieve real-time high-resolution completely electronic steerable volumetric medical noninvasive ultrasound imaging.

Computer Simulation↗