Calibration Of Transducers Research Articles

Metrological analysis of procedures established in the current standards applicable to the calibration of piezoelectric transducers used in ammunition pressure tests

This work investigates the statistical methods used in the calibration of piezoelectric transducers, which are critical for measuring transient pressure in ammunition testing. These transducers play a vital role in determining internal pressure during the combustion of ammunition propellant, a key factor in assessing ammunition safety and performance. The study focuses on evaluating the significance of the intercept in the linear regression model used for calibration and compares the uncertainty of the fit with the linearity error, a parameter employed by NATO to classify the usability of transducers. Additionally, the study delves into the theoretical background of piezoelectric transducers, the calibration process, and the associated statistical methods. It underscores that NATO mandates the use of a linear regression model with a zero intercept for calibration. However, the study suggests that examining the significance of the intercept could reveal systematic errors or issues with the transducer. The research also explores whether the uncertainty of the fit could serve as an alternative to the linearity error in evaluating transducer usability. In summary, the article investigates the calibration process of piezoelectric transducers, with a focus on the significance of the intercept in linear regression and the potential of using fit uncertainty as a metric for transducer usability. The findings could lead to enhanced calibration standards and better assessments of transducer performance in ammunition tests.

A self-reciprocity calibration of spherical transducers using boundary reflection in a spherical shell.

A self-reciprocity method is described for calibrating a spherical transducer in a spherical shell. The reciprocity constant is calculated using Green's function and the electroacoustic reciprocal principle in the spherical shell. A sensitivity correction is developed by calculating the transducer's receiving force in different fields. An experimental measurement setup is described to calibrate transducers with diameters of 20 and 30 mm in the frequency range from 25 to 63 kHz, calibrated in a 500 mm diameter spherical shell with a thickness of 2 mm. The largest discrepancy in calibration results between the self-reciprocity and three-transducer spherical-wave reciprocity method is around -1.4 dB. The self-reciprocity calibration method, with a smaller volume required than the three-transducer spherical-wave reciprocity method, has a potential advantage in calibrating the transducer at high hydrostatic pressure and varying water temperatures.

Determination of the absolute nonlinear parameters using a pulse-echo method in a terminal impedance-mismatched system

ABSTRACT The pulse-echo method is desirable in practice because it enables single-sided measurement of the absolute nonlinear parameter (β), allowing quantitative characterisation of material properties, such as early damage and elastic constants. Transducer calibration is an essential step to determine the absolute β. However, the current transducer calibration method requires dedicated systems or specific apparatuses for the pulse-echo setup. Impedance-mismatch configurations involving different types of apparatuses have been employed in various studies, but there has not been work investigating and solving the effects of terminal impedance on the determination of β. In this study, the theory of the terminal impedance effect on the transfer function, as well as the β measurements is derived. A practical calibration method is proposed to eliminate the influence of the impedance-mismatched problem and the restrictions of specific apparatuses or experimental configurations. Three simple and impedance-mismatched experimental configurations were designed with general apparatuses. Nonlinear experiments were performed to determine the β of water using planar and focused transducers in the pulse-echo systems with these configurations. The measured β agrees with the reference value, which verifies the effectiveness of the proposed correction method. The measured results using the three configurations are also discussed to give practical advice for building a nonlinear pulse-echo setup.

Calibration of multiple shunted piezoelectric transducers with correction for residual modes and shunt interactions

Piezoelectric shunt damping can be used for efficient vibration mitigation of a single or multiple vibration modes of a structure. Several analytical tuning expressions have been derived for numerous circuit topologies for a single shunt. However, when multiple shunted piezoelectric transducers are attached to a flexible structure, their individual interactions alongside the spill-over from residual modes affect the calibration accuracy. In this paper, explicit correction terms that represent these effects are presented for multiple shunted piezoelectric transducers targeting a single vibration mode. The correction terms are obtained from the evaluation of effective electromechanical coupling factors, while proper balancing between shunts follows from an assumed proportionality between shunt forces. The proposed correction method is applicable to general shunt architectures, for which tuning is available when targeting a single-degree-of-freedom structure. Its ability to regain nearby optimal damping properties is illustrated numerically for the classic series RL shunt.

Transduction, Calibration, and the Penetrability of Pain

Pains are subject to obvious, well-documented, and striking top-down influences. This is in stark contrast to visual perception, where the debate over cognitive penetrability tends to revolve around fairly subtle experimental effects. Several authors have recently taken up the question of whether top-down effects on pain count as cognitive penetrability, and what that might show us about traditional debates. I review some of the known mechanisms for top-down modulation of pain, and suggest that it reveals an issue with a relatively neglected part of the cognitive penetrability literature. Much of the debate inherits Pylyshyn’s stark contrast between transducers and cognition proper. His distinction grew out of his running fight with Gibson, and is far too strong to be defensible. I suggest that we might therefore view top-down influences on pain as a species of transducer calibration. This provides a novel but principled way to distinguish between several varieties of top-down effect according to their architectural features.

Acoustic streaming-based calibration of ultrasound transducers

The accurate determination of the transfer function of ultrasound transducers is important for their design and operational performance. However, conventional methods for quantifying the transfer function, such as hydrophone measurements, radiation force balance, and pulse-echo measurements, are costly and complex due to specialized equipment required. In this study, we introduce a novel approach to estimate the transfer function of ultrasound transducers by measuring the acoustic streaming velocity generated by the transducer. We utilize an experimental setup consisting of a water tank with a millimeter scale, an ink-filled syringe, and a camera for recording the streaming phenomenon. Through streaming velocity measurements in the frequency range from 2 to 8 MHz, we determined the transfer function of an unfocused circular transducer with a center frequency of 5 MHz and a radius of 5.6 mm. We compared the performance of our method with hydrophone and pulse-echo measurements. At the center frequency, we measured a transmit efficiency of 1.9 kPa/V using the streaming approach, while hydrophone and pulse-echo measurements yielded transmit efficiencies of 2.1 kPa/V and 1.8 kPa/V, respectively. These findings demonstrate that the proposed method for estimating the transfer function of ultrasound transducers achieves a sufficient level of accuracy comparable to pulse-echo and hydrophone measurements.

Calibration of an electroacoustic transducer without a primary standard.

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

Calibration, validation and testing of a rotational displacement transducer for measuring wheat leaf elongation rates

Flag leaf growth has been emphasized in the literature as an important secondary trait for wheat breeding under drought stress. To measure leaf elongation rate (LER) in monocotyledons such as wheat, the rotational displacement transducer (RDT) has already been used in several studies, mostly on maize. Still, a comprehensive calibration and measurement protocol of the sensor is lacking. To fill this gap, several experiments were performed: (i) to calibrate the sensor and test its resilience to physical disturbances and changes in environmental conditions, (ii) to validate the calibration on growing plants, and (iii) to compare growth rate in flag leaves of well-watered and drought-treated wheat (Triticum aestivum L.) plants. The study showed that calibration of RDT sensors with a height gauge resulted in very accurate and robust measurements of growth rate and drought stress dynamics in monocotyledons, such as wheat. To correctly interpret the sensor measurements and derive the underlying mechanism, it is however important to consider the complex architecture of the plant, as the RDT not merely measures leaf growth, but also any potential growth of supporting parts.

Modeling of Ammunition Dynamic Pressure Measurement Chain in Ballistic Tests.

The use of piezoelectric transducers for internal dynamic pressure measurements in ammunition testing provides a significant advantage in the development and performance analysis of weapons and ammunition. Knowledge of the electrical characteristics of the dynamic pressure measurement chain, which includes the piezoelectric transducer and the charge amplifier, is a relevant condition for the design of interior ballistics pressure measurement systems. Thus, this study aims to characterize and model a piezoelectric transducer and its associated charge amplifier. First, the piezoelectric transducer was characterized using impedance analysis and modeled using a least squares curve-fitting tool, according to the Butterworth-Van Dyke model. Next, the charge amplifier was characterized through response analysis based on known inputs and modeled using LTSpice simulation techniques and the least squares curve-fit tool. Consequently, a measurement chain model is presented and simulated for two cases with different impulse signals. The first impulse signal was obtained from an interior ballistics computer simulation, and in the second case, it was considered the negative step signal characteristic of the calibration of piezoelectric transducers by means of dead weight. From the simulations, it was possible to verify the effectiveness of the model, which provided results with a low error in relation to the original pressure curve, and its applicability is demonstrated by the result of the simulation of the pressure variation in the calibration, where the attenuation of the signal can be visualized as the characteristic of the input curve changes.

Binocular Vision-Based Method Used for Determining the Static and Dynamic Parameters of the Long-Stroke Shakers in Low-Frequency Vibration Calibration

The long-stroke shaker is essentially required for the calibration of low-frequency vibration transducers, whose performance parameters have significantly impact on the calibration accuracy. The accurate measurement of these parameters is the prerequisite to establish a reliable vibration metrology and traceability system. Currently, an optical collimator or a reference accelerometer is applied to get the static parameter, the laser interferometry or tri- axial sensor-based method is used to obtain the dynamic parameters. However, the former relies on an extra device which increases the complexity and cost of calibration system, and the latter is always difficult to accomplish the accurate and efficient measurement of these parameters. In this study, a binocular vision-based long-stroke shaker performance measurement method is investigated, which has ability to determine the static and dynamic parameters simultaneously during the calibration. This vision method obtains the shaker's bending by measuring the inclinations at the different positions of its guideway, and achieves the amplitude characteristic, distortion, repeatability as well as transverse ratio measurements by accurately acquiring the spatial displacements at different frequencies. Comparison experiments with the two commonly used inclination esti- mation methods, and the laser interferometry and sensor- based method demonstrate that the investigated method is able to get the satisfactory accuracies both for the static and dynamic parameters of long-stroke shaker in vibration calibration.

Alternative audiometric calibration methods: Evaluation of sound level measuring apps for audiometric calibration

Audiometric calibration, which includes the calibration of different audiometer transducers and the measurements of ambient noise levels, is historically carried out using Class 1 sound level meters. As technologies advance, many mobile applications (apps) have been developed to measure sound levels. These apps can provide alternative methods for audiometric calibration in places where sound level meters are not available, such as field testing environments, low-to-mid-income countries, and humanitarian settings. These apps, however, cannot be used for audiometric calibration without first evaluating their performance, which depends on multiple factors including the external components (if any), the operating system and the hardware of the electronic devices. The evaluation of the apps is actually the evaluation of the app and associated factors (i.e., the app systems). This paper discusses methods to assess several key functions of apps implemented in either Android or iOS operation system for audiometric calibration: 1) checking the measurement accuracy at all testing frequencies, 2) deriving and using correction factors, 3) determining the self-noise levels, and 4) evaluating the linear/measurement range. As audiometric calibration usually uses octave or 1/3 octave bands to measure sound pressure levels of tones and narrowband noises with relatively steady temporal characteristics, the accuracy of an app can be evaluated by comparing the levels measured by the app and a Class 1 sound level meter at each frequency. The level difference between the app and the Class 1 sound level meter at each frequency can then be used to calculate correction factors that can be added to subsequent levels measured by the app to improve its accuracy. In addition, methods to determine the self-noise level and the linearity range of apps are discussed. Sample measurement scenarios and alternative methods are provided to illustrate the evaluation process to determine whether an app is suitable for measuring ambient noise levels and for calibrating different audiometric transducers.

Orthogonalization of the measuring basis of triaxial vibration transducers by the method of successive approximations

The transversal sensitivity of tri-axial vibration transducers, which have found vast application in various vibration measuring and material testing systems, decreases the accuracy of measurements. We present a solution to the problem of eliminating the error attributed to the presence of the transverse sensitivity. The measurement error depends on many factors including the ratio of vibration components along the sensitivity axes, the width of the vibration spectrum, and the presence of intrinsic resonances of the vibration transducers in the main and transverse directions. The developed method provides almost complete compensation of the error. Analysis of the components of sensitivity vectors along the measuring directions showed that the transversal sensitivity vectors are in fact the parasitic penetrations from other directions, and can be decomposed along the measuring axes. To orthogonalize the sensitivity vectors during calibration, the sensitivity vectors should be rotated until they coincide with the orthogonal directions. A measuring basis with zero transverse sensitivities is thus obtained, and the sensitivity matrix is reduced to a diagonal form. With this approach the fundamentals and practical algorithm using successive approximations of triaxial transducer calibration with orthogonalization are outlined. Each orthogonalization step is illustrated by the current sensitivity matrix, showing the progress of transversal sensitivity reduction. The results of the developed tri-axial transducer coupled to a special preamplifier-converter with transversal sensitivities reduced to nearly zero values using the developed method are presented. Since calibration is carried out without dismantling of a vibration transducer, it can be carried out not only during its manufacture, but also during verification upon operation, which increases the service life. The use of the described technique not only improves the metrological parameters of vibration transducers, but also provides a significant reduction of the requirements for the accuracy of manufacturing their measuring system, thus reducing the production costs. The presented method is promising for the developing new precise multi-axis vibration transducers and measuring systems on their base.

Measurement of electroacoustic transducer sensitivity in extreme hydrostatic pressure environments

The measurement and acoustic calibration of electroacoustic transducers for underwater sound under extreme pressures (to 10,000 psi / 7km depth) and variety range of temperatures is a great challenge. Specialized facilities consisting of large pressure vessels with pressure and temperature control do exist at Navy faciliites (www.navsea.navy.mil + USRD) but operate to moderate pressures, have limited availability, are expensive and limited access. An alternative or supplement is to measure the change in the electro-mechanical impedance of the of a transducer and use equivalent electrical cirucuit analysis to determine the resulting change in all electrical, electromechanical, and mechanical properties. Having the pressure and temperature depedence of all the consitutent parameters allows an accurate pediction of the transduer performance sensitivity and frequency response (such as TVR Transmit Pressure per Volt, and receive voltage per pressure sensitivity. We measured transducer performance of several devices in the laboratory pressure vessels up to 10 000psi and report on findings.

Setup of a Broadband High-Current Measuring System for the Traceable Calibration of Current Transducers

In this work, we show the development of a broadband high-current measuring system for the traceable calibration of current transducers up to 2000 A. The system can generate a measurement current with frequencies up to 10 kHz and achieves a minimum uncertainty of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$77~\mu \text{A}$ </tex-math></inline-formula> /A up to a frequency of 1 kHz with a reference current of 20 A. In addition to this, nonsinusoidal current waveforms with harmonic frequency components up to 2 kHz can be provided by the measurement system. To the best of our knowledge, this is the first measurement system demonstrated, which is capable of broadband signals up to 2000 A in such a large bandwidth.

A Novel Technique for Estimation and Detection of Specular Reflections Leveraging High Frame Rate Ultrasound Imaging

The clinical interpretability of specular interfaces in ultrasound (US) imaging is heavily influenced by the anatomical knowledge of the operator and the transmit–receive beamforming employed for imaging. The violation of the conventional diffuse assumptions by highly directive specular reflections makes their detection challenging which increases the cognitive burden of operators in tissue characterization or calibrating the beam steering/transducer to ensure their detection. However, the areas for improved operator assistance and related workflow in this regard remain largely unexplored. This work proposes a novel method called tiered subaperture (SA) directivity indexing, which employs a SA-level measurement of energy in the reflections through multiangle plane wave transmissions to automatically identify the directivity of specular reflections. The reflection directivity is vectorized and visually fed as a characterized colored image to the operator to distinguish the specular patterns in the US data. The technique is illustrated for clinical use cases such as needle tracking in guided interventional procedures, anisotropy in MSK US, and bone fracture monitoring. The proposed method improves retention, enables freehand scans, and augmentation of hand–eye coordination for the operators for tissue characterization, beamforming, and transducer calibration thus aiding quicker diagnosis by saving procedure times.

Extrapolation errors of force transducer curve fitting equations

Calibration laboratories often face the challenge of the impossibility to perform full capacity range calibration of their force transducers, particularly below 10 % of the force transducer’s capacity. Sometimes these laboratories use curve fitting extrapolation to estimate and predict force transducer behavior within uncalibrated capacity ranges. This work deals with the study of extrapolation errors in force transducers to know and estimate prediction accuracies when using extrapolation for force transducer calibration in ranges below 10 % and between 50 % and 100 % of the transducer’s capacity. The results of this study showed that the magnitude of the extrapolation error is very close to the magnitude of the reproducibility error within calibrated capacity ranges in the laboratory.

A Proposed Algorithm for Determining the Suitable Number of Significant Digits of Force Transducer Calibration Constants

Precision measurement is one of the important goals of measurement and calibration. Positive measures are designed to provide researches with the highest accuracy and precision levels. In force measurements, force measuring instrument manufacturers are striving to achieve the best force measurement resolution to accompany the high level of calibration measurement capabilities achieved by the primary deadweight machines. In the calibration of the force transducers, polynomial equations which correlate, the applied load on the transducer and its corresponding output signal in mV/V are deduced. These equations contain numerical constants A, B and C. This paper introduces a mechanism to determine the suitable number of significant digits for these constants. Error analysis procedure for the calibration polynomial equation is proposed. This proposed algorithm safeguards the most accurate and realistic method for rounding the calibration constants

Calibration of Ultrasonic Transducer Based on Ultrasonic Logging Instrument for Shaft Sinking.

High-precision logging equipment is critical for measuring the borehole diameter and drilling offset in coal mining and petroleum drilling. We propose a module composition and positioning principle for an ultrasonic transducer based on an ultrasonic logging instrument for shaft sinking by drilling (ULISSD) for calculating the reflection distance. The logging distance, which is the primary performance index of a logging system, is determined by using the self-reception sensitivity and error of the ultrasonic transducer in a downhole system. To measure the error between the piezoelectric element of the transducer and the rubber seal of the borehole logging system, we developed an ultrasonic-transducer error-calibration device and a calibration method for a central-air-return-shaft-drilling project. This calibration device can eliminate the inherent error of the transducer and calculate the rate of propagation with high accuracy. The measurement error is reduced by approximately 1.5 mm; thus, the ULISSD measurement accuracy can be effectively improved in central-air-return-shaft drilling.

Calibration of reference torque transducer in one direction and use of its cubic coefficients in both directions with improved interpolation error

Calibration of reference torque transducer in one direction and use of its cubic coefficients in both directions with improved interpolation error

Design and calibration of a Tonpilz transducer for low frequency medical ultrasound tomography.

The design and performance of a transducer for low frequency ultrasound tomography is presented, motivated by recent research demonstrating that acoustic waves transmitting at frequencies between 10 kHz and 750 kHz penetrate the lungs and may be useful for thoracic imaging. An adaptation of the traditional Tonpilz design was developed, vibrational amplitude and electrical impedance were measured, and an optimal frequency was determined. The design is found to meet the desired mechanical, electrical, and safety specifications. Thus, it was considered a promising option for the target application of pulmonary imaging with ultrasound computed tomography between 50 and 200 kHz; highest efficiency achieved around 125 kHz and 156 kHz, and beam divergence of 40°.