Sensitivity Of Transducer Research Articles

Параметричні автогенераторні перетворювачі для вимірювання товщини матеріалів на основі конденсаторних чутливих елементів

The article examines the main characteristics of parametric autogenerator thickness measurement transducers with a frequency output signal. The design of the proposed autogenerator transducers is based on transistor structures with negative differential resistance. Capacitors with round and rectangular covers are used as parametric transducers for measuring the thickness of materials, which are passive elements of autogenerator transducers, which greatly simplifies the design of devices for measuring the thickness of materials. Mathematical models of autogenerator transducers were developed based on the principle of converting the energy of a constant electric field into the energy of an alternating electric field, which made it possible to obtain the conversion and sensitivity functions of autogenerator transducers without using a rather complicated method of obtaining Kirchhoff equations from nonlinear equivalent circuits of parametric transducers. It is shown that the main contribution to the change in the conversion functions and the sensitivity equation is made by the change in the thickness of the measured material, which causes a change in the equivalent capacitance and negative differential resistance in the oscillating system of autogenerators, which changes the output frequency of the autogenerator transducers. The sensitivity of thickness measurement transducers varies from 5.31 kHz/μm to 7.5 kHz/μm in the thickness range from 0 to 500 μm. Autogenerator transducers for thickness measurement with frequency output do not require analog-digital transducers and amplifiers for further processing of informative signals, which significantly reduces the cost of information-measuring equipment, and when working at ultra-high frequencies, it is possible to transmit information over considerable distances.

Magnetoelectrics for Implantable Bioelectronics: Progress to Date.

ConspectusThe coupling of magnetic and electric properties manifested in magnetoelectric (ME) materials has unlocked numerous possibilities for advancing technologies like energy harvesting, memory devices, and medical technologies. Due to this unique coupling, the magnetic properties of these materials can be tuned by an electric field; conversely, their electric polarization can be manipulated through a magnetic field.Over the past seven years, our lab work has focused on leveraging these materials to engineer implantable bioelectronics for various neuromodulation applications. One of the main challenges for bioelectronics is to design miniaturized solutions that can be delivered with minimally invasive procedures and yet can receive sufficient power to directly stimulate tissue or power electronics to perform functions like communication and sensing.Magnetoelectric coupling in ME materials is strongest when the driving field matches a mechanical resonant mode. However, miniaturized ME transducers typically have resonance frequencies >100 kHz, which is too high for direct neuromodulation as neurons only respond to low frequencies (typically <1 kHz). We discuss two approaches that have been proposed to overcome this frequency mismatch: operating off-resonance and rectification. The off-resonance approach is most common for magnetoelectric nanoparticles (MENPs) that typically have resonance frequencies in the gigahertz range. In vivo experiments on rat models have shown that MENPs could induce changes in neural activity upon excitation with <200 Hz magnetic fields. However, the neural response has latencies of several seconds due to the weak coupling in the off-resonance regime.To stimulate neural responses with millisecond precision, we developed methods to rectify the ME response so that we could drive the materials at their resonant frequency but still produce the slowly varying voltages needed for direct neural stimulation. The first version of the stimulator combined a ME transducer and analog electronics for rectification. To create even smaller solutions, we introduced the first magnetoelectric metamaterial (MNM) that exhibits self-rectification. Both designs have effectively induced neural modulation in rat models with less than 5 ms latency.Based on our experience with in vivo testing of the rectified ME stimulators, we found it challenging to deliver the precisely controlled therapy required for clinical applications, given the ME transducer's sensitivity to the external transmitter alignment. To overcome this challenge, we developed the ME-BIT (MagnetoElectric BioImplanT), a digitally programmable stimulator that receives wireless power and data through the ME link.We further expanded the utility of this technology to neuromodulation applications that require high stimulation thresholds by introducing the DOT (Digitally programmable Overbrain Therapeutic). The DOT has voltage compliance up to 14.5 V. We have demonstrated the efficacy of these designs through various in vivo studies for applications like peripheral nerve stimulation and epidural cortical stimulation.To further improve these systems to be adaptive and enable a network of coordinated devices, we developed a bidirectional communication system to transmit data to and from the implant. To enable even greater miniaturization, we developed a way to use the same ME transducer for wireless power and data communication by developing the first ME backscatter communication protocol.

Recording of ultra-low frequency electromagnetic emission during loading of a rock sample

The review of publications devoted to the study and features of the registration of electromagnetic emission observed during the loading of samples of rocks, metals, composite materials in laboratory conditions, as well as in areas of disintegration of rock massifs at mining sites is given. Electromagnetic emission observed during the destruction of rock samples in laboratory experiments and field conditions can appear itself not only in the high and low frequency ranges (1000–3·106 Hz and 500–1000 Hz, respectively), but also in the very low and ultra-low frequency (200–500 Hz and 0.01–200.00 Hz, respectively) ranges. However, the overwhelming majority of experimental studies of rock samples under the influence of a destructive load in laboratory conditions are aimed at measuring electromagnetic emission of the high frequency range. An instrumentation and measurement complex is described that allows recording electromagnetic emission in the ultra-low frequency range. The composition of the instrumentation and measurement complex includes magnetic modulation transducers of magnetic induction as magnetic field sensors. The methodology of laboratory experiments on recording electromagnetic signals arising from the influence of an external load on rock samples using an instrumentation and measuring complex is presented. An example of uniaxial loading of a basalt sample is given. When loading the sample under consideration, the amplitude of the electromagnetic emission pulses exceeds the background values of technogenic magnetic noise by two orders of magnitude. The high sensitivity of the magnetic modulation transducer of magnetic induction allows it to be used to register the components of magnetic induction in the process of destruction of rock samples in conditions of interference from technogenic magnetic noise. The results obtained are important for monitoring and forecasting the process of cracking before mining impacts, as well as for studying the geological environment and processes that generate low-frequency electromagnetic emission in the mining areas.

Near Stochiometric LiNbO3 Crystal: the Piezoelectric Features and the Shear Horizontal Guided Wave Transducer for Structural Health Monitoring up to 650 °C.

The application of shear horizontal (SH) guided wave transducers in high-temperature structural health monitoring (SHM) is a topic of significant interest across various industrial engineering sectors. In this study, we utilized the novelty piezoelectric crystal of near stoichiometric lithium niobate (NSLN), which exhibited a robust piezoelectric response (d15 = 77.6 pC/N@room temperature). Next, the pure thickness shear vibration mode d15' through size optimization was designed. It was demonstrated that the NSLN-based ultrasonic guided wave transducers utilizing the optimum d15' mode were proficient in transmitting and receiving pure fundamental SH wave (SH0 wave) along two orthogonal main directions (0° and 90°) over a wide frequency range (100-350 kHz), exhibiting strong response to the SH0 wave. Under the driving voltage of 100 V, the signal voltages of the NSLN-based transducer were found to be on the order of 200.3 and 11.8 mV at room temperature and high temperature of 650 °C, respectively. Moreover, the NSLN-based SH0 transducer showcased its better defect localization ability, and the signal-to-noise ratio (SNR) sensitivity of NSLN-based transducer was evaluated to be 16.1 dB at high temperature of 650 °C. To sum up, the ultrasonic wave transducer based on NSLN crystal demonstrated higher potential applications for in situ SHM under elevated temperatures.

Balancing ensemble averaging and signal stationarity when processing acoustic data recorded during a rocket launch

There are many important details to consider when collecting acoustical data during a rocket launch including system noise floor, dynamic range and transducer sensitivity. In this talk, the choice of signal processing parameters will also be shown to be important. Since the pressures are created by turbulence, ensemble averaging is key to reducing random variation. As such, the use of a Hanning window with 50% overlap would be customary for performing this type of processing. However, as the rocket lifts off, the source location moves, and the data can only be considered stationary for short blocks of time. Therefore, the ability to average is limited by non-stationarity. To balance these competing phenomena, an adjustable windowing function such as the Tukey window may be more appropriate than Hanning. Noise data collected at two different launches will be used to compare of the Hanning window with 50% overlap to that using of the Tukey window with a taper of α = 0.25, which filters 12.5% of the signal at each extremity, with 87.5% overlap. The use of both window types will be compared when estimating auto spectral densities and integrated overall levels. The effect of blocksize will also be determined.

Wide-bandwidth immersion ultrasound transducer made of Mn:PIMNT single crystal/epoxy 1–3 composite

The sensitivity and bandwidth of immersion ultrasound transducer directly determine the echo signal intensity and axial resolution of the immersion ultrasonic testing (IUT) equipment. The active piezoelectric material, which is the core part of the transducer, usually operates in a thickness-stretching vibrational mode. Hence, it is necessary for piezoelectric materials to possess high piezoelectric performance. In this work, a relaxor-based ferroelectric Mn:PIMNT single crystal with excellent electromechanical performance (d33=1220 pC/N, g33=37.87×10−3 Vm/N, and k33=90%) was used to fabricate a crystal/epoxy 1–3 composite transducer. The crystal-based transducer has a center frequency of 3 MHz. The −6 dB bandwidth is 111.4%, and the insertion loss is −25.2 dB, which are much better than PZT-5 H 1–3 composite transducer (74.5% and −32.9 dB). Additionally, the imaging test reveals that the 1–3 composite transducer made of Mn:PIMNT single crystal exhibits better axial resolution, which shows a good application prospect in the field of ultrasonic nondestructive testing.

Synergistic Enhancement of Bandwidth and Sensitivity of Phased Array Ultrasonic Transducer With Novel Acoustic Mismatch Structure

Synergistic Enhancement of Bandwidth and Sensitivity of Phased Array Ultrasonic Transducer With Novel Acoustic Mismatch Structure

Acoustic stack for combined intravascular ultrasound and photoacoustic imaging.

Multimodal intravascular ultrasound and photoacoustic (IVUS/PA) imaging is a promising diagnostic tool for cardiovascular diseases like atherosclerosis. IVUS/PA catheters typically require two independent transducers due to different frequency requirements, potentially increasing the catheter size. To facilitate multimodal imaging within conventional catheter dimensions, we designed, fabricated, and characterized a dual-transducer acoustic stack where a low-frequency (LF) PA receiver sits as a matching layer for the high-frequency (HF) US transducer. While the HF transducer operates around 50 MHz, the LF receiver targets frequencies below 15 MHz to capture most of the PA energy from atherosclerotic plaque lipids. Simulation results reveal that this configuration could increase the sensitivity of the HF transducer by 3.54 dB while maintaining bandwidth. Phantom experiments with fabricated stacks showed improved performance for the US transducer, validating the enhanced sensitivity and bandwidth. Following improvements in stack fabrication, the proposed acoustic stack is a viable design that can significantly enhance diagnostic accuracy for atherosclerosis, providing high-resolution, multifrequency imaging within a compact catheter form factor.

Self-Test of Air-Coupled Probe for Sensitivity Map Production Using Parabolic Reflector.

The spatial distribution of a transduction efficiency over the air-coupled probe surface was proposed as a convenient tool for the probe integrity inspection. In this research, a parabolic reflector is used for passive focusing of the acoustic wave on the surface of inspected probe. Therefore, no additional transducer is required for inspection: probe is used for self-inspection. This approach allows to avoid the expensive focused transducer and replaces it by the same-type air-coupled transducers as probe under test. Moreover, the use of the parabolic mirror for focusing is frequency-independent; therefore, such approach allows to inspect a wide range of the probes. Spread spectrum signals were used for excitation to improve the SNR and bandwidth coverage. The results of the experimental measurements of air-coupled transducer sensitivity map with natural and artificial defects implemented have been presented. Comparison with previously proposed techniques is given. It was found that defects presence distorts the focused beam, creating large sidelobes. Therefore, sensitivity map obtained with the proposed technique is lower quality than with previously proposed techniques. Beam profile measurements using a miniature microphone have been presented. Aperture-limiting mask has been proposed to reduce the sidelobes arising due to defects presence and resulting measurements quality has been improved.

Plasmon-associated DNA genotyping based on crystalline assemblies of metallic carbon nanotubes

Sensitivity and selectivity of modern electrochemical genotyping methods are insufficient to detect a single-oligonucleotide mismatch in low-concentration native DNA samples. Novel methods of tuning, controlling, and monitoring plasmon modes are necessary to achieve attomolar and higher sensitivity for the modern graphene-based transducers of molecular signals. The electrochemical DNA assay is promising one for applications in the molecular diagnostics of tumors with the genome single-nucleotide polymorphism (SNP) for simultaneously discriminating both wild-type and mutant alleles of the gene in very small concentrations. We offer the plasmon-associated DNA-genotyping method based on the screening effects in assemblies of Raman-optically active conjugates comprising DNA and metallic carbon nanotubes. The impedimetric DNA sensors of non-Faradaic type based on the plasmonic screening effect can be more sensitive than the Raman optical transducer based on Raman DNA optical activity resulting in the plasmon resonance due to liability of the Raman transducer parameters to environmental influence.

Elastic Waves Excitation and Focusing by a Piezoelectric Transducer with Intermediate Layered Elastic Metamaterials with and without Periodic Arrays of Interfacial Voids.

Optimization of the structure of piezoelectric transducers such as the proper design of matching layers can increase maximum wave energy transmission to the host structure and transducer sensitivity. A novel configuration of an ultrasonic transducer, where elastic metamaterial insertion is introduced to provide bulk wave mode conversion and to increase wave energy transfer into a substrate, is proposed. Configurations of layered elastic metamaterials with crack-like voids are examined theoretically since they can provide wide band gaps and strong wave localization and trapping. The analysis shows that the proposed metamaterial-based matching layers can sufficiently change wave energy transmission from a piezoelectric active element for various frequency ranges (relatively low frequencies as well as higher ones). The proposed configuration can also be useful for advanced sensing with higher sensitivity in certain frequency ranges or for demultiplexing different kinds of elastic waves.

Tuning the Refractive Index Sensitivity of LSPR Transducers Based on Nanocomposite Thin Films Composed of Noble Metal Nanoparticles Dispersed in TiO2

This work reports on the development of nanoplasmonic thin films consisting of Au, Ag, or Au-Ag nanoparticles dispersed in a TiO2 matrix and the optimization of the deposition parameters to tune their optical response. The thin films were produced by reactive DC magnetron sputtering of a Ti target with Au and/or Ag pellets placed on the erosion zone. The thicknesses (50 and 100 nm) of the films, the current density (75 and 100 A/m2) applied to the target (titanium), and the number of pellets placed on its surface were the deposition conditions that were used to tailor the optical (LSPR) response. The total noble metal content varied between 13 and 28 at.% for Au/TiO2 films, between 22 and 30 at.% for Ag/TiO2 films, and 8 to 29 at% for the Au-Ag/TiO2 systems with 1:1, 1:1.5, and 1:2 Au:Ag atomic ratios. After thermal annealing at 400 and 600 °C, LSPR bands were found for all films concerning the Au-TiO2 and Au-Ag/TiO2, while for Ag/TiO2, only for thin films with 28 and 30 at.% of Ag concentration. Refractive index sensitivity (RIS) was evaluated for Au and Au-Ag/TiO2 thin films. It was found that for bimetallic nanoparticles, the sensitivity can increase up to five times when compared to a monometallic nanoplasmonic system. Using Au-Ag/TiO2 thin films can decrease the cost of fabrication of LSPR transducers while improving their sensitivity.

Study of the phase characteristics of vibration sensors and conditions of orthogonalization of their measuring basis for the systems of vibration control and vibration testing of materials

To identify the most vibration-sensitive structures of the materials during vibration tests, it is necessary to determine the vibration vector in an orthogonal basis The effectiveness of the tests depends on the accuracy of the vector measurement. The transverse sensitivity of tri-axial vibration transducers, which have found vast application in various vibration measuring and material testing systems, leads to increased measurement errors and limits the frequency range of measurements. The errors can be reduced to almost zero using the proposed method of electronic orthogonalization, which involves rotation of the sensitivity vectors until they coincide with the orthogonal basis, resulting in zero transverse sensitivity. This approach has been successfully developed and works rather well in the low frequency band of the vibration transducer frequency response, wherein the amplitude-characteristics are linear and there is no phase shift in the channels. An emphasis is made on the influence of the phase characteristics of vibration sensors on the formation of orthogonalizing matrices that determine the requirements for an orthogonalizer. The structure of the installation for automated recording amplitude-frequency and phase-frequency responses of the vibration transducer, methodology and results of experimental study of a tri-axial piezoelectric accelerometer (TPA) with one inertia element and oblique-angle measuring basis are presented. The results obtained under vibration activated in three mutually perpendicular directions along the measuring axes show that the transducer measuring system is properly designed to provide for effective broadband orthogonalization of the measuring basis. The results obtained can be used to develop orthogonalizing transducers that eliminate transverse sensitivity in a wide frequency range, as well as to improve the design of sensors and their metrological characteristics.

An electrical impedance matching method of dual-frequency transducers for ultrasound internal imaging

A micro single transducer with two resonant frequencies can solve the inherent contradiction between detection depth and resolution by simultaneously emitting two frequency bands of ultrasonic waves. But the difference of impedance values in the two resonant frequency bands seriously affects dual-frequency echo signal efficiency. In order to improve the quality of transducer sensitivity, a dual-frequency electrical impedance matching method is proposed in the study. By selecting a specific matching structure to match one frequency without messing up the impedance of another frequency, the two frequencies can be designed independently to achieve preliminary impedance matching. The matching networks for single frequency are combined to form a complete dual-frequency matching circuit, and adjust the initial matching value to obtain a suitable matching state. The performances of the matching network have been tested and verified by experiments. After matching, the low-frequency and high-frequency sensitivities of the transducer increased 1.86 times and 2.26 times, respectively. In addition, system noise was also reduced by 29.6% after adding the matching network. The results demonstrate that this dual-frequency matching network can simultaneously increase the amplitude of high-frequency and low-frequency echoes to obtain better quality images.

Assessment of High Frequency Imaging and Doppler System for the Measurements of the Radial Artery Flow-Mediated Dilation

Objectives: In the article we describe the new, high frequency, 20 MHz scanning/Doppler probe designed to measure the flow mediated dilation (FMD) and shear rate (SR) close to the radial artery wall. Methods: We compare two US scanning systems, standard vascular modality working below 12 MHz and high frequency 20 MHz system designed for FMD and SR measurements. Axial resolutions of both systems were compared by imaging of two closely spaced food plastic foils immersed in water and by measuring systolic/diastolic diameter changes in the radial artery. The sensitivities of Doppler modalities were also determined. The diagnostic potential of a high frequency system in measurements of FMD and SR was studied in vivo, in two groups of subjects, 12 healthy volunteers and 14 patients with stable coronary artery disease (CAD). Results: Over three times better axial resolution was demonstrated for a high frequency system. Also, the sensitivity of the external single transducer 20 MHz pulse Doppler proved to be over 20 dB better (in terms of a signal-to-noise ratio) than the pulse Doppler incorporated into the linear array. Statistically significant differences in FMD and FMD/SR values for healthy volunteers and CAD patients were confirmed, p-values < 0:05. The areas under Receiver Operating Characteristic (ROC) curves for FMD and FMD/SR for the prediction CAD had the values of 0.99 and 0.97, respectively. Conclusions: These results justify the usefulness of the designed high-frequency scanning system to determine the FMD and SR in the radial artery as predictors of coronary arterial disease.

Ferroelectrets: Heterogenous polymer electrets with high piezoelectric sensitivity for transducers

Nowadays, the demand for advanced functional materials in transducer technology is growing rapidly. Piezoelectric materials transform mechanical variables (displacement or force) into electrical signals (charge or voltage) and vice versa. They are interesting from both fundamental and application points of view. Ferrooelectrets (also called piezoelectrets) are a relatively young group of piezo-, pyro- and ferroelectric materials. They exhibit ferroic behavior phenomenologically undistinguishable from that of traditional ferroelectrics, although the materials per se are essentially non-polar space-charge electrets with artificial macroscopic dipoles (i.e., internally charged cavities). A lot of work has been done on ferroelectrets and their applications up to now. In this paper, we review and discuss mostly the work done at University of Potsdam on the research and development of ferroelectrets. We will, however, also mention important results from other teams, and prospect the challenges and future progress trend of the field of ferroelectret research.

Improvement of the measuring ultrasonic electromagnetic-acoustic transducer

Based on the analysis of previously published research and studies, it has been established that despite their significant advantages over traditional “contact” sensors in measurements, testing and diagnostics of thin dielectric coated (via paint, plastic, etc.) metal products, the available electromagnetic-acoustic transducers provide insufficient sensitivity and significant uncontrolled (“dead”) zone. This situation complicates testing of thin sheets, pipes, shells, tanks etc., and sometimes makes it impossible to measure the remaining thickness of the metal.&#x0D; The analysis of available research has shown that the possibility of transducers sensitivity increases via traditional increase in the magnetic induction value, and the high-frequency current value is practically exhausted. At the same time, the prospects for improving the design of electromagnetic-acoustic transducers were determined. The problems of traditional transducers were solved through development of a new electronic control circuit. For this, the control unit was designed to be distributed between ultrasonic shear pulse excitation devices, and as a result, for the device of ultrasonic signals reflected from the metalwork reception, the device sensitivity was increased. In addition, to provide the possibility to test and measure thin metal product thickness, the electronic circuit was supplemented with means of interference suppression after the powerful supply of the high-frequency current of the converter, which allowed significantly reducing the “dead” zone.&#x0D; A special stand was constructed to experimentally test the capabilities of the transducer developed, including a powerful high-frequency current pulse generator, an amplifier of received ultrasonic pulses and a digital oscilloscope. It has been experimentally demonstrated that the new electronic circuit of the non-contact sensor allows it to be qualitatively matched with the probing pulse generator and the amplifier of the received ultrasonic packet signals. As a result, the sensitivity of the transducer was increased by 2.5...3 times in relation to the amplitudes of bottom pulses and interference. At the same time, the diagnostics of metal products with thickness 30...50% less than the traditional sensitivity threshold of non-contact device is ensured.

High Acoustic Impedance and Attenuation Backing for High-Frequency Focused P(VDF-TrFE)-Based Transducers.

Backing materials with tailored acoustic properties are beneficial for miniaturized ultrasonic transducer design. Whereas piezoelectric P(VDF-TrFE) films are common elements in high-frequency (>20 MHz) transducer design, their low coupling coefficient limits their sensitivity. Defining a suitable sensitivity-bandwidth trade-off for miniaturized high-frequency applications requires backings with impedances of >25 MRayl and strongly attenuating to account for miniaturized requirements. The motivation of this work is related to several medical applications such as small animal, skin or eye imaging. Simulations showed that increasing the acoustic impedance of the backing from 4.5 to 25 MRayl increases transducer sensitivity by 5 dB but decreases the bandwidth, which nevertheless remains high enough for the targeted applications. In this paper, porous sintered bronze material with spherically shaped grains, size-adapted for 25-30 MHz frequency, was impregnated with tin or epoxy resin to create multiphasic metallic backings. Microstructural characterizations of these new multiphasic composites showed that impregnation was incomplete and that a third air phase was present. The selected composites, sintered bronze-tin-air and sintered bronze-epoxy-air, at 5-35 MHz characterization, produced attenuation coefficients of 1.2 and >4 dB/mm/MHz and impedances of 32.4 and 26.4 MRayl, respectively. High-impedance composites were adopted as backing (thickness = 2 mm) to fabricate focused single-element P(VDF-TrFE)-based transducers (focal distance = 14 mm). The center frequency was 27 MHz, while the bandwidth at -6 dB was 65% for the sintered-bronze-tin-air-based transducer. We evaluated imaging performance using a pulse-echo system on a tungsten wire (diameter = 25 μm) phantom. Images confirmed the viability of integrating these backings in miniaturized transducers for imaging applications.

Ultrasonic needle hydrophone calibration in air by a parabolic off-axis mirror focused beam using three-transducer reciprocity

An acoustic field distribution investigation in air requires a small receiving sensor. Needle hydrophones seem to be an attractive solution, and it has previously been demonstrated that needle hydrophones designed for use in water can be used in air. The metrology problem is that an absolute sensitivity calibration is needed, because needle hydrophones are not characterized in air, especially for frequencies below 1 MHz, which is of interest for air-coupled ultrasound. Conventional, three-transducer/microphone reciprocity calibration requires measurements to be done in the far field. However, when transducer diameter is large and the frequency is high, the required measurement distance becomes very large: 3 m for a 20 mm source, transmitting at 1 MHz. Large propagation distance leads to high attenuation and nonlinear effects in air propagation, and distortion and losses accumulate. Small needle hydrophones have low sensitivity, so that high excitation amplitudes would be required, which can lead to transducer heating and increase nonlinearity effects. A derivative of the three-transducer reciprocity calibration method is proposed, where a large aperture transducer is focused onto a hydrophone, using hybrid of plane wave and spherical wave reciprocity. Use of a focused source minimizes the frequency-dependent diffraction effects, and the spherical wave approximation is valid at the focal distance, and low level excitation signals can be used. Focusing is accomplished using a parabolic off-axis mirror. Calibration is in transmission, which reduces the complexity of the electrical measurements. The corresponding equations have been derived for this setup. Calibration of the transducer and needle hydrophone absolute sensitivity is obtained.

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.