Sensitivity Of Transducer Research Articles

Matching long-period grating modes and localized plasmon resonances: effect on the sensitivity of the grating to the surrounding refractive index.

The sensitivity and dynamical range of an optical-fiber transducer consisting of a long-period grating coated with gold nanoparticles is investigated. For a grating with an 80μm spatial periodicity, the resonances close to the turning point lie within the 450-900nm spectral range. Employing a bottom-up production route, the localized surface plasmon resonance of gold nanoparticles is matched to the grating resonances; it is shown that this results in an increase in the refractive index sensitivity of the device. The device also shows increased dynamic range and enhanced refractive index sensitivity in water.

Induced electric potential in cortical bone and cartilage by ultrasound irradiation

LIPUS (low intensity pulse ultrasound) can reduce the time of bone fracture healing. The detailed mechanism of ultrasonic effects on bone, however, has not been clearly understood yet. One possible idea seems to be the piezoelectricity of bone. The purpose of this study is to evaluate the piezoelectricity of cortical bone and cartilage. In order to evaluate piezoelectricity of bone in the MHz range, bone transducers were fabricated. Circular plate cortical bone samples and cartilage samples (diameter; 10.0 mm, thickness; 1.00 mm) were used as piezoelectric materials of the transducer to receive ultrasound. The surface of bone plates was normal to the bone axis or the radial axis and that of cartilage plates was normal to bone axis. By irradiating ultrasound in the MHz range, induced electric potentials were successfully observed in all transducers. The maximum sensitivity of the cartilage transducer was about 93.6 nV/Pa and that of the bone transducer was about 27.5 nV/Pa. Induced electric potentials of cartilage transducers were always larger than those of bone transducers. The main part of the cartilage is type collagen. The results may indicate that the piezoelectricity of the cartilage and bone mainly comes from the collagen.

Carboxylic Acid-Functionalized Conducting-Polymer Nanotubes as Highly Sensitive Nerve-Agent Chemiresistors.

Organophosphates are powerful inhibitors of acetylcholinesterase, which is critical to nerve function. Despite continuous research for detecting the highly toxic organophosphates, a new and improved methodology is still needed. Herein we demonstrate simple-to-fabricate chemiresistive gas sensors using conducting-polymer polypyrrole (PPy) nanotube transducers, which are chemically specific and capable of recognizing sub-ppb concentrations (ca. 0.5 ppb) of dimethyl methylphosphonate (DMMP), a simulant of nerve agent sarin. Interestingly, the introduction of carboxylic groups on the surface of PPy nanotube transistors resulted in enhanced sensitivity to DMMP via intermolecular hydrogen bonding. Furthermore, it was found that the sensitivity of the nanotube transducer depended on the degree of the carboxylic group introduced. Finally, a sensor array composed of 5 different transducers including the carboxylated nanotubes exhibited excellent selectivity to DMMP in 16 vapor species.

The influence of temperature and humidity on the sensitivity of torque transducers

Abstract This paper presents a study of the effect of temperature and relative humidity on the sensitivity and the characteristics of torque transducers such as residual zero torque, reversibility and creep. Temperature and humidity coefficients of the sensitivity take positive as well as negative values. Linear dependence is found between the influence of temperature/relative humidity and the applied load. For some torque transducers, under temperature change the sensitivity has a transient overshoot reaching up to 3 times the steady amplitude. Also there is a small effect of temperature/relative humidity on the transducer’s parameters such as residual zero torque, reversibility and creep. Equations are presented to predict the effect of temperature/relative humidity changes on the sensitivity of torque transducers.

Calibration Methods of Acoustic Emission Sensors

This study examined outstanding issues of sensitivity calibration methods for ultrasonic and acoustic emission transducers and provides workable solutions based on physically measureable quantities, laser-based displacement measurement in particular. This leads to mutually consistent determination of transmitting and receiving sensitivities of sensors and transducers. Methods of circumventing problems of extraneous vibrations on free transmitters are used, giving the foundation for face-to-face calibration methods. Working on many ultrasonic and acoustic emission transducers, their receiving and transmitting sensitivities are found to be always different, while their ratios exhibit unexpected similarity. This behavior is attributed to monopolar pulse generation and bipolar received signals due to electrical charge transfer during elastic wave motion and reflection on the back face. This is verified through a quantitative piezoelectric sensing experiment. Displacement vs. velocity calibration terminology is clarified, redefining the “V/µbar” reference for contact sensor calibration. With demonstrated differences in the transmitting and receiving sensitivities of transducers, the requirement of the Hill-Adams equation invalidates the basic premise of the currently formulated reciprocity calibration methods for acoustic emission transducers. In addition, the measured reciprocity parameter for the case of through-transmission significantly deviates from the approximate theoretical prediction. It is demonstrated that three methods provide reliable sensor calibration results that are complimentary among them.

Measurement methods of ultrasonic transducer sensitivity

Sensitivity is an important parameter to describe the electro-acoustic energy conversion efficiency of ultrasonic transducer. In this paper, the definition of sensitivity and reciprocity of ultrasonic transducer is studied. The frequency response function of a transducer is the spectrum of its sensitivity, which reflects the response sensitivity of the transducer for input signals at different frequencies. Four common methods which are used to measure the disc-vibrator transducer sensitivity are discussed in current investigation. The reciprocitymethod and the pulse-echo method are based on the reciprocity of the transducer. In the laser vibrometer method measurement, the normal velocity on the transducer radiating surface is directly measured by a laser vibrometer. In the measurement process of the hydrophone method, a calibrated hydrophone is used to measure the transmitted field. The validity of these methods is checked by experimental test. All of the four methods described are sufficiently accurate for transducer sensitivity measurement, while each method has its advantages and limitations. In practical applications, the appropriate method to measure transducer sensitivity should be selected based on actual conditions.

Writer and Reader Head-to-Media Spacing Sensitivity Assessment in HAMR

We collate multiple experimental measurements of heat-assisted magnetic recording (HAMR) near-field transducer (NFT) and reader sensitivity measurements on spinstand to compare and contrast with the conventional perpendicular magnetic recording (PMR). The readback process shares many similarities, but differences appear due to the increased measured curvature of the prewritten track, which increases the observed pulsewidth (Pw50), lower readback amplitude due to reduced flux from the media transition (MrT), and increased coating thicknesses. We find that the reader head-to-media spacing (HMS) sensitivities and requirements converge toward the conventional scaling requirements. The HAMR write process is more complex due to the uncertainties associated with the optical properties and protrusion position of the NFT. However, accumulating multiple studies varying write HMS with coatings, NFT changes, and media changes, we consistently observe lower sensitivities compared with the conventional writer HMS, in line with modeled comparisons, leading to more relaxed requirements on the NFT clearance than the PMR write HMS. A 1.5 Tbpsi basic technology demonstration demo is shared using the HMS numbers in the bounds of the claims.

High Temperature Gallium Orthophosphate Transducers for NDT

A transducer has been manufactured leading towards development of an ultrasonic system to operate up to 580°C for non-destructive testing (NDT) and monitoring in power plants. The manufactured transducer has a simple design based on the piezoelectric single crystal gallium orthophosphate (GaPO4) which allows ultrasonic measurements to be performed up to considerably high temperature (HT) levels required in this study. Usually a critical aspect when performing HT ultrasonic NDT– acoustic coupling to the test-material, has been resolved using a commercially available HT silver adhesive which provides permanent installation of the transducer on the structure to be tested. This also means that for future application in an industrial environment drilling and/or machining intervention requirements will be reduced significantly. Finally, the GaPO4 transducer's sensitivity (f=3.5MHz) has been successfully tested through measurements on a steel block containing an artificial defect with known geometry (side-drilled hole (SDH) with d=0.8mm) up to the target temperature of 580°C keeping the defect's signal-to-noise ratio (SNR) above 6dB which is high enough for NDT practice.

Experimental damage evaluation of reinforced concrete steel bars using piezoelectric sensors

This study presents an experimental effort for the damage assessment of concrete reinforcing bars using bonded piezoelectric transducers and the implementation of an integration analytical approach based on the electromechanical admittance method. Tests are performed in (i) single steel reinforcing bars with predefined and artificially induced damages corresponding to two different damage states and (ii) steel reinforcing bars embedded in typical large scale reinforced concrete beams subjected to flexural load at two different loading levels (before and after yielding) that inevitably cause two different damage levels. The damage of the embedded steel bars in the concrete beams after yielding is the result of excessive elongation of the bars due to yielding caused by flexural deformation of the beams. Test measurements of healthy and damaged steel bars and reinforced concrete beams have been conducted using the developed monitoring system. The experimental program comprises data acquisition of current intensity curves for healthy and damaged bars as detected by the test instrumentation and implementation of the adopted admittance-based procedure to evaluate damages at different levels. It can be concluded that the sensitivity of the piezoelectric transducers greatly depends on the selection of the excitation frequencies. Admittance signatures showed a clear gradation of the examined damage levels. The experimental results provide cogent evidence that piezoelectric lead zirconate titanate transducers are sensitive to damage detection in concrete and in steel reinforcing bars from an early stage of the performed tests. Thus, the use of these sensors for monitoring and detecting concrete cracking and steel yielding by employing the electromechanical admittance approach can be considered as a highly promising non-destructive structural health monitoring method.

Impedance matching network for high frequency ultrasonic transducer for cellular applications

An approach for the design of an impedance matching network (IMN) for high frequency ultrasonic transducers with large apertures based on impedance analysis for cellular applications is presented in this paper. The main objectives were to maximize energy transmission from the excitation source to the ultrasonic transducers for cell manipulation and to achieve low input parameters for the safe operation of an ultrasonic transducer because the piezoelectric material in high frequency ultrasonic transducers is prone to breakage due to its being extremely thin. Two ultrasonic transducers, which were made of lithium niobate single crystal with the thickness of 15μm, having apertures of 4.3mm (fnumber=1.23) and 2.6mm (fnumber=0.75) were tested. L-type IMN was selected for high sensitivity and compact design of the ultrasonic transducers. The target center frequency was chosen as the frequency where the electrical admittance (|Y|) and phase angle (θz) from impedance analysis was maximal and zero, respectively. The reference center frequency and reference echo magnitude were selected as the center frequency and echo magnitude, measured by pulse-echo testing, of the ultrasonic transducer without IMN. Initial component values and topology of IMN were determined using the Smith chart, and pulse-echo testing was analyzed to verify the performance of the ultrasonic transducers with and without IMN. After several iterations between changing component values and topology of IMN, and pulse-echo measurement of the ultrasonic transducer with IMN, optimized component values and topology of IMN were chosen when the measured center frequency from pulse-echo testing was comparable to the target frequency, and the measured echo magnitude was at least 30% larger than the reference echo magnitude. Performance of an ultrasonic transducer with and without IMN was tested by observing a tangible dent on the surface of a plastic petridish and single cell response after an acoustic pulse was applied on a target cell.

Super-resolution photoacoustic imaging through a scattering wall.

The use of wavefront shaping to compensate for scattering has brought a renewed interest as a potential solution to imaging through scattering walls. A key to the practicality of any imaging through scattering technique is the capability to focus light without direct access behind the scattering wall. Here we address this problem using photoacoustic feedback for wavefront optimization. By combining the spatially non-uniform sensitivity of the ultrasound transducer to the generated photoacoustic waves with an evolutionary competition among optical modes, the speckle field develops a single, high intensity focus significantly smaller than the acoustic focus used for feedback. Notably, this method is not limited by the size of the absorber to form a sub-acoustic optical focus. We demonstrate imaging behind a scattering medium using two different imaging modalities with up to ten times improvement in signal-to-noise ratio and five to six times sub-acoustic resolution.

On the possibility of increasing the sensitivity and resolution of an immersion piezoelectric transducer

Issues of producing acoustic pulses in twoand three-mirror immersion transducer models in the process of the designing of their acoustic sections are considered. The possibilities of simultaneously increasing the sensitivity and resolution are evaluated. A calculation method for the relative amplitudes of the half periods of the emitted acoustic pulses of these transducers as function of the materials and immersion medium that are used is proposed. The effect of compressing an emitted acoustic pulse in the process of the creation of a three-mirror transducer model or a transducer with a protector is substantiated.

Accelerometer transverse sensitivity calibration; validation and uncertainty estimation

The National Metrology Institute of South Africa (NMISA) has implemented a system to measure the transverse sensitivity of vibration transducers. As a mechanical device, the principle sensing axis of an accelerometer is not 100 % perpendicular to the mounting axis. This gives rise to the effect that the accelerometer will produce an electrical output even when a mechanical input perpendicular to the principle measurement axis is applied. The quantification of this "defect" parameter is of importance when high accuracy acceleration measurements are performed using accelerometers. This paper gives a brief overview of the system developed by the NMISA to measure the transverse sensitivity of vibration transducers. The paper then explores the validation of the system along with the uncertainty of measurement associated with the calibration system.

Piezoelectric Sensor to Measure Soft and Hard Stiffness with High Sensitivity for Ultrasonic Transducers.

During dental sinus lift surgery, it is important to monitor the thickness of the remaining maxilla to avoid perforating the sinus membrane. Therefore, a sensor should be integrated into ultrasonic dental tools to prevent undesirable damage. This paper presents a piezoelectric (PZT) sensor installed in an ultrasonic transducer to measure the stiffness of high and low materials. Four design types using three PZT ring materials and a split PZT for actuator and sensor ring materials were studied. Three sensor locations were also examined. The voltage signals of the sensor and the displacement of the actuator were analyzed to distinguish the low and high stiffness. Using sensor type T1 made of the PZT-1 material and the front location A1 provided a high sensitivity of 2.47 Vm/kN. The experimental results demonstrated that our design can measure soft and hard stiffness.

Etched FBG written in multimode fibers: sensing characteristics and applications in the liquid fuels sector

In this work, a refractometric fiber sensor for the liquid fuels sector is described. The use of etched FBGs produced in multimode fibers is proposed to overcome the drawbacks associated with sensing high refractive index samples employing fiber transducers. The transducer sensitivity can be tailored by adjusting the final diameter of the etched Bragg grating. Due to a trade-off between the signal-to-noise ratio and the sensitivity, operational parameters of the sensor must be designed to match the expected refractive index dynamic range for specific applications. Metrological properties of the sensor are determined, resulting in resolution from 5.6 % v/v to 0.4 % v/v for refractive indexes ranging from 1.4562 to 1.4729. Specific applications regarding the quality assessment of biodiesel and conformity analysis of diesel-biodiesel blends are discussed.

Magnetic shape anisotropy effect on sensing performance and directional sensitivity in magnetostrictive nickel patch transducer

This article presents the magnetic shape anisotropy effect on sensing performance and directional sensitivity in a directional magnetostrictive patch transducer using a uniaxial comb-shaped nickel patch, for the use of ultrasonic guided Lamb wave technology in metallic planar structure. The uniaxial comb patch was modified from a disc-shaped patch made of polycrystalline nickel, so that its comb fingers were aligned to a specific radial direction to promote the magnetic shape anisotropy in the nickel patch. Previously, it was found that a magnetostrictive patch transducer using a nickel disc patch appeared to have omnidirectional sensitivity for sensing guided Lamb waves in an aluminum plate due to the isotropic magnetostrictive nature of polycrystalline nickel. In this work, we initially investigated a theoretical approach to determine demagnetization factor change caused by the geometrical shape modification of a nickel patch, which strongly correlated with a specific magnetization characteristic of the patch. Then, experimental guided Lamb wave analysis was followed to demonstrate the directional guided Lamb wave sensitivity of magnetostrictive patch transducers using nickel patches with three different geometrical configurations. We verified from the experimental guided Lamb wave testing that the proposed magnetostrictive patch transducer using the uniaxial comb-shaped nickel patch exhibited excellent directional sensitivity along the comb fingers’ orientation in the aluminum plate.

Effective Area Effects on the Final Device Sensitivity of Ion Sensor Transducers

Fluorine-doped tin oxide (SnO2:F) was used as the ion-sensing layer of an EGFET-pH sensor. The effective area affects the final results, as well as the sensor surface potential and sensitivity. The sensor miniaturization is highly required on medical applications, with that the effective area must be properly understood. Routine insertion and removal of total and partial surface areas in buffer solution were analyzed and compared. The results show that the routine changes considerable the sensor sensitivity. Variations in the double layer, Helmholtz plane, and Gouy-Chapman region play a significant role. The final sensitivities of the samples were compared with values available in the literature, even for other materials. The role that area normalization plays in quality assessment is discussed for proper future technological miniaturizations.

Comparative sensitivity of pressure gradient receivers of force and inertial types to sound pressure in plane wave

Among known constructing schemes of pressure gradient receivers (PGR)—a difference type (including two-point version), a force type, and an inertial one—only the last two types are applicable when receiver size is much smaller than a wavelength of plane wave. Each of these two PGR types has certain advantages/disadvantages for various applications. The objective is a comparison of these PGRs, having identical external dimensions, by their sensitivity to sound pressure. In the long-wave two-dimensional approach the expression for a sensitivity to sound pressure is derived for a force type PGR, in which plate bending piezoelectric transducer is installed in a passage of the cylindrical housing. Also, the expression is developed for the sensitivity to sound pressure of an inertial type PGR with a one-component accelerometer embedded into its cylindrical housing. We derived the expression to estimate required one-side pressure sensitivity of the bending piezoelectric transducer of the force type PGR to equalize the sensitivities of PGRs of both types to sound pressure when the vibration sensitivity of the accelerometer is known. Possibilities of increasing sensitivity of the force type PGR are considered. [The study was supported by the grant 15-IV-1-001 of Far Eastern Branch of Russian Academy of Sciences.]

Piezoelectric response of bone in the MHz range

The healing mechanism of bone fractures by low intensity ultrasound is not yet to be fully understood. As one possible initial process of this mechanism, we focus on the piezoelectricity of bone and demonstrate that bone can generate electrical potentials by ultrasound irradiation in the MHz range. We have fabricated ultrasonic bone transducers using bovine cortical bone as the piezoelectric device. Electrical potentials induced by the ultrasound irradiation were obtained from all transducers. The electrical potentials changed as a function of time during immersed ultrasonic measurements and became stable when the bone was fully wet. The sensitivities of bone transducers were around 1/1000 of a poly(vinylidene fluoride) ultrasonic transducer and did not depend on the magnitude and alignment of hydroxyapatite crystallites in bone. In addition, the magnitude of the induced electrical potentials changed owing to the microstructure in the cortical bone. The potentials of transducers with haversian structure bone were higher than those of plexiform structure bone, which informs about the effects of bone microstructure on the piezoelectricity.

System modelling and device development for passive acoustic monitoring of a particulate-liquid process

This paper presents the development of a passive ultrasonic monitoring system for the detection of acoustic emission (AE) created by chemical particles striking the inner wall of a reactor vessel. The finite element (FE) code PZFlex was used to analyze the complex interactions between chemical particles and the vessel wall. A 4-layer 2D model was developed comprising a liquid load medium and a glass-oil-glass combination corresponding to the jacketed vessel reactor. The model has been experimentally validated with excellent correlation achieved. The excitation function was derived from Hertz's theory and used as the model stimulus corresponding to particles striking the inner glass wall. Analysis of the FE simulations provided the transducer specifications for a passive ultrasonic monitoring system. The system comprises two transducers with complementary characteristics: narrow bandwidth/high sensitivity; wideband/low sensitivity. Importantly, the sensitivity of the resonant transducer provides discrimination of particle concentration. Moreover, the broader bandwidth of the off-resonant device demonstrates potential for in situ estimation of particle size. The performance afforded by this approach has considerable potential for real-time process monitoring in the chemicals and pharmaceutical industries.