Changes In Mechanical Impedance Research Articles

Intelligent monitoring and assessment on early-age hydration and setting of cement mortar through an EMI-integrated neural network

In this study, the authors presented a smart sensing method for monitoring and evaluating the early-age hydration and hardening process of cement mortar through the integration of the EMI technique with deep learning (DL) models. The main research works and contributions of this research are given as follows: The development of the penetration resistance was acquired by measuring the Vicat needle penetration depth. Meanwhile, the EMI spectra within two scanning frequency ranges, 1000 kHz and 3000 kHz, were continuously captured. The key innovation of this research is that a DL-based framework named EMI-integrated neural network (EMI-IntNet) was proposed, which could facilitate the achievement of intelligent monitoring and assessment. The EMI-IntNet, which combines a one-dimensional convolutional neural network (1D-CNN), a long short-term memory neural network (LSTM) and an attention mechanism, can accurately predict the dynamic penetration impedance from raw EMI data without any pre-processing or subjective judgment. Two datasets collected in two separate vibration modes (d31 and d33) were used to validate the effectiveness of the proposed method. The results show that the EMI-IntNet can quantitatively evaluate the dynamic penetration impedance of cement mortar with an error of less than 2 % and a coefficient of determination (R2) value over 0.99 for both datasets. The EMI-IntNet’s forecasting accuracy, noise immunity and adaptability were thoroughly investigated, which outperform that of the machine learning-based approaches, 1D-CNN and 1D-CNN-LSTM. In conclusion, the proposed method enables automatic data acquisition, feature extraction and identification of EMI signals, contributing to the intelligent monitoring and accurate assessment of the mechanical impedance change throughout the early-age hydration and setting of cement mortar.

Performance of Impulse Response Testing on Prismatic Members with Intermediate Joints

Nondestructive Testing (NDT) methods have extensively been used to assess the conditions of civil infrastructure in the recent decades. Among various NDT techniques, Impulse Response (IR) has a vast application due to its simplicity and low cost. However, factors such as reflections from changes in impedance along the investigated members can adversely influence the success of the method. Numerous numerical and experimental studies have already been performed to evaluate the effect of change in mechanical impedances such as bulging, necking and similar anomalies. In this study, the effect of the presence of joints connecting the investigated members to other members, as another source of impedance change, is demonstrated. A three-story steel-concrete composite column of a building was selected for testing and IR tests were conducted. The obtained mobility graphs were clear, and the height of the column was easily measured with an acceptable error. The results of this study show that although the joints located between the top and bottom of the tested member are sources of change in mechanical impedance, they do not result in concealing the resonant frequencies from the wave reflected from the bottom of the member. Thus, IR method seems to be applicable in determining the length of prismatic members with intermediate joints such as piles of unknown bridge foundations with bracing and columns of buried buildings.

A Study on Puncture Resistance of Composite Metal Foam Core Sandwich Panels

Steel–steel composite metal foam‐core sandwich panels (S‐S CMF‐CSP) with variety of thicknesses of components (face sheets and cores) are manufactured by attaching stainless steel face sheets to a S‐S CMF core using either solid‐state diffusion bonding or adhesion bonding. Scanning electron microscope imaging is used to evaluate the microstructure of diffusion bonded panels particularly at the interface of the core and face sheets. The puncture resistance of the sandwich panels is evaluated using a 0.50 caliber Mann gun barrel, modified to fire 2.54 and 3.175 cm diameter steel balls creating kinetic puncture energies up to 14 500 J. But, no complete penetrations through any of the sandwich panels are achieved. At lower impact velocities, tensile stresses resulted from the sudden changes in mechanical impedance between various layers of the sandwich panel recoil the ball back while at higher impact velocities, the high strain rate deformation at the point of impact along with the friction heat between the ball and panel surface fuses the ball to the target instantly resulting in debonding of adhesively bonded panels, whereas the diffusion bonded panels resist better. Sandwich panels with higher areal densities and thicker face sheets did not show major advantages over the panels with thinner face sheets.

Design and Applicability of a Mechanical Impedance Sensor for Vein Penetration Detection.

Intravenous needle insertion is typically conducted manually, with needles guided into vessels by feel while looking for a brief flash of blood. This process is imprecise and leads to mispositioned needles, multiple reinsertion attempts, increased procedure time and higher costs for the hospital. We present a method for indicating that the needle has reached the vein by measuring the change in mechanical impedance of the needle as it passes through different tissue layers. Testing in a phantom indicated that this has the potential to identify transitions through tissue boundaries.

Evaluation of Elastic Properties and Conductivity of Chitosan Acetate Films in Ammonia and Water Vapors Using Acoustic Resonators.

Novel bio-materials, like chitosan and its derivatives, appeal to finding a new niche in room temperature gas sensors, demonstrating not only a chemoresistive response, but also changes in mechanical impedance due to vapor adsorption. We determined the coefficients of elasticity and viscosity of chitosan acetate films in air, ammonia, and water vapors by acoustic spectroscopy. The measurements were carried out while using a resonator with a longitudinal electric field at the different concentrations of ammonia (100–1600 ppm) and air humidity (20–60%). It was established that, in the presence of ammonia, the longitudinal and shear elastic modules significantly decreased, whereas, in water vapor, they changed slightly. At that, the viscosity of the films increased greatly upon exposure to both vapors. We found that the film’s conductivity increased by two and one orders of magnitude, respectively, in ammonia and water vapors. The effect of analyzed vapors on the resonance properties of a piezoelectric resonator with a lateral electric field that was loaded by a chitosan film on its free side was also experimentally studied. In these vapors, the parallel resonance frequency and maximum value of the real part of the electrical impedance decreased, especially in ammonia. The results of a theoretical analysis of the resonance properties of such a sensor in the presence of vapors turned out to be in a good agreement with the experimental data. It has been also found that with a growth in the concentration of the studied vapors, a decrease in the elastic constants, and an increase in the viscosity factor and conductivity lead to reducing the parallel resonance frequency and the maximum value of the real part of the electric impedance of the piezoelectric resonator with a lateral electric field that was loaded with a chitosan film. This leads to an increase in the sensitivity of such a sensor during exposure to these gas vapors.

A Novel Measurement for Monitoring Mechanical Impedance Applied to Breakthrough Detection of Bone-Drill System

Based on a Chain Scattering Description and the Hilbert Huang Transform, this paper proposes a new measurement for monitoring dynamic changes of mechanical impedance without applying conventionally mechanical sensors. The proposed method is applied to the bone drilling system to detect the moment of bone breakthrough. The single frequency mechanical impedance of bone can be computed from the electrical signal of a DC motor in accordance with the proposed method. The experimental results demonstrate that the moment of bone breakthrough can accurately be detected by monitoring changes of mechanical impedance.

Load monitoring of pin-connected structures using piezoelectric impedance measurement

This paper presents a feasibility study on a developed impedance-based technique using Lead Zirconate Titanate patches for load monitoring of pin-connected structures, which are widely used in construction industry. The basic principle behind the load-monitoring technique is to utilize a high-frequency excitation signal (typically >30 kHz) through a surface-bonded piezoelectric sensor/actuator to detect changes in mechanical impedance of the structure due to the variations in structural loads. In order to verify the effectiveness of the developed technique, a tension-controllable structure with a pin connection was fabricated and investigated in this study. A load monitoring index was used to correlate the dominating peak frequency of the real part of the electrical impedance signature to the pin connection load. Experimental results obtained from twenty repeated tests prove that the proposed load-monitoring index increases as the load on the pin connection increases due to the enlarging true contact area of the pin connection. A 3D finite element method was also used to simulate and analyze the impedance signature of a pin connection model. Very good agreement exists between the numerical simulation’s results and the experimental results which demonstrates that the impedance-based technique can successfully be used to monitor the loading status of pin connections in practical applications.

Maturation of Mechanical Impedance of the Skin-Covered Skull: Implications for Soft Band Bone-Anchored Hearing Systems Fitted in Infants and Young Children.

Little is known about the maturational changes in the mechanical properties of the skull and how they might contribute to infant-adult differences in bone conduction hearing sensitivity. The objective of this study was to investigate the mechanical impedance of the skin-covered skull for different skull positions and contact forces for groups of infants, young children, and adults. These findings provide a better understanding of how changes in mechanical impedance might contribute to developmental changes in bone conduction hearing, and might provide insight into how fitting and output verification protocols for bone-anchored hearing systems (BAHS) could be adapted for infants and young children. Seventy-seven individuals participated in the study, including 63 infants and children (ages 1 month to 7 years) and 11 adults. Mechanical impedance magnitude for the forehead and temporal bone was collected for contact forces of 2, 4, and 5.4 N using an impedance head, a BAHS transducer, and a specially designed holding device. Mechanical impedance magnitude was determined across frequency using a stepped sine sweep from 100 to 10,000 Hz, and divided into low- and high-frequency sets for analysis. Mechanical impedance magnitude was lowest for the youngest infants and increased throughout maturation in the low frequencies. For high frequencies, the youngest infants had the highest impedance, but only for a temporal bone placement. Impedance increased with increasing contact force for low frequencies for each age group and for both skull positions. The effect of placement was significant for high frequencies for each contact force and for each age group, except for the youngest infants. Our findings show that mechanical impedance properties change systematically up to 7 years old. The significant age-related differences in mechanical impedance suggest that infant-adult differences in bone conduction thresholds may be related, at least in part, to properties of the immature skull and overlying skin and tissues. These results have important implications for fitting the soft band BAHS on infants and young children. For example, verification of output force form a BAHS on a coupler designed with adult values may not be appropriate for infants. This may also hold true for transducer calibration when assessing bone conduction hearing thresholds in infants for different skull locations. The results have two additional clinical implications for fitting soft band BAHSs. First, parents should be counseled to maintain sufficient and consistent tightness so that the output from the BAHS does not change as the child moves around during everyday activities. Second, placement of a BAHS on the forehead versus the temporal bone results in changes in mechanical impedance which may contribute to a decrease in signal level at the cochlea as it has been previously demonstrated that bone conduction thresholds are poorer at the forehead compared with a temporal placement.

Tidal breathing flow measurement in awake young children by using impedance pneumography

Characteristics of tidal breathing (TB) relate to lung function and may be assessed even in young children. Thus far, the accuracy of impedance pneumography (IP) in recording TB flows in young children with or without bronchial obstruction has not been evaluated. The aim of this study was to evaluate the agreement between IP and direct flow measurement with pneumotachograph (PNT) in assessing TB flow and flow-derived indices relating to airway obstruction in young children. Tidal flow was recorded for 1 min simultaneously with IP and PNT during different phases of a bronchial challenge test with methacholine in 21 wheezy children aged 3 to 7 years. The agreement of IP with PNT was found to be excellent in direct flow signal comparison, the mean deviation from linearity ranging from 2.4 to 3.1% of tidal peak inspiratory flow. Methacholine-induced bronchoconstriction or consecutive bronchodilation induced only minor changes in the agreement. Between IP and PNT, the obstruction-related tidal flow indices were equally repeatable, and agreement was found to be high, with intraclass correlation coefficients for T PTEF/T E, V PTEF/V E, and parameter S being 0.94, 0.91, and 0.68, respectively. Methacholine-induced changes in tidal flow indices showed significant associations with changes in mechanical impedance of the respiratory system assessed by the oscillometric technique, with the highest correlation found in V PTEF/V E (r = -0.54; P < 0.005 and r = -0.55; P < 0.005 by using IP or PNT, respectively). The results indicate that IP can be considered as a valid method for recording tidal airflow profiles in young children with wheezing disorders.

SPATIAL VARIABILITY OF THE SOIL MECHANICAL IMPEDANCE AND ITS CONNECTION WITH ELECTRICAL CONDUCTIVITY AND PRODUCTIVITY OF SUNFLOWER

The spatial variability of soil mechanical impedance on the basis of scientific-research center of Dnepropetrovsk State Agrarian University has been studied. The horizon heterogeneity of the soil cover may be areas with reduced soil mechanical impedance on the north-east of the field, which are surrounded by homogeneous sites with higher soil mechanical impedance. Cluster analysis allowed identifying three main groups (clusters) with the same type of soil mechanical impedance change - A, B, C. The soil spatial organization groups (clusters) have been established as having statistically different physical and biological properties. It was found that the soil mechanical impedance can act as an integrated indicator that indicates spatial variability of soil physical properties. Key words: the soil mechanical impedance, the productivity of sunflower, the optimal plant density, the spatial heterogeneity of soil properties.

The Study on Mechanical Impedance and Piezoelectric Impedance for Cantilever Beam Based on FEA Method

The mechanical impedance and the piezoelectric coupling impedance response spectrum, the resonant vibration mode and he resonance frequency of the cantilever beam was analyzed by means of FEA for getting the relationship between mechanical impedance and piezoelectric impedance. The results showed that: Through the comparison between the two, both resonance frequency and resonance modes are the same basically, which also showed that the change of piezoelectric impedance changes with the mechanical impedance change. Piezoelectric impedance is the electric reflection of mechanical impedance. It provides a sound theoretical basis and research methods for the piezoelectric impedance damage identification and health monitoring technology.

Temperature variation effect compensation in impedance-based structural health monitoring using neural networks

In this article, a new method for temperature compensation on the basis of artificial neural networks (ANNs) in impedance-based structural health monitoring (ISHM) has been introduced. ISHM using piezoelectric wafer active sensors (PWAS) has been extensively developed to provide detection of fault in structure. The principle of this method is based on the electromechanical coupling effect of PWAS materials. Any change in structure leads to changes in mechanical impedance of structure. The electrical impedance of PWAS can sense this change by the electromechanical coupling effect of PWAS. Therefore, the difference in this electrical impedance for undamaged and damaged structures can be considered as a damage index to detect the damage in structure. Since physical and mechanical properties of structure also PWAS materials are temperature dependent, so this electrical impedance of PWAS will be affected by temperature changes. Consequently, the variation in environmental or service temperatures can be detected erroneously as damage in ISHM method. In this article, a new method using ANN based on radial basis function (RBF) has been proposed and developed to compensate the temperature effect on the damage index. A steel plate and gas pipe with bolted joints are considered as two case studies for the performance evaluation of the proposed fault detection methodology. Results confirm that the proposed method using the ANN can be effectively utilized to compensate temperature variation for damage detection in different structures.

Experimental and theoretical analysis in impedance-based structural health monitoring with varying temperature

In the recent years, the piezoelectric wafer active sensors (PWASs) are increasing as a measurement tool in structural health monitoring techniques. In impedance-based structural health monitoring (ISHM) method, the electrical impedance of a PWAS bonded to the structure is measured and served as a defect detection index of the structure. The principle of this method is based on the electromechanical coupling effect of PWAS materials. As any change in the structure will lead to a change in mechanical impedance of structure, the electrical impedance of PWAS could sense this change by the electromechanical coupling effect of PWAS. Since the physical and mechanical properties of PWAS materials are temperature-dependent, so the electrical impedance of PWAS will change with varying temperature. Consequently, the changes in environmental or service temperatures could be detected in ISHM method as a defect. In this article, in order to consider the temperature dependency of PWAS material properties, a temperature-dependent model is developed for a PWAS bonded to an Euler Bernoulli cantilever beam. An aluminum (alloy 2024) beam was examined experimentally by ISHM method in order to validate the proposed model. The comparison of theoretical and experimental results demonstrates a good improvement in ISHM modeling where temperature variation is present.

Piezoelectric Vibration-Type Tactile Sensor Using Elasticity and Viscosity Change of Structure

We propose a new tactile sensor utilizing piezoelectric vibration. This tactile sensor has a high sensitivity, wide measurement range, pressure resistance, flexibility, and self-sensing function. This tactile sensor comprises two piezoelectric materials. One is used for the vibration of the sensor element and the other is used for the measurement of the change in mechanical impedance induced by an external force. We achieved the wide measurement range by implementing two ideas. One was to apply the external force to the sensor element through an elastic body and the other was to use two or more modes of vibration. Moreover, for the elastic body, it is preferable to use a material whose elasticity and viscosity are easily changed by an external force, such as a gel. In this study, first, this tactile sensor was analyzed, and then its characteristics were derived. The analytical results qualitatively corresponded to the experimental results. Next, a prototype tactile sensor was fabricated and evaluated. The evaluation results showed that this tactile sensor can measure a pressure of 2.5 Pa or less and a pressure of 10 kPa or more and its pressure resistance is 1 MPa or more.

Development of Diagnosing Method for Health Condition of a Joint Based on Piezo-electric Impedance Measurement

Infrastructures dealing with social activities and providing services to the daily life of people are almost impossible to be shut down for the regular damage detection procedures. However, according to the standards and codes for infrastructures, both early detections of the damage and continuous monitoring are necessary. In order to prevent unexpected accidents, numerous health monitoring techniques were developed to examine or monitor the damage or physical changes in the structures. This paper presents the development of Structural Health Monitoring based on Piezo-ceramic Embedded Impedance Measuring Technique. In order to automatically detect the abnormalities of structure due to damages, the diagnosis method is proposed. The loosening state of one bolt on one joint in the prototype structure is taken as the example of abnormality state. Since the fastening state of bolts affects the mechanical impedance in the structure, PZT patches were embedded on the structure so that the mechanical impedance change can be measured precisely by the variation of the electric impedance in PZT patches. An unusual fastening torque is recognized by the behaviour of impedance waveform obtained from a series of repeated tests. Then this torque is used as the threshold and based on it the diagnosing method, introducing the damage index ΔS, is proposed. The experimental results show that this method has successfully detected all unusual states during the experiments.

構造の弾性・粘性変化を利用した圧電振動型触覚センサ

We propose a new tactile sensor utilizing piezoelectric vibration. This tactile sensor has a high sensitivity, wide measurement range, pressure resistance, flexibility, and self-sensing function. This tactile sensor comprises two piezoelectric materials. One is used for the vibration of the sensor element and the other is used for the measurement of the change in mechanical impedance induced by an external force. We achieved the wide measurement range by implementing two ideas. One was to apply the external force to the sensor element through an elastic body and the other was to use two or more modes of vibration. Moreover, for the elastic body, it is preferable to use a material whose elasticity and viscosity are easily changed by an external force, such as a gel. In this study, first, this tactile sensor was analyzed, and then its characteristics were derived. The analytical results qualitatively corresponded to the experimental results. Next, a prototype tactile sensor was fabricated and evaluated. The evaluation results showed that this tactile sensor can measure a pressure of 2.5 [Pa] or less and a pressure of 10 [kPa] or more and its pressure resistance is 1 [MPa] or more.

Touch sensor for micromanipulation with pipette using lead-free (K,Na)(Nb,Ta)O3 piezoelectric ceramics

In the field of applied microbiology, a touch sensor for micromanipulation with a pipette is needed. Therefore, we previously developed a touch sensor using Pb(Zr,Ti)O3 (PZT). The piezoelectric material is used for vibration of the pipette and for measurement of the change in mechanical impedance caused by the pipette tip contacting the object being measured. However, the lead included in PZT can cause environmental problems. Therefore, in the present work, we developed a touch sensor using lead-free (K,Na)(Nb,Ta)O3 (KNNT) ceramics, which are strong candidates for lead-free piezoelectric ceramics. In this study, characteristics of a touch sensor utilizing piezoelectric vibration were theoretically derived. The results show that the piezoelectric constant d31 is very important: the higher the mode of vibration, the smaller the tip amplitude; the lower the mode of vibration, the higher the sensitivity. Also, the higher the elasticity or viscosity of the object in contact with the sensor, the higher the sensitivity. These theoretical results qualitatively correspond to the experimental results. The piezoelectric constant d31 of KNNT ceramics was measured, and its value was found to be greater than or equal to 100pm∕V. KNNT ceramics were applied to the touch sensor and its utility was confirmed.

High sensitive touch sensor with piezoelectric thin film for pipetting works under microscope

Isolation and separation of the target microbial cells is quite important in applied microbiology. We propose a new touch sensor for separation of the target cells on the plate using a micromanipulator with a glass pipette. Principle of this touch sensor is based on detection of mechanical impedance change after contact of the vibrating pipette tip with the plate. We fixed the sensor on the pipette holder and arranged the design of the sensing electrode to improve sensitivity of this sensor through FEM analysis. The prototype sensor has high sensitivity and high rigidity and is excellent in durability. This sensor is sensitive enough to protect the fragile pipette tip from collision. Thus, task of the micromanipulator to separate microbial cells under the microscope was improved.

High Sensitive Micro Touch Sensor for Micro Pipetting Works

Isolation and separation of the target microbe is quite important. We propose a novel touch sensor for separation of the target microbe on the plate using a micromanipulator with the glass pipette. Principle of this touch sensor is based on detection of mechanical impedance change after contact of the vibrating pipette tip with the plate. We improved the fixation method of the sensor with the pipette as well as electrode design of the sensor.We performed the FEM analysis to improve sensitivity of this sensor. The prototype sensor has high sensitivity and high rigidity and is excellent in durability. This sensor is sensitive enough to protect the fragile pipette tip from abrupt collision. Thus, separation task of the microbe by the micromanipulator under the microscope is improved.

Simultaneous Structural Health Monitoring and Vibration Control of Adaptive Structures Using Smart Materials

The integration of actuators and sensors using smart materials enabled various applications including health monitoring and structural vibration control. In this study, a robust control technique is designed and implemented in order to reduce vibration of an active structure. Special attention is given to eliminating the possibility of interaction between the health monitoring system and the control system. Exploiting the disturbance decoupling characteristic of the sliding mode observer, it is demonstrated that the proposed observer can eliminate the possible high frequency excitation from the health monitoring system. At the same time, a damage identification scheme, which tracks the changes of mechanical impedance due to the presence of damage, has been applied to assess the health condition of structures. The main objective of this paper is to examine the potential of combining the two emerging techniques together. Using the collocated piezoelectric sensors/actuators for vibration suppression as well as for health monitoring, this technique enabled to reduce the number of system components, while enhancing the performance of structures. As an initial study, both simulation and experimental investigations were performed for an active beam structure. The results show that this integrated technique can provide substantial vibration reductions, while detecting damage on the structure at the same time.