Inner damage identification and residual strength assessment of a 3D printed tunnel with marble-like cementitious materials using piezoelectric transducers

Quantitative damage identification of surrounding rock is important to assess the current condition and residual strength of underground tunnels.In this work,an underground tunnel model with marble-like cementitious materials was first fabricated using the three-dimensional(3D)printing technique and then loaded to simulate its failure mode in the laboratory.Lead zirconate titanate piezoelectric(PZT)transducers were embedded in the surrounding rock around the tunnel in the process of 3D printing.A 3D monitoring network was formed to locate damage areas and evaluate damage extent during loading.Results show that as the load increased,main cracks firstly appeared above the tunnel roof and below the floor,and then they coalesced into the tunnel boundary.Finally,the tunnel model was broken into several parts.The resonant frequency and the peak of the conductance signature firstly shifted rightwards with loading due to the sealing of microcracks,and then shifted backwards after new cracks appeared.An overall increase in the root-mean-square deviation(RMSD)calculated from conductance signatures of all the PZT transducers was observed as the load(damage)increased.Damage-dependent equivalent stiffness parameters(ESPs)were calculated from the real and imaginary signatures of each PZT at different damage states.Satisfactory agreement between equivalent and experimental ESP values was achieved.Also,the relationship between the change of the ESP and the residual strength was obtained.The method paves the way for damage identification and residual strength estimation of other 3D printed structures in civil engineering.

Novel Traveling Wave Sandwich Piezoelectric Transducer with Single Phase Drive:Theoretical Modeling,Experimental Validation,and Application Investigation

Most of traditional traveling wave piezoelectric transducers are driven by two phase different excitation signals,leading to a complex control system and seriously limiting their applications in industry.To overcome these issues,a novel traveling wave sandwich piezoelectric transducer with a single-phase drive is proposed in this study.Traveling waves are produced in two driving rings of the transducer while the longitudinal vibration is excited in its sandwich composite beam,due to the coupling property of the combined structure.This results in the production of elliptical motions in the two driving rings to achieve the drive function.An analytical model is firstly developed using the transfer matrix method to analyze the dynamic behavior of the proposed transducer.Its vibration characteristics are measured and compared with computational results to validate the effectiveness of the proposed analytical model.Besides,the driving concept of the transducer is investigated by computing the motion trajectory of surface points of the driving ring and the quality of traveling wave of the driving ring.Additionally,application example investigations on the driving effect of the proposed transducer are carried out by constructing and assembling a tracked mobile system.Experimental results indicated that 1)the assembled tracked mobile system moved in the driving frequency of 19410 Hz corresponding to its maximum mean velocity through frequency sensitivity experiments;2)motion characteristic and traction performance measurements of the system prototype presented its maximum mean velocity with 59 mm/s and its maximum stalling traction force with 1.65 N,at the excitation voltage of 500 V_(RMS).These experimental results demonstrate the feasibility of the proposed traveling wave sandwich piezoelectric transducer.

DYNAMIC CHARACTERISTICS OF AXIALLY-SYMMETRICAL ANNULAR CORRUGATED SHELL PIEZOELECTRIC TRANSDUCERS

The coupled extensional and flexural vibrations of an annular corrugated shell piezoelectric transducer consisting of multiple circularly-annular surfaces smoothly connected along the interfaces were investigated in the paper. Only a time-harmonic voltage is applied across two electrodes of the piezoelectric shell as the external loading. A theoretical solution was obtained using the classical shell theory. Based on the solution, basic vibration characteristics of resonant frequencies, mode shapes were calculated and examined.

Energy Conversion Efficiency of Rainbow Shape Piezoelectric Transducer

With the aim to enhance the energy conversion efficiency of the rainbow shape piezoelectric transducer, an analysis model of energy conversion efficiency is established based on the elastic mechanics theory and piezoelectricity theory. It can be found that the energy conversion efficiency of the rainbow shape piezoelectric transducer mainly depends on its shape parameters and ma- terial properties from the analysis model. Simulation results show that there is an optimal length ratio to generate maximum en- ergy conversion efficiency and the optimal length ratios and energy conversion efficiencies of beryllium bronze substrate trans- ducer and steel substrate transducer are （0.65, 2.21%） and （0.65, 1.64%） respectively. The optimal thickness ratios and energy conversion efficieneies of beryllium bronze substrate transducer and steel substrate transducer are （1.16, 2.56%） and （1.49, 1.57%） respectively. With the increase of width ratio and initial curvature radius, both the energy conversion efficiencies de- crease. Moreover, beryllium bronze flexible substrate transducer is superior to the steel flexible substrate transducer.

Integration of piezoelectric transducers(PZT and PVDF)within polymer-matrix composites for structural health monitoring applications:new success and challenges

This article investigates the interest of using in-situ piezoelectric(PZT and PVDF)disks to perform real-time Structural Health Monitoring(SHM)of glass fiber-reinforced polymer composites submitted to var-ious tensile loadings.The goal is to evaluate the working range and SHM potential of such embedded transducers for relatively simple mechanical loadings,with the long-term aim of using them to monitor complete 3D structures submitted to more complex loadings.SHM is performed acquiring the electrical capacitance variation of the embedded transducers.To study the potential links between the insitu capacitance signal and the global response of the loaded host specimens,a multi-instrumentation composed of external Nondestructive Testing techniques was implemented on the surfaces of the specimens to search for multi-physical couplings between these external measurements and the capacitance curves.Results confirmed the non-intrusiveness of the embedded transducers,and allowed estimating their working domain.PZT capacitance signal follows well the mechanical loadings,but the piezoceramic transducer gets damaged after a determined relatively low strain level due to its brittleness.The limits of this working domain are extended by using a stretchable PolyVinylidene Fluoride(PVDF)polymer transducer,allowing this one to perform in-situ and real-time SHM of its host tensile specimens until failure.

A unidirectional SH wave transducer based on phase-controlled antiparallel thickness-shear(d15)piezoelectric strips

In recent years,shear horizontal(SH)waves are being paid more and more attention to in structural health monitoring as it has only one displacement component.In this paper,a unidirectional SH wave transducer based on phase-controlled antiparallel thickness-shear(d15)piezoelectric strips(APS)is proposed.Here two pairs of identical APS were used each of which is a bidirectional SH wave transducer.By setting the interval between the two pairs of APS as 1/4 wavelength and the excitation delay between them as 1/4 period of the central operating frequency,unidirectional SH waves can be excited.Both finite element simulations and experiments were performed to validate the proposed design.Results show that SH0 waves were successfully excited only along one direction and those along the unwanted directions were suppressed very well.The proposed unidirectional SH wave transducer is very helpful to study the fundamentals and applications of SH waves.

Design and analysis of longitudinal–flexural hybrid transducer for ultrasonic peen forming

Ultrasonic peen forming(UPF)is an emerging technology that exhibits great superiority in both its flexible operating modes and the deep residual stress that it produces compared with conventional plastic forming methods.Although ultrasonic transducers with longitudinal vibration have been widely studied,they have seldom been incorporated into UPF devices for machining in confined spaces.To meet the requirements of this type of machining,a sandwich-type piezoelectric transducer with coupled longitudinal-flexural vibrational modes is proposed.The basic structure of the transducer is designed to obtain large vibrational amplitudes in both modes.Experimental results obtained with a prototype device demonstrate the feasibility of the proposed transducer.The measured vibrational amplitude for the working face in the longitudinal vibrational mode is 1.0μm,and electrical matching increases this amplitude by 40%.The flexural vibration characteristics of the same prototype transducer are also tested and are found to be slightly smaller than those of longitudinal mode.The resultant working strokes of the UPF impact pins reach 1.7 mm and 1.2 mm in the longitudinal and flexural modes,respectively.The forming capability of the prototype has been evaluated via 15-min machining on standard 2024-T351 aluminum plates.After UPF,an improved surface morphology with lower surface roughness is obtained.The aluminum plate test piece has an apparent upper deformation with an arc height of 0.64 mm.The measured peak value of the compressive residual stress is around 250 MPa,appearing at a depth of 100μm.The proposed longitudinal-flexural hybrid transducer thus provides a high-performance tool for plate peen forming in confined spaces.

Study on Enhancement Effect of Cavitation Caused by HIFU Piezoelectricity Transducer

An orthogonal ultrasonic irradiation system consisting of HIFU with frequency at 1.05 MHz combined with ultrasound with frequency at 28 kHz was applied in this paper.Effect of cavitation was detected by pH-value measurement and conductance measurement.The result shows that the effect of cavitation caused by ultrasound with frequency at 28 kHz is greatly enhanced by HIFU piezoelectricity transducer with frequency at 1.05 MHz.

Analysis on Output Power for Multi-direction Piezoelectric Vibration Energy Harvester

To predict the performance of multi-direction piezoelectric vibration energy harvester,an equation for calculating its output power is obtained based on elastic mechanics theory and piezoelectricity theory.Experiments are performed to verify theoretical analysis.When the excitation direction is along Y direction,a maximal output power about 0.139 mW can be harvested at a resistive load of 65kΩ and an excitation frequency of 136 Hz.Theoretical analysis agrees well with experimental results.Furthermore,the performance of multi-direction vibration energy harvester is experimentally tested.The results show that the multi-direction vibration energy harvester can harvest perfect energy as the excitation direction changes in XY plane,YZ plane,XZ plane and body diagonal plane of the harvester.

HIGH-FREQUENCY VIBRATIONS OF CORRUGATED CYLINDRICAL PIEZOELECTRIC SHELLS

Coupled extensional and flexural cylindrical vibrations of a corrugated cylindrical piezoelectric shell consisting of multiple pieces of circular cylindrical surfaces smoothly connected along their generatrix are studied. To validate the results for the case of relatively thick shells or equivalently high-frequency modes with short wavelengths, existing analysis is extended by considering shear deformation and rotatory inertia. An analytical solution is obtained. Based on the solution, resonant frequencies and mode shapes are calculated.

Design of Sandwich Transducer Based on the Equivalent Length Algorithm

The sandwich transducer structure is comprised of threecomponents along its main axis: the back metal cap, piezoelectricceramic stack and the horn. The purpose of this work is topresent a simplified method, referred as the equivalent lengthalgorithm, to design the actuator parameters including eachsegment length and the resonance frequency fs. The actuatorlength L and the propagation wavelength λ along its main axissatisfy the standing wave theory. So, define an equivalent lengthcoefficient for each part of the actuator, and then the sandwichstructure is regarded as a single material cylindrical rod withequivalent length L′. According to the standing wave theory, theequivalent length L′ of the actuator can be determined with thegiven resonance frequency fs, or vice versa. The phase length ofeach part of the actuator in the standing wave is optimized freelyin the design procedure. The actual length of each part of theactuator is determined by the equivalent length coefficient.Finally, the resonance frequencies of three given actuators arecalculated with this method. They are compared with thoseobtained through Ansys simulation and those measured by animpedance analyzer. The results show agreement.

Analysis of Vibrational Performance of A Piezoelectric Micropump with Diffuse/Nozzle Microchannel

Piezoelectric transducers of different external diameters are designed and fabricated and incorporated into micropumps. Through finite element analysis, it is shown that the volume efficiency of the micropump reaches its maximum value for the first mode of vibration. The variation of maximum displacement with frequency is determined under free and forced vibration. Results demonstrate that this variation shows the same trend for different driving waves at the same driving voltage. The maximum displacement under forced vibration is less than that under free vibration. The displacement increases with decreasing distance from the center of the transducer. The maximum displacement is inversely proportional to the diameter of the transducer and proportional to the driving voltage under both free and forced vibrations. Finally, the micropump flow rate and pressure are measured and are found to manifest the same trend as the maximum displacement under the same driving conditions. For a piezoelectric transducer of 12 mm external diameter, the maximum flow rate and pressure value are 150 μL/min and 346 Pa, respectively, under sine-wave driving at 100 Vpp driving voltage.

Accurate expression of neck motion signal by piezoelectric sensor data analysis

The development of high-precision sensors using flexible piezoelectric materials has the advantages of high sensitivity,high stability,good durability,and lightweight.The main problem with sensing equipment is low sensitivity,which is due to the mismatch between materials and analysis methods,resulting in the inability to effectively eliminate noise.To address this issue,we developed the denoising analysis method to motion signals captured by a flexible piezoelectric sensor fabricated from poly(l-lactic acid)(PLLA)and polydimethylsiloxane(PDMS)materials.Experimental results demonstrate that this improved denoising method effectively removes noise components from neck muscle motion signals,thus obtaining high-quality,low-noise motion signal waveforms.Wavelet decomposition and reconstruction is a signal processing technique that involves decomposing a signal into different scales and frequency components using wavelets and then selectively reconstructing the signal to emphasize specific features or eliminate noise.The study employed the sym8 wavelet basis for wavelet decomposition and reconstruction.In the denoised signals,a high degree of stability and periodic peaks are distinctly manifested,while amplitude and frequency differences among different types of movements also become noticeably visible.As a result of this study,we are enabled to accurately analyze subtle variations in neck muscle motion signals,such as nodding,shaking the head,neck lateral flexion,and neck circles.Through temporal and frequency domain analysis of denoised motion signals,differentiation among various motion states can be achieved.Overall,this improved analytical approach holds broad application prospects across various types of piezoelectric sensors,such as healthcare monitoring,sports biomechanics.

High Precision Ultrasonic Guided Wave Technique for Inspection of Power Transmission Line

Due to the merits of high inspection speed and long detecting distance, Ultrasonic Guided Wave（UGW） method has been commonly applied to the on-line maintenance of power transmission line. However, the guided wave propagation in this structure is very complicated, leading to the unfavorable defect localization accuracy. Aiming at this situation, a high precision UGW technique for inspection of local surface defect in power transmission line is proposed. The technique is realized by adopting a novel segmental piezoelectric ring transducer and transducer mounting scheme, combining with the comprehensive characterization of wave propagation and circumferential defect positioning with multiple piezoelectric elements. Firstly, the propagation path of guided waves in the multi-wires of transmission line under the proposed technique condition is investigated experimentally. Next, the wave velocities are calculated by dispersion curves and experiment test respectively, and from comparing of the two results, the guided wave mode propagated in transmission line is confirmed to be F（1,1） mode. Finally, the axial and circumferential positioning of local defective wires in transmission line are both achieved, by using multiple piezoelectric elements to surround the stands and send elastic waves into every single wire. The proposed research can play a role of guiding the development of highly effective UGW method and detecting system for multi-wire transmission line.

Principle and Experimental Verification of Novel Dual Driving Face Rotary Ultrasonic Motor

Existing rotary ultrasonic motors operating in extreme environments cannot meet the requirements of good environmental adaptability and compact structure at same time,and existing ultrasonic motors with Langevin transducers show better environmental adaptability,but size of these motors are usually big due to the radial arrangement of the Langevin transducers.A novel dual driving face rotary ultrasonic motor is proposed,and its working principle is experimentally verified.The working principle of the novel ultrasonic motor is firstly proposed.The 5th in-plane flexural vibration travelling wave,excited by the Langevin transducers around the stator ring,is used to drive the rotors.Then the finite element method is used in the determination of dimensions of the prototype motor,and the confirmation of its working principle.After that,a laser Doppler vibrometer system is used for measuring the resonance frequency and vibration amplitude of the stator.At last,output characteristics of the prototype motor are measured,environmental adaptability is tested and performance for driving a metal ball is also investigated.At room temperature and 200 V(zero to peak) driving voltage,the motor’s no-load speed is 80 r/min,the stalling torque is 0.35 N·m and the maximum output power is 0.85 W.The response time of this motor is 0.96 ms at the room temperature,and it decreases or increases little in cold environment.A metal ball driven by the motor can rotate at 210 r/min with the driving voltage 300 V(zero to peak).Results indicate that the prototype motor has a large output torque and good environmental adaptability.A rotary ultrasonic motor owning compact structure and good environmental adaptability is proposed,and lays the foundations of ultrasonic motors’ applications in extreme environments.

New Resonant Force Sensor Powered by Stabilized LD Source

On the basis of optically powered sensor principles,this paper introduces a practical scheme of an optically powered force sensor using a piezoelectric crystal worlding in close-loop resonant mode.A 3 mW LD stabilized is used as optical source.The optical powering distance reaches 500 m while the total power consumption of the micro power measuring head is only 0.275 mW.The key technical problems of the sensors are presented as well as experimental results.

Application of piezoelectric transient response in transducer acoustic power measurement

To explore a more convenient method for measuring the focused ultrasound power, a piezoelectric ceramic plate was used to receive ultrasonic signal directly. Due to an acoustic force acts on the surface of piezoelectric ceramic plate, the piezoelectric response was obtained by means of electromechanical analogy, which was composed of voltage response caused by forced vibration and high frequency attenuation response caused by natural vibration. The conversion relationship between output signal of piezoelectric ceramic plate and acoustic power of transducer was analyzed. The envelope of output piezoelectric signal was extracted in twice, and a voltage amplitude curve with sinusoidal distribution that could describe the changes of acoustic power was obtained. Under different drive voltage of transducer, the maximum peak voltage of envelope curve was found respectively. Their squared values were made a linear fitting with acoustic power measured by acoustic power meter, and then the proportional coefficient of theoretical relational expression was calibrated. The experimental results are in good agreement with the theory. The relative error between calibrated theoretical acoustic power and that measured by acoustic power meter was less than 8.7%. The paper can provide a guideline for measuring acoustic power of transducer by using piezoelectric signal.

Calculation Model for the Steady-State Vibration Amplitude of a New Type of Cascaded Composite Structure-Based Ultrasonic Transducer

The steady-state vibration amplitude is an important performance indicator of high-frequency ultrasonic transducers for ultrasonically assisted manipulating,machining,and manufacturing.This work aimed to develop a calculation model for the steady-state vibration amplitude of a new type of dual-branch cascaded composite structure-based ultrasonic transducer that can be used in the packaging of microelectronic chips.First,the steady-state vibration amplitude of the piezoelectric vibrator of the transducer was derived from the piezoelectric equation.Second,the vibration transfer matrices of the tapered ultrasonic horns were obtained by combining the vibration equation,the continuous condition of the displacement,and the equilibrium condition of the force.Calculation models for the steady-state vibration amplitude of the two working ends of the transducer were then developed.A series of exciting trials were carried out to test the performance of the models.Comparison between the calculated and measured results for steady-state vibration amplitude showed that the maximum deviation was 0.0221μm,the minimum deviation was 0.0013μm,the average deviation was 0.0097μm,and the standard deviation was 0.0046μm.These values indicated good calculation accuracy,laying a good foundation for the practical application of the proposed transducer.

An investigation on stress distribution effect on multi- piezoelectric energy harvesters

With the fast development of piezoelectric materials and due to its green and renewable characteristics, the piezoelectric energy harvesting technology has been paid more and more attention by pavement engineers. The stress distribution will significantly affect the piezoelectric material performance. In this paper, the effects of multiple piezoelectric elements on the generation of electrical energy and output power are studied. In the case of constant external load, the number of the piezoelectric units does not necessarily produce more energy. When the same multi piezoelectric units work together, if the stress state of the piezoelectric units is different, the total output energy affected by the connection mode. For uneven stress distribution, the optimal output mode is that each of the piezoelectric units rectified before connected in parallel.

High frequency wideband underwater acoustic transducer for ring shaped composite material

A kind of circular ring high frequency wideband underwater acoustic transducer is developed by using the Low Q value and broadband characteristics of the piezoelectricity composite material,and the dual mode coupling is used to broaden the bandwidth of the transducer by double ring stacking along the axial direction.Through theoretical analysis and simulation calculation,the geometric dimensions of the sensitive components are determined.The piezoelectric composite rings are processed and then the stack sensitive element can be made by stacking two piezoelectric composite rings with the same outer diameter and different thickness in axial direction by cutting piezoelectric ceramicsfilling the flexible polymer-coating electrode.Finally,the transducer can be made by pouring waterproof sound-permeable layer.The performances of transducer have also been tested in the water and the test results show that the resonant frequency is 410 kHz,the maximum transmit voltage response is 150 dB,the-3 dB bandwidth can reaches 60 kHz,the horizontal directivity（-5 dB） is 360°,and the vertical directivity（-3 dB） is 20°.It is also shown that the bandwidth of the transducer can be enlarged remarkably by using the method of stacking two different thickness piezoelectric composite rings along the axial direction,and the horizontal omnidirectional emission of acoustic wave can be realized