Non-contact Excitation Research Articles

Evaluation of dynamic stiffness of machine tool spindle by non-contact excitation tests

This paper presents a non-contact excitation method for evaluating the dynamic stiffness of a rotating spindle. The spindle response to an excitation force is measured, and frequency response functions (FRFs) are obtained. Based on the measured FRFs, dynamic uncertainty and its effect on cutting stability are investigated. Regenerative forces are generated using displacement feedback with a time lag element, and a closed-loop excitation test is executed automatically. The stability map obtained from the closed-loop test and the stability charts calculated from the FRFs are compared, and the uncertainty of the spindle dynamics during operations is clarified.

101 近距離場音波浮揚による平板の非接触加振とき裂検知への適用可能性(セッション1 損傷検知・信号処理)

101 近距離場音波浮揚による平板の非接触加振とき裂検知への適用可能性(セッション1 損傷検知・信号処理)

Damage detection in membrane structures using non-contact laser excitation and wavelet transformation

Abstract In this paper, a vibration testing and health monitoring system based on an impulse response excited by laser is proposed to detect damage in membrane structures. A high power Nd: YAG pulse laser is used to supply an ideal impulse to a membrane structure by generating shock waves via laser-induced breakdown in air. A health monitoring apparatus is developed with this vibration testing system and a damage detecting algorithm which only requires the vibration mode shape of the damaged membrane. Artificial damage is induced in membrane structure by cutting and tearing the membrane. The vibration mode shapes of the membrane structure extracted from vibration testing by using the laser-induced breakdown and laser Doppler vibrometer are then analyzed by 2-D continuous wavelet transformation. The location of damage is determined by the dominant peak of the wavelet coefficient which can be seen clearly by applying a boundary treatment and the concept of an iso-surface to the 2-D wavelet coefficient. The applicability of the present approach is verified by finite element analysis and experimental results, demonstrating the ability of the method to detect and identify the positions of damage induced on the membrane structure.

Resonance ultrasound spectroscopy for studying piezoelectricity and internal friction at elevated temperatures of quartz, langasite, and gallium nitride

Resonance ultrasound spectroscopy (RUS) is a powerful method for measuring elastic constants (Cijkl) of solids. It can be applied to determine the piezoelectric coefficients (eijk) as well, because they also affect the mechanical resonance frequencies. Precise frequency measurements in vacuum and unambiguous mode identification with laser-Doppler interferometry allowed us to determine Cijkl and eijk simultaneously for crystals including alpha quartz, which shows low piezoelectricity. We further developed a noncontact excitation and detection method with antennas through electromagnetic fields and study internal friction and carrier mobility of quartz, langasite, and GaN at elevated temperatures up to ~1200 K. This method is also successfully applied to developing ultrahigh-sensitive biosensors for diagnosis.

Numerical Investigation of Air-Coupled Generation of Lamb Waves in Isotropic Plates

In the case of non-destructive testing and evaluation (NDT & NDE) of plate materials and structures ultrasonic Lamb waves are used. Very often air-coupled ultrasonic transducers are used for non-contact Lamb wave excitation and reception. This method has a very serious drawback: global insertion losses for an air-coupled system may be 120 dB–160 dB typically. In order to improve this NDT method a better understanding of Lamb wave excitation process is needed. A numerical investigation was performed in order to evaluate air-coupled Lamb wave excitation in an isotropic single layer plate. It is shown how Lamb wave normal displacement amplitude depends on an incidence angle and the distance between the plate and the transducer. DOI: http://dx.doi.org/10.5755/j01.eee.20.1.6162

202 近距離場音波浮揚による非接触加振の研究(セッション5 音響・超音波利用)

This study concerns non-contact excitation of planer objects by using near-field acoustic levitation, in which a planer object having relatively large size and weight is levitated on a ultrasonic vibration plate with 10-100 μm air gap. This phenomenon has been studied as a non-contact transportation technology for a fragile thin plate such as flat panel display glass substrate. In this study, we investigate the possibility of this phenomenon as a technology for non-contact excitation of planer objects. In this paper, we propose a non-contact excitation method to vibrate the levitated object at arbitrary low frequency by modulating the ultrasonic amplitude of the vibration plate. An experimental study of non-contact excitation of plate specimens near the natural frequencies suggests that the system consisting of the vibration plate, the air gap, and the levitated plate can be modeled as a two-degree-of-freedom dynamical system.

2A32 Vibration Control Evaluation for Underwater Structures Using Non-contact Laser Excitation(The 12th International Conference on Motion and Vibration Control)

A system that uses non-contact laser excitation based on pulsed-laser ablation is proposed to evaluate vibration suppression of fully submerged underwater structures. Although impact testing with an impulse hammer is commonly used in vibration analysis due to the simplicity of the apparatus, impact testing has limitations in underwater applications. Additionally vibration testing in dangerous conditions (e.g., deep oceans, under ice, and nuclear reactor plants) is difficult. The proposed method yields the frequency spectrum by applying a pulsed-laser-ablation excitation force to the structure and measuring the output using a laser Doppler vibrometer. Because the direction, strength, and effective duration of the pulsed-laser-ablation force are essentially constant, it is possible to obtain the dynamic characteristics of an underwater structure using only the output frequency spectrum. The validity of the proposed system is demonstrated by comparing the frequency spectrum suppressed by passive vibration control to that without a control.

Correspondence - Acoustic waves in a structure containing two piezoelectric plates separated by an air (vacuum) gap

This paper presents experimental results for the characteristics of acoustic waves propagating in a structure containing two parallel piezoelectric plates (I and II) separated by an air gap. Plate I, made of Y-X lithium niobate, contained two interdigital transducers that excited and received an acoustic wave with shear-horizontal polarization. Piezoelectric plate II, made of lithium niobate, was placed above and between the transducers, separated by a fixed gap. For its certain orientation, the amplitude-frequency characteristic showed sharply defined resonant attenuation peaks, which were situated at an equidistant separation from each other. The depth of the peaks was observed to decrease with a wider gap between the plates. It has been stated that these peaks are associated with the resonant reflections of a slot acoustic wave across the width of plate II. Experimentally determined phase velocities and electromechanical coupling coefficient for the slot wave in the structure under study are in a good agreement with theoretical values for various crystallographic orientations of plate II. A comparison between the experimental and theoretical results has allowed us to state two conditions for the slot wave to exist. The structures described may be employed for noncontact excitation of acoustic waves in the plates and for the development of various liquid, gas, and temperature sensors.

A focused electric spark source for non-contact stress wave excitation in solids.

A focused electric spark is used as a non-contact acoustic source to excite stress waves in solids. The source consists of an electric spark source located at the near focus of an ellipsoidal reflector that focuses the acoustic disturbance generated by the spark source to the far focal point. Experimental studies using both contact and non-contact sensors indicate that the source has the capability to excite the Rayleigh surface wave and impact-echo mode (S1-zero-group-velocity Lamb mode) in a 250 mm thick concrete slab and to enable fully air-coupled testing of concrete specimens.

Bolt loosening analysis and diagnosis by non-contact laser excitation vibration tests

In this paper, a vibration testing and health monitoring system based on an impulse response excited by laser ablation is proposed to detect bolted joint loosening. A high power Nd: YAG pulse laser is used to generate an ideal impulse on a structural surface which offers the potential to measure high frequency vibration responses on the structure. A health monitoring apparatus is developed with this vibration testing system and a damage detecting algorithm. The joint loosening can be estimated by detecting fluctuations of the high frequency response with the health monitoring system. Additionally, a finite element model of bolted joints is proposed by using three-dimensional elements with a pretension force applied and with contact between components taken into account to support the bolt loosening detection method. Frequency responses obtained from the finite element analysis and the experiments using the laser excitation are in good agreement. The bolt loosening can be detected and identified by introducing a damage index by statistical evaluations of the frequency response data using the Recognition-Taguchi method. The effectiveness of the present approach is verified by simulations and experimental results, which are able to detect and identify loose bolt positions in a six-bolt joint cantilever.

Operational modal analysis of a rectangular plate using non-contact excitation and measurement

Operational modal analysis (OMA), or output-only modal analysis, has been extensively developed in the past decades and widely used especially when the input is unknown and difficult to measure. This paper presents a non-contact experimental technique for measuring modal parameters of a rectangular aluminum plate with free boundaries using only the output data, with the intention to apply the technique to turbine blades. OMA is used to analyze both the out-of-plane and in-plane vibrations of the plate in the frequency range of up to 15,000Hz, which can be an operation frequency range of a turbine blade, under white noise acoustic excitation in a direction of interest. It is shown that OMA can be performed when the types of measurement at the measurement and reference points are different, since the associated cross-correlation functions contain modal characteristics of the test structure. A single-point laser vibrometer and a free-field microphone are used to simultaneously measure the responses of the plate in a non-contact manner, with the microphone measurement serving as the reference. The pressure measured by the microphone near the reference point is shown to be proportional to the normal surface acceleration at the reference point, and the cross power spectral densities obtained by the current test method can be used for modal parameter estimation. A method for measuring the in-plane modes of the plate by shining the laser beam on the plate surface with an incident angle is developed. Experimental modal analysis (EMA) is also performed on the plate using an impact hammer and the laser vibrometer. The measured natural frequencies and mode shapes of the out-of-plane and in-plane modes of the plate using OMA and EMA are compared with those calculated using commercial finite element software. The maximum error between the measured and calculated natural frequencies of the plate is 1.53 percent for the first 18 elastic modes, including 16 out-of-plane and two in-plane modes. The modal assurance criterion values between the corresponding measured and calculated mode shapes of the plate are all above 93 percent.

A high amplitude, time reversal acoustic non-contact excitation (trance)

This paper describes the principle behind a high amplitude non-contact acoustic source based on the principle of time reversal (TR), a process to focus energy at a point in space. By doing the TR in an air filled, hollow cavity and using a laser vibrometer in the calibration of the system, a non-contact source may be created. This source is proven to be more energetic than an off the shelf focused ultrasound transducer. A scaled up version of the proposed source has the potential to allow nondestructive evaluation processes that require high amplitude, such as nonlinear elastic wave spectroscopy (NEWS) techniques.

Impact of the Flow on an Acoustic Excitation System for Aeroelastic Studies

The flow in turbomachines is highly unsteady. Effects like vortices, flow separation, and shocks are an inevitable part of the turbomachinery flow. Furthermore, high blade aspect ratios, aerodynamically highly loaded and thin profiles increase the blade sensitivity to vibrations. According to the importance of aeroelasticity in turbomachines, new strategies for experimental studies in rotating machines must be developed. A basic requirement for aeroelastic research in rotating machines is to be able to excite the rotor blades in a defined manner. Approaches for active blade excitation in running machines may be piezoelectric elements, magnetism, or acoustics. Contact-free excitation methods are preferred, since additional mistuning is brought into the investigated system otherwise. A very promising method for aeroelastic research is the noncontact acoustic excitation method. In this paper, investigations on the influence of an annular cascade flow on the blade vibration, excited by an acoustic excitation system, are presented for the first time. These investigations are carried out at the Aeroelastic Test Rig of the Royal Institute of Technology in Stockholm. By varying the excitation angle, the outlet Mach number, and the relative position of the excited blade to the excitation system, the influence of the flow on the acoustic excitation is quantified. The results show that there is a strong dependency of the excited vibration amplitude on the excitation angle if the outlet Mach number is increased, which implies that preferable excitation directions exist. Furthermore, it is shown that a benefit up to 23% in terms of excited vibration amplitude can be reached if the flow velocity is raised.

Damage detection of unidirectional carbon fiber–reinforced laminates with embedded magnetostrictive particulates: A preliminary study

Defects in composite laminates are difficult to detect because of the conductive and paramagnetic properties of composite materials. Timely detection of defects in composite laminates can improve reliability. This research illustrates the preliminary analysis and detection of delaminations in carbon fiber laminate beams using a single layer of magnetostrictive particles and noncontacting concentric magnetic excitation and sensing coils. The baseline analytical models also begin to address the intrusive nature of the magnetostrictive particles as well as relate the applied excitation field with the stress and magnetic flux densities induced in the magnetostrictive layer. Numerical methods are used to begin to characterize the presence of magnetostrictive particles in the laminate and the behavior of the magnetostrictive particles in relationship to the magnetic field used during sensing. Unidirectional laminates with embedded delaminations are used for simulations and experimentations. A novel, yet simplified fabrication method is discussed to ensure consistent scanning and sensing capabilities. The nondestructive evaluation scanning experiments were conducted with various shapes and sizes of damages introduced into carbon fiber–reinforced polymeric composite structures. The results demonstrate high potential for magnetostrictive particles as a low-cost, noncontacting, and reliable sensor for nondestructive evaluation of composite materials.

A compact frequency-domain photon migration system for integration into commercial hybrid small animal imaging scanners for fluorescence tomography

The work presented herein describes the system design and performance evaluation of a miniaturized near-infrared fluorescence (NIRF) frequency-domain photon migration (FDPM) system with non-contact excitation and homodyne detection capability for small animal fluorescence tomography. The FDPM system was developed specifically for incorporation into a Siemens micro positron emission tomography/computed tomography (microPET/CT) commercial scanner for hybrid small animal imaging, but could be adapted to other systems. Operating at 100 MHz, the system noise was minimized and the associated amplitude and phase errors were characterized to be ±0.7% and ±0.3°, respectively. To demonstrate the tomographic ability, a commercial mouse-shaped phantom with 50 µM IRDye800CW and 68Ga containing inclusion was used to associate PET and NIRF tomography. Three-dimensional mesh generation and anatomical referencing was accomplished through CT. A third-order simplified spherical harmonics approximation (SP3) algorithm, for efficient prediction of light propagation in small animals, was tailored to incorporate the FDPM approach. Finally, the PET-NIRF target co-localization accuracy was analyzed in vivo with a dual-labeled imaging agent targeting orthotopic growth of human prostate cancer. The obtained results validate the integration of time-dependent fluorescence tomography system within a commercial microPET/CT scanner for multimodality small animal imaging.

Measuring the performance of underplatform dampers for turbine blades by rotating laser Doppler Vibrometer

Underplatform friction dampers are commonly used to control the vibration level of turbine blades in order to prevent high-cycle fatigue failures. Experimental validation of highly non-linear response predictions obtained from FEM bladed disk models incorporating underplatform dampers models has proved to be very difficult so as the assessment of the performance of a chosen design. In this paper, the effect of wedge-shaped underplatform dampers on the dynamics of a simple bladed disk under rotating conditions is measured and the effect of the excitation level on the UPDs performances is investigated at different number of the engine order excitation nearby resonance frequencies of the 1st blade bending modes of the system. The measurements are performed with an improved configuration of a rotating test rig, designed with a non-contact magnetic excitation and a non-contact rotating SLDV measurement system.

Acoustic impact-echo investigation of concrete delaminations using liquid droplet excitation

Impact-echo testing is an effective technique to map delaminations on concrete bridge decks. Non-contact acoustic measurement techniques are used to measure responses excited by a transient point load. Non-contact excitation using falling liquid droplets is demonstrated to excite the resonant modes associated with delamination defects. Slow and fast liquid flows produce large and small droplets with varying impact parameters. Spectrograms of acquired acoustic data demonstrate the effectiveness of the technique to detect concrete delaminations. Photography reveals the size differences of the droplets. Non-contact excitation and measurement can be deployed in situations where mechanical coupling to the material is undesirable.

Electromagnetic-acoustic transformations and high-resolution sounding systems: new possibilities and new formulations

The main ideas on the structure of non-stationary electromagnetic response of geo-medium and its "non-classical" manifestations have been considered. A phenomenon of direct and inverse electromagnetic-acoustic transformation in the skin-layer of the source of electromagnetic field is being examined, as a result of which not only noncontact excitation of acoustic disturbance in geo-medium becomes possible but also noncontact obtaining of information on its extinction rate and velocity of propagation. Possibilities of high-resolution sounding systems creation are analyzed, which are electromagnetic by their realization form and acoustic ones by their structure.

Identification and removal of adverse effects of non-contact electromagnetic excitation in Oberst Beam Test Method

Although the Oberst Beam Test Method is widely used in practice, detailed information about how to perform a successful Oberst beam experiment is quite limited. In this paper, first, the effects of various parameters in an Oberst test rig, including the amplitude of the excitation, mounting conditions, input excitation type and the length of the test sample, are examined in an attempt to improve the accuracy of the estimated material properties. As it is observed that the electromagnetic effect created by a non-contact exciter can be the most significant source of error in estimated material properties, this paper then presents the results of extensive tests so as to quantify the level of the adverse effects of non-contact electromagnetic excitation. It is found that non-contact electromagnetic exciter creates a stiffness effect that can be modelled as a spring attached between the non-contact exciter location on the Oberst beam and the ground. In contrast to the common belief that the use of non-contact electromagnetic excitation has little drawbacks, it is shown that such excitation can introduce very significant level of errors in identified material properties. This paper also proposes a method for removing the adverse effects of the electromagnetic excitation in order to obtain more accurate material properties for uniform as well as composite beams.

Reliability Test Platform for High-Speed Motorized Spindle Based on Magnetic Loading

In order to accurately emulate the operation conditions of high-speed motorized spindle in the reliability experiment, a dynamic loading system is proposed. This system allows simultaneously loading torque, radial and axial force against the spindle. The torque load is carried out by the electric dynamometer; the non-contact vibration exciter completes the radial load; the axial load is carried out by a self-made electromagnet. Moreover, this system also can detect out the basic features and failure data of the motorized spindle during the loading. And these sampling data provide a quantitative elevation for its reliability analysis. This paper presents a simple solution to the high-speed motorized spindle reliability research where the loading experiment is designed with the spindle whose maximum rotational speed is 18000rpm.