High Frequency Resonant Mode Research Articles

Shape Optimization of Rectangular Plates for Vibration-Based Fatigue Testing

Abstract In vibration-based high cycle fatigue testing, a base-excited plate is driven at a high frequency resonant mode until failure. In one vibration-based method involving a cantilevered square plate, a mode often referred to as the “two-stripe” mode is sometimes used because it exists at high frequencies and produces large uniaxial bending stresses along the free edge that are suitable for fatigue testing. The purpose of this work is to precisely investigate how the dimensions of a more generally rectangular plate influence performance when driven at the two-stripe mode. Included are the results of many thousands of modal analysis simulations. From these simulations, general trends with respect to resonant frequencies, frequency isolation, and stress fields in the plate are examined. Results of select geometries were then experimentally validated using a 1000 lb shaker. It is generally shown that, compared with square plates, rectangular plates with 1.37 length-to-width ratio exhibit more favorable stress distributions and frequency isolation. Recommendations are also given for how to quickly select preferable plate dimensions when planning a test based around the operating frequencies of the test setup.

Dual-axis control of flexure-based motion system for optical fibre transceiver assembly using fixed-order controller

High-frequency resonant modes appearing in the flexure-based motion systems are the key factors that limit the motion/positioning performance. This paper presents an approach to design the fixed-order (low-order) controller for the flexure-based motion system, which is used for industrial optical fibre transceiver alignment and assembly. The uniqueness of the proposed algorithm is that one single controller can simultaneously stabilize the uncertain high-frequency resonant modes for both x and y-axis motion. Especially, the resulted controller can significantly enhance the tracking and disturbance rejection ability in low frequency. The novelty of the proposed method is mainly twofold. First, the finite-frequency specifications are introduced to robust control of the polytopic systems. As the entire-frequency specifications have the trend to place the dominant poles towards the central polynomial, the finite-frequency specifications largely relax the conservatism for the performance optimization. Second, a new and practical method is proposed to choose the central polynomial by designing a nominal controller, where two different central polynomials are utilized for x and y-axis separately for the practical applications, so that the stability and performance are guaranteed but the conservatism is reduced. Experiments are evaluated on the 2DOF flexure-based motion system, and the results show that the tracking error using designed fixed-order controller has a more than 50% reduction compared with the same-order notch filter based nominal controller, with respect to both the sinusoidal and triangular references.

Vibration-Based Bending Fatigue of a Hybrid Insert-Plate System

A hybrid bending specimen system was developed to reduce material waste when using the vibration-based fatigue method to gather high cycle fatigue (HCF) data. In the vibration-based fatigue method, a base-excited plate specimen is driven into a high frequency resonant mode until failure. Compared to the axial testing methods, vibration-based failure better represents the conditions and surface-initiated cracks experienced by structural components subject to high frequency vibrations, like blades and vanes in gas turbine engines. In addition, the method produces data over 40 times faster than conventional axial testing methods. Only a small portion of the vibration-based bending specimen is needed to determine crack initiation failure. In order to reduce material waste, a hybrid bending system was designed to test a small specimen held in a reusable carrier plate, thereby reducing material costs to gather HCF data. The final optimized design, the Bruns-Zearley plate specimen, produced fatigue data using 95 % less material. The results are comparable tofatigue data acquired from standard vibration-based plate specimen methods within a 95 % confidence interval.

Hysteresis Modeling and Inverse Feedforward Compensation for PZT Actuator in Dual-Stage Hard Disk Drive

With the growth of hard disk storage, it would be difficult to meet the specification of the high track density with conventional single actuator. Therefore the next generation of high speed hard disk drive uses the concept of dual-stage actuated hard disk drive where a secondary actuator is mounted onto the VCM actuator. This helps to achieve higher servo bandwidth and, therefore, more precise tracking. Improved tracking error allows higher track density and hence higher storage capacity. Piezoelectric actuator has been a popular choice as the secondary stage. However, the piezoelectric actuators exhibit an unavoidablecharacteristic of hysteresis which causes inaccuracies and oscillations in the system responses.In this paper, the hysteresis behaviour is investigated for asuspension based PZT actuator which is used as the secondary actuator of HDD available in the market. The Generalized Prandtl-Ishlinskii (GPI) hysteresis model which is a phenomenological based model is obtained usingnon-linear least square curve-fitting. In the secondexperiment, a second order linear dynamics model of the PZT actuator is obtained using frequency response identificationmethod. High frequency resonance modes of the PZT actuator are eliminated using a notch filter. By integrating the obtained GPI hysteresis model with this second-order lineardynamics, a nonlinear dynamic model and an inverse feedforward controller are developed.Preliminary simulation results demonstrate that inverse feedforward controller can be appliedfor precise tracking of triangular and multiple frequency sinusoidal trajectories.

High-field multi-frequency ESR in the S=2 heisenberg antiferromagnetic chain compound MnCl3(bpy)

We report the results of high-field multi-frequency electron spin resonance (ESR) experiments on a powder sample of MnCl3 (bpy) (bpy=2, 2′-bipyridine). This compound is one of the rare examples of the spin (S) 2 quasi one-dimensional (1D) Heisenberg antiferromagnets (HAFs), and magnetic properties of tiny single crystal samples were reported previously (G. E. Granroth et al., Phys. Rev. Lett. 77, 1616 (1996).). In our previous paper on this compound (M. Hagiwara et al., J. Phys.: Conf. Ser. 400, 032014 (2012).), we reported, for the S=2 1D HAF, good agreement between experiment and calculation for the temperature dependence of magnetic susceptibility and the high-field magnetization process at 1.3 K. In this work, we have observed some high-frequency resonance modes with zero-field gaps of about 800 GHz that may correspond to antiferromagnetic resonance modes with orthorhombic anisotropy in a long-range-ordered phase that emerged at low temperatures above the critical field at which the energy gap (Haldane gap) closes. The single-ion anisotropy constant D evaluated from the analysis of these ESR modes is larger than that reported previously.

Alkanethiol-functionalized terahertz metamaterial as label-free, highly-sensitive and specificbiosensor

Specific biorecognition is essential for many biological processes, for which highly sensitive and label-free biosensors are strongly demanded. The recently developed metamaterials are a potential choice for biosensing due to their exotic properties. In the current work, a label-free and specific sensor for streptavidin–agarose (SA) was fabricated based on terahertz metamaterial functionlized by octadecanthiols and biotins. Both low and high frequency resonant modes from the metamaterials are found applicable for the detection of SA, and a redshift up to 6.76GHz for the high frequency mode was measured in the undiluted commercial solution. The low frequency mode is attributed to inductor–capacitor (LC) oscillation, while the high frequency mode originates from the plasmonic dipole oscillator, both of which are highly sensitive to the micro-environment change. Adsorption of SA of different concentrations causes different redshifts, and the replacement of high refractive-index substrate with low refractive-index substrate can efficiently promote the sensitivity, well agreeing with the numerical simulation. Moreover, for a particular biomolecule, the sensitivity can be further improved by optimizing the metamaterial design. This method might be very helpful for desirable biorecognition in biology, medicine, and drug industry.

Attenuation of High Frequency Mechanical Resonances Using Multirate Low-Pass Filter in HDDs

In this paper, the design method of a multirate digital filter to handle high frequency resonant modes in hard disk drives (HDDs) or other mechanical actuators is proposed. Instead of using many notch filters, one low-pass filter will handle multiple mechanical resonance modes. The proposed multirate digital filter has robust resonance cancellation capability with comparable or even lower phase loss than using notch filters. The proposed scheme can well handle the high frequency mechanical resonances in the sense of robustness to variations of resonance frequencies and simplicity to implement in practice. The effectiveness of the proposed method is verified by application to a real HDD servo system.

Identification and High Bandwidth Control of Hard Disk Drive Servo Systems Based on Sampled Data Measurements

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> One of the key factors that determines the track density of a hard disk drive (HDD) is the performance characteristics of the HDD servo system, the control system that positions the <emphasis emphasistype="smcaps">read/write</emphasis> magnetic head close to the center of the desired track of the HDD. For most HDD servo systems, the deviation of the position of the magnetic head from the center of the desired track is measured whenever the head passes over sectors, referred to as servo burst sectors that carry prewritten position data. The position error signal (PES) is, therefore, generated at discrete points in time, the rate of which is limited by the number of the prewritten servo burst sectors and the spinning speed of the disk. This limited natural sampling rate puts limitations on how high the bandwidth of the controller can be as well as making it difficult to identify the continuous time modes which occur at frequencies close to or higher than the sampling frequency. In this paper, we first introduce a method for identifying the open-loop continuous-time dynamics of such HDD servo systems by processing the available sampled PES data. The method is based on exciting the system with two orthogonal sinusoids and constructing a linear complex equation that relates the sampled PES points with the unknown values of the transfer function. Then, we design a high bandwidth HDD servo controller with improved performance characteristics. In our control design we employ the “ACORN estimator” that generates estimates of the head position by processing the servo burst and data sector measurements, to provide PES estimates at higher sampling rates during <emphasis emphasistype="smcaps">read</emphasis>. Our control design is tested on an actual disk drive. The effect of the higher sampling rate, generated by the ACORN estimator, on the seek time and steady-state performance is evaluated. While our results show that the use of a higher sampling rate provides some improvement, the presence of varying high frequency resonance modes limits further increase in bandwidth that is now possible due to the higher sampling rate. Consequently, the proposed control scheme is expected to have additional benefits in future generations of disk drives employing dual stage actuators. </para>

Goodman Diagram Via Vibration-Based Fatigue Testing

A new vibration-based fatigue testing methodology for assessing high-cycle turbine engine material fatigue strength at various stress ratios is presented. The idea is to accumulate fatigue energy on a base-excited plate specimen at high frequency resonant modes and to complete a fatigue test in a much more efficient way at very low cost. The methodology consists of (1) a geometrical design procedure, incorporating a finite-element model to characterize the shape of the specimen for ensuring the required stress state/pattern; (2) a vibration feedback empirical procedure for achieving the high-cycle fatigue experiments with variable-amplitude loading; and finally (3) a pre-strain procedure for achieving various uniaxial stress ratios. The performance of the methodology is demonstrated with experimental results for mild steel, 6061-T6 aluminum, and Ti-6Al-4V plate specimens subjected to a fully reversed bending, uniaxial stress state.

Development of a novel vibration-based fatigue testing methodology

A novel testing methodology has been developed to determine the fatigue limit strength of structural materials at high frequencies. The procedure involves the use of a base-excited plate specimen driven into a high frequency resonant mode which allows completion of a fatigue test in a few hours. The use of a step-testing method allows determination of the fatigue limit strength of the material corresponding to a very large number of cycles, 10 6 or 10 7 in this case. The methodology consists of a topological design procedure, incorporating a finite element model, to produce the shape of the specimen necessary to achieve the required stress state/pattern, and a forced vibration-based fatigue procedure for conducting the high cycle fatigue experiments with variable-amplitude loading. The successful application of the methodology is demonstrated by the experimental results from steel, 6061-T6 aluminum, and Ti-6Al-4V plate specimens subjected to fully reversed uniaxial and biaxial bending stress states. Results are compared with existing data produced using traditional fatigue test machines.

Design Considerations for Very High Frequency Resonant Mode DC/DC Converters

The demand for higher switching frequencies in power converters has rekindled interest in resonant mode topologies. Conventional resonant converter circuits, however, are not optimized for high-frequency operation. A new resonant mode dc/dc converter topology exhibits desirable characteristics including zero switching losses, elimination of snubbers, simple control strategy, and circuit operation that is insensitive to parasitics such as diode reverse recovery. Analysis and design techniques are discussed in detail and are experimentally verified with a 150-W prototype converter operating in the frequency range 500 kHz-1 MHz.

High Intensity Beam Instabilities in the Brookhaven AGS

Transverse resistive wall instabilities and longitudinal reactive wall instabilities have both been observed in the Brookhaven AGS. Recently an instability has been observed characterized by individual coherent phase oscillations of the twelve beam bunches. This instability is believed to be caused by high frequency resonance modes in the rf cavities introduced by recent modifications. A simple analysis shows that voltages induced in these parasitic resonances by the beam can couple the phase oscillations of the individual bunches. A normal mode analysis of the system predicts unstable normal modes with properties similar to the observations. Modifications to the rf cavities to suppress these undesirable effects have been devised.

A High-Frequency Resonant Mode in Lattice Vibrations

A two-impurity problem in lattice vibrations is investigated with particular attention to that in-band mode which becomes a localized mode of lower frequency when two impurities are well separated with each other. The cosine transform of the propagator of the classical motion of one of the impurities is calculated as an application of the results obtained in a preceding paper, and on the other hand the optical absorption by the impurities is studied by supposing that they are charged while atoms of the host crystal are uncharged. By taking a simple cubic lattice as a model, it is shown that this in-band mode gives rise to a sharp peak in the high frequency region when the cosine transform or the absorption coef­ ficient is plotted as a function of frequency. Such a sharp peak in the in~band region can be considered as being due to a resonant mode which is quasi-localized around two impu­ rity atoms. A discussion is also given of a high-frequency resonant mode in one-and few­ impurity problems.