Improved Resonator Method Research Articles

Improved resonance method for fatigue test of full-scale wind turbine blades

To further reduce the power of exciter in the common fatigue testing methods and increase the testing frequency to decrease the fatigue testing time, this paper proposes an improved fatigue testing method—Tug Fatigue Testing system (TFTs). The advantages of this new fatigue testing method are low power and high testing frequency of its exciter due to no exciter with moving masses attached to the blade. In TFTs, exciters mounted on the ground or fixed bracket can be used to excite the blade in the uniaxial or biaxial fatigue test. In this paper, the mechanical model of TFTs is established to compare the motor power required by exciters in TFTs and the inertial exciters and the shear load on the blades in both ways. Furthermore, a test of a 56.5 m blade will be performed to verify the feasibility of the new method. In addition, the bending moment distribution of an 80 m blade excited by TFTs was measured and compared with the bending moment distribution of the same blade excited by inertial resonance excitation to evaluate its excitation effect. The test results prove that this improved method needs lower power of exciter, produces smaller shear loads, and provides a higher test frequency in the flap-wise test direction than common inertial resonance excitation. Biaxial fatigue tests can also be conducted by this new method.

Measurement of the Young’s modulus using micro-cantilevered beam actuated by electrostatic force

Determining the Young’s modulus accurately is important in micro-electro-mechanical systems (MEMS) design. Generally, the Young’s modulus of a micro-component is measured by the resonance method, of which the actuation is electrostatic force. However, this method does not take the effect of the electrostatic force on the resonant frequency into consideration. Thus, the test error becomes more obvious as the DC voltage increases. In this paper, an improved resonance method, determining the Young’s modulus of a micro-cantilever beam, is proposed, which takes the nonlinearity of the electrostatic force into consideration. This method has three obvious advantages: only one simple micro-cantilevered beam sample is needed; it is unnecessary to find the initial thickness of the gas film between the beam and the substrate; the accuracy of the measurement result of the Young’s modulus is improved. In order to obtain the resonant frequency of a cantilevered beam actuated by a DC voltage, the dynamic equations of the micro-cantilevered beam in multi-field coupled situations are established, and the effect of the electrostatic force on the resonant frequency of the micro-beam is investigated. Results show that, the Young’s modulus can be found by measuring the resonant frequency and DC voltage. The dynamics performances of the micro-structure are influenced by the nonlinearity of the electrostatic force, and the electrostatic effect should be observed especially when the beam becomes smaller, through general studies. Finally, the experimental principle of measuring the Young’s modulus is designed and conducted to verify these theories. The Young’s modulus of brass is measured exactly.

The improved resonator method for measuring the complex permittivity of materials

An improved resonator method for determination of the complex permittivity of materials in a reflective resonator is presented. The method is specific in the following. In the obtained relationship, imaginary part e2 of the permittivity of an investigated material is determined using the variation of the resonance frequency and coupling coefficient of the resonator observed when a specimen is introduced, which increases the measurement accuracy. The method is approbated in the investigations of high-resistance silicon specimens.

Improved Resonator Method for Microwave Testing of Magnetic Composite Sheets

The applications of magnetic composites in electromagnetic shielding, resonance imaging, and biomedical drug research are growing rapidly. Therefore, there is a huge demand to characterize these materials in order to obtain their dielectric and magnetic properties in the microwave frequency range. In this paper, a novel rectangular cavity method is proposed to obtain the complex permeability and permittivity of the test sample placed in the $E$ -plane of the rectangular cavity. The proposed method eliminates the need of physical relocation of a specimen in the $H$ -plane, which is usually required in the case of presently available methods to characterize the magnetic samples. The closed-form formula for this unified approach is developed from the first principle, and is later modified to consider some practical consideration. The proposed method is first numerically tested and verified for various standard samples, where the data are taken from the literature. Thereafter, the $X$ -band rectangular cavity is designed and fabricated to measure a number of available samples. The significance of the proposed approach can be appreciated from the fact that even for finite-size samples, the permeability and permittivity can be extracted with the typical errors of 5% and 2%, respectively.

Measurement of the complex permittivity of polycrystalline diamond by the resonator method in the millimeter range

An improved resonator method is developed, which allows for a change in the resonator coupling coefficient at insertion of the sample during the measurement of the imaginary part of the material permittivity. The method makes it possible to measure small samples. The permittivity at a frequency of 27GHz is measured for rods made of polycrystalline CVD diamond plates of 57 and 100mm in diameter grown in the microwave plasma in methane−hydrogen mixtures, and the loss tangent tan δ is determined at a level of the order of 10−3.

BROADBAND COMPLEX PERMITTIVITY MEASUREMENT OF LOW LOSS MATERIALS OVER LARGE TEMPERATURE RANGES BY STRIPLINE RESONATOR CAVITY USING SEGMENTATION CALCULATION METHOD

A system has been developed for measuring the complex permittivity of low loss materials at frequencies from 500MHz to 7GHz and over a temperature range up to 1500 - C using stripline resonator cavity method. Details of the design and fabrication of the cavity were discussed. Particular features related to high-temperature operation were described. An improved resonance method at high temperature for determining complex dielectric properties of low-loss materials was developed. The calculation process was given by a physical model of the stripline resonator cavity at high temperature. The paper brought forward the method of segmentation calculation according to the temperature changes over the cavity, which matched the actual situation of high temperature measurements. We have verifled the proposed method from measurements of some typical samples with the available reference data in the literature.

A finite plate technique for the determination of piezoelectric material constants

An improved resonator method is presented for the determination of piezoelectric material constants. The improved method addresses a fundamental limitation of the measurement methods recommended in the current IEEE Standard on Piezoelectricity: the relations between vibrator response and material constants presented in this Standard are based upon the 1-D approximation of an essentially infinite flat plate with a uniform distribution of vibratory motion. The calculation or measurement of the effects due to the nonuniform vibrational amplitude distribution in a laterally bounded plate is a nontrivial task. The practical result is that the current IEEE 176-1987 resonator method recommendations are of limited usefulness in the determination of intrinsic piezoelectric material constants. This limitation can, however, readily be overcome using an improved measurement technique based on measurands unaffected by the vibrational amplitude distribution. In the improved technique, the measurands of choice are the zero-mass-loading, fundamental mode, thickness-field excitation (TE) antiresonance, or lateral-field excitation (LE) resonance frequencies. A recommended experimental procedure, using the preferred measurands, is presented.