New double indentation technique for measurement of the elasticity modulus of thin objects

In this paper we introduce a new method to determine the Young's modulus of thin (biological) samples. The method is especially suitable for small objects with a thickness of a few hundred micrometers. Such specimens cannot be examined with existing tests: compression and tensile tests need well-known geometry and boundary conditions while classic indentation tests need relatively thick pieces of material. In order to determine the elastic modulus we use the indentation theory as proposed by Sneddon and correct it with a finite element calculated kappa factor to compensate for the small thickness. In order to avoid material deformations at the contact zone between the sample bottom and the sample stage, we replace the sample stage by a second indentation needle. In this way the sample can be clamped between two identical needles and a virtual mirror plane is introduced. The new method was used on four test-materials and results agreed well with the outcome of a standard compression method applied on large samples of the same materials. As an application example the technique was applied on thin biological samples, namely middle ear ossicles of rabbits

On-chip laser Doppler vibrometer for arterial pulse wave velocity measurement

Pulse wave velocity (PWV) is an important marker for cardiovascular risk. The Laser Doppler vibrometry has been suggested as a potential technique to measure the local carotid PWV by measuring the transit time of the pulse wave between two locations along the common carotid artery (CCA) from skin surface vibrations. However, the present LDV setups are still bulky and difficult to handle. We present in this paper a more compact LDV system integrated on a CMOS-compatible silicon-on-insulator substrate. In this system, a chip with two homodyne LDVs is utilized to simultaneously measure the pulse wave at two different locations along the CCA. Measurement results show that the dual-LDV chip can successfully conduct the PWV measurement

Magnetostriction strain measurement: heterodyne laser interferometry versus strain gauge technique

Deformation of the ferromagnetic material, known as magnetostriction, causes vibrations and noise of electrical machines and transformer cores. A setup by using heterodyne laser interferometers has been built to measure the magnetostriction strains as a function of the applied magnetic field. The measurement results on a sample of nonoriented electrical steel are presented in this work. These results are compared with those obtained by using a strain gauge setup. The laser measurements are less disturbed by noise, especially for measurements under low amplitude magnetisation. In addition, contrary to the strain gauge samples, the sample preparation for the laser setup does not require removal of the protective coating. Measurement results on the coated samples are highly helpful for the calculation of the magnetostriction noise of the device. The coated samples show smaller deformation, since the coating applies tensile stress to the material. For the case of the same nonoriented material the reduction of the magnetostriction strains in amplitude is about 20%

Magnetostriction measurement and the contribution of magnetostriction to the noise of a one-phase transformer

Deformation of magnetised electrical steel samples, known as magnetostriction, is a main contributor to the noise of electrical machines and especially transformers. In this work, the magnetostriction strains of such samples are measured by using a heterodyne laser vibrometer setup. The results are used to model the data and perform a Finite Element (FE) calculation for one-phase transformer test geometry. To validate the FE data, a transformer test model is built with the same geometry as of that of the FE model. A comparison of the FE data with the measured vibrations of the magnetised test transformer will be reported later

Magnetostrictive deformation of a transformer: a comparison between calculation and measurement

Magnetostriction, which refers to the deformation of the core material of transformers and electrical machines, is a main contributor to the total noise. In this work, a technique is proposed to calculate the magnetostrictive deformations of the core of the aforementioned devices. This technique is based on finite element approach with an artificial neural network model of the magnetostrictive behaviour of the core material. The strain measurements are carried out by using a dual heterodyne laser interferometer setup. The proposed technique is then applied to a single-phase test transformer core. As a validation, the vibration of the magnetised core of the same setup is measured by using a laser scanning vibrometer

Magnetostriction measurement by using dual heterodyne laser interferometers

Electrical machines and transformers have a core built out of laminations of ferromagnetic materials. A portion of the vibrations and noise of these devices is due to magnetic forces and magnetostriction arising from the magnetic core. Magnetic forces are well known, and analytical methods are extensively used to calculate them. Magnetostriction can be defined as the deformation of the ferromagnetic material in the presence of a magnetic field. Unlike magnetic forces, magnetostriction shows a rather complex behavior. It varies for every material, and it depends on the applied magnetic field and external pressure. Therefore, magnetostrictive behavior of every material needs to be determined experimentally by means of strain measurements. Strain gauge measurement techniques have been used before at the Electrical Energy Laboratory (EELAB), Ghent University, Ghent, Belgium. In this paper, a new measurement method using dual heterodyne laser interferometers is proposed to overcome the drawbacks of the old method. The proposed measurement setup and the working principles are explained. The possibility to apply both techniques on one and the same sample can also reveal some interesting results about the quality of both techniques

Frequency extraction for BEM-matrices arising from the 3D scalar Helmholtz equation

The discretisation of boundary integral equations for the scalar Helmholtz equation leads to large dense linear systems. Efficient boundary element methods (BEM), such as the fast multipole method (FMM) and H-matrix based methods, focus on structured low-rank approximations of subblocks in these systems. It is known that the ranks of these subblocks increase with the wavenumber. We explore a data-sparse representation of BEM-matrices valid for a range of frequencies, based on extracting the known phase of the Green's function. Algebraically, this leads to a Hadamard product of a frequency matrix with an H-matrix. We show that the frequency dependency of this H-matrix can be determined using a small number of frequency samples, even for geometrically complex three-dimensional scattering obstacles. We describe an efficient construction of the representation by combining adaptive cross approximation with adaptive rational approximation in the continuous frequency dimension. We show that our data-sparse representation allows to efficiently sample the full BEM-matrix at any given frequency, and as such it may be useful as part of an efficient sweeping routine