Roman Doleček

General temperature field measurement by digital holography

This paper presents a digital holographic method for measurement of periodic asymmetric temperature fields. The method is based on a modified Twyman-Green setup having double sensitivity. For measurement only one precisely synchronized and triggered digital camera is used. The periodicity and self-similarity of each cycle of the measured phenomenon combined with the precisely synchronized camera capture allow one to obtain data later used for three-dimensional (3D) measurement. The reconstruction of 3D temperature field is based on tomographic approach.

Measurement of piezoelectric transformer vibrations by digital holography

A method for the measurements of the out-of-plane displacement on the surface of vibrating object is presented herein. This method is based on frequency-shifted time-averaged digital holographic interferometry, employing the principle of phase shifting. This approach allows for significant noise reduction, which results in high sensitivity of measurements. This method makes it possible to measure vibrations with amplitudes in the nanometer range over the whole measured surface. This method was applied to the visualization of the out-of-plane vibration modes of piezoelectric transformers. The amplitude and modal shapes were measured with a very high resolution. Furthermore, aspects influencing the measurement errors are discussed and the measurement results by holographic method were compared with the well-established single-point laser interferometry measurement method.

Frequency Shifted Digital Holography for the Measurement of Vibration with Very Small Amplitudes

A method for measurements of nanometer‐scale vibrations based on frequency shifted time average digital holographic interferometry employing the principle of the phase shifting technique is presented. This approach allows a reduction of noise and results in a higher sensitivity. The method has been applied to study the normalized vibration amplitude and the structure of vibration modes of piezoelectric transformers and actuators. In addition, quantitative information on the vibration amplitudes has been obtained in some cases.

Ferroelectric domain pattern in barium titanate single crystals studied by means of digital holographic microscopy

In this article, we report on the observation of a ferroelectric domain pattern in the whole volume of the ferroelectric barium titanate single crystal by means of digital holographic microscopy (DHM). Our particular implementation of DHM is based on the Mach–Zehnder interferometer and the numerical processing of data employs the angular spectrum method. A modification of the DHM technique, which allows a fast and accurate determination of the domain walls, i.e. narrow regions separating the antiparallel domains, is presented. Accuracy and sensitivity of the method are discussed. Using this approach, the determination of important geometric parameters of the ferroelectric domain patterns (such as domain spacing or the volume fraction of the anti-parallel domains) is possible. In addition to the earlier DHM studies of domain patterns in lithium niobate and lithium tantalate, our results indicate that the DHM is a convenient method to study a dynamic evolution of ferroelectric domain patterns in all perovskite single crystals.

Holographic contouring and its limitations in nearly specularly reflecting surface measurement

The applicability of the digital holography to grinded surfaces shape measurements is experimentally examined with regard to the surface micro-roughness of brittle materials (optical glass). Multi-wavelength phase shifted digital holographic interferometry (holographic contouring) is used and its performance is analyzed. Holographic contouring is a great candidate for the precise shape measurement technique, which can be applied to the iterative manufacture process of optical elements. Optical surface artifacts with different radii of the spherical (convex and concave) shapes were prepared with different micro-roughness. Their optical surfaces were then holographically recorded using a designed setup. Two different measures were selected to estimate the quality of the holographic recording: first, the intensity profile of the reconstructed surface deviation as a consequence of the micro-roughness decrease, where the shape of the intensity profile develops as the surface is altering from strongly diffusive to almost specular; second, the correlation of the phase fields (surfaces shapes), which were holographically recorded using two light beams of different wavelengths. In this situation, the correlation function decreases with an increase in the noise amount in data. The presented preliminary results indicate that the multi- wavelength holographic contouring can be used for surface measurements of high-quality polished and nearly specular surfaces. On the other hand, the application of holographic contouring to polished surface measurement still represents a challenging task and remains unresolved even with the multidirection illumination.

3D form inspection of grinded optical surfaces by digital holography

Paper presents the method for shape measurement by digital holography based on wavelength contouring. The method employs multiple measurements from different illumination directions followed by stitching of the individual measurements by least square method. This approach is promising in measuring of steeper surface slopes more accurately

Noise suppression in curved glass shells using macro-fiber-composite actuators studied by the means of digital holography and acoustic measurements

The paper presents methods and experimental results of the semi-active control of noise transmission in a curved glass shell with attached piezoelectric macro fiber composite (MFC) actuators. The semi-active noise control is achieved via active elasticity control of piezoelectric actuators by connecting them to an active electric shunt circuit that has a negative effective capacitance. Using this approach, it is possible to suppress the vibration of the glass shell in the normal direction with respect to its surface and to increase the acoustic transmission loss of the piezoelectric MFC-glass composite structure. The effect of the MFC actuators connected to the negative capacitance shunt circuit on the surface distribution of the normal vibration amplitude is studied using frequency-shifted digital holography (FSDH). The principle of the used FSDH method is described in the paper. The frequency dependence of the acoustic transmission loss through the piezoelectric MFC-glass composite structure is estimate...

Experimental study on SPDT machining of Gallium Phosphide

Gallium Phosphide (GaP) is widely used semiconductor material, but can be also used as a material for visible and infrared optical elements. Combination of its optical and mechanical properties such as high mechanical durability, transparency from visible to infrared wavelengths and high refractive index makes it very interesting material for design of high performance optical systems in NIR and MWIR. Manufacturing of optical elements for such wavelength ranges is shifting from traditional grinding and polishing techniques to a more versatile SPDT machining. It is therefore useful to employ SPDT in production of optical surfaces on GaP. As the GaP is similar to GaAs, but harder and more brittle, all all the problems already known for GaAs are present. Here we report results of experiments with SPDT machining of optical surfaces on GaP substrates and comparison with classical machining methods.

Disc Piezoelectric Ceramic Transformers

In this contribution, we present our study on the discshaped and homogeneously poled piezoelectric ceramics transformers working in various planar-extensional vibration modes. Transformers are designed with electrodes divided into wedge, axisymmetrical ring-dot, moonie, Smile or Jin-Jiang segments. Electrodes are designed on one side of the transformer; opposite side is fully electroded. A set of transformers with different electrode pattern has been prepared from hard PZT ceramics (type APC841, diameter 20mm, thickness 0.8mm). Transformation ratio, efficiency, input and output impedance were measured for low-power signal. Transformer efficiency and transformation ratio were measured as a function of frequency and impedance load in the secondary circuit. Parameters were further measured for the fundamental and second resonance. Optimum impedance for the maximum efficiency has been found. Maximum efficiency and no-load transformation ratio can reach almost 100% and 52 for the fundamental resonance of ring-dot transformers and 98% and 67 for the second resonance of wedge 2 segment transformers. Maximum impedance was reached at optimum impedance, which is in the range from 500 Ω to 10k Ω depending on the electrode pattern and size. Fundamental vibration mode and its overtones were further studied using frequency modulated digital holographic interferometry. Normal displacement distribution on the transformer surface was visualized. The shape of vibration mode was influenced by the mechanical clamping of the transformer during its operation. Operating shapes were also simulated by the finite element method. Complementary information has been obtained by the infrared camera visualization of surface temperature profile at higher driving power.

Planar acoustic metamaterials with the active control of acoustic impedance using a piezoelectric composite actuator

In the paper, there are presented methods for a precise active control of the acoustic impedance of large planar structures, e.g glass plates or shells, by means of distributed flexible piezoelectric composite actuators which are connected to passive or active electronic shunt circuits. Design of tunable acoustic metamaterials is realized using Finite Element Method simulations and their acoustic properties are evaluated using acoustic transmission loss measurements. Static and dynamic displacements of the metamaterials produced by electric voltage are measured using Digital Holographic Interferometry. We believe that deep understanding of presented systems should result in future applications that improve the quality of everyday life.