Search

Measuring the efficiency of piezo energy harvesters (PEHs) according to the definition constitutes a challenging task. The power consumption is often established in a simplified manner, by ignoring the mechanical losses and focusing exclusively on the mechanical power of the PEH. Generally, the input power is calculated from the PEH’s parameters. To improve the procedure, we have designed a method exploiting a measurement system that can directly establish the definition-based efficiency for different vibration amplitudes, frequencies, and resistance loads. Importantly, the parameters of the PEH need not be known. The input power is determined from the vibration source, therefore, the method is suitable for comparing different types of PEHs. The novel system exhibits a combined absolute uncertainty of less than 0.5% and allows quantifying the losses. The approach was tested with two commercially available PEHs, namely, a lead zirconate titanate (PZT) MIDE PPA-1011 and a polyvinylidene fluoride (PVDF) TE LDTM-028K. To facilitate comparison with the proposed efficiency, we calculated and measured the quantity also by using one of the standard options (simplified efficiency). The standard concept yields higher values, especially in PVDFs. The difference arises from the device’s low stiffness, which produces high displacement that is proportional to the losses. Simultaneously, the insufficient stiffness markedly reduces the PEH’s mechanical power. This effect cannot be detected via the standard techniques. We identified the main sources of loss in the damping of the movement by the surrounding air and thermal losses. The latter source is caused by internal and interlayer friction.

The charge constant of piezoelectric material is one of the crucial constant values. At the present time, the measurement of this value is mostly realized by means of three techniques: the frequency method, the laser interferometer technique, and the quasi-static method. These techniques have been practically applied to piezoelectric ceramic samples. Our paper presents comparison of the individual methods with regard to their accuracy and the demands placed on the instrumentation and preparation of the piezoelectric material samples. A soft ceramic product marketed under the production code of NCE51 was used in the experiments. The methods are described in detail, including the process of sample preparation, description of the experiments, and procedure of alculating coefficients from the measured values. Nábojová konstanta piezoelektrického materiálu je jednou z nejdůležitějších. Pro její měření jsou dnes nejčastěji používány tři metody – frekvenční metoda, měření pomocí laserinterferometru a kvazistatická metoda. Náš příspěvek se věnuje porovnání jednotlivých metod z pohledu přesnosti metod, nároků na přístrojové vybavení a nároků na přípravu vzorků piezomateriálu. Jednotlivé metody jsou podrobně popsány, včetně postupu přípravy vzorků, popisu experimentů a způsobu výpočtu koeficientů z naměřených hodnot.

Systems for measurement power characteristics of piezo harvesters in dependence on a frequency and a load resistance are not commonly used due its complexity. Therefore, the parameters are usually measured manually near its resonant frequency. In some cases, it is convenient to measure the characteristics in a broader range of parameters. Then, in order to achieve more precise results and effective measurement we decided to develop our own measurement system. The system controls an effective value of vibrations, sets a frequency and a load resistance for measuring a power generated by a piezo harvester and measures a tip displacement of the harvester. These quantities are used for a characterisation of piezo harvesters. Moreover, the voltage and current on vibration exciter are measured to evaluate the overall efficiency of the harvester. The system was tested on a harvester MIDE PPA-1001 for various added weights and vibration levels from 0.1 to 0.5 g. The measured data analysed and the efficiency was calculated as a ratio between a vibration power consumed by the harvester and its electrical output. The evaluated overall efficiency varies between 10 and 15 % nearby its optimal working conditions.

This paper presents the most important historical facts about all forensic medicine workplaces in the Czech Republic since the beginning till present day, including a perspective on how to establish a new one. Each of the University Forensic Medicine Institutes or district Departments is covered by at least one author. The oldest institute is in Prague and in Brno, the youngest is in Pardubice.

This paper presents the most important historical facts about all forensic medicine workplaces in the Czech Republic since the beginning till present day, including a perspective on how to establish a new one. Each of the University Forensic Medicine Institutes or district Departments is covered by at least one author. The oldest institute is in Prague and in Brno, the youngest is in Pardubice., U radu su ukratko navedeni najvažniji podaci o povijesti svih medicinskih odjela za sudsku medicinu u Češkoj Republici od samih početaka pa do današnjice, uključujući perspektivu i mogućnosti za osnivanje novih. Svaki od sveučilišnih instituta i okružnih odjela zastupa minimalno jedan autor. Najstarija povijest sudske medicine je naravno u Pragu i u Brnu. Najmlađi odjel je u Pardubicama.

This paper deals with distribution of magnetic field inside paired coils in Helmholtz arrangement. Helmholtz coils consist of two separate coils. Their mutually arrangements is advantageous for generation of uniform magnetic field. The simulation of field uniformity was realized. Further, the Helmholtz coils was made and the amplitude of magnetic field vector was measured. The comparison between simulation and really obtained results is discussed in this paper. Článek se zabývá studiem rozložení magnetického pole uvnitř cívek v Helmholtzově uspořádání. Helmholtzova cívka se skládá ze svou samostatných cívek. Jejich vzájemné uspořádání je výhodné pro dosažení homogenního magnetického pole. Byla realizována simulace homogenity magnetického pole a dále byla Helmholtzova cívka vyrobena a bylo provedeno měření magnetické indukce v této cívce. Článek se zabývá srovnáním provedené simulace a reálného měření.