This article is devoted to the comparison of the influence of the piezoelectric matrix properties on the magnitude of the resulting charge when a thin piezoelectric membrane of circular cross section, made from aluminium gallium nitride (Al-GaN), is loaded. The size of change of the electric charge was determined by the numerical analysis and the by the change of the properties of the piezoelectric matrix. The matrix constants were obtained from various sources introduced in world databases.KEYWORDS: piezoelectric, gallium nitride, constitutive equations, average, variance, deviation IntroductionThin Al-GaN membranes have different configurations for their application. In the case of a membrane of a circular cross section (as shown in Fig 1, in the analysed device), it is most common for the measurement of pressure. To apply pressure onto the membrane, it must be fixed around its circumference. The internal structure of piezoelectric materials is highly dependent on their manufacturing process, which then is reflected on their properties. Even a small change in the properties of the piezoelectric material can lead to more pronounced changes in the electrical charge obtained in the so called direct piezoelectric effect, or the change in the properties can lead to significantly different deformations in an inverse piezoelectric effect. Using a numerical methods, we can predict the behaviour of the pressure sensors. It is possible to simulate the different properties of the Al-GaN material and to obtain the assumed values of the electrical charge, respectively the deformation of the material. The first part of the article is devoted to the comparison of the results of 10 sets with different material constants for the aluminium gallium nitride material. Applied material constants were taken from research reports and contributions introduced in world databases [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In the second part of the article, we compare the obtained results with the results measured during the experiment [17]. The investigated modelThe numerical model is based on a thin membrane used in experimental measurements. The configuration and geometrical properties of the membrane are shown in Fig. 1. It is made of a piezoelectric Al-GaN layer over GaN. The ratio of each corresponding layer is 99.9524% GaN overlaid with 0.0476 % Al-GaN. The membrane is circular with a diameter of 750 µm. The membrane is placed over a ceramic substrate measuring 350 x 350 µm. The thickness of each layer is 4.22 µm and 0.02 µm for GaN and Al-GaN respectively. Once a charge is created, a thin 2D layer of electron gas is produced between the layers and it acts as a transmitter for the Unauthenticated Download Date | 5/12/18 6:08 AM
This paper deals with the idea of an energy harvesting (EH) system that uses the mechanical energy from finger presses on the buttons of a computer mouse by means of a piezomaterial (PVF2). The piezomaterial is placed in the mouse at the interface between the button and the body. This paper reviews the parameters of the PVF2 piezomaterial and tests their possible implementation into EH systems utilizing these types of mechanical interactions. The paper tests the viability of two EH concepts: a battery management system, and a semi-autonomous system. A statistical estimate of the button operations is performed for various computer activities, showing that an average of up to 3300 mouse clicks per hour was produced for gaming applications, representing a tip frequency of 0.91 Hz on the PVF2 member. This frequency is tested on the PVF2 system, and an assessment of the two EH systems is reviewed. The results show that fully autonomous systems are not suitable for capturing low-frequency mechanical interactions, due to the parameters of current piezomaterials, and the resulting very long startup phase. However, a hybrid EH system which uses available power to initiate the circuit and eliminate the startup phase may be explored for future studies.
INTRODUCTION: The purpose of this paper is to present the development and design of an abdominal retractor which allows a single person to perform operations and the fi xation of the operation instruments can be done with one hand. The additional devices make the operation more comfortable for surgeons. METHODS: Conventional measuring devices have been designed and applied for determining axial forces in a surgeon's forearm during operations. The same forces must be transmitted by the frame of the retractor. Thus a simple truss structure of a retractor was done. Several types of fi xations have been proposed and tested using the rapid prototyping. Finally, the abdominal retractor was manufactured from stainless steel. RESULTS: The simple-to-use abdominal retractor was built. The standard surgery instruments were modifi ed due to the fi xation system of the frame. A wide variety of additional useful devices, such as a lamp, video camera etc., were also proposed. CONCLUSION: The present abdominal retractor is user-friendly and all components are easily sterilized by conventional methods (Fig. 7, Ref. 6).
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