Yunus Uzun

Power characteristics of a new contactless piezoelectric harvester

This paper reports the preliminary results of a new designed harvester system called as the contactless piezoelectric wind energy harvester (CPWEH). It consists of three piezoelectric layers attached with the non-magnetic bars in different lengths in order to produce maximal power for a wide wind wide speed regime. Preliminary magnetic design has proven that three layers can be excited by the magnetic forces synchronously and this situation prevents to damage the piezoelectric layers since it does not make any physical contact to the layer. According to the results, this new harvester produces electrical power at low wind speeds such as 2.5 m/s. The harvested power can be obtained from the range of 2.5 mW to 17 mW. Therefore the efficiency of the harvester having a single piezoelectric layer has been introduced three times in the proposed design and implementation.

Experimental and Theoretical Explorations on the Buckling Piezoelectric Layer Under Magnetic Excitation

In the present study, experimental and theoretical explorations on the buckling features of a wind energy harvester have been performed. The harvester consists of a piezoelectric layer, which has a certain stiffness and voltage conversion rate. A blade rotates on a shaft carrying a magnet and sweeps the tip of the layer causing a serial buckling effect resulting in energy generation. Since the modeling of the buckling under a magnetic strength includes nonlinear terms over displacements, one requires a detailed study on the characteristics of buckling phenomena. It has been proven that the piezoelectric beam having the magnet at its tip can produce regular and chaotic dynamics for different frequencies (i.e. the rotation speed). In addition, there exist a number of quasi-periodic regions on the parameter space. The overall result indicates that the large area of complicated dynamics requires a detailed study in order to stabilize the position and velocity of the layer tip, thereby a much stabilized energy conversion from mechanical to electrical can be obtained. The present survey on the dynamics of the harvester is a new study and is considered as a two-parameter diagram [i.e. the wind speed (frequency) and magnetic strength]. Mainly, single-, double-, triple- and quadruple-type phase space portraits have been observed and the ripples on the maximal and minimal values of the beam velocity have been observed for certain rotation speeds. These results can be used in order to stabilize the harvester in terms of the reduction of total harmonic distortion in the generated waveform.

Nonlinear Problems in Piezoelectric Harvesters Under Magnetic Field

This chapter focuses on the nonlinear problems in the piezoelectric harvester systems under the magnetic field. In this manner, the chapter initially mentions an introductory section on the studies of piezoelectric harvester dynamics. After the introductory section, the basic properties of the piezoelectric systems and their energy harvester applications will be presented. Since the harvesters have a complicated structure under the magnetic field, the electromagnetic design, modeling and algebraic studies of a novel harvester study will be pointed out. After the presentation of a theoretical outline on the harvester systems, the experimental setups will be explained in detail. Thus, a complete picture of the problem will be produced in order to sustain a comparable study on the theory and experiment. The main dynamic quantities such as displacement and velocity of the vibrating piezoelectric layer as function of the system parameters will be explored. According to results, the effect of periodic magnetic flux can give varieties of responses from regular dynamics to chaotic one. Phase space constructions, Poincare sections and FFTs are evaluated depending on the parameter sets including the excitation frequency f, amplitude Uc of electromagnet and the distance d. It is proven that the periodic magnetic flux can exert high frequency velocity fluctuations nearby the minimal and maximal values of the velocity, whereas the situation differs for the position. Therefore it will be pointed out that the magnetic field mostly governs the velocity by yielding complicated vibrations. According to the detailed analyses, the FFTs prove the high frequency responses in addition to the main frequency. When f differs from the natural frequency of the system f 0, the responses become chaotic. It is proven that lower and higher frequency fluctuations in displacement and velocity, which are different from f 0 decrease the electrical power harvested by the piezoelectric pendulum. Indeed, it is remarkable to get a relation between the rms values of displacement/velocity and the harvested power according to the measurements. Thus this relation can be used to estimate the power output in harvester systems. The piezoelectric harvester generates much energy when f is closed to f 0 and the distance to the magnetic device should be closer in order to decrease the nonlinearities in displacement and velocity. The pendulum-like harvesters as the most preferable ones can be applied to many devices or units as a power source. The maximal power for these magnetically-excited structures can be estimated by the system parameters. At the end of the chapter, the recent techniques of maximal power point tracking (MPPT) and proposed controller units are explained for the piezoelectric harvester systems in order to optimize the harvested power.

Design of broadband RF-DC converter

Almost all of the wireless devices are supplied by chemical batteries. These batteries have a number of disadvantages. In this study, a broadband RF energy harvester was designed to providing the use of wireless devices without batteries or increasing battery life. The system is designed to work between 500 MHz and 900 MHz. Thus, the proposed system can be obtained electrical energy from both DTV and GSM signals at the same time. The system efficiency which is mentioned above frequencies ranges is close to 80% for 0 dBm input power level.

Design and simulation of a new dual-band RF energy harvester with high efficiency

In recent years, it is one of the biggest disadvantages of wireless sensors have vital importance that they are supplied by batteries. It is possible to overcome this deficiency by RF energy harvesting systems. In this work, the system generating electrical energy efficiently from two different RF signals have different frequencies is presented. Compared with conventional single frequency RF energy harvester, with the proposed dual band RF energy harvester, an increase is achieved 39% and 78% for 575 MHz and 900 MHz input frequencies at 0 dBm signal level, respectively. In a wide range of frequencies in the range of 400 MHz to 1000 MHz, the efficiency is obtained over 50% from the proposed system. Thus, the system can be used efficiently in an environment including any one or more DTV and GSM signal. The proposed circuit can be used effectively on the RF signals have the level of more than -15 and -10 dBm.

Effects of nonlinearities in a magneto-piezoelectric system

This paper focuses on the theoretical and experimental analyzes on the dynamics of a magneto-piezoelectric pendulum system under the magnetic excitation. Initially, it handles the theoretical modelling of the problem including the mechanical, magnetic and electrical terms of the system. The theoretical formulation of the pendulum system is realized based on the experimental parameters. Then, a detailed experimental survey has been carried out for the system parameters, namely the magnetic field frequency f and amplitude V (i.e. proportional to the amplitude of the field). In the last part, the nonlinear patterns from the theoretical and experimental studies are discussed. It will be pointed out that the periodic magnetic flux can cause different responses in the magneto-piezoelectic system from regular dynamics to chaotic one. Phase space constructions, Poincare sections, FFTs and THDs are determined for certain parameter sets. A sample harvester application of the system will also be introduced at the end of the paper.