Giuseppe Venchi

Analytical Model of a Vibrating Electromagnetic Harvester Considering Nonlinear Effects

In this paper, an analytical model of a vibrating electromagnetic harvester, taking into account nonlinear effects, is presented. Knowing the acceleration applied to the harvester system, the model is able to predict the performance of the harvester in terms of induced voltage on the load. The energy transducer consists of four magnets, two movable and two fixed, arranged in a way such that both fixed magnets repel the moveable one. The model was implemented in Simulink and exploits the results of a finite element method (FEM) solver (Flux2D) to estimate the non-linear electromagnetic repulsion force and the flux linkage by the coil. To evaluate the effect of a load applied to the harvester, the effect of the Lorentzs force, caused by the interaction of the current that flows in the coil and the flux density of the moveable magnet, was taken into account. As a consequence, the error in the estimate of induced voltage, at resonance, is reduced from about 80% to 7%. Finally, at resonance, the maximum power that could be delivered by the harvester and dissipated on a resistive load was estimated to be about 6 mW.

A Fluxgate Magnetic Sensor: From PCB to Micro-Integrated Technology

In this paper, a double-axis micro Fluxgate magnetic sensor is presented. The device represents an evolution of a PCB dual axis sensor previously realized. In the PCB version the experimental results exhibit excellent agreement with the simulations performed using a tool based on the finite element method. Using the same design approach a version of double-axis Fluxgate structure is here proposed to be realized in IC technology. The accurate study of the magnetic field distribution allows a 75% area saving for the IC version with respect to a direct scaling of the PCB version. Imposing an external magnetic field of about 60 muT, the simulated differential output voltage of the micro-integrated Fluxgate sensor achieves a peak value of 1 mV with 5 mA sinusoidal excitation current peak at 100 kHz. The integrated microstructure shows a linearity error of about 1.15% of the full scale, in the range of plusmn50 muT, with a sensitivity of about 0.45 mV/muT

PWM Power Audio Amplifier With Voltage/Current Mixed Feedback for High-Efficiency Speakers

High-efficiency speakers significantly improve electrical to sound power conversion efficiency by reducing the power dissipation over the speaker coil. However, they require some equalization of the input signal. In this paper, a new driving technique based on a pulsewidth-modulation switching amplifier is presented. This exploits a double voltage/current feedback to obtain automatic equalization. Furthermore, the double feedback allows the output resonant filter to be included in the feedback path, compensating for its nonlinearity. Finally, the mixed feedback acts as intrinsic current limiter. Both theoretical analysis and simulations demonstrate that this system is feasible. The results were also confirmed by measurements using a prototype

Development and analysis of a PCB vector 2-D magnetic field sensor system for electronic compasses

A high-sensitivity vector two-dimensional (2-D) magnetic sensor system for low magnetic field measurements has been realized and tested. The system, made in PCB technology, consists of a double-axis Fluxgate magnetic sensor and the readout electronic circuitry, based on second-harmonic detection. The amorphous magnetic materials Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick) were used as the ferromagnetic core of the sensor. By applying a sinusoidal excitation current having a 450-mA peak at 10 kHz with Vitrovac 6025Z, the measured magnetic sensitivity was about 1.25 mV//spl mu/T. This value seems to be adequate for the Earths magnetic field detection (/spl plusmn/60 /spl mu/T). The full-scale linearity error was about 1.5%. By using the thicker Vitrovac 6025X and a sinusoidal excitation current having a 600-mA peak at 10 kHz, a maximum sensitivity of approximately 1.68 mV//spl mu/T with a linearity error of about 1.55% full scale in the range of /spl plusmn/60 /spl mu/T were measured. Due to the use of commercially available ferromagnetic materials, the vector 2-D magnetic sensor system presented is characterized by a very simple fabrication process, thus allowing low-cost devices to be designed.

Electronic interface for Piezoelectric Energy Scavenging System

The paper focuses on an electronic interface for systems, called Piezoelectric energy scavenging systems (PESS), which convert the energy of mechanical vibrations into electrical energy using a piezoelectric transducer. The output of the transducer is a strong and irregular function of time hence, to obtain a suitable supply source, an AC-DC conversion is needed. Classical rectifiers (half/full bridge or voltage doubler) with an output storage capacitor do not fit very well, since they work as peak detectors, converting only input voltages which are higher than their output voltage. The paper shows an electronic interface which is able to efficiently harvest the energy associated to the randomic voltage waveform delivered by a piezoelectric transducer. Its working principle is based on an inductive step-up converter; an active driving circuit is used to set the phases of the converter. The energy is stored into a capacitor which is also used to supply the active elements of the step-up converter, realizing a completely autonomous energy scavenging system. For this reason the whole circuitry has been designed with a very low-power consumptions, about 700 nA. A prototype was diffused in 5 V CMOS STMicroelectronics technology and measurements showed its effectiveness.

A Self-Powered Electronic Interface for Electromagnetic Energy Harvester

This paper presents a self-powered, active electronic interface for an energy harvesting system including a vibration-based electromagnetic transducer. The transducer provides a peak voltage of 3.25 V when operated close to its mechanical resonance frequency (about 10.4 Hz) and the power converter has been designed to transfer the harvested energy to a storage capacitor. The circuit is a full-cycle inductive step-up ac/dc converter able to process every voltage pulse coming from the transducer; furthermore, it is supplied by the harvested energy, making the system fully autonomous. The interface has been designed exploiting an accurate model of the transducer in simulations. A printed circuit board version of the interface has been simulated and built to gather experimental results and validate the idea. The system demonstrated to be able to build a voltage across the storage capacitor, which is limited only by the safe operating area of the devices.

Development of a leakage flux measurement system for condition monitoring of electrical drives

The aim of this paper is to investigate the possibility to employ a simple external flux coil to monitor the operating conditions of induction motors of different sizes, supplied at low voltage, from the mains or from power converters. The state of the art of the literature concerning the analysis of the stray flux around induction machines, in different positions and with different types of search coil, is here reported. Then, the flux probe here used is presented, together with several acquisitions of stray flux in three positions around the motor and with different techniques of signal analysis. These acquisitions are also compared with measurements collected by means of a commercial flux sensor. The final purpose is to find the best combination of position, sampling frequency, filter, etc. which can give the more interesting information about the “health” condition of the motor.

Active autonomous AC-DC converter for Piezoelectric Energy Scavenging Systems

The paper focuses on an electronic interface which can be used into Piezoelectric Energy Scavenging Systems (PESS). These systems convert the energy of mechanical vibrations into electrical energy using a piezoelectric transducer to realize a power supply for low power electronic systems. To obtain a suitable supply source an AC-DC conversion of the output signal of these transducers is needed and, since the output power level of the energy scavenger can be very low, the conversion should be as efficient as possible. This paper shows an active voltage doubler AC-DC converter for PESS. A novel driving circuitry topology is presented; it has the advantage to be tolerant with respect to the process variations. The converter uses exclusively a fraction of the harvested energy to supply itself and a bias circuit has been designed to make the total current consumption supply independent. A test chip was diffused in 5 V CMOS STMicroelectronics technology. Experimental results show the effectiveness of this solution and efficiencies higher than 90% have been obtained for different load values.

Active self supplied AC-DC converter for piezoelectric energy scavenging systems with supply independent bias

The paper focuses on an electronic interface which can be used into piezoelectric energy scavenging systems (PESS). These systems convert the energy of mechanical vibrations into electrical energy using a piezoelectric transducer to realize a power supply for low power electronic systems. To obtain a suitable supply source an AC-DC conversion of the output signal of these transducers is needed and, since the output power level of the energy scavenger can be very low, the conversion should be as efficient as possible. This paper shows an active voltage doubler AC-DC converter for PESSs. A novel driving circuitry topology is presented; it has the advantage to be tolerant with respect to the process variations. The converter uses exclusively a fraction of the harvested energy to supply itself and a bias circuit has been designed to make the total current consumption supply independent. The simulation results show that the efficiency of the AC-DC converter can be as high as 94%. The circuit will be diffused in 0.35 mum CMOS STMicroelectronics technology.

Self-Supplied Integrable Active High-Efficiency AC-DC Converter for Piezoelectric Energy Scavenging Systems

In recent years a lot of studies focused on energy-scavenging systems (ESS). An important motivation for these studies is the development of portable devices (PD) and of wireless sensor networks (WSN). An ESS can be partitioned in two sections: the energy-scavenger itself and the electronic interface. The first one is the energy transducer while the second one is the electronic circuit which manages the energy. One of the most important objectives of the electronic interface is to realize the required ac-dc conversion. Since the output power level of the energy-scavenger can be very low, the conversion should be as efficient as possible. The goal of this paper is to design an active, high efficiency voltage doubler ac-dc converter for piezoelectric ESS which exclusively uses a fraction of the harvested energy to supply its active devices. The circuit was diffused in 0.35mum BCD6s technology. The simulation results show that it is possible to obtain a maximum efficiency of the ac-dc converter equal to 91%. Premiliminary experimental measurements were performed and the results obtained are in good agreement with simulations