Automated setup for magnetic hysteresis characterization based on a voltage controlled current source with 500 kHz full power bandwidth and 10 A peak-to-peak current.

This paper describes the design of a system for the characterization of magnetic hysteresis behavior in soft ferrite magnetic cores. The proposed setup can test magnetic materials exciting them with controlled arbitrary magnetic field waveforms, including the capability of providing a DC bias, in a frequency bandwidth up to 500 kHz, with voltages up to 32 V peak-to-peak, and currents up to 10 A peak-to-peak. In order to have an accurate control of the magnetic field waveform, the system is based on a voltage controlled current source. The electronic design is described focusing on closed loop feedback stabilization and passive components choice. The system has real-time hysteretic loop acquisition and visualization. The comparisons between measured hysteresis loops of sample magnetic materials and datasheet available ones are shown. Results showing frequency and thermal behavior of the hysteresis of a test sample prove the system capabilities. Moreover, the B-H loops obtained with a multiple waveforms excitation signal, including DC bias, are reported. The proposal is a low-cost and replicable solution for hysteresis characterization of magnetic materials used in power electronics.

A real-time two-dimensional pulsed-wave Doppler system.

An experimental system was developed to acquire and visualise in real-time two-dimensional (2-D) velocity maps. Data acquisition is performed by using a modified commercial echograph based on a 5-MHz, 128-element linear-array transducer with electronic focussing and beam steering. Additional electronics were integrated into the echograph to implement a 2-D Doppler system capable of measuring the velocity component on the scanning plane. Suitable axial and lateral scanning methods were studied to obtain Doppler measurements over a scanning area. A colour image of the estimated velocity field is presented in real time on a personal computer using different visualisation techniques. The system performance was tested experimentally both in vitro and in vivo on a human carotid artery.

Pyroelectric PVDF sensor modeling of the temporal voltage response to arbitrarily modulated radiation.

Our design of transducer arrays for custom pyroelectric sensors is mainly devoted to IR laser beam characterization and control. It benefits from some of the properties of PVDF film such as low cost, low weight, mechanical flexibility, chemical stability (inert), and compatibility of thick film interconnection technologies on metallized films. By using the temporal characteristics of the source intensity and starting from a standard equivalent one-dimensional model of a multilayer thick-film transducer in the frequency domain, we developed a computer model of the PVDF sensor that determines the temporal response to arbitrarily modulated radiation. The validation of the model accuracy has been carried out with a simulation procedure performed on a PVDF sensor designed for accurate beam alignment of low power laser beams. In this case, an iterative algorithm also was developed to estimate some thermal and physical properties of the front absorbing and the metallization layers that are generally barely known. We present a fitting procedure to determine these properties by using the temporal pyroelectric response to a square wave modulated laser diode that provides a reliable reference signal.

A 3-D PW ultrasonic Doppler flowmeter: theory and experimental characterization.

A complete 3-D ultrasonic pulsed Doppler system has been developed to measure quantitatively the velocity vector field of a fluid flow independently of the probe position. The probe consists of four 2.5 MHz piezocomposite ultrasonic transducers (one central transmitter and three receivers separated by 120 degrees ) to measure the velocity projections along three different directions. The Doppler shift of the three channels is calculated by analog phase and quadrature demodulation, then digitally processed to extract the mean velocity from the complex spectrum. The accuracy of the 3-D Doppler technique has been tested on a moving string phantom providing an error of about 4% for both amplitude and direction with an acquisition window of 100 ms.

Piezo-polymer transducers for ultrasonic imaging in air.

Airborne polyvinylidenefluoride transducers have been designed for robotic applications in air. Characteristics of transducer prototypes are: working frequencies from 61 kHz to 86 kHz, quality factor Q from 4 to 6, and two-way insertion loss of about 90 dB. The small dimension, the lightness, and the low-cost fabrication technology allow the development of arrays or matrices for ultrasonic imaging systems in air. In this work two different image reconstruction algorithms are proposed: the first carries out a combined spectral and aperture synthesis for detecting isolated scatterers with a spatial resolution of about 2 mm; the second is based on an accurate ranging algorithm with sub-millimeter resolution at distances up to 50 cm. Finally, this work's application to the reconstruction of three-dimensional object profiles is discussed.

Nearly real-time visualization of arbitrary two-dimensional sections from three-dimensional acquisition.

This work presents a system for the reconstruction of cross-sections with arbitrary orientations derived from three-dimensional (3D) echographic scanners. The interest for this powerful diagnostic tool has prompted us to develop a low-cost processing board that inserts easily into a stand-alone echograph. The proposed system is able to reconstruct high-resolution cross-sections at one frame per second with a time lag of about 60 s due the 3D acquisition process. The board, based on three pipelined DSP devices, has been designed to process volumetric data collected with a commercial echograph by means a rotating probe synchronized with the ECG signal. The resolution of the reconstruction algorithm implemented on the processing unit has been evaluated both with synthetic 3D data and with experimental data from a phantom.

Ultrasonic transducers as a black-box: equivalent circuit synthesis and matching network design.

A new modeling technique for ultrasonic transducers is developed in order to build an analytical model in the Laplace s-domain. The model is intended for use in analog circuit CAD system for the front-end electronic design and to visualize the acoustic pulse modifications under different excitation conditions. The transducer is characterized by two analytical functions representing the driving point impedance and the electroacoustic transfer function. The transfer function is obtained as the ratio of the transducer axial response and the excitation voltage. The reference responses of the impedance and transfer function are derived by the Fourier transform of the measured signals. The model is derived by the measurements of the driving point current and voltage, and the field axial response is sensed by a hydrophone. The procedure for the model identification is described. The results of testing 5-MHz transducer for medical applications are presented. An approach for the design of broadband matching networks using a constant resistance network is reported.