Interface electronic systems for broadband piezoelectric ultrasonic applications: Analysis of responses by means of linear approaches

Abstract

There are a wide variety of applications where broadband piezoelectric systems are used, mainly in order to obtain ultrasonic information for detection or visualization of the internal parts in diverse structures. These applications require external inspections with ultrasonic waves and the use of an echo-graphic procedure. The main application areas are in industry and medicine. Most broadband piezoelectric applications require the design of very specific interface electronic systems, since the conventional continuous wave (CW) electronic schemes and the conventional analysis methods are not applicable. In order to obtain a good discrimination of internal structures, it is convenient to improve the signal to noise ratio. Therefore, it is necessary to guarantee a high efficiency in the ultrasonic process. In addition, short ultrasonic pulses must be used in order to obtain good axial resolution. The above-mentioned practical questions impose some technological requirements over the electronic systems used for broadband ultrasonic applications: 1. The use of a pulsed regime for the ultrasonic inspection process, which involves a transient electrical excitation of the piezoelectric transmitter. 2. Sensitivity considerations determine that the transducer should be excited with very short electrical pulses (spikes) of several hundreds of volts at peak amplitude. 3. A high efficiency in emitter and receiver piezoelectric sub-processes, under broadband conditions, is required in order to optimise the coupling between spike generators and piezoelectric emitters, as well as between piezoelectric and electronic receivers. It is not easy to attain simultaneously all these requirements because parameters influencing the response amplitudes act in a crossed way. Specifically, the optimum setting of one of the parameters depends on the settings of the others. As a typical example, to obtain a good dynamic range on the received echo-signals, by using broadband piezoelectric arrays in medical imaging In this chapter, the characteristics required for the high voltage stages needed for driving broadband piezoelectric transducers are explained. The dependence of the driving pulses with matching networks and the external loads is also analysed. A simple circuital block diagram for interfacing transducers with the reception stages, in ultrasonic applications, is also presented. Finally, a detailed analysis of electrical responses in high-voltage pulsed driving of piezoelectric transducers is performed in the time domain, taken into account some typical working conditions. For this purpose, several expressions related to the driving waveforms are introduced and discussed from a series of analytical linear approaches associated with practical situations in medical and industrial ultrasonic applications. © Springer-Verlag Berlin Heidelberg 2008.