Linear Ultrasound Transmitter Based on Transformer with Improved Saturation Performance

Ultrasound methods are currently employed in a wide range of applications. They are integrated in complex electronics systems, like clinical echographs, but also in small and compact boards, like industrial sensors, embedded systems, and portable devices. Ultrasound waves are typically generated by energizing a piezoelectric transducer through a high-voltage sequence of small sinusoidal bursts. Moreover, in several applications, the ultrasound board should work in a wide frequency range. This makes the transmitter, i.e., the electronics that drives the transducer, a key part of the circuit. The use of a small transformer simplifies the electronics and reduces the need of high-voltage power sources. Unfortunately, the transformer magnetic core, when subjected to the sequence of bursts employed in ultrasound, is particularly prone to saturation. This phenomenon limits the maximum voltage and/or the minimum frequency the transformer can be employed for. In this work, a transmitter based on a transformer is proposed. Inspired by the technique currently employed in the power network transformers, we added a prefluxing circuit, which improves the saturation performance 2-fold. The proposed transmitter was implemented in a test board and experimented with two commercial transformers at 80 Vpp. Measurements show that the proposed prefluxing circuit moves down the minimum usable frequency 2-fold: from 400 to 200 kHz for one of the two transformers, and from 2.4 to 1.2 MHz for the other.