Abstract：Low intensity ultrasound can stimulate brain tissues. We designed a programmable ultrasound generator for brain stimulation. From a computer the generator receives the stimulate variables, based on which an embedded FPGA chip generates the stimulation pulses. The output power is controlled by setting the duty cycle of the power amplifier at the last stage, which works in switching style for high efficiency. An impedance matching network is inserted between the output terminal and the ultrasound transducer so that the rectangular waveform is transformed to sine. The variables of the pulses are easy to understand and adjust compared to those of the general-purpose functional generators because they are designed especially for brain stimulating. The highest ultrasound frequency of the generator is 2MHz and the maximum output power is more than 157.1 watts. Twelve SD rats were experimented with the generator and a home-made 500kHz transducer, when rat brains were stimulated under the condition of spatial-peak temporal averaged intensity Isppa=5.36W/cm2, 90% success rate was achieved in terms of the responsive muscle contracting. The test results and animal experiments show that the generator we designed is capable to be used in the research work of brain stimulation.
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