Design of dynamic filter for veterinary B-ultrasound, in order to obtain the echo image with the best resolution within the full detection depth, the dynamic filter to be designed is a bandpass filter group whose passband gradually moves downward with the increase of time (depth). The filter group consists of 64 filters. In the selection of filters, FIR filters with linear phase are adopted, and the traditional hardware description method of using multipliers to realize multiplication and accumulation is abandoned. Instead, the hardware structure of the filter is realized on the field programmable gate array based on distributed algorithms. In the platform of the fully digital veterinary B-ultrasound system, the ultrasonic probe used is a convex array probe with 128 array elements, the center frequency is 3.5MHz, and the 6dB bandwidth is 71%.

Generation of veterinary B-ultrasound filter coefficients In order to realize the dynamic filtering processing of the ultrasonic echo signal of the animal body, the detection depth of the fully digital veterinary B-ultrasound is evenly divided into 64 segments, and 64 bandpass filters are used to correspond to it. The sampling frequency of the ultrasonic echo signal is 40MHz, and the filter order is 32

First, in Matlab, the Hamming window function is selected to generate the filter coefficients by using the given filter order and bandwidth using the FDATool tool. Then, using the powerful RAM storage function of the FPGA chip, the filter coefficients are quantized into 8-bit complement numbers during the initialization phase and stored in the RAM of the FPGA chip. During the operation phase of the veterinary B-ultrasound system, the filter coefficients are obtained from the RAM through precise timing control and input into the hardware implementation part of the FIR type dynamic filter. Taking the 1st and 32nd bandpass filters as examples, two filter characteristic diagrams are obtained under Matlab simulation. With the increase of depth, the spectrum of the filter gradually moves to the low end of the frequency band, so it can well match the frequency components of the ultrasound echo signal, filter the strong echo signals with low frequencies on the surface and the interference with high frequencies in the deep part, so as to obtain the veterinary B-ultrasound echo image with the best resolution within the full detection depth.