key parameters and control of high focused piezo(一)

The measurement of ultrasonic working frequency, focal length, focal spot, sound intensity, side lobes and other key parameters and the quality of the focused sound field are the key to HIFU piezo ceramic technology engineering, which have an inseparable relationship with the performance, efficacy and scope of HIFU equipment.The operating frequency of the HIFU treatment system is generally between 2OMhz. If the frequency of ultrasound is too low, the focal spot is too large, and the loss of focused ultrasound is not achieved, and the principle of surgical conformal treatment is not achieved. If the ultrasonic frequency is too high, the focal length is too small, the treatment is time- consuming, and the frequency of the sound wave is too high. Considering the relationship between the tissue absorption coefficient and the ultrasonic frequency, ability of penetration is inevitably affected. For Hifu piezoelectric crystal ball, how much is the ultrasonic working frequency appropriate? In other words, the frequency is determined and the corresponding focal  can be determined. The focal length determines the effective depth of treatment for HIFU. In human tissues, the liver and kidney lesions are about 20 mm shallow, the prostate lesions are about 150 mm , and other human tissues are basically in the range of 20 mm. In addition to the above factors, the focal length must be considered high. As for frequency propagation of ultrasonic waves in biological tissues. Standard stipulates of the industry that the maximum sidelobe level of the focused sound field should be less than 1 sd B and the maximum sound intensity in the focal length should be at least 10 w/c. When it is designing the system, which measures to control the focus quality of the focused sound field to highlight .the main lobe is making the treatment of high focus piezoelectric ceramics safe and effective.

The focusing of the acoustic lens does not require phase and amplitude control of the primitive, but the transducer must be matched by the load. Otherwise, efficiency of the electroacoustic conversion is lower, and the electrical power of the large is consumed by the self-heating of the transmission cable and the transducer. The multi-concave spherical focusing transducer has high requirements on the performance consistency and phase consistency of the primitive. Otherwise, the difference in the bonding process will seriously affect the quality of the focused sound field,because the number of primitives is too large, the transducer is required. It is also unrealistic to perform matching and phase amplitude control, so the focus transducer cannot control the focused sound field;as for a multi-element self-focusing transducer, if the focus of each ultrasonic high focusing piezo pickups cannot point to the same one, The distribution of the focus ultrasound parameters is relatively poor, the focal spot will inevitably be too large, and the side lobes will be high, which will affect the therapeutic effect. Therefore, while ensuring the processing accuracy of the transducer and the 7Mhz high focusing piezo to ensure the uniformity of the thickness, measures must be taken to eliminate the influence of the phase and amplitude difference of the resonant frequency of the transducer on the focused sound field.