researching on multi-frequency HIFU piezo transducer

In order to realize the HIFU ultrasound piezo, the traditional methods mostly use a single frequency ultrasonic transducer, and the use of the same focusing system to achieve the focus of the two frequency ultrasound is rarely reported. In 1996, Japanese scholar S. Umemura et al. studied a technique that is using ultrasonic to activate acid red to kill tumor cells. In order to achieve second harmonic and fundamental superposition, a special multi-frequency focused ultrasound transducer was developed. It is to adhere 16 layers of PZT wafers of different frequencies to the convex surface of the aluminum spherical shell by epoxy resin respectively, as a result, two kinds frequency of high intensity focused ultrasound probes are realized on the concave side of the aluminum spherical shell, and the two focal points coincide. In 1999, by studying the phenomenon of low frequency ultrasonic cavitation, it was found that under certain conditions, dual-frequency acoustic cavitation was significantly better than single-frequency ultrasound. they developed a new multi-frequency focusing transducer later , 400 kHz and 800 kHz multi-frequency transducer to activate porphyrin and its derivatives. The emissive high-frequency PZT wafer is placed in the low-frequency PZT ring with epoxy resin and adhered to the plane of the plexiglass lens. 

The radiant end of the plexiglass is made into a concave spherical surface to make the ultrasonic region of the two frequencies ultrasonic. Basically, the purpose of the two frequencies is achieved. After studying the ultrasound field of the multi-frequency high intensity focused piezoelectric ceramic, it is found that the sound scattering of the two columns of sound waves generated by the multi-frequency transducer,which widens the spectrum of the sound field,it is increasing the probability of cavitation cavitation, thus enhancing the ultrasonic cavitation. The effect enhances the synergistic anticancer of ultrasound and hematoporphyrin.A dual-frequency composite HIFU transducer was developed by cutting a concave spherical piezoelectric ceramic wafer into two transducers in a concentric circle, it is using a dual-frequency operation mode. The results show that the different frequency of sound wave in the dual-frequency mode promotes the cavitation effect, which causes the focal spot ratio generated by the HIFU transducer in the dual-frequency mode, and the focal spot area in the single-frequency mode is significantly larger. In addition, a multi-focal and beam-controllable transducer has been developed by a dual-lens lens. The structure of the transducer is improved, and a cavity is left on the opposite side of the piezoelectric crystal, so that the portion of the ultrasonic wave that propagates backward is regularly reflected back to coincide with the energy of the sound wave propagating forward to improve the ultrasonic wave. It is efficiency of the transducer. Some scholars have improved the transducer to reduce the sound intensity of the source and reducing the irradiation time of healthy tissue. It is proposed to introduce a new high focus ultrasound piezo with dual-frequency ,it is operation mode and single-frequency operation mode, and use two modes to isolate the body. Pig liver tissue was irradiated for comparison. the damage caused by the dual-frequency mode HIFU is significantly larger than that of the single-frequency mode, and it has the advantages of simple structure and compared with the phased array focusing transducer.

Due to the absorption and reflection of sound beams by gas and bone, the application of HIFU piezo technology in such media is limited. Some scholars have proposed to design a transducer with split-volume emission. The concave piezoelectric material HIFU piezo of the transducer is divided into ten pieces of equal area, and each piezoelectric wafer has a driving power source. During the treatment, when a rib is encountered to block the sound wave of one of the pieces, it can be stopped by turning off the driving power. This avoids the impact of the ribs on the sound field and avoids possible damage to the ribs during Hifu treatment piezoelectric crystal. The designed "dual mode" phased array focusing transducer has both therapeutic and imaging capabilities. This transducer divides the surface of a spherical array into 2048 array elements, and its simulated sound field shows good focusing characteristics.