Focusing principle of ultrasonic phased array

For a multivariate linear array transducer with Zn+1 array elements, if all the array elements emit sound waves at the same time,Let the sound pressure value of the array element at point F be p: then the total sound pressure of point F value is: p

Since the distances of the respective line elements are reaching the point F to be focused in the medium are different, and the speed of sound in the uniform medium is constant, the time at which the sound waves of HIFU piezo ceramic are emitted by the respective array elements,which reaches the point F is also different. According to the distance between each array element and the point F, a certain delay is added when each array element transmits a signal, so that the array element is far from the point F that first transmits a signal, and the array element that is closer to the point F emits a signal. And controlling the length of each HIFU piezoelectric sensor so that all signals reach point F at the same time, a focused sound field can be formed. This approach allows the transducer array to be equivalent to a concave transducer when is transmitting a signal.

In the field of clinical cancer treatment, high-intensity focused ultrasound (HIFU) treatment technology as a non-invasive tumor thermal therapy technology,which has been used in the treatment of liver tumors, uterine fibroids, breast cancer, kidney cancer, pancreatic cancer and other deep abdominal cavity ,Among solid tumors. The multi-array spherical coronal ultrasound treatment probe is a new type of probe for the Hifu piezoelectric ceramic transducer system, which can realize focus scan treatment flexibly and quickly by means of electronic focusing. However, this type of probe has a complicated structure and many array design parameters, which makes design and manufacture difficult. How to obtain a multi-array spherical coronal ultrasound treatment probe with ideal focusing effect is at a lower cost and a simpler design method and manufacturing method.

This topic proposes a new type of probe design, which is using a limited number of regular hexagons of the same shape and size.As a probe array element, the flat ceramic is densely laid out by the spherical crown surface, and finally a high intensity focused ultrasonic probe is manufactured at low cost. The content of the thesis mainly includes two parts. First, a developing platform for two-dimensional high-intensity focused ultrasound probes was built. The platform includes a spherical crown surface treatment sound field array structure design and process manufacturing of a probe realized by 3D printing and CNC technology.

The probe development platform has certain scientific research and application, basically meets the technical platform requirements of ultrasonic high focus piezo treatment probe design and development,which provides a simple platform for the array structure design of HIFu treatment probe, and provides a simple, low cost and fast probe process manufacturing solution. Finally, with the platform, this thesis develops a multi-element spherical Hifu piezo transducer impedance probe with a matrix element of 125mm, a regular hexagonal element with a side length of 2.5mm, a resonant frequency of 2MHz and a radius of curvature of 60 mm. The sound field results in the array structure shows that the focal length is 1.5x l.5x7.5mm, the maximum deflection range on the focal plane is 6mm, and the maximum axial deflection distance along the beam emission direction is 6mm. In addition, the performance test of the probe found that the probe has a minimum focal depth of physical focus of up to 1x1x3m under short pulse excitation.