Development of prototype PVDF-based ultrasound transducer for thermoacoustic imaging

This work presents the comprehensive design, development, and experimental validation of two prototypes ultrasound piezoelectric sensors. These sensors are specifically developed for the purpose of thermoacoustic imaging and ionoacoustic tomography , respectively. Both sensors utilize polyvinylidene fluoride (PVDF) as the piezoelectric material. PVDF was chosen for its outstanding characteristics, compared to the state-of-the-art PZT ultrasound sensor. The relationship between the physical structure and the acoustic characteristics of the PVDF transducer was simulated using both a Finite Element Model (FEM) and an Analytical Model. The simulations demonstrated that most relevant sensor variables, such as the frequency response and sensitivity, are significantly influenced by the physical arrangement of the transducer. Printed circuit board (PCB) technology was used to accurately define the sensor's active area, while simultaneously reducing the complexity and cost. The first sensor is developed by using PVDF material with a thickness of 20 µm. It is specially designed for thermoacoustic imaging and has an active area of 0.3x10mm millimeters, which has the bandwidth of 10MHz. The sensor is configured with a Multichannel array design. This design is crucial for achieving optimal imaging results with resolution in the range of 10 microns. At the same time multichannel format allows for future applications of bioimaging. The second sensor utilizes PVDF-TrFE material with a thickness of 1.2mm, which is specifically designed for ionoacoustic tomography in hadron therapy. The scope of this sensor is to accurately measure the deposition of dose during treatment. This sensor has a bandwidth of 1 MHz and is equipped with three parallel channels, each of which has dimensions of 3x30 mm. The design of these sensors was carefully developed using analytical modeling and finite-element simulations to optimize their directivity, frequency response, and sensitivity. Both sensors were subjected to acoustic behavior validation, and preliminary experimental findings were provided to confirm the acoustic behavior of both sensors. Such a sensor would be used for further acoustic characterization by using an amplifier and finally used as a potential candidate for sensing of cells in photoacoustic bioimaging or in hadron therapy monitoring