Design and fabrication of ultrasound linear array transducer based on polarization inversion technique

It has been well known that fabrication of the ultrasound array transducer is very difficult mainly due to the thin piezoelectric layer. Since the center frequency of the ultrasound array transducer is inversely proportional to the thickness of the piezoelectric layer, as the center frequency is increased, fabrication of the array transducer becomes more difficult. To solve this problem, in this paper, the polarization inversion technique (PIT) was employed to increase the center frequency of the array transducer without making the piezoelectric layer thin. Additionally, the PIT can increase the frequency bandwidth of the transducer by using its multiple-resonance feature. According to the finite element analysis (FEA) simulation, when the total thickness of the piezoelectric layer was fixed at 311 μm, the conventional transducer had a center frequency of 4.5 MHz and −6 dB bandwidth of 71.4%, while the proposed transducer with PIT had a center frequency of 8.1 MHz and −6 dB bandwidth of 83.2%. In the case of conventional transducer with about 8 MHz center frequency, the thickness of the piezoelectric layer was 155 μm, and −6 dB bandwidth was 72.3%. Subsequently, we fabricated a prototype transducer with PIT and verified that the center frequency and −6 dB bandwidth were 7.8 MHz and 81.3%, respectively. Therefore, the PIT can be a useful method for manufacturing the ultrasound array transducer with high frequency and broad bandwidth.