Transparent ultrasound transducers (TUTs) have gained significant traction in the fields of photoacoustic (PA) and ultrasound (US) applications. TUTs possess the unique capability to transmit and receive ultrasound waves while maintaining optical transparency. As a result, TUTs simplify the PA imaging process and facilitate seamless integration with other optical imaging modalities. However, the limited sensitivity of TUTs has been a primary challenge hampering their widespread adoption in PA setups. One often overlooked factor contributing to this limitation is the electrical impedance mismatch between the transducer and the data acquisition system. Here, we designed and studied the utilization of a filter-based electrical impedance matching (EIM) circuits to enhance the sensitivity of lithium niobate-based TUTs. In our approach, the fabricated TUTs incorporate a quarter-wavelength Parylene-C matching layer and epoxy as a backing layer. Our results demonstrate that the integration of the EIM circuit yields substantial improvements in the sensitivity, bandwidth and axial resolution of both pulse-echo US signals and PA signals. PA imaging of leaf phantoms were compared with and without EIMs to further showcase the performance enhancements that can be achieved by integrating EIM with TUTs. Overall, these results demonstrate that EIM circuits can be employed to improve the performance of TUTs.
2-D Ultrasound (US) Transducer (2D-UST) arrays facilitate scan-less volumetric photoacoustic imaging (3D-PAI), but are typically high-cost, involve laborious fabrication process, and permit limited scalability in design with respect to array parameters like element count, aperture size, center frequency ( š¯‘“c) and array pitch. In this work, we report a novel, 2-D matrix UST array fabricated on a printed circuit board (PCB) substrate (2D-PCB-UST array) at low-cost and without the need of advanced cleanroom fabrication technologies. Further, the 2D-PCB-UST array parameters can be easily modified with PCB design software. We demonstrate the scalability by fabricating two arrays, (i) an 8×8 array with 1.5 mm pitch and š¯‘“c 40 MHz, and (ii) an 4×4 array with 1.2 mm pitch and š¯‘“c 11 MHz. Initial characterization results demonstrate wideband PA receive sensitivity, characterized by the 6-dB fractional bandwidth for both low and high frequency UST arrays. Phantom imaging results demonstrate 3D-PAI capabilities despite low element count and sparse array geometry.
Recently, piezoelectric transparent ultrasound transducers (TUTs) have gained the attention of the photoacoustic imaging community. The ability to illuminate living subjects through the TUT and minimal acoustic coupling requirements allows for miniaturization, reduces cost, and increases the ease of multimodal integrations. TUTs, therefore, have great potential for photoacoustic imaging; however, challenges remain on matching their acoustic sensitivity to conventional opaque piezoelectric transducers. Various noise sources arising from TUT fabrication and electronics limit their sensitivity. This paper discusses various TUT-specific noise considerations that are detrimental to signal to noise ratio. We also assess the effect of different design considerations by comparing different TUTs. The results can help optimize TUTs design for improving performance, thus paving the way for powerful TUT based photoacoustic applications.
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