A photoacoustic imager with light illumination through an infrared-transparent silicon CMUT array

Jingkuang Chen*, Mengli Wang, Jui Ching Cheng, Yu Hsin Wang, Pai Chi Li, Xiaoyang Cheng

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

35 Scopus citations


A novel hardware design and preliminary experimental results for photoacoustic imaging are reported in this paper. This imaging system makes use of an infrared-transparent capacitive micromachined ultrasonic transducer (CMUT) chip for ultrasound reception and illuminates the image target through the CMUT array. The cascaded arrangement between the light source and transducer array allows for a more compact imager head and results in more uniform illumination. Taking advantage of the low optical absorption coefficient of silicon in the near infrared spectrum as well as the broad acoustic bandwidth that CMUTs provide, an infrared-transparent CMUT array has been developed for ultrasound reception. The center frequency of the polysilicon-membrane CMUT devices used in this photoacoustic system is 3.5 MHz, with a fractional bandwidth of 118% in reception mode. The silicon substrate of the CMUT array has been thinned to 100 ¿m and an antireflection dielectric layer is coated on the back side to improve the infrared-transmission rate. Initial results show that the transmission rate of a 1.06-m Nd:Yag laser through this CMUT chip is 12%. This transmission rate can be improved if the thickness of silicon substrate and the thin-film dielectrics in the CMUT structure are properly tailored. Imaging of a metal wire phantom using this cascaded photoacoustic imager is demonstrated.

Original languageEnglish
Article number6189183
Pages (from-to)766-775
Number of pages10
JournalIEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Issue number4
StatePublished - 04 2012
Externally publishedYes


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