Fig. 4.

(A) Photoacoustic time traces from an artificial blood vessel, recorded with air-coupled ultrasound transducers with center frequency of 200 kHz and 1 MHz (the recorded signals are averaged 512 times), reprinted with permission from [120] (B) Photoacoustic images obtained by raster scanning of the air-coupled transducer (a) Photograph of the imaged ink channels. (b)–(e) Photoacoustic images of the phantom after the recorded signals have been averaged 1, 10, 100, and 1000 times respectively, Reprinted from [121], with the permission of AIP Publishing. (C) Schematic diagram of the PA sensor and PA images of red blood cells smeared on a glass substrate, M is the microphone, SC is the sample chamber, S is substrate, reprinted with permission from [122].