Figure 1.

Working principle of a sensor with an open-cavity structure: (a) the conceptual split of an étalon sensor having a cavity layer sandwiched by two PC structures from the middle of the cavity layer; (b) only half of the structure is used in TIR geometry, owing to the TIR, a mirror image of the PC structure results in a virtual étalon structure; and (c) a PC-TIR optoacoustic sensor with an open cavity, which ultimately enables optimizing the ultrasound detection sensitivity and bandwidth.