Figure 4.

Experimental testing of PC-TIR sensors in comparison with a piezoelectric transducer. (a) Ultrasonic signals from an 80-MHz transducer detected with a PC-TIR sensor having a PMMA cavity thickness of 2.65 μm (inset: ultrasonic pulse-echo signal detected with the piezoelectric transducer); (b) frequency spectrum of the signals measured with the PC-TIR sensor and square-root of the pulse-echo spectrum; (c) frequency transfer function for the 2.65-μm sensor obtained by dividing the PC-TIR spectrum by the pulse-echo spectrum; and (d) frequency spectra of the ultrasound signals measured with four different PC-TIR sensors having different cavity thicknesses.