LDV enables visualization of the acoustic field shape, for example pressure waves vs standing waves, by measuring the magnitude of acoustically-induced displacements propagating through the system. We obtain LDV measurements and present representative heat-maps that represent the mean displacements measured within the region of interest on the devices. In the kHz frequency domain at 1 Vp-p applied voltage, we observe a bulk acoustic pressure wave with mean displacements in the nanometer range (Fig. and) as a function of the amplitude (0.5 Vp-p and 1.5 Vp-p not shown). As can been seen in Video S1, an alternating deflection of the respective finger pairs causes a pressure wave across the injection nozzle region of our acoustofluidic device. Table lists the respective values for the displacements across the entire set of operating parameters investigated. In contrast to this, we do indeed observe a focused SAW propagating through the system (Video S2) when operating the device near the calculated resonance and across a range of MHz frequencies and amplitudes. The acoustic wave focuses to the injection nozzle region of our device with a notable decrease in the mean displacement (Fig. and). We expect that the discrepancy between our physical observations in the audible frequency range in contrast with the calculated resonance frequency is caused by embedding the IDTs with matched channel heights into the same PDMS slab. For example, other researchers have observed significant damping of SAWs when directly overlying PDMS onto hard metal IDTs patterned on LiNbO3 substrates . We consider whether the observed phenomena of relatively large mean displacements produced by the acoustic pressure wave (kHz) vs reduction in the mean displacement of the SAW (MHz) propagating through our devices is due to damping or thermal contributions. We use infrared imaging to visualize thermal excitations using the same conditions measured by LDV, to determine the characteristics of the physical properties. When the device is operated in the pressure wave mode at 10 kHz and 1 Vp-p, we observe minimal increases in thermal energy (Fig 3 ). In comparison, at 36 MHz and 1 Vp-p, the parameter combination where our device generates SAWs, the temperature in the device drastically increases up to 323 K (Fig. ).