Development of acoustic systems for ultrasound attenuation measurement in polydimethylsiloxane (PDMS)

Ultrasound absorption by polydimethylsiloxane (PDMS) can have a significant impact on the acoustic radiation force needed for stimulation of cells in organ-on-a-chip. Hence, finding the PDMS attenuation coefficient is the key to determine the fraction of absorbed acoustic energy in microfluidic systems. To measure the attenuation coefficient of PDMS, two methods were compared: a vector network analyzer (VNA) and a pulse transmission method. Ten PDMS samples with thicknesses ranging from 2.5 to 18.5 mm were tested both before and after 24-hour water immersion. The attenuation coefficient of PDMS, commonly used in microfluidics, was determined within a frequency range relevant to human health, i.e. 1-3 MHz. For a representative 5 mm thick microfluidic chip, the fraction of absorbed acoustic energy (E) is estimated to be approximately 21% at 1 MHz and 68% at 3 MHz. This level of absorption is expected to substantially modulate cell stimulation mediated by acoustic radiation forces.