The influence of carrier layer material in ultrasonic particle manipulation devices

The use of acoustic radiation forces for the manipulation of particles, bacteria and cells is drawing increasing interest. Resonators using quarter-wavelength sized fluid chambers have been developed, where an acoustic pressure node is positioned near the reflector layer surface such that particles may be pushed close to or onto this surface. The thickness of the reflector layer has already been shown to greatly influence the performance of such resonators. These devices have applications in bio-sensing where a concentrate of particulates can be collected or particulates can be contacted with a sensor surface directly. A coupling layer is usually incorporated into the device and is located between the transducer and fluid layer. The ability of this layer to act as an acoustic matching layer depends on its acoustic properties and thickness. Here, the performance of various carrier layer materials in a near quarter-wavelength device is investigated and compared using modelled and experimental data. Results indicate that where the carrier layer thickness is selected for optimum performance, the resonator performance is comparable for most high Q factor carrier layer materials. However, for some materials the performance of the resonator, is highly sensitive to the coupling layer thicknesses and in turn can constrain the flexibility of the acoustic design.