We demonstrate a simple and efficient device for the continuous label-free separation of microparticles using travelling surface acoustic waves (TSAW). A focusing interdigitated unidirectional transducer released high frequency (133.3 MHz) TSAW normal to the fluid flow direction to segregate 3 μm particles from 10 μm particles with a separation efficiency of 100%. The TSAW based separator does not necessitate a tight alignment of the PDMS microchannel with the transducer.

Multi-channel multi-frequency electrical impedance tomography (EIT) systems require a careful calibration to minimize systematic errors. We describe novel calibration methods for the recently developed KHU Mark1 EIT system. Current source calibration includes maximization of output resistance and minimization of output capacitance using multiple generalized impedance converters. Phase and gain calibrations are used for voltmeters. Phase calibration nulls out the total system phase shift in measured voltage data. Gain calibrations are performed in two steps of intra- and inter-channel calibrations. Intra-channel calibration for each voltmeter compensates frequency dependence of its voltage gain and also discrepancy between design and actual gains. Inter-channel calibration compensates channel-dependent voltage gains of all voltmeters. Using the calibration methods described in this paper, we obtained 1 MOmega minimal output impedance of the current source in the frequency range 10 Hz-500 kHz. The reciprocity error was as small as 0.05% after intra- and inter-channel voltmeter calibrations. To demonstrate effects of calibration in reconstructed images, we used a homogenous phantom from which uniform images should be produced. Reconstructed time- and frequency-difference images using uncalibrated data showed spurious anomalies. By using calibrated data, standard deviations of time- and frequency-difference images of the homogenous phantom were reduced by about 40% and 90%, respectively.

A method for improving the size-based particle separation technique known as pinched flow fractionation (PFF) has been demonstrated experimentally and analyzed by performing numerical calculations. Since the particles in the pinched region are pushed by an optical scattering force, the original particle position with respect to the wall is modulated. This position modulation in the pinched region is amplified in the broadened region along the streamline. This enhancement of separation is achieved by imposing an optical force on the original PFF design. Three different polystyrene latexes (PSLs) with diameters of 2, 5, and 10 μm were separated with PFF and optically enhanced PFF (OEPFF) devices. The separations achieved with the two devices were compared and enhancements in the separation distance by factors of up to approximately 15 were achieved. Theoretical calculations were also performed to interpret these results.

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