We describe a miniaturized MEMS particulate matter (PM) monitor that employs the deposition of particulates from a sample stream onto a 1.6 GHz piezoelectric thin-film bulk acoustic wave resonator (FBAR) by means of thermophoresis, and determination of the mass deposited by measuring the resonant frequency shift of a Pierce oscillator. Real-time measurements made in an environmental chamber over several weeks and during a week-long field study in a residence showed excellent correlation with the responses of other commercial aerosol instruments. An added mass of 1 pg could be resolved with the sensor, and the level of detection was 18 µg / m 3 . The monitor weighs 114 g, has a volume of approximately 245 cm 3 , consumes less than 100 mW, and would cost less than $100 USD in small quantities. Efforts to further miniaturize the sensor and integrate it with a cell-phone are described.
The authors present a method based on dynamic force microscopy to characterize subnanometer-scale mechanical vibrations in resonant micro-and nanoelectromechanical systems. The method simultaneously employs the first eigenmode of the microscope cantilever for topography imaging and the second eigenmode for the detection of the resonator vibration. Here, they apply this scheme for the characterization of a 1.6 GHz film bulk acoustic resonator, showing that it overcomes the main limitations of acoustic imaging in contact-mode atomic force microscopy. The method provides nanometer-scale lateral resolution on arbitrarily high resonant frequency systems, which makes it applicable to a wide diversity of electromechanical systems.
A standing acoustic field excited by an ultrasonic flexural plate wave (FPW) device is shown to trap microspheres and cells suspended in a pressure-driven flowing liquid. Capture is achieved by counteracting the viscous drag forces on a particle with acoustic radiation pressure. The suitability of this technique for biochemical analysis is demonstrated with two experiments: (1) acoustically trapped streptavidin-coated 1 µm microspheres conjugated to fluorescent 200 nm biotinylated microspheres; and (2) perfusion of the membrane permeant fluorescein diacetate across acoustically trapped cells. Biochemical interaction was monitored with a fluorescence microscope. Efforts to integrate acoustic traps with on-chip FPW microfluidic pumps are also described. 0-7803-7582-3/02/$17.00 (c) 2002 IEEE 2002 IEEE ULTRASONICS SYMPOSIUM-475
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