Micro-transducers

To accommodate smaller liquid flows of about 10 pl/min, micro-ultrasonic nebulizers have been designed. Although basically similar in operation to standard ultrasonic nebulizers, in these micro varieties, the end of a very-small-diameter capillary, through which is pumped the sample solution, is in contact with the surface of the transducer. This arrangement produces a thin stream of solution that runs down and across the center of the face of the transducer. The stream of sample... 

Because most applications for micro-channel heat sinks deal with liquids, most of the former studies were focused on micro-channel laminar flows. Several investigators obtained friction factors that were greater than those predicted by the standard theory for conventional size channels, and, as the diameter of the channels decreased, the deviation of the friction factor measurements from theory increased. The early transition to turbulence was also reported. These observations may have been due to the fact that the entrance effects were not appropriately accounted for. Losses from change in tube diameter, bends and tees must be determined and must be considered for any piping between the channel plenums and the pressure transducers. It is necessary to account for the loss coefficients associated with singlephase flow in micro-channels, which are comparable to those for large channels with the same area ratio. 

The micro reactor properties concern process control in the time domain and process refinement in the space domain [65]. As a result, uniform electrical fields are generated and efficiency is thought to be high. Furthermore, electrical potential and currents can be directly measured without needing transducer elements. The reactor fabrication methods for electrical connectors employ the same methods as used for microelectronics which have proven to satisfy mass-fabrication demands. 

Wilkins JR. Pressure transducer method for measuring gas production by micro organisms. Applied Microbiology. 1974 27 135-140. 

Fig. 2.1 Schematic diagram of the CMR [22]. 1, reactants for processing 2, metering pump 3, pressure transducer 4, micro-wave cavity 5, reaction coil 6, temperature sensor 7, heat exchanger 8, pressure regulator 9, microprocessor controller ...

G. Ocivirk, E. Verpoorte, A. Manz, and H.M. Widmer, Integration of a micro liquid chromatograph onto a silicon chip. Proceedings Transducers (Stockholm, Sweden) 756-759 (1995). 

P. Ruther, M. Ehmann, T. Lindemann, and O. Paul. Dependence of the Temperature Distribution in Micro Hotplates on Heater Geometry and Heating Mode , Proc. IEEE Transducers 03, Boston, MA, USA (2003), 73-76. 

Figure 1.186 Schematic of the recycle-flow micro mixer with five mixing elements [56] (by courtesy of Transducer Research Foundation).

Micro electrode arrays can also be produced by thin film technology and silicon micromachining. Electrochemical analysis using planar thin film metal electrodes as transducer can be done with high performance in vitro [59]. 

Mobius H, Ehrfeld W, Hessel V, Richter Th (1995) Sensor controlled processes in chemical micro reactors, In Transducers 95 - Eurosensors IX, Proc. of 8th Int. Conf. on Solid-State Sensors and Actuators/Eurosensors IX, Stockholm, p 775... 

Verpoorte, E., Manz, A., Widmer, H.M., van der Schoot, B., de Rooji, N.F., A three-dimensional micro flow system for a multi-step chemical analysis. Transducer 1993, 939-942. 

Developments in micro-processing have made it much easier to monitor and to control conditions in the course of manufacture, and to prepare and maintain written records. Injection moulding may be supervised with the help of melt thermocouples fitted in the nozzle, pressure transducers in the hydraulic line and in the mould, and a transducer to monitor linear movement of the screw. Information from these sensors may be displayed and depicted in relation to the control limits (upper and lower) and the operator thus made aware immediately of variations that could be significant. Conditions can be corrected more rapidly and if need be any mouldings that might not be satisfactory diverted for examination. Should the number of suspect products exceed a limit set in advance, a line can be shut down automatically. 

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