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Trebbels D.,Institute For Mikro Und Informationstechnik Der Hahn Schickard Gesellschaft Hsg Imit | Kern A.,Institute For Mikro Und Informationstechnik Der Hahn Schickard Gesellschaft Hsg Imit | Fellhauer F.,Institute For Mikro Und Informationstechnik Der Hahn Schickard Gesellschaft Hsg Imit | Huebner C.,Mannheim University of Applied Sciences | Zengerle R.,Albert Ludwigs University of Freiburg
IEEE Transactions on Instrumentation and Measurement

Time-domain reflectometry (TDR) is a well-known measurement principle for evaluating frequency-dependent electric and dielectric properties of various materials and substances. Although TDR is a proven method, the high price for TDR measurement equipment and complex laboratory setups is often a limiting factor for cost-sensitive applications or large-scale field experiments, where a large number of TDR meters is required. This paper reports on the development of a new miniaturized low-cost TDR meter capable of sampling a repetitive rectangular waveform, which is used as an excitation signal. The developed sampling circuit is based on a digital delta modulator (DM) and allows for capturing the waveform of a repetitive measurement signal. A 1-MHz signal can be captured with a virtual sampling resolution of 1 ps within a measurement interval of 1 s. The generated pulses have a rise time of 2 ns and can be captured with an amplitude resolution of approximately 10 bit and an accuracy of approximately 8 bit. The developed digital DM architecture is implemented inside a small field programmable gate array and integrated into a miniaturized low-power TDR meter prototype for battery-powered outdoor applications. The captured measurement data are stored on integrated micro-SD card memory and can be read out either via a Universal Serial Bus, an RS-485 bus system, or a wireless interface. The TDR meter is controlled by an integrated microcontroller and a real-time clock and therefore can operate completely independent from any additional control setup. The TDR meter targets applications within the field of geoscience and agricultural monitoring, where large-scale measurement systems are required. © 1963-2012 IEEE. Source

Trenkle F.,Albert Ludwigs University of Freiburg | Haeberle S.,Institute For Mikro Und Informationstechnik Der Hahn Schickard Gesellschaft Hsg Imit | Zengerle R.,Albert Ludwigs University of Freiburg | Zengerle R.,Institute For Mikro Und Informationstechnik Der Hahn Schickard Gesellschaft Hsg Imit
Sensors and Actuators, B: Chemical

We present a new peristaltic micropump offering three key features: (i) a disposable pump body and a re-useable actuator unit, (ii) an intrinsic normally-closed mechanism blocking unintended liquid flows up to a pressure of 100 kPa and (iii) a backpressure independent pump performance up to 40 kPa. The modular concept basing on a re-usable actuator unit and a low-cost disposable microfluidic chip enables an easy and cost-efficient exchange of all contaminated parts after use, which addresses especially the needs in the health care sector. The intrinsic normally-closed feature blocks liquid flow in both directions up to a pressure difference of 100 kPa when the electric power is off. The micropump is actuated in a peristaltic manner by three piezostack actuators. Up to a frequency of 15 Hz the pump rate increases linearly with operation frequency leading to a pump rate of 120 μL/min. This was proved for an operation voltage of 140 V by pumping water. In addition the pump rate is independent on backpressure up to 40 kPa and shows a linear decrease for higher pressure differences. The maximum achievable backpressure at zero flow rate was extrapolated to be 180 kPa. As for all peristaltic micropumps, the pump is bidirectional, e.g. the pump direction can be changed forward to reverse mode. © 2010 Elsevier B.V. All rights reserved. Source

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