Steffen Doerner

A new device with PZT ultrasonic transducers in MEMS technology

Thick-film piezoelectric transducers have been produced and tested for implementation into a MEMS ultrasonic sensor array. The arrays are intended to be used for beam forming in sensing applications for fluidics in channels at millimeter or micrometer scale (e.g. flow rate measurement, detection of beads, bubbles). Stripe and matrix aligned elements have been fabricated for one-dimensional and two-dimensional beam steering, respectively. In this contribution we further concentrate on an improved Q-factor and PZT layer homogeneity as a major requirement for the transducer elements.

Analogue and digital sensor interfaces for impedance spectroscopy

Impedance spectroscopy is a non-invasive method of sensing electrical material properties. This approach is also suited for sensors transducing non-electrical properties into an electrical impedance. As yet, impedance spectroscopy has only been applicable with laboratory instrumentation, covering a broad frequency and impedance measurement range. By restricting to measurement ranges required by specific applications it is possible to implement the method in sensor interfaces. An interface with substantially analogue circuitry was developed and applied to quartz crystal resonators for sensing density and viscosity of liquids. Additionally, a fully digital interface was realized which is mainly intended for capacitive measurements in liquids. As it samples occurring signals directly and performs a real time sine regression of the acquired probes, it is faster and more precise than the analogue sensor electronics. However, both interfaces have the same precision like laboratory devices for their specified application which is demonstrated with reference measurements.

Wideband impedance spectrum analyzer for process automation applications

For decades impedance spectroscopy is used in technical laboratories and research departments to investigate effects or material characteristics that affect the impedance spectrum of the sensor. Establishing this analytical approach for process automation and stand-alone applications will deliver additional and valuable information beside traditional measurement techniques such as the measurement of temperature, flow rate, and conductivity, among others. As yet, most of the current impedance analysis methods are suited for laboratory applications only since they involve stand-alone network analyzers that are slow, expensive, large, or immobile. Furthermore, those systems offer a large range of functionality that is not being used in process control and other fields of application. We developed a sensor interface based on high speed direct digital signal processing offering wideband impedance spectrum analysis with high resolution for frequency adjustment, excellent noise rejection, very high measurement rate, and convenient data exchange to common interfaces. The electronics has been implemented on two small circuit boards and it is well suited for process control applications such as monitoring phase transitions, characterization of fluidal systems, and control of biological processes. The impedance spectrum analyzer can be customized easily for different measurement applications by adapting the appropriate sensor module. It has been tested for industrial applications, e.g., dielectric spectroscopy and high temperature gas analysis.

Universal impedance spectrum analyzer for sensor applications

A compact impedance spectrum analyzer has been developed that is well suited for the use in process control. Various sensor elements connected to the sensor electronics allow an adaptation to different measuring applications. Digital signal processing minimizes the insertion of noise and distorting effects to the system. Facilities are provided to calibrate the sensor with a reference.

Capacitive sensor for methanol concentration measurement in direct methanol fuel cells (DMFC)

A compact in-situ measurement of methanol concentration in the liquid feed of direct methanol fuel cells (DMFC) by a capacitive sensor is presented. The measurement approach uses impedance spectrum analyzer electronics and is suitable for use under process conditions. Calibration of the measurement system for the required temperature range is done with selected reference liquids.

A New Test Device for Characterization of Mechanical Stress Caused by Packaging Processes

This paper reports on a new method for estimation and minimization of mechanical stress on MEMS sensor and actuator structures due to packaging processes based on flip chip technology. For studying mechanical stress a test chip with silicon membranes was fabricated. A network of piezo-resistive solid state resistors created by diffusion was used to measure the surface tension pattern between adjacent membranes. Finite element method simulation was used to calculate the stress profile and to determine the optimum positions for placing the resistive network.

Single board impedance analyzer and transient analysis of QCR sensor response

QCR (quartz crystal resonator) sensors afford the visualization and continuative research of chemical, biochemical or microreactor processes. In this context, the resonant frequency and the attenuation of the sensor are important parameters. The paper discusses a new concept for measuring both parameters within very short cycle times which allow the tracking of fast dynamic processes during those reactions.

Compact RF Impedance-Spectrum-Analyzer For Lateral Field Excited Liquid Acoustic Wave Sensors

A compact RF impedance-spectrum-analyzer (RF-ISA) has been developed and applied to a Lateral Field Excited (LFE) liquid acoustic wave sensor, which is sensitive to both, the mechanical and the electrical liquid property changes. The developed RF-ISA was used to determine the impedance spectrum of a LFE sensor exposed to various liquids with varying electrical and mechanical properties and to calculate the series resonance frequency and resistance at the sensors conductance maximum. The combination of the LFE sensor and the RF-ISA electronics results in a compact and portable liquid sensing unit, which not only has many sensing applications but also can provide insight into the piezoelectric excitation and transduction mechanisms.

Real Time Kinetic Analysis with Quartz Crystal Resonator Sensors

Fast impedance analysis-based measurements of resonant frequency (shift) and equivalent resistance (change) of liquid loaded quartz crystal resonator (QCR) sensors have been used for kinetic analysis of film formation at the interface between a liquid analyte and the sensor. Kinetic constants provide an independent set of data and allow for an unambiguous material property determination in the so-called non-gravimetric regime. A sequential injection system (SIS) has been developed which enables fast specimen sampling with minimum dispersion effects

Ceramic injection molded clevis sensor for online substance concentration measurement

The current research presents recent respective to the work development of a ceramic clevis sensor for online substance concentration measurements. The aim is to develop a robust and acid-resistant sensor device, which can be easily included in existing procedural pipeline systems. To achieve those goals a lot of factors had to be checked. For the substance concentration measurements a capacitive sensor effect has been chosen. With this method even low substance concentrations down to one-tenth of a per cent can be indentified.