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Prof. Ivo W. Rangelow


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Sensor technology

ARCH-type infrared sensors

Infrared detection systems require preferably un-cooled thermal infrared sensor arrays for imaging techniques fabricated in bulk quantities by CMOS compatible planar wafer processes.  ARCH-type infrared sensors could be the solution.  The main innovation in the design of ARCH-type sensors is the separation of the different bimorph materials. This causes an outstanding thermal insulation of both materials with different thermal expansion coefficients, compared to conventional systems.

Based on this design a frame-like bimorph high sensitive detector was developed with excellent thermal insulation between the absorption and detection areas.

The "ARCH" approach:

  • "ARCH" is a brand new development, also based on bimetal effect. But the materials are spatially separated and carefully picked to get a sensitivity that is by one factor higher than that of known sensors.
  • Current sensitivity lies between 250 and 500mK NETD. Goal of further optimization is getting below 75mK NETD which is considered sufficient for "low-cost" applications.
  • The ARCH chip has been nominated for the AMA innovation award 2013 and chosen for the top 5 developments:
    News on (29 Apr 2013 20:09 GMT+1)
    List of nominees (from, 29 Apr 2013 20:09 GMT+1)

The ARCH innovation is an infrared detector based on a novel uncooled micro mirror sensor. This thermographic system allows for contactlessly measuring object temperatures from large distances and visualizing them in realtime. The innovation core is a micro sensor consisting of a 2D matrix of micro mirrors which converts thermal radiation (IR at 7-14µm wavelength) into a microscopic mirror movement. The sensor is simple and cheap in production due to latest micro technology and does not consume any energy on operation. The mirror movements are captured using a simple optical system (laser diode, CCD) and presented as realtime thermal image. This innovation posesses distinctive cost advantages over recent IR technologies.

First applications will be:

  • thermographic alarm systems for the private sector
  • fire detection
  • and of course low-cost IR cameras for automotive sector
micro mirror principle
micro mirror array

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Propagation of acoustic surface waves

Our department is engaged in the phenomena of propagation of surface acoustic waves (SAW) on piezoelectric substrates. The use of SAW devices in sensor systems results from the dependence of the surface wave propagation velocity on:

  • Temperature
  • Pressure
  • Mechanical stress or
  • Chemical substances.

Passive telemetric sensor technology is a field of growing importance.  Within the field of application of these systems new applications for sensor technology are made possible. Sensors can be mounted in inaccessible places such as rotating machine parts while data acquisition can be wireless. 

Figure 1 shows the set-up of a passive SAW telemetric sensor system. The data acquisition device sends radio signal to the sensor and processes the sensor’s answer for data extraction.

Figure 1

SAW resonators are especially suited such passive telemetric sensor technology. They offer a number of advantages such as: 

  •  Simple fabrication technology
  • Robustness
  • High Q factor
  • Large life time
  •  Passive operation (no power supply required) 

 Our department works  SAW based solutions for telemetric sensor systems for applications in the field of veterinary medicine and power engineering (especially for temperatures around 600°C).  Most important are sensors for temperature and pressure measurements as well as detectors for mechanical stress and strain. The basic set-up of an one-port SAW resonator is shown in figure 2. 

Figure 2

An interdigital transducer generates SAW waves on a piezoelectric substrate because of the inverse piezoelectric effect. Waves propagating out of both ends of the transducer are reflected by two refection grids. The reflected waves are received by the transducer. Depending on the geometry of the resonators standing waves occur at the so-called center frequency. 

The typical frequency response of the S11 parameter of an one-port SAW resonator at a center frequency of f0=433.347 MHz  is depicted in figure 3.


Figure 3

 The principle of operation is based on the detection of the shift of the center frequency depending on the quantity to be measured.  The dependence of the center frequency on the pressure of a SAW pressure sensor is shown in figure 4. 

Figure 4

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Translation: B. Volland, A. Reum
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