Lab

Measurement and Sensor Technology Group

Featured projects (1)

Project
Investigation of piezoelectret energy harvesting systems using the piezoelectric transverse effect, such as cantilever beams and diaphragms.

Featured research (7)

Laser-based powder bed fusion as an additive manufacturing process allows the integration of sensors at any location within the manufactured part. This allows for manufacturing smart parts that can be integrated into complex structures for monitoring applications, as they can perform in-situ measurements. Especially, monitoring of force and torque is gaining increasing interest. However, a proper strain transmission from the mechanically loaded part to the embedded strain sensing element must be ensured, as the performance of such sensors is strongly dependent on it. In this work, we present an approach for additively manufactured deformation elements in a disruptive manner with integrated strain gauges using a steel plate as measuring element carrier. In order to evaluate the strain transmission, and, thus, the performance of the additively manufactured deformation elements, we compare them to a conventionally manufactured deformation element with identical geometry. The strain gauges are applied after manufacturing at locations with a proper strain, which are determined by a finite element analysis. Loading these additively and conventionally manufactured prototypes with 15 N results in only 0.1 % linearity and 0.2 % hysteresis error. Furthermore, a nearly linear temperature behavior of manufactured prototypes with a TK <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> of up to 0.3 %/10 K and a TK <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> of up to 0.6 %/10 K is achieved. These results confirm that a proper strain transmission is ensured within the additively manufactured deformation elements, making them competitive with conventionally manufactured deformation elements. Thus, the disruptive manufacturing process introduced is suitable for fabricating structural integrated force sensors based on strain gauges.
Capacitive micromachined ultrasonic transducers (CMUTs) represent an accepted technology for ultrasonic transducers, while high bias voltage requirements and limited output pressure still need to be addressed. In this paper, we present a design for ultra-low-voltage operation with enhanced output pressure. Low voltages allow for good integrability and mobile applications, whereas higher output pressures improve the penetration depth and signal-to-noise ratio. The CMUT introduced has an ultra-thin gap (120 nm), small plate thickness (800 nm), and is supported by a non-flexural piston, stiffening the topside for improved average displacement, and thus higher output pressure. Three designs for low MHz operation are simulated and fabricated for comparison: bare plate, plate with small piston (34% plate coverage), and big piston (57%). The impact of the piston on the plate mechanics in terms of resonance and pull-in voltage are simulated with finite element method (FEM). Simulations are in good agreement with laser Doppler vibrometer and LCR-meter measurements. Further, the sound pressure output is characterized in immersion with a hydrophone. Pull-in voltages range from only 7.4 V to 25.0 V. Measurements in immersion with a pulse at 80% of the pull-in voltage present surface output pressures from 44.7 kPa to 502.1 kPa at 3.3 MHz to 4.2 MHz with a fractional bandwidth of up to 135%. This leads to an improvement in transmit sensitivity in pulsed (non-harmonic) driving from 7.8 kPa/V up to 24.8 kPa/V.
Bite force is an important characteristic of the masticatory systems functional state. Especially force asymmetries are potential indicators for malfunctions such as temporo-mandibular disorders or dysgnathia. By measuring bilaterally, i.e. simultaneously on the left and right side, it is possible to quantify asymmetries. Currently, there is a lack of bite force sensors combining a low measurement uncertainty (less than 5%) with the capability of measuring bilaterally. We present a 1000 N nominal bite force sensor with a height of 9 mm, which enables bilateral measurements over a wide range of mouth openings. The sensor is based on four load cells which are placed between two bite forks. The dimensions of these forks build upon anthropomorphic data of the human dental arch and are designed such that the bite force is transmitted by the two premolar and the first molar teeth. The developed sensor is characterized using a universal testing machine, resulting in a linearity error of ± 1.2% full scale. An asymmetric application of force is quantifiable with an error less than 4.1% from 100 N on. Therefore, the bite force sensor builds a promising basis for medical studies aiming at the support of diagnosis and therapy with objective data.
Piezoelectrets are artificial ferroelectrics that are produced from non-polar air-filled porous polymers by symmetry breaking through high-voltage-induced Paschen breakdown in air. A new strategy for three-layer polymer sandwiches is introduced by separating the electrical from the mechanical response. A 3D-printed grid of periodically spaced thermoplastic polyurethane (TPU) spacers and air channels was sandwiched between two thin fluoroethylene propylene (FEP) films. After corona charging, the air-filled sections acted as electroactive elements, while the ultra-soft TPU sections determined the mechanical stiffness. Due to the ultra-soft TPU sections, very high quasi-static (22,000 pC N-1) and dynamic (7500 pC N-1) d33 coefficients were achieved. The isothermal stability of the d33 coefficients showed a strong dependence on poling temperature. Furthermore, the thermally stimulated discharge currents revealed well-known instability of positive charge carriers in FEP, thereby offering the possibility of stabilization by high-temperature poling. The dependences of the dynamic d33 coefficient on seismic mass and acceleration showed high coefficients , even at accelerations approaching that of gravity. An advanced analytical model rationalizes the magnitude of the obtained quasi-static coefficients of the suggested structure indicating a potential for further optimization.

Lab head

Mario Kupnik
Department
  • Department of Electrical Engineering and Information Technology

Members (20)

Roland Werthschützky
  • Technische Universität Darmstadt
Christian Hatzfeld
  • Technische Universität Darmstadt
Baris Bayram
  • Middle East Technical University
Markus Hessinger
  • Technische Universität Darmstadt
Alexander Unger
  • Technische Universität Darmstadt
Gianni Allevato
  • Technische Universität Darmstadt
Jan Hinrichs
  • Technische Universität Darmstadt
G. M. Sessler
G. M. Sessler
  • Not confirmed yet
Xiaoqing Zhang
Xiaoqing Zhang
  • Not confirmed yet
Yuan Xue
Yuan Xue
  • Not confirmed yet
Bastian Latsch
Bastian Latsch
  • Not confirmed yet