Gerald Prof. Dr.-Ing. Gerlach

A Laser Intensity Modulation Method for the Evaluation of the Polarization State of Embedded Piezoceramics

In this work we evaluate the polarization state of PZT plates and rods embedded into low temperature co-fired ceramics, polymers and epoxy resin by measuring the pyroelectric current spectrum as a result of temperature oscillations generated by illuminating the sample surface with a square-wave-modulated laser beam. Changes in pyroelectric current amplitude and phase produced by small periodic perturbations around the equilibrium are related to the polarization state of the embedded PZT and to thermal losses governing the return of the system to the equilibrium. The latter allows evaluating the thermal contact of PZT with the embedding material by means of transfer functions H(iω) describing amplitude attenuation and phase lag at each modulation frequency.

Nondestructive Evaluation of Polarization in LTCC/PZT Piezoelectric Modules by Thermal Wave Methods

This work investigates the polarization behavior of low-temperature cofired ceramic (LTCC)/PZT sensor-actuator-modules fabricated by packaging of ceramic PZT plates between alumosilicate-corundum LTCC green layers and subsequent sintering at elevated temperatures. Polarization evaluation was done by applying the laser intensity modulation method (LIMM) where a thermal wave travelling into the ferroelectric PZT ceramic plate is generated by an intensity-modulated laser beam. The penetration depth of the thermal wave was varied with the modulation frequency allowing the separation of pyroelectric response contributions at different regions from the surface to the frequency-dependent penetration depth of the thermal wave.

Evaluation of polarization of embedded piezoelectrics by the thermal wave method

This work demonstrates the benefit of the thermal wave method for the evaluation of the polarization state and the polarization profile, respectively, of embedded piezoelectrics. Two types of samples were investigated: A Low Temperature Cofired Ceramics (LTCC)/PZT sensor-actuator and a Macro-Fiber Composite (MFC) actuator. At modulation frequencies below 10 Hz, the pyroelectric response was governed by thermal losses to the embedding layers. Here, the sample behavior was described by a harmonically heated piezoelectric plate exhibiting heat losses to the environment characterized by a thermal relaxation time.

Evaluation of the pyroelectric response of embedded piezoelectrics by means of a Nyquist plot

In this work, we evaluate the pyroelectric response of PZT plates and rods embedded in epoxy resin, low temperature cofired ceramics and polyamide by measuring the pyroelectric current spectrum originated by temperature oscillations generated by illuminating the sample surface with a square-wave-modulated laser beam. Transfer functions H(iω) describing amplitude attenuation and phase lag at each modulation frequency were analyzed by means of a Nyquist plot. Changes in pyroelectric current amplitude and phase produced by small periodic perturbations around the equilibrium are related to thermal losses governing the return of the system to the equilibrium. This allows evaluating the thermal contact of PZT with the embedding material.

Evaluation of the Polarization State of Integrated Piezoelectric Sensors and Actuators Using the Thermal Wave Method

In this work, we investigate the polarization state of a Low-Temperature-Cofired-Ceramics (LTCC)/PZT sensor-actuator and a Macro-Fiber Composite (MFC) actuator. An analytical solution for a 1-D thermal problem was derived for an embedded piezoelectric plate. Transient thermal analysis of the more complicated MFC actuator was performed using finite element modelling. At modulation frequencies below 10 Hz both modules are well described by a harmonically heated piezoelectric plate exhibiting heat losses to the environment.

Evaluation of the polarization state of piezofiber composites

In this work, the polarization state of piezofiber composites consisting of lead zirconate titanate (PZT) fibers embedded in epoxy resin was evaluated by means of thermal wave methods. The average pyroelectric coefficient was found to be one order of magnitude less than that of PZT ceramic plates. The pyroelectric current spectrum was recorded during irradiating the composites with an intensity-modulated laser beam. We obtained a homogeneous polarization of the samples and were able to detect differences in the polarization magnitude. Additionally, the thermal conductance at the interface between PZT and epoxy resin was estimated. The thermal diffusivity of the material was determined by three different methods: (i) by means of the frequency dependence of the pyroelectric coefficient, (ii) by the laser flash analysis, and (iii) by calculation based on a parallel connection model. Its value yielded approximately 0.4 mm2/s.