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  • 1
    Electronic Resource
    Electronic Resource
    Thermal wave probing of pyroelectric distributions in the surface region of ferroelectric materials: A new method for the analysis (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5363-5370 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the investigation of polarization distributions in pyroelectric materials, the laser intensity modulation method (LIMM), which is based on thermal waves, is widely used. With this method, the sample under investigation is heated by the absorption of intensity modulated light at one surface, while the pyroelectric current is measured. The thermal excitation generates a thermal wave penetrating into the sample. The penetration depth is varied with the modulation frequency. A new procedure for the reconstruction of the polarization distribution from a measured pyroelectric current spectrum is introduced. This procedure is especially well suited for polarization probing near the sample surface. An approximation for the polarization distribution is calculated from a measured pyroelectric spectrum in a very simple and direct way, avoiding mathematical instabilities. The calculation can be performed during the measurement of a pyroelectric current spectrum. This makes LIMM an on-line procedure. The new technique of analysis is applied to the measurement of thin depolarized layers near the surface of homogeneously poled ferroelectric polymer films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351975
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  • 2
    Electronic Resource
    Electronic Resource
    A method for the measurement of the thermal, dielectric, and pyroelectric properties of thin pyroelectric films and their applications for integrated heat sensors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6361-6367 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method is described that enables the simultaneous or consecutive determination of the specific heat, the thermal diffusivity, the dielectric constant, and the pyroelectric coefficient of thin pyroelectric films. The sample is heated by the absorption of intensity modulated light at one surface. The pyroelectric current and the transient temperatures of the sample surfaces are recorded as a function of the modulation frequency of the chopped light. The transient temperature recording is performed via thin-film bolometers. Analysis procedures for the determination of the specific heat, the thermal diffusivity, and the spatially varying pyroelectric coefficient are introduced and discussed. A simulation of the performance of integrated pyroelectric ir sensors on silicon chips is performed by a coupling of the pyroelectric material to a heat sink. It is shown that the response of pyroelectric ir sensors integrated on silicon chips is influenced by heat wave interference effects. Experimental results are given using thin pyroelectric PVDF films. It is shown that the use of pyroelectric polymers for integrated pyroelectric sensors is a good choice, due to their low thermal conductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346882
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of signals from superposed relaxation processes (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2759-2767 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: System functions of many linear physical systems or autocorrelation functions of their output signals are often a sum of relaxator terms with different relaxation times and amplitudes. In the time domain a superposition of exponential decays e−γt is observed, while in the frequency domain a sum of relaxator terms of structure 1/(γ+iω) is measured. Thus, the response is either the Laplace transform of the system function or its Stieltjes transform, respectively. In both cases it is the task of an analyst to gain the relaxation times and weights from the measured signal. An exact reconstruction of the system function is limited by the noise, measuring time, and number of points measured. In this paper procedures for the approximate reconstruction of the system function are introduced. The equivalence of most of them is shown and their properties are discussed. An expression for the limit of resolution is derived for a given signal-to-noise ratio. The results are applicable to experimental data from various physical systems. For illustration the autocorrelation function of the light scattered from polymer solutions and the response of photoconductors are used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348634
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  • 4
    Electronic Resource
    Electronic Resource
    Piezo- and pyroelectricity of a polymer-foam space-charge electret (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4503-4511 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Charged closed-cell polypropylene polymer foams are highly sensitive and broadband piezoelectric materials with a quasistatic piezoelectric d33 coefficient about 250 pC/N and a dynamic d33 coefficient of 140 pC/N at 600 kHz. The piezoelectric coefficient is much larger than that of ferroelectric polymers, like polyvinylidene fluoride, and compares favorably with ferroelectric ceramics, such as lead zirconate titanate. The pyroelectric coefficient p3=0.25 μC/m2 K is small in comparison to ferroelectric polymers and ferroelectric ceramics. The low density, small pyroelectric coefficient and high piezoelectric sensitivity make charged polymer foams attractive for a wide range of sensor and transducer applications in acoustics, air-borne ultrasound, medical diagnostics, and nondestructive testing. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355719
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  • 5
    Electronic Resource
    Electronic Resource
    Air-gap capacitance cell for the investigation of porous or solvent containing dielectric films (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1845-1852 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An air-gap capacitance cell is presented, designed for temperature dependent dielectric spectroscopy on materials that cannot be contacted with surface electrodes: materials such as porous foams and membranes or solvent containing polymer resins. The capability of the system is demonstrated with measurements up to 300 °C, performed on a 60 μm porous poly(tetrafluoroethylene) (PTFE) and on a precured hybrid system of a porous PTFE, soaked with the low-k aromatic ether polymer: poly(1,1,1-triphenyl ethane perfluorocyclobutylether). The measurement system allows recording of the dielectric loss spectra with high resolution, barely influenced by thermal expansion or ionic conductivity. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1464655
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  • 6
    Electronic Resource
    Electronic Resource
    Poled polymers for sensors and photonic applications (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5531-5558 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A brief survey of the electrical and optical properties of poled polymer electrets for sensors and photonic applications is given. Semicrystalline ferroelectric polymers are highly suitable for piezo- and pyroelectric applications, while amorphous polymers containing molecular dipoles with acceptor and donor groups linked by delocalized π electrons (A-π-D) are interesting for photonic applications. The large variety of poling techniques, such as electrode, corona, electron-beam, and photothermal poling, is discussed in detail together with specifically developed poling techniques for ferroelectric or amorphous polymers. Methods for the experimental investigation of the polar order are based on the piezo-, and pyroelectric effect, birefringence, the electro-optical effect and second-harmonic generation. Newly developed thermal analysis techniques and dipole relaxation spectroscopies complement traditional techniques, such as thermally stimulated depolarization and broadband linear and nonlinear dielectric relaxation spectroscopy. The compatibility of polymers with semiconductor technology is illustrated with selected applications in hybrid integrated thermal and acoustical imaging devices, electro-optical modulators and second-harmonic generators. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363604
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  • 7
    Electronic Resource
    Electronic Resource
    Pyroelectrical investigation of charged and poled nonlinear optical polymers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5306-5315 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A compact and easy-to-use experimental set-up for pyroelectric investigations of poled nonlinear optical (NLO) polymers is reported. The arrangement allows for the investigation of the NLO dipole relaxation under isothermal or nonisothermal (e.g., linear heating of the polymer) conditions. Furthermore, polarization patterns in the plane of a polymer film and polarization profiles in its thickness direction can be measured in the same experimental set-up. In waveguide structures, it is possible to determine the thicknesses of an active guiding layer and of the claddings, if their thermal parameters are known. The isothermal pyroelectric relaxation data are discussed within the framework of phenomenological relaxation functions. It is found that they cannot be fitted with the stretched exponential function, a result which is in agreement with broadband dielectric-relaxation measurements. Pyroelectric experiments are the only method for investigations of all these problems in one and the same easy-to-use set-up.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355732
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  • 8
    Electronic Resource
    Electronic Resource
    Pulsed electrothermal technique for measuring the thermal diffusivity of dielectric films on conducting substrates (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6124-6128 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple technique for measuring the thermal diffusivity of dielectric films on thermally sinking substrates is proposed and demonstrated. It is an outgrowth of the thermal pulse technique for measuring charge and polarization profiles. The thermal diffusivity is derived from the transient electrical response induced by a thermal pulse applied to a dc voltage-biased sample. Because the response is proportional to the bias voltage, the signal-to-noise ratio is adjustable independently of the thermal pulse energy and may be made as large as required for determining the diffusivity with high precision. Measuring times of around 1 ms or shorter are sufficient for polymers with thicknesses up to 10 μm. Experimental results for two different polyimide films spin coated on crystalline silicon substrates are presented and discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363687
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  • 9
    Electronic Resource
    Electronic Resource
    Dielectric barrier microdischarges: Mechanism for the charging of cellular piezoelectric polymers (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5283-5287 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Charged closed-cell polymer foams have been found to be highly sensitive piezoelectric materials. Charging is shown to arise from dielectric barrier microdischarges within the voids of the cellular polymer. Above the threshold voltage for breakdown in the voids, the microdischarges are evidenced by light emission from the polymer, as well as by displacement-voltage hysteresis loops. Monitoring light emission during breakdown is shown to provide a quick check for the suitability of foams for piezoelectric applications. Additionally it allows for the visualization of micropores in foams in a nondestructive way. The piezoelectric response of the foam can be switched by applying dc-voltage pulses of alternating polarity above the breakdown threshold, thereby showing the feasibility of patterning the piezoelectric properties within the film plane. Although piezoelectric foams are nonferroelectric, the experiments prove similarities to ferroelectric materials with respect to hysteresis behavior, as well as a threshold (coercive) field for switching of the polarization and piezoelectricity. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459751
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  • 10
    Electronic Resource
    Electronic Resource
    Charge stability of pulsed-laser deposited polytetrafluoroethylene film electrets (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2941-2943 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pulsed-laser deposited (PLD) polytetrafluoroethylene (Teflon-PTFE) films from press-sintered powder targets are found to be highly crystalline, with spherulite sizes adjustable over more than one order of magnitude by suitable thermal annealing. Films with large spherulites show an excellent charge stability, comparable and even superior to commercially available Teflon-PTFE foils. PLD-PTFE enlarges the family of Teflon materials and may thus become interesting for potential miniaturized electret devices. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122637
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