Determination of the complex-valued elastic moduli of polymers by electrical impedance spectroscopy for ultrasound applications

Abstract

A method is presented for the determination of complex-valued compression and shear elastic moduli of polymers for ultrasound applications. The resulting values, which are scarcely reported in the literature, are found with uncertainties typically around 1% (real part) and 6% (imaginary part). The method involves a setup consisting of a cm-radius, mm-thick polymer ring glued concentrically to a disk-shaped piezoelectric transducer. The ultrasound electrical impedance spectrum of the transducer is computed numerically and fitted to measured values as an inverse problem in a wide frequency range, typically from 500 Hz to 5 MHz, both on and off resonance. The method was validated experimentally by ultrasonic through-transmission around 1.9 MHz. Experimentally, the method is arguably simple and low cost, and it is not limited to specific geometries and crystal symmetries. Moreover, by involving off-resonance frequencies, it allows for determining the imaginary parts of the elastic moduli, equivalent to attenuation coefficients. Finally, the method has no obvious frequency limitations before severe attenuation sets in above 100 MHz.

Constant-Power versus Constant-Voltage Actuation in Frequency Sweeps for Acoustofluidic Applications

“…Fit the Pz27 material parameters using ultrasound electrical impedance spectroscopy (UEIS), following the method described in Ref. [21]. 4.…”

“…The material parameters of the specific Pz27 transducer used in this study, were obtained by electrical impedance spectroscopy (UEIS), following the procedure described in Ref. [21], based on the measured Z(f ) of the unloaded transducer. The result is shown in Fig.…”

“…Numerical simulations were performed using both the fitted values, and the values for Pz27 given in Ref. [21]. The discrepancy between the two resulting spectra emphasizes the need of obtaining fitted material parameters for the specific transducer used in the study.…”

“…The values of the material parameters for the liquid, polystrene particles and glass capillary tube are taken from the literature. The material parameters for the glue layer and the piezoelectric transducer were obtained via ultrasound electrical impedance spectroscopy, as described in [21]. The material parameters used in the numerical simulations are summarized in Table 2.…”