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PEtra: A Flexible and Open-Source PE Loop Tracer for Polymer Thin-Film Transducers

Marc-Andre Wessner, Federico Villani, Sofia Papa, Kirill Keller, Laura Ferrari, Francesco Greco, Luca Benini, Christoph Leitner

Abstract

Accurate characterization of ferroelectric properties in polymer piezoelectrics is critical for optimizing the performance of flexible and wearable ultrasound transducers, such as screen-printed PVDF devices. Standard charge measurement techniques, like the Sawyer-Tower circuit, often fall short when applied to ferroelectric polymers due to low-frequency leakage. In this work, we present PEtra, an open-source and versatile piezoelectric loop tracer. PEtra employs a transimpedance amplifier (LMP7721, TI) to convert picoampere-level currents into measurable voltages, covering a frequency range of 0.1 Hz to 5 Hz for a gain setting of 10^7 V/A, and 0.1 Hz to 200 Hz for gain settings between 10^3 V/A to 10^6 V/A (10-fold increments). We demonstrate through simulations and experimental validations that PEtra achieves a sensitivity down to 2 pA, effectively addressing the limitations of traditional charge measurement methods. Compared to the Sawyer-Tower circuit, PEtra directly amplifies currents without the need for a reference capacitor. As a result, it is less susceptible to leakage and can operate at lower frequencies, improving measurement accuracy and reliability. PEtra's design is fully open source, offering researchers and engineers a versatile tool to drive advancements in flexible PVDF transducer technology.

PEtra: A Flexible and Open-Source PE Loop Tracer for Polymer Thin-Film Transducers

Abstract

Accurate characterization of ferroelectric properties in polymer piezoelectrics is critical for optimizing the performance of flexible and wearable ultrasound transducers, such as screen-printed PVDF devices. Standard charge measurement techniques, like the Sawyer-Tower circuit, often fall short when applied to ferroelectric polymers due to low-frequency leakage. In this work, we present PEtra, an open-source and versatile piezoelectric loop tracer. PEtra employs a transimpedance amplifier (LMP7721, TI) to convert picoampere-level currents into measurable voltages, covering a frequency range of 0.1 Hz to 5 Hz for a gain setting of 10^7 V/A, and 0.1 Hz to 200 Hz for gain settings between 10^3 V/A to 10^6 V/A (10-fold increments). We demonstrate through simulations and experimental validations that PEtra achieves a sensitivity down to 2 pA, effectively addressing the limitations of traditional charge measurement methods. Compared to the Sawyer-Tower circuit, PEtra directly amplifies currents without the need for a reference capacitor. As a result, it is less susceptible to leakage and can operate at lower frequencies, improving measurement accuracy and reliability. PEtra's design is fully open source, offering researchers and engineers a versatile tool to drive advancements in flexible PVDF transducer technology.

Paper Structure

This paper contains 8 sections, 2 figures.

Table of Contents

  1. Introduction
  2. Materials and Methods
  3. Circuit Design
  4. Transducer Model
  5. Circuit Simulation and Optimization
  6. Circuit Characterization
  7. Results and Discussion
  8. Conclusion

Figures (2)

  • Figure 1: (a) shows a block diagram of the pe loop tracer in a transducer testing setup. A high-voltage source excites the transducer, generating a current amplified and measured by an oscilloscope. The light blue square details PEtra's input protection circuit (fuse and clipping diodes), selectable feedback network (resistors and low-pass capacitors), and the LDO connecting the TIA to the power supply. (b) shows the physical printed circuit board of PEtra with five marked interaction points. "Transducer In" indicates the current input and virtual ground for transducer characterization, while "Voltage Supply" powers the device. "Gain Switch" refers to the DIP switch for selecting gain, and "Oscilloscope Out" provides the signal output. The LMP7721 TIA, the core of PEtra, is also highlighted.
  • Figure 2: Device characterization results with the input current on the x-axis (logarithmic scale) and the SNR in decibels on the y-axis for each gain setting. Blue dots represent individual current measurements, while the red curve illustrates an exponential regression model extrapolating these currents into lower SNR regions.