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• Sea Trial of the System

  Luicer's Lab • 07/03/2025 at 16:02 • 0 comments

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  Introduction

  Once the complete system was developed, it was time to test it at sea. The goal was to take the transducer and control board on a kayak and check its performance at different depths. For this, it was necessary to design a waterproof enclosure to protect the electronics and develop a mobile app that could communicate with the control board and display the data in real time.

  For this first test, a transducer with a 20 mm diameter and 4 mm thick piezoelectric crystal operating at 500 kHz was used. Although it is a small sensor working at a relatively high frequency, it was expected to reach depths of up to 15 meters.

  In the future, a larger transducer is planned to improve the system’s range and sensitivity.

  Waterproof Enclosure for the System

  The waterproof enclosure designed is shown below:

  The enclosure is completely waterproof and features an IP68 switch to activate the system. It also has a holder to secure the mobile phone.

  Inside, the electronics are arranged as follows:

  The control board is powered at 5 VDC by a DC/DC converter that steps down the voltage from two 18650 batteries connected in series.

  Kivy App

  An Android app was developed using the Kivy framework. The application communicates with the board’s HC-06 module via Bluetooth, using the Pyjnius library and the serial port profile.

  The app has two main screens. On the first, the Bluetooth connection is established and measurement parameters are entered, such as:

  • Ultrasound signal frequency
  • Number of pulses
  • Display scale
  • Measurement interval

  The second screen displays the measurement of ultrasound intensity as a function of depth, similar to a conventional fish finder.

  Sea Trial

  For the sea tests, the entire system was transported on a kayak and its operation was checked at different depths.

  The transducer was manually submerged in the water:

  The measurement results were as follows:

  As you can see, the system is able to display the seabed at depths between 0 and 15 meters, since the bottom line appears in the correct position. However, it was observed that the depth detection algorithm does not work optimally in this range, as it is tuned for shorter distances.

  Video

  Here you can watch a complete video showing the system in operation:

  Conclusions and Next Steps

  The sea trial was successful, demonstrating that the system can measure depth up to about 15 meters using a small, low-cost transducer.

  Looking ahead, the next steps will be:

  • Improve the depth calculation algorithm, as it is currently optimized for short distances and high sampling rates.
  • Design a larger transducer to increase sensitivity and radiated acoustic power. The current electronics, thanks to the use of a transformer and high-current MOSFETs, allow the use of more powerful transducers without issues.

  We will continue to share updates and improvements

• Modeling and Simulation of a Piezoelectric Transducer

  Luicer's Lab • 05/25/2025 at 08:33 • 0 comments

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  Introduction

  After developing a measurement system for the frequency response of piezoelectric transducers, a numerical model was implemented in LTspice for a 20 mm diameter transducer fabricated with a PZT4 ceramic. This model was calibrated using experimental data. Although some physical parameters were estimated due to lack of manufacturer data, the objective is to obtain a representative model that captures the main electromechanical behavior of the device, rather than an exact reproduction.

  The model is based on the adaptation by Kubov V.I. of the multilayer piezoelectric transducer model developed by J. Deventer, as described in “PSpice Simulation of Ultrasonic Systems” (2000, Jan van Deventer, Torbjorn Lofqvist). The adaptation is available at Ultrasonic_Model.

  Material properties for PZT4 were sourced from the manufacturer’s datasheet. Where data was unavailable, values were estimated to fit the measured response.

  LTspice, a widely adopted and freely available circuit simulation tool, was used for all simulations.

  Transducer Model

  The transducer model, operating in thickness mode, was implemented in LTspice as follows:

  The model includes the following components:

  • A PZT4 piezoelectric disk, 20 mm in diameter and 4 mm thick, with a thickness mode resonance at 500 kHz.
  • A cork back layer.
  • A PETG matching layer (the housing material), with a thickness of one quarter wavelength at the operating frequency.
  • The acoustic load of water, represented by the radiation impedance at the transducer interface.

  The density and sound velocity for each material were approximated from published literature.

  Simulation Results

  The simulated electrical impedance of the transducer, defined as the ratio of input voltage to current, is shown below:

  The output acoustic power delivered to water, for a 100 Vrms sinusoidal excitation, is depicted below. At 500 kHz, the radiated power is approximately 5 W (6.9 dBw):

  The simulation predicts a resonance frequency near 500 kHz, consistent with the design specifications.

  Experimental Validation

  A comparison between simulated and measured impedance is presented below (see characterization):

  The simulated and experimental results show good agreement after parameter adjustment. Note that the model only considers the thickness vibration mode; in practice, additional modes contribute to the measured impedance spectrum, accounting for some discrepancies.

  It is also important to note that the physical parameters of piezoelectric ceramics can vary significantly due to manufacturing tolerances, limiting the accuracy of the model.

  TVR Estimation

  The Transmit Voltage Response (TVR) is a key parameter, defined as the sound pressure level (SPL) at 1 meter from the transducer per 1 V input referred to a $1\mu Pa$

  , as a function of frequency. TVR is typically measured using calibrated hydrophones; in this study, it is estimated from the validated simulation model.

  The TVR is calculated as:

  $$TVR=10\cdot {\log }_{10}\left(\frac{P_{Zl}}{V_{in}^2}\right)+DI+170.08$$

  where $P_{Zl}$is the radiated acoustic power, $V_{in}$ is the input voltage, and $DI$ is the directivity index. For a 20 mm disk at 500 kHz, $DI\approx 26dB$.

  The simulated TVR as a function of frequency is shown below:

  Backlayer Material Study

  To evaluate the influence of the backlayer, simulations were performed using three materials:

  • Air (very low acoustic impedance)
  • Cork (low acoustic impedance)
  • Epoxy resin (medium acoustic impedance)

  The model configuration is illustrated below:

  The simulated radiated power for each backlayer material is shown:

  The corresponding TVR calculations are presented below:

  Results indicate that lower backlayer acoustic impedance increases radiated power and improves TVR.

  Conclusions and Future Work

  A representative LTspice model of a piezoelectric transducer has been developed and validated against experimental data. The model enables estimation of TVR and analysis of design parameters, such as backlayer...

  Read more »

• Frequency response measurement of a piezoelectric transducer

  Luicer's Lab • 02/25/2025 at 21:30 • 0 comments

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  Introduction

  Once several ultrasonic transducers have been built, it becomes necessary to analyse their behaviour to ensure that the piezoelectric crystals meet the declared specifications.

  A first feasible analysis is to measure their frequency response. To achieve this, the sensor must be excited at different frequencies while measuring its equivalent impedance. This will allow us to determine the most suitable frequencies for the transducer’s operation and the power it can transmit to water.

  In this post, two transducers will be analysed: one built using a 4 mm thick piezoelectric crystal with a theoretical resonance frequency of 500 kHz and another using a 10 mm thick piezoelectric crystal with a theoretical resonance frequency of 325 kHz.

  Transducer with a 20 mm diameter and 4 mm thick crystal:

  Transducer with a 50 mm diameter and 10 mm thick crystal:

  Diagram and Operation.

  The diagram of the system used to obtain the frequency response of sonar transducers is as follows:

  The custom sonar controller is used as a signal generator to excite the transducer. Then, a commercial oscilloscope is used to measure the voltage applied to the transducer. The transducer’s current is measured with the oscilloscope by reading the voltage across a serial resistor.

  Both the sonar controller and the oscilloscope are connected to a computer to generate the frequency sweep and calculate the impedance.

  Set up.

  The set up for taking the measurements is as follows:

  A graphical interface has been programmed in Python using the KIVY framework to automate the process. This software communicates via Bluetooth with the sonar controller board to generate the frequency sweep and through VISA with the oscilloscope to obtain the RMS values of voltage and current.

  The measurements are taken with the transducer submerged in a container of water.

  Results

  The results of the measurements are as follows:

  Transducer with a 20 mm diameter:

  Transducer with a 50 mm diameter.

  In both cases, two main peaks are observed: one at the thickness resonance frequency and another at the radial resonance frequency.

  • In the case of the first transducer, the thickness resonance frequency is 510 kHz, and the radial resonance frequency is 100 kHz.
  • In the case of the second transducer, the thickness resonance frequency is 325 kHz, and the radial resonance frequency is 40 kHz.

  These values match the manufacturer’s specifications and the theoretical calculations. Additionally, other resonance frequencies can be observed, depending on the construction of the piezoelectric crystal.

  An important result from the measurement is the resonance impedance of the transducers, which represents the radiation resistance of the transducer in water. From this value, the power transmitted by the transducer to the water can be calculated. The resonance impedance is the impedance at the resonance frequency, which can be approximated to the local minimum in the graph. For example:

  • In the case of exciting the 20 mm sensor with a 150 Vrms signal at 510 kHz, the transmitted power would be V ² /Zres=150 ² /200 =112,5 Watts
  • In the case of exciting the 50 mm sensor with a 150 Vrms signal at 325 kHz, the transmitted power would be V ² /Zres=150 ² /50 =450 Watts.

  The impedance resistance of the 50 mm transducer is higher than that of the 20 mm transducer, thus demonstrating that the larger sensor is capable of transmitting more ultrasonic power and, therefore, will have a greater range.

  Conclusions and Future Work.

  A system has been developed to obtain the frequency response of the sonar transducers. Based on these data, a model of the transducer can be created in the future, and the parameters of an equivalent circuit can be calculated.

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