Effect of the acoustic impedance in ultrasonic emitter transducers using digital modulations

Abstract

The existing technologies using electromagnetic waves or lasers are not very efficient due to the large attenuation in the aquatic environment. Ultrasound reveals a lower attenuation, and thus has been used in underwater long-distance communications. For high data-rates and real-time applications it is necessary to use frequencies in the MHz range, allowing communication distances of hundreds of meters with a delay of milliseconds. To achieve this goal, it is necessary to develop ultrasound transducers able to work at high frequencies and wideband, with suitable responses to digital modulations. This work shows how the acoustic impedance influences the performance of an ultrasonic emitter transducer when digital modulations are used and operating at frequencies between 100 kHz and 1 MHz. The study includes a Finite Element Method and a MATLAB/Simulink simulation with an experimental validation to evaluate two types of piezoelectric materials: one based on ceramics (high acoustic impedance) with a resonance design and the other based in polymer (low acoustic impedance) designed to optimize the performance when digital modulations are used. The transducers performance for Binary Amplitude Shift Keying, On-Off Keying, Binary Phase Shift Keying and Binary Frequency Shift Keying modulations with a 1 MHz carrier at 125 kbps baud rate are compared.

Wideband and Wide Beam Polyvinylidene Difluoride (PVDF) Acoustic Transducer for Broadband Underwater Communications

“…To ensure optimal operation, the force that the transducer can apply to the medium must be higher than the resulting acoustic wave force generated by the transducer deformation, otherwise, the piezoelectric material will not be able to produce a homogeneous displacement across the entire surface, generating acoustic waves with low amplitude and distortion. Through Equations (6)–(8), it is possible to obtain the maximum stack thickness [3]:ntp≤12πcρS33Ef…”

“…One of the major advantages of using low acoustic impedance is related to the high transfer of energy between the transducer and the medium, decreasing the resonance effect significantly. The water’s acoustic impedance is around 10 6 kg/m 2 s, the PVDF is 3.3 × 10 6 kg/m 2 s and the PZT is around 31.5 × 10 6 kg/m 2 s, which results in an internal reflection coefficient of 88% for PZT and around 28.7 % for PVDF [3], as presented in the Table 1. Table 1 allows for a comparative view of some characteristics of PZT-5H and PVDF which will be used in the simulations of Section 4.…”

“…Acoustic waves propagate more easily in an underwater environment [1] than the radio frequency (RF) and optic waves, but attenuation, ambient noise, Doppler Effect, low and variable sound speed, multipath and sound refraction (scattering) air bubbles and particles in suspension represents a considerable obstacle in underwater wireless communications [2]. One solution for higher data rates is to increase the carrier frequency [3]. However, increasing the frequency also will increase the attenuation and this represents a major drawback.…”

Development of High-accuracy Multi-degrees-of-freedom Indoor Ultrasonic Positioning Approach for Automated Guided Vehicles

“…Even if the ultrasonic signal strength reaches the threshold valve, uncertain wave loss cannot be avoided, causing an uncertain time delay and positioning error. (9)(10)(11) The waveform of an ultrasonic wave at the start time of receiving is shown in Fig. 1.…”

On the Shaping of a Short Signal at the Output of the Receiving Piezoelectric Transducer in the Radiation-Reception System

“…Currently, there is a large number of theoretical works devoted to the analysis of the operating modes of piezoelectric transducers. Among them, we can note, for example, [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. The number of works devoted to the study of piezoelectric transducers in the various fields of modern acoustics (biomedical research, hydroacoustics, flaw detection, etc.)…”