The specific challenge is thus to advance the state-of-the-art in the research of, and innovation in, new high performance lead-free piezoelectric materials for military underwater sensors applications to replace PZT, with a view to future phases of development and industrialization, leading to the prospective establishment of at least one European supply chain in this domain. 

New materials can also provide the opportunity to generate additional benefits, for example, enlarging the operational frequency bandwidth of sensors or source generators, improving duty cycle limitations or reducing the sensor size. These opportunities can upgrade the performance of the sensors and should hence be considered in the evaluation of materials and processes to be studied. 

The proposals should carry out research actions for the development of advanced lead-free piezoelectric materials with physical and piezoelectric properties, enabling the substitution of PZT in military underwater applications. These research actions may be extended to disruptive ceramic technology processes, such as 3D printing, and material engineering to enhance current piezoelectric properties. Moreover, increasing the technological maturity of lead-free piezoelectric materials for PZT substitutions in military underwater applications, and assessing these new materials for military underwater applications on representative test transducers could also be considered. Furthermore, increasing the manufacturing readiness level of promising lead-free piezoelectric materials and enabling one or more European industrial suppliers of lead-free piezoelectric materials for sonar transducers is a benefit of research activities in this area. In addition, the proposal must pay particular attention to potential synergies and complementarity to other ongoing R&D projects at national, multinational and on-going dual-use initiatives at European Union level, to avoid unnecessary duplication. 

The proposals must cover the following activities: 

• Generating knowledge, with in particular: 

• • The review of the scientific and industrial state-of-the-art lead-free piezoelectric materials and innovative synthesis processes
  • The identification of the relevant materials and processes
  • The identification of manufacturing technologies for lead-free piezoelectric materials
  • The review of the available operational specifications
  • The definition of a roadmap for materials and processes development 

• Integrating knowledge, with in particular:

• • The identification and assessment of EU industrial suppliers for the production of lead-free piezoelectric materials, including technology transfer. 

In addition, proposals may address: 

• Studies, with in particular: 

• • The formulation, synthesis, physical and structural characterization, piezoelectric characterization of new composition of lead-free piezoelectric material.
  • The study of innovative process alternatives to current ceramic machining and advanced sintering processes. 

• Design, with in particular:
  • The material specifications and advanced material characterization (piezoelectric tensor measurement) at sample and transducer levels.
  • The integration of parameters in transducer modelling, fabrication of representative transducer, which should be partially tested in real environmental conditions (e.g., assessment of linearity response with respect to stress and temperature, pressure and temperature cycling, endurance tests). 

Functional requirements 

The research to be conducted should meet the following functional requirements: 

– Replace PZT by lead-free suitable piezoelectric materials and assess their performance level, aspiring to have no loss in performance or even a potential gain, against the following (not exhaustive): 

• For Active transducers: maximal Source Level, matched electrical bandwidth, power density, efficiency, and more generally for high drive, temperature, stress and electric field handling, duty cycle, power linearity 
• For Passive transducers: signal to noise ratio, stress handling (depth rating/for deep-sea applications), frequency bandwidth, and sensitivity. 

– The choice of lead-free piezoelectric materials may differ depending on military underwater applications (passive or active transducers), and different use cases should be addressed. For both use cases (active, passive), the loss, or gain, versus actual PZT transducers will be addressed through a redesign phase of equivalent lead-free transducers. These lead-free transducers shall undergo a series of pre-qualification tests (not exhaustive): 

• Functional evaluation: source level, signal to noise ratio, sensitivity, frequency bandwidth, directivity, efficiency, linearity with power, endurance test 
• Environmental evaluation: pressure and temperature cycling, vibrations, shocks. 

Expected impact 

The research should contribute to: 

• reduction in pollution, which is a part of the European Green Deal, 
• Strong technological differentiators compared to non-European sonar suppliers, 
• Emergence of one or more European supply chains, 
• Patenting of new formulations and processes, 
• Compliance with REACH regulations on hazardous substances and obsolescence anticipation, 
• Sustainability components for underwater applications