piezoelectric materials

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Piezocomposite Materials

MSI's piezocomposite materials are an excellent choice for sonar and ultrasound transducer applications. They provide high electro-mechanical energy coupling to water, air, plastics, composite materials and other low acoustic impedance media. Transducers made from piezocomposite are highly efficient and inherently broadband.

MSI injection molded piezocomposites offer the following advantages over conventional monolithic piezoelectric ceramics:

• Wider bandwidth (Q < 3 typically)
• Lower acoustic impedance
• Higher electromechanical coupling
• Higher receive and transmit response
• Higher efficiency over a broad bandwidth
• Rapid ring down
• Durability and shock resistance to Navy Class A requirements
• Lighter weight
• Single pieces available in large areas (up to 0.5m square)
• Conformable to curved structures
• Design flexibility:

Readily aperture shaded for beampattern control
Can be continuously curved without facets
Readily electroded in complex patterns

MSI's piezoelectric composites take two forms:

In these designations the first number refers to the mechanical connectivity of the active (piezoelectric ceramic) phase in the composite and the second number refers to the mechanical connectivity of the inactive (polymer) phase.

Piezocomposite materials can be made in a number of configurations to optimize their properties to your application. Important variable parameters are:

The key attribute of 1-3 piezocomposite that dominates its piezoelectric performance is its high piezoelectric coupling coefficient. The thickness mode piezoelectric coupling coefficient of 1-3 piezocomposite is determined by the length mode coupling of the ceramic rods that make up the active phase in the composite, and is typically in the range 0.6 to 0.7. The thickness mode coupling of the pure ceramic is much lower, typically less than 0.5, because the ceramic is stiffly coupled in all directions and energy is transmitted in three dimensions, whereas piezocomposite transmits and receives largely in one dimension. Since the efficiency of piezoelectric materials is approximately proportional to coupling coefficient squared, it follows that the efficiency of the piezocomposite is almost twice that of the piezoceramic from which it is made. The result is that piezocomposite, with its inherent electromechanical directionality, high coupling and broad bandwidth, enables transducer designers to send and receive the acoustic energy where it is most needed.

Most of the piezocomposites that MSI manufactures for transducer applications are of the 1-3 type. These are usually made using MSI's patented piezoceramic injection molding process is most cost-effective for large quantities, but MSI can also dice composite for very high frequencies or for small quantities of a special configuration requiring unique ceramic pillar dimensions and spacing.

MSI can supply injection molded or diced 1-3 piezocomposite materials with thickness mode resonance frequencies between 50kHz and 2MHz. Resonant transducer frequencies below 50kHz can be achieved with mass-loading techniques. MSI offers special piezocomposite materials capable of operating at static pressures as high as 200MPa (30 kpsi) and temperatures from -40 to > 150°C.

Injection Molded Piezoceramics

A key MSI core technology is its ability to manufacture the piezoceramic and piezocomposite materials needed for actuators and transducers by a patented ceramics injection-molding process. (MSI also holds other key patents in injection molded piezoelectric ceramics, including specialty actuation devices, tube arrays, piezocomposite materials and devices.)

Injection molding is widely used in the plastics industry for rapid mass production of complex shapes at low cost. MSI has adapted this technology to produce net shape piezoceramics, greatly facilitating the manufacturing of large volumes of complex ceramic parts having uniform part dimensions and uniform piezoelectric properties, without the need for expensive diamond grinding.

MSI's injection molding process utilizes a heated thermoplastic mix of lead zirconate titanate or lead magnesium niobate ceramic powder and a wax-based binder. The mix is injected as a liquid into a cooled cavity under pressure to form the ceramic component. The binder is removed from the injection-molded part by a low temperature heat treatment. The part is then carefully sintered to produce the final shape with minimal final machining, followed by electroding and poling to produce a functional piezoelectric ceramic component.

To ensure materials consistency, MSI formulates its own piezoelectric compositions. However, we can also injection mold externally manufactured ceramic powders for customers who need special materials. Injection molding consistently produces a high quality, high performance product. A key benefit is the uniformity of the ceramic, which has fewer voids than conventional dry-pressed ceramic. MSI's close control over the ceramic microstructure results in materials that have uniform grain size, thus enhancing their mechanical and dielectric breakdown strength under high drive conditions.

MSI operates its piezoelectric ceramic injection molding process with positive control of all the key molding and material variables. Material properties, molding conditions and process output are constantly monitored to insure that consistent product is produced. Documentation and traceability is maintained throughout the process to ensure quality from ceramic formulation through materials and transducer fabrication and testing.