Instrumentation and measurement
A Large Number of Options: Miniaturized Piezo Ceramics and their Applications
October 29, 2018
Piezoelectric materials can generate a charge shift when force is applied or when an electrical field changes the dimensions. These effects were discovered by Jacques and Pierre Curie at the end of the 19th century. They named it the “piezo effect”. The term is derived from the ancient Greek word “piezo” for “pressure” or “squeeze”. Piezoelectric materials are true jack-of-all-trades, because it is not only possible to use the piezo effect for manufacturing actuators but for sensor applications as well. Because piezoceramic components are available with very small dimension and in various shapes, it is possible to integrate and use them in a variety of applications.
The areas of application in actuator and sensor technology for piezo ceramics are wide ranging and cover a diversity of business sectors, because they achieve high dynamics with frequencies up to several thousand Hertz and can for example, generate ultrasound oscillation in gases or fluids. There are no mechanical components to limit resolution and also no mechanical wear because motion is based on crystalline solid-state effects. This makes it possible to make adaptive fine adjustments to miniaturized optical elements in semiconductor or silicon photonics applications, for example, lenses or exit areas of optical fibers as well as mirrors. This is also how miniaturized actuators and sensors are created for nanodispensing and fluidics or precision miniaturized displacement measuring. Because they are very compact and are very efficient in the space they are installed in, it is also possible to use them in drives for mobile devices or lab-on-a-chip technology.
Different Geometries, Dimensions, and Materials
The requirements that piezoceramic sensors or actuator elements also need to meet are as varied as the applications they are used for. For this reason, PI Ceramic offers piezoelectric components in many different versions – even lead-free – piezo materials, and in various different geometries such as disks, plates, tubes, cuboids or in virtually any special form and OEM customizations (image1). The different shapes can be manufactured with external dimensions smaller than 1 mm. Vacuum-compatible versions are also possible such as special, application-specific electrical connectors, integration of assemblies made available or developed by the user, as well as gluing and casting. As a result, there is virtually no limit to the application possibilities.
Piezo tubes for example, provide radial and axial displacement or, when controlled in segments, scanning motion on the XY level. They are manufactured to the tightest tolerances (0.05 mm) and can be manufactured in series with diameters as small as 0.8 mm. For example, they can be used as miniature scanners, in alignment, systems for controlling an optical signal or as a further example, used in medical endoscopes.
Piezo Tubes for Scanning Applications
An example of this is the innovative Scanning Fiber Endoscope (SFE) for large area, full-color imaging with a diameter of only 1 mm. This scanning fiber endoscope makes high-quality, laser-based video images possible with minimal invasive procedures, and can supply new results for biological research. The main component of this technology is a single optical waveguide that vibrates at mechanical resonance and in this way, scans RGB laser light onto the image. The resonant optical single-mode fiber is driven laterally by a tubular piezoelectric actuator in a very compact coaxial design (image 2). The lateral vibration movement can be modelled. During operation, the fiber moves in a spiral scan pattern. The application-specific actuator has a diameter of 0.45 mm and a length of only 4 mm. The electrical voltage that is applied to the SFE during operation is low because the tubular piezo corresponds electrically to a small capacitor. Typically, the voltage supplied during operation is lower than 20 V at 5.5 mW electrical power. Similar scanning applications are also possible with bending actuators that achieve relatively large displacements even over the smallest area.
Piezo Disks: Pumps for Microfluidics
It is possible to create high-performance drive solutions for piezoelectric materials that more than fulfil the requirements needed for microdispensing pumps. They work with high speeds and have short response time times and this makes high pumping frequencies and low rates possible. The variable strokes allow the dispensing process to be controlled with high precision. Because very different setups are possible, a customized solution can be found for virtually any task.
Researchers at the Fraunhofer Research Institution for Microsystems and Solid State Technologies (EMFT) are working on an active implant that will be able to regulate internal eye pressure both effectively and permanently. The implant consists of a micropump system, sensor-based pump control, an integrated battery pack for noncontact power supply as well as a telemetry module for transmitting the data. It can be applied directly onto the eyeball. A disk-shaped piezo element that is applied directly onto the silicon substrate is the driving force for the micropump (image 3). It generates the required linear motion exactly and on top of that, also adapts itself perfectly to the application environment.
Even with counterpressure, the pumping rates necessary for the therapy can be achieved by varying the switching frequencies or the amplitude of the piezo displacement via a corresponding controller. The pump in the eye implant has a maximum pumping rate of 30 microliters per second and, depending on the symptoms, can either wet the eye or pump out any aqueous humor.
Piezoceramic components are available in various designs, different – also lead-free – materials, and in a number of geometries such as disks, plates, tubes, cuboids or virtually any other desired shape and OEM customization (Image: PI)
The resonant optical single-mode fiber is driven laterally by a tubular piezoelectric actuator in a very compact coaxial design (Image: PI)
The driving force of the micropump is a high-dynamics disk-shaped piezo element that is applied directly to a silicon disk (Image: PI)
Annemarie Oesterle, Product Manager at PI Ceramic GmbH
PI Ceramic in Brief
PI Ceramic, a PI (Physik Instrumente in Karlsruhe) subsidiary located in Lederhose, Germany, is one of the global leaders for actuator and sensor piezo products. PI Ceramic currently employs over 320 staff, including no less than 70 engineers, in piezo research, development and manufacture. A broad range of expertise in the complex development and manufacturing process of functional ceramic components in conjunction with state-of-the-art equipment ensures high quality, flexibility and adherence to supply deadlines. The company supplies piezoceramic solutions for all important high-tech markets from industrial automation and the semiconductor industry, medical technology, mechanical engineering, and high-precision engineering to the aeronautics industry and the automotive sector.