Mouser - White Papers

Mouser Electronics White Paper Polycrystalline ceramics that exhibit piezoelectric phenomena— called piezoceramics—are some of the most effective piezoelectric materials and can be cleverly designed to create a wide range of haptic feedback devices. Piezoceramics' ability to act as both haptic actuators and sensors can enable devices to produce vibrotactile or surface effects, depending on the application. This dual functionality allows piezoceramics to convert electrical energy into mechanical vibrations and vice versa. Key performance parameters for such piezoelectric haptic devices include the vibration frequency range, acceleration, force, displacement, response time, actuation and sensing electronics complexity, and power consumption. Other factors to consider are the size, weight, and cost of such devices, as this will also dictate their viability for specific haptic applications. Mechanisms of Vibration & Displacement A piezoelectric actuator experiences stress and physical deformation when exposed to an external electric field. This can be seen as an elongation or contraction of the shape and geometry of a piezoelectric material. Hence, a mechanical system can be designed around this electrically actuated material that allows for mass displacement, mechanical motion, and even vibration if a mass can be moved over adequate displacement fast enough to be perceived. A simple piezoelectric actuator is a cantilever, a floating beam of piezoelectric material that, when exposed to an electric field across the thickness of the material, causes the beam to bend along its length to achieve displacement of the beam's end. If this beam were weighted at the end, that weight could be rapidly displaced, which would induce vibrations along the beam and the support structure for the beam. More complex mechanical systems can be made that allow for a wide range of motion and vibration capabilities from piezoelectric actuators, which can also be used as sensors with the appropriate electronics. Enabling Technologies in Piezoelectric Devices The development of advanced enabling technologies has expanded the possibilities for piezoelectric devices, enhancing their functionality in haptic systems and beyond. Actuators Piezoelectric actuators, also called piezo actuators, can be fabricated in virtually any 3D arrangement with mechanical structures that allow for simple motion to complex mini-motor actuator systems. The most common types of piezo actuators are stack, shear, and bimorph. Stack actuators are stacks of thin piezoelectric disks, typically piezoceramics, that all expand as a function of the voltage applied. This piezo actuator can be used for simple linear displacement or combined with mechanical systems to enable vibration and even "amplified" displacement. A shear piezo actuator is also constructed as a stack, but when voltage is applied, its layers undergo shear deformation. Shear actuators are useful for precise XY positioning and, in combination with other piezo actuators, they can achieve XYZ positioning. A bimorph actuator is a piezo actuator in combination with a thin metallic disk and results in a simple and repeatable "amplified" motion. Given the degrees of freedom enabled by piezo actuator design, an extremely diverse range of piezo actuator types is available (Figure 5), each with advantages and applications. Sensors & Transducers Leveraging the inverse piezoelectric effect, piezo actuators and specifically designed piezo transducers can be used along with signal-conditioning electronics to create piezo sensors. A few common piezo sensors, such as accelerometers and force sensors, are widely used in everyday electronics and advanced scientific research applications. Piezoelectric ultrasonic sensors are also increasingly common in robotics, such as autonomous mobile robots (AMRs) used in the latest automated factory technology. These piezo sensors are often used to detect touch, pressure, and motion. Microcontrollers & Signal Processing Signal processing, driving, and control electronics are needed for piezo actuators and sensors to function. These electronics process and transmit the signals generated by piezo sensors and provide the necessary drive voltages for piezo actuators.

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