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Mouser Electronics White Paper Haptic Feedback Design Haptic feedback design can be as simple as providing a control signal for a single vibration frequency in response to a touch or as complex as emulating the physical sensation of touching various textures. The complexity of the haptics depends on the advancement of the control algorithms of the haptic devices (including feedback), the haptic actuator's capabilities, and the haptic rendering's limitations. To provide real-time and realistic haptics, a haptic system needs to have a wide frequency bandwidth (~50Hz to 500Hz for vibrotactile feedback), very low latency time (milliseconds or fractions of a millisecond), and wide amplitude range for vibrotactile or force feedback. Such a system also needs to include feedback from the interface device to ensure the haptic response closely follows the control algorithms from the haptic rendering system simulating the virtual environments or objects. The most accurate control systems for this are closed- loop control systems, which use real-time feedback from sensors to adjust control algorithms for precise actuation of the haptic devices. Increasingly, machine learning (ML) and artificial intelligence (AI) algorithms are incorporated into haptic rendering and control algorithms to provide more realistic responses to virtual environments. Power Management for Piezoelectric Devices Many piezoelectric devices for haptic systems run on battery energy storage or energy-harvesting systems. This means that haptic devices in portable electronics, wearables, or medical devices often have a limited power supply capability. Consequently, these need high- performance piezoelectric actuators and sensors that are extremely energy efficient and can provide enhanced user experiences with minimal power draw. Advancements in battery and ultra-capacitor technologies mean that future piezoelectric systems built into portable devices may benefit from higher energy-density storage systems. Integrating Piezoelectric Devices with Other Systems Piezoelectric devices and audio systems are becoming essential for haptic feedback. The rise of AR/VR, the ubiquity of portable electronic devices, and the growing adoption of wearables for personal and medical use provide an expanding opportunity for piezoelectric technology. The latest piezoelectric technology can deliver better performance in much more efficient and compact packages than legacy vibrotactile, force feedback, and pressure sensors. This means that more capable haptic feedback devices and systems can be integrated into emerging technologies. Denser and more capable haptics can create a more realistic experience. As response time is critical for this real-world feel, this is another crucial area for optimizing piezoelectric actuators and sensors. Comparative Analysis and Future Trends Currently, the most widely used vibrotactile haptic devices are ERMs and LRAs. ERMs can only oscillate using a sine wave of a singular frequency. LRAs can be controlled by frequency and amplitude to some degree, but with a resonant frequency of around 150Hz to 300Hz, they have a limited range of operation to convey refined tactile information. On the other hand, piezo actuator elements can be designed to resonate at tens of kHz, far beyond the frequency that humans can sense (50Hz to 500Hz). As a result, piezo actuators can offer precise control across the entire effective touch frequency range, accurately replicating the tactile sensations of touch (Figure 10).

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