Utilizing Piezoelectric Elements for Haptic Feedback

The term haptic originates from the Greek word meaning "to grasp" or "to perceive," and in engineering contexts, it refers to technologies that leverage the sense of touch. In electronic systems, haptics is commonly used to describe force or tactile feedback mechanisms integrated into devices to enhance human-machine interaction.

From an engineering standpoint, haptic feedback is typically realized through mechanical actuators that generate controlled vibrations, movements, or forces. These actuators—ranging from eccentric rotating mass (ERM) motors and linear resonant actuators (LRAs) to piezoelectric elements—simulate real-world physical sensations such as pressure, weight, and surface texture. By incorporating the tactile modality, haptics supplement visual and auditory cues, enabling more intuitive and responsive digital interfaces. This is particularly important for applications requiring precise input validation or immersive user experiences, including virtual object manipulation.

The increasing demand for enhanced interactivity has accelerated the adoption of haptic technologies across multiple sectors. From game controllers and touchscreens in consumer electronics to feedback-enabled controls in automotive dashboards and surgical simulation in healthcare, haptics is becoming a key component in both user experience and system functionality. This article will take a closer look at haptic feedback, including the underlying technologies and the benefits of using piezo elements in haptics.

Common haptic actuator technologies

Haptic actuators are electromechanical transducers that generate tactile sensations, such as vibration, displacement, or pressure, by converting electrical energy into mechanical motion. These actuators serve as the functional core of haptic feedback systems, enabling precise physical responses in user interfaces.

Several actuation technologies are employed in haptic systems, each with distinct operating principles and performance characteristics:

• Piezoelectric Actuators utilize piezo elements that mechanically deform and oscillate in response to an applied electric field, delivering high-frequency, low-displacement feedback with low latency. (See Same Sky’s lineup of piezo elements.)
• Eccentric Rotating Mass (ERM) Motors consist of an off-center mass mounted on a DC motor shaft. When driven, the rotation of the unbalanced load produces vibrational forces, typically at lower frequencies. These are common in mobile devices and low-cost applications.
• Electroactive Polymer (EAP) Actuators use dielectric polymers that expand or contract under an electric field. These materials can produce smooth, flexible movement profiles but often require high driving voltages.
• Linear Resonant Actuators (LRAs) operate by driving a magnetic mass along a single axis using alternating electromagnetic fields. Tuned to a resonant frequency, LRAs deliver more efficient, directional feedback with faster response times than ERMs.
• Voice Coil Actuators (VCAs) employ Lorentz-force principles, where a coil suspended in a magnetic field moves linearly in response to current. VCAs offer wide bandwidth operation and precise control over amplitude and frequency.

Each actuator type presents trade-offs in terms of frequency response, power efficiency, integration complexity, and feedback fidelity. Selection depends on the target application—whether it's subtle tactile cues in wearable devices, immersive haptics in AR/VR interfaces, or robust feedback in automotive touchscreens.

Piezoelectric element basics in haptic feedback

The piezoelectric effect refers to the generation of an electric charge in certain materials when subjected to mechanical stress. Importantly, this phenomenon is reversible: when an electric field is applied to these materials, they undergo measurable mechanical deformation. This reversible property is foundational to the operation of piezoelectric actuators used in haptic feedback systems.

In haptic applications, piezo elements are primarily driven by the inverse effect to produce micro-scale displacements or vibrations in response to an input voltage. Due to their bidirectional nature, these elements can also be configured as force or pressure sensors, allowing for dual-function integration in touch-sensitive interfaces or closed-loop systems.

One common actuator configuration is the piezo bender, which consists of two piezo layers bonded together with opposing polarization. When voltage is applied, one layer expands while the other contracts, causing the structure to bend. This flexural displacement is ideal for applications requiring high precision and localized movement.

In contrast, multilayer piezo elements stack numerous thin piezo layers in parallel, significantly increasing mechanical output while reducing the operating voltage. These structures are advantageous in scenarios where higher force or displacement is required, such as in larger haptic surfaces or low-power embedded systems with limited voltage headroom.

The deflection amplitude of a piezo element is directly proportional to the input signal, enabling high-resolution control over both static positioning and dynamic vibration profiles. Unlike many other actuator types, piezo elements support fine-grained modulation of position and amplitude independently, making them well-suited for applications where signal nuance or encoded feedback is critical.

Figure 1: The “bending” of a piezoelectric element. (Image source: Same Sky)

Piezo element benefits in haptics design

Piezoelectric elements used in haptic feedback systems capitalize on the inverse piezoelectric effect to generate rapid, high-force mechanical displacement. Their inherent material properties allow for response times typically under 1 millisecond, enabling real-time tactile feedback with minimal latency—critical in applications requiring high precision and instantaneous user response.

Unlike mass-driven actuators (e.g., ERMs or LRAs), piezo devices do not rely on inertia or resonance of a suspended element. As a result, they exhibit lower power consumption and faster settling times. These attributes make them particularly well-suited for integration into battery-operated or portable systems where energy efficiency and form factor are tightly constrained.

The slim, low-profile geometry of piezo elements facilitates compact mechanical integration. This allows engineers to embed multiple piezo actuators in a single design to amplify the net haptic output or deliver spatially resolved tactile signals across a user interface. Such configurations can be used to simulate motion, directional cues, or pressure gradients in applications like touchpads, wearable devices, and capacitive touchscreens.

Piezo actuators offer high configurability in terms of drive signal frequency, amplitude, and waveform, supporting a range of feedback textures and effects. In addition, the technology is available in diverse mechanical and electrical formats—including custom diameters, thicknesses, voltage ratings, and mounting styles—allowing for tailored solutions across automotive, medical, industrial, and consumer electronics markets.

Piezo element design considerations

Designing a piezo-based haptic feedback system requires careful consideration of several key factors:

• Driven Mass: Match actuator force to the inertial load to ensure effective vibration transmission.
• Element Type: Choose between single-layer or multilayer elements based on voltage, displacement, and size constraints.
• Mechanical Envelope: Ensure the actuator fits within the available space and mounting orientation.
• Actuation Axis: Define the direction of movement to select the appropriate element geometry.
• Power and Driver: Align the system’s power supply with the piezo’s capacitive load and select a compatible driver for efficient excitation.
• Frequency Requirements: Target the element’s resonant frequency or desired bandwidth for optimal tactile feedback.
• Thermal Conditions: Confirm the piezo element’s operating temperature range matches the system’s environmental conditions.

Summary

Integrating effective and user-friendly haptic feedback into a product demands careful evaluation of actuator performance, including vibration strength, response sensitivity, positional accuracy, footprint, and power efficiency. Piezoelectric elements are well-suited for these demands, offering precise, low-power operation across a wide range of conditions. Same Sky’s portfolio of piezo elements supports various sizes and configurations, making them a versatile solution for both tactile feedback and vibration sensing in modern electronic systems.