The term 'haptic' originates from Greek and means' to grasp 'or' perceive '. In engineering, it refers to the technique of utilizing touch. In electronic systems, touch is commonly used to describe the force or tactile feedback mechanisms integrated into devices to enhance human-machine interaction.
From an engineering perspective, tactile feedback is typically achieved through mechanical actuators. These actuators can generate controlled vibrations, movements, or forces, including eccentric rotating mass (ERM) motors, linear resonant actuators (LRAs), and piezoelectric elements, which can simulate physical sensations in the real world such as pressure, weight, and surface texture. By combining tactile modalities, tactile technology supplements visual and auditory cues, making digital interfaces more intuitive and responsive. This is particularly important for applications that require precise input validation or immersive user experience, including virtual object manipulation.
The increasing demand for enhanced interaction has accelerated the application of tactile technology in multiple fields. From game controllers and touchscreens in consumer electronics to feedback controllers in car dashboards and surgical simulations in healthcare, haptic technology is becoming a key component of user experience and system functionality. This article will provide a detailed introduction to tactile feedback, including basic technologies and the advantages of using piezoelectric elements in tactile technology.
Common tactile actuator technologies
Tactile actuator is an electromechanical sensor that generates tactile sensations such as vibration, displacement, or pressure by converting electrical energy into mechanical motion. This actuator is the functional core of the tactile feedback system, which can achieve precise physical response in the user interface.
There are multiple actuation techniques available for tactile systems, each with its own unique working principle and performance characteristics:
Piezoelectric actuators utilize piezoelectric elements to generate mechanical deformation and oscillation under the action of an external electric field, thereby providing high-frequency, small displacement, and low delay feedback signals. (Please refer to the Same Sky piezoelectric element series).
The Eccentric Rotating Mass (ERM) motor consists of eccentric mass blocks installed on the DC motor shaft. When driving, the rotation of an unbalanced load usually produces low-frequency vibration forces. This technology is commonly used in mobile devices and low-cost applications.
Electroactive polymer (EAP) actuators use dielectric polymers that expand or contract under the action of an electric field. This type of material can generate smooth and flexible motion curves, but usually requires higher driving voltages.
The working principle of a linear resonant actuator (LRA) is to drive a magnetic block along a single axis using an alternating electromagnetic field. Compared to ERM, tuning the LRA to the resonance frequency can provide more efficient and faster response time directional feedback.
Voice coil actuator (VCA) utilizes the principle of Lorentz force, which means that a coil suspended in a magnetic field will move linearly under the action of current. VCA operates in broadband and can precisely control amplitude and frequency.
Each type of actuator requires a trade-off between frequency response, power efficiency, integration complexity, and feedback fidelity. The specific choice depends on the target application - whether it's subtle tactile cues in wearable devices, immersive touch in AR/VR interfaces, or strong feedback in car touchscreens.
Basic knowledge of piezoelectric components in tactile feedback
The piezoelectric effect refers to the generation of electric charges in certain materials when subjected to mechanical stress. Importantly, this phenomenon is reversible: when an electric field is applied to these materials, measurable mechanical deformation occurs. This reversible characteristic is the basic working principle of piezoelectric actuators used in tactile feedback systems.
In tactile applications, piezoelectric elements are mainly driven by reverse effects to generate micro scale displacement or vibration based on input voltage. Due to their bidirectional nature, these components can also be configured as force or pressure sensors, integrating dual functionality into touch sensitive interfaces or closed-loop systems.
Piezoelectric bending device is a common actuator structure composed of two piezoelectric layers with opposite polarizations bonded together. When a voltage is applied, one layer will expand while the other layer will contract, causing the structure to bend. This type of flexural displacement is very suitable for applications that require high precision and local movement.
In contrast, multi-layer piezoelectric elements stack many thin piezoelectric layers in parallel, significantly increasing mechanical output power while reducing operating voltage. In situations where greater force or displacement is required, such as in low-power embedded systems with large tactile surfaces or limited voltage amplitudes, these structures have significant advantages.
The deflection amplitude of piezoelectric elements is proportional to the input signal, thereby achieving high-resolution control of static positioning and dynamic vibration curves. Unlike many other types of actuators, piezoelectric elements can independently fine tune their position and amplitude, making them highly suitable for applications that require subtle signal differences or coding feedback.
Piezoelectric components' bending '
Figure 1: The "bending" of piezoelectric components. (Image source: Same Sky)
The advantages of piezoelectric elements in tactile design
The piezoelectric elements used in tactile feedback systems utilize the anti piezoelectric effect to generate rapid, high force mechanical displacement. The inherent material properties of piezoelectric elements typically result in response times of less than 1 millisecond, enabling real-time tactile feedback with minimal delay, which is crucial in applications that require high precision and instantaneous user response.
Unlike mass driven actuators such as ERM or LRA, piezoelectric devices do not rely on the inertia or resonance of suspension components. Therefore, piezoelectric devices have lower power consumption and faster stabilization time. These characteristics make piezoelectric devices particularly suitable for integration into battery powered or portable systems where energy efficiency and external dimensions are strictly limited.
The slender and flat geometric shape of piezoelectric elements facilitates compact mechanical integration. Therefore, engineers can embed multiple piezoelectric actuators in a single design to amplify tactile net output or achieve spatial distribution analysis of tactile signals on the user interface. In applications such as touchpads, wearable devices, and capacitive touch screens, these configurations can be used to simulate motion, directional cues, or pressure gradients.
Piezoelectric actuators have high configurability in terms of driving signal frequency, amplitude, and waveform, supporting various feedback textures and effects. In addition, the technology also offers a variety of mechanical and electrical forms, including customized diameters, thicknesses, rated voltages, and installation methods, providing tailored solutions for the automotive, medical, industrial, and consumer electronics markets.
Design considerations for piezoelectric components
Designing a tactile feedback system based on piezoelectric technology requires careful consideration of the following key factors:
Drive block: Match the push rod force with the inertial load to ensure effective vibration transmission.
Component type: Choose single-layer or multi-layer components based on voltage, displacement, and size limitations.
Mechanical envelope surface: Ensure that the actuator is installed within available space.
Activation axis: Determine the direction of motion to select the appropriate shape of the component set.
Power supply and driver: Match the system power supply with the capacitive load of the piezoelectric device, and select compatible drivers to achieve efficient excitation.
Frequency requirement: Determine the resonant frequency or required bandwidth of the component to obtain optimal tactile feedback.
Thermal conditions: Confirm that the operating temperature range of the piezoelectric element meets the environmental conditions of the system.