Audio Haptics: Technologies and Applications

Introduction

Haptic technology refers to creating a sense of touch through mechanical feedback, often by vibrations or forces. In audio haptics, this typically means using audio-frequency vibrations to provide tactile feedback that can be felt by a user. Traditionally, devices relied on visual displays or audible cues to convey information, but there is growing recognition that “sometimes, it just needs to be felt more than it needs to be heard.” By integrating haptic feedback, modern interfaces engage the sense of touch to enhance user experience across consumer electronics, automotive interfaces, medical simulators, and virtual/augmented reality systems. For example, a smartphone may vibrate when a notification arrives, or a car’s touchscreen might “click” under your finger when you press a virtual button – these are everyday instances of audio haptics at work.

Audio haptic actuators convert electrical signals (often the same kinds of signals that drive speakers) into mechanical vibrations that stimulate our skin’s touch receptors. Human skin is sensitive to vibrations roughly in the range of 10–500 Hz, with peak sensitivity around 150–300 Hz where specialized mechanoreceptors (Pacinian corpuscles) are most responsive. By generating vibrations in these frequency bands and with suitable intensity, haptic devices can effectively mimic the feel of taps, clicks, buzzes, or textured surfaces. Haptic feedback thus adds a “third dimension” to user interfaces, complementing visual and auditory feedback with tactile sensation.

Over the past decades, several electromechanical actuator technologies have been developed to deliver vibrotactile feedback. PUI Audio, a company traditionally known for audio components, expanded into haptics in 2022, reflecting the industry-wide rise in demand for tactile interfaces. PUI’s lineup now includes a range of haptic actuators – from simple vibrating motors to advanced resonant and piezoelectric devices – “ensuring that when a tactile response or alert is necessary it can be felt clearly.” In the sections below, we delve into all the major technologies relevant to audio haptics, with a focus on those in PUI’s portfolio, and discuss how each works and where it is applied.

Eccentric Rotating Mass (ERM) Actuators

Exploded view of an Eccentric Rotating Mass (ERM) vibration motor, showing an off-center weighted mass attached to the motor’s rotor. When the rotor spins, the uneven weight creates centrifugal force that causes the motor to vibrate, producing the characteristic “buzz” or rumble of an ERM device.

The Eccentric Rotating Mass (ERM) actuator is one of the oldest and simplest haptic technologies. It consists of a small DC motor with a weight mounted off-center on its shaft. As the motor spins the off-axis mass, it generates an oscillating centrifugal force – essentially a rapid sequence of tiny “jerks” as the heavy side of the rotor swings around. This causes the entire device (and whatever it’s attached to) to vibrate. The vibration frequency is determined by the rotation speed of the motor, which in turn depends on the applied voltage. Higher voltage spins the motor faster, increasing the vibration frequency and intensity. ERM actuators are known for producing a rumbling effect: a broadband, somewhat rough vibration that is excellent for getting the user’s attention even if it isn’t very precise.

ERM vibration motors were the workhorse of early mobile phone and pager alerts. They are inexpensive, easy to drive (a simple DC voltage or PWM will suffice), and reasonably strong in terms of absolute vibration force. Their simplicity, however, comes with some trade-offs. Because the motor must overcome inertia, there is a ramp-up time and coast-down time – the vibration doesn’t start and stop instantaneously. Typical ERM motors might take on the order of tens of milliseconds to spin up or change speed, which means you can feel a slight lag or “motorboating” effect especially at lower frequencies. This makes ERMs less ideal for very crisp, short haptic pulses or complex vibration patterns. Additionally, the vibrations are not easily controllable in frequency content – they tend to produce a mix of frequencies corresponding to the rotation and its harmonics rather than a single, clean tone. In practice, designers vary the drive voltage to modulate intensity, rather than trying to play specific vibration “notes” as one might with a speaker.

Despite these limitations, ERMs are effective for simple alerts where a general buzz is sufficient. They remain widely used in devices like low-end cell phones, smart watches or fitness bands (for basic buzz notifications), gaming controllers (the classic “rumble pack” feel), and many hand-held industrial or medical devices that need a vibration alert. PUI Audio’s haptic portfolio includes numerous ERM actuators in different sizes (as small as 6 mm diameter) and form factors. These range from coin-shaped vibrating discs to cylinder motors with eccentric weights, available with mounting options like leadwires, solder pads, or spring contacts. Designers can choose an ERM motor based on the required vibration strength and available space; for example, a larger ERM with a heavier offset weight can produce a stronger rumble, but takes more current and physical volume. Overall, ERM actuators provide a simple, cost-effective solution when precise timing or frequency shaping of the haptic feedback is not critical but a “noticeable tactile feedback is desired.”

Key Characteristics of ERM Haptics:

• Mechanism: DC motor with an off-center mass; vibration frequency and strength increase with rotation speed. 
• Strengths: Very simple to implement and drive (direct voltage control), inexpensive, and capable of a strong “buzzing” vibration feel over a range of frequencies (determined by motor RPM). Great for general alerting. 
• Limitations: Slower response (tens of milliseconds spin-up/down) and less precise control – cannot produce very sharp clicks or complex patterns easily. Vibration intensity is tied to speed, and changing frequency quickly is difficult. Also, ERMs can generate audible noise (whirring sound) due to the motor. 
• Typical Applications: Basic vibration alerts in phones, wearables, game controllers, and indicators where a coarse but unmistakable vibration is needed. Often used when “precise vibration patterns aren’t critical but a noticeable tactile feedback is desired.”

Linear Resonant Actuators (LRA)

Exploded view of a coin-style Linear Resonant Actuator (LRA). An LRA contains a moving mass attached to a spring and a voice coil. When an AC signal drives the coil at the LRA’s resonant frequency (typically around 100–200 Hz), the mass oscillates up and down, producing a strong vibration in a single axis.

The Linear Resonant Actuator (LRA) is a more advanced type of haptic actuator, notable for its efficiency and quick response. Internally, an LRA resembles a tiny speaker that has had its diaphragm removed. It usually consists of a movable mass (often a magnet) attached to a spring, with a voice coil assembly that can drive the mass back and forth. When an alternating current drives the coil, it creates a magnetic field that makes the mass oscillate along one axis (hence “linear”). The key is that the mass-spring system is tuned to a specific resonant frequency, often in the range of ~150 Hz (common in many LRAs). If the drive signal matches that frequency, the LRA produces a very strong vibration for relatively little power, much like a swing that’s being pushed at just the right interval.

Because LRAs leverage resonance, they respond quickly and with high intensity to the correct drive frequency. There is effectively no “spin-up” delay as in an ERM – “the user will feel a vibration as soon as the coil is excited, and the mass moves”. This means LRAs can create sharp, well-defined haptic pulses (for example, a crisp click or a short buzz) with minimal latency. It also means they are more power-efficient: you don’t waste energy outside the resonance. LRAs are typically driven by specialized haptic driver ICs that output an AC waveform at the resonant frequency; these drivers often include features to auto-tune or track the resonance to ensure maximum vibration strength. By varying the amplitude of the AC drive, one can modulate the vibration strength precisely, and by using bursts or patterns of pulses, very nuanced tactile effects can be achieved. Indeed, LRAs enable “high-resolution, responsive vibration patterns to deliver information to the user”, and designers often craft custom vibration sequences (different pulse counts, spacings, and intensities) to convey different alerts or UI cues.

However, LRAs have a narrow bandwidth of optimal operation. They generate the strongest feedback only near their resonant frequency. Driving them at significantly lower or higher frequencies results in much weaker vibrations. In practice, most LRA-based feedback uses the fixed resonant frequency (or one of a couple of resonant modes) and varies the amplitude and duration rather than the frequency. This is acceptable for most user-interface haptics, which rely on patterns of pulses (on/off modulation) more than distinct frequency tones. Another consideration is that LRAs require an AC drive; unlike ERMs, you cannot simply hook up a DC battery – a driver circuit is needed to provide an oscillating signal (often a boosted voltage in the tens of volts peak-to-peak). Despite these considerations, the benefits of LRAs have made them extremely popular in today’s compact devices.

LRAs “fit into some of the smallest form factors available for haptic actuators” and are found in many smartphones, smartwatches, fitness bands, and other wearables where conserving power and space is crucial. They provide a cleaner and more immediate tactile response for things like touch-screen virtual buttons, keyboard typing feedback, or notifications, without draining a battery quickly. PUI Audio’s introduction of haptics included LRA offerings recognizing this demand. Notably, PUI developed the industry’s first surface-mount LRA: the HD-LA1307-SM, a 13 mm × 13 mm device with a patent-pending design that can be solder-reflowed onto circuit boards. This LRA delivers up to 1.8 G of acceleration at 154 Hz (its resonant frequency) in a sealed, IP-rated package. The ability to pick-and-place an LRA in manufacturing like any other component is a significant innovation, simplifying integration into consumer electronics. Applications of such an LRA range from handheld virtual reality controllers and gaming consoles to medical simulators and industrial or consumer touch interfaces, where immediate and immersive feedback is needed. In these scenarios, the LRA’s fast and subtle vibrations can be synchronized with on-screen events or audio cues – for example, enhancing a VR experience by providing a tactile thump when an object is “grabbed,” or confirming a button selection on a touchscreen with a sharp click feeling.

Importantly, haptic designers often pair LRA feedback with other sensory stimuli. Research and industry practice have found that vibrations are “often supplementary to another stimulus, like audio effects or information on the screen, but also may be used as an independent source of information”. In a smartphone, for instance, a soft tick sound might play in tandem with an LRA vibration when a key is tapped, heightening the perception of a physical button press. LRAs, with their responsiveness, excel at these multisensory, high-fidelity feedback tasks.

Key Characteristics of LRA Haptics:

• Mechanism: Moving mass on a spring (magnet+coil) oscillating along one axis. Optimized to vibrate strongest at a fixed resonant frequency (typically in the 100–200 Hz range). Must be driven by an AC signal at that frequency for peak performance. 
• Strengths: Immediate response with no ramp-up latency, highly power-efficient at resonance, and capable of very crisp, high-definition vibration patterns. Compact form factors (small and thin), making LRAs ideal for phones and wearables. They provide a “direct, linear response” to drive signals, allowing precise control of vibration intensity. 
• Limitations: Narrow frequency range of strong operation – essentially a one-note instrument (vibration strength drops off if not at the resonant freq). Requires an AC driver (can’t be driven by DC directly), and typically provides lower amplitude force outside its resonance. Also, if an LRA is driven continuously at resonance, the fixed frequency might make the tactile sensation less varied (mitigated by pattern design). 
• Typical Applications: Nearly all modern smartphones and smartwatches use LRAs or similar linear actuators for haptics due to their efficiency and fast response. They are used for touch feedback (screen keyboards, UI confirmation clicks), notifications (short buzzes), and interactive feedback in devices like VR controllers. LRAs are preferred in “compact and power-sensitive applications like wearables and smartphones” where a high-quality tactile experience is needed without big motors. 

Voice Coil Actuators (VCA)

Diagram of a Voice Coil Actuator (VCA) for haptics. By increasing the size of the coil, magnet, and moving mass (compared to an LRA), VCAs can deliver stronger forces over a wider frequency range. They operate on the same principle as a loudspeaker’s voice coil motor, but without a diaphragm to produce sound.

A Voice Coil Actuator (VCA) – also sometimes called a voice coil motor (VCM) in this context – is essentially a scaled-up linear actuator that operates on the same electromagnetic principle as an LRA, but isn’t narrowly tuned to a single frequency. In a VCA, a voice coil moves a mass or a shaft within a magnetic field, just like how a loudspeaker coil moves a speaker cone. The difference is that a haptic VCA usually doesn’t have a cone or diaphragm attached; the “payload” is the mass itself or whatever interface you want to shake (for instance, a touchpanel or a larger surface). Because it’s not relying on resonance, a VCA can be driven with arbitrary waveforms across a broad frequency spectrum – it can produce low-frequency rumbles and higher-frequency textures or clicks, up to the limits of its mechanical and magnetic design.

VCAs bring haptic feedback “to the next level” by providing more substantial force and a more realistic feel of impacts, clicks, and vibrations. They tend to be larger and heavier than LRAs, but this larger moving mass means they can impart a stronger impulse. For example, a small linear resonant vibrator might give you a gentle tick, whereas a larger voice coil actuator could produce a sharp jolt or a thump you might even hear slightly. In fact, one notable aspect of VCAs is their ability to replicate some auditory effects alongside tactile feedback. A powerful VCA vibrating at low frequencies can be felt and heard (like a tiny speaker); this can enrich the multisensory experience – think of a simulation where you not only feel a “boom” but also faintly hear it. This coupling of sound and feel can make the feedback more immersive.

Because VCAs are not constrained to one frequency, designers can program complex haptic feedback profiles. For instance, a VCA could output a short 100 Hz burst followed immediately by a 300 Hz buzz, creating a combined tactile sensation of a “click” followed by a texture, which might simulate flipping a toggle switch that has some mechanical detent. Such control is harder to achieve on an LRA which wants to oscillate mostly at one frequency. Wide-frequency bandwidth also allows VCAs to scale up for larger systems. In automotive or industrial applications, a VCA (sometimes in the form of a solenoid or linear motor) can be used to provide haptic feedback on large surfaces like car touchscreens or control panels. For example, some automotive touch displays use electromagnetic linear actuators to make the whole screen vibrate with a distinct thunk, simulating a button press – these actuators must be strong enough to move a mass like a display and usually operate at a resonance of the assembly, but can cover wide bandwidth for different effects.

The trade-off for VCAs’ performance is generally size and power. They tend to consume more current and require more space compared to LRAs or piezos for an equivalent level of vibration. “This increased capability comes at the cost of higher power consumption,” as designers must account for battery or power budgets when using VCAs. Additionally, larger moving parts can mean more mechanical noise or wear (though still usually quite durable). In portable devices, only premium smartphones or tablets have sometimes used larger linear actuators (for instance, Apple’s “Taptic Engine” is effectively a type of voice-coil linear actuator, designed to give a wider range of tactile effects than a tiny resonant buzzer). These deliver superb haptic quality – crisp and strong – but occupy more internal space and are costlier. Console game controllers historically used simple ERM motors for rumble, but newer designs (like the PlayStation 5’s adaptive triggers and advanced rumble) use voice-coil actuators to produce a richer variety of feedback, from the crunch of gravel to the tension of a trigger pull. Those implementations show how VCAs can greatly enhance realism in interactive experiences by virtue of their dynamic range.

PUI Audio’s haptic category includes Voice Coil Actuators up to 25–32 mm in size, indicating their focus on providing substantial feedback. These devices can deliver multiple G’s of acceleration and are suited for applications like larger touch interfaces or peripherals. For instance, a PUI VCA could be embedded in a heavy control knob or in a vehicle’s center stack display to give that strong tactile confirmation to the user. In designing with VCAs, engineers often leverage the fact that “LRAs and VCAs operate best at specific frequencies” (they still have resonant modes), but unlike LRAs, VCAs can be driven off-resonance to cover a broader operational band. Proper control algorithms (and sometimes closed-loop feedback) can ensure the actuator hits the desired acceleration and timing. Drivers for VCAs are usually more akin to audio amplifiers, delivering an analog or PWM-driven waveform into the low-impedance voice coil.

Key Characteristics of VCA Haptics:

• Mechanism: An electromagnetic voice-coil motor moving a mass or an interface. Essentially a direct-drive linear motor for haptics, not tied to one resonant frequency (though it will have resonances). Often larger mass and stroke than LRAs. 
• Strengths: Much stronger vibration output and more “realistic” tactile feel, with the ability to cover a wide frequency range and even output complex vibration profiles (multiple tones or changing frequencies) simultaneously. Can provide both low-frequency rumble and higher-frequency texture, enriching multisensory feedback. Fast response (though an LRA at resonance can match response time, a VCA can be fast across its range). Good for driving heavy loads (e.g., whole panels or larger equipment feedback). 
• Limitations: Larger physical size and higher power consumption than other actuator types for equivalent output. They generate the strongest vibrations near their own resonant frequency and require more current to produce high forces at other frequencies (so efficiency is lower outside resonance). Design complexity and cost are higher, and they may need robust mounting due to the stronger reactive forces. 
• Typical Applications: High-end and demanding haptics use cases – gaming controllers, VR haptic modules, automotive touchscreens, simulated controls, and premium smartphones or trackpads – where rich and powerful feedback is desired. In automotive, for example, linear actuators (solenoid-based) are used to give convincing feedback on large displays with only ~3 ms latency. In VR/AR, a VCA can simulate impacts or textured vibrations that an LRA cannot. They are also seen in professional simulators (flight or surgical simulators) to render realistic tactile cues. Essentially, VCAs fill roles where smaller actuators aren’t enough and a broad spectrum of haptic output is needed. 

Piezoelectric Actuators

Piezoelectric actuators represent a different approach to audio haptics – instead of electromagnetic coils and moving masses, they use the deformation of piezoelectric materials to create vibrations. When a voltage is applied to a piezoelectric ceramic element, it mechanically deforms (expands, contracts, or bends, depending on the design). These tiny motions can occur very rapidly and with extremely low power consumption, making piezo actuators ideal for high-speed and high-frequency haptic feedback. Typically, piezo haptic actuators come in the form of thin plates or discs (often laminated in a unimorph or bimorph structure). For example, a common design is a piezo bender: a piezo ceramic bonded to a metal substrate. As the piezo tries to elongate or contract with voltage, the differing expansion between the layers causes the device to bend. By driving it with an AC signal, the bender flexes up and down, generating vibrations. Piezo actuators can also be designed as small ultrasonic diaphragms or tactile pixels in arrays.

One of the standout advantages of piezo actuators is their ultra-thin profile. They can be literally paper-thin – on the order of 0.2–0.5 mm in thickness for many devices. This flat form factor allows integration in places where an LRA or VCA motor would never fit. For instance, behind a smartphone display or a wearable’s screen, you can place a piezo film to create localized haptic zones. Piezo actuators also have no moving parts in the traditional sense (no magnetic mass flying around); this means virtually no mechanical wear and extremely long lifetimes. They are silent in operation (except for any sound from the vibrating surface itself) and very lightweight.

In terms of performance, piezo actuators are incredibly fast – they can react in under a millisecond, far faster than any motor-based solution. They can also operate across a wide frequency range, from a few hertz up into ultrasonic frequencies. In fact, piezo elements are what drive ultrasonic haptics (more on that in a later section). Within the human tactile band, piezos can generate a variety of effects: a strong high-frequency (~200–300 Hz) vibration for texture, or a low-frequency (50–100 Hz) buzz for alerts, or even audible clicks if driven in the audio range. This broad bandwidth and speed means they can create very crisp, short impulses – for example, simulating the sharp click of a button or the ticking of a rotary dial with fine resolution. They are also extremely energy-efficient; the piezo only draws current when changing state (to charge or discharge its capacitance), and maintaining a vibration at resonance can be done with minimal continuous power. This is why piezos are touted for battery-powered devices that need frequent haptic feedback without draining the battery.

However, piezo actuators come with their own challenges. The displacement (motion amplitude) of piezo elements is generally small, on the order of microns. This means the raw movement and force is less pronounced than what you might get from a magnetic actuator of comparable size. In practical terms, a single thin piezo patch might not feel as “strong” to a user as a larger LRA or ERM, especially in free air. To get a noticeable effect, piezos are often coupled to a surface or structure – for example, glued to the back of a touchscreen so that their tiny bending movement causes the whole glass to vibrate, effectively amplifying the feel. Even then, the tactile sensation from piezos can be more subtle; one article notes that “the feedback is less pronounced than with the other technologies” (ERM or linear motor) when using a piezo on a display, though it can still be effective. Another implication of the small displacement is that higher drive voltages are required to get sufficient movement. It’s common for piezo haptic drivers to use 30 V, 50 V, or even higher peak voltages. As one industry source points out, piezo actuators often need at least around 24 V to operate and more to maximize effect. This necessitates a step-up driver circuit (a boost converter feeding an amplifier), which adds complexity. Nonetheless, driver ICs for piezo haptics (from companies like TI, Boréas, TDK, etc.) are available and optimize the waveform to get strong kick from the piezo without excessive ringing.

Piezo actuators have become especially important in automotive and appliance interfaces, where space is tight and reliability must be high. Modern cars with touchscreens and touch surfaces use piezo haptics to reintroduce tactility – the piezos can make a flat panel feel like it has clicking buttons, helping drivers keep eyes on the road. Piezos’ fast response (a few milliseconds) means the vibration can be synchronized perfectly with the user’s touch, avoiding that “artificial lag” that slower motors have (e.g., an ERM might feel a bit delayed). PUI Audio offers a range of piezo actuators in their haptics lineup, with devices ranging roughly from 12 mm to 27 mm in size – these likely correspond to small benders that can be embedded in various equipment. Such piezo haptic elements are ideal for creating localized feedback on touch surfaces or even for adding a gentle tap/knock sensation in lightweight devices.

An interesting attribute of piezo elements is that they are bidirectional: they can also act as sensors. When you press or bend a piezo, it generates a voltage (the piezoelectric effect in reverse). This means a piezo haptic element can double as a force or touch sensor, detecting how hard a user is pressing. Some systems take advantage of this; for instance, a piezo under a trackpad can detect a hard press and then provide a click feedback in response – using the same element for input and output. In automotive touchscreens, piezos have been used not only to provide feedback but also to measure the user’s push, enabling features like press harder to select or variable resistance. According to one analysis, in a car haptic panel a “greater pressure on the display generates a greater voltage” from the piezo, which could be used to trigger different responses, like adjusting volume faster when you press harder. While this capability is intriguing, implementing it adds complexity and is still emerging. Nonetheless, it showcases the versatility of piezo actuators in human-machine interfaces.

Key Characteristics of Piezo Haptics:

• Mechanism: Relies on the piezoelectric effect – voltage induces strain in a crystal/ceramic material. Often implemented as flat bender elements that flex when driven with AC signals. No moving magnetic parts; purely solid-state vibration. 
• Strengths: Extremely thin and compact (can be as thin as 0.2–0.5 mm), making them easy to embed in tight spaces like displays or wearables. Very fast response (sub-millisecond) and capable of high-frequency vibrations for fine textures. Low power consumption: highly energy-efficient for short pulses or sustained vibrations. Long lifespan due to no wear-out parts. Can cover a broad frequency range with one device, including ultrasonic (enabling exotic effects like friction modulation on touchscreens). 
• Limitations: Lower output displacement and force – the vibration may be weaker or more subtle compared to an equivalently sized electromagnetic actuator. Often needs mechanical amplification (coupling to a larger surface) to be effective. High drive voltage requirements (dozens of volts) meaning more complex driver circuits and safety considerations. Additionally, while thin, the mounting of piezos must be done carefully (bonding to surfaces) to get consistent results. Piezo actuators also typically provide localized feedback; making a whole device vibrate strongly with piezos might require multiple units or larger piezos (which can get expensive). 
• Typical Applications: Automotive touchscreens and controls (to simulate button clicks on flat panels, improving safety by allowing “eyes-free” operation), consumer electronics like smartphones (some devices have used piezo actuators under screens or in flat backs for haptics), laptops trackpads (certain designs use piezo for the click sensation), wearable displays, and ultra-thin devices where ERM/LRA can’t fit. Also used in specialty devices: for instance, Braille displays or tactile tablets can use an array of tiny piezo pins, and ultrasonic mid-air haptic arrays use piezo ultrasonic transducers. In general, piezo haptics are chosen when “precise, localized feedback” is needed in a slim form factor, especially if the device can accommodate the high-voltage driver. 

Driving Haptics Actuators

ERM actuators are simple to drive, but performance and control granularity depend on the circuit implementation.

1. Basic Voltage Drive:
   For on/off control, the actuator may be connected directly to a DC voltage source (e.g., regulated supply or battery) at the rated voltage. Applying this voltage initiates rotation of the internal eccentric mass. For instance, PUI’s HD-EM1305-SC-R actuator is rated for 3.0 VDC, with a typical operating speed of 13,000 RPM. The corresponding vibration frequency can be approximated by converting rotational speed (in RPM) to Hz:
                    
   
   This reflects the fundamental oscillation rate of the unbalanced rotating mass and provides a coarse estimate of the dominant vibration frequency felt by the user. Actual perceptual response may include harmonics and system resonances. 
2. PWM + MOSFET Drive:
   For dynamic control, pair a microcontroller(MCU) with a drive circuit constructed with discrete components. The most common configurations involve PWM outputs from the microcontroller controlling a MOSFET drive circuit. The examples below illustrate a high-side MOSFET drive circuit  and an H-Bridge. The drive circuit on the Top controls the ERM using the method described in (1); however, switching the actuator on and off is controlled by a microcontroller’s PWM output. The drive circuit on the Bottom builds upon this concept but uses an independent MOSFET circuit to control the actuator’s Forward Drive, Forward Braking, Reverse Drive, and Reverse Braking. These additional controls, paired with other MCU PWM outputs, give high-resolution control over the actuator’s start time, stop time, and vibration pattern.

High Side MOSFET drive circuit

H Bridge

3. Drive Considerations:
For situations requiring complex control, a specially designed driver chip may be used to simplify the design of the circuit. Often, these chips have integrated digital libraries with pre-programmed vibration patterns- just send a digital command from the microprocessor to the chip, which manages the rest. Complex amplifiers and boost circuitry are typically included in these packages, and extended capabilities include auto-resonance detection, audio-to-vibration, and much more. See the table below for a limited list of recommendations by PUI Audio- other available options may match your application’s requirements.

Linear Resonant Actuators (LRAs) require an AC drive signal at their resonant frequency, typically 150–250 Hz. A dedicated haptic driver IC, such as the TI DRV2605 or DRV2625, is commonly used to drive them. These chips use auto-resonance tracking to deliver sharp, precise haptic feedback. 

Piezo haptic actuators (PAs) require a high-voltage AC drive, often ±30 V to ±100 V or higher. A boost converter combined with a high-voltage piezo driver IC, such as the TI DRV2667, is typically used to generate the boosted supply and high-voltage amplifier. These devices are controlled via I²C or analog input and provide crisp clicks and fast response in thin form factors.

LRAs may need resonance calibration, piezo drivers should be checked for clean voltage output, and ERMs just require verifying smooth vibration strength. These quick checks ensure reliable and consistent performance.

The table below shows key features from various manufacturers and the available libraries for different Haptics drivers-

Texas Instruments supports some of the best-documented and most widely used haptic ICs, especially for ERM and LRA. Their piezo options are also strong, though libraries are less polished. The DA728x family is one of Renesas’ most advanced haptic driver lines, designed for ERM, LRA, and piezoelectric actuators. These drivers are widely used in wearables, AR devices, and handheld controllers. 

After choosing your Haptics actuator and driver, the setup is simple. Initialize the driver over I2C, select the correct actuator type, and enable the output so the device is ready to respond to commands. Once initialized, you can trigger vibrations using built‑in effects for ERM and LRA or send basic waveforms for Haptic actuators. This lets you quickly verify the haptic response without extensive customization.

Performance Metrics & Datasheet Specifications

PUI Audio’s haptics portfolio includes a wide range of vibrotactile actuators ERM, LRA, VCA, and piezo each delivering a distinct tactile feel tailored for different applications. Key performance parameters include

Optimizing Haptic Performance Through Effective Mechanical Mounting

Mechanical mounting plays a critical role in the performance, reliability, and feel of haptic actuators. Whether using ERM, LRA, VCA, or piezo actuators, the way the device is mounted directly affects vibration transfer, tactile sharpness, and long-term durability. Below are best practices and design considerations for achieving optimal haptic feedback across various applications.

1. Adhesive Mounting

Adhesive mounting is commonly used for flat internal surfaces and low-profile designs.

Key Guidelines

• Rigid Mounting Surface: The surface must be stiff and non-flexing. Excess flex can introduce fatigue and lead to premature failure.
• Isolated Adhesive Contact: Only the adhesive pad should touch the enclosure. Any additional rigid contact points may create unwanted noise or buzzing during vibration.

This method is ideal for compact enclosures where simplicity and assembly efficiency are priorities.

2. Structural Ribs and Molding Features

Structural ribs can be added to increase stiffness and securely locate the haptic motor while reducing material usage.

Design Considerations

• Contoured Rib Support: Ribs can be shaped to match the outer body of the motor, providing continuous support along one side.
• Retaining Walls: Integrating molded retaining walls adds further security and prevents motor shift under repeated vibration.
• Adhesive for Final Fixation: Once the motor is seated within the rib structure, a self-adhesive can be used to lock it in place. 

This approach enhances stability and ensures consistent vibration directionality.

3. Molded Mounts

A molded mount encloses the actuator in a custom-designed plastic housing.

Advantages

• Serviceability: Screws allow easy removal, replacement, or repositioning.
• Motor Specific Fit: The molded cavity is specifically formed to match the motor’s geometry, ensuring tight and consistent placement.

Molded mounts offer strong mechanical robustness, especially for products subjected to frequent motion or harsh environments.

4. Directionality of Vibrations

ERM and LRA actuators generate vibrations along different axes depending on their construction. For effective haptic feedback, these vibrations must be properly directed toward the user.

Placement and mounting orientation should therefore reflect the actuator’s vibration pattern to maximize tactile clarity.

5. General Mounting Recommendations

Regardless of method, these foundational practices help ensure efficient vibration transfer and long-term reliability:

• Cleanliness: All bonding surfaces must be free of dust, grease, particulates, or oils to maintain bond strength.
• Maximized Bond Area: Larger adhesive contact surfaces improve vibration transmission and reduce energy loss.
• Material Compatibility: Verify adhesive compatibility with the actuator housing and the mating surface (often glass, plastic, or coated film).
• Low Profile: For handheld or mobile devices, mounting solutions should add minimal thickness.
• Reliability Testing: Perform drop tests, vibration tests, thermal cycling, and humidity exposure to qualify the mounting method.
• Environmental Durability: Consider the full life-cycle environment including temperature swings and chemical exposure to ensure materials maintain adhesion and performance.

6. Haptic Configuration Strategies

Single Haptics Device

When using one LRA or vibration motor, feedback intensity will vary across the user interface. The strongest sensation will naturally occur closest to the actuator’s location. 

Multiple Haptics Devices

Using multiple actuators enables:

• More precise, localized haptic cues
• Enhanced safety (e.g., cycling controls) by enabling users to identify activated functions without looking
• Ability to assign distinct vibration patterns or intensities
• More immersive and customizable user experience
• Flexibility for future feature upgrades

7. PCB vs. Back-Housing Mounting Options

Back-Mounted LRA

• LRA is glued to the inside back of the housing
• Buttons or controls are located on the front
• Vibration travels through the case instead of the PCB
  This provides strong feedback to the enclosure while isolating the actuator from delicate PCB components.
  

PCB-Mounted LRA (Beside Buttons)

• LRA is attached to the PCB using adhesive or a small bracket
• A rubber gasket or foam isolates the motor from nearby buttons
  This approach allows tight integration but requires damping materials to prevent unwanted vibration transfer.

Emerging and Specialized Haptic Technologies

Beyond the mainstream actuators above (which PUI and similar suppliers focus on), there are other notable technologies in the realm of audio haptics. Some are emerging in research or niche applications, pushing the boundaries of how we can create touch sensations:

• Tactile Transducers for Immersive Audio: In entertainment and simulation, large bass shakers or tactile transducers are used to turn low-frequency audio into strong vibrations you can feel through floors, furniture, or even wearables. These devices are essentially oversized voice coil actuators that mount to a chair, couch, or platform. They reproduce the sub-audible frequencies (20–200 Hz) of audio content as physical vibration, adding a visceral dimension to movies, music, or VR experiences. For instance, a home theater seat with a bass shaker lets viewers feel the rumble of an explosion or the kick of a bass drum. One audio engineering article describes that tactile transducers are used in home theaters, commercial cinemas, arcade games (for special effects), amusement park rides, and even in applications for the hearing impaired (to convey sound through vibrations). A typical bass shaker contains a moving mass driven by a voice coil against a spring or housing; unlike a normal speaker, the goal is to maximize felt vibration rather than airborne sound. These often require a dedicated amplifier and are fed by the LFE (low-frequency effects) channel of an audio system. While outside the scale of personal devices, they illustrate audio haptics at the macro level – essentially using the same technology as an audio subwoofer but bolted to your seat for direct body feedback. Companies like ButtKicker and Earthquake Sound produce such transducers for enthusiasts. In simulation rigs (racing or flight sims), multiple transducers can be placed at corners of a platform to provide feedback cues (engine vibrations, road texture, etc.). The key advantage is creating an immersive environment where you not only hear the sound but feel it, engaging the mechanoreceptors in sync with auditory cues. 
• Mid-Air Ultrasonic Haptics: A cutting-edge area of audio haptics is the use of ultrasound to create tactile sensations in mid-air, without any wearable device or direct contact. This technology uses an array of ultrasonic transducers (usually emitting at ~40 kHz, well above audible range) that are coordinated to focus sound waves at a point in space. Where the ultrasound beams converge, they produce a tiny pressure oscillation – an acoustic radiation pressure – that can be felt on the skin if you place, say, your hand at that focal point. By rapidly moving this focal point or modulating its intensity, the system can stimulate the skin’s touch receptors to create feelings of taps, textures, or shapes in mid-air. Companies like Ultraleap (formerly Ultrahaptics) have commercialized this: their array projects invisible “buttons” or tactile shapes onto the user’s hands as they interact with a gesture interface. One can imagine feeling a hovering toggle switch or a virtual slider under your fingertips even though there’s nothing there – only intersecting sound waves. According to Ultraleap, “phased arrays of ultrasonic speakers transmit waves timed to coincide at a point in space,” creating a controllable focal point of haptic feedback. Since the skin isn’t very sensitive to a steady ultrasound point, these focal points are typically amplitude-modulated at lower frequencies (within 1 Hz to a few hundred Hz) to produce a palpable sensation. For example, a 40 kHz ultrasound beam might be modulated at 200 Hz; the user feels that 200 Hz vibration at that spot on their palm. Researchers have demonstrated mid-air haptic effects like feeling virtual raindrops, or a ghostly outline of an object. Recent advances showed that adding lateral motion or rotation to the ultrasonic stimulation can significantly enhance the perceived force and even create textures like “smooth” or “rough” in mid-air. The big appeal is no touch or wearables required – a truly contactless interface, which is useful for interactive kiosks (e.g., touchless controls that you can feel, for hygiene) and VR/AR where you want to touch virtual objects. While this tech is still maturing (the forces are gentle, and focal points are not extremely fine resolution yet), it represents an innovative crossover of audio and haptics: literally using sound beams to produce touch. 
• Electrostatic and Surface Haptics: Another approach outside of PUI’s electromechanical offerings involves modulating friction or using electrostatic forces on surfaces. Electrostatic haptic panels can create a feeling of texture on a glass touchscreen by applying a high-voltage, high-frequency oscillating electric field. The field changes the friction between your fingertip and the glass (via the Johnsen-Rahbek effect or similar), making the glass feel “stickier” or “slippery” in patterns as you slide your finger. This can simulate bumps or grooves – for instance, giving you the sensation of a slider groove or a dial detent on a totally smooth screen. Companies like Senseg (acquired by Immersion) and research groups have developed such electrovibration techniques. The frequencies involved are often in the several kHz range (again, ultrasonic or audio-frequency voltages) but the effect is a kinesthetic one of friction. Similarly, some ultrasonic surface haptics use piezo actuators to vibrate a panel at ultrasonic frequencies, creating a thin layer of air or altering the friction so that textures can be felt. These technologies are in specialized products (some high-end automotive touch displays, tactile tablets for visually impaired, etc.) and showcase that audio-frequency signals (whether electrical or acoustical) can be harnessed in non-traditional ways to create tactile sensations. While PUI’s portfolio doesn’t directly cover electrostatic touch surfaces, it’s part of the broader landscape of haptics which also includes exotic actuators like electroactive polymers (EAP) (flexible polymer films that contract when zapped with high voltage) and pneumatics or hydraulics for force-feedback. Many of these emerging actuators are noted in research literature as promising for the future of haptic interfaces, though they face their own challenges (e.g., EAPs require very high voltage and are still limited in force, and pneumatic systems are too bulky for most portable uses). 

In summary, the field of audio haptics is rich and continually evolving. Technologies range from the very tangible (spinning motors and buzzing magnets) to the almost magical (invisible ultrasound touch). Each approach has its niche. By focusing on the core categories – ERM, LRA, VCA, and piezo – we cover the solutions most widely used in today’s devices, many of which PUI Audio provides as ready components. By also understanding the outlying methods (like mid-air haptics or tactile transducers), we gain insight into where the industry might head, as user experiences demand even more immersion and realism.

Conclusion

Audio haptic technologies have become indispensable for designing modern interactive devices, bringing the sense of touch into harmony with sight and sound. We’ve explored how different actuator types contribute uniquely to this goal: from the simple buzzing motors that provide basic alerts, to resonant actuators that deliver crisp, information-rich vibrations, to powerful voice-coil drivers that can shake interfaces with realism, and ultra-thin piezo films that make even flat glass come alive with tactile feedback. Each technology involves a conversion of electrical energy (often leveraging audio-frequency signals) into mechanical motion that our skin can perceive – hence the term audio haptics. The choice of haptic actuator in a design hinges on the desired user experience: an affordable rumble for a notification, a sharp click for a touchscreen, a dynamic pulse for a game, or perhaps a gentle mid-air touch in a futuristic gesture-controlled system.

PUI Audio’s foray into haptics underscores the synergy between audio and tactile engineering. Audio transducers and haptic actuators share principles – a speaker and a linear actuator are cousins, one meant to be heard and the other felt. By offering haptic components alongside traditional audio devices, companies like PUI enable product designers to craft multi-sensory interfaces where sound and touch complement each other. As noted, vibrations often accompany audio or visual cues to reinforce feedback, and doing this effectively requires a deep understanding of the technologies at hand.

Moving forward, we can expect haptic feedback to grow even more sophisticated. The demand for richer user experiences in AR/VR, automotive safety, remote healthcare, and consumer gadgets drives innovation. We may see hybrid solutions – perhaps piezo and voice-coil combinations, or new materials – to achieve stronger yet finer-grained touch sensations. Mid-air haptics might find mainstream use, letting people “feel” buttons or textures without touch, which could revolutionize interface design in public or sterile environments. What remains constant is the goal: to reduce the gap between the digital and physical world by engaging our sense of touch. Audio haptics technologies, in all their forms, are the tools making this possible, and a comprehensive grasp of these tools is crucial for any engineer or designer aiming to deliver the next intuitive, “feelable” interface.

In conclusion, audio haptics is a vibrant field blending physics, physiology, and creativity. From a tiny vibrating motor in a smartwatch to an ultrasonic array projecting tactile shapes in thin air, the spectrum of technologies we now have at our fingertips (literally) is remarkable. By leveraging the right haptic solution for the right application – whether inside PUI’s offerings or beyond – developers can ensure that important information and interactions are not just seen and heard, but also felt, enriching how we experience the digital world.