MagnetIO: Passive yet Interactive Soft Haptic Patches Anywhere
Alex Mazursky

Shan-Yuan Teng

University of Chicago
alexmazursky@uchicago.edu

University of Chicago
tengshanyuan@uchicago.edu

Romain Nith

Pedro Lopes

University of Chicagornith@uchicago.edu

University of Chicago
pedrolopes@uchicago.edu

Figure 1: (a) We propose a new type of haptic actuator, which we call MagnetIO, that is comprised of two parts: any numberof soft interactive patches that can be applied anywhere and one battery-powered voice-coil worn on the user’s fingernail. (b)When the fingernail-worn device contacts any of the interactive patches it detects its magnetic signature and (c) makes thepatch vibrate. (d) To allow these otherwise passive patches to vibrate, we make them from silicone with regions doped withneodymium powder, resulting in soft and stretchable magnets. (e) This novel decoupling of traditional vibration motors allows
users to add interactive patches to their surroundings by attaching them to walls, objects or even other devices or appliances
without instrumenting the object with electronics.

ABSTRACT
We propose a new type of haptic actuator, which we call MagnetIO,
that is comprised of two parts: one battery-powered voice-coil wornon the user’s fingernail and any number of interactive soft patches
that can be attached onto any surface (everyday objects, user’s
body, appliances, etc.). When the user’s finger wearing our voicecoil contacts any of the interactive patches it detects its magnetic
signature via magnetometer and vibrates the patch, adding haptic
feedback to otherwise input-only interactions. To allow these passive patches to vibrate, we make them from silicone with regions
doped with polarized neodymium powder, resulting in soft andstretchable magnets. This stretchable form-factor allows them to be
wrapped to the user’s body or everyday objects of various shapes.
We demonstrate how these add haptic output to many situations,such as adding haptic buttons to the walls of one’s home. In our
technical evaluation, we demonstrate that our interactive patches
can be excited across a wide range of frequencies (0-500 Hz) andcan be tuned to resonate at specific frequencies based on the patch’s
geometry. Furthermore, we demonstrate that MagnetIO’s vibration
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https://doi.org/10.1145/3411764.3445543

intensity is as powerful as a typical linear resonant actuator (LRA);
yet, unlike these rigid actuators, our passive patches operate as
springs with multiple modes of vibration, which enables a wider
band around its resonant frequency than an equivalent LRA.

CCS CONCEPTS• Human computer interaction (HCI); • Interaction devices;• Haptic devices;

KEYWORDS
soft magnets, ubiquitous haptics, fabrication
ACM Reference Format:
Alex Mazursky, Shan-Yuan Teng, Romain Nith, and Pedro Lopes. 2021.
MagnetIO: Passive yet Interactive Soft Haptic Patches Anywhere. In CHI
Conference on Human Factors in Computing Systems (CHI ’21), May 08–
13, 2021, Yokohama, Japan. ACM, New York, NY, USA, 17 pages. https://doi.org/10.1145/3411764.3445543

1

INTRODUCTION

Today’s interactive devices increasingly instrument every kind of
surface, effectively adding interactive functionality even to passive
everyday objects such as walls, tables, and rapidly prototyped objects [14, 28, 64, 75, 76], as well as to the user’s body [35, 36, 61].
To enable sensing these interactions, researchers engineered conformable/stretchable sensing devices so that these can comfortably
fit around non-planar surfaces, which is the case for everyday objects or the human body. This led to a mature field of on-body or

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Alex Mazursky et al.

Figure 2: (a) Our device is built from the same principle as traditional linear resonant actuators (LRA), i.e., based on moving
a magnetic mass using a coil and a spring. (b-c) However, our device decouples these components into two parts: one active
element containing the coil, which the user wears on their fingernail; and, many passive elements, which are comprised ofsilicone with regions doped with neodymium powder which together realize a spring & magnet.
on-object sensing technologies that are easy to deploy and ideal for
prototyping or enabling interactions in ubiquitous settings.
However, the converse is not the case, while sensing can bedone in a distributed fashion around the user and in conformableform-factor, the same is not true for actuation. Researchers arestill looking for techniques that allow deploying large numbersof actuators without the constraints of power delivery to every
single individual actuator, wireless communication across all actuators, microcontrollers, etc. As a result, while we have a range
of interactive techniques to deploy sensing “patch”-like devices
everywhere, these patches typically do not exhibit any form of
haptic response, i.e., they can sense the user’s touch (e.g., to turnon/off the user’s home-alarm) but they cannot vibrate in responseto that touch (e.g., to indicate the alarm is on/off), not at least, without requiring vibration motors or other haptic actuators, which inturn require batteries and circuitry. Ultimately, all these dramatically limit the ubiquitous application of these interactive patch-likedevices.
In this paper, we engineered and explored a new alternative foradding haptic feedback to everyday surfaces, which is depicted in
Figure 1. Our approach, which we call MagnetIO, introduces a new
type of haptic actuator that is passive (i.e., requires no electronics,
no battery, etc.) until the user’s finger, which is instrumented witha wearable voice-coil, touches it, causing it to vibrate.

2

OUR APPROACH: MAGNETIO

MagnetIO is composed of many passive interactive patches andone nail-worn device, which features a miniaturized and customengineered voice-coil, inertial measurement unit (IMU), battery,
microcontroller and wireless. MagnetIO’s complete voice-coil andcircuitry fits entirely on the user’s fingernail, thus leaving the fingerpad unobstructed to feel interactions with the user’s environment
and the vibrations from our passive patches.
The design principle that enables our interactive patches
to vibrate is that they are made from silicone doped withneodymium powder, resulting in stretchable magnets that are thus
attracted/repelled by the wearable coil. Conceptually, we liken our
approach to a linear resonant actuator (LRA, typical vibration element in most commercial mobile devices), which is comprisedof a magnet attached on a spring and a coil, which we depict inFigure 2

To better illustrate our design, we make an analogy to the innerworkings of an LRA: when current is supplied to the LRA’s coil,
it produces a magnetic field which attracts or repels the magnet.
By performing this multiple times, the momentum of this magnetspring assembly creates a feelable vibration (Figure 2a).
In our case, our design takes a sharp conceptual turn from thatof the LRA as we purposely decouple the magnet-spring from thecoil (Figure 2b). This allows us to scale up the output by placing
many spring-magnet pairs everywhere, which are activated when
the user’s wearable coil contacts them (Figure 2c). The advantage
is that our design requires only one coil, meaning it also only requires one driver circuit, one communication module and one battery. Furthermore, all our interactive patches are passive since we
implement them using silicone, an elastic material that allows us
to achieve the “spring” component; subsequently, some regions
are doped with neodymium powder, which allows us to realize the“magnet.” Therefore, our soft-magnets realize the “spring-magnet”
component typical of LRAs. The result is that MagnetIO patches areeasy to place anywhere because they are stretchable and soft, andyet they deliver haptic output to the user, appearing as interactive
patches.
Moreover, unlike approaches that attach vibration actuators directly to the user’s fingerpad, MagnetIO can trigger vibrations
whenever a user touch any of our haptic patches, while simultaneously leaving the user’s fingerpad free (thus, minimizing impacts
to dexterity).
Note that while our main contribution is on realizing haptic output for these soft patches via our soft magnets, we also demonstrate
one possible sensing mechanism by using the magnetic signatureof the patches themselves, i.e., the user’s fingernail-worn device
detects the unique ID of each patch by using a 3DOF magnetometer to read each patch’s unique 3D magnetic field (see details in
Implementation). Naturally, there are several other possible passive
implementations, each with their idiosyncratic pros/cons, such as
RFIDs [17, 39, 60], acoustic IDs [21], optical (barcodes [24], QR
codes [49, 53], Anoto pen-like patches [50]), etc.

3

RELATED WORKThe work presented in this paper builds primarily on the fields ofubiquitous interfaces, especially instrumented interactive surfaces,
and haptics, with emphasis on soft and magnetic-based actuators.

MagnetIO: Passive yet Interactive Soft Haptic Patches Anywhere

3.1

Adding Input to Everyday Objects andSurfaces

To enable the vision of ubiquitous computing [62], many researchers have engineered techniques that add input to everyday objects and surfaces. A common approach to adding input to objects is
to apply a flexible resistive or capacitive sheet to the surface [37, 46,76]. For example, PrintSense [14] utilized an network of electrodes
printed on a flexible substrate to add input to surfaces. Electrick [75]combined conductive materials with Electric field tomography toachieve touch input on a wider variety of objects, such as tools andtoys. Similarly, ObjectSkin [16] used hydroprinting to transfer sensors and circuits onto irregular objects. Sprayable User Interfaces[64] enabled large-scale interactive surfaces via spray-on sensors.
Additionally, many other techniques are available, even acoustic
techniques have been used to add touch input to objects [38].

3.2

Passively Adding Input to Everyday Objects
And Surfaces

The key issue with the previous approaches is that they all add
electronics onto the objects they are enabling. As such, we quickly
reach a limit to the vision of ubiquitous interfaces, as all objects
require batteries, circuits, etc. As an alternative to this, researchers
have investigated passive input techniques. Passive input is advantageous in that it does not require instrumenting the object
with electronics, but instead, typically instruments the user withsensors, such as cameras, etc. For instance, computer vision canbe used to detect interaction with surroundings, as demonstrated
by early works like Light Widgets [13] and more recently withdepth cameras as in WorldKit [66]. Acoustic techniques can also
be used for passive input: Acoustic Barcodes [21] and Scratch
Input [22] both utilized the physical surface roughness of objects to detect input. Furthermore, electrical techniques are another popular method for passive input; notably Touché [45] realizes gestural detection on any electrically conductive surface
and time-domain reflectometry adds multitouch to wires [65]. Finally, 3D printed ferromagnets have been used to encode information directly in 3D printed objects; allowing users to scan theobject with a magnetometer, like how one would scan a conventional barcode. Here, users swipe their smartphone’s magnetometer
across the surface of the object to read out its unique magnetic
identifier [26].

3.3

Adding Haptic Output To Everyday Objects
And Surfaces

When it comes to adding haptic output to everyday objects andsurfaces, the most common technique to instrument objects withhaptic feedback is to simply embed actuators within the device, as
we do with mobile phones [41, 42, 73]. However, this approach tends
to lack haptic fidelity and design flexibility. One versatile solution tothis challenge was put forth by Magtics, which introduced a tactile
array of rigid actuators inside a flexible casing that could conformto curved objects [40]. Tactlets also explored a flexible form factor
for adding electrovibration feedback to everyday objects [15].
Evidently, when compared with adding input to the environment, adding haptics is far less explored. The limitations that we

CHI ’21, May 08–13, 2021, Yokohama, Japandiscussed for active sensing (i.e., it requires electronics & batteries
on every object) become dramatic for haptic output, because haptic
actuators require even more power than their sensing counterparts.
To overcome this limitation, MagnetIO takes a sharp conceptual
turn with respect to the traditional design of a haptic device, it
decouples the device into two parts: one active that the user carries
and many completely passive parts, that can be attached to objects
and surfaces without the need for electronics.
Conceptually, our proposal relates to Sekiguchi et al.’s “Ubiquitous haptics” vision, in which any interactive device around theuser’s environment, be it a surface or an everyday object, was
not only added with input capability but also displays haptic feedback [47]; they proposed realizing vision this using active haptic devices based on motorized actuators. We build on this concept but allow this to scale to practical uses with many devices.
This is only possible because, instead, our concept uses passive
patches applied ubiquitously in the user’s environment, rather
than requiring batteries & electronics inside every surface or object the user interacts with. For our passive patches to produce
actual haptic feedback, we were inspired by two hardware techniques: (1) soft actuators and (2) magnetic actuators, which we
discuss below.

3.4

Soft Actuators

Advances in materials science and mechanical engineering brought
soft actuators to interactive devices. A wide range of soft actuators
have been developed based on different working principles:
pneumatics [1, 54, 57], hydraulics [19, 20], acoustofluidics [2],electroactive polymers [9, 11, 74, 77], twisted and coiled polymers[18], gels [34], and electrorheological and magnetorheologicalfluids [27, 30, 31, 44, 48, 69]. Many have been adapted to realize
deformable devices, shape-changing output, and so forth [3, 7, 43].
For instance, HapBead [19] added a bead in a soft microfluidic
channel around the finger pad to generate tactile sensations
caused by the bead moving around. HapSense [74] demonstrated
a wearable electroactive polymer for tactile feedback. MagnetIO
differs from the approach in HapSense by its decoupling between
the active and passive components. Additionally, MagnetIO is
made from softer materials (silicone vs. PVDF), allowing it toconform to more irregular objects and body parts.
Recently, researchers in soft robotics have become particularlyinterested in soft magnetic materials for sensing and actuation(note that in these mechanics-focused works, and in this paper,“soft” refers to the low-modulus of the materials involved, rather
than the magnetic properties). Unlike electrically-controlled or
fluid-driven systems, magnetic materials lend themselves well tountethered operation because they may be sensed and actuated
without contact. For example, magnetic microrobots may be steered
within an environment by controlling an external magnetic field[25, 68]. Additionally, magnetic skins have been used as tactile andwearable sensors with minimal need for wiring [4, 23]. Researchon fabrication has demonstrated the ability to design soft magnets
with custom polarity by manipulating the applied magnetic field
during curing; this allows for tunable behavior when the cured
magnet is exposed to a field, resulting in programmable shapes andlocomotion [25, 29, 68].

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Figure 3: (a) Our user at home, wearing our coil, surrounded by surfaces with interactive patches. (b) They tap their wall,
which has a passive patch that controls their home alarm. (c) The user feels the patch vibrate to indicate that their alarm is
now disabled.

3.5

Magnetic-Based Haptics

Magnets have been used to convey haptic feedback across a wide
range of applications. Permanent magnets have been identified
as a passive actuator (no electrical power required) for providing
haptic feedback [52, 70–72, 78, 79]. However, permanent magnets
lack control; they cannot be turned off and the intensity of their
feedback can only be changed by physically displacing them. Thus,
many interactive devices rely on electromagnets so that the output
magnetic force is controllable [51, 55].
Many of the proposed systems are based on 2D electromagnet
arrays. For example, FingerFlux utilized an array of electromagnets with a nail-mounted permanent magnet to provide haptics
on tabletops [63]. Similarly, Actuated Workbench used magnets tomove tangibles on a table [56]. More recently, M-Hair proposed
coating the body’s hair in iron powder so that it may receive haptic
feedback from electromagnets moved on top of the user’s skin [8].
However, the arrays of electromagnets used here are extremely
bulky and prevent wearable, mobile and/or scalable form factors.
To make magnetic actuators more mobile, many devices relyon custom electromagnetic coils. For instance, Magnetips designed
a single coil worn on the back of mobile devices for delivering
feedback to a nail-worn permanent magnet [32]. Magtics created a
flexible haptic device based on the hybrid of hard electromagnetic
actuators in a flexible case [40].
Unfortunately, prior approaches to magnetic-based haptics do
not easily scale to many applications because: (1) they require
power; (2) the magnets are rigid, so they cannot conform to objects
or the human body. To address these issues, MagnetIO uses one
wearable coil and many interactive patches made from flexible
silicone and stretchable magnets. The result is the first one-to-manysystem for ubiquitous vibrotactile haptics.

4

WALKTHROUGH: ADDING MAGNETIOPATCHES EVERYWHERE

To give the reader a complete picture of how MagnetIO allows auser to control their environment with ad-hoc interactive haptic
patches, we describe a walkthrough via the example of a user intheir home, using our MagnetIO patches to control a wide-range ofinteractive appliances such as internet-of-things (IoT) devices.

Figure 3a shows our user, wearing our wearable voice-coil on
their index finger, walking into their home.
Figure 3b shows that as they walk in, they tap a MagnetIO patchthat has been attached to their door. In response to tapping thepatch, they feel two consecutive vibrations (tzzz, pause, tzzz) confirming that their home-alarm is now disabled, which is depictedinFigure 3c. Note that this user can also perform this action in
the dark (i.e., eyes-free, which we did not illustrate for the sake ofvisual clarity) because our MagnetIO patches are inherently haptic
interfaces designed to vibrate on touch.
Now that we depicted an interaction with MagnetIO from theuser’s perspective, let us examine what is happening from thedevice’s perspective. In other words, we will describe how ourpatches work to deactivate the user’s IoT home alarm.
Figure 4 depicts the principle behind MagnetIO interactions.
First, as depicted in
Figure 4a, as the user taps on the patch to deactivate their homealarm, the wearable-coil approaches the patch and senses its ID, i.e.,
the wearable-coil recognizes that the particular patch the user istouching is the “home-alarm” ON/OFF patch. To sense the ID of apatch, the wearable-coil makes use of its inertial measurement unit,
which includes a 3DOF magnetometer. Using the magnetometer
data, the wearable-coil detects the patch that the user is interactingwith by comparing the current reading to pre-trained magnetic
signatures. These magnetic signatures are just an example of one
many possible ways our system could sense the ID of each patch(refer to Implementation for details). Alternatively, our system could
utilize a wide variety of sensing mechanisms, such as RFIDs [17,39], acoustic IDs [21], optical IDs [49, 53], etc. After the wearablecoil has identified that the user touched the “home-alarm” patch,
it communicates to the user’s IoT home-alarm via its Bluetoothmodule, informing it to switch to the “OFF” state. Finally, as depictedinFigure 4b, the home-alarm confirms the new state by sending amessage to the wearable-coil, which the wearable device renders
haptically by energizing the coil in a vibrotactile pattern. This
creates a magnetic field which in turn attracts the magneticallydoped region of the interactive patch, making the patch vibrate
under the user’s finger.

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CHI ’21, May 08–13, 2021, Yokohama, Japan

Figure 4: (a) When the user’s finger approaches an interactive patch, its magnetometer reads and recognizes its unique 3D
magnetic ID and (b) activates the wearable-coil, generating a magnetic field that vibrates the patch under the fingerpad.

Figure 5: The user touches the top magnet and slides their finger down to the middle magnet where they feel the strongest
vibration, indicating the last setting used and continue to slide down to the bottom to reset the thermostat to the lowest setting.

Figure 6: (a) The user peels off the patch. Because our interactive patches are passive and soft, they can be applied to a varietyof objects: (b) smartwatch bracelet, (c) water bottle, (d) and even washed (still works while wet).Besides our sticker patch, we
also implemented a strap-like patch, depicted in Figure 7, that can be wrapped around objects, such as handles, bottles, etc.
These types of patches are ideal for cylindrical objects such as the gaming controller depicted in Figure 7a.
Next, as depicted in Figure 5a, the user taps on another patch on
the wall to adjust their thermostat.
Figure 5b, depicts how the user slides their finger across thepatches, at each step, they feel a short vibration that hapticallysignals each temperature level. However, as depicted in
Figure 5c, when they cross the middle patch, they feel a strong
vibration (a haptic detent) that indicates that this is the last usedsetting.
MagnetIO patches are versatile because they are passive, made fromstretchable silicone. Figure 6a illustrates how our user detaches apatch from the wall and attaches it to new objects. These patches
are sticky as their underside is made of a layer of skin safe adhesive,

making our patches also suitable for ad-hoc on-body interfaces.
In fact, MagnetIO patches are even weather-proof. For instance,
Figure 6d depicts a user washing their smart kettle instrumented
with an interactive patch. Because MagnetIO’s patches operate via
magnetism alone (for both sensing and actuation, no circuitry is
inside the patch), the interaction will not be affected so long as thewearable coil remains dry.
In Figure 7, our user stretches the patch around the grip of thecontroller, which enhances its functionality by allowing them tomode-switch in their game, while keeping their eyes on the game
menu; again, an eyes-free interaction.

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Alex Mazursky et al.

Figure 7: (a) The user holds a strap-like patch and (b) stretches it around their gaming controller, enabling (c) an eyes-free I/Ospace for controlling modes and menus.

Figure 8: Since our interactive patches are made from silicone, they may easily include Braille to assist Blind users.
Now, the user’s partner, who is Blind, walks into the room. Despite being visually-impaired, their partner also makes use of MagnetIO patches to control their home. Since MagnetIO are interactive
haptic patches, they can serve as useful interfaces for visuallyimpaired users. Especially, because MagnetIO patches are simply
cast from silicone, one can add tactile bumps that encode messagesin Braille, as depicted in Figure 8. This allows our visually-impaired
user to use the thermostat interface by adding a side patch with
Braille annotations. The user then feels the Braille to know whichpatch this is e.g., “thermostat” or “setting 1”, and so forth (Figure8b), and then make use of MagnetIO’s vibrations to know they haveselected a setting on the interface (Figure 8c).
While our walkthrough exhibits the key principles behind how
MagnetIO allows to deploy haptic patches everywhere, these do
not depict an exhaustive list. We designed MagnetIO to be attachedto many more objects and believe that it will inspire researchers touse, or even create, passive haptics patches that can be anywhere.

5

CONTRIBUTION AND LIMITATIONS

Our key contribution is that we propose, explore, and engineer
conformable interactive patches that can be placed ubiquitously toprovide touch input and more importantly haptic feedback. The
conceptual result of MagnetIO is the first one-to-many system for
ubiquitous vibrotactile haptics.
Our approach has the following benefits: (1) while traditional
actuators each require their own power supply/electronic-circuits,
MagnetIO decouples the powered coil component from the passive
magnetic elements, allowing us to actuate many interactive patches
using only one active component, resulting in haptics patches thatscale; (2) our interactive skins offer a conformable I/O space that
can adapt to many shapes and body parts that pose challenging
to existing, rigid actuators (LRAs, etc.); (3) our nail-worn device

leaves the fingerpad free to interact with one’s surroundings, yethaptic sensations are still delivered directly to the fingerpad; (4) our
fabrication technique enables customizable geometries, magnetic
fields and even aesthetics; (5) in contrast haptic devices based solely
on permanent magnets, the use of our wearable coil allows us toprogram custom tactile waveforms and/or turn off haptic sensations
only-on demand, i.e., these are truly interactive.
Our approach is limited in that: (1) the use of soft elements has
its downsides, as our actuators are subject to mechanical losses
from hysteresis and yield a reduced magnetic field strength whencompared to rigid, sintered magnets; (2) our approach only generates haptic sensations when the wearable-coil is on top of the soft
patch, i.e., these patches cannot vibrate by themselves, which is
why we believe they are useful for adding vibrations to touch basedinteractions; (3) the object being instrumented with our interactive
patches must be larger than the patches themselves; lastly, (4) as ourapproach is based on magnets it is not advised for instrumenting
ferromagnetic objects, as these attract the magnets and dampen the
resulting vibrations.

6

IMPLEMENTATION

To help readers replicate our design, we now provide the necessary
technical details and fabrication process. Furthermore, to accelerate
replication, we provide all the source code of our implementation1 .
MagnetIO devices have two principal components: (1) many of
our silicone-based interactive passive patches, which have regions
doped with neodymium powder (Nd2 Fe14 B) and can be attachedto surfaces; and (2) our nail-worn device, which can make ourpatches vibrate via its electromagnetic coil; the latter is entirely
1 lab.plopes.org/#MagnetIO (software, firmware, schematics, 3D files, simulation scripts,

evaluation scripts).

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CHI ’21, May 08–13, 2021, Yokohama, Japan

Figure 9: The key mechanism behind our soft magnets: (a) this thin beam act as a spring that connects the magnet (darkregion at center) to the base (silicone around it, with cut-outs). (b) Schematic side view depiction of our mechanics that allow
the magnet to vibrate even as the user presses down; note that as the fingerpad lands on the center of the patch, it is mostly
supported by the silicone walls outside the cutout.
self-contained, i.e., it has input (via a 9DOF IMU), output (electromagnetic coil), processing, battery and wireless.

6.1

Mechanics Our Of Passive Patches That
Can Vibrate

The key behind the design of our patches is that they embody thesame mechanics that allow a linear-resonant actuator (LRA) tovibrate, yet they are stretchable and passive. In other words, they
implement a mass and spring, depicted in
Figure 9, that respond to applied magnetic field. Because of silicone’s intrinsic elasticity, it naturally behaves like a spring. To
allow the soft magnet to achieve amplitudes needed for “feelable”
vibrations, we designed the spring mechanism as a long and slender
beam (3.75 mm length, 0.5 mm thickness). Furthermore, we foundthat an optimal 1 mm for the beam-spring’s width maximized feelable vibrations (see Technical Evaluation for details).
Moreover, as depicted in Figure 9b, we designed the hollow
cutout at the center of each patch with a diameter of 9mm, whichis slightly smaller than 10-14mm of the average fingerpad diameter[10]. Thus, as the fingerpad lands on the center of the patch, it
is mostly supported by the silicone walls outside the cutout. This
allows the magnet to vibrate freely in the airgap and contact thefingerpad even when the finger pushes down.

6.2

Fabrication of Our Soft Magnets: Doping
Silicone With Magnetic Powder

Our passive patches are made of two parts: a soft stretchable magnet made of silicone mixed with permanent magnetic powder(Nd2 Fe14 B) adhered to a flexible silicone mechanism that enables
vibration.
Prior to the start of the fabrication, the magnetic powder isfiltered through a 200 µm mesh. Smaller particles allow for morestretchability, as we validated in our Technical Evaluation.
Figure 5 illustrates our fabrication process. First, we fabricate our
1.5 mm soft magnets by mixing the silicone (Dragonskin FX Pro)
and NdFeB powder. The mixture is hand-stirred for 10 minutes andcast to a 3D printed mold to shape the magnet; the process is thesame for the tactile magnet (that sits at the center of our patches)
and the ID magnets (that sit at the edges of the patch, solely for the
purpose of shaping its magnetic signature).

The mold is held between two strong permanent magnets (N520.75” x 0.75”, K&J Magnetics). This strong magnetic field (∼1.1 T)
magnetizes and aligns the polarities of the individual particles. This
process results in a composite with a strong, permanent magnetic
field, while remaining flexible due to the silicone holding it together.
With a goal of maximizing magnetic field strength to produce strong
vibrations, we use an NdFeB weight concentration of 80%.
Next, the rest of the patch, which embodies our springmechanism, is cast using pure silicone. For the spring mechanism,
Dragonskin FX Pro silicone is used for its elasticity. The magnets
and mechanism may be cured at room temperature (which takes∼40 minutes for Dragonskin FX Pro) or inside a dehydrator in a
few minutes.
After both the silicone mechanism and soft magnets have cured,
the interactive patch is assembled by adhering the magnets to themechanism with silicone glue (Sil-poxy). The total thickness of apatch is 2.5 mm.
We designed MagnetIO patches to be attached to a wide varietyof objects of different shapes, textures, and sizes. To adhere ourpatches to surfaces such as walls, objects and even skin, we add a
final layer of sticky silicone adhesive (Skin Tite) to the back of ourpatches. Other types of patches can be made with longer straps ofsilicone (as used in Figure 7 around the gaming controller) or evenin custom shapes (e.g., smartphone sleeve made from silicone with
our magnets embedded or a beating heart for a child’s toy, shown
later in Envisioned Examples).

6.3

Engineering Our Nail-Worn Device

Our nail-worn device is comprised of a voice-coil and PCBs forprocessing sensing and actuation, shown in
Figure 11. Our voice-coil is optimized to provide strong magnetic
forces while maintaining a compact, lightweight footprint that does
not occlude the user’s fingerpad, allowing the user to still touch
objects and feel the haptics of their surroundings.
The coil in our voice-coil is made from copper enameled wire
(28 AWG wound for 42 turns. To concentrate the coil’s magnetic
field, we designed a ferromagnetic core to fit around the windings.
To make the core comfortable to wear and to bias its magnetic
field downwards to the fingerpad, we designed a computationallyoptimized ferromagnetic core made from silicone doped with ironpowder (70 wt% iron powder, 30 wt% silicone). We describe this

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Alex Mazursky et al.

Figure 10: We fabricate our devices by: (a) doping silicone with magnetic powder, (b) casting the doped silicone mixture into
3D printed molds of desired shape, (c) curing the mixture in a strong, external magnetic field, (d) casting our mechanism outof silicone, and (e) adhering the soft magnets to the silicone mechanism.

Figure 11: (a) Components used in our device; (b) Circuit diagram of our implementation.
optimization process in our Technical Evaluation. The final coil
design weighs 2 grams.
We engineered a custom PCB for MagnetIO’s finger-worn device,as shown in
Figure 11. At the center of the coil, we place a 9DOF IMU(MPU-9250, 3-axis magnetometer, 3-axis gyroscope, and 3-axis
accelerometer) to read the local magnetic field and sense proximity
to any patch.
On the user’s finger, we place our PCB that houses our motor
driver (DRV8850, Texas Instruments), Bluetooth enabled microcontroller (nRF52811, Nordic Semiconductor), and battery (40 mAh).
The motor driver can provide up to 5 A of current, but typically 1 A
is sufficient to cause a haptic patch to vibrate. With this one small
battery, our device allows for only ∼100 haptic interactions. Yet,
one can triple its battery-life by adding a second 80mAh battery on
the first finger phalanx. The complete finger-worn device including
battery weighs only 4 grams. The coil measures 18.25 mm indiameter and 3 mm thick, while the wearable controller and battery
measure 17 mm x 11 mm with 7 mm thickness.

6.4

Sensing by Means of Detecting theMagnetic Signature of a Patch

While the focus of our paper is on the vibrations produced by ournovel soft patches, these only become interactive when the loop
is closed, i.e., only when they exhibit both output and input. We
acknowledge that detecting touch and/or the ID of the interactive
patch that the user’s finger is contacting with can be achieved using
a variety of methods previously explored, such as radio [17, 39],
acoustic [21], or optical [53, 53] IDs.

However, for the sake of completeness, we also implemented an
input identification technique that relies solely on the magnetic
properties of a patch. To achieve this, as depicted in Figure 12, weadded four small bar magnets (which we call ID magnets) aroundthe main vibration magnet, which we call the tactile magnet. Allfour rectangular magnets are also soft and were produced using thesame method as the tactile magnet. The purpose of these rectangularmagnets is to encode an ID by means of shaping the 3D magnetic
field such that each patch exhibits a different magnetic field whenread by the 3DOF magnetometer, which is featured on our wearable
nail-worn coil.
The principle behind our encoding system is as follows: byvarying the orientation of the ID magnets, unique 3D magnetic
fields can be produced; the number of combinations achieved bythis technique is obviously limited but other sensing techniques
are also possible. Furthermore, the tactile magnet can also exhibit
two polarities, which contributes to a larger number of combinations. Each of the four ID magnets may be oriented in one offour ways (north facing up, down, left, or right). The magnetic
fields of each individual magnet interact at the center of the patch
and the net magnetic field is read by the magnetometer. As wedemonstrate in detail in our Technical Evaluation, we can reliably identify eight patches at 99.06% accuracy just using simple
threshold-based identification (if-then-else) based on the physicalprinciples that guide magnetism. Certainly, one could alternatively
feed the magnetometer data into a more sophisticated classifier(e.g., SVM, DNN, and so forth) to potentially expand both in accuracy and sample size or even fuse the 9DOF of the IMU for morerich data.

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CHI ’21, May 08–13, 2021, Yokohama, Japan

Figure 12: (a) Each patch has one central tactile magnet surrounded (the one that vibrates) and four small bar magnets whoseorientation shapes the 3-D magnetic field. (b) When a user touches a patch, the magnetometer reads the patch’s unique magnetic field to recognize; thus, enabling the input side of the interaction.

7

TECHNICAL EVALUATIONS

We characterized the performance of our proposed device in fivetechnical evaluations. To aid the reader in understanding the different validations we performed, we present an overview of ourevaluations with a preview of their respective results:
I. Impact of particle size on elasticity: we found that our
choice of doping silicone with small particles (<200 µm) improved stretchability, a key feature since we want our patches
to stretch and conform around objects.
II. Measuring & optimizing the vibration response of oursoft patches: we found that (1) a 1 mm spring width and (2) amagnet diameter of 7.5 mm optimizes the resulting vibrations
to the feelable range of the human skin; and (3) that placing
magnets at least 5 mm apart from each other minimizes any
interference from the magnetic field of adjacent magnets.
III. Measuring & optimizing the magnetic field of our coil:
we found that we could tune the shape of the magnetic
field of our coil by (1) computationally simulating it; and(2) adding an iron-doped silicone. The result is that unlike
conventional magnets that radiate in a symmetric pattern,
our field is biased towards the fingerpad. We also found thatmost of MagnetIO’s vibrations happen at the patch, which
vibrates 16x stronger than the coil.
IV. Comparing MagnetIO’s vibration to a Linear Resonant Actuator: we found that our device vibrates with asimilar intensity as an LRA driven at 4V with a wider frequency bandwidth due to its soft spring.
V. Identifying patches by means of magnetic signatures:
while the entire focus of our paper is on the haptic vibrations
we produce via our soft patches, for the sake of completeness,
we also evaluated our straightforward sensing method that
identifies patches based on their magnetic signature. We
found that this can identify eight patches with an accuracyof 99.06%.

7.1

Technical Evaluation I. Impact of Particle
Size on Elasticity

To enable our patches to fit around different surfaces, especiallythose that are non-planar such as the everyday objects or the human
body, it is critical that they allow for deformations, i.e., these should

stretch. Our choice of implementing our interactive patches fromsilicone allows for this. However, as one dopes the silicone withneodymium powder to enable them to vibrate as a response to ourcoil, it decreases the elasticity (i.e., an increase in elastic modulus as
found by [4]). Thus, to maximize the elasticity of our soft magnets,
we explored refining the neodymium powder particle size using asimple mesh filter.
Figure 13 depicts the results of a simple elongation test of two
soft magnets with comparable properties (size, volume, mass, 80
wt% particle concentration) under 25 grams of load, except thatthe soft magnet represented by the orange data is made by doping
silicone with particles <200 µm; conversely the other soft magnet
is made from particles >200 µm.
Our results show that fabricating soft magnets using particles
smaller than 200 µm allows elongation up to 150% of the original
size. Furthermore, not only a smaller particle size improves elasticity, it also slightly increases the magnetic field, which in turnincreases haptic performance. As a takeaway from this evaluation,
we recommend researchers and practitioners use our approachto quickly improve the quality of their devices by refining theneodymium particle size using a simple mesh filter.

7.2

Technical Evaluation II. Measuring &Optimizing the Vibration Response of Our
Soft Patches

To understand the haptic response of our soft magnets we conducted an experimental evaluation aimed at measuring the impactthat each design factor has on the resulting vibration. We measured
the impact of: (1) the width of our beam-springs, (2) the magnet’s diameter, and (3) interference from any adjacent magnets. To measure
the vibration generated, we placed a piezoelectric vibration sensor(AB1070B-LW100-R) below each patch. The coil was held stationary
directly above the patch at 6 mm away. Data was recorded at 3300
Hz and processed using a Fast Fourier Transform to examine thefrequency response. In our plots, “magnitude” denotes the actual
analog reading as measured by our piezoelectric sensor.
7.2.1 Impact of the spring width’s in resulting vibration profile. In all
our haptic patches, the spring width is a major factor that determines
the amount of resulting vibration over a range of frequencies. As
such, we measured the vibration of four of the same magnets (8 mm

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Alex Mazursky et al.

Figure 13: Comparison of soft magnets made with large (>200 µm) and small particles (<200 µm): magnetic flux density (left)and elongation under 25 grams of load (right).

Figure 14: Magnitude of vibrations of the same soft magnets but with four varying spring widths. Frequency was swept between
0 to 500 Hz (in 20 Hz steps). Shaded regions depict a 90% confidence interval.
diameter, 1.25 mm thick, 34.1±3.2 mT measured at surface) when
attached via four different spring widths (1 mm, 2 mm, 4 mm, and6 mm). To gather insights about a wide range of frequencies, we
swept our coil in a square wave pattern from 0 to 500 Hz in stepsof 20 Hz. Three repetitions were performed for each magnet.
Figure 14 depicts our results for the measured magnitude of thevibrations of these four different spring widths, over a wide rangeof frequencies (0-500 Hz). By examining the resonant frequencies(sharp peaks in the response) we found that increasing the spring’s
width increases the resonant frequency. This is in line with simple
vibrational theory, where increasing the spring constant increases
the natural frequency. We found that the thicker springs (4 mmor 6 mm) dampen the resulting vibrations. Conversely, we foundthat the thinner springs (1 and 2 mm) result in a strong vibration.
In fact, the 1 mm spring exhibits a maximum vibration a lower
frequency peak of ∼100 Hz when compared to the 2 mm spring,which resonates maximally at ∼300 Hz.
As a takeaway from this evaluation, we recommend researchersand practitioners use a spring width of 1 mm, resulting in a soft
magnet design with a resonant frequency at ∼100 Hz. From here
on, all our soft magnets will utilize a spring width of 1 mm. Note
that, depending on the type of application, it might be also worth
utilizing also the 2 mm spring which vibrates maximally at a higher
frequency of ∼300 Hz.

7.3

Impact of the Magnet’s Diameter on
Resulting Vibration Profile

The next factor that impacts the resulting vibration is the diameterof the magnetic region doped with neodymium. As such, using thesame apparatus, we measured the vibrations of four soft magnets
with varying diameters (6 mm, 7 mm, 7.5 mm, and 8 mm). We fixed

the spring width at 1 mm according to the findings of our previous
experiment.
Figure 15 depicts the results for the magnitude of the vibrationsof these four magnets with varying diameters, as they vibrate overa wide range of frequencies (0-500 Hz). This is again aligned withwhat is expected by vibrational theory, where increasing the massdecreases the natural frequency. We found that the larger diameter
magnet at 8 mm provides mostly only one resonant mode, i.e., itvibrates maximally at ∼100 Hz. Then, for diameters below 8 mm,
we found a wider range of frequency modes, i.e., these magnets
have a few frequencies at which they can vibrate strongly. For
instance, soft magnets with a diameter of 6 mm or 7 mm vibrate
the strongest at ∼400 Hz. Lastly, at a diameter of 7.5 mm, the soft
magnet’s strongest vibrations occur at 240 Hz and 310 Hz.
As a takeaway from this evaluation, we recommend researchersand practitioners to use a diameter of 7.5 mm, resulting in a soft magnet design with a resonant frequency at ∼240 Hz, which leverages
the fact that the human skin is very sensitive at those frequencies[58]. From here on, all our soft magnets will utilize a diameter of
7.5 mm with spring width of 1 mm. Note that, the larger 8 mm
diameter might be worth exploring for applications requiring alower frequency ∼100 Hz. However, we advise against using soft
magnets with diameters below 7.5 mm for haptic applications (with
1 mm spring width), as these resonate at higher frequencies (∼400Hz) at which the human skin is not particularly sensitive [58].
7.3.1 Impact of Adjacent Magnets In Resulting Vibration Magnitude.
Next, because our approach allows users to easily attach these softinteractive patches to objects and the environment to create simple
interfaces, the soft magnets may end up neighboring each other.
Since this meant that adjacent magnets could potentially interferewith each other’s magnetic fields and decrease the vibrations, weMagnetIO: Passive yet Interactive Soft Haptic Patches Anywhere

CHI ’21, May 08–13, 2021, Yokohama, Japan

Figure 15: Magnitude of vibrations for four soft magnets with varying diameters of the region that is doped with neodymium(same spring widths of 1 mm). Frequency was swept between 0 to 500 Hz (in 20 Hz steps).

Figure 16: Magnitude of vibration (at resonant frequency) of three adjacent soft magnet placed at 5 mm of each other. As
observed, there is very little influence of permanent magnetic field of the adjacent magnets
decided to measure it. We utilized the same apparatus as in ourprevious experiments, but attached three consecutive magnets separated by 5 mm. As we were interested in measuring the impactof each magnet’s field on the adjacent magnet, we attached themagnets to individual stands connected only at the base; allowing
us to measure the impact of the field strength independently ofvibrations that propagate through the apparatus (these depend on
the material that the magnets are attached to and is a known problem in any vibration-based interface [12]). Then, we proceeded tovibrate, using our coil (at the resonant frequency of 240 Hz), eachmagnet, one at a time, but measured not only the magnitude of thismagnet but also its two adjacent neighbors.
Figure 16 depicts our results of the magnitude of the vibrations(normalized to the maximum) of the soft magnet being excitedas well as its two neighbors. As expected, the adjacent magnets
exhibit a minute vibration, since their permanent magnetic fields
interact with that of the coil and vibrate in response. However, we
also found that these vibrations are very small, i.e., ∼10% of the
maximum at the nearest neighbor and less than 1% of the maximum
at the further neighbor. A straightforward empirical test (placing
another person’s finger over the adjacent magnets) did not revealthat one could confidently feel these vibrations in adjacent magnets.
As a takeaway from this evaluation, we recommend researchersand practitioners to keep adjacent soft patches at least at 5 mm ofeach other.

7.4

Technical Evaluation III. Measuring &Optimizing the Magnetic field of Our Coil

While in our previous evaluations we characterized the vibrationof our soft magnets to precisely optimize their frequency/intensity,
we now turn our attention toward optimizing & evaluating ourwearable coil. The objective is simple: maximize the field strength
at the user’s fingerpad without increasing the coil size. First, we

performed finite element simulations to design an iron-doped corewith a geometry that concentrates the field at the user’s fingerpad.
Then, we experimentally confirmed that it improved the magnetic
field strength by 40%.
7.4.1 Impact of An Iron Core on the Resulting Magnetic Field. Electromagnets are comprised of a coiled wire spun around a magnetic
core made from a ferromagnetic material such as iron [33]; thisferromagnetic core concentrates the magnetic flux and results in amore powerful magnet. This is commonly seen in various types haptic devices, e.g., DC motors, solenoids, etc. Inspired by this principle,
we engineered our wearable coil to benefit from a ferromagnetic
core. However, because our electromagnet is nail-worn, a pure ironcore would be heavy and not ergonomically follow the shape ofthe fingernail. Therefore, we engineered a silicone doped with iron,which increases magnetic field, yet is soft.
We evaluated the effect of an iron-doped silicone core by meansof: (1) a simulation, which enable us to determine in detail theadvantages of our design; and (2) an empirical validation with aGaussmeter, which we present later, that provides confirmation of
the advantage but displays less resolution than the former simulation.
First, we performed a finite element method (FEM) simulation tocompare the magnetic flux density between our initial coil design
against our coil design with an added iron-doped core. As with anyother materials of this paper (e.g., software, firmware, circuits, 3Dmodels) the simulation files are provided to assist researchers withreplication or building on top of our design1 . All our simulations
were conducted using Finite Element Method Magnetics (FEMM), a
computational solver for magnetics, electrostatics, etc., widely usedin physics [5]. Our simulations were set to match our physical coiland are defined as follows: inner and outer diameter of 11 and 16.75
mm, respectively; thickness of 2.5 mm, which provided enoughspace for 42 turns of 28 AWG enameled copper wire. The coil was

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Alex Mazursky et al.

Figure 17: (a) Our simulation is run as a slice of the coil. The magnetic flux contour was calculated for (b) a coil without a core(c) the same coil with a silicone-iron composite core and (d) the same coil but with a core that biases the field to one face ofthe coil.
excited with 4.8 A to match our benchtop power supply. For theiron-doped silicone core model, the coil was encased in a composite(70 wt% iron powder, 30 wt% silicone) and a magnetization curvefor the material was imported to capture the core’s ferromagnetic
behavior [67]. Since our coil’s geometry is symmetrical, we simulate
only its cross-section (Figure 17a).
Our simulation results are depicted in Figure 17b,c, as a slice ofthe cross-section. We confirmed that adding a silicone-iron core
increased the magnetic field produced by concentrating the flux
within the core.
7.4.2 Impact of Core Geometry In The Shape On The Resulting
Magnetic Field. Having confirmed that adding a ferromagnetic core
concentrates the magnetic field, we explored whether the ferromagnetic core’s geometry would allow us to design a wearable
electromagnet that exhibits an asymmetric magnetic field, i.e., concentrates the magnetic field at the fingerpad, where it is needed for
haptic interactions.
Our resulting design is a “pot”-shaped ferromagnetic core (Figure17d). By means of FEM simulation, we found that leaving one of
the faces open “forces” the magnetic field lines to “jump the gap”,
thus concentrating the field along that face. This effectively biases
the magnetic field to one side, making it asymmetric towards theuser’s fingerpad.
7.4.3 Experimental Validation Of Core Design. Finally, we empirically evaluated our coil design by fabricating two coils: a coil with
our silicone-iron doped core and pot-shaped geometry; and he same
coil but without a core (baseline). Then, we powered the coils byconnecting them to our MagnetIO device one at a time. Using a
gaussmeter (TD8620) mounted on a caliper, we measured the magnetic field strength as a function of distance (from 0 mm to 12 mm
away from the coil; <12 mm being the thickness of a typical finger[59]. Because we hypothesized that the field in our custom coil is
asymmetric (biased towards the fingerpad) we measured the fieldstrength in two locations: (a) at the center of the coil, and (b) at theedge of the coil, where we expected the field to concentrate.
Figure 18 depicts our results of the magnetic field strength (in mT)
measured at increasing distance from the surface of the coil where
the field has been biased. Overall, we found that at any distance,
our custom coil (with its soft-iron core and asymmetric magnetic
field) produces stronger fields, which is critical since magnetic force
rapidly decays over distance. Importantly, when measured directly
at a finger’s thickness away (12 mm) at the center of the coil, thefield strength is 40% greater for the coil with a ferromagnetic corecompared to no core.
As a takeaway from this evaluation, we recommend researchersand practitioners to optimize their wearable electromagnets todirect the magnetic field where it is most useful for the haptic effects.
We have not seen this much in the design of interactive devices
and believe it might enable improvements in existing interactive
devices that are based on electromagnets, such as Magnetips [32]or Magtics [40] just to cite a few.
7.4.4 Measuring the Vibrations at the Patch vs. Vibrations at the Coil.
Last, since the electromagnetic forces act equally and opposite toeach other on the interactive patch and wearable coil, both the patch
and coil vibrate when excited. To determine the degree to which thecoil and magnet vibrate, we placed a piezoelectric sensor beneatheach of them and excited the patch at its resonant frequency. We
found that the patches vibrate 16x more than the coil, likely due
to the coil’s greater mass and constraints. Thus, we found that thetactile sensation is greater at the patch, as intended for any haptic
application.

7.5

Technical Evaluation IV. Comparing
MagnetIO’s vibration to a Linear Resonant
Actuator

To put our results into perspective, we compare our chosen soft
magnet (1 mm spring width; 7.5 mm diameter) with a conventional
linear resonant actuator (LRA). As we established, the LRA is themost similar haptic device to our approach, except that its innerworkings are rigid and thus not stretchable. For this comparison
we used the C10-100, which was driven using a function generator
and its driver at a nominal 4 V.
Figure 19 depicts our results for the magnitude of the vibrationsof our soft magnet vs. the LRA, as they vibrate over a wide range of
frequencies (0-400 Hz). As expected, the LRA resonates at 150 Hz,
which is consistent with its specifications. Also as expected, oursoft magnet (with 7.5 mm diameter and a spring of 1mm) resonates
at both 240 Hz and 310 Hz. Surprisingly, when comparing themagnitudes of each device at their resonating frequency, these arecomparable, i.e., our soft magnets vibrates as much as an LRA. Notethat our device does this while remaining stretchable. Furthermore,
our interactive patches operate consistently over a wider rangeof frequencies than an LRA; this may be attributed to the larger

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CHI ’21, May 08–13, 2021, Yokohama, Japan

Figure 18: The addition of a ferromagnetic core increased the magnetic field strength at (a) the coil’s center as well as at (b) thecoil’s inner diameter.

Figure 19: Magnitude of vibrations for our soft magnet design (MagnetIO) vs. a traditional LRA (C10-100 at 4 V).

Figure 20: Interactive Patch Confusion Matrix Across 320 Trials.
degrees of freedom that arise from the fact that our patches are
made from soft materials [6].

7.6Technical Evaluation V. Identifying
patches’ ID by means of magnetic
signatures

Lastly, to test the accuracy of our simplistic identification based
solely on magnetic signatures of the patches, we fabricated eightinteractive patches, each with a random orientation of their ID
magnets. It is extremely important to note that these patches were
not custom made. We simply fabricated 32 bar magnets (the small
ID magnets) and randomly placed these on each patch without evenchecking their orientation; this depicts the worse-case scenario for
our simple approach. Then, while wearing our nail-worn device
with magnetometer, we recorded the 3-axis magnetic field whentouching each patch. The readings were converted into a simple

rule-based classifier (if-then-else) that classified each patch basedon the incoming magnetometer readings. Then, to evaluate thesensing accuracy, one participant touched each patch in a previously
randomized ordering (320 touches, 40 touches per patch). For eachtouch, we recorded the ID predicted by our classifier.
Figure 20 depicts the resulting confusion matrix. We found theoverall accuracy across all trials to be 99.06%. This is a sufficientresult for simple interactive use, despite using random orientationsof the small ID magnets.
While this approach to identifying the interactive patch is relatively simple, i.e., a series of rules based on the physical principles
that shape magnetic fields, one could alternatively feed the magnetometer data into a more sophisticated classifier (e.g., SVM, DNN,
and so forth) to potentially expand in accuracy and sample size.
Lastly, note that we purposely used only the 3DOF of magnetometerdata for identification to understand the magnetic-only approach;however, our IMU provides an extra 6DOF (3DOF from gyroscope

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Alex Mazursky et al.

Figure 21: An example of an envisioned ad-hoc interface created by a user for their living room using six patches .

Figure 22: Examples of how MagnetIO can enhance everyday objects by creating an ad-hoc I/O space; these objects can now
sense touch interactions and vibrate in response.
and 3DOF from accelerometer) which can be fused with the magnetometer data for a more sophisticated identification approach.

8

ENVISIONED APPLICATIONS ENABLED BY
MAGNETIO

To illustrate the versatility of our approach we demonstrate a wide
range of applications, where we utilize MagnetIO patches attached
to a variety of objects to propose new interactions with haptic feedback. Broadly speaking, we organize our proposed applications into
four categories: (1) ad-hoc & ubiquitous haptics; (2) eyes-free use;
(3) adding interactivity to everyday objects; and (4) adding interactivity everywhere, even to outdoor objects, exposed to weather
conditions.

8.1

Benefit#1: Scalability—Enabling Ubiquitous
Ad-Hoc Haptic Interfaces

Figure 21 depicts an example of how a user might instrument theirliving room using six MagnetIO patches, to create ad-hoc interfacesthat fit their own needs, such as (a) haptic buttons for their e-reader;(b) haptic controls for their smart-dehumidifier, (c) volume control
with haptic detents on their armchair; (d) additional settings withhaptic feedback on their smart thermostat; (e) haptic feedback asthey touch their plant’s pot to select the amount of water from theirwatering system; and, (f) controls for their fan with haptics when
they touch the “eco” setting.
Additionally, MagnetIO patches can weave interactivity into
playful everyday objects. Figure 22 shows how patches can (a) add
dynamic interaction to a children’s coloring book; (b) add tactile
cues to board games; and (c) add play, stop, record buttons withhaptic feedback for their guitar’s looper.
8.1.1 Benefit#2: Conformability—Adding MagnetIO Patches To NonPlanar Objects, Outdoors, etc. Furthermore, we believe MagnetIO
patches are especially useful for realizing interfaces attached toobjects that are not planar, which is depicted in Figure 23. For instance, (a) music player control on their headphones; (b) additional
buttons with haptic feedback for a gamepad; and (c) added to one’s
favorite toy to feel its heartbeat.
More interestingly, Figure 24 depicts how our patches can provide interactions in extreme environments, such as contexts where
significant forces are applied or drastic weather changes.
Figure 24a depicts a user who has instrumented their bike handle
with MagnetIO patches to receive turning signals from their phone’s
GPS navigation application. When the user wants to check driving
directions, they place their fingers on a MagnetIO patch that buzzes
once or twice, in response to the navigation-application’s messages,
to notify them to turn on the next intersection to the left or right,

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CHI ’21, May 08–13, 2021, Yokohama, Japan

Figure 23: Examples of how MagnetIO patches can conform to objects of various shapes.

Figure 24: Two examples of applying MagnetIO patches inextreme contexts with significant forces or weather changes,
such as this bike’s handle; however, because our patches are
passive and soft, they resist these adverse conditions.

respectively. Here, the MagnetIO patches survive adverse weather
conditions because they are completely passive.

9

CONCLUSION

We presented MagnetIO, a new type of haptic actuator comprisedof two parts: one battery-powered voice-coil worn on the user’s
fingernail and many of interactive soft patches that can be attached
onto any surface (everyday objects, user’s body, appliances, etc.).
When the user’s finger wearing our coil contacts any of the interactive patches it detects its magnetic signature via magnetometerand makes the patch vibrate, adding haptic feedback to otherwise
input-only interactions. To allow these passive patches to vibrate,
we fabricated them from silicone with regions doped with polarized
neodymium powder, resulting in soft and stretchable magnets. This
stretchable form-factor allows our patches to be wrapped to theuser’s body or everyday objects of various shapes.
It is this novel technical implementation, based on the decomposing the inner-workings of a linear resonant actuator, that gives
rise to MagnetIO’s unique feature, it is a one-to-many haptic device,i.e., one active part (an electromagnetic-coil worn the fingernail)powers many passive actuators.
We demonstrated a range of applications that make use of MagnetIO’s patches to realize ubiquitous haptics, i.e., surfaces and objects
around the user can now exhibit interactive behavior (they canvibrate upon touch).
Furthermore, in our technical evaluation, we demonstrated that
our interactive patches can be excited across a wide range of frequencies and can be tuned to resonate at specific frequencies basedon the patch’s geometry. Furthermore, we demonstrate that MagnetIO’s vibration intensity is as powerful as a typical linear resonant
actuator (LRA); yet, unlike these rigid actuators, MagnetIO’s patches
operate as springs with multiple modes of vibration, which enables
a wider band around its resonant frequency than an LRA.
We tend to think of MagnetIO not as an end-product but as a
hardware & fabrication technique that will inspire the creation of a
new type of passive-haptic interactive devices that can even unlock
new use cases. As such, we plan to publish the detailed fabrication
process, hardware schematics and code as open-source to accelerate
future research.

ACKNOWLEDGMENTS
We would like to thank Robert Kovacs for his valuable feedback.
Secondly, we would like to thank the University of Chicago’s The
Center for Data and Computing (CDAC) for their funding andsupport.

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