Palpable Pulse: An exploration of ferromagnetic interfaces to visualize personal health data

Jason Zhu
5 min readMar 9, 2020



This post is a catalogue of ongoing experiments to create a “tangible” interface that displays personal health data. As this post continues to mature, I hope to expand my scope beyond pulse and the material explorations beyond ferrofluids.

Personal Health
Our personal health habits influence nearly all aspects of our daily lives. Sleep quality can influence our mental health while tachycardia (rapid heartbeat) can suggest psychological stress. It comes as no surprise that personal health devices—such as Fitbit—have staked their fortunes on their ability to catalogue, analyze, and display personal health data. While these have proven valuable to many people, the interfaces are exclusively digital.

This begs the question of how strongly do passive digital interfaces influence user behavior? In Fitbit’s case, the interface is static and only accessed upon a user’s own volition of an occasionally generated push notification. Given how many digital application vie for their users attention, I would hypothesize that there is tremendous potential for physical interface that can physically represent personal health data to supersede its digital counterpart. A physical interface, perhaps situated on ones desk, is able to embed itself as not only a more present force in one’s life but as a more relatable entity—it’s much harder to understand the impact of a poor nights sleep seeing a number than it is to see it’s damage physically represented. While this goal remains distant, this inquiry is a step towards realizing it.

Ferrofluid Interfaces
Ferrofluids have long interested me for its unique properties. While solid magnets can be leveraged to move other materials to produce interfaces, ferrofluids are the material. As such, ferrofluids harbor an interesting potential as a “tangible” interface (though I would not recommend touching one!). While ferrofluids are often portrayed as jet black and spiky, when manipulated in a certain way they can appear distinctly organic and nearly life-like.

Initial Concept Development

While there are many personal health data points I can explore, I decided to replicate pulse data first given its steady and easily understood nature.

Before I was able to try to physicalize this effect, I spent a lot of time conducting experiments to familiarize myself with ferrofluid and its unique properties. First, I moved traditional magnets closer to and farther away from a petri dish of ferrofluid. This quickly became redundant and I switched to an electromagnet to simulate the movement of my hand. By varying the voltage being sent over the DC power supply, I was able to see how ferrofluid would respond in a more consistent manner. This worked to demonstrate the principle, but the form and effect was still rudimentary at best.

The next step was to determine how I might map pulse to an electromagnet. I used a MOSFET to help vary the voltage without having to physically turn the power supply’s knob, some simple Arduino code to send pulses (on/off) with a slight delay, and a CDS photoresistor to increase or decrease the pulse delay. This really served as the foundation of what was to come next.

Left: Varying a DC power supply voltage which reduced or increased the magnetic field. Right: Controlling the delay between pulses using a CDS photoresistor

Exploring Variations in Form

With the effect of a heart beat mostly replicated, there was still some ways to go in order to create a more compelling form. Wanting to get away from the spikiness of unmodified ferrofluid, I moved to do some experiments with acrylic paint and various liquids.

Acrylic Texturing

Liquid Suspension

Suspending ferrofluid in a liquid revealed a far more organic form that could be previously realized. My first few liquid suspension tests were unsuccessful because of ferrofluid would stain the container’s surface almost immediately. This was mitigated using a mixture of 65% isopropyl alcohol and 35% deionized water. Another solution that worked was using paraffin though this did not produce the intended effect.

With the staining problem solved, I used a medium sized electromagnet and a glass jar to conduct a few experiments. What was interesting about these results was that unlike the petri dish, the jar had a slightly curved bottom. This, when combined with the liquid mitigated the spikes that would have otherwise occurred.

Left: A medium sized electromagnet and a glass jar with a slightly curved bottom. RIght: Ferrofluid suspended in paraffin

The most interesting results came when I switched to a smaller electromagnet. Whereas the large electromagnet dispersed its field in a wider area, the small electromagnet concentrated its magnetic field in a much smaller area. When taking the curved glass surface into consideration, the form really looked and felt organic.

Left: A small blob of ferrofluid centered in the middle. Right: a large blob of ferrofluid off-centered and unable to recenter without intervention.

Ferrofluids, Magnets, and Liquid?

The most novel discovery of this inquiry occurred by accident. When doing some tests, I accidentally dropped a large magnetic ball into the mixture. The ferrofluid quickly surrounded the magnetic which had a stronger relative magnetic field that the electromagnet. While the ball did not move as much, it did spark a few more explorations (detailed below).

Right: Ferrofluid surrounding a magnetic ball. Center: Ferrofluid surrounding a few magnetic disks on top of a pulsing electromagnet. Right: Ferrofluid surrounding a few magnetic disks inside a liquid mixture sitting atop a pulsing electromagnet.

A Tangible Interface

The last experiment used a small magnet surrounded by ferrofluid to replicate a pulse in a physical format. This is still a work in progress.

Additional Explorations

One additional experiment worth noting is a literal translation of a pulse through a 3D heart. Featured Below

Left: Constructing the piece. Right: Putting the piece together.
Testing the 3D representation during a public exhibition.

Resources & Literature

Coming soon!