Hi, I'm Craig, a researcher, engineer, and curious inventor

I'm currently a post doctoral researcher at the Human-Computer Interaction Institute at Carnegie Mellon University in the Future Interfaces Group. My research lies at the intersection of haptics, electromechanical systems, and human computer interaction. My work has won awards at various haptics and HCI venues, and led to several patents on new actuation mechanisms.

Before CMU, I was the VP of Research and Development at Tanvas, where I developed novel electroadhesive touchscreens based on my PhD research at Northwestern University in Ed Colgate and Michael Peshkin's lab for surface haptic technology development.

cshultz [at] cmu.edu

Selected Research

TriboTouch: Micro-Patterned Surfaces for Low Latency Touchscreens 🏆

Touchscreen tracking latency, often 50ms or more, creates a rubber-banding effect in everyday direct manipulation tasks such as dragging, scrolling, and drawing. In this research, we demonstrate how the addition of a thin, 2D micro-patterned surface with 5 micron spaced features can be used to reduce motor-visual touchscreen latency. When a finger, stylus, or tangible is translated across this textured surface frictional forces induce acoustic vibrations which naturally encode sliding velocity. This high-speed 1D acoustic signal is fused with conventional low-speed, but high-spatial-accuracy 2D touch position data to reduce touchscreen latency. Published at CHI 2022.

Mouth Haptics in VR using a Headset Ultrasound Phased Array 🏆

Today’s consumer virtual reality systems offer limited haptic feedback via vibration motors in handheld controllers. Rendering haptics to other parts of the body is an open challenge, especially in a practical and consumer-friendly manner. The mouth is of particular interest, as it is a close second in tactile sensitivity to the fingertips. In this research, we developed a thin, compact, beamforming array of ultrasonic transducers, which can render haptic effects onto the mouth. Importantly, all components are integrated into the VR headset, meaning the user does not need to wear an additional accessory or place any external infrastructure in their room. Our haptic sensations can be felt on the lips, teeth, and tongue, which can be incorporated into new and interesting VR experiences. Published at CHI 2022.

LRAir: Non-Contact Haptics Using Synthetic Jets 🏆

We propose a new scalable, non-contact haptic actuation technique based on a speaker in a ported enclosure which can deliver air pulses to the skin. The technique is low cost, low voltage, and uses existing electronics. We detail a prototype device’s design and construction, and validate a multiple domain impedance model with current, voltage, and pressure measurements. A non-linear phenomenon at the port creates pulsed zero-net-mass-flux flows, so-called ”synthetic jets”. Our prototype is capable of 10 mN time averaged thrusts at an air velocity of 10.4 m/s (4.3W input power). A perception study reveals that tactile effects can be detected 25 mm away with only 380 mVrms applied voltage, and 19 mWrms input power. Published at IEEE Haptics Symposium 2022.

The Application of Tactile, Audible, and Ultrasonic Forces to Human Fingertips Using Broadband Electroadhesion 🏆

We report an electroadhesive approach to controlling friction forces on sliding fingertips which is capable of producing vibrations across an exceedingly broad range of tactile, audible, and ultrasonic frequencies. Vibrations on the skin can be felt directly, and vibrations in the air can be heard emanating from the finger. Additionally, we report evidence from an investigation of the electrical dynamics of the system suggesting that an air gap at the skin/surface interface is primarily responsible for the induced electrostatic attraction underlying the electroadhesion effect.

We developed an experimental apparatus capable of recording friction forces up to a frequency of 6 kHz, and used it to characterize two different electroadhesive systems, both of which exhibit flat force magnitude responses throughout the measurement range. These systems use custom electrical hardware to modulate a high frequency current and apply surprisingly low distortion, broadband forces to the skin. Recordings of skin vibrations with a laser Doppler vibrometer demonstrate the tactile capabilities of the system, while recordings of vibrations in the air with a MEMS microphone quantify the audible response and reveal the existence of ultrasonic forces applied to the skin via electronic friction modulation. Implications for surface haptic and audio-haptic displays are briefly discussed. Published in IEEE Transactions on Haptics 2018.

On the Electrical Characterization of Electroadhesive Displays and the Prominent Interfacial Gap Impedance Associated with Sliding Fingertips 🏆

We report on the characterization of two variable friction electroadhesive displays using careful electrical and electrochemical impedance measurements. We qualitatively and quantitatively examine the properties of the skin, body, surface coating, and various electrode interface impedances in isolation using different contact interface conditions and measurement types. A lumped series impedance model explains how all impedances are related during normal usage, and the linearity of this model is shown to be valid under certain assumptions, such as high applied frequencies or small applied currents. Speculation as to the physical mechanisms underlying each impedance element is also given. This analysis unambiguously verifies the existence of a previously hypothesized key electrical system parameter: the sliding interfacial impedance (or air gap impedance). This parameter represents the large increase (100-1000 percent) in overall electrical impedance observed when a finger is sliding versus when it is stationary. It is concluded that this impedance increase cannot be explained by other measured electrical impedance elements in the system and that it vanishes again when the finger comes to rest. Published in IEEE Haptics Symposium 2018.

Exploring Affective Communication Through Variable-Friction Surface Haptics 🏆

This paper explores the use of variable friction surface haptics enabled by the TPad Tablet to support affective communication between pairs of users. We introduce three haptic applications for the TPad Tablet (text messaging, image sharing, and virtual touch) and evaluate the applications with 24 users, including intimate couples and strangers. Participants used haptics to communicate literal texture, denote action within a scene, convey emotional information, highlight content, express and engage in physical playfulness, and to provide one’s partner with an experience or sensation. We conclude that users readily associate haptics with emotional expression and that the intimacy of touch in the contexts we study is best suited for communications with close social partners. Published at ACM CHI 2014.

TPad Fire: Surface Haptic Tablet

The TPad Fire is a handheld haptic device that incorporates a variable friction surface and a tablet computer. The device is designed to enable research and design in human-computer interaction by being affordable, easy to use, and easily available. An example application is given and advances over previous devices are listed as well. The full device design, as well as example programs, were posted online. Published at HAID 2013.