Back in the olden days of the previous millennium, long before the digital revolution compressed entire albums and even movies into ultra-high-fidelity files that users could download in seconds, hundreds of millions of people relied on physical tape to store albums on cassettes (or 8-tracks) and video on low-resolution VHS cassettes.
But what if sticky tape – not audio or video tape – were a viable recording medium, too?
“There has long been an interest in developing devices that don’t need electricity and don’t have the same vulnerabilities as electronic computers,” says Nathan Keim, a professor of Physics at Pennsylvania State University.
In a New Journal of Physics paper, he and co-authors explore the soft matter physics of storing and retrieving mechanical imprints following rearrangement or distortion. For instance, how can partially peeling and reapplying everyday sticky tape mechanically store retrievable information? In other words, how can sticky tape function as a memory material?
Currently, researchers and engineers use memory materials for various purposes.
For instance, the insulator vanadium dioxide can “remember” stimuli including electrical currents, a valuable property for storing and processing data; a strong, reusable adhesive employs a temperature-activated shape-memory polymer; a liquid metal lattice rubber exoskeleton can, when heated, spring to full form from storage as a ball; a textile from wool waste can be programmed to metamorphose into desired shapes for use in fashion, aerospace, and robotics; and a robotic fabric can shift shape and rigidity for armor, self-erecting tents, and parachutes.
For Keim and colleagues, the goal is to design a memory material or mechanical memory system than can add memories without losing previous ones. An everyday example of a mechanical memory device is a combination lock which, as Keim says, “must remember the sequence of turns of the dial in order to open,” and does so by employing a property called return-point memory.
In most return-point memory systems, input reshaping the system must alternate, as when one turns a combination lock one direction and then another past the zero mark to form the next memory. Reversing steps at any time in such a system reverts it to its previous state, thus deleting the memories (as when one enters the wrong combination and spins the dial back past zero to resume attempting entry).
Seeking to design a system that could “remember a series of events without alternating the input,” Keim’s team discovered how to “store the sequence of multiple memories with a single-directional input in ordinary adhesive tape,” and learned that “the strength of the memories is tunable – meaning we can adjust how strong the memories are – and they can be erased to reset the system.”
Building an automated, pressure-measuring device for peeling tape at set distances and then reapplying the tape helped researchers demonstrate that “peeling the tape partway results in a line of strong adhesion at the stopping point that remains when you lay the tape back down,” says physicist Sebanti Chattopadhyay, the first author of the paper. “You can then repeat this multiple times by peeling the tape successively shorter distances establishing multiple lines, or memories.” The device retrieves memories by peeling tape past the marked distances, and measures the increased force required for peeling at each marker.
As Chattopadhyay explains, “Peeling past the lines erases them and resets the system. But we can also tune the strength of the memories, making them require different amounts of force to peel past, which means that each line could represent different information. We can even make some strong enough to persist after resetting the system.”
A key feature in the tape memory, says Keim, is that the information recorded last is always the first retrieved, which permits “a simple type of mechanical computation,” like “a test used for working memory in neuroscience, called a one-back comparison. Subjects are presented with a series of stimuli and have to compare each one with the previous stimulus. Because the last memory formed in the tape is always the one you encounter first during peeling, we can always compare a memory to the one that directly preceded it.”
The Penn State research could one day help designers fashion zero-electricity devices that can perform simple calculations without ”the same vulnerabilities as electronic computers,” says Keim. While he states that such devices won’t likely be made of tape, unlocking the secrets of memory materials will lead to useful developments “that we can’t yet imagine.”
Source: Pennsylvania State University
