A new exhibit at 91自拍 takes a look at the world鈥檚 smallest computer 鈥� the Michigan 鈥淢icro Mote.鈥� Making things smaller has been part of electronics technology since the field鈥檚 beginnings. Smaller tends to make things faster and use less power. Recently, researcher Gordon Bell observed that this miniaturization takes place according to a regular pattern and prompts new categories (or 鈥榗lasses鈥� as he calls them) of computer device at more or less regular intervals.
Bell鈥檚 Law is a corollary to, and consequence of, Moore鈥檚 Law, which tracks the same process of miniaturization in terms of number of transistors. While Moore鈥檚 Law provides guidance about the density of integrated circuits, Bell鈥檚 Law addresses what kind of computers can be made from those circuits. Bell鈥檚 new classes of computer bring with them new markets, ecosystems, and鈥攎ost importantly鈥攏ew types of user. Proliferation and miniaturization have been the two forces in the long game of computing.
Roughly every decade a new, lower priced computer class forms based on a new programming platform, network, and interface resulting in new usage and the establishment of a new industry.
The evolution of computer classes as observed by Bell鈥檚 Law
The above graph shows how computer classes have changed over time. For example, on the left of the graph, and covering the years 1955-75, mainframes with volumes in the 1,000,000,000,000 cubic millimeter range (about room-size) were what most computers looked like.
The evolution of platforms and ecosystems moved through minicomputers (microwave oven to refrigerator sized), workstations, personal computers, and so on.
The right-most point on this chart shows millimeter-scale sensors, also known as 鈥渕otes鈥� or 鈥渟mart dust,鈥� which, when deployed in large numbers, can form wireless sensor networks (WSNs). Motes are entire computer systems the size of a grain of sand that sense some environmental variable like pressure, temperature, vibration, or light. They are designed to be cheap and ubiquitous, self-powered and able to communicate with each other.
What is smart dust? Smart dust is made up of millimeter-scale self-contained microelectromechanical devices that include sensors, computational ability, bi-directional wireless communications technology, a power supply and the ability to self-organize into ad hoc networks. As tiny as dust particles, smart dust motes can be spread throughout buildings or into the atmosphere to collect and monitor data.
An early vision for smart dust? Vincent van Gogh, The Sower at Sunset.
While the chart shows motes arriving in 2020, smart dust has been here for a while, at least as an idea. Kris Pister at UC Berkeley first coined the term in about 1996, concluding that within a few more years, 鈥淲e will program the walls and the furniture, and some day even the insects and the dust.鈥� One of the sponsors of Pister鈥檚 鈥淪mart Dust鈥� project was DARPA 鈥� the Defense Advanced Research Projects Agency, a US research funding agency that supports technologies with possible military potential. Since it鈥檚 founding in 1958, DARPA has been a critical force in pushing forward technologies that were at the time speculative and unproven. Some of its notable successes: the internet (via APRANET), GPS, stealth technology, the computer mouse, VLSI design, supercomputing, and (coming soon) driverless cars. DARPA, of course, also develops defense technologies (and all the above spinoffs started as such). DARPA鈥檚 vision and reason for supporting the Smart Dust project was to 鈥渟prinkle鈥� huge numbers of motes onto a battlefield as a way of gathering intelligence and increasing situational awareness for soldiers on the ground. Since motes talk to each other over wireless networks, they can form a 鈥榖lanket鈥� of sensors over an area delivering potentially life-saving information in real-time.
But smart dust has applications far beyond this slightly science fiction scenario. Pister lists some of these:
Somewhat speculatively, he continues, 鈥淢icro-motors, combined with Smart Dust, raise the interesting possibility of making synthetic insects.鈥� As with all well-intentioned plans, there may be problems with such insects, as Control Agent Maxwell Smart reminds us.
Skipping ahead from Pister鈥檚 early and foundational work to the present day, researchers at the University of Michigan under the direction of Professors David Blaauw, Dennis Sylvester, David Wentzlof and Prabal Dutta have recently announced the creation of the 鈥淢ichigan Micro Mote.鈥� The design is a true breakthrough: an early version鈥攃alled Phoenix鈥搘as so small it could be inserted into the human eye to monitor intraocular pressure, a critical measurement for people with glaucoma.
Today鈥檚 version is a multi-layered integrated circuit with built-in solar cells, battery, microprocessor, sensors, radio and memory. The Michigan motes currently come in three types, measuring temperature, pressure or images. (The imager currently outputs images at 160 x 160 pixel resolution).
The three types of Michigan Micro Mote
Michigan Micro Mote temperature sensor balanced on edge of a penny
Close-up of the Michigan Micro Mote temperature sensor
Since motes need to be energy-independent, they gain their energy from a battery or by harvesting light energy with a photocell (or both). Some motes can even harvest vibrational, thermal or biological energy. Even better than having enough power though, is not needing it in the first place. To this end, Michigan researchers have reduced the power consumption of the motes to unimaginably small levels. The glaucoma monitor mentioned above consumed only 35 pW of power in standby mode. For an idea of how just how small this is, a single human cell consumes 1 pW.
The Micro Mote is a 鈥榮andwich鈥� of either 7 or 8 layers, some of which can be 鈥榤ixed and matched鈥� to provide specific functionality. Let鈥檚 look at the Imager Micro Mote.
Close-up of the Michigan Micro Mote imager
Cross section of the Michigan Micro Mote imager showing individual layers
Michigan Micro Mote display in 91自拍 lobby
The Micro Mote is both evolutionary and revolutionary: Evolutionary in the sense that it makes use of Moore鈥檚 Law鈥檚 prediction about ever-shrinking circuit sizes; revolutionary in the unique way in which multiple layers are packaged and interconnected to create a single device using infinitesimally small amounts of energy. As predicted by Bell鈥檚 Law, as the mote has emerged into a viable computing platform, new applications have come into view:
Michigan Micro Mote display in 91自拍 lobby
Since seeing is believing, the 91自拍, working with the University of Michigan, has created a unique display about the Micro Mote in our lobby.
It鈥檚 a simple but effective display: big things come in small packages. Poised on the pointy end of three golf tees are the three types of Micro Mote鈥� a thimble nearby contains many dozens of Micro Motes. Can you guess how many? (Ask at the front desk for the answer). For those of you with a good sense of computer history (and humor), there is also a punched card with a Micro Mote hidden in a single punched hole of the card. (Punched cards were used from the earliest days of computing in the 1940s until about 1980). Consider the implications of that: the hole in the punched card represents a single bit鈥攖he Micro Mote, which fits snugly inside it, is a complete computer system.
The potential of motes is fascinating and the technical virtuosity of the Michigan team is nothing short of stunning. It鈥檚 extremely difficult working at this scale where power management is so difficult鈥攎otes must sip so little energy it鈥檚 barely measureable, even with special instruments. The Micro Mote is the result of many years of work by a highly focused research team pushing the boundaries of the possible.
Yet there is also some concern about how motes will be deployed in our world. Like seemingly all technologies, from a hammer to a website, both good and bad outcomes are possible. Most often, good and bad uses of a technology exist at the same time. When it comes to motes, privacy advocates raise issues about undetectable surveillance while medical doctors await clinical applications that will improve patient monitoring. Security experts raise concerns about the potential vulnerability of wireless sensor networks to hacking (a problem especially if they are used in infrastructure applications) while environmental scientists can鈥檛 wait to place motes throughout their favorite field or forest canopy.
How much smaller can things really get? Fictitious male supermodel Derek Zoolander with his ridiculously small cell phone.
Only a few decades ago, these same motes, which can be dropped out of an airplane by the thousands, would have each weighed several tons and occupied a large room. It seems impossible that we have come to this point. Yet the relentless incrementalism of Moore鈥檚 Law and the passage of time gets us here. Can we go beyond Micro Motes? Do we need to? Is this the end of Bell鈥檚 Law? Stay tuned.
Special thanks to Catherine June and Professors Blauuw and Sylvester at for their assistance and for donating Micro Motes to the Museum鈥檚 permanent collection.