Millimeter wave communications can carry enormous amounts of data, but the fastest wireless paths are also easily defeated by ordinary walls, glass, furniture, and people. Engineers at the University of California San Diego have now demonstrated a strikingly simple workaround: thin, 3D-printed tiles that redirect millimeter wave signals around obstacles without power, wiring, or software control.
The prototype system, called FlowForm, used passive metasurfaces costing about $2 each to improve indoor millimeter wave coverage. Across five real environments, the researchers reported an average link-rate increase of up to 94% and a coverage expansion of up to 114%. The result is not a consumer product or a finished 6G standard. It is a practical demonstration that a network of inexpensive reflectors could eventually make very high-frequency wireless systems easier and cheaper to deploy.
What Is Millimeter Wave Communication?
Millimeter wave communication, or mmWave, uses high-frequency radio bands generally treated as beginning around 24 GHz. Their wide bandwidth supports very high data rates, making mmWave important to advanced 5G and future 6G. The trade-off is that these signals are readily absorbed, reflected, or scattered by people, furniture, glass, and walls.
mmWave systems focus energy into narrow, directional beams. This improves efficiency but makes a link sensitive to distance, slight movement, and objects entering the path.
Why Do Walls Defeat High-Speed Wireless Signals?
NIST measurements of 5G mmWave obstacles found that leaves, wooden doors, plasterboard, and glass can all reduce signal strength. Because links are directional, a person can also interrupt the path between an access point and a device.
Networks have traditionally responded with more access points, active relays, or powered intelligent surfaces that steer reflections in real time. FlowForm asks whether a network of simple, fixed reflectors can provide some of that coverage without extra power or control electronics.
How Do the $2 FlowForm Tiles Work?
Each FlowForm tile is approximately 20 by 20 centimeters, or 6 by 6 inches. The researchers used 3D-printed plastic structures and a conductive coating to create thousands of engineered elements. The final design used 6,400 elements, each smaller than the wavelengths it interacts with.
These elements are not conventional antennas. They adjust the phase of an incoming wave so that energy is reflected in a chosen direction. The signal does not curve around a corner like a rope or pass through a wall. Instead, the tile redirects energy along a new straight line in open space, like a shaped mirror redirecting a light beam.
The tiles are customized for a site. Before installation, engineers map the access point, walls, ceilings, furniture, receivers, and areas that need coverage. An offline optimization process then chooses where to mount each tile and how to configure its microscopic structure. Once installed, the tile has no battery, power supply, control wire, or runtime coordination system.
Why FlowForm Uses “Major” and “Minor” Signal Flows
A single reflector can serve a nearby receiver, but coordinated surfaces create more reliable routes. FlowForm groups them into a hierarchy inspired by streams feeding into larger rivers, with the signal moving outward through reflection.
Major flows build the wireless backbone
Major flows are narrow, highly focused paths between an access point and one or more tiles. They can pass a signal over a longer distance and then around an obstruction before reaching another tile. FlowForm uses near-field focusing to concentrate the reflected energy at the next surface.
These relays do not regenerate or amplify a signal. They redistribute incoming energy, and every hop adds some loss, so researchers expect one to three major-flow hops in typical indoor designs.
Minor flows spread coverage toward users
At the end of a major flow, other tiles create wider “fan” beams that cover users from several angles. These alternate paths let the access point’s normal beam scanning select a strong route as people move, without knowing that engineered surfaces are involved.
What Did the University of California San Diego Tests Show?
The team evaluated FlowForm on a millimeter wave radio testbed in five distinct indoor environments, comparing it with other passive layouts and leading alternatives under the tested conditions.
| Measure or feature | Reported result | What it means |
|---|---|---|
| Passive tile fabrication cost | About $2 per unit | Low-cost component, not the cost of planning, installation, or a complete network |
| Tile size | 20 × 20 cm | Small enough to place on a wall or ceiling |
| Elements per tile | 6,400 | Each engineered element is smaller than the relevant wavelength |
| Real-world environments | 5 | Tests covered multiple indoor layouts rather than one ideal laboratory room |
| Average link capacity | Up to 94% improvement | Average gains varied by environment; “up to” is not a universal result |
| Network coverage | Up to 114% expansion | Measured area receiving useful coverage increased in the strongest test |
| Multi-access-point throughput | 43% additional gain | Reported for a tested multi-access-point, multi-user configuration |
| Power and runtime coordination | None for the passive tiles | No battery, wiring, or tile-side software control |
The detailed FlowForm paper published at ACM SIGCOMM 2026 is the appropriate source for the architecture, results, and limitations. The public-facing claim that speeds were “nearly doubled” is a useful summary of the 94% average capacity improvement, but the result depended on the environment and baseline.
How FlowForm Differs From Active Reconfigurable Intelligent Surfaces
Active intelligent surfaces change their reflection electronically, providing flexibility but requiring power, control electronics, and coordination software. FlowForm removes those components by designing several fixed paths before installation.
Earlier work on programmable wireless environments and intelligent surfaces explains the broader goal of turning walls and ceilings into cooperative infrastructure. FlowForm pursues it with fixed, passive surfaces.
The trade-off is adaptability: a fixed tile cannot follow every room change, so FlowForm relies on multiple pre-engineered paths and ordinary access-point beam scanning to select the best route.
The $2 figure is the approximate fabrication cost of one tile, not a complete coverage system. Site surveys, design, installation, calibration, maintenance, and the access point still cost money. The promise is that cheap, unpowered surfaces may replace multiple powered reflecting units.
What Is the Difference Between 5G, 5G mmWave, and Wi-Fi?
5G is not a single frequency. It can use low bands for reach, mid-bands for a balance of coverage and speed, or high bands for maximum capacity over shorter distances. A “5G” label therefore does not automatically mean mmWave.
Common 2.4 and 5 GHz Wi-Fi uses longer wavelengths that diffract around obstacles better, so it usually tolerates walls and indoor clutter better than mmWave. It is not always slower, especially when the wired connection is multi-gigabit.
| Technology | Typical role | Strength | Main weakness |
|---|---|---|---|
| Low- and mid-band 5G | Mobile coverage over wide areas | Good reach and building penetration | Lower capacity than very high-band spectrum |
| 5G mmWave | Very high-capacity links over shorter distances | Large bandwidth and multi-gigabit potential | Susceptible to blockage and distance |
| Wi-Fi | Local home, office, and public access | Good indoor coverage and mature, inexpensive access | Depends on router, band, congestion, and obstacles |
| Future 6G | Next-generation mobile and industrial wireless | Potential for higher capacity, lower latency, and sensing | Standards, spectrum, devices, and coverage remain under development |
Which US Carriers Use 5G mmWave?
All three major US carriers use multiple 5G bands, but their mmWave footprints differ. Verizon markets mmWave as 5G Ultra Wideband, while AT&T and T-Mobile combine high-band spectrum with lower and middle bands.
A broad “5G” map may not include continuous access to the fastest mmWave layer. Verizon’s coverage checker distinguishes network categories, and T-Mobile notes that availability depends on location and device.
Could These Tiles Make Home Wi-Fi or 5G Better?
Not immediately. FlowForm was designed for mmWave access points using IEEE 802.11ad or 802.11ay procedures. Most home routers do not use these high-frequency links, so the tested tile design would not automatically improve an ordinary 2.4 or 5 GHz Wi-Fi network.
Commercial adoption would require several missing steps:
- Fabrication and durability: thousands of cells must be calibrated consistently and survive handling, dust, moisture, and scratches.
- Site-specific design: engineers need an affordable way to map a room and generate suitable patterns.
- Bandwidth testing: a design optimized for one channel may not work across every mmWave band.
- Standards and certification: commercial networks must demonstrate safety, interference control, and interoperability.
- A business model: a building owner or operator must recover the installation and maintenance cost.
The researchers have filed a provisional patent and expressed interest in collaboration. That points toward possible commercialization, but there is no announced date for consumer tiles.
Are There Health Concerns About Reflecting mmWave Signals?
FlowForm tiles do not generate radio energy; they redirect energy already emitted by an access point. ICNIRP states that compliant 5G exposure is not expected to cause adverse health effects. Higher frequencies are absorbed more superficially under compliant exposure limits, but network operators must still ensure that reflected energy does not push local exposure above applicable limits.
Frequently Asked Questions
Is mmWave faster than Wi-Fi?
It can support much higher rates than conventional Wi-Fi because it offers more bandwidth, but distance, obstacles, device support, and network load determine the actual result.
What are the main drawbacks of mmWave?
Short reach, poor penetration through many materials, sensitivity to people and objects, and difficult indoor coverage are the main drawbacks. Directional beamforming helps, but it requires careful alignment and added infrastructure.
Do the $2 tiles amplify signals?
No. They redistribute reflected energy and cannot create additional power. FlowForm relies on focusing and alternative reflection paths rather than electronic amplification.
Will FlowForm work with any Wi-Fi router?
No. The tiles were designed for site-optimized mmWave networks, not ordinary 2.4 or 5 GHz routers.
Are the tiles available to buy now?
No. The $2 figure is a prototype fabrication cost, not a retail price for a complete installation.
Could a Network of Boring Surfaces Be the Key to 6G?
FlowForm does not show that one $2 tile can transform an entire network. It demonstrates that coordinated passive, unpowered surfaces can rival more complex active hardware in real indoor environments.
Before adding another powered device to every troublesome corner, engineers can sometimes shape the space itself to provide better paths. FlowForm still needs refinement, but it suggests that solving future wireless coverage may not always mean making the electronics smarter.
