HoverTap™ is a board level touch and in-air gesture sensing module for OEMs and system integrators. Display manufacturers, kiosk manufacturers and ATM and vending machine makers build this touch module into their own rugged, outdoor, medical and vandal proof products, as a drop in replacement for a conventional touchscreen. This article is about the one number every integration team eventually has to ask: how much cover material (glass, polycarbonate, an air gap, or all three stacked together) can sit in front of a touch sensor before the sensor stops working?
Why cover thickness limits PCAP
Standard projected capacitive touch (PCAP), the technology behind almost every consumer touchscreen, runs out of range behind thick covers for two separate reasons.
The first is thickness itself. PCAP senses a fingertip by measuring a tiny, localized change in capacitance at the surface of the panel. That signal weakens fast with distance, so in a typical design, cover glass past roughly 2 to 6mm pushes the change below what the controller can reliably separate from electrical noise. A display maker can retune sensitivity and claw back some of that range: the most advanced PCAP controllers can manage about 10mm of glass with a bare finger, or about 6mm of glass through a 5mm glove, depending on screen size and stack-up. But cover thickness and glove thickness draw on the same signal budget, so every added millimetre of one takes range away from the other.
The second, separate limitation is air gap, and it isn’t just a matter of distance. PCAP sensors are typically bonded directly to the cover, in solid contact, because capacitance depends on the dielectric material sitting between the finger and the sensing electrodes. Air has a much lower dielectric constant than glass, so introducing an air gap weakens the electric field far more than the same thickness of solid cover material would. That’s a big part of why PCAP panels are almost always optically bonded to their cover lens rather than left with a gap behind it: it isn’t only about optical clarity, it’s what keeps the sensor able to detect a fingertip at all. Once any air gap is introduced, PCAP effectively loses most of its sensing range.
This is why “PCAP cover glass thickness limit” is one of the most common searches from engineers trying to spec a touch screen behind anything thicker than ordinary consumer glass, and why PCAP is a hard fit for any design that needs a floating or shock-isolated cover, above all when thick protection, thick gloves and rain all have to work at the same time. The same question arrives as touch through polycarbonate, touch through Lexan or Makrolon, touch through laminated security glass and touch through armor glass (armour glass). The material changes; the physics does not.
Infrared frames: the real weakness is the exposed sensor
Infrared (IR) touch frames solve the distance problem a different way: instead of measuring capacitance, they project a grid of infrared beams parallel to and just above the surface of the screen and detect where a fingertip breaks the beam path. Because the sensing happens at the surface plane rather than through the material, IR frames are largely indifferent to what the cover is made of or how thick it is.
The real weakness is environmental. The emitters and receivers sit exposed in a visible bezel around the perimeter of the display. Dust, condensation, sun glare and physical knocks can all disrupt or damage the beam path, and once that happens the frame doesn’t just get less accurate, it stops registering touch at all. For a sealed, tamper proof or vandal proof design, that exposed bezel is often the first thing to fail.
HoverTap: touch and in-air gesture control through up to 20 mm of cover glass and air gap
HoverTap uses a different sensing principle again, HoverCore™, an electric-field method that tracks a fingertip’s 3D position in the space above and through the cover, rather than measuring a localized change at one point on a surface. That’s what lets the combined thickness of cover material plus air gap reach up to 20mm.
That number depends on which capability the application needs:
- Multi-touch, which most integrators default to, reaches up to ~13mm of cover and air gap combined.
- Single-touch reaches further: up to ~20mm of cover and air gap combined.
- Hover and proximity detection reach further still, up to 100mm above the surface, because that mode isn’t limited by cover thickness the way touch is.
Exact ranges vary by module size. If a specific combination of cover, air gap and touch mode is load-bearing for your design, just ask us for the numbers on your target module, or send it to us as part of an evaluation request.
Why an air gap helps instead of hurting
The air gap isn’t something HoverTap merely tolerates. In a rugged or outdoor design, it’s doing real mechanical work. Impact-rated covers are almost always polycarbonate or a semi-flexible laminate rather than tempered glass, specifically because they flex under a strike instead of cracking. That flex has to go somewhere. Bond the cover directly to the display and the impact travels straight into the LCD behind it, so a hit the cover itself shrugs off can still leave you with a cracked panel or dead pixels.
Leave a gap, and the cover has room to flex into before it ever reaches the glass behind it. A sensing method that only works within a couple of millimetres of the surface can’t tolerate that gap, since its entire usable range gets spent on the cover material with nothing left for the air behind it. That’s the PCAP problem described above, restated as a mechanical constraint. Electric-field sensing doesn’t have that constraint, which is the actual engineering reason HoverTap’s spec is written as cover material plus air gap, combined, rather than cover thickness alone. It is also what lets integrators reach IK10 on the finished product, in IP65 and IP67 enclosures, with a sacrificial cover that can be replaced without replacing the display.
What this looks like in integration
HoverTap is built to drop into a design the way a conventional touchscreen would: HDMI in, USB-HID out, plug and play, presenting to the host system as a standard touch screen with no custom driver required. There are two routes to get there: a bonded sensor applied to a display you already use, which also makes it a retrofit path for a product already in the field, or a pre-integrated module with the sensor factory-bonded to an LCD NZTech supplies, including optical bonding where the design calls for it. Both are described on the Products page.
Current modules run M7A (7″), M13B (13.3″), M15B (15.6″) and M43A (43″), with larger and custom sizes available on request. On certification: HoverTap carries UL 62368-1 at the component level; CE, FCC, RoHS, REACH, IP and IK ratings are the integrator’s to pursue on the finished product, same as with any other component-level display module.
On the software side, HoverTap presents as a standard USB-HID device out of the box. Touch, long hold, swipe, twirl and hover each map to a standard touchscreen, mouse or keyboard command, so an existing touchscreen UI works without modification the moment HoverTap is plugged in. In-air gestures are optional, not a separate integration path: a UI picks them up automatically just by accepting the extra HID commands.
How the technologies compare
| Technology | Max cover + air gap | Air gap tolerance | Glove compatibility | Rain-compatible (no false touches) | Sensor protected from the environment |
|---|---|---|---|---|---|
| Standard PCAP | 2 to 6mm typical; most advanced PCAP controllers can manage about 10mm with a bare finger, or about 6mm with a 5mm glove | Little to none: built for a bonded stack, and an air gap costs most of the sensing range | Yes, but glove thickness trades against cover thickness | Handled on most advanced PCAP controllers; the hard case is water plus a thick glove plus a thick cover together | Yes: sensing happens inside the sealed panel |
| Infrared (IR) frame | Largely thickness-independent | Yes, sensing happens above the surface | Yes | No: moisture and dust in the beam path cause false or missed touches | No: emitters and receivers sit exposed in the bezel |
| HoverTap (electric-field) | Up to ~13mm multi-touch; up to ~20mm single-touch | Yes, by design | Heavy tactical, work and surgical gloves | Yes, with gloves and a thick cover in place | Yes: sealed, one-piece front, nothing exposed |
Why HoverTap excels for integrators
- No bezel to seal or trap dirt in. The sensor sits behind a flat, one-piece front. Nothing protrudes, nothing needs gasketing around a frame, and nothing is exposed to the environment the way an IR frame’s emitters and receivers are.
- Built around the operator’s glove. Heavy tactical, work or surgical gloves all register through the full cover and air gap stack, so the interface accommodates the glove instead of the glove being chosen to suit the touchscreen.
- Rain and condensation don’t cause false touches. Because sensing isn’t a simple surface-capacitance measurement, water on the cover doesn’t read as a fingertip the way it can on a conventional touchscreen, and that holds with thick gloves and a thick cover in place.
- Drops into an existing design. HDMI in, USB HID out: a 1:1 drop in replacement for the touchscreen already in the product, not a new subsystem to design around.
Benefits at a glance
- No driver required. HID output means the host sees a standard pointing device.
- UL 62368-1, component level. A real certification an integrator can build on, honestly scoped to the module.
- Four current sizes. M7A, M13B, M15B, M43A, from 7″ to 43″, with custom sizes available.
- Two integration paths. Bonded sensor or pre-integrated module, whichever fits the design.
- Engineered and commissioned in Canada. Manufactured largely in Taiwan, with final assembly and commissioning done here in Canada.
- A real evaluation path. Test a configured unit in your own enclosure before committing to anything.
Sending us an evaluation request
If a design is close enough to the edge of these numbers that it matters, the fastest way to find out is to test it. NZTech’s evaluation unit programme ships a HoverTap module configured to your cover material, thickness and touch mode, so you can run it against your own enclosure for two weeks before deciding anything.
Tell us the cover material and thickness, the air gap you’re designing to, whether the application needs single- or multi-touch, and the module size you’re targeting. We’ll configure a unit around those numbers rather than send a generic one. Evaluation units ship to OEMs and system integrators with the datasheet, mechanical drawing and STEP file; custom sizes and lead times are quoted on request.
