Vishay’s Latest IR Emitters Feature Opaque Side Walls for Reduced Side EmissionsNovember 25, 2019 by Gary Elinoff
The new construction reduces the side emissions that can cause a halo effect in camera images.
Vishay recently announced three new devices: the VSMY5890X01, VSMY5850X01, and the VSMY5940X01. These units, built on its SurfLight surface emitter chip technology, are IR emitters for 850nm, 890nm, and 940nm, respectively.
Contained in a 2mm x 1.25mm x 0.8mm 0805 surface-mount packages, the company describes the unit as the “the industry’s smallest package to offer opaque side walls.”
The VSMY5890X01. Image from Vishay
Applications for the new IR emitters may include automotive sensors, IR point sources, optical switching, and miniature light barriers.
Opaque Side Walls
Competing PCB packages generally employ transparent epoxy to embed the emitter chip. The result has been side emissions that often cause a halo effect in camera images.
The opaque side walls of the three new Vishay devices are said to prevent unwanted side emissions, making them a useful option for position tracking in virtual or augmented reality applications.
Vishay posits that the new devices can be useful in virtual or augmented reality applications. Image from Vishay
The opaque side walls might also simplify designs by eliminating the need for external barriers, such as rubber rings or other types of external barriers.
Vishay claims that this feature can eliminate steps in the manufacturing process and reduce cost, weight, and overall BOM.
Aside from emitting at different frequencies, the specifications for the three devices are remarkably similar. They feature rise and fall times of 7ns and forward voltages down to 1.6V at 100 mA.
The new devices are built on Vishay’s SurfLight surface-emitting technology. Image from Vishay
All three devices operate at a range of -40°C to +110°C. They are AEC-Q101 qualified, RoHS compliant, and halogen-free. They also support lead-free reflow soldering.
Delivering Infrared Light in a Tight Beam
The new IR sources emit their energy in a very tight beam with the angle of half intensity, (ϕ) being equal to ±60°.
As a receiver moves past 60° away from a point directly above and perpendicular to the surface of the diode, the emitted IR radiation intensity falls off by half.
Relative infrared power vs. angular displacement. Image from Vishay
The three new devices are also described as delivering the intensity of 13 mW/steradian.
What is a Steradian?
A mathematical definition of a steradian—a solid angle—can explain the tight nature of the infrared light beam that these three IR emitters generate.
For a sphere radius “r,” 1.0 steradians would be the area on the surface of that sphere equal to r2. Any sphere describes 4 * π (or: 4 * 3.14), or about 12.5 steradians.
One steradian, A = r2.. Image used courtesy of Alex Ryer
So the sun, for example, radiates all its energy equally over its 12.5 steradians. If instead, all that energy was delivered only through 1.0 steradians, it would be 12.5 times as intense, but only over 1/12.5, or 8% of its surface.
Around the Industry
Everlight offers a series of surface-mounted IR LED emitters. One example, the HIR11-21C/L11/TR8, offers a peak wavelength of 850nm. Radiant intensity is 1 mW/sr at 20mA.
Osram’s SFH 4043’s peak wavelength is 950nm. Its angle of half intensity is ±70° and radiant intensity is 6mW/steradian.