How smartphone lidar can test blood, milk, etc. • The register

Could the light detection and ranging (lidar) sensors of your future smartphone replace laboratory equipment in health and food safety applications? It sounds like a possibility.

Researchers at the University of Washington to count the handset’s lidar can determine the properties of fluids, saving you the hassle of using expensive lab equipment. The amount of liquid needed for a lidar test on a smartphone is also significantly less than in a medical lab, they said.

One application of lidar would be to test blood for clotting. The researchers also found that their method was able to determine the fatty properties of milk and whether the liquid had been adulterated, and to identify a particular liquid among ten samples.

Typically, fluid measurement for things like blood viscosity is done using radio signals, which display phase and amplitude differences as a function of clotting factor. This particular test requires a vessel filled with blood to a depth of almost an inch. And patients who need blood clotting measurements should take them regularly.

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Understanding how researchers repurposed lidar sensors from smartphones for their experiments means understanding the basics of how lidar works. Your phone’s lidar fires pulses of light to measure the distance to various objects in the camera’s view to help the device take better photos.

Point a laser, including a near-infrared lidar pulse, at a diffuse surface and you’ll see what’s called laser speckle. This shimmer can be picked up by a phone’s camera. Therefore, you can fire a lidar pulse from a handset onto a surface and have the same device observe the resulting speckle.

“When the variation in surface height is greater than the wavelength of the laser, light from different points on the surface in the camera’s pixel resolution travels through different paths and therefore overlaps each other to create constructive and destructive interference patterns,” as the university team put it. in a document about technology.

Laser spots in liquids are affected by any particle in the liquid larger than the wavelength of the laser, usually around 800 nm. As these particles move, the speckle pattern changes and the phone’s camera can capture it for software analysis.

This is where you’ll find the science at the heart of research. Based on Brownian motion, particles in a liquid move differently depending on the viscosity of the liquid. Armed with this knowledge, the academics were able to obtain an indirect measure of viscosity by examining the temporal variance of laser speckle.

This discovery, we are told, allowed researchers to distinguish between clotted and non-clotted blood with a single lancet-sized drop, to differentiate between different types of milk, and whether the milk had been adulterated, and to distinguish 10 classes of liquid with an average accuracy of 91.5%.

The transmission power of the lidar is an issue. For some liquids, especially clear or translucent liquids, the laser pulse output power from the sensor is too low, preventing readings from being taken. This is an academic study, after all it is not an expedition product.

Beyond milk and blood, researchers point to other uses of laser speckle imaging that could be tested with a smartphone, such as burn assessment, birthmark monitoring, blood flow tracking in retinas and non-medical uses such as microplastic analysis. Again, this is only in the experimental stage.

Apple’s iPhone 12 Pro and iPhone 13 Pro are handhelds with lidar that come to mind. The academic team said their paper had been accepted into the March 2022 edition of ACM’s Proceedings on Interactive, Mobile, Wearable, and Pervasive Technologies. ®

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