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MEMS MEMS ultrasonic sensor: Pushing the boundaries of AR/VR technology

Author / Editor: Luke James / Erika Granath

A MEMS (micro-electromechanical system) is a miniature machine that features both mechanical and electronic components, with the typical MEMS ranging in size from less than one micrometer to several millimeters.

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Estimates from 2017 peg the AR/VR market as being worth around US$11 billion by 2025.
Estimates from 2017 peg the AR/VR market as being worth around US$11 billion by 2025.
(Source: Adobe Stock)

The growing AR/VR market

As more and more augmented reality (AR) and virtual reality (VR) headsets have become widely available at affordable price points, the global market for AR/VR technology has grown significantly; estimates from 2017 peg the market as being worth around US$11 billion by 2025.

Although AR/VR systems were primarily thought of as technologies for entertainment purposes such as gaming, their use is now being seen more and more in an ever-growing list of industries and fields such as healthcare, transportation, retail, education, and transportation.

Making the technology more realistic

With the latest AR/VR systems being used in increasingly complex and intimate settings, such as the simulation of surgical procedures in virtual spaces, there is a pressing need to make the technology more realistic. Some of the ways that this can be achieved is by improving time-of-flight (ToF) sensors, which allow AR/VR systems to measure the distance to an object, and sensor-based location tracking.

The former, ToF, measures the distance to an object based on the time difference between the emission of light (or infrared ray or ultrasound) and its return to the sensor after it is reflected by the object. Of the three, ultrasonic can most accurately measure the distance to an object, even if it is highly reflective, because it is not affected by glass or other transparent objects, nor is it affected by lighting conditions, size, color, or other factors.

Unfortunately, traditional ultrasonic ToF sensors are too large to be embedded into AR/VR headsets.

Pushing the boundaries of AR/VR with an ultra-small MEMS-based ultrasonic sensor

TDK has developed a solution to this challenge, however: a new ultra-small ultrasonic ToF sensor named CH-101. It boasts one-thousandth of the volume of a traditional ultrasonic ToF sensor, and it is the world's first one to be MEMS-based.

A MEMS (micro-electromechanical system) is composed of several parts that typically include micro sensors, microprocessors, microactuators, units for data processing, and parts that can interact with exterior components. Unlike regular mechatronic devices, MEMS are usually manufactured by using the same batch fabrication techniques that are used to create integrated circuits. Using MEMS fabrication, microsensors, and microactuators can be integrated on the same substrate.

TDK's CH-101 product combines a piezoelectric micromachined ultrasonic transducer (PMUT), power-efficient digital signal processor (DSP), and low-power CMOS ASIC in a package measuring in at 3.5 x 3.5 x 1.25 mm.

The PMUT is responsible for emitting piezoelectric ultrasonic sound and receiving echoes from objects within the sensor's field of view. When it is combined with the DSP—a specialized microprocessor designed to process digital signals—it can be used for a broad range of new and more specialized AR/VR applications, including the sensing of an object's prevision, collision detection, and distance measuring.

Other potential applications include smart homes and buildings, robotics, wearable consumer and healthcare electronics, and smartphones.