TDK launches the world's first MEMS ultrasonic time-of-flight sensor

     Ultrasonic time-of-flight (ToF) sensors are generally considered the best distance sensors for automotive, industrial, and drone and robotics applications. It has many advantages over optical or infrared sensors. It provides the most accurate distance measurement, is not affected by the size or color of the target object, is not disturbed by ambient noise, and can be used in direct sunlight. These advantages, along with their rugged, accurate and reliable features, make ultrasonic sensors widely used in industrial and automotive applications. However, until today, ultrasonic sensors still require complex signal processing and are not suitable for consumer electronics due to their large size.

     TDK has introduced a MEMS-based micro ultrasonic sensor product that can provide the same performance and reliability as traditional ultrasonic sensors, but with one-thousandth the size and power consumption as low as one-hundredth of traditional products. The tiny sensors are so small that they can be integrated into compact consumer products to enable ultrasonic detection, for example, in smartphones and wearables. To measure distance, the sensor first emits an ultrasonic pulse and then listens for the reflected echo of the object within the sensor's field of view. Each echo travels at the speed of sound, and the distance from the sensor to the target can be accurately measured by measuring the flight time of the echo.

     Currently, two products are available to provide engineering samples to customers, namely the CH-101 with a maximum sensing range of 100 cm and the CH-201 long range sensor with a maximum sensing range of 500 cm. These micro-devices, in a compact 3.5mm x 3.5mm LGA package, combine a piezoelectric MEMS ultrasonic sensor (PMUT) with a custom CMOS system-on-chip (SoC) to complete all ultrasonic ToF signal processing (Figure 1). Both the CH-101 and CH-201 are powered by a 1.8V power supply and feature a convenient I2C interface for easy integration into consumer electronics.

     Despite its tiny size, this new MEMS ultrasonic sensor offers exceptional performance. For example, the CH-201's distance measurement signal noise at 120cm is only 0.35mm (1σ), which is one hundredth of the noise of the ToF sensor outside the competing magenta. In addition, the CH-101 and CH-201 provide a field of view (FoV) of up to 180 °, enabling detection of the entire space range with only one component. A variety of housing reference designs are also available, allowing customers to achieve the desired horizontal and vertical field of view by changing the shape of the area around the sensor's acoustic port to focus and guide the ultrasonic beam.

     The ultra-low-power system-on-chip (SoC) controls the entire ToF process: sending ultrasonic pulses, digitizing the received ultrasonic echoes, detecting the ToF to the nearest target and returning the 16-bit ToF signal via I2C. System-on-chip (SoC) enables wake detection applications to always be active; Total current consumption is as low as 8 µA at 1 sampling measurement per second. Because the drivers are written in C, developers can easily use CH-101 and CH-201 in embedded systems. In addition, a single microcontroller can control multiple CH-101 and CH-201 sensors, enabling complex multi-sensor measurement functions.

     The new MEMS ultrasonic sensor is the product of choice for applications such as drones and robotics, where other types of distance sensors do not provide the required performance. They are also ideal for smart home products such as smart speakers, where neither passive infrared (PIR) nor optical proximity sensors are as effective as ultrasonic sensors. This tiny ultrasonic sensor can also precisely track objects, for example, in virtual reality and augmented reality (VR/AR) systems, tracking handheld game controllers. Smartphones are another important application area: Because the CH-101 has a wide field of view that enables accurate distance measurement even when mounted on the top or bottom of the phone, designers can omit the optical proximity sensor on the front of the phone, allowing for a full-screen design of the phone.