The world's first MEMS ultrasonic time of flight (ToF) sensor

The world's first MEMS ultrasonic time of flight (ToF) sensor

tenco 2019-04-15

The MEMS - based miniature "silicon - chip sonar" provides millimeter - precision distance sensing with the lowest power consumption in the industry.The MEMS ultrasonic sensor can be used for range measurement, position tracking, personnel presence detection and obstacle avoidance applications in consumer electronics, robotics, unmanned aerial vehicles and other fields.

Ultrasonic time of flight (ToF) sensors are generally considered to be the best range sensors for automotive, industrial and unmanned aerial vehicle and robot 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 environmental noise, and can be used in direct sunlight environment.These advantages, along with their ruggedness, accuracy and reliability, enable ultrasonic sensors to be widely used in industrial and automotive applications.Even today, however, ultrasonic sensors require complex signal processing and are too large for consumer electronics.

One thousandth of the size, one hundredth of the power consumption

Now, TDK has launched a micro ultrasonic sensor based on MEMS. Compared with traditional ultrasonic sensors, it can provide the same performance and reliability, but its size is only one thousandth of the traditional products, and the power consumption is low to one hundredth of the traditional products.The tiny sensors could be integrated into compact consumer products to enable ultrasound detection, for example in smartphones and wearable devices.When measuring the distance, the sensor first emits ultrasonic pulses, and then listens for the echo of the target object in the sensor field of view.Each echo travels at the speed of sound, and the distance from the sensor to the target object can be accurately measured by measuring the time of flight of the echo.

Currently, two products are available to provide engineering samples to customers: the ch-101 sensor with a maximum sensing range of 100 cm and the ch-201 long-distance sensor with a maximum sensing range of 500 cm.These micro-devices use a compact 3.5mm x 3.5mm LGA package that combines piezoelectric MEMS ultrasonic sensor (PMUT) with a custom CMOS on-chip system (SoC) to complete all ultrasonic ToF signal processing (figure 1).Both ch-101 and ch-201 are powered by 1.8v power and have convenient I2C interfaces that can be easily integrated into consumer electronics.

High precision range measurement performance and wide field of view

Despite its small size, this new MEMS ultrasonic sensor delivers superior performance.For example, the ch-201 distance measurement signal noise at 120 cm is only 0.35 mm (1 sigma), which is one percent of the noise of the ToF sensor outside the competitive magenta.In addition, CH - 101 and CH - 201 can provide view (FoV), the highest can be up to 180 °, so can be implemented just a part of the entire space range of detection.A variety of shell reference designs are available to enable the customer to focus and guide the ultrasonic beam by changing the shape of the area around the acoustic port of the sensor to achieve the required horizontal and vertical field of view.

Figure 2: the distance noise of ch-201 sensor is only 1% of that of traditional infrared ToF sensor (left).The narrow-field housing is one of the reference designs available, and the transducer ultrasonic beam can be shaped to achieve the desired field of view (right).

Ultra-low power consumption on-chip system (SoC) controls the whole ToF processing process: sending ultrasonic pulse, digitizing the received ultrasonic echo, detecting ToF to the nearest target and returning 16-bit ToF signal through I2C.On-chip system (SoC) enables wake detection applications to be in a working state at all times;The total current consumption is as low as 8 A at one sampling measurement per second.Because 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, contributing to complex multi-sensor measurement functions.

Extremely wide range of potential applications

The new MEMS ultrasonic sensor is the product of choice for applications such as drones and robots, 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 passive infrared (PIR) and optical proximity sensors are less effective than ultrasonic sensors.The tiny ultrasonic sensors can also accurately track objects, such as handheld game controllers in virtual reality and augmented reality (VR/AR) systems.Smartphones are another important area of application: because the ch-101 has a wide field of view, allowing for accurate distance measurements even when mounted on the top or bottom of the phone, designers can omit the optical proximity sensor in front of the phone to achieve a full screen design.

In range measurement and object detection applications, designers previously forced to choose between large ultrasonic sensors and laser-based infrared ToF sensors can now benefit from the capabilities of new ultrasonic sensors:

Provides accurate, low-latency distance measurements at speeds of up to 100 samples per second and position noise of less than 1mm

In applications such as personnel proximity, movement and activity detection, the sensor can always keep working state with low power consumption up to 15 W

To detect objects in the field of up to 180 °, so a sensor to detect the room scene

It works perfectly under all lighting conditions, even in direct sunlight

It can detect objects of any color, including transparent objects, which improves the detection ability of target objects

Protect your eyes by avoiding laser-based infrared sensors