FAQ

Functions and performance

• What can the sensors detect?

  The presence and location of moving objects. For example, they can determine whether there are people in a room and where they are positioned.

• What are the applications?

  The main uses are human presence detector with a range of about 10m for home security systems, white goods including room air conditioners, and so on. Other applications where the highly sensitive detection capabilities of the sensors can be put to good use include surveillance systems and gesture UI devices.

• How do they differ from other motion sensors?

  Because radio-wave ranging sensors operate at millimeter (or quasi-millimeter) frequency band, they are less affected by environmental factors such as temperature and weather conditions. Along with their ability to detect the location of moving objects, the sensors also benefit from high sensitivity, allowing them to detect even tiny movements such as breathing.

• How do radio-wave ranging sensors work?

  The sensors are equipped with a transmitter and antenna for transmitting radio waves, a receiving antenna and a receiver for receiving the radio waves reflected back from objects, and a signal processing unit that detects target(s) from the received signals. The sensor receives the echoes of its transmitted signal reflected back from detected objects. The signal is then processed and analyzed to extract information about whether objects are present, where they are located, and how they are moving.

• Can the sensors work underwater?

  No.

• What is the difference between 2D and 3D sensors?

  Whereas 2D sensors are able to detect the location of objects in a two-dimensional plane, 3D sensors are able to do so in a three-dimensional space.

• What is the difference between 24GHz and 60GHz sensors?

  24GHz sensors generally have lower detection accuracy, but have lower power consumption. 60GHz sensors take advantage of their wider bandwidth to provide high detection accuracy.

• What are the features of Socionext’s radio-wave ranging sensors?

  Socionext’s radio-wave ranging sensors free customers from the task of antenna design by integrating the millimeter-waveband antennas into the LSI, that requires special expertise. Similarly, the on-chip signal processing circuit included in some sensors can process the detected signals and convert them into information about whether objects are present and their range and angle. This eliminates the need for the customer to process the sensor signals.

• What sort of modulation is used?

  The sensors mainly use FMCW, a form of linear frequency modulation.

• At what frequency bands do the sensors operate?

  The evaluation kit for 24GHz radio-wave ranging sensors is able to use the following frequency range.
  FMCW: 24.06 [GHz] to 24.24 [GHz] The evaluation kit for 60GHz radio-wave ranging sensors is able to use the following frequency range.
  FMCW: 57.1 [GHz] to 63.9 [GHz]
  Note, however, that the frequency bands able to be used in practice will depend on the frequency allocation rules in the country of use. Please confirm these before using the sensors.

• What are frame rate and chirp time?

  Frame rate indicates the frequency of measurement. Chirp time is the time taken for each FMCW frequency sweep. It is possible to perform multiple sweeps (chirps) within one frame. Both frame rate and chirp time are configurable.

• What is the ranging accuracy?

  The theoretical resolution for distance separation when operating with a 180MHz bandwidth in the 24GHz band is around 83cm. The resolution for distance separation when operating with a 6.8GHz bandwidth in the 60GHz band is around 2cm. In practice, however, this detection accuracy can be further improved through signal processing.

• What sorts of materials are transparent to the radio wave?

  Radio waves are able to pass through materials such as ABS, acrylic, glass, cloth, and wood, However, due to factors such as reflection at material boundaries, detection performance may vary depending on the material, material thickness, and distance between the material and sensor.

• Will the sensors still work if they are dirty?

  The sensors are less affected by environmental factors than infrared sensors. However, contaminants such as moisture or dirt may degrade detection performance by causing reflection or refraction of the millimeter-wave signal.

• Can objects be detected if they are not moving?

  Socionext’s radio-wave ranging sensors are equipped with circuits designed for motion detection. Accordingly, completely static objects such as a vase or a sofa will not be detected when using the onboard signal processing circuit. People, on the other hand, can be detected as they continue to make tiny movements such as breathing, even when standing still.

• Is it possible to count the number of people present in the range of 0.1m to 10m?

  The theoretical radar separation resolution in the depth direction for a 24GHz radio-wave ranging sensor operating with a 180MHz chirp bandwidth (bw) is c/(2 × bw) = 83.3 cm, with the actual resolution being about twice that. This means that people standing close together will be detected as a single object, making it difficult to count them as two separate people. 60GHz sensors, on the other hand, can detect separation as long as there is a gap of about 10cm (c: light speed, bw : chirp band width).

• What is the maximum range for detecting people?

  While it depends on the operating conditions, detection is generally possible at distances up to about 8m to 14m.

• What is the closest range at which objects can be detected?

  While detecting objects at zero meters is theoretically possible, under realistic operating conditions it is about 10cm.

• What is the angular detection accuracy?

  About ±20°. However, the SC1221 radio-wave ranging sensor has an accuracy of about ±10°.

• What is the maximum number of people that can be detected?

  About six. Performance is slightly lower for 24GHz radio-wave ranging sensors as they have a lower distance separation resolution.

• Can the sensors distinguish between people, pets, and plants?

  It is not possible to distinguish the type of object reliably from the detection results alone. When using a 3D sensor, however, simplistic distinctions can be made based on estimations of object height and so on.

• To what extent are the sensors affected by environmental factors?

  They are less affected than other types of sensors by factors such as rain and snow. Heavy rain, however, may shorten the detection range.

• I have heard that radio-wave ranging sensors are capable of detecting breathing and heart beat. Is this true for Socionext sensors?

  Socionext’s radio-wave ranging sensors are able to detect the small movements associated with pulse and respiration. However, there is no capability for distinguishing between the two. Ultimately, it is up to the user to decide how they are to be used.

• Is a datasheet available with detailed SPI and I²C interface specifications?

  Details of the SPI/I²C access (handshake) protocol are included on the datasheet.

• What is the bus speed (for SPI and I²C)?

  The maximum supported baud rates are 50Mbps (SPI) and 400kbps (I²C).

• Can the transmission power be changed?

  The transmission (TX) power is set at the time of product shipment and cannot be modified by the customer. On the 60GHz radio-wave ranging sensors, however, the TX power can be user-specified as either -10dBm or 0dBm.

• What factors do I need to consider when designing my own circuit board?

  Performance may vary widely depending on how the sensor is mounted. Attention needs to be paid to things like the layout of other components around the sensor and the gap between the sensor and case. For details, please refer to the application notes that we supply for each product. (The application notes are not publicly available and are only supplied to customers who use the sensors.)

• I do not understand how sensor signal processing works. Can you provide an explanation?

  As the signal processing circuits in Socionext’s radio-wave ranging sensors are built-in, there is no need for customers to prepare their own signal processing software. Any customers wanting to use their own signal processing software or to implement flexible processing should contact Socionext sales.

• Is there a risk of interference with other radio equipment?

  In practice, interference is unlikely to cause any problems as long as different frequencies are used. While interference can happen when other equipment is using the same frequency band, because each radar transmission lasts for only about 1/2000th of a second in normal operation, the probability of both devices transmitting at the same time is low. As the results are consolidated from multiple detection frames, the effect of interference will be very minor unless transmissions overlap multiple times.

• Do the sensors comply with overseas technical certification?

  Reference reports on the results of compliance testing conducted using our evaluation kits are available for North America, Europe, and China (24GHz).