Comparison of ultrasonic sensors with conventional distance measurement technologies.

Conventional technologies commonly used to measure the distance between objects and determine their position include Bluetooth Low-Energy (BLE), RFID-based tracking devices, ultra-wideband (UWB) systems, and ultrasonic sensors.

29.09.2021
 

Conventional technologies commonly used to measure the distance between objects and determine their position include Bluetooth Low-Energy (BLE), RFID-based tracking devices, ultra-wideband (UWB) systems, and ultrasonic sensors. Speaking of broadband sensors, we mean wireless communication, which uses a wide band, which is over 20% or over 500 MHz.

What are the key requirements for real world applications of social distance alerts and contact tracking in today's environment?

"Distance measurement accuracy, low power consumption for longer battery life, and a smaller and more reliable device with near-zero false warnings," said Joseph Bousaba, president of Chirp Microsystems, a TDK group company that develops ultrasonic sensors.


Figure 1: Comparison of technologies used in sensors for measuring distance. Source: Ultrasonic Sensors Can Measure Distances Between Workers Instantaneously © TDK

The distance measurement for ultrasonic sensors is very accurate, less than 1 cm. In the case of UWB, it is already 10 cm, and in the case of BLE, even several meters, which is not enough, for example, to detect two people approaching the recommended safe distance of about 2 m during a pandemic. Moreover, ultrasonic sensors use much less energy than UWB, so a small, compact proximity tag can work for several days on a single battery charge.

 
 

Practical application of the ultrasonic sensor in the social distance monitoring system.

The CH101, developed by Chirp, is an ultrasonic ToF sensor that combines a piezoelectric ultrasonic transducer (PMUT), an energy-saving digital signal processor (DSP) and a CMOS ASIC power supply in a housing measuring just 3.5mm × 3.5mm. The ultrasonic transducer mounted on the sensor transmits an ultrasonic pulse and receives the wave reflected from the object. By using ToF technology, you can accurately detect the distance to the object. Thanks to far-reaching miniaturization, the CH101 sensor can be integrated into products such as badges worn by employees.

CH101 sensor

Tags or IDs can be used for both social distancing alerts and for contact tracking. When two workers wearing a tag come within 6 feet (approximately 1.83 m) of each other, the tags may issue a warning. Moreover, the implementation of BLE into the tag structure enables it to record meetings with others and store the history of meetings in a database. If an employee is found to be infected, all contacts can be traced.


Figure 2: Technologies that use radio waves, including UWB, can give false alarms to people approaching each other through a wall or window (left). Ultrasound determines contact in the air with a minimal amount of false alarms (right). Source: Ultrasonic Sensors Can Measure Distances Between Workers Instantaneously © TDK

Joseph Bousaba also places emphasis on energy consumption. 'UWB works while searching for other devices, which constantly keeps them in pairing mode and thus increases energy consumption, while ultrasonic sensors significantly reduce energy consumption'. Generally, UWB uses approximately 400 mW in receive mode, while Chirp ultrasonic sensors require 0.7 mW to operate, which is more than 500 times less power. According to Bousaba, it is not expected that the battery will need to be charged for a week (i.e. approximately 40 hours) of actual use. Minimizing the top-up costs is another key factor from the point of view of those responsible for monitoring in factories with a large number of employees.

Source: © TDK & https://tek.info.pl

BLE devices and accompanying software from Dialog Semiconductor were also presented, offering a more accurate solution for implementing the accurate distance measurement functionality required for contact tracing.
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