Ultrasonic Tag Helps Enforce Social Distancing

Article By : Junko Yoshida

Ultrasonic sensors might just be the wireless technology best suited to enabling contact tracing and social distancing.

Ultrasonic sensors might just be the wireless technology best suited to enabling contact tracing and social distancing. It does so “more accurately, reliably and much more power- and cost-efficiently,” claimed Joseph Bousaba, president of Chirp Microsystems, a TDK group company, in an interview with EE Times.

Source: Chirp

Fortune 500 companies, eager to get employees back to warehouses and manufacturing floors, are looking for apps and wearable devices that can alert workers when they violate social distancing precautions and come too close to one another. The companies also want these wearable devices to keep track of which workers have come into close contact with whom, when and for how long.

Wireless technology race
These embedded devices can come in different forms and shapes. Companies looking to implement such technologies are exploring options that include wristbands, lanyard clips, badges and tags, all embedded with wireless technologies.

Wireless contenders for such tasks include Bluetooth Low-Energy (BLE), RFID trackers, ultra-wideband (UWB), and ultrasonic sensors — including Chirp’s MEMS-based ultrasonic time-of-flight (ToF) range sensor.

Required for the job are: “accuracy in distance measurement, low power consumption, longer battery life, smaller device and reliability,” said Bousaba.  Given the criteria, the horse race for a technology to support social distancing and contact tracing has already narrowed down to UWB and ultrasound, Bousaba added.

Obviously, accuracy is the biggest factor in measuring social distance. Ultrasound offers less than 1 cm accuracy. In contrast, UWB provides an accuracy of 10 to 20 cm, while BLE comes in at 1 to 2 meters. That alone illustrates, according to David Horsley, co-founder, CTO and engineering at Chirp, “BLE just doesn’t cut it.”

BLE has another strike against it.

Initially, BLE was pitched for contact tracing, because the technology is already designed in smartphones. Norway, for example, has adopted a centralized approach to design a contact-tracing app called Smittestopp (translated as “infection stop”). The app collects user data via Bluetooth and GPS location integrated inside a cell phone. Last week, the Norwegian data inspectorate, responding to privacy concerns, placed a temporary ban on the processing of personal data associated with the app, reported ZDNet.

Horsley sees it as a sign that cellphones don’t cut it as an ideal device for contact tracing.

How are they implemented?
Obviously, smartphones used by the general public don’t satisfy privacy concerns.

But how exactly would wireless technology-based wearable devices work inside corporations?

Tags or badges can support both social distancing and contact tracing, explained Horsley. When a worker gets within six feet of another worker, the badge either lights up or sounds a beep. The tag also automatically records an encounter between the two workers, storing the data inside the tag.

The tag — which also incorporates BLE or ZigBee — connects to the database, at the end of the workers’ shift. So, if any worker tests positive for Covid-19 the next day, all his or her contacts are traceable.

It’s up to each system company to design each tag or badge. Chirp shares an example reference design for ultrasonic tag as follows.

Chirp Ultrasonic Tag Reference Design. (Source: Chirp)

Used in the reference design is CH101, Chirp’s MEMS ultrasonic ToF range sensor. Housed in a 3.5 mm x 3.5 mm package, it combines a MEMS ultrasonic transducer with a power-efficient digital signal processor (DSP) on a custom low-power mixed-signal CMOS ASIC.

The sensor handles a variety of ultrasonic signal-processing functions, enabling customers flexible industrial design options for a broad range of use-case scenarios, including range-finding, presence/proximity sensing, object-detection/avoidance, and position-tracking.

UWB vs. BLE vs. Chirp
Among various wireless technologies pitched for social distancing and contact tracing, how does Chirp’s MEMS-based ultrasound technology stack up?  Chirp shared the following table.

Comparison among ranging technologies. (Source: Chirp)

Notable implementation issues, shown above, include size and power consumption. Because UWB requires an antenna, the UWB-based solution ends up getting bigger than BLE and Chirp’s miniaturized ultrasonic.

Power consumption, of course, is an even bigger problem, and the way UWB and ultrasound behave when each is used for social distancing reveals another clear difference between the two technologies. When tags are not paired, they remain in the pairing phase. That means, as UWB tags continue to search for other devices to pair, they must be in a receive mode, which alone drains a lot of battery power.

Bousaba explained that it’s analogous to what any cell phone user would experience, when he is too far from a cell tower. Searching for other devices can drain the battery quickly, since the receiver must remain on for a substantial duty cycle to ensure discovery within the allotted time.

In general, Bousaba said that UWB consumes 400 mW, while it takes ultrasound only 400 µW during pairing phase.

Further, Chirp’s ultrasonic sensors enables low latency detection when two tags are in close proximity. It happens within 1 second, said Bousaba, enabling real-time alarm via direct tag to tag communication via ultrasound. The ultrasonic sensors offers up to 180-degree horizontal field of view. It will take two sensors if it is necessary to enable 360-degree view.

‘Near zero’ false positives
The real claim-to-fame is ultrasound-based sColutions’ ability to create “near zero false positives,” according to Bousaba.

For example, if a barrier separates two users, ultrasound will reflect off the barrier regardless of the material. No social contact is recorded unless there is a path through the barrier through which air can travel.

On the other hand, for RF-based solutions in UWB, the RF wave will not reflect off a barrier unless it is conductive. Users on opposite sides of solid walls or glass partitions will record false positive social contact, which could lead to unnecessary quarantine and psychological stress, according to Chirp.

Of course, UWB could mitigate such false positives by adding tags to barriers or building gateways. But adding anything to the infrastructure invites more complexity and additional installation costs, explained Bousaba.

Ready for the general public?
While the business community sees the wireless technology for social distancing or contact tracing as “essential,” Chirp’s Horsley cautioned, “We are not sure if this will be broadly embraced by the general public.”

Nonetheless, in the business world, Chirp already has customers lined up. Some, initially skeptical of ultrasound sensors, tested it in edge-case scenarios, coming away satisfied with the results, said Bousaba. Chirp hopes to see its ultrasonic sensors start replacing UWB.

How much do these tags cost and when will Chirp be ready to roll it out? Bousaba said, “We hear some of UWB tags cost over $199. We believe we can enable solutions below $100 with our sensor technology.”

Even at $100, tagging each employee is a major investment, especially at a time when some meat-packing companies aren’t even shelling out much less money to test their own employees.

Bousaba said, “Most of our customers are Fortune 500 types of companies.”

Given that companies hope to mobilize social distancing and contact tracing as soon as possible in factories and warehouses, Chirp said with its readily available ultrasonic ToF range sensors, customers can have tag solutions in the market in the third quarter this year. Chirp is working with multiple system integrators and customers to build tag solutions based on the CH101.

Horsley added, “Time is of the essence here.” He noted that the University of California Berkeley, for example, is interested in tags for students coming back to campus in September. Berkeley is where Horsley got his PhD. Today, he is faculty co-director of the Berkeley Sensor and Actuator Center (BSAC).

In the pandemic era, with no vaccine and no effective cure for Covid-19, the quest is on for technologies that might ameliorate the social and economic crisis.

Wireless technology that enables social distancing and contact tracing is hardly the be-all and end-all. But at least, Horsley said, “We are glad for the opportunity to apply our technology for good.”

Leave a comment