Contactless sensors are proving their worth, as the coronavirus crisis focuses attention on the need to count numbers of people in spaces, even to measure the temperature of individual humans within their field of vision.
No-contact sensors provide the solid basis to solutions for access control and body temperature measurement – both of which provide countermeasures to the Covid-19 threat – and recent developments, have made these vital devices more dependable and reliable. Such sensors can also replace ‘touch-based’ switches to operate lights and other services, eliminating a further potential infection vector.
Automated access control facilitates the distancing required for effective infection control within buildings, rooms and even crowd-controlled open spaces, while temperature measurements can detect the presence or absence of people, or to confirm that a system is operational.
For all these situations, thermal sensors represent a well-established option where the application calls simply for the detection of people. More pertinently, accurate human temperature monitoring will alert building operators to a fever and potential Covid-19 infection amongst those seeking to gain access.
Such sensors need a wide field of view, so that they can detect the presence and location of people, and other issues in a space, accurately and reliably. The Omron D6T thermal sensor, for example, is based on an infrared sensor which measures the surface temperature of objects without touching them. It does this by using a thermopile element, which absorbs radiated energy from the target object.
The MEMS thermopile is integrated with a custom designed sensor ASIC that bundles a signal processing microprocessor and algorithm into a tiny package. As a result, the sensor is said to offer the highest signal-to-noise ratio (SNR) in the industry. Clear and reliable measurements can easily be interpreted by the system.
Separating people from the background
A matrix type of sensor makes it easy to separate human and background temperatures (See above). Practical applications therefore depend on the number of sensor elements and how close the array is to the human. Using infrared detectors means there is no attenuation of signals by the atmosphere, so resolution depends entirely on the sensor’s field of view (FOV).
Many such applications can be served by established products, ranging from a single sensor element, up to arrays of 1024 elements. The D6T 4x4 sensor can measure face temperature at distances up to 1m for access control, whilst the D6T single-eye sensor is more suitable for wrist or forehead wearable devices. With suitable calibration, temperature accuracy on the D6T 4x4 sensor can reach ±0.2degC giving a reliable identification of fever.
At longer distances, the wide-angle version of the device based on 32 x 32 elements provides a view across 90.0° by 90.0°. This equates to a square field of view measuring 200cm x 200cm, so allows people to be detected in a whole room from a single point. In this case, reduced precision makes fever detection somewhat unreliable at long distances. Nevertheless, it is accurate where the target is 100cm away, and it is even possible to make reliable temperature measurements where the face is partially obscured, for example by glasses, goggles or a PPE face mask.
Reducing COVID infection
Dealing with a pandemic requires more than just data. Intelligence in the form of human vision technology adds a further dimension to coronavirus countermeasures based on optical sensors. Smart optical sensors such as HVC-2 image sensors (See below), can detect faces, facial features and human bodies – even estimating age and gender of the humans in the captured images.
Any embedded developer can add face recognition functionality to a system without the need to understand the algorithms or the optical design. This in turn makes it possible, for example, to link with databases for tracing coronavirus victims and tracking their contacts.
Human Vision Components are modular solutions, and each provides ten key image sensing functions: detection of a human face, hand or body, face recognition, gender detection, age estimation, mood estimation, facial pose estimation, gaze estimation and blink estimation. In each case, the module returns a value together with a degree of certainty, allowing programmers to configure the response appropriately for each individual application. No personal or private data are stored, so these devices do not compromise the subject’s privacy.
The technology comes in a very compact configuration. It can be readily integrated into established systems or implemented as part of a new design.
Basic sensing functions could aid distancing in the workplace or public spaces by counting the number of people in the room or detecting when people are too close together. More sophisticated solutions – for example applied to digital signage, vending machines and payment stations - will help eliminate the need for physical human contact. One example: automatic face detection, age estimation and gender estimation could reduce the amount of physical interaction for customers who stand in
front of the digital signage. Such an approach could be used identify people in at-risk categories and present them with specially targeted messages.
Using these sensors, a variety of infection-limiting precautions could be integrated together using one set of vision modules. The data they collect can be responded to automatically, saved or collated centrally, and passed to an operator only when necessary. Applied to workplaces, it could track individuals through the premises, recognising when arrive and leave, and reducing physical contact by setting-up heating, ventilation and lighting to individual requirements.
The range of applications extends beyond public spaces and the workplace. Medical and care facilities are another sector where image sensors can help in the fight against Covid-19. From access control based on body temperature or facial recognition, the image sensor can help maintain distancing and reduce overcrowding, additionally separating the infected from the healthy.
Contactless switching
Pre-COVID, we all reached for the light switch in a room without a second thought, but these days we are more cautious. Doors, drinks dispensers, soap dispensers, toilet flushes – every day in the workplace and other public environments we touch countless switches that have also been touched by hundreds of complete strangers. This is no longer acceptable to many, and may indeed become the subject of regulatory restrictions. Fortunately, contactless sensors provide an ideal solution that can easily be implemented in environments where the spread of harmful bacteria and viruses needs to be reduced. The latest devices offer exceptional performance, with a longer detection distance and a convergent light beam that triggers accurately on an object within a tightly specified target area, ignoring any objects in the background or foreground.
Omron B5W-LB LCR sensors are reliable and offer repeatability of their detection performance, even when presented with target items of different colours and types of surface including reflective surfaces. With digital outputs, designers are offered a simple and easy to integrated electronic control that reliably delivers the expected performance.
Who knows what the ‘new normal’ will actually look like? Without a doubt though, there is a real need for changes to the workplace and the home in the light of our recent experience.
Opto-sensing technology has an important part to play, and it may well be that contactless switches will become the norm even when COVID is a distant memory.
Author details: Gabriele Fulco, European Product Marketing Manager Sensors, Omron Electronic Components Europe B.V
