by Sergey Komarov | February, 7th, 2019
Small, portable, adaptable optical sensors offer robust performance for intelligent solutions in a wide variety of connected applications and performance environments. Their inherent flexibility and integration capabilities give designers a programmable option that allows manufacturers to take advantage of volume cost savings and the ability to get their systems to market quickly.
In a data-driven world, connected devices have created profound impact. Smartphones are essentially a vast, globally distributed network of connected cameras, while the more recent introduction of Internet of Things (IoT) ecosystems is creating other widely distributed networks of highly instrumented devices. We don’t yet know the full impact of these emergent networks. We do know, however, that most of their utility relies upon deploying one or more sensors to detect a change in diverse environments of the real world—such as a heart rate, system temperature, or moisture measurement in a crop field—and turn it into an electrical signal that can be measured. This challenge requires sensors that are highly integrated, small, robust, stable over the long term, and draw little power if they are to meet the needs of IoT devices and service the trend toward increased portability. They also need to be adaptable as it’s likely that the measurement capabilities demanded of devices in the field will evolve while they are in use.
Versatility And Performance In Optical Sensors
One of the most versatile tools in these situations is the optical sensor which can look at things (such as products on a manufacturing line), through things (such as liquids flowing through tubes), or at reflections off things (such as surfaces that have been processed in some way). However, achieving the kind of accurate, repeatable measurements that make later analysis meaningful isn’t easy. For example, as anyone who has fitted a screen protector to their phone will know, there are an increasing number of materials available with low reflectance.
Many are being pressed into service in medical devices, for example in the windows through which sensors detect bubbles or contamination in flowing liquids. Making sense of the resultant signals demands a sensor whose sensitivity levels and output are programmable to cope with varying levels of reflectance and low-contrast situations.
It’s also worth noting that sensor signals can often be quite ‘delicate’, that is, they are often small currents or voltages measured in electrically noisy situations from sensing devices whose performance changes with environmental factors, such as ambient light or temperature, and over their operational lifetime. Managing the extraction and conditioning of such signals into valid, stable, and repeatable measurements demands analogue support circuitry that itself can be subject to ageing and drift.
Answering Application Demands Through Integration
One obvious solution to many of these challenges is greater integration; to turn a standalone sensor into a low-power sensing module that includes all its supporting circuitry, has programmable sensitivity and thresholds, and whose flexibility enables it to serve many markets and therefore to be sold at lower cost than the discrete alternative.
Integration offers many benefits. An integrated sensor uses less power and up to 80% less space than the discrete alternative, increasing the portability and/or operating lifetime of the devices in which it is used by reducing the sensor’s current draw and making room for a bigger battery. The integrated signal-conditioning circuitry handles temperature compensation to ensure consistent performance in varying environments, and automatically calibrates and adjusts the sensor’s output as components, such as the IR emitter, age.
The integrated circuitry also makes it easier to achieve useful levels of immunity to ambient light, obviously a very important issue in optical sensing. One way to accomplish this is to filter out any DC and ultra-low frequency components from the sensor’s photocurrent, on the basis that the intensity of ambient light varies slowly compared to the desired sensing signal. The integrated circuitry can also be used to calibrate the sensor to deal with challenges such as low-reflectance materials. To do this, the current to the IR emitter is ramped up steadily until the reference level for the photodetector is reached. Once it is, the current value of that LED drive is stored in on-chip memory to represent recognition of that surface in a specific situation.
Connected medicine demonstrates the need for versatility
Maintaining a sterile environment is just one challenge in developing medical equipment, made more complex as equipment operates in close contact with a patient. In a home care setting, sensors must reduce patient risk by enabling the equipment to be self-diagnosing – for example a home-based blood dialysis machine must correctly and consistently detect the presence of cartridges and waste products such as blood and other fluids. Optical devices are optimized to address this risk, measuring and sensing a range of conditions without physical contact. Portability of equipment is enhanced, as the sensor consumes minimal power while being highly integrated, as small as possible, and able to withstand a tough environment.
Flexible design solves more real-world computing challenges
In a data-driven world, dynamically adaptable optical sensing is becoming increasingly important. Integration helps overcome many of the issues involved in using discrete optical sensors, while programmability means a single sensor type is suitable for many end markets, enabling volume cost savings that make it more accessible.
Everything—from the rate at which crops grow to the rate at which your heart beats—can be captured, analyzed, and acted upon by computers. This headlong rush to instrument and optimize the world is driven by the proliferation of connected devices, as well as the IoT and the concept of connectivity in global industrial settings.
Flexibility is playing a greater role in designing the systems that literally run the world. Small and portable, and offering robust performance, adaptable sensors are clearing the way for smart solutions that not only get to market quickly but also span the spectrum of connected applications and performance environments.