By Debbie Sniderman, contributing writer
If we can’t find alternative sources of energy for ultra-low-power optoelectronic devices that are mostly asleep, can we do even more with less? They are here to stay, used in devices like e-reader and retail sign displays, mobile photodetectors used in drones, photosensors used to indicate maintenance, and as gas sensors.
The trend is that more devices, displays, and sensors are being designed to run on static batteries or alternative energy sources, according to Walter Garcia Brooks, Field Applications Engineer for TT Electronics’ OPTEK product brand. Therefore, the need for ultra-efficient devices is becoming more critical to technology development.
Beyond being small, battery-powered devices must operate in ultra-low power-consumption mode; otherwise, batteries will be drained quickly. One reason behind this trend is mobility. “In the past, opto sensors could be connected by wires, but today, sensors and devices are connected by the internet, wirelessly, through Bluetooth, or are mobile, in wearables, phones, or on drones, and powered by batteries,” Brooks says.
“This change is creating a lot of innovative ideas and has been good for the optoelectronic sensor industry. Now, it’s not enough for sensors to only be smart; they have to be intelligent and make decisions on their own,” he says. “We have to add more intelligence that used to be in the peripheral circuits into the sensors themselves, more systems inside chips that analyze their environment all the time and determine when it’s appropriate to use certain parts and when it’s not. Their number-one priority is energy efficiency.”
“Power management in sensors never used to be part of the equation in the past. The motherboard handled it, in the case of a printer, or inside an engine control unit in a car. Now, the most common way to have this intelligence and remain cost-competitive is to use ICs integrated with photodetectors in a single chip,” Brooks says.
The best-powered optoelectronic sensors consume single-digit micro-amps, and the trend is heading downward to nano-amps. Brooks predicts that in about 10 years, when pico-amp devices proliferate, we will see a further proliferation of optoelectronic sensors in mobile applications. It’s at that point that the sensor consumes less energy than what is captured by the device.
“It’s always a moving target and the technology is in constant change, and the energy harvested depends on the surface area of the photocell. Five years ago, photocells could maintain sensors to working for five years, but as things get smaller, customers wanted to do the same with a photocell half as big,” he says. “In battery devices, future battery technologies will be better, and we hope that there will be batteries that hold more charge. But the trend is to make more with what we currently have.”
Another dramatic change is that it is not enough to think only about device hardware, but also its software. Decades ago, devices were controlled by hardware. Now, powered statically by batteries, most of the control is via both software and hardware.
“It’s important for designers to understand the software side of the sensors and understand how to program them,” he says. “And it is critical to understand the energy budget that they have throughout the life of the battery. A photosensor detecting autodispense in a bathroom soap machine sleeps after its last use and doesn’t know when the next cycle is. It may have to wake up every five seconds to check for the next cycle or it could be two seconds.”
Ultra-low-power devices will continue to do more with what is available. They will alert people not only during normal operation but can also detect and send a signal via the internet or a network when the battery is low. “Before, if the battery was dead, people would approach a device and it would be off. Now, the devices have to alert the user when to do maintenance,” Brooks says.
Not all ultra-low-power devices need to wake themselves up, as is the case with ultra-low-power displays that require power only when the display is to be changed, discussed later in this issue. But in either case, integration is key to doing more with less.
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