The use of infrared sensors to accurately measure the chemical composition of materials or gases in military applications is well known. Now, however, given their rapidly declining price tag, these IR sensors are gaining traction in Internet of Things M2M applications, including medical diagnostics, imaging and industrial process controls, fire detection and remote gas leak detection, pollution monitoring, and real-time combustion control.
There are three major wavelength/frequency categories for the IR spectrum: near-, mid-, and far-IR. Near-IR involves fiber optic, IR sensors in the 700 nm – 1400 nm (0-7 µm – 1.4 µm) range. Mid-IR includes heat-sensing devices in the 1400 nm –3000 nm (1.4 µm – 3 µm) range, and far, or thermal imaging IR, involves 3000 nm –1 mm (3 µm – 1000 µm); all markets are seeing an uptick in sales and product development.
According to a recent market research report by ReportsnReports,¹ mid-IR sensor markets totaled $789 million in 2012 and are forecast to reach $7 billion by 2019. The impetus for growth includes price-performance increases and unit cost decreases from a high of $3,000 per unit to $300, in some cases, all the way down to approximately $8 per unit. Size has also migrated from bench sizes to portable units.
A WinterGreen Research study, Mid-IR Sensor: Market Share, Strategy and Forecasts, Worldwide, 2013 to 2019,² focuses on how sensors are becoming part of network systems in the IoT, fueling substantial demand. What is new is the use of new types of lasers for a wide array of sensing applications, from industrial process controls and environmental monitors to new medical diagnostics.
Infrared sensors are used to sense characteristics in its surroundings by emitting and/or detecting infrared radiation and are capable of measuring the heat being emitted by an object and detecting motion.
Some of the most important tools for maintaining a clean, safe, and healthy environment are sensors, sensor systems, and sensor networks that detect the presence and quantify the amount of specific chemical trace gases. Once the source is located, monitoring also provided by sensors supports mitigation and compliance.
This is also true for industrial process and automotive monitoring and health, especially in breath analysis. Today’s standard expensive and time-consuming medical tests will give way to breathalyzers able to diagnose medical conditions on the spot. Medical care will become more proactive and remote care more accurate for today’s aging population.
Infrared vision has several applications. It can visualize heat leaks in houses, help doctors monitor blood flow, identify environmental chemicals in the environment, allow art historians to see under layers of paint, and integrate it with contact lenses or wearable electronics.
For optical communication, a modulated IR light beam transmitted by an emitter LED is received by a silicon photodiode. Infrared Data Association standards provide the basis for IR communication. IR technology is the most commonly used technique for remotely controlling appliances, an important aspect of its use in IoT and in connected-home applications.
The Melexis MLX90614 family consists of infrared thermometers for non-contact temperature measurements. Both the IR-sensitive thermopile detector chip and the signal-conditioning ASSP are integrated in the same TO-39 can. Thanks to its low-noise amplifier, 17-bit ADC and DSP unit, a high accuracy and resolution of the thermometer is achieved. The thermometer comes factory calibrated with a PWM and SMBus (System Management Bus) output. The10-bit PWM is configured to continuously transmit the measured temperature in the range of -20 to120˚C, with an output resolution of 0.14˚C. The operation of the MLX90614 is controlled by an internal-state machine (Figure 1), which controls the measurements and calculations of the object and ambient temperatures and does the post-processing of the temperatures to output them through the PWM output or the SMBus-compatible interface.
IoT applications for the device include:
- Home-entertainment products
- Medical/ healthcare equipment
- Applications examples
- High-precision non-contact temperature measurements
- Thermal-comfort sensor for mobile air-conditioning control system
- Temperature-sensing element for residential, commercial, and industrial building air conditioning
- Automotive blind-angle detection
- Home appliances with temperature control
- Movement detection
- Multiple-zone temperature control – up to 127 sensors can be read via two common wires
- Body-temperature measurement
Figure 1: Block diagram of the Melexis MLX90614 family. The parts feature small size, low cost and power, easy integration, and high accuracy for many IoT applications.
The Vishay TSSP77P38 IR Detector for Mid-Range Proximity Sensor (Figure 2) is a compact infrared-detector module for proximity-sensing applications. It receives 38 kHz-modulated signals and has a peak sensitivity of 940 nm. The length of the detector’s output pulse varies based on the amount of light reflected from the object detected.
Figure 2: IoT-based applications for the device (block diagram at bottom) include navigational sensors for robotics, sensors for large-format touch panels, and object detection in parking lots, ATMs, and more.
The TSSP77P38 is a compact infrared-detector module for proximity-sensing applications. It receives 38 kHz modulated signals and has a peak sensitivity of 940 nm. The length of the detector’s output pulse varies in proportion to the amount of light reflected from the object being detected.
Another interesting example is the Intersil ISL29021 Digital Proximity Sensor with Interrupt Function, (Figure 3) an integrated-proximity and infrared sensor with a built-in IR LED driver and I²C interface. It provides infrared sensing for proximity estimation featured with interrupt function.
Figure 3: Applications for the ISL29021 (block diagram above) include mobile devices, consumer devices and industrial and medical proximity sensing.
For infrared and proximity sensing, an internal ADC is based on a charge-balancing A/D conversion technique that digitizes the output signal from the photodiode array when the internal IR LED driver is turned on and off. A noise-cancellation scheme rejects unwanted IR noise. The driver output current is user selectable up to 100 mA to drive different types of IR emitters LEDs.
Four different modes of operation can be selected via the I²C interface: programmable IR sensing once, programmable proximity sensing once, programmable continuous IR sensing, and programmable continuous proximity sensing. The ISL29021 supports both hardware and software interrupts that remain asserted until the host clears it through an I²C interface for proximity detection.
In summary, as both IR and wireless technologies advance, new applications for short- and medium-range communications and control will emerge. IR wireless, used in intrusion detectors, home-entertainment control, robot-control systems; medium-range, line-of-sight laser communications, cordless microphones, headsets, modems, and a host of peripherals, will be in greater demand as an ever-greater number of “things” connect.
For more information on the parts discussed in this article, use the links provided to access product pages on the Digi-Key website.