Based on a market study conducted by Intechno Consulting, the world sensor market (all sensing principles) is growing steadily with an average annual growth rate of seven percent from $20 B in 1994 to $40 B by 2004. An emerging segment of this huge market is related to microwave sensors. According to market forecasts from Frost & Sullivan and ABI Inc., radar applications are expected to build to a $1 B market within five years, as shown in Figure 1 . Clearly, the commercial microwave sensor market is experiencing a boom. Radar technology provides what the market needs: a reliable, accurate and noncontact sensing of distance, movement and presence.
Industrial Sensors
A significant industrial application of radar sensor technology is the measurement of liquid or solid material level in process tanks. Most level measurement principles require a mechanical contact to the process, but use of contactless measurement principles is increasing rapidly. Radar offers the best performance in terms of robustness to extreme temperature, pressure, dust and aggressive chemicals. World revenues from shipments of radar level-sensing instruments are growing 15 percent per year and are expected to reach $280 M by 2003.
New competitors are currently entering this market, creating a market growth that puts price pressure on radar level-sensing instruments, which originally were high profit products. The majority of installed radar level meters operate at 5.8 and 10 GHz. However, the next generation of radar systems with 24 GHz technology pose strong competition to the existing products for two reasons: The 24 GHz level gauge can be built smaller and lighter. Hence, it can be mounted to narrow tank flanges and is much easier to handle. In addition, sharp antenna patterns that maximize the level echo while minimizing disturbing reflections are possible, providing high accuracy and measurement reliability.
The new 24 GHz systems not only utilize advanced microwave technology, they also incorporate modern digital signal processing (DSP) features such as self-calibration, self-diagnosis and automatic parameter setup, which provide the user with easy installation and low maintenance. Besides level sensing, radar technology is used in several industrial niche applications such as turbine diagnosis, moisture measurement in paper production and object detection within manufacturing lines. Figure 2 shows an increasingly common contactless measurement gauge.
Automotive Sensors
In the automotive industry, a highly competitive car market exists. Advanced features are used to distinguish cars while safety is a major consideration in new car purchases. It is not surprising that radar technology has gained strong support from leading members of the automobile industry. The automotive radar market is expected to dynamically grow to a volume of roughly $300 M to $500 M by 2003.
The revolutionary approach of automotive distance warning systems is to use front, side and backup radar systems to monitor obstacles, as shown in Figure 3 . This car vision system determines distance from and speed of detected objects and alerts drivers if they are too close to an obstacle. Radar appears to be the best sensor principle since alternatives such as laser and ultrasound fail under bad weather conditions when they are needed most.
The first 77 GHz adaptive cruise control (ACC) radar was scheduled to be available in Mercedes Benz S-class cars this spring. Besides the forward-looking radar, increasing interest is being expressed in short-distance sensor functions such as lane-change aid, park distance control (PDC), precrash detection, occupant sensing and a stop-and-go option for second-generation ACC radar systems. It is not yet clear at which frequencies these novel automotive sensors will operate, but the 24 GHz band could be a good choice with respect to production maturity and cost. The in-car sensor functions are likely to be realized using an optical basis.
The parking aid is a well-established car option that was introduced by BMW in 1991. All PDC systems shipped currently are based on an ultrasonic principle. However, ultrasound is likely to be replaced as soon as radar is offered at the same price level. As a customer benefit, radar is more robust and the microwave modules are mounted invisibly behind the bumper.
Airbag systems are another potential application for radar and light detection and ranging technology. Conventional airbag systems are triggered by acceleration or pressure sensors. Sophisticated signal processing is required to determine very quickly whether or not an accident occurred and at what time the airbags must be deployed. A precrash detection using radar could help to further improve the reliability of airbags, especially with respect to the side airbag, which is the most critical type. An additional idea behind adaptive inflation of the so-called smart airbag is the use of an in-car sensor to determine the shape and position of the occupant on each seat. The technology for future optical three-dimensional (3-D) camera chips for passenger detection is currently in development.
Although the car sensor functions discussed in this article are not yet completely mature, it is not difficult to imagine microwave and optical vision systems making their way into future automobiles. A survey of the automobile industry has determined that an appropriately priced device designed to reduce collisions could become as popular as other safety devices such as airbags and automatic braking systems, which have gained an impressive market share.
Consumer Sensors
Consumer applications, a very fragmented market, have put the strongest price pressure on sensor devices. The sensor element is only a small portion of the end product. Here, radar again competes with less-expensive principles such as ultrasound and infrared sensors. Despite the technical advantages of radar, it cannot be successful unless ultra-low cost microwave sensor elements become feasible.
The most popular radar application is motion sensing. Typical end-customer products are door openers and automatic light switches. Microwave sensors can be mounted invisibly behind dielectric covers, which is a clear advantage over other technologies. Radar motion sensors have been available for some time and it is now possible to produce a simple planar 2.4 or 5.8 GHz Doppler radar module for roughly $5. However, this cost is still higher than an IR sensor. The semiconductor industry is working on radar chips capable of operation to 100 GHz. In parallel, optical 3-D camera technology is being established. The higher the frequency, the better the sensor resolution and the smaller and cheaper the sensor element can be. The industrial, scientific and medical band at 61 GHz would be suitable for low cost sensors such as proximity switches.
Future $3 sensor elements will open up the market for interesting products in household applications. An intelligent home environment may contain functions ranging from smart doors and lights, enhanced safety alarm features, wireless identification and data transmission to more sophisticated products such as 3-D imaging cameras for cleaning robots and smart cooking.
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