From Images to Movement, Devices Catch Data

Driven in part by the Internet’s insatiable need for data and in part by emerging body and machine monitoring applications, manufacturers are producing sensor devices that measure a variety of parameters: pressure, temperature, and acceleration along with ECG and EEG signals generated by the human body. The devices range from venerable RTDs to innovative MEMS-based devices.

And the sensors don’t act alone. They often get an assist from companion devices that provide signal conditioning, wireless communications capability, and computing power. Technology demonstrations and product introductions during the second half of 2011 suggest what might be in store for this year in automotive, human-performance, medical, aerospace, and other applications areas.

One high-flying example incorporating vision sensors as well as an accelerometer comes from Jonas Pfeil, a computer engineer and recent graduate with a master of science degree from the Technical University of Berlin. Pfeil and colleagues demonstrated a throwable panoramic camera that eliminates the time-consuming process of acquiring multiple images and stitching them together.

Pfeil’s innovation is to incorporate 36 fixed-focus, 2-megapixel mobile phone camera modules mounted in a robust 3-D-printed spherical enclosure that is padded with foam and handles like a ball (Figure 1). When the ball is thrown straight up, the accelerometer monitors launch trajectory, triggering the image sensors when the ball reaches its apogee and movement is at a minimum. When the ball is caught, images can be downloaded over USB and displayed on a spherical panoramic viewer. As of this writing, Pfeil and colleagues planned to present the technology at Siggraph Asia in December.

Figure 1. Throwable Panoramic Camera
Courtesy of Jonas Pfeil, jonaspfeil.de/ballcamera

Automotive Applications

More down-to-earth sensor presentations occurred during the Automotive Testing Expo North America last October. At that show, for example, Meggitt Sensing Systems showcased its recently expanded product line offerings for automotive testing, including high-performance piezoelectric, piezoresistive, and variable capacitance (VC) accelerometers; shock and vibration sensors; dynamic and static pressure transducers (piezoelectric and piezoresistive); acoustic sensors and instrumentation; displacement sensors; servo accelerometers and inclinometers; inertial measurement units; linear variable differential transformers (LVDTs); electromagnetic and piezoelectric structural excitation devices; conditioners; calibration systems and services; and signal-conditioning electronics, cables, and accessories.

Specific products highlighted at the show included the Endevco^® Model 2226C, a compact and lightweight adhesive-mounted piezoelectric accelerometer designed for general-purpose vibration testing of smaller structures and objects; the Model 7264C Series of low-mass DC response piezoresistive shock accelerometers designed to measure the long duration transient shocks associated with automotive crash testing and other applications requiring minimal mass loading and a broad frequency response; and the Model 4830A, a handheld accelerometer signal-output simulator and tachometer for verification of instrumentation settings and cable integrity within automotive test cells.

The company also focused on the Endevco Model EM46AQ ½” random incidence microphone and iTEDS-enabled preamplifier set (per IEEE 1451.4-2004) designed to support larger channel count precision acoustic measurement requirements within automotive interior noise and NVH-related applications. In support of automotive airbag inflation, vehicle transmission, and hydraulic systems testing, the company presented the Endevco Model 8510C rugged, miniature, high-sensitivity, high-resonance gage piezoresistive pressure transducer series featuring nonlinearity of <1% to 3x over-range with 4x minimum burst pressure, 20k g shock resistance, and high stability in temperature transients. Finally, the company highlighted the Sensorex SX12 series of rugged, high-accuracy miniature LVDTs designed for high-precision displacement measurements within a variety of embedded automotive applications including production line assembly, control and welding, and laboratory test-bench linear displacement and force and traction.

MEMS Accelerometers

MEMs-based accelerometers have been the focus of several manufacturers. In September, for example, Colibrys (Switzerland) announced its MS9001.D, a MEMS-based tilt sensor targeted at industrial and aerospace markets for use in platform stabilization applications. The company reported that the product already has been qualified for use in conjunction with satellite communications and scanning radar antennas, remote surveillance cameras, industrial tabletops, or fire-control servo-systems.

Colibrys said its silicon-based MEMS accelerometers offer advantages as precision tilt sensors in terms of size, power consumption, and cost and that its sensors provide high precision and linearity almost independent of the operating environment. Stephan Gonseth, product development manager at Colibrys, said in a press release, “This new product is Colibrys’ first MEMS-based motion sensor designed specifically for use in ±1g tilt, control, and measurement applications. The MS9001.D is offering the traditional advantages of Colibrys inertial products, such as long-term stability, low temperature coefficient, or high reliability under harsh environments on top of low power and low noise, generally required for precise measurements.” The device comes in a standard small LCC 20 ceramic package measuring 8.9 mm x 8.9 mm.

Human Performance

While Colibrys highlighted industrial and aerospace applications, in October Analog Devices touted an application in human performance potential for its MEMS inertial sensing technology—specifically helping a scientific research center reduce the risk of injury and improve the performance of competitive rowers. The center, Roessingh Research & Development (RRD) in the Netherlands, specializes in ambulatory 3-D analysis of human motion and uses the Xsens MVN System to study rowing kinematics. The Xsens MVN System, in turn, was developed by Xsens Technologies B.V. of the Netherlands; the system combines Analog Devices’ iMEMS^® inertial-sensing technology with sensor fusion algorithms and biomechanical models to produce accurate 3-D movement and kinematic output. In this latest application, MVN provides coaches with comprehensive, accurate information about the movement, timing, and behavior of individual rowers or assembled rowing teams (Figure 2).

Figure 2. Figure 2. Competitive Rower Equipped With Analog Devices’ iMEMS Inertial Sensing Technology to Help Study Rowing Kinematics
Courtesy of Xsens Technologies B.V.

Xsens MVN is equipped with 17 motion trackers containing more than 80 iMEMS inertial sensors and 17 Blackfin^® DSPs from Analog Devices.  iMEMS inertial sensors integrate proprietary iMEMS sensor designs with signal-processing technology.

In the RRD pilot studies, rowers wore the Xsens MVN system while rowing for 20 minutes. The data was rendered via the Rowing Coach Assistant (RCA) software application built by RRD using the Xsens MVN SDK to precisely replicate the real-time 3-D movements of the rowers. The highly accurate and detailed rowing cycle data analysis of RCA provided the RRD research team with clear live visualization of coordination issues. Rowing coaches can use this information during training to optimize and correct movements or reduce the risk of injury to the rowers.

“As a key enabling technology within Xsens’ motion capture solutions, iMEMS inertial sensing devices are allowing RRD to apply advanced motion tracking technology to competitive rowing in ways previously unexplored,” said Chris Baten, program manager at RRD, in a press release. Bill Murray, product line director of the MEMS/sensor technology group at Analog Devices, said that in addition to keeping athletes in top form, the company’s MEMS inertial-sensing technology can improve navigation in medical robots, help industrial operators extend factory equipment life, and prevent automotive rollovers.

Targeting Health Care

A combination of MEMS accelerometers with other sensors can support personal health monitoring and portable medical device applications, said Charles G. Sodini, the LeBel Professor of Electrical Engineering at MIT, at his DesignMed keynote address last September. He hopes to see point-of-care instrument technology progress as rapidly as computer technology has and, to that end, is working through the Medical Electronic Device Realization Center (MEDRC) at MIT to revolutionize medical device design.

Sodini cited several applications MEDRC is addressing or will address in the future: wearable products such as cuffless blood-pressure devices, minimally invasive monitors, point-of-care instruments (including lab on a chip), data communications techniques (including body-coupled body-area networks in which the body itself is the communications medium), and imaging systems (including smart ultrasound devices that reduce technician training requirements).

Sodini described a wearable heart monitor that incorporates mechanical, electrical, and optical sensors to make ballistocardiogram (BCG), ECG, and photoplethysmography (PPG) measurements, respectively. (BCG relates to the body’s mechanical recoil in response to a heartbeat while PPG is an optical technique that can measure blood oxygen saturation.) The prototype device is worn on the ear, which, he said, is a great anchor that can support everything from eyeglasses to Bluetooth headsets.

MEDRC won’t be manufacturing such devices. Sodini said MEDRC’s focus is on encouraging strong interaction among medical device and microelectronics companies as well as physicians and clinicians. The goal is to derive precompetitive technology that industrial members of MEDRC can turn into products.

Other organizations investigating portable health and medical technologies include Imec and Holst Centre. In October, they announced a body patch that integrates an ultra-low-power ECG chip and a Bluetooth Low Energy (BLE) radio, combining power-efficient electronics and standardized communications to support long-term monitoring in health, wellness, and medical applications (Figure 3). The system integrates components from Imec and Holst Centre’s Human++ R&D program. Human++ researchers designed the system in collaboration with DELTA; the system is integrated in DELTA’s ePatch platform.

Figure 3. ECG Patch Combining an Ultra-Low-Power SoC With BLE
Courtesy of Imec

The patch measures ECG signals plus tissue-contact impedance and includes a 3-D accelerometer to monitor physical activity. The device processes and analyzes acquired data locally and transmits relevant events and information via BLE. The patch can monitor, process, and communicate on a minimal energy budget.

When computing and transmitting the heart rate, the entire system consumes 280 µA at 2.1 V, running continuously for one month on a 200-mAh Li-Po battery. When transmitting accelerometer data (at 32 Hz) on top of the heart rate, the power consumption remains below 1 mA in continuous operation, giving about one week of autonomy.

At the heart of the patch is an ECG SoC, a mixed-signal ASIC custom designed to provide ECG monitoring and high processing power at low energy consumption. Next to monitoring ECG signals, the SoC also examines the contact impedance, providing real-time information on the electrode contact quality.

The ECG SoC can run algorithms for motion artifact reduction (based on adaptive filtering or principal component analysis) and beat-to-beat heart-rate computation (based on discrete or continuous wavelet transforms). It has additional computation power to run application-specific algorithms such as epileptic seizure detection, energy expenditure estimation, or arrhythmia monitoring. The built-in 12-bit ADC is capable of adaptive sampling—sampling QRS waves at high frequency, and the other waves at a lower frequency—achieving a compression ratio of up to 5.

Giving Sensors an Assist

Sensors rarely act alone in an application; they require support in terms of communications, as in the BLE component of Imec’s monitor. Another communications support mechanism comes from austriamicrosystems, which announced in August that Echowell has selected its AS3900 27-MHz frequency shift keying (FSK) low-power transceiver IC with an integrated link manager for its new bicycle metering platforms that monitor a user’s speed, mileage, and heart rate. Previously, Echowell had used other wireless technologies at various frequencies, which required discrete design solutions and long design times.

Johnsy Varghese, marketing manager for wireless products at austriamicrosystems, said the AS3900’s high level of integration, ease of use, and low power capabilities, plus its capability to perform well in close proximity to the human body, make it well suited for applications like Echowell’s bike computers and other fitness and medical products.

The AS3900 transceiver features a built-in star network-management protocol and operates in the 27-MHz worldwide ISM band. Operation in this band avoids the interference found in the popular but cluttered 2.4-GHz band and results in a lower amount of energy being absorbed by the human body (SAR or specific absorption rate), making it suitable for transmitters operated close to the human body in body area network (BAN) or medical body area network (MBAN) implementations. The transceiver requires only 2.5 µA in standby polling mode and typically 3.8 and 4.9 mA in receive and transmit modes, respectively. It transmits data at up to 212 kb/s.

Processing Capabilities

If you are looking for a low-power device with processing capabilities to assist with your sensor applications, you could consider the ML610Q4xx Series microcontrollers, which target applications requiring comprehensive control over the operation of battery-powered devices used for the measurement and display of temperature, humidity, and carbon monoxide in industrial and commercial environments. Applications include building controls, test and measurement, and the transportation and storage of perishable products such as food and pharmaceuticals.

In an interview at the Embedded Systems Conference Boston in September, Alec Melnick, senior product marketing manager at the company, said the new devices feature an RC-type analog-to-digital converter (RC-ADC) that provides accurate (±1.0°C) temperature measurement using only a minimal number of small, passive components. The typical range for CS as shown in Figure 4 is 700 to 1,000 pF.

Figure 4. Lapis ML610Q4xx Low-Power Microcontroller With External RC-ADC Components

In operation of the RC-ADC, discharged capacitor CS1 is charged when the microcontroller passes a load-sensitive oscillating signal through fixed-value resistor RT1. The microcontroller calculates and records the amount of time that it takes to charge CS1. The device discharges CS1 and recharges it with the same oscillating signal through the variable value component, RS1, whose resistive value is dependent upon an environmental condition (temperature, for example, if RS1 is an RTD).

The device then uses the ratio of the amount of time needed to charge CS1 through known RT1 vs. unknown RS1 to calculate RS1. The power consumed while using the RC-ADC normally is no more than 0.90 mW (0.30 mA at 3.0 V), and a measurement takes less than 2 seconds.

Yet another temperature-monitoring application contends with high-voltage challenges. In November, Data Translation announced the addition of two new ultra-high-isolation Ethernet measurement instruments to its MEASURpoint™ product line. The ISO-Channel™ design provides up to ±3,500-V high-voltage rejection using galvanic isolation techniques to preserve small signals generated from thermocouples, RTDs, and other sensitive sensors in harsh, high-voltage noise environments. Target markets for the instruments include wind, gas, battery, and solar-energy installations where high-isolation protection is required to ensure data-acquisition integrity in noisy and often remote settings.

Key features include high isolation to earth ground (±1,400 V continuously or 2,500 V for transients on Model DT8875 or ±3,500 V continuously or 5,000 V for transients on Model DT8876); channel-to-channel isolation of 2,800 V (DT8875) or 7,000 V (DT8876); a high stability, 24-bit resolution delta-sigma ADC per channel; and up to 40 simultaneous differential inputs (DT8875) or 20 simultaneous differential inputs (DT8876). The instruments support thermocouples and RTDs; accuracy is ±0.24°C with type B, E, J, K, N, R, S, and T thermocouples. The instruments also support 4-wire, 3-wire, or 2-wire PT100, PT500, or PT1000 RTDs with accuracy to ±0.03°C. The sample rate is up to 10 Hz per channel. The instruments come with MEASURpoint Framework and web-based applications.

You can expect to see continuing innovative sensor introductions throughout this year, serving applications ranging from industrial control to home health monitoring. Illustrative of this trend in the industrial space, as this article went to press, Macro Sensors announced an upgraded series of intrinsically safe stainless-steel HLR Series LVDT linear position sensors (Figure 5) for use in hostile environments such as gas/steam turbine plants, chemical process plants, and paper mills. Rated for operation to 212°F (100°C), the HLR sensors now are UL/ULC listed for use in hazardous locations.

Figure 5. Stainless-Steel HLR Series LVDT Linear Position Sensors for Hostile Environments
Courtesy of Macro Sensors

On the healthcare front, the University of Pittsburgh just demonstrated its eButton, a device worn on the chest (like a pin) by people attempting to lose weight. The eButton contains a miniature camera, accelerometer, GPS, and other sensors to capture data and information of health activities, eliminating the need for daily self-reporting. The eButton prototype was the result of research from a four-year NIH Genes, Environment, and Health Initiative grant that ended in 2011.