New-TechEurope Magazine | November 2017 | Digital Edition

Sensors Special Edition

device which integrates a 3-axis gyroscope, 3-axis accelerometer and 3-axis magnetometer with a digital motion processor in a multi- chip module measuring just 3mm x 3mm x 1mm. Each sensor features a self-test mode, while the integrated motion processor handles calibration as well as the motion processing algorithms, reducing the workload on the host processor. Under Pressure As mentioned above, one of the biggest applications for MEMS in medical applications is pressure sensors. They can be used in ventilators to monitor respiration rates, in dialysis equipment to measure the inlet and outlet blood pressure for flow regulation, and even in eye surgery. MEMS pressure sensors can be used for the detection of oxygen, carbon dioxide, calcium, potassium and glucose in blood, as

applied to the treatment of scoliosis, by measuring how often and how tightly braces are being worn by patients, in a bid to overcome the barriers that can impede progress. A Body in Motion As MEMS are manufactured via the same techniques used in conventional semiconductor production, some integrated device manufacturers are well positioned to develop and supply MEMS sensors. A presentation at the Medical MEMS and Sensors Conference 2017 (Santa Clara, November, 2017) given be Analog Devices’ Engineering Manager of High Performance Sensors, Mark da Silva PhD, entitled ‘Ultra Low Power Implantable Inertial MEMS Sensors’, shows the direction some semiconductor manufacturers are moving. Implantable inertial MEMS sensors could be used to monitor the movement of limbs in real-time, while similar sensors implanted in the back could be used for spinal cord stimulation for the treatment of pain. Ultra low power MEMS accelerometers, such as the ADX362 series from Analog Devices, are already available and being used in a wide array of applications, including hearing aids and home healthcare. This 3-axis accelerometer can measure both dynamic and static acceleration (for detecting shock, for example) and consumes just 10nA in sleep mode and as little as 270nA when in a motion triggered mode. Because it doesn’t use under- sampling, as some MEMS sensors do, the sensor’s full bandwidth is

sampled for both 8-bit and 12-bit output resolutions. This can be as low as 1mg/LSB at a ±2 g range and the family has a standard noise level of 500μg/√Hz, which can be further reduced to 175μg/√Hz through a lower noise mode. As shown in Figure 1, the ADXL362 also integrates antialiasing filters and a temperature sensor, as well as an analogue-to-digital converter (ADC), SPI interface and digital logic. All of the features of the ADXL362 can be evaluated using the Arduino- compatible EVAL-ADXL362-ARDZ shield, which features an LCD for displaying the tilt and temperature data provided by the sensor. The board is also compatible with Analog Devices’ EVAL-ADICUP360 development board, which includes both Arduino and Pmod interfaces. Taking sensor integration to a higher level, the ICM-20948 from TDK InvenSense isa9-axismotiontracking

Figure 1: The ADXL362 from Analog Devices is an ultra-low power 3-axis ac- celerometer ideal for healthcare applications

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