Low-power implantable accelerometer: activity monitoring/posture sensing

September 15, 2015 // By Graham Prophet
A ‘medical-grade’ motion sensor from STMicroelectronics will enable new implantable-device designs, the company believes: as an off-the-shelf solution, the motion sensor lowers the cost and time-to-market barriers for medical-device developers.

MIS2DH is an ultra-low-power 3-axis accelerometer specifically designed for medical applications, including implantable devices classified by U.S. Food and Drug Administration (FDA) as Class III. ST has many years of experience in developing custom motion sensors for leading medical-equipment manufacturers; the company says it has applied this expertise in an off-the-shelf solution that can enable functions such as activity monitoring and posture sensing to be included in a wide range of medical applications.

Features of the MIS2DH include:

- 3-axis accelerometer;

- ultra-small size (2 x 2 x 1mm);

- ultra-low power consumption (down to 2 µA in low-power mode);

- ±2g/±4g/±8g/±16g selectable full-scale;

- 8-, 10- and 12-bit operating modes;

- 1 Hz – 5 kHz output data rate;

- FIFO buffer and programmable interrupt to minimise system power consumption;

- I ²C/SPI digital outputs;

- 1.71 -3.6V operating voltage.

ST comments; Implantable medical devices such as cardiac pacemakers, ICDs (Implantable Cardioverter Defibrillator), and neurostimulators have been successfully used for many years to prolong the lives of patients with heart problems or to make life better for people with chronic pain conditions. Today, there is a growing interest in the medical world in exploring how new implantable devices could help treat other chronic problems such as high blood pressure, epilepsy, and tremor-related conditions. For most of these applications, an embedded accelerometer capable of measuring the activity and posture of the patient is important to manage the stimulus delivered by the implantable device and therefore to improve the effectiveness of the treatment.

A major obstacle for SMEs (Small and Medium Enterprises) wanting to develop innovative new medical devices has, ST asserts, been the high costs associated with custom-designed sensors and obtaining FDA certification. The MIS2DH addresses this problem by combining a 3-axis mechanical element and an integrated electronic circuit in a single package, along with a set of collaterals required by customers seeking FDA Class III approval: