Advancements in medical technology is showing rapid growth. While ultra-low-power sensors and wireless communications are enabling remote sensing, advances in nanotechnology and MEMS sensing are allowing ever more parameters to be sensed, measured and recorded. Without the availability of accurate and reliable sensors to act as the interface between patient and equipment, modern medical technology would not exist, says Mark Patrick. 

 

Modern hospitals are filled with technology to assist doctors and nurses with detecting, diagnosing and monitoring patient conditions. Sophisticated technology is now able to monitor a wide range of physiological parameters including blood pressure, heart rate, blood oxygen and more. However, this technology would not exist without the availability of accurate and reliable sensors to act as the interface between patient and equipment.

 

This sector is showing strong growth. In fact, research firm MarketsandMarkets forecasts that the market will grow to $15 billion by 2020, which is an average annual growth rate of 8.5 per cent. The growth is due to a combination of factors, including patients increasing their expectations of healthcare, people living longer, and the need for medical facilities to control costs in the face of restricted budgets.

The technology itself is also driving growth, as ultra-low-power sensors and wireless communications enable remote sensing, and advances in nanotechnology and MEMS sensing allow ever more parameters to be sensed, measured and recorded. Combining this via multifunction sensors and sensor fusion is leading to ever more applications being created on an almost daily basis.

 

Sensing the signs

Simpler sensors are dedicated to a single function, measuring parameters such as pressure, temperature or flow, and these may be used in single-function monitors such as blood pressure monitors or thermometers, or may form part of a more complex system such as an MRI machine, CT scanner or X-ray machine.

 

Sensing flow is important in a variety of medical applications including anesthesia delivery machines, oxygen concentrators, respirators and ventilators. Omron’s D6F-01A1-110 is a MEMS-based flow sensor for highly accurate airflow measurement within a 0 to 1 litre/min. flow range, offering an accuracy of ±3 per cent. An alternate device is Honeywell’s HAFBLF0400C4AX3, which uses an ASIC to calibrate and temperature-compensate the results. The high-precision airflow sensor is often used in anesthesia applications and for breathing assistance via nebulizers. The sensor measures with a 2.5 per cent accuracy over a 400SCCM range.

 

Pressure is another important parameter to be measured in medical applications, including intra-uterine pressure (IUP). The P162 from Amphenol mounts directly on a printed circuit board (PCB) and uses piezoresistive technology to convert pressure to an electrical signal. The sensor can measure pressures up to 300 mm Hg gauge and is supplied as a tiny 1150 µm x 725 µm die.

 

Temperature is one of the most fundamental parameters to measure, so it is no surprise that there is a variety of sensors available that are used in many different types of medical equipment. One device is the 700-DS600U temperature sensor from Maxim, which is primarily used in infusion pumps that provide intravenous medicines, liquids and nutrients. The sensor can measure temperatures in the range 40°C to 125°C at an accuracy of ±0.5°C. Also from Maxim is the board-mounted MAX30205MTA+, which measures temperatures to an accuracy of ±0.1°C between 0°C and 50°C. The device incorporates a high-resolution analog-to-digital converter (ADC) to offer a digital output that complies with the ASTM E1112 clinical thermometry specification when soldered to the PCB. As well as being used in professional medical applications, the device is also commonly found in consumer fitness trackers. The monitoring of a baby’s body temperature is crucial when it is in an incubator. The MA300TA103C biomedical NTC thermistor from Amphenol is ideal for this continuous monitoring requirement, covering the range 0°C to 50°C.

 

In many cases, the temperature sensor is in contact with the patient, but the Melexis MLX90614ESF-BAA-000-TU uses infrared (IR) technology to perform noncontact temperature measurement. The PCB-mounted solution consists of a pair of integrated circuits – an ASIC for signal conditioning and a thermopile detector sensitive to IR energy. The sophisticated solution has an accuracy of ±0.5°C over a range of -40°C to 85°C.

 

Multifunction sensors and fusion

A highly accurate sensor can provide a lot of useful information within medical applications. However, by combining multiple sensors of different types, sensor fusion is able to deliver a sensing system that adds up to more than the sum of its parts. To humans, this is nothing new, as we combine sight, touch, taste and smell every day to perceive the world around us. However, this is a relatively new concept in the world of sensing, and it is generating exciting possibilities.

 

While every system is different, most sensor fusion setups have three main stages – acquiring the data from sensors, merging (fusing) the data and then combining the decisions. The acquisition stage involves several sensors collecting different types of information such as physical parameters or images. Next, the data is processed to extract the relevant information it contains. The data is then fused using a set of sophisticated decision algorithms.

 

One application of sensor fusion is found in motion detection, where the information from 3D magnetometers, 3D gyroscopes and 3D accelerometers is merged to create a nine-axis system. Each of the sensors provides unique information and each is sensitive to different forms of interference including vibration, drift and EMI. By combining the data a complete picture of any movement can be created, and the noise effects eliminated.

 

STMicroelectronics’ SensorTile (STEVAL-STLKT01V1) combines a MEMS accelerometer, magnetometer, gyroscope, pressure sensor and MEMS microphone in a small (13.5 mm x 13.5 mm) turnkey sensor fusion board based on a STM32L4 32-bit ARM Cortex-M4 microcontroller.

A similar device is NXP’s FXOS8700CQR1, which combines a three-axis magnetometer and a three-axis accelerometer in a single sensor. The device has onboard I2C and SPI serial interfaces, enabling designers to select the most suitable digital interface. The highly sensitive accelerometer offers 14-bit resolution, with the magnetometer providing 16 bits of data. The sensor offers three acceleration ranges (±2g, ±4g and ±8g) to suit different applications. 

 

Both the STMicroelectronics device and the NXP device are suited to a wide range of patient monitoring applications, and are useful during rehabilitation as well as to monitor activity and any impact incurred during falls.While sensor fusion combines the data from multiple sensors into a single information set, multifunction sensors enable multiple parameters to be monitored through a single, albeit sophisticated, sensor.

The multifaceted data can provide immediate monitoring of the current health of any patient, and it can also be stored and retrieved later for trend analysis, possibly in combination with similar data from other patients. 

 

One area where multi-parameter sensors are used is in the field of cardiac medicine, where an integrated health-monitoring chest-worn device with a microcontroller board, an electro-cardiogram (ECG) sensor, a temperature sensor, an accelerometer and a vibration motor can provide all the information necessary to monitor a condition.

 

The biopotential figures generated from electrical signals within the human body can be monitored by Maxim’s MAX30001. The analog portion of this sensor includes biopotential and bioimpedance (BioZ) sensors creating a single biopotential channel for waveforms, heart rate and pacemaker edge detection, as well as a bioimpedance channel for measuring respiration. The system is useful for a wide range of cardiac monitoring and assessment, including the detection of arrhythmia and the monitoring of heart rate, respiration and hydration. It can also be used for bio-authentication as well as ECG-on-demand for patients who need constant monitoring.

 

A further benefit of the modern sensing technology is that it enables the design of simple, robust and portable monitoring systems that can be used by patients away from a medical facility. Including the ability to transmit data back to medical professionals allows patients to be monitored and assessed while they go about their daily lives at home or at the office. It also allows 24/7 monitoring to pick up ailments that may be sporadic and will not necessarily show up while the patient is with a medical professional.

---------------------------------

About the Author:

Mark Patrick is the Supplier & Technical Marketing Manager EMEA of Mouser Electronics. Mark joined Mouser Electronics in July 2014 having previously held senior marketing roles at RS Components. Prior to RS, Mark spent 8 years at Texas Instruments in Applications Support and Technical Sales roles and holds a first class Honours Degree in Electronic Engineering from Coventry University. For details, contact Helen Chung, Asia PR Specialist of Publitek, on email: helen.chung@publitek.com

----------------------