Electronic systems in medical equipment, devices and probes rely on senor signals as a basis for control activities, accurate diagnosis and treatment. Designing sensors to exacting specifications that withstand the rigors of medical applications, with compliance to needed registrations like FDA and CE, enable innovative systems that transform concepts into smart, connected creations.
Although sensor design in life critical applications can seem complex, selecting the proper sensor can be simple if the application and the parameters that need to be monitored are clearly understood. For example, medical environments typically incorporate application-specific as well as standard and custom product requirements that need to be considered from product concept through manufacturing. Additionally, multiple sensor technologies may be present in one application.
Knowing how a specific sensor technology can be applied to a unique medical environment helps designers implement effective sensing solutions.
Accurate Patient Monitoring
Recent medical advancements have exemplified how sensors are moving innovations forward, enabling a deeper understanding of medical conditions as well as improving patient care and wellbeing.
Optic-based sensors are being used in medical applications where selection of peak wavelength is a priority, such as in pulse oximetry (SpO2) and can be packaged into complete probe assemblies for pulse oximetry monitoring applications. TE Connectivity (TE) provides optic sensors with dual LED, bi-wavelength emitters and spectrally paired photo detectors and a SpO2 probe platform that includes reusable finger clips, soft silicone boots and a range of disposable sensors.
An extremely versatile sensor technology, piezoelectric fluoropolymer film has unique capabilities and produces voltage or charge proportional to dynamic strain. The film is suited for many different custom designs, configurations and applications. In medical applications, a piezo film sensor can be placed under the nose or in a chest strap to detect the respiration rate in patients. And the thin profile of the film sensor makes it suitable for wearable medical device applications.
Digital humidity and relative humidity and temperature sensors from TE incorporate a unique capacitive cell in their design. These low power devices are suitable for OEM cost-sensitive applications with tight space constraints, and medical applications are no exception. In fact, humidity sensors provide a number of ways to monitor air quality in respiratory applications and can be employed in various formats, not just as singular components.
Advancements in ceramic design for NTC (negative temperature coefficient) thermistors allow stand-alone patient temperature monitoring applications to be more and more accurate, while increasing patient comfort through less invasive temperature sensing methods. These advancements also allow packaging methods that are smaller and smaller, enabling use in new and innovative patient temperature monitoring applications.
As PCB (printed circuit board) modules, humidity transducers provide frequency (digital) output and can be calibrated for accuracy in the range of 3-5% for relative humidity from 10-95%. They can also be packaged for voltage (analog) output and designed for 2% accuracy in ranges from 10-95% relative humidity (RH) for use in air quality applications in which compensation for humidity is required.
Uses in Repiratory Care
Board level, low pressure sensors installed in the mask of a respirator or ventilator measure and provide feedback of continuous air pressure as well as detect and assist in the inhalation and exhalation cycle.
Also in the mask box are thermopile temperature sensors to monitor CO2 levels in a patient’s exhalation pattern, while skin temperature sensors placed on the body or face monitors body temperature. Temperature sensors placed in the airway delivery system measure and control the temperature of the air being supplied to the patient.
SpO2 photo optic sensors connected to the ventilator or respirator itself detects heart rate and saturated oxygen levels in the blood.
On the tank, magneto-resistive position sensors monitor the remaining water levels to sense if levels become too low, while humidity sensor components, assemblies or PCB modules integrated into the water tank or heater monitor and control humidity levels to maintain breathing comfort.
In CPAP (continuous positive airway pressure) equipment, board level low pressure sensors are placed inside or outside the pump or mask to monitor continuous air pressure. When used inside the CPAP machine, these sensors count inhalation and exhalation occurrences.
Humidity levels in CPAP machines are also controlled for breathing comfort by the same sensor components, assemblies and PCB modules as used in respirators and ventilators. In this instance, the sensors are integrated into the breathing mask or humidity generator monitor.
Sensors provide critical data in the study of sleep apnea as well. NTC temperature sensor skin patches located on the forehead and limbs measure body temperature, while SpO2 photo optic sensors used inside a wearable fingertip pulse oximeter measure saturated blood oxygen levels and pulse.
Piezo film sheets can be used either as a patch on the nose to detect vibration such as snoring or placed under the nose to monitor breathing patterns. When placed on the forehead and limbs, this film detects body movement and disturbances during sleep.
In the delivery of anesthesia, a piezo film used as a Neuromuscular Transmission (NMT) sensor can monitor the depth of anesthesia for improved patient care.
These few examples of sensors innovating medical applications only touches the surface of what can be accomplished to improve patient care, monitoring and overall quality of life. Below is a list of other sensor technologies that can effectively be used to monitor physical properties throughout medical applications.
To learn more about TE’s specific sensors used in medical applications click here.
TYPICAL SENSOR TECHNOLOGIES USED IN MEDICAL APPLICATIONS
Pressure
• Piezoresistive MEMS silicon chip
• Microfused bonded silicon strain gage
• Media isolated pressure capsules
• Bonded Foil Strain Gage (BFSG)
• Miniature MEMS strain gage
Temperature
• NTC thermistors
• Miniature thermocouples
• Non-contact thermopiles (Passive IR)
• Platinum thin film Resistance
Temperature Detector (RTD)
• Digital temperature chip technology
Humidity
• Proprietary capacitive
• Combination humidity and temperature modules
Photo Optic
• Dual-wavelength
• Photo diode sensors
• Combination emitter and sensor module
Force and Load
• Piezoresistive MEMS silicon chip
• Microfused bonded silicon strain gage
• Bonded Foil Strain Gage (BFSG)
Piezoelectric
• Piezo polymer film
• Piezo ceramic
Liquid Level
• Single point reed switch
• Single point ultrasonic
• Continuous ultrasonic
• Invasive
• Non-invasive
Position
• Linear LVDT
• Rotary Variable Differential Transformer (RVDT)
• Cable extension (Stringpot)
• Linear magnetoresistive
• Rotary magnetoresistive
• Tilt and angle sensors
Vibration and Acceleration
• MEMS based accelerometer
• Piezoelectric based accelerometer
• Single, biaxial and triaxial configurations