Choosing the Right Sensors for BioMedical Applications

Ever increasing aging population is the driving factor for patient auto-monitoring systems. Moreover, the consistency, repeatability and low cost of these systems make them more popular. Sensor-studded monitoring systems are also versatile in this category due to their applications in both hospitals and homes.

It is simple to select a sensor if there is a clear understanding of the application and the parameters to be monitored. Implantable sensors are the most complicated sensors, followed by sensors utilized in catheters (through incision), sensors employed in body cavities, external sensors that get exposed to body fluids, and sensors for external applications.

Implantable Sensors

Implantable sensors must have a small form factor, lightweight and need to be compatible with body mass and run at very little power. Most importantly, these sensors must not deteriorate over time and FDA approval is must as they are Class III medical devices. Moreover, they are in high in cost and a specialist’s help is required for their implantation.

Sensors that can operate without power are ideal, but their number is very few at this time. Piezoelectric polymer sensors are small and durable and do not require power, making them suitable for vibration detection applications such as pacemakers. The sensor is capable of differentiating between different physical activities such as walking and running. A miniature Piezo film vibration sensor with a length of 15/100 of an inch and a pacemaker housing it are depicted in Figures 1 and 2.

Figure 1. Miniature Piezo film sensor enlarged about 10x

Figure 2. Pacemaker X-ray

It is possible to power implanted sensors by external sources such as an RF energy wand. The sensor implanted in the body will get power from the RF energy wand when it positioned close to the sensor. Now, the sensor can monitor patient conditions, send the information back to the wand through RF link, and get back to hibernation.

Sensors Utilized in Catheters (Through Incision) and in Body Cavities

The criticality of prerequisites for sensors inserted through an incision, normally a catheter tip, is lesser than those of for implantables, but FDA approval is still compulsory. The surgical procedure to be performed decides the duration of the function of these sensors, which can be powered through external sources. Temporary temperature sensor catheter probe is shown in Figure 3. These thermistors can operate without external power.

Figure 3. Temporary temperature sensor catheter probe

Catheter ablation sensors are also examples for temporarily inserted sensors through incision. The catheter tip carries a RF energy source and a force load cell sensor. Besides sending data, the RF energy burns out dead tissue in the ablation process. The Microfused sensing technology from Measurement Specialties holds potential to provide a triaxial force-sensing system capable of measuring tissue contact forces in all three dimensions concurrently.

Silicon MEMS-based disposable pressure sensors are utilized in intrauterine pressure (IUP) sensors to take contraction pressure and frequency measurement during childbirth, as shown in Figure 4. It is possible to build additional features such as amnion fluid infusion and extraction into these sensors.

Figure 4. Intra-uterine pressure sensor

Oral and rectal probes are some of the examples for sensors utilized in body cavities. These small and rugged temperature sensors are coated with a soft material to provide protection to the inner layer of the organs of patients from sustaining damage caused by contact. Micro-Thermocouple sensors, as shown in Figure 5, are flexible fine gage thermocouples capable of providing rapid and accurate temperature measurements. Measurement Specialties’ Micro-Thermocouples are made of only bio-compatible materials, which make them suitable for medical applications.

Figure 5. Micro-Thermocouple sensors

External Sensors Exposed to Fluids

There are many different disposable external sensors are available such as the disposable blood pressure sensor (DPS), as illustrated in Figure 6. Although these sensors are placed outside the body, they will be exposed to body fluids. These sensors are utilized in intensive care units and surgical procedures to provide continuous monitoring of the patient’s blood pressure. It is necessary to replace these sensors every 24 hours to prevent contamination. Another example is the sensors utilized in the inflation of angioplasty balloons.

Figure 6. Disposable blood pressure sensor

Devices and External Applications

The following are the examples for medical devices that use sensors for external applications wherein the sensors are exposed to neither body fluids nor medication:

• String pot position sensors for remote surgical tool positioning and patient bed positioning for CT scans/X-rays, as shown in Figure 7

Figure 7. String pot position sensor

• Magneto-resistive sensors in syringe pumps for detecting flow rate, occlusion, and empty syringe
• Force load cells for infusion pumps to detect occlusion (tube blockage), as shown in Figure 8

Figure 8. Infusion pump force load cell

• Piezoelectric (and also pyroelectric) sensors for sleep apnea study
• MEMS and load cell-based sensors to conserve oxygen and monitor oxygen tank levels
• Ultra-small MEMS-based accelerometers for measuring tremors in patients with Parkinson’s disease
• MEMS-based pressure sensors for cuff blood pressure sensor kits
• NTC temperature sensors for skin/body temperature measurement, as shown in Figure 9

Figure 9. Reusable NTC thermistors

• Piezo film transmitter/receiver to detect bubble introduction in infusion pumps/syringe pumps, as shown Figure 10

Figure 10. Piezo film transmitter/receiver

About Measurement Specialties

Measurement Specialties is a global designer and manufacturer of sensors and sensor-based systems which measure pressure/force, position, vibration, temperature, humidity, and fluid properties. Measurement Specialties' products are used as embedded devices by original equipment manufacturers (OEMs) or as stand alone sensors for test and measurement to provide critical monitoring, feedback and control input.

This company is at the heart of many everyday products and provide a vital link to the physical world.

Measurement Specialties is an applications company and this company understands that embedded solutions often require customized designs. The portfolio for Measurement Specialties includes technologies capable of measuring most physical characteristics and allows them to design the right sensor for the application.

Physical property, electrical input/output and package configuration are all important considerations when developing products to meet their customers’ needs.

This company continues to expand its technology portfolio and geographic reach through the acquisition of strategically complementary companies. Measurement Specialties' operations in the US, Europe and China provide resources close to their customers. This global footprint allows this company to offer the lowest cost of ownership to OEMs.

Measurement Specialties value proposition is to understand the customer's sensing needs and develop a solution that meets their performance and cost objectives. At Measurement Specialties, Measurement Specialties are Sensing Your World.

This information has been sourced, reviewed and adapted from materials provided by Measurement Specialties.

For more information on this source, please visit Measurement Specialties.