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Wearable health sensors have long been available, and an ingestible, absorbable bacteria-based sensor has also been developed (it has passed FDA (U.S. Food and Drug Administration) review). Sensors are commonly applied in medical electronics.
An ingestible bacteria-based sensor can fully contact gastric fluid in the stomach and generate distinct signals depending on the time of ingestion. These signals are transmitted through body tissue to a battery-powered patch on the skin, enabling detection of various signals and physiological and behavioral metrics such as heart rate, posture, and activity. The ingestible sensor is expelled from the body like high-fiber food and typically remains functional for about seven days.
Pressure Sensors
Pressure sensors are transducers that convert force or weight into electrical signals. In medical applications they are called medical pressure sensors. They must be highly accurate and compact for portability, especially when devices attach directly to a patient. When a sensor is integrated into a monitoring instrument, standard housing materials such as stainless steel and anodized aluminum are typically used. If the device contacts the body or bodily fluids directly, special stainless steels that can withstand high-pressure steam sterilization or disposable sensor designs are used.
Medical pressure sensors were originally used for bed weight monitoring. Today, small pressure sensors are applied in areas prone to human error, such as infusion pumps. To adjust flow rate precisely and allow nurses to monitor at any time, pressure sensors are used in infusion pumps to measure the weight of infusion bags. When the liquid weight differs from a preset value, the sensor immediately sends an alarm to the connected device and communicates with the controller.
Non-contact Temperature Sensors
Non-contact thermometers measure heat emitted as infrared radiation from a distant source. In the absence of a dedicated fiber-optic temperature sensor or a combination of an infrared fiber and an infrared sensor, non-contact line-of-sight surface measurements are appropriate. AgClxBr1-x is considered a suitable choice for measurements at low temperatures. These halide fibers are flexible, water-insoluble, and non-toxic. For these reasons, silver halide infrared optical fibers are used in infrared spectroscopy, radiation measurement, thermography, and industrial and medical thermal imaging.
Biosensors
Biosensors are sensitive to biological substances and convert their concentrations into electrical signals. They consist of an immobilized biorecognition element (such as enzymes, antibodies, antigens, microorganisms, cells, tissues, nucleic acids, or other bioactive materials), an appropriate physicochemical transducer (for example, oxygen electrodes, photodetectors, field-effect transistors, piezoelectric crystals), and signal amplification circuitry.
In clinical practice, enzyme electrodes were the earliest and remain among the most widely used sensor types. Microbial sensors replace enzymes with microorganisms that have specific biological properties. Biosensors have been applied to monitor various bacteria, viruses, and their toxins. A typical biosensor used in pharmaceutical analysis is the SPR biosensor, which uses surface plasmon resonance to measure biomolecular binding in real time.
Implantable Sensors
Implantable sensors are small, lightweight, biocompatible, and require very low power. Importantly, they must not degrade over time. Power requirements are one of the main challenges for implantable sensors. Sensors that require no external power would be ideal, but such devices are not currently available on the market. Piezoelectric polymer sensors are compact, reliable, operate without external power, and can work for extended periods. These sensors can be used in implanted cardiac pacemakers to monitor patient activity and heart rate changes in real time. For example, when an abdominal aortic aneurysm requires resection and replacement with a synthetic tubular graft, a sensor can be implanted during surgery to monitor pressure leaks at the surgical site.
Other Medical Uses of Sensors
Sensors are widely used in monitoring instruments across clinical environments such as operating rooms, emergency departments, intensive care units, and increasingly in patient homes. These monitors track and display major physiological parameters including electrocardiogram, pulse oximetry, blood pressure, respiration, and temperature. Monitors may be standalone devices or multi-parameter systems.
Oxygen concentrators reduce the proportion of nitrogen in inhaled air while increasing oxygen concentration. They are used by patients who cannot efficiently transfer oxygen into the bloodstream, such as some pulmonary patients. Flow sensors in oxygen concentrators must be capable of measuring ultra-low flows, for example down to 0.1 cubic centimeters. Airflow sensors can detect when a patient begins exhaling so the system can reduce flow accordingly, making exhalation easier and more comfortable.
Low-pressure and ultra-low-pressure plastic-encapsulated silicon pressure sensors can detect the moment a patient begins inhalation, enabling efficient oxygen delivery and avoiding waste when the patient is not inhaling. This shortens system response time and improves overall efficiency, allowing smaller, lower-power, and more portable oxygen concentrators. A stainless steel media-isolated pressure sensor can also monitor buffer tank pressure and provide feedback to the compressor to maintain appropriate pressure.
