TEMPERATURE SENSORS

Clinical need

Little changes in temperature can cause huge differences in the environment

Body Temperature

Temperature changes

Physiological basis

of the detected signal

Excessive temps.

Diseases

Skin Blood Flow

Examples

in biomedical instrumentation

Basic Principles

Principles

Electrical sensors

Infrared

Quiz

Sources

Questions

Examples

in biomedical instrumentation

Telemetry

Thermal imaging

TEMPERATURE SENSORS

in digital thermometers

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Thermal imaging systems Thermal imaging sensors are microelectromechanical systems chips that contain detectors sensitive to electromagnetic IR radiation. Each being radiates between the permitted range of the system, which is then perceived by the detectors and converted to measurable ways such as voltages. Those results are amplified and digitized, transforming them into temperature values.

Telemetry temperature measuring systems NASA developed an ingestible temperature-monitoring capsule. It is composed by: an epoxy shell capsule covered with an outer silicone coat with a miniature battery, a communication coil, PWB and hybrid circuit assemblies on ceramic substrate. The sensor used is a resonator crystal oscillating at a temperature dependent frequency.

Infrared These thermometers use the infrared radiation emitted by the body (just when it is higher than 0º). The thermometer detects the infra radiation and focuses it with a lense to a biosensor which changes this energy into an electrical impulse. Distance and emissivity are really important factors. *Emissivity: effectiveness in releasing energy in thermal radiation

• These thermometers base their measurements in electrical variations. The temperature variation of the body causes alterations in the electrical properties of the sensors, creating a metal alloy, rising or lowering its conductivity. The results of these variations are shown on a LCD screen.

Vital parameter Excessively high or low temperatures could cause metabolic issues, alter organs’ function and even create tissue damage. That is why temperature is a vital parameter.

Hypothermia / Fever Hypothermia: It is when the temperature of the body goes beyond the normal values. (36ºC) Organs stop working, the body starts shaking and blood vessels vasoconstrict. Fever: It is when the body temperature goes up, higher than the accepted values. (37.5ºC) It is usually an inflammatory and infectious reaction to kill infectious agents.

Temperature The body temperature gives important information regarding the physiological state of the individual. Thermoregulation: process by which the temperature is maintained regardless of external temperatures. If the body’s temperature gets too hot or cold a signal is sent to the skin, glands, muscles and organs to stabilize the temperature. For example when the temperature rises the body excretes sweat and when the temperature lowers, a shiver reflex causes the muscles contract to produce heat. The hipotalamus is the natural termoregulator, it is where information arrives and is processed. The temperature of human body is around 37ºC with a variation of +/-0.2º

Temperature changes

• The core body temperature has slight variations due to the circadian rhythm.
• In women there may also be temperature changes during the menstrual cycle.
• When a patient is in shock a drop in temperature is an early warning.
• A rise in the body’s temperature could indicate a viral illness or an infection.
• During surgery an anesthesia the patient's body temperature lowers.

Skin Blood Flow Temperature sensors are placed in fixed positions around the skin, variations of the thermal conductivity can be followed. SBF is related to brain activity and therefore, are part of diagnostic tools to analyze the vascularization of skin that has been burnt or operated on.

References Lim, Byrne, Lee; Human thermoregulation and measurement of body temperature in exercise and clinical settings; Ann Acad Med; 37:347-353; 2008 Bräuer, Perl, Quintel; Perioperatives Wärmemanagement; Der Anaesthesist; 55:1321-1340; 2006 Sessler; Temperature monitoring and perioperative thermoregulation; Anesthesiology; 109:318-338; 2008 Osilla, E. V., Marsidi, J. L., & Sharma, S. (2022). Physiology, Temperature Regulation. In StatPearls. StatPearls Publishing. Harsanyi, G. (2000). Sensors in Biomedical Applications. BudapestUniversity of Technology and Economics. Retrieved from: FRONTMATTER (weebly.com) FDA. (2021). Thermal Imaging Systems (Infrared Thermographic Systems / Thermal Imaging Cameras) | FDA Thermometers1) What happens when there are excessively low or high temperatures? a) Organs functions are altered b) Metabollic issues c) Tissue damage d) All of...Wordwall - Cree mejores lecciones de forma más rápida

Thermocouples: According to Seebeck, an electromotive force exists across a junction of two dissimilar metals. Two wires of dissimilar metals are connected, in this junction temperature is measured with the voltage. By heating the wire, the electrons get excited and move, with the measurement of the potential of the electrons, the temperature is calculated. Thermistors: Semiconductors made of ceramic materials that are thermal resistors with a high negative temperature coefficient. They react to temperature changes Radiation thermometry: As there is a known relationship between the surface temperature of an object and its power, temperature can be measured without physical contact. Fiber-optic: It is a prism of single crystal with undoped GaAs at the end of two optical fibers which are side by side. One of the fibers transmits the light from a diode to the sensor, it passes through GaAs and is collected by the other fiber and detected and displayed in the reading instrument.