Can pyroelectric infrared sensors be used to measure body temperature?

2020-03-23   By Arttronix

As we all know that Infrared temperature sensor is the key component of the body thermometer. During the spreading of the corona-virus in China, the shortage of infrared sensors is one of the important reason that we can’t get the Non-Contact Infrared Thermometer.

Let us take a look at the classification of Infrared temperature sensor:

It can be classified as the following types according to the materials used for energy conversion:

Pyroelectric type: triglyceride sulfate, lithium tantalate, etc .;

Thermopile type: N-type and P-type polysilicon;

Diode type: single crystal or polycrystalline PN junction;

Thermal capacitor type: bi-material film;

Thermistor type: vanadium oxide, amorphous silicon, etc.

 

Among the above sensors, do you really understand the application of each type? Today let us analysis the Thermopile and Pyroelectric type.

Thermopile sensor

The thermopile sensor converts the temperature difference into electrical energy using the Seebeck effect. As its name implies, it is composed of two or more thermocouples in series, and the output is the superposition of the thermoelectric potentials of each thermocouple. In this way, when using a thermopile to measure temperature, the shortcoming of the potential difference generated by a single thermocouple is too small to be difficult to measure, thereby avoiding the use of expensive high-precision operational amplifiers.

Structurally, the radiation receiving surface is divided into several blocks, each of which is connected with a thermocouple and then connected in series to form a thermopile. According to different applications, practical thermopile can be made into filament type and film type, and also can be made into multi-channel type and array type device.
Thermopile sensor.png

Thermopile infrared detectors can be configured with various lenses and filters to achieve applications in a variety of application scenarios including temperature measurement, qualitative / quantitative analysis of gas components, and medical equipment. At present, this sensor has been widely used in the fields of forehead thermometer, ear thermometer, smart home appliances, lamp switches, food temperature detection and other fields.

Pyroelectric Sensor

Pyroelectricity converts the temperature difference into electrical energy, using the pyroelectric effect, that is, when certain crystals, such as lithium tantalate and triglyceride sulfate, are heated, the two ends of the crystal will generate equal amounts of charges with opposite signs

The pyroelectric infrared sensor is composed of a sensitive unit, an impedance converter and a filter window; the compensation pyroelectric sensor also has a temperature compensation element. In order to prevent the external environment from interfering with the sensor output signal, the above components are vacuum-sealed in a metal tube.
Pyroelectric Sensor.png

Pyroelectric materials have been widely used in many fields such as human induction, security alarm, flame detection, and harmful gas analysis.In addition to the automatic switching of corridors and burglar alarms, it is also widely used in the following areas: air conditioners and drinking fountains that automatically shut down when the room is empty; televisions can judge that no one is watching or the circuit is automatically turned off after the audience has fallen asleep; Automatically turn on the monitor or automatic doorbell when people approach; video cameras or digital cameras automatically record animal or human activities ...

Can pyroelectric infrared sensors be used to measure body temperature?

 

From the above introduction, we know that pyroelectric infrared sensors are mainly used for motion detection, which is difficult to achieve body temperature measurement, because this sensor measures dynamic temperature difference (ΔT / dt). The reactor measures the static temperature difference (ΔT). In other word, for a pyroelectric sensor, when a human body appears and stops in front of it, the charge induced on the surface of the pyroelectric element will gradually disappear. Therefore, the human body temperature measured by a pyroelectric sensor cannot be accurately captured.

Summary of the comparison of both pyroelectric and thermopile detectors.png

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