Ear Thermometer

How to Find Your Best Ear Thermometer

The creator was Dr. Benzinger worked from 1947 to 1970 at the Naval Medical Research Institute in Bethesda, Maryland where he studied temperature regulation and helped create the field of bio thermodynamics. He created the ear thermometer while looking for a way to take someone’s temperature and receive a reading as fever. Because the eardrum shares blood vessels and the hypothalamus, Benzinger decided to use the ear canal to take a reading. Until that time, attaching electrodes to the hypothalamus was the only way to have a brain temperature reading. Prior to Benzinger’s creation of the ear thermometer, temperature readings were obtained by placing a thermometer in the mouth or under the arm. The ear temperature correlates with the brain temperature and is therefore if taken, the body temperature reading.

Braun ear thermometer

Theodor Hannes Benzinger died in Bethesda in 1999 at the age of 94 and was born in Stuttgart, Germany. He was also the inventor of a device and made many other contributions to science and medicine like the modification of the second law of thermodynamics and to measure calorie reduction.
Body temperature is monitored using ear thermometers which measure the infrared energy in clinical settings. When data collection is completed, the device beeps and a readout of temperature is created on a liquid crystal display.

Innovo forehead and ear thermometer

This kind of temperature from the eardrum was found to be an indicator of body core temperature. The eardrum is situated close to the hypothalamus, that’s the temperature regulator of the body. The membrane is thin and almost transparent, so you would assume that it tracks the temperature so gives a great indication of the temperature.

The energy falls on a thin crystal which develops a cost proportional to that accumulated energy. Discharging the crystal sends a current pulse through conversion circuits and filters which compare data to be tabulated by the sign and calculate a body temperature for the display.

Braun thermoscan ear thermometer

Radiation is emitted by all objects above absolute zero temperature, and the radiation from an isolated object in the body temperature has a characteristic wavelength dependence given by the blackbody radiation curve. This radiation curve peaks at a wavelength of about 9340 nm in the infrared, in comparison with the visible wavelength range of 400-700 nm. This peak can be determined from the Wien displacement law. Presuming that the pyroelectric detector develops an electric charge proportional to the energy that falls during the set time on it, the energy discrimination necessary for a given precision could be calculated using the Stefan-Boltzmann law which relates energy to temperature.

best ear thermometer

The ratio of the radiated energy with 1°C fever would be [(38 +273)/(37 + 273)]4 = 1.013 since the radiated energy is proportional to the fourth power of the absolute temperature. You would then have to achieve a resolution of 1.3\% or better to detect that temperature difference.

Not using the details of the detector, I would guess that the sensors use an infrared wavelength window on the steep part of the blackbody curve and use how the blackbody curve shifts downward in wavelength in addition to upwards in total intensity as the temperature rises.

kinsa smart ear thermometer

So that the resolution does not have to be high this could give an enhanced change in radiation during the window of the detector. As an example, the radiation via a certain wavelength window can be computed for 37 °C and compared with that in another temperature. We also have Galileo thermometers!

Walgreen ear thermometer

At 37 °C the radiated intensity peak is at 9344 nm in the Wien law. If you choose a 500 nm window at 5500 nm, the radiated intensity is about half that, but the change in electricity through a window from 5500 to 6000 nm varies by 0.15\% when you increase the temperature by 0.1°F, a sensitivity twice that quoted above. Learn more on Wikipedia page and go to our forehead thermometer page.

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Ear Thermometer