Temperature sensor for measuring human body temperature

Satish;

A properly-selected thermistor can give you good accuracy in the temperature range that you need and they have a far greater output than an RTD.

Satish;

There are tiny thermistors mounted in the point of a hypodermic needle that will measure the temperature of a body wherever you like-- this is an invasive method, of course.

A non-invasive (and non-trivial) method of measuring internal body temperatures is to use a microwave radiometer. In the low GHz range, the body has sufficient microwave attenuation to be a decent blackbody radiator. In this area of the spectrum, the Rayleigh-Jeans Approximation holds true and the RF power emission is proportional to absolute temperature. This method is complex and expensive, but-- depending on the frequency choice-- temperature measurement from virtually any tissue depth is possible.

Hi Niel,

Can you elaborate on the use of microwave radiometer in core body temperature? I'm interested in learning more about this technique. Is there any papers that you know of that you could direct me to ? I would love to talk more about this with you if you sometime.

Son;

Any object above 0 degrees Kelven radiates energy; very hot objects, such as the sun, radiate at mainly the visible and infrared wavelengths but cooler objects have their peak energy radiated at longer wavelengths. Look up the "Wein Displacement Law".

A microwave radiometer measures energy in the short radio wavelengths that are radiated by an object. In the case of a human body, the choice of wavelength determines how far into the body the energy is measured. By chosing a wavelength that has sufficient attenuation in the depth that the measurement is desired, the internal temperature can be determined. Very high attenuation prevents looking deep into the body-- think of the IR sensors, the IR attenuation is so high that it only barely penetrates the skin. This is why IR thermometers measure skin temperatures. At too long a wavelength, the body tissues become rather transparent to RF and a measurement cannot be made. I'm sure a bit of research can uncover some wavelength vs attenuation in human tissue data. Tissue is a high percentage of water so it may be around 2.4GHz.

Microwave radiometers are not simple or cheap, but they are far more feasible these days with low noise solid-state amplifiers. Another factor is the antenna used to focus on the area to be measured.  At millimeter wavelengths, pyramidal horns become small enough to be practical and generate a reasonably small beamwidth. These wavelengths raise the radiometer complexity and cost, however.

Read about radio astromony-- measuring temperature with a radiometer is the fundamental principle.