Pressure and temperature are among the most critical measurands in modern commerce. Yet some of the world’s most accurate tools to measure those quantities rely on surprisingly antique technologies that do not lend themselves to miniaturization, portability, or wide dissemination.
For example, NIST’s largest national standard manometer (an ultrasonic interferometer manometer, or UIM for short) is based on a 3-meter vertical column of mercury and operates on basically the same principle that Evangelista Torricelli introduced in 1643 for measuring pressure. Similarly, the most sensitive temperature instrument for the range of about -300 °C to 1,000 °C is a standard platinum resistance thermometer (SPRT), first proposed before the Royal Society by Sir Charles William Siemens in 1871.
These instruments provide very low uncertainties. But mercury manometers are large, typically immobile, and very costly to purchase and maintain. Moreover, mercury is a neurotoxin whose use is being phased out worldwide. SPRTs are expensive, extremely delicate, and require frequent recalibration. Thus neither technology is well suited to the goals of the NIST-on-a-Chip program.
Now, however, NIST researchers are at work on a new generation of pressure and temperature instruments, based on photonic techniques and quantum principles, which can be built cheaply with small dimensions and distributed widely while offering uncertainties equal to or lower than traditional methods.
In addition, photonic sensors hold the promise of high-sensitivity, chip-scale technology to measure absorbed doses of ionizing radiation (gamma rays and x-rays) and electron beams at small spatial scales. In that range, no fully satisfactory dosimetry methods exist at present, despite pressing needs in advanced precision medicine and manufacturing.