Manufacturing Bits: Sept. 8

Calibrating a microphone
The National Institute of Standards and Technology (NIST) has developed a faster and more accurate way to calibrate a microphone.

NIST’s new calibration technique makes use of lasers, a promising technology that could supplant today’s methods. The technology could one day be used to calibrate sensitive microphones in factories, power plants and other settings like fabs. The technology could help monitor factory machinery via sound. It could be used to monitor workplace or community noise levels.

A microphone is a device, which takes sound pressure waves and converts them into signals. To calibrate a microphone, the industry measures the sensitivity of the unit to the pressure waves using a technique called the reciprocity method, according to NIST.

“In a reciprocity calibration, two microphones are connected to each other via a small hollow cylinder called an acoustic coupler,” according to NIST. “One microphone produces a sound that the other microphone picks up. After a measurement has been taken, the microphones’ functional positions can be swapped, with the transmitter acting as receiver and vice versa.”

This process is repeated several times using three laboratory microphones. “By exchanging the microphones’ roles between measurements, researchers can be sure of the sensitivity of each of the three microphones without the need for a previously calibrated microphone,” according to NIST. “Once this master set of microphones has been calibrated, it can be used to directly calibrate customers’ microphones.”

NIST is developing a new and improved solution. NIST’s new laser method has fewer uncertainties and is 30% faster than the traditional method currently used at NIST and other organizations.

NIST’s laser-based calibration method measures the physical vibrations within the diaphragm of the microphone. For this, NIST uses a laser Doppler vibrometer. The instrument shines a laser beam onto the diaphragm of microphone. The beam bounces off the surface and is recombined with a reference laser beam, according to NIST.

The subtle shifts in frequency are measured. It follows the same principle as the Doppler effect. In one example of this effect, the sound of an ambulance outside your window has a higher-pitched sound as it approaches and lower-pitched as it moves away, according to NIST.

To test its method, NIST used nine standard microphones. They were tested at two frequencies—250- and 1,000-hertz. The technology is still far from being commercialized. Going forward, NIST plans to calibrate new and different types of microphones with various frequencies. They will also try to turn the method into a suitable primary calibration technique.

Acoustic reporter genes
The California Institute of Technology has developed a way to look inside single cells in organisms using sound.

The new technique makes use of what researchers call acoustic reporter genes. These genes use sound instead of light to see how cells in an organism are behaving.

Living organisms are complex. The human body contains about 37 trillion cells, according to Caltech. Even the fruit fly might have 50,000 cells.

To monitor these cells, researchers have devised a technique called acoustic reporter genes. In simple terms, reporter genes are tiny snippets of DNA. Researchers can insert them into an organism’s genome to monitor an organism, according to Caltech.

Typically, reporter genes have encoded fluorescent proteins. When light is projected onto the cells, they will light up, according to Caltech. The problem? Light does not penetrate very far through living tissues.

So, researchers have developed reporter genes that use sound instead of light. “These genes, when inserted into a cell’s genome, cause it to produce microscopic hollow protein structures known as gas vesicles,” according to Caltech. “These vesicles are normally found in certain species of bacteria that use them to stay afloat in water, but they also have the useful property of ‘ringing’ when struck by ultrasound waves.”

This technique represents an increase of more than 1000-fold in sensitivity over the previous technique. “In comparison to previous work on gas vesicles, this paper allows us to see much smaller quantities of these gas vesicles,” said Daniel Sawyer of Caltech. “This is like going from a satellite that can see the lights of a small town to one that can see the light from a single lamppost.”