Crafting bits: September 8


Calibrate 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 uses lasers, a promising technology that could supplant current methods. The technology could one day be used to calibrate sensitive microphones in factories, power stations and other settings like factories. The technology could help monitor machinery in the factory via sound. It could be used to monitor noise levels in the workplace or in the community.

A microphone is a device that picks up sound pressure waves and converts them into signals. To calibrate a microphone, industry measures the device’s sensitivity to 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 sound that the other microphone picks up. After a measurement, the functional positions of the microphones can be swapped, the transmitter acting as the receiver and vice versa.

This process is repeated several times using three laboratory microphones. “By swapping the roles of the microphones between measurements, researchers can be sure of the sensitivity of each of the three microphones without needing a pre-calibrated microphone,” according to NIST. “Once this main set of microphones has been calibrated, it can be used to directly calibrate customer microphones. “

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

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

Subtle changes 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 sounds higher as it approaches and lower as it moves away, according to NIST.

To test its method, NIST used nine standard microphones. They have been tested at two frequencies: 250 and 1000 hertz. The technology is still far from commercialization. In the future, NIST plans to calibrate new and different types of microphones with different frequencies. They will also try to transform the method into a suitable primary calibration technique.

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

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

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

To monitor these cells, researchers have developed a technique called acoustic reporter genes. Simply put, reporter genes are tiny pieces 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 on cells, they light up, according to Caltech. The problem? Light does not penetrate very far through living tissue.

So, researchers developed reporter genes that use sound instead of light. “These genes, when inserted into a cell’s genome, cause the production of 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 ultrasonic waves.”

This technique represents an increase in sensitivity of more than 1000 times compared to the previous technique. “Compared to previous work on gas vesicles, this article allows us to see much smaller amounts of these gas vesicles,” said Daniel Sawyer of Caltech. “It’s like going from a satellite that can see the lights of a small town to another that can see the light of a single lamppost. “

Marc LaPedus

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Mark LaPedus is editor-in-chief for manufacturing at Semiconductor Engineering.

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