The new ultrasound sensor will allow you to “listen” to the bacteria - how it works

Engineers from the University of Queensland in Australia have developed a new type of ultrasonic sensor, the sensitivity of which is far superior counterparts. The sensor is called ultra-ultrasound. He is able to catch the vibrations of individual cells and bacteria in the human body and assess whether they function normally.

We tell how it works.

Photo by Saroj Regmi / CC BY
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Why do you need such a sensor

Ultrasound is actively used in the diagnosis of diseases, for example, for ultrasound. In a classic ultrasound device, the emitter and receiver are made of piezoelectric crystals. When applying to them a variable electric charge mechanical vibrations occur. Oscillations create high-frequency sound waves that are beyond the ears of a person.

These waves are reflected from surfaces with high acoustic impedance. Piezoelectric elements register these reflections and allow you to form an image of an object on the monitor screen. However, such systems have an important drawback - low resolution. With their help, you can get a detailed image of the internal organ, but you can not register a separate cell.

Researchers from the University of Queensland in Australia undertook to solve this problem. They developed a high sensitivity sensor capable of recognizing the movement of cells and even air molecules.

How does the invention

Unlike classical piezoelectric elements, the sensor does not emit acoustic waves. It only captures the radiation emitted from the objects of study or the air around them. A silicon disk with a diameter of 148 μm and a thickness of 1.8 μm is responsible for the registration of waves. In shape, it resembles a bicycle wheel with four spokes. When an acoustic wave hits this disc, a resonance occurs and the signal is amplified.

In the center of the silicon disk there is a thin stand connecting it with the camera of the optical resonator. Through this camera passes a standing light wave. It responds to disk vibrations under the influence of sound and changes its shape. These changes are captured by a photodetector, which is also located in the optical resonator. Received by the sensor information allows you to determine the shape of the object.

Advantages and disadvantages

The developers note that the new sensor is able to recognize ultrasonic waves with the level of acoustic pressure from 50 μPa (approximately 8 dB) at a frequency from 80 kHz to 1 MHz. This is two orders of magnitude superior to other ultrasonic sensors. According to the engineers, the device is able to pick up acoustic vibrations at a higher frequency, but during the experiments such waves attenuated too quickly in the air and did not have time to reach the sensor.

The new sensor will allow contactless study of the smallest living organisms. Bacteria or viruses are usually removed from the environment and placed under a microscope for examination, which can lead to changes in their behavior. With the help of unicellular technology, it will be possible to study right where they live, for example, in air or soil.

The sensor has several drawbacks. The first is the disk stand in the device is not isolated from acoustic pressure. Because of this feature, the sensor picks up frequencies above 800 KHz worse: an additional resonance occurs in the space under the disk, which increases the noise level. For some frequencies it can reach 50%.

Photo by Lee Maguire / CC BY

The second drawback is that the surface of the disk perceives the signal unevenly. In different parts of it, mechanical resonance occurs only under the influence of a narrow frequency range. If the frequency of the sound to be heard is unknown, it is difficult to detect it.

Analogs devices

The first analogue of the sensor is a piezoelectric sensor, which we spoke about at the beginning. Obviously, the main disadvantage of piezoelectric sensors is low sensitivity. But there are several technologies to solve this problem. For example, the metal surface of the sensors is replaced by more susceptible to vibrations of nanofibres.

Also, to increase the resolution, piezoelectric sensors are placed in water: this technology is used in measurement systems based on photoacoustic effect. Liquid medium due to the occurrence of nonlinear effects enhances the sound vibrations that are formed in the instrument, which simplifies the detection of waves.

It is worth noting another type of sensor - optomechanical, which is used to study the shape of objects of light. The laser source and the mechanical resonator are combined on a thin plate, oscillating with the smallest changes in the light signal. These oscillations are then monitored by a photo detector.

Optomechanical sensors are comparable in sensitivity to ultra-ultrasound and are able to register individual molecules. However, they can not recognize objects that are smaller than the length of the light wave.

Experts note that in the future, sensitive ultrasound (and optomechanical) sensors will be used in smart homes, where they will become part of gas leak detection systems.

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