Photosensitive Sensor

Photosensitive Sensor

A photosensitive sensor is a device that converts radiant energy (light) from the Infrared and Visible light spectrum into an electrical output. These sensors can detect objects based on their contrast, colors, or surface conditions.

Diffuse-reflective Sensors emit light from one end of their housing, called the N end, and receive reflected light from another, called the F end. The Sensor detects objects that interrupt the reflected light.

Light Dependent Resistor

Light Dependent Resistor, or LDR, is a passive electronic component that changes its resistance according to the intensity of the light falling on it. Using this property, it is possible to create an electronic sensor that can detect the presence of light. The LDR consists of semiconductor material, such as cadmium sulfide (CdS), cadmium selenide (CdSe) or indium antimony (InSb).

When light falls on the surface of an LDR, it liberates electrons from the valence band to the conduction band. This increases the number of electrons that can conduct electricity and reduces the overall resistance of the device. The photocurrent produced by this process is proportional to the intensity of the light and its wavelength. This can be measured using a simple multimeter by setting it to ohms mode and placing the multimeter lead across the volt/ohm output of an LDR.

This sensor can be used to produce an analog output, which could be fed into a comparator or other circuit to generate an on/off signal. It is important to note that this sensor is not as accurate or fast as photodiodes or phototransistors, and therefore may not be appropriate for all applications. Additionally, the power dissipated by an LDR is quite high, so it is necessary to use heat sinks on all devices that will be powered by this sensor.

Phototransistor

Basically, a phototransistor is a transistor whose action depends on the amount of light falling on it. It consists of two terminals emitter and collector, which work like normal transistors. The difference is that the phototransistor has a base region that is sensitive to the intensity of radiation coming from outside.

When the light falls on the phototransistor’s base region, it generates hole electron pairs in the reverse-biased base-collector junction. The pair’s movement under the influence of the electric field induces current in the base region, which in turn injects Microwave sensor electrons into the emitter. The resulting photodiode current is equal to the base current multiplied by the current gain of the transistor.

A phototransistor’s sensitivity, or collector current (IC), depends on the material it is made from and its size. Homo-structure devices, or single material configurations, can have gains ranging from 50 to several hundred and are typically designed with silicon. Hetero-structure or multiple material configurations can include gain levels higher than 10,000, but are less common due to high production costs.

Another important factor for a phototransistor is its response time, which refers to how quickly the output changes with the change in light intensity. A low rise and fall time ensures quick operation and is essential in applications where the light level constantly changes. A fast response time also helps to suppress background noise.

Photoconductive Cell

A Photoconductive Cell is a semiconductor device whose electrical conductivity varies according to the intensity of light falling on it. It is also known as Light Dependent Resistor (LDR). The cell consists of a semi-conducting material like cadmium sulphide or germanium, embedded with metal electrodes on either side to facilitate the flow of current. When it is exposed to light, the absorption of electrons & holes by the semiconductor increases, hence decreasing its resistance. This causes the output current to increase. The major drawback of the Photoconductive Cell is its temperature sensitivity. This can cause a substantial variation in its resistance for a specific light intensity.

The two materials normally used in the manufacture of the Photoconductive Cell are cadmium sulfide & cadmium selenide. Both of these materials respond rather slowly to changes in light intensity. The response time of a cadmium photosensitive sensor selenide cell may be up to 10 ms whereas that of the cadmium sulfide cell is around 100 ms. Its spectral response is similar to the human eye, thus making it a good choice for applications like street lights or automatic iris control on cameras.

However, if you need a sensor that can detect light pulses quickly, then the Phototransistor is the right device for you. The phototransistor consists of a bipolar NPN transistor with its base region electrically unconnected, while the collector to emitter terminal is connected. The light rays strike the phototransistor’s base region and trigger the PN-junction to generate pairs of electron-holes, thus increasing the conductivity of the collector to emitter terminal.

Transmissive Cell

We demonstrate that a simple, low-resolution imaging approach can reliably identify ECM fiber density differences between cell pairs that are correlated with mechanical signals transmitted from one to the other. The signal appears as a visible band of increased fiber density extending along the connecting axis between cells and can be visualized with standard microscopy (Fig. 1A).

To quantify this signal we first transformed the images to rotate their X’, Y’ and Z’ axes and then sampled a set of 32 orientations (see Methods section). For each of these transformations, we performed a same-versus-different pair analysis where we compared the mean fiber intensity of the shifted quantification window toward or away from the communicating partner.

The results show that the correlation between a contracting cell and its neighbor exceeds the correlation of a non-contracting cell with its neighbor, indicating that the signal is primarily caused by the mechanical interaction of the cell with the ECM (Fig. 1C). The same-versus-different pair analysis also shows that the increase in fiber density is correlated with the distance between the cells: the closer the two cells are, the larger the difference in their measured fiber intensity.

To verify that the increased ECM fiber intensity is mainly due to communication between the cell pairs we performed a similar same-versus-different pair analysis on cells separated by different distances. We found that the same-versus-different correlations were significantly smaller for pairs of cells at a distance of 4 versus 9 cell diameters, suggesting that the observed signal is dominated by ECM-cell communication and not by a combination of long-range signals from other sources such as afferent nerve impulses or local cell activation.