# Detecting specific wavelength via changing sensor Voltage

#### Spange-Bob

Joined Feb 24, 2019
5
Is It possible that via changing a sensor voltage detecting a specific wevelength?
do we have this kind of sensor?

#### AlbertHall

Joined Jun 4, 2014
11,102
What are you trying to detect - light, microwaves, radio, audio?

#### Yaakov

Joined Jan 27, 2019
2,358
It's hard to understand what you are saying, but maybe a varactor is something like it.

#### BR-549

Joined Sep 22, 2013
4,938
Your sure can, only it's not a sensor, it's a circuit.

#### Spange-Bob

Joined Feb 24, 2019
5
I've meant microwaves

#### BR-549

Joined Sep 22, 2013
4,938
If you ever study electronics, you will find that frequency is a rate, or a change in something.

It can be a change in voltage, or current, or impedance, capacitance, inductance.......or anything else.

And, we can control one change, with another change.

To be able to understand these complex relationships, one has to study and understand the basics.

Microwaves are not basic.

Why are you asking the question? What did you have in mind. Microwaves.....are used for hundreds of different things.

#### MisterBill2

Joined Jan 23, 2018
8,214
It is common to tune a microwave resonant cavity circuit using a voltage-variable capacitance diode, but that does not detect a specific frequency, it only changes a resonant frequency.
To get any kind of useful answer you will need to provide a whole lot more information as to what you are trying to accomplish. Otherwise the responses will just be guesses.

#### MisterBill2

Joined Jan 23, 2018
8,214
That might possibly be the other goal, a sensor whose output voltage varies with the frequency detected. That even makes a bit more sense. If that is the intention, then the answer is "sort of". There are devices that are tunable, and calibrated in frequency or wavelength, and have detectors to indicate the amplitude of the signal that they are tuned to.

If this is a student homework assignment then the discussion needs to be different.

#### Yaakov

Joined Jan 27, 2019
2,358
It is common to tune a microwave resonant cavity circuit using a voltage-variable capacitance diode, but that does not detect a specific frequency, it only changes a resonant frequency.
To get any kind of useful answer you will need to provide a whole lot more information as to what you are trying to accomplish. Otherwise the responses will just be guesses.
Varactor was my guess, too.

#### sparky 1

Joined Nov 3, 2018
488
one circuit is a frequency selective power meter.
An adjustable 3 pF capacitor for example can be mechanical plate type or reverse diode type.
When that desired frequency approaches resonance in a frequency selective circuit the voltage rises.

In a varactor a voltage with very low current typically sourced thru 100K Ohm resistor.
This voltage adjusts the capacitance. In a 3 pF mechanical plate capacitor the plates move to adjust.
So a varactor can accomplish this eloquently at a 3pF range. Adding selectivity to narrow the band.