Normally noise is an annoying feature of electronic circuits. As designers strive to minimize power consumption, voltages and currents decrease while resistances within the circuits increase. At the same time, operating frequencies and with them bandwidth increase.
As we know, the thermal noise voltage of a resistor is given by this simple relationship:
Vnoise= √(k*T*B*R)
where:
k= 1.38*10^-23 J/K = Boltzman constant
T = absolute temperature in degrees Kelvin
B = bandwidth in Hertz
R = resistance in Ohm.
Example: at room temperature (~300 °K), a bandwidth of 1 GHz (not uncommon for modern processors) a resistor of 1 MOhm will develop an RMS noise voltage of ~4mV (RMS).
Let’s turn this unwanted noise to our advantage with this little circuit:
An RMS voltage of 4mV is not enough to get the diode conducting (although some peaks of the noise will be well above 4mV due to the statistical distribution of the noise voltage. But we can easily use a 10GOhm resistor creating ~400mV (RMS) noise voltage, just enough to open a Schottky diode. If we put a few of these resistors in series, e.g. 10 resistors, we create a 100GOhm resistor which will supply ~1.3V (RMS) of noise voltage. Subtracting 0.3V for the Schottky diode, the capacitor will be charged to ~1V, enough to drive some low energy circuit.
Alternatively, a high Ohm resistor can easily be constructed from two parallel wires laid out in a few centimeters distance in air without actually touching each other. Resistance and therefore output voltage can easily be adjusted trimming the distance between the wires. Take care not to overload the diode and capacitor!
The resistor will be cooled since the energy drawn from it in form of electrical charge is taken from the input of thermal energy to the resistor.
Now for the fun part: Build a few of these generators, e.g. 12, and power a fan, e.g. a 12V PC fan, from them. Use the fan to blow warm air to the resistors to compensate the loss from the conversion of thermal to electrical energy. The air will be cooled (because thermal energy is transferred to the resistors) and you have free air conditioning. The hotter it gets, the more electrical energy is created by the resistors, the better the air conditioning will work.
As we know, the thermal noise voltage of a resistor is given by this simple relationship:
Vnoise= √(k*T*B*R)
where:
k= 1.38*10^-23 J/K = Boltzman constant
T = absolute temperature in degrees Kelvin
B = bandwidth in Hertz
R = resistance in Ohm.
Example: at room temperature (~300 °K), a bandwidth of 1 GHz (not uncommon for modern processors) a resistor of 1 MOhm will develop an RMS noise voltage of ~4mV (RMS).
Let’s turn this unwanted noise to our advantage with this little circuit:
An RMS voltage of 4mV is not enough to get the diode conducting (although some peaks of the noise will be well above 4mV due to the statistical distribution of the noise voltage. But we can easily use a 10GOhm resistor creating ~400mV (RMS) noise voltage, just enough to open a Schottky diode. If we put a few of these resistors in series, e.g. 10 resistors, we create a 100GOhm resistor which will supply ~1.3V (RMS) of noise voltage. Subtracting 0.3V for the Schottky diode, the capacitor will be charged to ~1V, enough to drive some low energy circuit.
Alternatively, a high Ohm resistor can easily be constructed from two parallel wires laid out in a few centimeters distance in air without actually touching each other. Resistance and therefore output voltage can easily be adjusted trimming the distance between the wires. Take care not to overload the diode and capacitor!
The resistor will be cooled since the energy drawn from it in form of electrical charge is taken from the input of thermal energy to the resistor.
Now for the fun part: Build a few of these generators, e.g. 12, and power a fan, e.g. a 12V PC fan, from them. Use the fan to blow warm air to the resistors to compensate the loss from the conversion of thermal to electrical energy. The air will be cooled (because thermal energy is transferred to the resistors) and you have free air conditioning. The hotter it gets, the more electrical energy is created by the resistors, the better the air conditioning will work.