Eco Tech: Semitransparent solar cells to begin a new era of solar electronics

Eco Factor: Flexible solar cells that can be printed onto any material.
Being rigid, heavy and opaque, traditional solar cells have limited uses. However, being reliable, these cells have reduced carbon emissions by a considerable amount. To reduce the amount of CO2 in the atmosphere even further, some ingenuity in solar cell design was required, and that has finally been brought by researchers at the University of Illinois. John A. Rogers, a professor of material science and engineering, has developed a new technology which enables solar cells to be printed on many materials, making them flexible and efficient at the same time.
The technology is based on the use of ultrathin, semitransparent cells enabling developers to print cells on plastic rolls that could be unfurled for dozens of uses or stamped onto fabric for energy-generating shirts. The technology has been licensed to Semprius, a semiconductor company in Durham, N.C., which could roll out the initial prototypes in a year. The ultrathin solar cells are first fabricated on semiconductor wafers using conventional techniques and are then transferred onto another material using a soft rubber stamp, which is used to print these solar cells onto any flexible material.
To control the flexibility and the transparency of these cells, their density on any material has to be altered. Thus altering the density would enable developers to integrate these cells into windscreens that generate electricity for your electric or hybrid car. Another use of the technology could be in clothes that have the capability to charge your gizmos whenever you wear them.

Operational Amplifiers

Ideal Operational Amplifiers

As well as resistors and capacitors,Operational Amplifiers, or Op-amps as they are more commonly called, are one of the basic building blocks of Analogue Electronic Circuits.Operational amplifiers are linear devices that have all the properties required for nearly ideal DC amplification and are therefore used extensively in signal conditioning, filtering or to perform mathematical operations such as add, subtract, integration and differentiation.

An ideal Operational Amplifier is basically a three-terminal device which consists of two high impedance inputs, one called the Inverting Input, marked with a negative or "minus" sign, (-) and the other one called the Non-inverting Input, marked with a positive or "plus" sign (+).

The third terminal represents the op-amps output port which can both sink and source either a voltage or a current. In a linear operational amplifier, the output signal is the amplification factor, known as the amplifiers gain (A) multiplied by the value of the input signal and depending on the nature of these input and output signals, there can be four different classifications of operational amplifier gain.

Voltage–Voltage "in" and Voltage "out"

Current–Current "in" and Current "out"

Transconductance–Voltage "in" and Current "out"

Transresistance–Current "in" and Voltage "out"

Since most of the circuits dealing with operational amplifiers are voltage amplifiers, we will limit the tutorials in this section to voltage amplifiers only, (Vin and Vout).

The amplified output signal of an Operational Amplifier is the difference between the two signals being applied to the two inputs. In other words the output signal is a differential signal between the two inputs and the input stage of an Operational Amplifier is in fact a differential amplifier as shown below.

Differential Amplifier

The circuit below shows a generalized form of a differential amplifier with two inputs marked V1and V2. The two identical transistors TR1 and TR2 are both biased at the same operating point with their emitters connected together and returned to the common rail, -Vee by way of resistor Re.

The circuit operates from a dual supply+Vcc and -Vee which ensures a constant supply. The voltage that appears at the output, Vout of the amplifier is the difference between the two input signals as the two base inputs are in anti-phase with each other. So as the forward bias of transistor,TR1 is increased, the forward bias of transistor TR2 is reduced and vice versa. Then if the two transistors are perfectly matched, the current flowing through the common emitter resistor, Re will remain constant.

Like the input signal, the output signal is also balanced and since the collector voltages either swing in opposite directions (anti-phase) or in the same direction (in-phase) the output voltage signal, taken from between the two collectors is, assuming a perfectly balanced circuit the zero difference between the two collector voltages. This is known as theCommon Mode of Operation with the common mode gain of the amplifier being the output gain when the input is zero.

Ideal Operational Amplifiers also have one output (although there are ones with an additional differential output) of low impedance that is referenced to a common ground terminal and it should ignore any common mode signals that is, if an identical signal is applied to both the inverting and non-inverting inputs there should no change to the output. However, in real amplifiers there is always some variation and the ratio of the change to the output voltage with regards to the change in the common mode input voltage is called the Common Mode Rejection Ratio or CMRR.

Operational Amplifiers on their own have a very high open loop DC gain and by applying some form of Negative Feedback we can produce an operational amplifier circuit that has a very precise gain characteristic that is dependant only on the feedback used. An operational amplifier only responds to the difference between the voltages on its two input terminals, known commonly as the "Differential Input Voltage" and not to their common potential. Then if the same voltage potential is applied to both terminals the resultant output will be zero. An Operational Amplifiers gain is commonly known as theOpen Loop Differential Gain, and is given the symbol (Ao).

Equivalent Circuit for Ideal Operational Amplifiers

Op-amp Idealized Characteristics

PARAMETER AND IT'S IDEALIZED CHARACTERISTIC

Open Loop Gain, (Avo)

Infinite- The main function of an operational amplifier is to amplify the input signal and the more open loop gain it has the better. Open-loop gain is the gain of the op-amp without positive or negative feedback and for an ideal amplifier the gain will be infinite but typical real values range from about 20,000 to 200,000.

Input impedance, (Zin)

Infinite- Input impedance is the ratio of input voltage to input current and is assumed to be infinite to prevent any current flowing from the source supply into the amplifiers input circuitry (Iin =0). Real op-amps have input leakage currents from a few pico-amps to a few milli-amps.

Output impedance, (Zout)

Zero- The output impedance of the ideal operational amplifier is assumed to be zero acting as a perfect internal voltage source with no internal resistance so that it can supply as much current as necessary to the load. This internal resistance is effectively in series with the load thereby reducing the output voltage available to the load. Real op-amps have output-impedance in the 100-20Ω range.

Bandwidth, (BW)

Infinite- An ideal operational amplifier has an infinite frequency response and can amplify any frequency signal from DC to the highest AC frequencies so it is therefore assumed to have an infinite bandwidth. With real op-amps, the bandwidth is limited by the Gain-Bandwidth product (GB), which is equal to the frequency where the amplifiers gain becomes unity.

Offset Voltage, (Vio)

Zero- The amplifiers output will be zero when the voltage difference between the inverting and the non-inverting inputs is zero, the same or when both inputs are grounded. Real op-amps have some amount of output offset voltage.

 From these "idealized" characteristics above, we can see that the input resistance is infinite, so no current flows into either input terminal (the "current rule") and that the differential input offset voltage is zero (the "voltage rule"). It is important to remember these two properties as they will help us understand the workings of the Operational Amplifier with regards to the analysis and design of op-amp circuits.

However, real Operational Amplifiers such as the commonly available uA741, for example do not have infinite gain or bandwidth but have a typical "Open Loop Gain" which is defined as the amplifiers output amplification without any external feedback signals connected to it and for a typical operational amplifier is about 100dB at DC (zero Hz). This output gain decreases linearly with frequency down to "Unity Gain" or 1, at about 1MHz and this is shown in the following open loop gain response curve.

Open-loop Frequency Response Curve

From this frequency response curve we can see that the product of the gain against frequency is constant at any point along the curve. Also that the unity gain (0dB) frequency also determines the gain of the amplifier at any point along the curve. This constant is generally known as the Gain Bandwidth Product or GBP.

                 Therefore, GBP = Gain x Bandwidth or A x BW.

For example, from the graph above the gain of the amplifier at 100kHz = 20dB or 10, then the

                             GBP = 100,000Hz x 10 = 1,000,000.

Similarly, a gain at 1kHz = 60dB or 1000, therefore the

                       

                       GBP = 1,000 x 1,000 = 1,000,000. The same!.

The Voltage Gain (A) of the amplifier can be found using the following formula:

                      

                               Voltage Gain(A)=V(out)/V(in)

and in Decibels or (dB) is given as:

             

                                             20log(A) 20log(V(out)/V(in))

An Operational Amplifiers Bandwidth

The operational amplifiers bandwidth is the frequency range over which the voltage gain of the amplifier is above 70.7% or -3dB (where 0dB is the maximum) of its maximum output value as shown below.

Here we have used the 40dB line as an example. The -3dB or 70.7% of Vmax down point from the frequency response curve is given as 37dB. Taking a line across until it intersects with the main GBP curve gives us a frequency point just above the 10kHz line at about 12 to 15kHz. We can now calculate this more accurately as we already know the GBP of the amplifier, in this particular case 1MHz.

Example No1.

Using the formula 20log (A), we can calculate the bandwidth of the amplifier as:

37 = 20logA therefore, A = anti-log (37÷20)=70.8

GBP÷A = Bandwidth, therefore, 1,000,000÷70.8 = 14,124Hz, or 14kHz

Then the bandwidth of the amplifier at a gain of 40dB is given as 14kHz as previously predicted from the graph.

Example No2.

If the gain of the operational amplifier was reduced by half to say 20dB in the above frequency response curve, the -3dB point would now be at 17dB. This would then give the operational amplifier an overall gain of 7.08, therefore A = 7.08.

If we use the same formula as above, this new gain would give us a bandwidth of approximately141.2kHz, ten times more than at the 40dB point. It can therefore be seen that by reducing the overall "open loop gain" of an operational amplifier its bandwidth is increased and visa versa. In other words, an operational amplifiers bandwidth is proportional to its gain. Also, this -3dB point is generally known as the "half power point", as the output power of the amplifier is at half its maximum value at this value.

Operational Amplifiers Summary

                                         OP -AMP SYMBOL

We know now that an Operational amplifiers is a very high gain DC differential amplifier that uses one or more external feedback networks to control its response and characteristics. We can connect external resistors or capacitors to the op-amp in a number of different ways to form basic "building Block" circuits such as, Inverting, Non-Inverting, Voltage Follower, Summing, Differential, Integrator and Differentiator type amplifiers.

Op-amp Symbol

An "ideal" or perfect Operational Amplifier is a device with certain special characteristics such as infinite open-loop gain Ao, infinite input resistance Rin, zero output resistance Rout, infinite bandwidth 0 to ∞and zero offset (the output is exactly zero when the input is zero).

There are a very large number of operational amplifier IC's available to suit every possible application from standard bipolar, precision, high-speed, low-noise, high-voltage, etc in either standard configuration or with internal JFET transistors. Operational amplifiers are available in IC packages of either single, dual or quad op-amps within one single device. The most commonly available and used of all operational amplifiers in basic electronic kits and projects is the industry standard μA-741.

In the next tutorial about Operational Amplifiers, we will use negative feedback connected around the op-amp to produce a standard closed-loop amplifier circuit called an Inverting Amplifier circuit that produces an output signal which is 180o"out-of-phase" with the input.

COLOUR AND LIFE

Colour for Life is the art of living in colour; we offer you whole person development and holistic living. Colour for Life is an overall concept of experiencing everything as colour, be it advertising, clothing, décor or even your very own personalised colour art.
Colour Psycho-Dynamics is the unique approach to personal development; it is about empowering the individual using the medium of colour and expressive arts, enabling you to live your own best life.
Colour for Life offers you the key to a life of purpose and meaning.
Colour Specialist Mark Wentworth created Colour For Life as an extension of his knowledge of the many different areas of colour and its effects on our well-being. His work and extensive experience have shown that by using this powerful tool, colour can enable people to fulfil their true-life purpose.
Colour Psycho-Dynamics is the art of using colour and expressive arts to enable individuals to re-connect with their own greatness. Thus, they may enjoy living their lives according to their own true path and purpose. Having found his own true life purpose, Mark is dedicated to helping others find their way using the most wonderful, natural tool within easy reach – Colour!
                 
                  "Only within yourself exists that reality for which you long.
            I can give you nothing that has not already it's being within yourself.
                  I can throw open to you no picture gallery but your own soul."
                                                                                                  --Herman Hesse--

ART AND LIFE

Anti-mimesis is a philosophical position that holds the direct opposite of mimesis. Its most notable proponent is Oscar Wilde, who held in his 1889 essay The Decay of Lying that "Life imitates Art far more than Art imitates Life". In the essay, written as a Platonic dialogue, Wilde holds that such anti-mimesis "results not merely from Life's imitative instinct, but from the fact that the self-conscious aim of Life is to find expression, and that Art offers it certain beautiful forms through which it may realise that energy.".
Wilde's antimimetic philosophy has had influence on later writers, including Brian Friel. McGrath places it in a tradition of Irish writing, including Wilde and writers such as Synge and Joyce that "elevate blarney (in the form of linguistic idealism) to aesthetic and philosophical distinction", noting that Terry Eagleton observes an even longer tradition that stretches "as far back in Irish thought as the ninth-century theology of John Scottus Eriugena" and "the fantastic hyperbole of the ancient sagas". Wilde's antimimetic idealism, specifically, McGrath describes to be part of the late nineteenth century debate between Romanticism and Realism.
Antimimesis, as set out by Wilde in Decay of Lying is the reverse of the Aristotelian principle of mimesis. Far from art imitating life, as mimesis would hold, Wilde holds that art sets the aesthetic principles by which people perceive life. What is found in life and nature is not what is really there, but is that which artists have taught people to find there, through art. Wilde presents the fogs of London as an example, arguing that although "there may have been fogs for centuries in London", people have only "seen" the "wonderful brown fogs that come creeping down our streets, blurring the gas lamps and turning houses into shadows" because "poets and painters have taught [people] the loveliness of such effects". "They did not exist", asserts Wilde, "till Art had invented them.".
Halliwell asserts that "far from constituting the ne plus ultra of antimimeticism", the notion that life imitates art actually derives from classical notions that can be traced as far back as the writings of Aristophanes of Byzantium, and does not negate mimesis but rather "displace[s] its purpose onto the artlike fashioning of life itself". Halliwell draws a parallel between Wilde's philosophy and Aristophanes' famous question about the comedies written by Menander: "O Menander and Life! Which of you took the other as your model?", noting, however, that Aristophanes was a pre-cursor to Wilde, and not necessarily espousing the positions that Wilde was later to propound.
George Bernard Shaw agreed with Wilde. In his preface to Three Plays he wrote "I have noticed that when a certain type of feature appears in painting and is admired as beautiful, it presently becomes common in nature; so that the Beatrices and Francescas in the picture galleries of one generation come to life as the parlor-maids and waitresses of the next.". He stated that he created the aristocratic characters in Cashel Byron's Profession as more priggish than real aristocrats because at the time of writing he had yet to discover that "what [he] supposed to be the real world does not exist, and that men and women are made by their own fancies in the image of the imaginary creatures in [his] youthful fictions, only much stupider". Shaw, however, disagreed with Wilde on some points. He considered most attempts by life to imitate art to be reprehensible, in part because the art that people generally chose to imitate was idealistic and romanticized.