Filters, electrical, wave

Piezoelectric filter A kind of electromechanical device in which electrical signals are converted to a mechanical wave by using a piezoelectric crystal. Thus, the former electric wave is delayed as it propagates across the crystal, and this delay is used to reinforce a desired frequency bandwidth with very high Q values. The quartz crystal is an example of the piezoelectric elements used for these filters [i],... 

Because only acoustic waves at specific frequencies can efficiently propagate between the faces of bulk wave crystals, these devices are electronically used as frequency filters and the frequency-determining elements in oscillator circuits. As filters, bulk wave crystals will only pass electrical signals occurring over narrow frequency ranges centred about each resonant frequency. Additional frequency-selective circuitry is typically used to limit signal transmission to the... 

Further, if within the electrical circuit the ohmic resistance R can be neglected, the ic wave leads to the potential by 90°, as is known, which means that shows a positive 7t/2 phase angle shift ( between tt/2 and zero. Our main objective in AC polarography, however, is the faradaic current, so a separating condenser is placed between the amplifier and normal resistor in order to filter out the d.c. current and to evaluate the ac current component. As we want to understand the relationship between idc(i ) and iac(i ) as a function of Edc and Eac applied, we may consider Fig. 3.41(a) and (b). 

In a lock-in used in resistance bridges for cryogenics, the reference signal may be either sinusoidal (as in LR-700) or a square wave (as AVS-47 Picowatt). The square wave reference (easier to produce at low frequencies) increases the output signal level by a factor 1.23, thus compensating the noise, increased by (1.23)1/2. A sinusoidal reference allows to use lower cut-off filters on the electric wiring of the cryostat. 

The signals were recorded as electrical potential in millivolts. The well known Maxwell s formula and an adjustable empirical coefficients were used to obtain the equivalent volume fraction of liquid [43]. Since it is known that kinematic waves exist only in the frequency of some few Hertz, hardware low pass filter with 20 Hz cutting frequency was included for each channel in the electronic unit. The filter was tuned at 82.66 Db. Data were acquired by a computer at 100 Hz. The following comments regarding the above apparatus description are in order ... 

Donor-doped PZTs have higher permittivities and d coefficients than acceptor-doped materials and are therefore more suitable for converting mechanical into electrical vibrations. They have higher dissipation factors than acceptor-doped materials and are therefore not as suitable for wave filters. If this were not the case, their low ageing coefficients would be an advantage. 

Piezoelectric crystals, notably quartz, are used to control or limit the operating frequency of electrical circuits. A well-known example is their use in quartz clocks . The fact that a dielectric body vibrating at a resonant frequency can absorb considerably more energy than at other frequencies provides the basis for piezoelectric wave filters. The equivalent circuit for a piezoelectric body vibrating at frequencies close to a natural frequency is given in Fig. 6.3. At resonance the impedance due to L, and C falls to zero and, provided that Rx is small, the overall impedance is small. 

Capacitors are used to store electric energy, especially for shorter periods of time, and substitute -> batteries in some cases. They smooth the output of full or half-wave rectifiers in power supplies or are part of electric frequency - filters. 

Some of the present industrial uses of diamond coatings include cutting tools, optical windows, heat spreaders, acoustic wave filters, flat-panel displays, photomultiplier and microwave power tubes, night vision devices, and sensors. Because its thermal conductivity and electrical insulation qualities are high, diamond is used for heat sinks in x- ray windows, circuit packaging, and high-power electroific devices. Moreover, the high chemical stability and inertness of diamond make it ideal for use in corrosive environments and in prosthetic devices that require biocompatibility. 

---