Planar inductors

Balachandran S, et al. MEMS tunable planar inductors using DC contact switches. In 34th European microwave conference 2004. 

Coplanar waveguides (CPW) 2-3 Metal-insulator-metal (MIM) capacitor 4 Planar inductors 3 RF electrical isolation 1... 

Planar inductors are suited for both thick-film, thin-film, and LTCC applications. Typical members of this group are meander and spiral inductors (Figure 9.22). Meander inductors offer the lowest inductance vs. size. Their inductance value is determined by tiie length and the unit line inductance. Because of the adverse magnetic-field orientation of adjacent line segments, there is no increase of the overall inductance [6]. The inductance is directly proportional to the meander lengtii. Meander inductors are usually used for low inductances and delay lines. Because the meander is more or less a transmission line, the distributed character is dominating in most cases. 

Planar inductor shapes (a) meander, (b) circular spiral, (c) rectangular spiral. 

Other types of new AT-containing ligands have been described as effective chiral inductors for copper-catalyzed asymmetric cyclopropanation. Hence, Fu and Lo [42] prepared a new planar-chiral hgand, namely the C2-symmetric bisazaferrocene (structure 34 in Scheme 18), which was fbimd to be efficient for the cyclopropanation of various olefins with large diastereomeric excesses and ee values up to 95%. 

The antenna in an RFID is typically implemented as a spiral inductor or as a dipole antenna, depending on the frequency of operation of the tag. This frequency of operation depends on the application, government-imposed standards, physical constraints, etc. The most common frequencies for operating RFID tags are <125 kHz (called the LF band), 13.56 MHz (called the HF band), 900 MHz (called the UHF band), and 2.4 GHz (called the microwave band). For various reasons, 125 kHz tags are not compatible with planar processing and thus will not be considered here. 

The principle of duality concerns the transformation between two apparently different circuits, which have similar properties when current and voltage are interchanged. Duality transformations are applicable to planar circuits only, and involve a topological conversion capacitor and inductor interchange, resistance and conductance interchange, and voltage source and current source interchange. 

Arguably, the most important RFID operating frequency used today is 13.56 MHz RFID. At this frequency, power is stiU inductively coupled. However, given the higher frequencies used, it is possible to use planar spiral inductors. These may be fabricated at substantially lower costs than the wound coil inductors used in LF RFID as a result, 13.56 MHz RFID has received substantial attention as a candidate frequency for low-cost RFID applications [2]. In the presence of liquids, 13.56 MHz RFID works well, but is moderately susceptible to interference from metals nearby. However, compared to other candidate frequencies, 13.56 MHz RFID is generally considered to be the most promising frequency for use in RF barcodes. 

Capacitors and inductors can be formed onto surfaces (not necessarily planar) using ink-jet printing processes by creating local 3D structures. Figures 11-21 and 11-22 schematically illustrate one method of printing capacitors and inductors. For a capacitor, bottom electrode, dielectric, and top electrode are printed successively, and this process could be repeated for a multilayer capacitors. Both the area and thickness of the dielectric could be varied to select the value of the capacitance. 

Planar circular inductors are considered ground less if their distance to the adjacent ground plane is larger than the inner diameter of the coil [32]. 

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