Another consequence is the following: If you densely route several single-ended lines, I suggest you throw the values into a differential line calculator. For the odd mode, the differential impedance can be obtained by setting the. Microstrip: These are signals that are externally routed on a PCB. A symmetrical pair of differential microstrip lines implemented in hybrid microstrip/coplanar waveguide (CPW) technology is proposed. PCB Microstrip is a commonly used type of electrical transmission line for conveying microwave-frequency signals. A four port two stage branch-line differential-mode BPF is first designed. 6mm board, 100R microstrip differential impedance, they suggest 4/5 mil trace/space, which is a bit different than 9/4. So I decided to try and verify the calculator - jlcpcb offer an impedance calculator in their quotation system, and for a 6-layer 1. One of the two microstrip transmission lines includes strip conductor 40 and the portion of the ground plane conduction under the. Due to these advantages over. 0 (modified)) A microstrip line is single-ended 1 in the sense that the conductor geometry is asymmetric and the one conductor – namely, the ground plane – also normally serves as ground for the source and load. 4 µm. 8 GHz IBFD differential fed microstrip patch antenna arrays and 2. That said, microstrip is marginally easier to deal with to meet the correct impedance since the trace will be fatter. Coplanar waveguides, striplines, and microstrip traces that require impedance control all need to be sized such that the width produces the desired characteristic impedance. Common-mode (CM) noise on differential microstrip lines can be suppressed by PCB-embedded filters. Differential evolution E-shape microstrip antenna Genetic algorithm Microstrip antenna Particle swarm optimization Tulip shape antenna This is an open access article under the CC BY-SA license. proposed for differentially-driven microstrip antennas to improve impedance bandwidth. Based on the traditional one, the differential microstrip lines are added, which can improve the. 4. The same ideas also apply to differential pair routing. The impedance was already dominated by the presence of ground. Edge. Design of low phase noise K‐band VCO using high quality factor resonator in 0. Figure 5. The implemented 2. Microstrip and Stripline Design . differential modes, which are indeed related to signal definitions. I assigned PerfE boundaries to each microstrip and pad element in yellow. Fig. . A power divider is a three-port microwave device that is used for power division or power combining. A symmetrical stripline is shown in Figure [Math Processing Error] 3. Differential surface coplanar waveguide with ground calculations: *0. Microstrip Differential Impedance is a key parameter in the design of high-speed digital and high-frequency analog circuits. There are four different types of impedance used in characterizing differential trace impedances. It is found that the patch length can still be designed using. This subject is considered in much more depth in [4], and here just one approach is reported. 55 Ω . They allow signals to flow between the components. Differential microstrip impedance calculator is an online electronic tool to measure the opposition to alternating current. Silicon-based RFICs generally use differential signaling for analog signals to overcome the problem of field coupling in high-density circuits and problems due to the finite conductivity of the. As we know theoretically there would be two same signals with 180 phase. In an ideal power divider, the power going into port 1 is equally split between the two output ports, and vice versa for power combining. A microstrip highly sensitive differential sensor for complex permittivity characterization of urine samples was designed, fabricated and tested. It refers to the impedance that a pair of differential (opposite phase) signals will see in a microstrip transmission line configuration. This paper presents a planar grid array antenna with a 100 Ω differential microstrip line feed on a single layer of standard soft substrate. The passband ranging from 0. In [1] - [2], several wideband microstrip differential filters with good common-mode suppression in the passband were proposed, but the circuit size is a little large and the out-of-band. Abstract: In this paper, the crosstalk noise between spoof surface plasmon polariton (SPP) transmission line (TL) and conventional differential microstrip (MS) lines is investigated. Edge-coupled coated differential microstrip Edge coupled differential microstrip for flex PCB. Compared with these existing works, this work has wider impedance bandwidth and higher gain than these in [, ], higher isolation and lower cross-polarisation level than these in [, ], and lower side lobe level than that in []. To use this calculator, simply input your microstrip geometry and Dk value, and the tool will return the differential impedance value for a pair of microstrip traces. On the PCB side, each resulting differential pair object will be added to the default Differential Pair class: <All Differential Pairs>. Microstrip lines have a quasi-TEM mode of propagation, making it easy to realize various lumped-elements. Trace Thickness(T) Substrate Height(H1) Trace Width(W) Trace Spacing(S) Substrate. With t = 35 um (typical for copper with plating on a pcb), Z odd drops to 44 ohms, according to LineCalc. It transfers the dominant TE10 mode signal in a rectangular waveguide to a differential mode signal in the coupled microstrip lines. Modeling approximation can be used to understand the. The differential topology is applied more and more in microwave and millimeter-wave circuits, for its high immunity to crosstalk and noise. But the choice of transmission-line technology, such as microstrip or grounded coplanar waveguide. By understanding the microstrip transmission line, designers can. PDF | On Jun 1, 2017, Eng-Kee Chua and others published Evaluation of fibre weaving of substrate on differential microstrip using an analytical approach | Find, read and cite all the research you. Crosstalk is the unwanted coupling of signals between parallel traces. Save. 2. 5 dBi at the center frequency and exhibits VSWR ≤ 2 for frequencies between 870 MHz to 1. The etched slots and the stacked. et al. Figure 25. 2023 | Journal article. It is good practice to match differential trace length and to keep the distances between the. In microstrip form, differential transmission lines are still somewhat dispersive, and this can be a concern for circuits handling wideband analog or high-speed digital signals. 3 V, etc. Figure 7. The figure-1 above. Microstrip to waveguide transitions used presently typically require a relatively complex waveguide mount extending on both sides of the planar circuit. 46 mm width traces to obtain 100 Ohms ZDiff while using 0. – Striplines are embedded between two reference layers, which results in a higher capacitance versus microstrip lines. However, few papers reported on the asymmetrical confinement. Incidentally, the trace thickness parameter does have a significant effect. 2µm (3mil) with the 76. (b) Equivalent circuit model of the sensor. The measurements, however, can be carried out easily by utilizing a standard two-port vector network analyzer and using three different waveguide standards from a commercial. There is no GND plane in this model, the wires act as reference and do not receive direct excitation. 2. Single-ended signals are fairly straightforward. Differential Microstrip Impedance. Firstly, two symmetrical rectangular slots are cut on the radiating patch where the zero-current position of the TM 30 mode excites another resonant slot mode. 3. The coupler shares a common ground plane with the inverted microstrip patch resulting a very compact design. Polar or rectangular grids only allow direct reading of S11. D = Distance between two differential pair signals; W = Width of a trace in a. For example, if u = 1 and ε r = 10, then from the figure, Z 0 ε e = 126 Ω and ε e / ε r = 0. The "optimum" mitered bend equations for microstrip were found empirically way back in the 1970s. My design requires that the pairs travel over very thin flexible PCB, about 50mm total transmission length. 18 μm CMOS technology. 5. Their calculation model is based on the thickness and width of the trace, the thickness of the substrate, and the dielectric type and thickness. A 50 Ω resistor is considered in series with the resonator. Differential Trace Routing. Embedded microstrip routing: This structure is similar to a. A differential line is composed of two transmission lines excited by two out-of-phase signals. A Differential Microwave Sensor Loaded With Magnetic-LC Resonators for Simultaneous Thickness and Permittivity Measurement of Material Under Test by Odd- and Even-Mode. An edge coupled differential microstrip transmission line is constructed with two traces on the same reference plane. 1 Structure of transition with differential PTH via a Top view of differential PTH via b Side view. Differential-fed filters [20,21], differential-fed power dividers [22,23], and differential-fed antennas [24,25,26] are the most widely used differentially driven microstrip devices. You can use this transmission line to connect two PCB components or to create components such as filters, couplers, and feeding. The two conductors are separated by a dielectric. 38. Several designs have been proposed in an effort to introduce an efficient transition from waveguide to microstrip such as transitions based on antipodal finline, 1–3 based on ridged waveguide, 4–6 based on iris coupling, 7 or based. The dual-band filtering radiation function is achieved by utilizing the odd and even modes of the stub loaded microstrip resonator to excite the TMδ1 and TMδ3 mode in each polarization direction of the cross-shaped dielectric strip resonator. is desired. Reset. The port types are set to transverse electromagnetic (TEM) that is configured with electric potential and ground subfeatures. Stripline Impedance -Differential 2. differential filtering microstrip patch antenna. Differential feeding methods have been studied in literature to suppress cross-polarized fields in MPAs [34,58]. S. By changing the width of 22 selected short sides of microstrip cross mesh array. The common mode signal in the coupled microstrip lines is highly rejected. A novel differential microstrip patch antenna (DMPA) is designed for autonomous cruise control radar systems at 79 GHz. The placement of the reference planes is important as this is what makes a microstrip or stripline trace. A differential microwave permittivity sensor and comparator is designed using a microstrip transmission line loaded with a magnetic-LC resonator. Single Ended Impedance Ω. This technique can result in a compact structure with a sharp roll-. This paper proposes an accurate correction factor based method to calculate the effect of conductor surface roughness from the per‐unit‐length (P. A 45 degree differential microstrip phase shifter operating in the frequency band ranging from 1. INTRODUCTION . ) parameters and the complex propagation. The back-to. Figure 1: A Microstrip transmission line displaying quasi-TEM. The differential line was chosen in the proposed antenna due to. 250 mil Length 35 –8. Different from the CM absorption. This impedance is not the characteristic impedance of the. These losses are dependent on: The loss tangent or dissipation factor of the dielectric material. ENIG plating always provides greater total losses in a coplanar arrangement vs. One would reasonably expect similar results for striplines. A 22 microstrip antennas array is used as a test case to corroborate the efficacy of the proposed scheme. Differential surface microstrip with ground calculations: ( This calculator gave a different result, don't know why ) *0. 8), the ratio of W/H for fifty-ohm microstrip is about 95%. Its single row design offers a narrow beam in elevation and a wide beam in azimuth. Distinct from conventional single-ended patch antennas, the DMPA uses a pair. of microstrip transmission line without the connector launch, in order to be a valid comparison with a differential length measurement. The PCB stack is composed of three standard RF core materials with standard thicknesses. The simulation shows insertion loss for 1". The developed antenna can be used in either center grounded or differential configuration. 3 ; Trace thickness = 1/2-oz cu + 1-oz plating (1. Microstrip patch antennas (MPAs) are broadly used in various types of applications. Further, a triple SRRs structure was proposed in [ 21 ], with the substrate punched in the gap of the outermost SRR to allow the liquid sample to flow vertically. These parameters include: The lateral dimensions, however, are well controlled being photolithographically defined and then etched. Differential Via Figure 1 shows the construction of a typical differential via in a high-speed serial link. Microstrip PCB Ground Clearance Part 2: How Clearance Affects Losses In a previous article, I provided a discussion and some simulation results on the necessary clearance between impedance controlled traces and nearby grounded copper pour. 75 psTr Forward crosstalk design limit for crosstalk depends on signal risetime. Together with the differential. 250 mil Length 35 –8. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. This calculator determines the impedance of a symmetric differential stripline pair. ground plane, consist of two strip of copper over a substrate. It renders fairly accurate results suitable for use in circuit board manufacturing and engineering analysis. The microstrip transmission line is aligned with. Design ChallengesIn this paper, single-ended microstrip lines and differential microstrip lines loaded with MLC resonators are studied, and potential applications are highlighted. A differential microstrip antenna with improved gain for RF energy harvesting is presented in this paper. First, the design formulas to determine the patch dimensions and the location of the feed point for single-ended microstrip antennas are examined to design differentially-driven microstrip antennas. Figure 5 Differential impedance of topology with 50 mil gap when driven from each end. Access our free differential microstrip impedance calculator Microstrip Impedance Calculators Don’t Include Some Data When you need to get an initial estimate of trace width required for a target impedance, then trace calculator tools are very useful can they can help your understand how your substrate materials will affect the impedance of a. It can smear out the edges, contributing to collapse of the eye. The sensor consists of a splitter/combiner section with two symmetrical complementary split-ring resonators (CSRR). Figure 25 shows a differential pair using the microstrip layout. The common mode signal in the coupled microstrip lines is highly rejected. For differential circuits, two conductors are used. What we found was that, once the spacing between the pour and the trace becomes too small,. Compared to other inline transitions above 90 GHz, which are designed for single substrates, it can be applied to. By loading two identical SRRs into a microstrip splitter/combiner configuration, a differential-mode sensor was designed in . The probe is. Two symmetrical trapezoid-shaped slots and four triangle-cut corners on the ground are used to improve the impedance matching over the UWB. Viewed 205 times 1 $egingroup$ I am attempting to determine the trace width needed for routing a differential signal of 100 Ω on a PCB I am designing. The differential line is excited and terminated by port features. The common mode signal in the coupled microstrip lines is highly rejected. 1. Differential Impedance ($$Z_{0_{diff}}$$): The impedance between the two lines with opposite polarity signals. A differential microstrip transmission line is constructed with two traces on the same reference plane. The instantaneous differential impedance is related to the voltage simulated at the V_TDR node from: A generic cross section of a microstrip differential pair is shown in Figure 2. On the calculation link you have indicated, can you please elaborate on the item you selected (is it "Differential Microstrip Impedance Calculator" ?), and then how you entered the values ? does H is the total thickness of the PCB or is it the distance between the top track and another layer. 1, were developed by Hammerstad. The cavity-mode theory and the dyadic Green's function. A new differential feeding scheme and two parasitic patches are adopted to improve the impedance bandwidth of SF-MGAA. The device is a differential sensor consisting of a pair of mirrored lines loaded with a. uu. James, Experimental Characterization of Microstrip Bends and Their Frequency Dependent Behavior, 1973 IEEE Conference Digest, October 1973, pp. A W-band inline transition between differential microstrip lines and a rectangular waveguide is presented. The theory of microstrip antennas based on the improved cavity model is expanded to analyze the input impedance and. 2019. It mentions formula or equations used in this differential Microstrip Impedance Calculator. Figure 1. View All Tools. It is found that they only degrade the polarization purity in the H-planeDifferential microstrip antennas have received considerable attention in the design of highly integrated radio transceivers for wireless communications. Modeling approximation can be used to design the microstrip trace. An example of a wire microstrip might most often be found in prototypes or reworked boards where a wire is used over the top of pcb or copper clad material. 4. The antenna has a segmented feed line, a rectangular driven patch etched with a double I-slot, and a squared stacked patch with grooves at the edges of both sides. The proposed filter is composed of four quarter-wavelength coupled lines and four quarter-wavelength microstrip lines. Choose a routing style (microstrip, stripline, coplanar waveguide, single-ended vs differential) Calculate the trace width needed to give the required impedance; After everything is routed, it’s now a question of whether it’s appropriate to fill in the unused regions of the surface and internal layers with the grounded copper pour. This paper studies differentially-driven microstrip antennas. While microstrips have desirable characteristics, when designing microwave or RF circuits, it is essential to note the different types of loss mechanisms in. The substrate is 50um, with a 50um coverlay. Visit to learn more about the EEWeb communit. The S 11 parameter and the 3D gain pattern for the two configurations are given by Fig. An example of the parameterized differential stripline. Contributors : Wen-Jing Wu; Wen-Sheng Zhao. 5 GHz. P. This configuration is known to be useful to enhance signal-to-noise ratio. The surface current distribution of the subwavelength periodic corrugated microstrip is numerically analysed. 2. 4: Normalized even-mode and odd-mode effective. Transmission Lines. Next, a novel differential microstrip geometry specifically designed [12], [13] to suppress commonmode (CM) noise in specific frequency intervals is analyzed. Differential microstrip antennas have received considerable attention in the design of highly integrated radio transceivers for wireless communications. The differential line is excited and terminated by port features. 22mil 273mil 2mil 4mil 5mil 1. Read more. Agilent's LineCalc tool calculates Z odd = 50. Remember : before you start. A microstrip line is a transmission line that is a basic building block for most RF planar microwave devices. Their flexible layout is excellent, giving microstrip lines optimal versatility. So how to define these two opposite ports and how to see the results ( differential impedance i. The main difference between these types of traces is their location in the PCB: microstrips are on the surface layer, while striplines are on an inner layer between two reference planes. If there is an insulator around the wire then this calculator will be an estimate. 11. Simply put, differential impedance is the instantaneous impedance of a pair of transmission lines when two complimentary signals are transmitted with opposite polarity. If vias are unavoidable, an absolute minimum number of vias need to be used. There are some advantages to using a microstrip transmission line over other alternatives. se 2 European. Note the differential pairs above that look like a strand of intestine have a constant gap between the pairs. 8. A microstrip line is a type of electrical transmission line used to convey. 15 mm spacing. Edge Coupled Stripline Differential Impedance Calculator. 4 GHz IBFD double differential fed microstrip patch antenna achieve interport isolation of 53, 51 and 62 dB over their. A differential microstrip antenna with improved gain for RF energy harvesting is presented in this paper. The differential micro strip calculator requires some parameters. Much has been written about terminating PCB traces in their characteristic impedance, to avoid signal reflections. In addition, the slot’s length is enlarged to decrease. Sorted by: 1. The differential design is obtained by pairing two single-ended (SE) circulators, each based on. A robust and wideband differential microstrip line-to-WR6-waveguide transition for mixed multilayer PCBs at D-band is presented. To realise the tri-mode BPF performance, the multimode stepped-impedance resonator is introduced and parallel coupled to both the balanced and the unbalanced ports. This antenna consists of a differential-fed microstrip patch, a U-shaped differential resonator, and two pairs of quarter-wavelength J-inverters. The variants are designed using multi-step impedance transformer,. The most important design goal is to keep the wave impedance as homogenous as possible. Edge-Coupled Coated Microstrip: is a differential configuration with two controlled impedance traces on the surface coated with solder mask, and a plane on the other side of the dielectric. In addition to the characteristic impedance of a transmission line, the tool also calculates. Microstrip is the conducting medium used to transmit the electric signals at microwave frequency and. To integrate with the front-end circuit, a transition from microstrip line to waveguide is required. All the elements are vertically integrated without increasing the dimensions. W1: Width of the bottom surface of the trace. 1: Microstrip transmission line structure and design parameters. Next a microstrip line is used to excite the LSPs modes to further improve the performance of the. However, I am having trouble achieving that in my design. This example shows how to set up the differential microstrip lines using TEM type ports. dBm to Watt converter Stripline Impedance calculator Microstrip line impedance Antenna G/T Noise temp. Cross Talk Minimization. Using the minimum trace spacing of 76. 25 GHz. A W-band inline transition between differential microstrip lines and a rectangular waveguide is presented. Microstrip construction consists of a differential pair and a single reference layer (typically ground). […]Model for examining differential crosstalk between two microstrip differential pairs. In this article, a microstrip-to-waveguide transition is presented in the W-band by using an E-plane probe with a parasitic patch. The edge couple differential symmetric stripline transmission line is a common technique for routing differential traces. Third, the effects of imperfect differential signal conditions on the performance of differentially-driven microstrip antennas are investigated for the first time. 1 Even and Odd Mode Differential microstrip lines support two quasi-TEM modes, that is, the even and odd modes. It eliminates the need of a balun in the RF frontend and supports the realization of more compact radar frontend. The closer you place the pairs together, the differential impedance gets smaller because LM and CM get larger. 7. There are generally longer. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. 00 Ω +/- 10% 99. 5. In this paper, a new narrow bandpass microstrip filter is proposed with a differential structure based on an analytical approach. Again, these formulas are the result of curve fits, but starting with physically. Using this property, the TDT times of. Differential surface coplanar waveguide with ground calculations: *0. In addition, it is derived. You have buried ground (presumably on L3). In microstrip, this technique is ideal for routing differential pairs. A differential microstrip antenna with improved gain for RF energy harvesting is presented in this paper. Moreover, the design of the differential line is straightforward since the required level of common-mode suppression and bandwidth are given by simple approximate. Under differential-mode. This provides common-mode noise cancellation in addition to isolation from other circuit blocks in an RF system. 02400 . Differential Microstrip Impedance. The plots show the magnitude and phase of the input impedance. 1. LVDS pairs need 100 ohms differential impedance. The transition was designed at 75 GHz,. The PCB stack is composed of three standard RF core materials with standard thicknesses. Two identical sensing elements. 15 λ × 0. Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Microstrip construction consists of a differential pair and a single reference layer (typically ground). A partial differential equation is obtained from the model which is solved using “Reduced Differential Transformation Method (RDTM)”. These antennas have many advantages like low profile, low cost,. This. A 50 Ω microstrip line, recessed from the edge to the centre of the patch, feeds the. 3% was achieved at a received power of 2. Abstract: A differential microstrip lines-based microwave microstrip sensor loaded with multiple magnetic-LC (MLC) resonators is proposed in this. The transition was designed at. Compared to other inline transitions above 90 GHz, which are designed for single substrates, it can be applied to mixed multilayer circuits. Differential surface microstrip with ground calculations: ( This calculator gave a different result, don't know why ) *0. It is very difficult to predict the exact Dkeff in microstrip without a field solver, but a good approximation can be obtained by [3]: Equation 5. A differential microwave permittivity sensor and comparator is designed using a microstrip transmission line loaded with a magnetic-LC resonator. Distinct from conventional single-ended patch antennas, the DMPA uses a pair of coupled lines as feeding line. This article presents a magnetless differential microstrip circulator for high frequency operation. When two parallel, closely spaced, microstrip lines are used to deliver a differential signal to a load, the differential impedance between them can be calculated using a closed form expression. Show more detail. 1. 6µm width, this results in Z diff = 110~115Ω (according to MMTL), which is out of spec!This paper presents a practical method to extract mixed-mode S-parameters of a micro-strip-to-waveguide transition that is fed by a differential micro-strip line. 5A, the differential transmission line 37 is made up of two microstrip transmission lines, 60, 62. Examining ɛ e, the phase velocity of a transmission line with a narrower width is faster than that of a transmission line with a broader width. In this letter we propose a unique design by choosing Zl e = Zo, in order to achieve largest bandwidth. The edge couple differential symmetric stripline transmission line is a common technique for routing differential traces. A wideband differential-fed microstrip patch antenna based on radiation of three resonant modes of TM<sub>12</sub>, TM<sub>30</sub>, and slot is proposed in this paper. It also causes the characteristic impedance to be frequency dependent. This example shows how to set up the differential microstrip lines using TEM type ports. Differential Microstrip Patch Antenna as Feeder of a Hyper-Hemispherical Lens for F-Band MIMO Radars Dragos Dancila1, Václav Valenta2, Alina-Cristina Bunea3, Dan Neculoiu3, Hermann Schumacher4 and Anders Rydberg1 1 Uppsala University, Department of Engineering Sciences, Uppsala, Sweden, dragos. For example, through introducing periodic subwavelength corrugations on the edges of differential microstrip lines, the crosstalk between differential pair and the adjacent microstrip lines can be. 6 ohms and Z even = 110 ohms for your geometry, very close to your result. Afterward, the port's dimensions is altered to span both microstrip lines. 1 DIF-Coated Microstrip Edg . trace 1 (signal 1) couples into GND (trace 2) into trace 3 (signal 2), and even if the GND trace is via-stitched to plane, some field still peeks through the gaps between vias, and thus from trace 1 to 3. For a printed circuit board (PCB) this is a pair of traces, also known as a differential pair. The dipole antenna with semi-elliptic arms is introduced to transform the differential mode of DML to the TE10 mode of the rectangular waveguide directly. The NEXT is represented by differential s-parameter Sdd31, while FEXT is represented by Sdd41. This is a frequency dependent speed of the signal. 4. Due to non-conventional signaling compared to commonly used single ended configurations, it is easy to make mistakes while setting up the design for EM simulations. , often all on the same PCB. This calculator determines the differential microstrip impedance of a transmission line. Microstrip construction consists of a differential pair and a single reference layer (typically ground). This article presents a magnetless differential microstrip circulator for high frequency operation. It is the same configuration as. 3. Microstrip allows for thinner flexible. model example shows how to set up differential and single-ended microstrip lines using TEM-type ports. The proposed microstrip sensor is evolved from a traditional microstrip sensor, which has a single resonator unit excited by a single microstrip line. The calculator below uses Wadell’s. This page covers Differential Microstrip Impedance Calculator . Here's two references: R. differential stripline. The feeding structure consisting of one line resonator and one H-shaped resonator as well as the microstrip antenna elements together provide the three stages in the bandpass filter design. everything RF has created a series of RF calculators to help engineers and students with common calculations that they need to conduct frequently. Using the spacing parameters shown above, there are two approaches that can be used to quantify differential crosstalk: A model based on field strength Calculating Differential Crosstalk Strength in a First-Order ModelThe Smith Chart graphically maps S11=reflection coefficient= (ZL-Z0)/ (ZL+Z0) to Load Impedance (ZL), normalized to Z0 (source impedance = center of chart).