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A compact, low-profile button antenna for off-body communication is reported. The proposed antenna is composed of coupled circular strips, Y-shaped and L-shaped slots. This configuration covers the application bands such as 0.867 GHz (industrial, scientific, and medical bands), 2.38 GHz (medical body area network), and 5.8 GHz (wireless local area network/industrial, scientific, and medical bands). The percentage bandwidth obtained at the said operating bands is 4.37, 2.10, and 2.56, respectively. The directional radiation pattern obtained from the developed antenna ensures the low backward radiation to the body tissue, thereby, making it more suitable for WBAN applications. The simulated gain and efficiency obtained at the operating bands are 2.5/3.52/4.8 dBi and 78%/85%/89%, respectively. To validate the simulation results, the antenna is fabricated and some experimental results on the body tissue are performed. The SAR value obtained follows the Federal Communication Commission (FCC) limit. [ABSTRACT FROM AUTHOR]

This communication presents the design of a compact loop antenna with independent frequency tuning. The proposed antenna consists of a feed line fed by a $50~\Omega $ coaxial probe and four resonating arms on the adjacent sides of the feed line. The two outer resonating arms are directly coupled to the feed line and the other two inner resonating arms are coupled to the outer arms. The proposed antenna has a footprint of 25 mm $\times 10$ mm $\times0.2$ mm. The designed antenna operates at 0.9, 2.4, 3.5, and 5.5 GHz. Each of these bands is individually tuned using varactor diodes. Thus, the aggregation of these tunable bands provides wide bandwidth. The impedance bandwidth and percentage bandwidth of the antenna are 270/1000/400/700 MHz and 33%/47.6%/11%/12.7%, respectively. Furthermore, the gain and efficiency of the antenna are 1.7/1.3/2.1/2 dBi and 60%/63%/65%/69%, respectively. The prototype antenna is fabricated and tested. The measured impedance and radiation characteristics of the antenna are in good correlation with the simulation results. [ABSTRACT FROM AUTHOR]

In this paper, a portable system for noninvasive detection of fractures in human bones is presented. A planar microwave ring resonator is used as the sensor. The proposed planar microwave sensor is designed using the finite integration-based CST Microwave Studio and tested on a human bone covered by porcine tissues. Fracture induced in the bone was detected by monitoring the transmission characteristics of the sensor as it scans the affected region. The resonant frequency of the ring resonator has been observed at every scan point, and the values are plotted using iterative curvature-based interpolation, improved new edge directed interpolation, and Lanczos imaging technique. The extent of fracture is then derived from the image. The average accuracy of the detected fracture for Lanczos method of resampling was 98.86%. The specific absorption rate was below the minimum level of 1.6 W/Kg at every point of scanning. Portable noninvasive monitoring of fractures in the tibial bone will help in immobilizing the affected part at an earlier stage, thereby reducing the recovery time for patients. [ABSTRACT FROM AUTHOR]

A compact frequency-agile multiband filtenna is presented in this letter. The proposed reconfigurable filtering antenna performs independent switching between four operating bands viz. 1.8 GHz (GSM), 2.4 GHz (Bluetooth), 3.5 GHz (WiMAX), and 5.2 GHz (WLAN). This switching allows the unused bands to be utilized by the secondary user, making the antenna suitable for cognitive radio applications. An elliptical wideband monopole antenna is excited through a reconfigurable bandpass filter (BPF) integrated onto the 50 Ω transmission line. The BPF comprises four distinct structures to tune to four different frequencies using p-i-n diodes. The proposed filtenna has the reflection coefficient less than −20 dB for all the desired operating bands. Furthermore, this multiband filtenna offers gain of about 1.1, 2.6, 3, and 3.4 dBi at the four frequency bands. The prototype filtenna is fabricated, and the simulation results are verified experimentally. [ABSTRACT FROM AUTHOR]

A reconfigurable frequency-selective surface (RFSS) for electromagnetic shielding applications is presented in this letter. The unit cell of the proposed RFSS contains a pair of shorted square loops separated by a uniform distance. Wideband RFSS with the frequency tuning ratio of 1:2.34 achieved by varying the horizontal spacing is proposed. The RFSS covers the frequencies 3.5, 5, and 5.8 GHz shielding the WiMAX, WLAN, and ISM/WiMAX bands, respectively. The prototype of the proposed RFSS is fabricated and loaded on to the mechanical tuning setup. The tuning setup has a box frame with rotating shafts attached to the bevel gears to control the horizontal spacing. The use of collapsible linkage mechanism ensures uniform spacing during reconfigurable operation. The simulated results are validated with measurements. The proposed FSS offers wideband frequency tuning for electromagnetic shielding applications. [ABSTRACT FROM AUTHOR]

In this paper, a novel planar microwave sensor for nondestructive measurement of strain during testing of printed circuit board (PCBs) is proposed. Planar microstrip patch bridged on both sides with squared split ring resonator is used to measure strain. Measurement of stress of isotropic dielectric materials in their linear elastic region that are uses as PCB substrates is also done using the proposed method. The designed microwave probe works at a frequency of 2.45 GHz. The feasibility of the use of time-domain reflectometry method to monitor strain in materials is presented here. The proposed sensor exhibits a sensitivity of about 333 ps for every 1% change in strain. Finite integration technique and real-time measurements have been done to corroborate the relation derived between the transmit time and the strain experienced by the material. The correlation between the simulated and measured strain is about 99.3%. The proposed sensor can be used for faster and accurate testing of PCB substrates without requiring complex calibrations. [ABSTRACT FROM PUBLISHER]

A novel reconfigurable 3-D frequency selective surface (FSS) exhibiting bandstop response is proposed in this paper. The unit cell of the proposed 3-D FSS is constructed from concentric threaded cylinders. The proposed novel 3-D FSS achieves reconfigurability by sliding technique. It offers frequency tuning from 1.86 to 3.10 GHz by sliding the outer cylinder over the inner cylinder. The proposed FSS offers bandstop response in the L- and S-band microwave frequencies. In addition, the proposed 3-D FSS provides polarization- and angular-independent operation. The prototype of the 3-D FSS is fabricated, and the simulation results are validated using measurements. [ABSTRACT FROM PUBLISHER]

This paper proposes a method for detection of cracks in bare printed circuit board sheets before etching of interconnects and mounting dies. A microwave planar sensor probe is designed, and the impedance matching property is used for anomaly detection in flame retardant-4 sheets. The proposed technique and apparatus is first validated through finite-integration-based technique and then through measurement. The resonant frequency information thus obtained is then plotted on a 2-D gradient representation matrix. A novel Windows VB-based application software is developed to determine the dimensions of the crack in the sample through various interpolation operations and dimensioning technique on the image matrix. These are then effectively displayed in a graphical user interface. [ABSTRACT FROM AUTHOR]

This letter presents the design and implementation of a compact microstrip filter with frequency and bandwidth (BW) reconfiguration. The proposed filter consists of a transmission line coupled with a U-shaped microstrip line resonator. Varactor diodes are deployed at specific locations and are tuned to achieve BW and frequency reconfiguration from 0.8 to 1.5 GHz. The transition from the bandpass mode to the bandstop mode is achieved by reconfiguring the transmission zeros simultaneously. The filter percentage lower passband edge tuning and 17.33% higher passband edge tuning. The proposed filter has simple geometry, low profile, and offers a higher level of operational flexibility in the designed frequency range. The filter is tuned with the help of simple actuators requiring simple bias circuitry. The prototype filter is fabricated, and the simulation results are validated using the experimental measurements. [ABSTRACT FROM AUTHOR]

A novel angular independent dual-band FSS with closely spaced response is discussed in this letter. The proposed single layer FSS comprises of unit cell resembling crooked cross geometry convoluted and branched to provide dual resonant paths. The FSS functioning as a band stop filter at 2.54 and 3.54 GHz works as a shielding component for S band operation. The unit cell size of the proposed FSS is 0.088 \lambda \times 0.088 \lambda where \lambda corresponds to the wavelength of the first resonant frequency. Both the bands are closely spaced providing the frequency ratio of upper to the lower resonant frequency value of 1.39. Additionally, the proposed dual-band FSS is symmetrical in nature, thereby providing identical stop-band response for both TE and TM operation modes. It also exhibits highly stable angular stability. Prototype of the proposed FSS is fabricated and its simulated results are compared with the experimental results. [ABSTRACT FROM PUBLISHER]

This letter proposes a novel method of noninvasive detection of voids in fiber reinforced plastics (FRPs). An ideal nondestructive evaluation method for the detection of subsurface defects that utilizes the capabilities of a magnetoinductive planar microstrip sensor is examined through a finite-integration-based model in this letter. A combination of magneto inductive waveguide as (MIW) and a patch radiator is used as the sensing element. The magnetoinductive waveguide increases the sensitivity of the patch to the presence of voids in the FRP. [ABSTRACT FROM PUBLISHER]