scholarly journals Noninvasive, near-field terahertz imaging of hidden objects using a single-pixel detector

2016 ◽  
Vol 2 (6) ◽  
pp. e1600190 ◽  
Author(s):  
Rayko Ivanov Stantchev ◽  
Baoqing Sun ◽  
Sam M. Hornett ◽  
Peter A. Hobson ◽  
Graham M. Gibson ◽  
...  
Keyword(s):  
Silicon Wafer ◽  
Ex Vivo ◽  
Imaging Techniques ◽  
Near Field ◽  
Circuit Board ◽  
Thz Radiation ◽  
Single Element ◽  
Far Field ◽  
Thz Imaging ◽  
Subwavelength Resolution

Terahertz (THz) imaging can see through otherwise opaque materials. However, because of the long wavelengths of THz radiation (λ = 400 μm at 0.75 THz), far-field THz imaging techniques suffer from low resolution compared to visible wavelengths. We demonstrate noninvasive, near-field THz imaging with subwavelength resolution. We project a time-varying, intense (>100 μJ/cm2) optical pattern onto a silicon wafer, which spatially modulates the transmission of synchronous pulse of THz radiation. An unknown object is placed on the hidden side of the silicon, and the far-field THz transmission corresponding to each mask is recorded by a single-element detector. Knowledge of the patterns and of the corresponding detector signal are combined to give an image of the object. Using this technique, we image a printed circuit board on the underside of a 115-μm-thick silicon wafer with ~100-μm (λ/4) resolution. With subwavelength resolution and the inherent sensitivity to local conductivity, it is possible to detect fissures in the circuitry wiring of a few micrometers in size. THz imaging systems of this type will have other uses too, where noninvasive measurement or imaging of concealed structures is necessary, such as in semiconductor manufacturing or in ex vivo bioimaging.

Calibration of MEMS Strain Sensors Fabricated on Silicon

2001 ◽  
Author(s):  
Li Cao ◽  
Chuck Hautamaki ◽  
Jia Zhou ◽  
Tae Song Kim ◽  
Sue Mantell
Keyword(s):  
Silicon Wafer ◽  
Near Field ◽  
Strain Sensor ◽  
Field Strain ◽  
Sensor Calibration ◽  
Far Field ◽  
Calibration Technique ◽  
Gage Factor ◽  
Mems Sensor ◽  
Aluminum Specimen

Abstract A calibration technique for measuring MEMS strain sensor performance is described. The sensor calibration technique entails developing a repeatable relationship (gage factor) between the change in sensor nominal resistance and the strain measured at the sensor. The calibration technique involves creating a “pseudo” strain sensor consisting of a strain gage mounted on a silicon wafer. Two identical test specimens are evaluated: the pseudo sensor mounted (with adhesive) on an aluminum specimen (or embedded in a specimen), and a MEMS strain sensor mounted on an aluminum specimen (or embedded in a specimen). The dimensions of the silicon wafer for both the pseudo sensor and MEMS sensor are identical. The specimens are loaded by tensile test. For the pseudo sensor specimen, a relationship is established between the strain applied to the specimen (far field strain) and the strain at the sensor (near field strain). Once the relationship between near field and far field strain is known, a relationship between near field strain and change in resistance of the uncalibrated MEMs sensor is established. This relationship between strain at the sensor and change in resistance is the gage factor. Two different MEMS strain sensor designs were fabricated by patterning polysilicon on a 500 micron thick silicon wafer: monofilament and membrane sensors. Gage factors for the MEMS sensors were determined following the calibration procedure. The results also lead to a conclusion that wafer geometry influences the strain transfer to the sensor.

An Innovative Package EMC Solution Using a Highly Cost-Effective Sputtered Conformal Shield

2016 ◽  
Vol 2016 (DPC) ◽  
pp. 002152-002181 ◽  
Author(s):  
Nozad Karim ◽  
Rong Zhou ◽  
Jun Fan
Keyword(s):  
High Speed ◽  
Metal Layer ◽  
Near Field ◽  
Cost Effective ◽  
Circuit Board ◽  
System Level ◽  
Normal Operation ◽  
Far Field ◽  
Wide Range ◽  
The Cost

High-speed digital and wireless devices radiate undesired electromagnetic noises that affect the normal operation of other devices causing electromagnetic interference (EMI) problems. Printed circuit board (PCB) and system-level shielding may alleviate inter-system EMI between the PCB board and the outside environment, but does not prevent intra-system EMI within the shielding enclosure. Package and System in Package (SiP) level shielding is often used to minimize intra-system EMI issues. An external metal lid is traditionally employed to prevent noise emission from a device, but the cost and size of this technique makes it unattractive for modern electronics. Conformal shielding is gaining momentum due to its size and height advantages. However, high cost and complexity of the sprayed coating shield prevents it from being used for a wide range of low cost commercial applications. In this paper, an innovative shielding technology with sputtered metal conformal shield is investigated using a specially designed test vehicle. By sputtering a conductive material onto a package, a very thin (typically a few μm) metal layer is constructed on the top and around four sides of the package. This thin sputtered metal layer adds virtually zero penalty to the package size. The cost and complexity of the sputtering process is significantly lower compared to a spraying process. Several types of shielded and unshielded modules were built and extensively tested for both far-field and near-field shielding effectiveness (SE) in a semi-anechoic chamber. The performance of the sputtered conformal shield is compared to that of an unshielded module and the sprayed shield. The measured results show that the sputtered shield performs equally well to a sprayed shield, in far field test, with most measurements better than 40 dB of SE. In near field testing, sputtered shields mostly outperform the sprayed shield, especially when compared in the entire scanned region. A well-designed sputtered conformal shield can, therefore, be a very cost-effective EMI solution for a wide range of packages, such as SiP. Also in the paper, a full wave 3D HFSS model is presented and simulated results for both far and near field are compared with measured data.

scholarly journals Mid infrared digital holography and terahertz imaging

2015 ◽  
Author(s):  
Massimiliano Locatelli
Keyword(s):  
Digital Holography ◽  
Imaging Technique ◽  
Imaging Techniques ◽  
Imaging Systems ◽  
Thz Radiation ◽  
Interferometric Imaging ◽  
Thz Imaging ◽  
Spectroscopic Information ◽  
Military Security ◽  
The Military

Mid IR and Far IR (THz) regions have been attracting a continuously growing interest, especially for imaging applications. Mid IR imaging systems are widespread in the military, security and medical fields and are, consequently, in continuous development. Even greater expectation is placed on THz imaging techniques, because of the well-known capacity of THz radiation to penetrate many common materials and to provide important spectroscopic information about various strategic stuffs. In this scenario Digital Holography, a quite recent interferometric imaging technique, is proving to be mature enough to play a key role among the other imaging techniques, both in the Mid IR and in the Far IR.

Magnetic Tag Antenna for UHF Near-field and Far-Field RFID Applications

2015 ◽  
Vol 5 (2) ◽  
pp. 119
Author(s):  
Mondher Dhaouadi ◽  
M. Mabrouk ◽  
T. Vuong ◽  
A. Ghazel
Keyword(s):  
Near Field ◽  
Far Field ◽  
Rfid Applications

Far field modeling of the Mamala Bay outfalls

1998 ◽  
Vol 38 (10) ◽  
pp. 323-330
Author(s):  
Philip J. W. Roberts
Keyword(s):  
Field Model ◽  
Near Field ◽  
Far Field ◽  
Field Modeling ◽  
Visitation Frequency ◽  
Statistical Variation ◽  
Long Time ◽  
Harmonic Average ◽  
Ocean Outfall ◽  
Acoustic Doppler Current Profilers

The results of far field modeling of the wastefield formed by the Sand Island, Honolulu, ocean outfall are presented. A far field model, FRFIELD, was coupled to a near field model, NRFIELD. The input data for the models were long time series of oceanographic observations over the whole water column including currents measured by Acoustic Doppler Current Profilers and density stratification measured by thermistor strings. Thousands of simulations were made to predict the statistical variation of wastefield properties around the diffuser. It was shown that the visitation frequency of the wastefield decreases rapidly with distance from the diffuser. The spatial variation of minimum and harmonic average dilutions was also predicted. Average dilution increases rapidly with distance. It is concluded that any impact of the discharge will be confined to a relatively small area around the diffuser and beach impacts are not likely to be significant.

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