Electronically reconfigurable metal-on-silicon metamaterial

Reconfigurable metamaterial-based apertures can play a unique role in both imaging and in beam-forming applications, where current technology relies mostly on the fabrication and integration of large detector or antenna arrays. Here, we report the experimental demonstration of a voltage-controlled, silicon-based electromagnetic metamaterial operating in the W-band (75-110 GHz). In this composite semiconductor metamaterial, patterned gold metamaterial elements serve both to manage electromagnetic wave propagation while simultaneously acting as electrical Schottky contacts that control the local conductivity of the semiconductor substrate. The active device layers consist of a patterned metal on a 2-{\mu}m-thick n-doped silicon layer, adhesively bonded to a transparent Pyrex wafer. The transmittance of the composite metamaterial can be modulated over a given frequency band as a function of bias voltage. We demonstrate a quantitative understanding of the composite device through the application of numerical approaches that simultaneously treat the semiconductor junction physics as well as wave propagation.Comment: 28 double-spaced pages, 8 figure

Wavelength optimization for quantitative spectral imaging of breast tumor margins.

A wavelength selection method that combines an inverse Monte Carlo model of reflectance and a genetic algorithm for global optimization was developed for the application of spectral imaging of breast tumor margins. The selection of wavelengths impacts system design in cost, size, and accuracy of tissue quantitation. The minimum number of wavelengths required for the accurate quantitation of tissue optical properties is 8, with diminishing gains for additional wavelengths. The resulting wavelength choices for the specific probe geometry used for the breast tumor margin spectral imaging application were tested in an independent pathology-confirmed ex vivo breast tissue data set and in tissue-mimicking phantoms. In breast tissue, the optical endpoints (hemoglobin, β-carotene, and scattering) that provide the contrast between normal and malignant tissue specimens are extracted with the optimized 8-wavelength set with <9% error compared to the full spectrum (450-600 nm). A multi-absorber liquid phantom study was also performed to show the improved extraction accuracy with optimization and without optimization. This technique for selecting wavelengths can be used for designing spectral imaging systems for other clinical applications

Average of extracted errors for tissue parameters with increasing number of wavelengths.

<p>Average extracted % error of [THb], [βc], and <µ_s’> for 5, 6, 7, 8, and 12 total wavelengths selected from 450–600 nm in 1 and 10 nm increments.</p

Bland-Altman plots of MC extractions using various wavelength combinations.

<p>Bland-Altman plots assessing the agreement of MC extractions of [THb], [βc], <µ_s’>, [THb]/<µ_s’>, and [βc]/<µ_s’> in adipose, fibroglandular, and malignant tissue types using the full spectrum versus the optimized reduced wavelength spectrum with 8 wavelengths (470, 480, 490, 500, 510, 560, 580, 600 nm) shown in black and the regularly spaced intervals (400, 420, 440, 470, 500, 530, 570, 600 nm) shown in red. The solid lines indicate the mean difference (bias) between the extractions; the dashed lines indicate the 95% limits of agreement.</p

Example spectral images of negative and positive margins obtained with and without optimization.

<p>Representative margin maps of [βc]/<µ_s’> for normal (A–C), ductal carcinoma in situ (E–G), and invasive ductal carcinoma (I–K) using the full 450–600 nm spectrum, the optimized 8 wavelengths, and the un-optimized evenly spaced 8 wavelengths. Corresponding correlation coefficients for the 61-wavelength spectra and the reduced 8-wavelength spectra are shown. Distribution of the extracted βc/µ_s’ are shown in (D), (H), and (L) for each case, along with the threshold values used in the predictive model to separate positive from negative margins.</p

Average µ_a (450–600 nm) of liquid phantoms containing hemoglobin, crocin, and polystyrene microspheres.

a<p>Each absorber level was tested for 2 scattering levels (avg µ_s’ = 9 cm⁻¹ and avg µ_s’ = 12 cm⁻¹) for a total of 20 phantoms.</p

Effect of increasing spectral bandpass.

<p>(a) Simulation of the effect increasing spectral bandpass on a diffuse reflectance spectrum representing 10 µM [THb], 5.5 µM [βc], and 3.11 avg <µ_s’>. (b) Average extracted errors of [THb], [βc], avg <µ_s’> with increasing spectral bandpass.</p

Dominant absorbers of breast tissue in the UV-visible spectrum.

<p>Molar extinction coefficient of oxy- and deoxy- hemoglobin and β-carotene in the 400–600 nm range.</p

Comparison of the percent difference between median adipose and malignant tissue and fibroglandular and malignant tissue to the percent change of extractions using the optimized wavelengths and evenly spaced wavelengths to the full 450–600 nm spectrum.

<p>[THb]: total hemoglobin; [βc]: β-carotene; <µ_s’>: reduced scattering coefficient; A: adipose tissue; FG: fibroglandular; M: malignant tissue; Positive percent difference indicates that the benign tissues (A and FG) had greater extracted values; negative percent difference means the malignant sites were greater. A positive extraction percent change indicates an over-estimation of the extracted parameters while a negative percent change indicates an under-estimation of the parameters.</p