Abstract: According to various embodiments, an array of elements forms an artificially-structured material. The artificially-structured material can also include an array of tuning mechanisms included as part of the array of elements that are configured to change material properties of the artificially-structured material on a per-element basis. The tuning mechanisms can change the material properties of the artificially-structured material by changing operational properties of the elements in the array of elements on a per-element basis based on one or a combination of stimuli detected by sensors included in the array of tuning mechanisms, programmable circuit modules included as part of the array of tuning mechanisms, data stored at individual data stores included as part of the array of tuning mechanisms, and communications transmitted through interconnects included as part of the array of elements.

Abstract: A hydrophone with crossed pairs of geophones is provided with a strong light weight housing allowing use at several thousand feet deep in the ocean while still maintaining good sensitivity. The cruciform housing has a cylindrical portion conforming to each of the four geophones so that each cylindrical wall has small diameter and requires small thickness. The cylindrical portions are joined to a central body to complete the housing.