Patent Publication Number: US-2016228058-A1

Title: Signal stabilization in a non-resistive contact sensor assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is U.S. continuation patent application of, and claims priority under 35 U.S.C. §120 to, U.S. nonprovisional patent application Ser. No. 13/846,306, filed Mar. 18, 2013, incorporated by reference herein, now U.S. Pat. No. 9,234,924, which &#39;306 application is a U.S. continuation patent application of, and claims priority under 35 U.S.C. §120 to, U.S. nonprovisional patent application Ser. No. 13/834,918, filed Mar. 15, 2013, incorporated by reference herein, now U.S. Pat. No. 9,239,347, which &#39;918 application is a U.S. nonprovisional patent application of, and claims priority under 35 U.S.C. §119(e) to, U.S. provisional patent application 61/695,986, filed Aug. 31, 2012, incorporated by reference herein. Additionally, the entirety of each of the following commonly-assigned U.S. patent applications, and any application publication thereof, is expressly incorporated herein by reference:
         (a) U.S. provisional patent application 61/671,647, filed Jul. 13, 2012 and entitled “REDUCING MOVEMENT AND ELECTROSTATIC INTERFERENCE IN A NON-RESISTIVE CONTACT SENSOR ASSEMBLY”;   (b) U.S. provisional patent application 61/759,827, filed Feb. 1, 2013 and entitled “SIGNAL STABILIZATION IN A DIELECTRIC SENSOR ASSEMBLY”;   (c) U.S. nonprovisional patent application Ser. No. 13/834,664, filed Mar. 15, 2013, and entitled, “REDUCING MOVEMENT AND ELECTROSTATIC INTERFERENCE IN A NON-RESISTIVE CONTACT SENSOR ASSEMBLY”; and   (d) U.S. nonprovisional patent application Ser. No. 13/835,762, filed Mar. 15, 2013, and entitled, “SIGNAL STABILIZATION IN A DIELECTRIC SENSOR ASSEMBLY”.       

    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under contract number W911NF-12-C-0004 awarded by DARPA. The government has certain rights in the invention. 
    
    
     COPYRIGHT STATEMENT 
     All of the material in this patent document is subject to copyright protection under the copyright laws of the United States and other countries. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in official governmental records but, otherwise, all other copyright rights whatsoever are reserved. 
     BACKGROUND OF THE PRESENT INVENTION 
     1. Field of the Present Invention 
     The present invention relates generally to electric field sensors, and, in particular, to signal stabilization in a non-contact resistive contact sensor assembly. 
     2. Background 
     Conventional electrodes act as a current transducers converting ionic currents into electronic ones so electrophysiological status can be assessed. The uses for this approach are many and broadly range from assessment of neural (EEG), cardiac (ECG), and skeletal (EMG) muscle activity. 
     This approach requires conductive contact with the source and has inherent problems. The first of these is the requirement of clean skin exposure. This requirement may compromise continuous usability due to the effects of environmental contaminants, both on the skin and in the atmosphere; extremes of temperature and their resulting general effect on skin due to physiological reactions such as “goose bumps” and excessive sweating as well as other phenomena; and potential reactions to conductive materials. The process of preparing skin and securing a good conductive contact can also decrease compliance, especially in if intended for continuous day to day use. Furthermore, during exercise, the physicality can result in electrodes being displaced. Other issues include shorting between electrodes, especially when placed in close proximity to each other, and charge transfer which has potential safety implications as well as the issue of the measurement process corrupting the signal. 
     The problems, outlined above, may be at least partially solved by the use of capacitive electrodes (non-resistive contact sensors) as they acquire signals through capacitive coupling, not requiring resistive contact with the source. They provide many benefits, including the fact that no electrical contact is required, and so no skin preparation or conducting pads are necessary and they can be readily moved or relocated to get an optimal signal. In addition, they can be miniaturized, they have very low power requirements, and they can be embodied as passive electric field sensors with the result that adjacent sensors do not interfere with each other. 
     The use of capacitive electrodes for electrophysiological monitoring is not a recent innovation, with Richardson describing it for acquisition of the cardiac signal in 1967 1 . This system was, however, flawed being prone to problems including poor signal to noise ratio, voltage drift, electrostatic discharge and parasitic capacitance. These are still problems with capacitive sensor technologies today. Many of those problems have been addressed, at least partially, but problems with signal stability interference still plague this technology. Signal stability interference is especially problematic during movement. Movement may lead to a variety of issues that may compromise continuous signal acquisition including contact electrification between the body surface and the sensor electrode; charge build-up on the body resulting in baseline shift and potential saturation if occurs too rapidly; and movement of the sensor relative to the body that can also lead to baseline shift and saturation (railing).  The insulated electrode: a pasteless electrocardiographic technique . Richardson P C. Proc. Annu. Conf. on Engineering in Medicine and Biology 7: 9-15(1967) 
     When dry contact electrodes are placed in direct contact with a person, and particularly when they are moved, triboelectric effects (electrical charges created by sliding friction and pressure) are frequently generated. Triboelectric effects of this nature may cause contact electrification where static charges may be delivered to the pick-up electrode. This static charge can produce a near-direct current (DC) or very low frequency drift in the sensor that may interfere with the physiological alternating current (AC) signal that is being measured or may saturate the sensor causing railing, after which the sensor takes time to return to being able to produce a useful physiologically-relevant output. If the electrode moves relative to the body, it will also pick up a geoelectric displacement signal. That is, the effect of the body, an electrically active structure, moving through the geoelectric field, which is on the order of 100Vm −1 , will cause relative polarization of the sensor that will displace the baseline and may cause the sensor to saturate. An additional source of interference is that of clothing moving on the body. As clothing moves on the body, charge separation can occur when materials that are separated on the triboelectric series donate or receive electrons from each other. After a material becomes charged it may discharge onto the surface where an electric potential is being measured, thereby interfering with signal acquisition. 
     Various issues can arise as a result of these various forms of interference. For example, issues may arise in the signal acquisition phase due to corruption of the signal from local electrical activity, in the signal referencing phase due to poor referencing of the signal to an appropriate earth, and during the transfer of the signal to processing units where the signal may be susceptible to interference. Thus, a need exists for devices, methods, and/or systems for reducing interference and stabilizing the signals being acquired and processed. 
     SUMMARY OF THE PRESENT INVENTION 
     Broadly defined, the present invention according to one aspect is a non-resistive contact sensor assembly, including: an electric field sensor device, including a dry electrode component for receiving an electrical signal from an object of interest and a signal processing component for processing the electrical signal; and a casing in which the signal processing component is surrounded or embedded. 
     In a feature of this aspect, the signal processing component includes an A/D converter for converting the electrical signal from the object of interest to a digitized signal. 
     In another feature of this aspect, the signal processing component is electrically shielded from the dry electrode component by an internal partition. In further features, the internal partition is provided in the form of a circuit board; the signal processing component is an A/D converter, and wherein the assembly further comprises at least one additional signal processing component, electrically shielded from the dry electrode component by the internal partition, for processing the output of the A/D converter; the assembly further includes an amplifier component that is distinct from the dry electrode component, and wherein the signal processing component is electrically shielded from the amplifier component by the internal partition; the internal partition is a structural extension of the casing; the signal processing component is a transmitter for transmitting a resulting digitized signal to another location (wirelessly and/or or over a data cable physically connected to the assembly); and/or the assembly further includes a circuit board on which the signal processing component is mounted, and wherein the circuit board is electrically shielded from the dry electrode component by the internal partition. 
     In another feature of this aspect, the casing is part of a housing for the assembly, and wherein the dry electrode component is exposed to the exterior of the housing. In a further feature, the casing is electrically isolated from the dry electrode component. 
     In another feature of this aspect, the dry electrode component is adapted to avoid resistive contact with a surface of the object of interest. In a further feature, the dry electrode component is adapted to avoid resistive contact with human skin. 
     In another feature of this aspect, the casing is adapted to made direct resistive contact with a surface of the object of interest. In a further feature, the dry electrode component is adapted to avoid resistive contact with human skin. 
     In another feature of this aspect, the assembly is in the form of a sensor head. 
     In another feature of this aspect, the casing is electrically grounded. In further features, the casing is electrically grounded via a ground connection to a power cable physically connected to the assembly; and/or the casing serves as a reference with regard to the electrical signal from the object of interest. 
     In another feature of this aspect, the casing is a conductive casing that acts as an electrical reference with regard to the electrical signal from the object of interest. 
     Broadly defined, the present invention according to another aspect is a non-resistive contact sensor assembly, including: an electric field sensor device, including a dry electrode component for receiving an electrical signal from an object of interest by capacitively coupling with the entity; a housing in which the signal processing component is surrounded or embedded; and an anode and a cathode, distinct from the dry electrode component, that together provide a stable surface field, thereby allowing more focused acquisition of the electrical signal from the object of interest. 
     In a feature of this aspect, the distinct anode and cathode are disposed in the housing with the dry electrode component. 
     In another feature of this aspect, the distinct anode is exterior to the housing. 
     In another feature of this aspect, the distinct cathode is exterior to the housing. 
     In another feature of this aspect, the stable surface field is subtracted computationally during post-acquisition processing of the electrical signal from the object of interest. 
     In another feature of this aspect, the assembly is in the form of a sensor head. 
     Broadly defined, the present invention according to another aspect is a non-resistive contact sensor assembly, including: an electric field sensor device, including a dry electrode component for receiving an electrical signal from an object of interest by capacitively coupling with the entity; a cover in which the signal processing component is surrounded or embedded; and a biasing structure, disposed on the outside of the cover, that are adapted to press the dry electrode component against a surface of the object interest when biased by an external structure. 
     In a feature of this aspect, the biasing structure is a spring. In a further feature, the spring is a mechanical spring with a polymeric, metallic, and/or fiber material construction. 
     In another feature of this aspect, the biasing structure is comprised of compressive material. In a further feature, the compressive material is selected from a group comprising rubber, felt, elastomeric, polymeric, closed cell foam and analogues. 
     In another feature of this aspect, the assembly is arranged in a helmet that comprises the external structure. 
     In another feature of this aspect, the assembly is arranged beneath a belt that comprises the external structure. 
     In another feature of this aspect, the assembly is arranged beneath jewelry that comprises the external structure 
     In another feature of this aspect, the assembly is arranged beneath an article of clothing that comprises the external structure. 
     In another feature of this aspect, the assembly is arranged in a piece of furniture that comprises the external structure. 
     In another feature of this aspect, the assembly is arranged in a vehicle seat that comprises the external structure. In features of this aspect, the vehicle seat is an automobile seat, an airplane seat, a rail locomotive seat, or a wheelchair seat. 
     In another feature of this aspect, the assembly is in the form of a sensor head. 
     Broadly defined, the present invention according to another aspect is a non-resistive contact sensor assembly as shown and described. 
     Broadly defined, the present invention according to another aspect is a sensor head for a non-resistive contact sensor assembly as shown and described. 
     Broadly defined, the present invention according to another aspect is a method of reducing movement in a non-resistive contact sensor assembly, as shown and described. 
     Broadly defined, the present invention according to another aspect is a method of signal stabilization in a non-resistive contact sensor assembly, as shown and described. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, embodiments, and advantages of the present invention will become apparent from the following detailed description with reference to the drawings, wherein: 
         FIG. 1  is a schematic diagram of a non-resistive contact sensor assembly in accordance with a first preferred embodiment of the present invention; 
         FIG. 2  is a schematic diagram of a non-resistive contact sensor assembly in accordance with another preferred embodiment of the present invention; 
         FIG. 3  is a schematic diagram of a hybrid sensor assembly in accordance with another preferred embodiment of the present invention; 
         FIG. 4A  is a schematic diagram of a non-resistive contact sensor assembly in accordance with another preferred embodiment of the present invention; 
         FIG. 4B  is a schematic diagram of a non-resistive contact sensor assembly in accordance with another preferred embodiment of the present invention; 
         FIG. 5A  is a fragmentary, partially schematic top view of a portion of a wearable sensor belt in accordance with one or more preferred embodiments of the present invention; 
         FIG. 5B  is a fragmentary, partially schematic top view of a portion of another wearable sensor belt in accordance with one or more preferred embodiments of the present invention; 
         FIG. 6  is a fragmentary, partially schematic front view of the wearable sensor belt of  FIG. 5A ; 
         FIG. 7  is a fragmentary, partially schematic front view of the wearable sensor belt of  FIG. 6 , shown with the sensor casing removed; 
         FIG. 8  is a fragmentary, partially schematic top view of the portion of the wearable sensor belt of  FIG. 5A , shown in use against the chest of a human; 
         FIG. 9  is a front perspective view of a an exemplary wearable sensor belt attached around the chest of a human wearer in accordance with one or preferred embodiments of the present invention; 
         FIG. 10  is a fragmentary front perspective view of the wearable sensor belt of  FIG. 9 ; 
         FIG. 11  is an exploded fragmentary front perspective view of the wearable sensor belt of  FIG. 10 ; and 
         FIG. 12  is an exploded fragmentary rear perspective view of the wearable sensor belt of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     As a preliminary matter, it will readily be understood by one having ordinary skill in the relevant art (“Ordinary Artisan”) that the present invention has broad utility and application. Furthermore, any embodiment discussed and identified as being “preferred” is considered to be part of a best mode contemplated for carrying out the present invention. Other embodiments also may be discussed for additional illustrative purposes in providing a full and enabling disclosure of the present invention. As should be understood, any embodiment may incorporate only one or a plurality of the above-disclosed aspects of the invention and may further incorporate only one or a plurality of the above-disclosed features. Moreover, many embodiments, such as adaptations, variations, modifications, and equivalent arrangements, will be implicitly disclosed by the embodiments described herein and fall within the scope of the present invention. 
     Accordingly, while the present invention is described herein in detail in relation to one or more embodiments, it is to be understood that this disclosure is illustrative and exemplary of the present invention, and is made merely for the purposes of providing a full and enabling disclosure of the present invention. The detailed disclosure herein of one or more embodiments is not intended, nor is to be construed, to limit the scope of patent protection afforded the present invention, which scope is to be defined by the claims and the equivalents thereof. It is not intended that the scope of patent protection afforded the present invention be defined by reading into any claim a limitation found herein that does not explicitly appear in the claim itself. 
     Thus, for example, any sequence(s) and/or temporal order of steps of various processes or methods that are described herein are illustrative and not restrictive. Accordingly, it should be understood that, although steps of various processes or methods may be shown and described as being in a sequence or temporal order, the steps of any such processes or methods are not limited to being carried out in any particular sequence or order, absent an indication otherwise. Indeed, the steps in such processes or methods generally may be carried out in various different sequences and orders while still falling within the scope of the present invention. Accordingly, it is intended that the scope of patent protection afforded the present invention is to be defined by the appended claims rather than the description set forth herein. 
     Additionally, it is important to note that each term used herein refers to that which the Ordinary Artisan would understand such term to mean based on the contextual use of such term herein. To the extent that the meaning of a term used herein—as understood by the Ordinary Artisan based on the contextual use of such term—differs in any way from any particular dictionary definition of such term, it is intended that the meaning of the term as understood by the Ordinary Artisan should prevail. 
     Regarding applicability of 35 U.S.C. §112, ¶6, no claim element is intended to be read in accordance with this statutory provision unless the explicit phrase “means for” or “step for” is actually used in such claim element, whereupon this statutory provision is intended to apply in the interpretation of such claim element. 
     Furthermore, it is important to note that, as used herein, “a” and “an” each generally denotes “at least one,” but does not exclude a plurality unless the contextual use dictates otherwise. Thus, reference to “a picnic basket having an apple” describes “a picnic basket having at least one apple” as well as “a picnic basket having apples.” In contrast, reference to “a picnic basket having a single apple” describes “a picnic basket having only one apple.” 
     When used herein to join a list of items, “or” denotes “at least one of the items,” but does not exclude a plurality of items of the list. Thus, reference to “a picnic basket having cheese or crackers” describes “a picnic basket having cheese without crackers,” “a picnic basket having crackers without cheese,” and “a picnic basket having both cheese and crackers.” Finally, when used herein to join a list of items, “and” denotes “all of the items of the list.” Thus, reference to “a picnic basket having cheese and crackers” describes “a picnic basket having cheese, wherein the picnic basket further has crackers,” as well as describes “a picnic basket having crackers, wherein the picnic basket further has cheese.” 
     In various aspects, the present invention relates to methods of attenuating or eliminating unwanted movement or electrostatic interference on signals acquired via non-resistive contact sensors from various entities, both biological and other. Such sensors may be used by themselves, or may be used in combination with other sensors. The sensor data is utilized for detecting properties of the entities. 
     For biological entities, the invention utilizes an electric field sensor or sensors for the measurement of the structural and functional characteristics of organs and other structures where the electric field sensor does not have resistive contact with the organism, conferring multiple advantages. In various aspects, the present invention relates to sensors, sensor housings, fastenings and sensor systems including devices and installations for assemblies for detecting structural and functional signatures associated with electric potentials that may detect a displacement signature within the geomagnetic field, and/or specific components and/or structures that are a component of that entity or entities. There is preferably no resistive contact between the entity and the signal transduction component of the electric field sensor or sensors. Other sensor types may be added in to provide further information, such as for the identification and elimination or attenuation of unwanted electrostatic or movement signal associated with the recording of non-resistive contact electric fields from that entity, in whatever state, such as during active or passive movement. 
     In particular, the present invention, in various aspects, relates to novel methods and apparatuses for stabilizing the target signal when using an electric field sensor or sensors of the type that does not have resistive contact with the entity, generally an organism, which is being monitored. In various aspects, the invention relates to combinations and permutations of: applying an electric field to electrically stabilize the sensor zone; the use of a conductive casing to act as a reference for the signal that is being acquired; the use of an analog to digital converter in the sensor head to digitally fix the signal; the use of a barrier (guard or shield) between the analog to digital converter to mitigate signal corruption the converter; a logic board to process the signal in the sensor head; a compressive material, spring, or another component in tension against another fixed structure, such as a helmet, to hold the referencing component and/or the electrode firmly on the surface of the entity being measured; a cable or wireless transmitter to transmit the digitized signal; and/or a resistive contact electrode that may be incorporated into the reference casing or used as a separate component to add signal acquisition resilience. 
     Referring now to the drawings, in which like numerals represent like components throughout the several views, one or more preferred embodiments of the present invention are next described. The following description of one or more preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
       FIG. 1  is a schematic diagram of a non-resistive contact sensor assembly  10 , or at least a sensor head thereof, in accordance with a first preferred embodiment of the present invention. The sensor assembly  10  includes a electric field sensor device  12 , an analog-to-digital (A/D) converter  18 , an internal partition  22 , a power and data cable  24 , and a housing  14 . The sensor device  12  is at least partially surrounded by, or embedded in, the housing  14 , at least portions of which may be made of anti-triboelectric material. In various respects, the sensor assembly  10  and sensor device  12  may have one or more characteristics described in the &#39;664 application. 
     The sensor device  12  includes a dry electrode component  16  that is exposed to the exterior of the housing  14  and is arranged to avoid resistive contact with the skin or other surface  20  on which the sensor assembly  10  is placed. However, the sensor electrode  16  is capacitively coupled to the skin or other surface  20  of the entity being analyzed and may be in physical contact with the surface  20  so long as resistive contact is avoided. In at least some embodiments, physical contact is avoided so as to avoid resistive contact. 
     The housing  14  includes a conductive casing (shielding)  15  that makes direct resistive contact with the skin or other surface  20  on which the sensor assembly  10  is placed but is electrically isolated from the electrode  16 . The casing  15 , which as noted makes resistive contact with the surface  20 , is grounded by a ground connection  26  to the power and data cable  24  to the unit  10 . The casing  15  may thus serve as a reference with regard to a target signal  30  from the object of interest. 
     After the signal from the electrode  16  is amplified, it is converted to a digital signal by the A/D converter  18 . Notably, the A/D conversion is carried out within the confines of the sensor casing  15 , and in at least some embodiments, the amplification is likewise carried out within the confines of the sensor casing  15 . The A/D converter  18  is also shielded from the electrode  16  itself by the internal partition  22 , which is designed to provide an electrical field barrier against the electrode  16  and the amplification thereof. In this regard, it will be appreciated that in at least some embodiments, amplification likewise takes place on the opposite side of the partition  22  from the A/D converter  18 . Advantageously, the shielding offered by the partition  22  helps to prevent the A/D converter  18  from being affected by interference caused by various electrical effects. The partition  22  may take any of a variety of forms, including as a structural extension of the casing  15 . 
     Other processing components may also be shielded from the electrode  16  and amplification by the partition  22 . In at least some embodiments, the partition  22  is provided in the form of a circuit board, and the other processing components may be disposed on the circuit board  22 . In other embodiments, a circuit board is provided, but is separate from the partition  22  and is shielded by the partition  22  from the electrode  16  and amplification. Furthermore, in addition to, or included within, the other processing components, a transmitter (not shown) may be provided, within the casing  15  and shielded by the circuit board or other partition  22 , for transmitting a resulting digitized signal to another location. Such transmission may occur wirelessly or over the power and data cable  24 , and is similar protected from interference by the casing  15  and the circuit board or other partition  22 . 
       FIG. 2  is a schematic diagram of a non-resistive contact sensor assembly  110 , or at least a sensor head thereof, in accordance with another preferred embodiment of the present invention. The sensor assembly  110  includes an electric field sensor device  112  at least partially surrounded by, or embedded in, a cover  114 , which may be of anti-triboelectric material. In various respects, the sensor assembly  110  and sensor device  112  may have one or more characteristics described in the &#39;664 application. Furthermore, the sensor device may incorporate characteristics of the sensor device  12  of  FIG. 1 , described previously. The sensor device  112  of  FIG. 2  includes a non-resistive contact electrode component  116 , an anode  128 , and a cathode  132 . In at least some embodiments, the non-resistive contact electrode component  116  is interior to the cover  114 , but this is not required. Furthermore, although in the illustrated embodiment the anode  128  and cathode  132  are exterior to the cover  114 , it will be appreciated that in some embodiments, it may be possible to locate the anode  128  and cathode  132  interior to the cover  114 . 
     An electric field  140  is produced by the anode  128  and cathode  132  to stabilize the electric potential, and particularly the surface electric potential, around the sensor assembly  110 . This, in turn, allows more focused acquisition of the target field (signal)  130  being produced by the entity. 
     In  FIG. 2 , the sensor assembly  110  is shown making contact with the surface  20  of the entity being measured or analyzed. The electrode  116  capacitively couples to the entity to measure the target signal  130 . The anode  128  produces an electron flow  140  toward the cathode  132 , thereby providing a stable surface field. This field can be subtracted computationally as needed during post-signal acquisition processing. 
       FIG. 3  is a schematic diagram of a hybrid sensor assembly  210 , or at least a sensor head thereof, in accordance with another preferred embodiment of the present invention. In this sensor assembly  210 , two regions  242 , 244  surround a non-resistive contact electric field sensor device  212 , including a dry electrode component (not separately shown). The inner region  244  could include a triboelectrically neutral or relatively neutral material, such as but not limited to cotton. One purpose in using such material is to avoid the buildup of electrostatic or other charges, because the material will be at least relatively resistant to, if not able to avoid altogether, accepting or donating electrons. The outer region  242  includes a conductive material and may include fastening/elastic/compressive materials. In various respects, the sensor assembly  210  and its components may have one or more characteristics described in the &#39;664 application. 
     The sensor assembly  210  is used in conjunction with a conventional resistive contact electrometer to provide two interrogation routes of the electrical activity of the entity being measured, thereby enhancing the robustness of the overall system. At the periphery of the sensor assembly  210 , the outer region of conductive material  242  makes resistive contact with the surface of entity whose signal is being measured or analyzed, thereby serving as the conductive portion of an electrode component of an electrometer used in a traditional ECG or other electrophysiological detection system. Meanwhile, the non-resistive contact electric field sensor device  212  operates as described herein and/or as described in the &#39;664 application. Thus, two routes are provided for signal acquisition for an ECG system, thereby providing robustness to the overall system. In various versions of such an embodiment, the electrode component may be active or passive. Furthermore, it will be appreciated that such a sensor assembly  210  may be used with other devices as well, such as galvanometers and the like. 
       FIG. 4A  is a schematic diagram of a non-resistive contact sensor assembly  310 , or at least a sensor head thereof, in accordance with another preferred embodiment of the present invention. The sensor assembly  310  includes an electric field sensor device  312  at least partially surrounded by, or embedded in, a cover  314 , which may be of anti-triboelectric material. In various respects, the sensor assembly  310  and sensor device  312  may have one or more characteristics described in the &#39;664 application. Furthermore, the sensor device may incorporate characteristics of the other sensor devices described herein. The sensor device  312  of  FIG. 4A  includes a dry electrode component  316  that is interior to the cover  314 . The sensor assembly  310  may also include one or more springs  346  disposed in locations that, when biased by an external structure  50 , tend to push the sensor assembly  310  against the surface  20  of an object to which the sensor assembly  310  is being applied. This force tends to hold the sensor assembly  310  in place on the object surface  20 , reducing triboelectric effects and the like that would otherwise be caused by relative movement of the sensor assembly  310 . This, in turn, makes accurate acquisition and processing of the target signal  30 . Various types may be suitable for use as the springs  346  of the present invention. 
       FIG. 4B  is a schematic diagram of a non-resistive contact sensor assembly  410 , or at least a sensor head thereof, in accordance with another preferred embodiment of the present invention. The sensor assembly  410  is similar in many respects to the sensor assembly  310  of  FIG. 4A  and includes an electric field sensor device  312  at least partially surrounded by, or embedded in, a cover  314 , which may be of anti-triboelectric material. In various respects, the sensor assembly  310  and sensor device  312  may have one or more characteristics described in the &#39;664 application. Furthermore, the sensor device may incorporate characteristics of the other sensor devices described herein. The sensor device  312  of  FIG. 4B  includes a dry electrode component  316  that is interior to the cover  314 . The sensor assembly  410  also includes compressive material  348  disposed in a location or locations that, when biased by an external structure  50 , tend to push the sensor assembly  410  against the surface  20  of an object to which the sensor assembly  410  is being applied. This force tends to hold the sensor assembly  410  in place on the object surface  20 , reducing triboelectric effects and the like that would otherwise be caused by relative movement of the sensor assembly  410 . This, in turn, makes accurate acquisition and processing of the target signal  30 . Materials suitable for use with the present invention as a compressive material  348  may include rubber, felt, elastomeric, polymeric, closed cell foam and analogues, mechanical springs made out of polymers, metals, fibers, or any other material now known or hereafter developed that performs the function in an equivalent manner. 
     It will be appreciated that the external structure  50  that biases the sensor assemblies  310 , 410  of  FIGS. 4A and 4B  against the object surface  20  may be a portion of a helmet, belt, article of clothing, furniture, vehicle seating, or the like. With regard to vehicle seating, it will be appreciated that such seating could include seating for automobiles (including trucks), boats and other watercraft, rail locomotives, airplanes, motorized and non-motorized wheelchairs, and other vehicles. 
     A further embodiment is to use multiple sensors in an array so that if one or more signals is compromised by interference or otherwise with the sensor/s or its/their data acquisition then other sensors within the array can be used to gain a useful signal. 
       FIG. 5A  is a fragmentary, partially schematic top view of a portion of a wearable sensor belt  500  in accordance with one or more preferred embodiments of the present invention. As shown therein, the wearable sensor belt  500  includes a sensor assembly  510  mounted on a tensioning belt  502 . The tensioning belt  502  that is sized to facilitate the belt  500  being fastened around a portion  20  of a human body (shown in  FIG. 8 ), such as a thoracic region (chest, upper back, or the like), head, arm, leg, or the like. The tensioning belt  502  preferably includes at least one elasticated section to assist in maintaining the sensor assembly snugly against the region  20  of the body being monitored. In addition to the elasticated section, the belt  502  may include one or more tensioning devices  504  disposed in the vicinity of the sensor assembly  510  in order to help provide additional biasing force to hold the sensor assembly  510  against the body  20 . However, in some embodiments, such as that shown in  FIG. 5B , the tensioning devices are omitted. Furthermore, the belt  502  may include a buckle, hook and loop fasteners (VELCRO®), or the like (not shown) in order to provide a better overall fit, provide greater biasing force against the sensor assembly  510 , position the sensor assembly  510  better, or the like. 
       FIG. 6  is a fragmentary, partially schematic front view of the wearable sensor belt  500  of  FIG. 5A . With reference to  FIGS. 5A and 6 , the sensor assembly  510  includes a plurality of electrodes  516  that are contained within, but exposed to the exterior of, a sleeve  514  that is resistant to triboelectric charging with human skin  20 . In at least some embodiments, the sleeve  514  is made from neoprene. Also contained within the sleeve are one or more processing and communications components  562 , one or more batteries  564 , and various electrical connections  566 . In at least some embodiments, the processing and communications  562  and most or all of the electrical connections  566  are provided in the form of a printed circuit board. The processing and communications components  562  preferably include wireless communication capabilities such as those provided via BLUETOOTH®, ZIGBEE®, or the like. The electrodes  516 , processing and communications components  562 , battery or batteries  564 , electrical connections  566 , and surrounding sleeve  514  together define a sensor casing  515 . 
     The sensor assembly also includes a support wall  570  on which some or all of the various other components are carried. In some embodiments, a shelf  572  extends from the support wall  570  and provides support for the sensor casing  515 . In some embodiments, a flange attachment  576  extends from the support wall  570  and mates with a corresponding groove, recess, or the like in the sensor casing  515 . In this regard,  FIG. 7  is a fragmentary, partially schematic front view of the wearable sensor belt  500  of  FIG. 6 , shown with the sensor casing  515  removed, thereby revealing the flange attachment  576 . In some embodiments, including the one illustrated herein, both are provided. The support wall  570  may, for example, be constructed from a semi-rigid material such as polycarbonate. The shelf  572  likewise may, for example, be constructed from a semi-rigid structure, which may or may not be of the same material as that used for the support wall  570 . Materials suitable for use in the support wall  570  and/or shelf  572  include plastics, such as polycarbonate; synthetic fibers, such as KEVLAR®; composites; layered composites; and the like. One possible exemplary construction may include carbon Kevlar with other materials such as cotton or polycarbonate layered in between. 
     In order to help ensure that the electrodes  516  themselves remain pressed against the skin surface  20  to which they are being applied, one or more biasing structures may be provided so as to transfer the force applied by the tensioning belt  502  to the electrodes  516 . Such biasing structures may include a spring  578 , a solid body  580  of a compressive material, or the like. Materials suitable for use in such a body  580  include neoprene closed cell foam, neoprene, and the like. As shown in  FIG. 5A , two or more such structures  578 , 580  may be utilized in combination with each other. 
     In use, the wearable sensor belt  500  is attached around the body part with the electrodes against or adjacent the skin  20 .  FIG. 8  is a fragmentary, partially schematic top view of the portion of the wearable sensor belt  500  of  FIG. 5A , shown in use against the chest of a human. As shown therein, the belt  502  has been tightened against the chest. The tensioning devices  504  assist in making sure that the electrodes  516  are held against the skin  20 , as are the springs  578  and compressible bodies  580 . The sensor assembly  510  is thus positioned reliably against the skin surface  20 , with the electrodes  516  remaining in contact even during vigorous activity by the wearer. 
       FIG. 9  is a front perspective view of a an exemplary wearable sensor belt  700  attached around the chest  720  of a human wearer in accordance with one or preferred embodiments of the present invention, and  FIG. 10  is a fragmentary front perspective view of the wearable sensor belt  700  of  FIG. 9 . As shown therein, the wearable sensor belt  700  includes a sensor assembly mounted on a tensioning belt  702 . In at least some embodiments, the tensioning belt  702  may have some or all of the characteristics described with regard to the tensioning belt of  FIG. 5A . The sensor assembly includes a pair of electrode assemblies  716 , a processing and communications component assembly  762 , and a battery assembly  764 . Each electrode assembly  716  includes at least one electrode having characteristics similar to those of electrodes described elsewhere herein, including the electrodes  516  of  FIG. 5A . Likewise, the processing and communications component assembly  762  includes processing and communications components having characteristics similar to those described elsewhere herein, including those of the processing and communications components  562  of  FIG. 5A , and the battery assembly  764  may include a battery like the battery  564  of  FIG. 5A . In at least some embodiments, the processing and communications components, battery, and electrodes are connected to one another via ribbon wiring  766 . One or more of the communications component assembly  762 , the battery assembly  764 , the electrode assemblies  716 , and/or the ribbon wiring  766  may be encased in a triboelectric charging-resistant case or sleeve, including that described with respect to the wearable sensor belt  500  of  FIG. 5A . 
       FIG. 11  is an exploded fragmentary front perspective view of the wearable sensor belt  700  of  FIG. 10 , and  FIG. 12  is an exploded fragmentary rear perspective view of the wearable sensor belt  700  of  FIG. 10 . As shown therein, each electrode assembly  716  includes a clip  708  to fasten the main body  706  of the electrode to the belt  702 . Furthermore, the housing components  763 , 765  of the processing/communications assembly  762  and battery assembly  764 , respectively, may be fastened to the belt  702  via a snap assembly, wherein a button  776  for each is disposed on the belt  702 , and a corresponding prong  777  is disposed on the back of each set of respective housing components  763 , 765 . 
     Various advantages may be achieved using one or more of the foregoing embodiments of the present invention. The robustness of the measurement of the electrical signature of an entity or sub-component of that entity may be increased. A signal being measured or analyzed may be protected closer to the source, thereby protecting it from corruption. The stability of the signal may be enhanced. The signal-to-noise ratio for an electric field sensor may be enhanced. The effect of electrostatic charge interference with an electric field sensor may be minimizes or eliminated entirely. The use of electric field sensors during exercise and daily activities may be increased, as can the usability of electric field sensors with different types of clothing and when clothing is moving due to exercise or external forces (like wind). Similarly, the usability of electric field sensors may be increased when there is external contact that would otherwise knock the sensor loose or that would result in charge transfer to the entity being measured or analyzed. Conversely, the likelihoods of contact electrification, sensor DC drift, and sensor saturation may all be decreased. 
     Based on the foregoing information, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those specifically described herein, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing descriptions thereof, without departing from the substance or scope of the present invention. 
     Accordingly, while the present invention has been described herein in detail in relation to one or more preferred embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purpose of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended to be construed to limit the present invention or otherwise exclude any such other embodiments, adaptations, variations, modifications or equivalent arrangements; the present invention being limited only by the claims appended hereto and the equivalents thereof.