An implantable microminiature stimulator and/or sensor (microdevice) is housed within a sealed housing that includes all the requisite electronic circuitry for inductively receiving power and control signals to sense of biopotential or other biomedical signals and/or to generate electrical stimulation pulse(s) between opposing electrodes. In a preferred embodiment, the housing of the microdevice is tubular, with opposing electrodes extending from each end. The electrodes are self-attaching electrodes that attach to a nerve or muscle without suturing. The electrodes are configured to helically curl around the desired nerve, thereby permitting the microdevice to stimulate the nerve or muscle, or sense signals associated with the nerve or muscle, using a minimal amount of energy. The electrodes and microdevice are sufficiently small to allow attachment to a single nerve, thereby preventing tethering of the nerve or muscle, and to allow their implantation within living tissue through small incisions or puncture holes. The muscle or nerve to which the microdevice is attached may be of any type, e.g., skeletal, smooth or cardiac.

BACKGROUND OF THE INVENTION 
The present invention relates to implantable medical devices, and more 
particularly to an implantable microminiature stimulator (or 
"microstimulator") or microminiature sensor (or "microsensor") adapted to 
securely attach to one or more muscle or nerve fibers (or muscles or 
nerves) and to electrically stimulate the muscle nerve at the point of 
attachment in a controlled manner, or to sense one or more specific 
parameters that originate at or near the point of attachment. More 
particularly, the invention relates to an implantable microstimulator 
and/or microsensor (hereafter referred to as a "microdevice" or 
"microdevices") that uses helical electrodes for sensing, stimulating, 
and/or anchoring. 
Neurological disorders are often caused by neural impulses failing to reach 
their natural destination in otherwise functional body systems. Local 
nerves and muscles may function, but, for various reasons, injury, stroke, 
or other cause, the stimulating nerve signals do not reach their natural 
destination. For example, paraplegics and quadriplegics have intact nerves 
and muscles and only lack the brain to nerve link, which stimulates the 
muscles into action. 
Prosthetic devices have been used for some time to provide electrical 
stimulation to excite muscles, nerves or other tissues. Such devices have 
ranged in size and complexity from large, bulky systems feeding electrical 
pulses by conductors passing through the skin, to small, implanted 
stimulators which are controlled through telemetry signals, such as are 
discussed in U.S. Pat. No. 4,524,774 (invented by Hildebrandt). Other 
devices have comprised a centrally-implanted stimulator package sending 
stimulation signals to a multitude of distant target sites using a network 
of implantable leads and electrodes. Unfortunately, when a lead and 
electrode are attached to a muscle or nerve from a centrally-implanted 
stimulator package, the muscle or nerve is, in effect, tethered by the 
lead, which may cause discomfort, irritation and damage to the patient as 
the muscle or nerve moves with a limb or body organ associated with the 
muscle or nerve. What is needed, therefore, is a way to stimulate a muscle 
or nerve without tethering the muscle or nerve. 
Complications, including the possibility of infection, arise in the use of 
muscle, nerve or other stimulators which have conductors extending through 
the skin or which have nerve-stimulating electrodes that puncture or 
penetrate the epineurium. Further, in the use of implanted stimulators, 
difficulties arise in providing suitable, operable stimulators which are 
small in size and have the capability to receive and store sufficient 
energy and control information to satisfactorily operate them without 
direct connection. Hence, what is needed is an implantable stimulator that 
avoids the use of through-the-skin conductors, epineurium-penetrating 
electrodes, or other tissue-penetrating electrodes, and is small enough to 
facilitate easy implantation, yet has sufficient capacity to receive and 
store energy and control information so as to provide useful muscle or 
nerve stimulation. 
Disadvantageously, the construction of a tiny microstimulator or 
microsensor (microdevice) presents problems of its own, which are not 
encountered in the construction of larger-sized biomedical appliances. An 
extremely small size involves problems and solutions of a different nature 
than are ordinarily encountered. The appropriate design of a suitable, 
small microdevice which can be easily implanted, such as by expulsion 
through the lumen of a needle, is difficult to achieve. Notwithstanding 
the small size and required shape, the microdevice structure must contain 
means for receiving and storing sufficient energy to provide the desired 
stimulating pulses or the desired sensing function, as well as electronic 
circuitry that provides control of the characteristics desired for the 
stimulating pulse or sensing signal. 
Further, the electrodes used with a microdevice must also be carefully 
selected. Such electrodes must not complicate the implantation process, 
i.e., the electrodes too must be small and flexible, yet be of sufficient 
strength and length to be securely attached to the muscle or nerve they 
are to stimulate or from (or near) which a desired parameter is to be 
sensed. 
The present invention advantageously addresses the above and other needs. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the invention, a source of electrical 
energy located outside the skin, modulated by desired control information, 
is used to selectively control and drive numerous, small stimulators, each 
attached to (or otherwise electrically coupled to) a particular nerve, 
muscle, or muscle or nerve fiber located within a specific location within 
a patient's body. Thus, for example, a desired, progressive muscular 
stimulation may be achieved through the successive or simultaneous 
stimulation of numerous stimulators, directed by a single source of 
information and energy outside the body. 
In accordance with another aspect of the invention, an implantable 
microdevice, e.g., a microstimulator or microsensor, is housed within a 
small, sealed, housing. Such housing includes all the requisite electronic 
circuitry for sensing a specified parameter or generating electrical 
stimulation pulses that can be applied to a selected nerve or muscle, as 
well as circuitry for inductively receiving power and control signals from 
an external source. In a preferred embodiment, opposing electrodes extend 
from each end of the housing. The electrodes are configured for self 
attachment to a desired muscle or nerve, thereby permitting the 
microdevice to stimulate the muscle or nerve, and/or to sense a given 
parameter at or near the muscle or nerve. In some instances, e.g., when 
sensing certain parameters, the electrodes simply anchor the microdevice 
to a desired sensing location. Any type of electrode attachment scheme 
known in the art may be used to attach the electrode to the muscle or 
nerve, such as using helical, deep brain, chip, or cuff electrodes. The 
use of helical electrodes is preferred, because such electrode can be 
easily wrapped around the muscle or nerve, and the helical shape of the 
electrode, like a spring, firmly holds the electrode in contact with the 
muscle or nerve. Advantageously, the electrodes and microdevice(s) are 
sufficiently small to allow attachment to a single muscle or nerve, 
thereby preventing tethering of the muscle or nerve. 
In accordance with a further aspect of the invention, a single microdevice 
includes circuitry for performing both the stimulating and sensing 
function. 
In accordance with yet another aspect of the invention, the microdevice 
includes telemetry circuitry so as to provide telemetry functions as well 
as stimulating and/or sensing functions. Such telemetry function allows 
limited information, e.g., a signal sensed by the sensing function, to be 
telemetered to an external location. Such telemetered information may be 
used as diagnostic information, e.g., to signal whether a lead or 
electrode has broken, or as control information, e.g., to signal whether 
the amplitude of a stimulating pulse needs to be adjusted. In the case of 
telemetering control information, a feedback system can thus be 
established that includes the implanted microdevice and an external 
controller in order to control the operation of the implanted microdevice 
in a desired manner. 
In accordance with an additional aspect of the invention, the microdevice 
is of a size and weight that allows its implantation through a very small 
incision in the patient's skin. In some embodiments, such incision may be 
as small as the puncture hole of a hypodermic needle, with the microdevice 
being implanted through the lumen of such needle. In other embodiments, 
the incision may be made in conventional manner, but is still of very 
small dimensions, e.g., having linear dimensions of no more than about 5 
to 10 mm. 
Thus, one embodiment of the invention may be characterized as an 
implantable microstimulator that includes: (1) a microstimulator module 
having electronic circuitry housed therein that inductively receives power 
signals from an external source and generates electrical stimulation 
pulses as a function of control signals, which control signals are also 
received from the external source; and (2) first and second opposing 
electrodes electrically connected to the electronic circuitry and 
extending from the microstimulator module, with the electrical stimulation 
pulses being electrically applied to the first and second electrodes. The 
first and second electrodes have distal ends configured for self 
attachment to a muscle or nerve, e.g., by curling about the muscle or 
nerve. Advantageously, the microstimulator module, including the first and 
second electrodes, are of a size, shape and weight so as to permit their 
implantation within living tissue through a very small incision, e.g., a 
puncture hole made by a needle, with the microstimulator being implanted 
through the lumen of such needle. Further, as required, the first and 
second electrodes may be attached to the same muscle or nerve, with the 
microstimulator module being supported therebetween, thereby providing a 
complete implantable microstimulator module that moves or "floats" with 
the muscle or nerve. Hence, tugging of the nerve from an electrode 
tethered to a larger, non-floating stimulator is avoided. 
Additionally, another embodiment of the invention may be characterized as 
an implantable microdevice of a size capable of insertion through an 
incision having linear dimensions of no more than about five (5) to ten 
(10) mm. Such microdevice includes: (1) a hermetically-sealed housing 
which is inert to body fluids and tissue; (2) helically shaped, inert, 
metallic electrodes hermetically sealed to the housing; (3) electronic 
control circuitry encapsulated within the hermetically-sealed housing; (4) 
a coil for receiving an alternating magnetic field to provide operating 
power and control for the microstimulator; and (5) at least one capacitor 
encapsulated within the hermetically-sealed housing for storing energy 
received through the coil. The electronic control circuitry is configured 
so that the microdevice functions as either a microstimulator, a 
microsensor, or as both a microstimulator and microsensor. Telemetry 
capability may also be selectively included within the electronic 
circuitry encapsulated within the hermetically-sealed housing. 
Yet a further embodiment of the invention may be viewed as an implantable 
microdevice, e.g., a microstimulator, adapted for implantation within a 
patient's body. Such microdevice includes: (1) a hermetically-sealed 
housing that is inert to body fluids and tissue, the housing being of a 
size no greater than approximately 2 mm in diameter and 10 mm in length 
and being of a shape capable of implantation through a lumen of a needle; 
(2) a first electrode comprising an electrically-conductive stem extending 
into the housing and hermetically sealed to the housing at or near one end 
thereof, the first electrode further including a first distal end adapted 
for self-attachment to a muscle or nerve fiber or a bundle of muscle or 
nerve fibers; (3) a second electrode comprising an electrically-conductive 
stem extending into the housing and hermetically sealed to the housing at 
or near the other end thereof, the second electrode including a second 
distal end adapted for self-attachment to a nerve or muscle fiber or a 
bundle of nerve or muscle fibers; (4) a ferrite core encapsulated within 
the housing would with a prescribed number of turns of a fine, 
electrically-conductive wire, forming a coil; (5) electronic circuitry 
encapsulated within the housing and disposed at or near one end of the 
ferrite core; and (6) means for electrically connecting the electronic 
circuitry electrically to the coil and the first and second electrodes. In 
operation, information and power are received by the coil, inside the 
body, from an alternating magnetic field modulated in accordance with 
information, where the alternating magnetic field is generated from a 
source and location outside the body. Depending on the type of electronic 
circuitry used within the housing, the microdevice senses information 
through the electrodes, stimulates nerves or muscles through the 
electrodes, or both senses and stimulates through the electrodes. 
Telemetry functions may also be included within the electronic circuitry. 
Still an additional characterization of the invention is that of a method 
of stimulating muscles or nerves within living tissue, or sensing signals 
derived from or near selected muscles or nerves within living tissue. Such 
method includes the steps of: (a) fabricating a microdevice, the 
microdevice having electrical circuitry within a miniaturized housing, the 
electrical circuitry being adapted to receive power and control signals 
from a source external to the microstimulator and to: (i) generate 
electrical stimulation pulses controlled by the control signals, with the 
electrical stimulation pulses, when generated, being applied between first 
and second terminal connection points located within the housing, when the 
microdevice is used as a microstimulator, or (ii) sense a prescribed 
signal present at said first and second terminal connection points, when 
the microdevice is used as a microsensor, and telemeter the sensed signals 
to the external source; (b) connecting first and second electrodes to the 
first and second terminal connection points, respectively, each of the 
first and second electrodes having attachment means at or near a distal 
end thereof for self-attachment to a muscle or nerve; (c) hermetically 
sealing the housing so that the first and second electrodes extend 
therefrom, whereby everything within the housing is protected from body 
fluids and tissue; (d) implanting the housing with the electrodes 
extending therefrom within the living tissue; (e) attaching the distal 
ends of the electrodes to at least one muscle or nerve; and (f) 
controlling the microdevice with the control signals so as to provide a 
specified microstimulator or microsensor function. 
It is thus a feature of the invention to provide an implantable microdevice 
that can attach to a muscle or nerve without tugging on or tethering the 
nerve. 
It is another feature of the invention to provide such a microdevice that 
is implantable through a very small incision in the patient's skin, 
thereby minimizing the amount of surgery required to implant it. 
It is a further feature of the invention to provide an implantable 
stimulator and/or sensor system, utilizing a plurality of microdevices, 
wherein each of the microdevices is independent of the other microdevices. 
Thus, should there be an infection, it will most likely not spread to 
other microdevices because there is no physical connection between them. 
Hence, in the event of an infection, a massive explant surgery should not 
be required. 
It is yet another feature of the invention to provide a microdevice having 
helical electrode(s) that may be implanted by a surgeon having a fiber 
optic probe with saline flowing therethrough. The fiber optic probe allows 
the surgeon to view the nerve or muscle by looking through the fiber optic 
probe, when properly positioned, and to use a hollow needle, e.g., 10 
gauge, with a stylet attached to the microdevice to screw or otherwise 
position the helical electrode(s) around the muscle or nerve, and 
therefore complete the implant procedure by leaving only a few puncture 
wounds in the patient. 
It is still an additional feature of the invention to provide a microdevice 
having opposing helical electrodes extending from each end thereof, with 
each helical electrode having a proper spiral direction associated 
therewith so as to allow both electrodes to be readily implanted by a 
surgeon during the same implant procedure while causing minimal puncture 
wounds to the patient. 
It is another feature of the invention to provide an implantable 
microdevice that has electrodes that are self-attaching, and that 
therefore do not require any sutures. Such self-attaching electrodes may 
be used to anchor the microdevice so that it can perform its desired 
stimulating and/or sensing function. In some applications, e.g., sensing 
magnetic fields, sensing body position, sensing body acceleration, sensing 
saturated oxygen, which functions can be performed without the need for 
external electrodes, and hence where it is not necessary for electrically 
active electrodes to touch live tissue, the helical "electrodes" (helical 
wires) are simply used as anchors to hold the microdevice in a desired 
implant location. 
It is an additional feature of the invention to provide such a microdevice 
that can be used to stimulate or sense the same muscle or nerve bundle in 
two different locations, thereby sensing or stimulating more than one 
population of muscle or nerve fibers within the bundle, while maintaining 
no mechanical or electrical interaction between the two sensing or 
stimulation sites.

DETAILED DESCRIPTION OF THE INVENTION 
The following description is of the best mode presently contemplated for 
carrying out the invention. This description is not to be taken in a 
limiting sense, but is made merely for the purpose of describing the 
general principles of the invention. The scope of the invention should be 
determined with reference to the claims. 
The present invention relates to a microdevice that uses a self-attaching 
electrode to anchor or otherwise secure the microdevice in a desired 
implant location, e.g., to a desired nerve bundle or muscle tissue. The 
microdevice may comprise an electronic stimulating device that derives 
operating power from an externally applied alternating magnetic field; 
with the microdevice being controlled by control information that 
modulates such magnetic field. Alternatively, the microdevice may comprise 
an implantable microsensor that senses a desired biomedical parameter, 
e.g., voltage, body position, pressure, magnetic field, chemical 
parameters such as pH, oxygen, salinity, glucose concentration, or the 
like, converts such sensed parameter to an electrical signal (if not 
already an electrical signal), and telemeters such sensed signal to a 
location outside the body. Such microsensor likewise derives operating 
power from an externally applied alternating magnetic field; with the 
microsensor being controlled, as required, by control information that 
modulates such magnetic field. Further, the microdevice may comprise a 
device that provides both stimulating and sensing functions. 
The design and operation of a microdevice is described in U.S. Pat. No. 
5,193,539. The microdevice circuitry is hermetically sealed in a tiny 
tubular housing, as described in U.S. Pat. No. 5,193,540. The teachings of 
the '539 and '540 patents, while directed to a microstimulator, are also 
applicable to a microsensor. Both the '539 and '540 patents are 
incorporated herein by reference. 
The microdevice of the present invention interfaces with a nerve bundle or 
"nerve" (note, for purposes of this application, a nerve bundle or "nerve" 
is made up of a plurality of nerve fibers), or with a muscle bundle or 
"muscle" (a muscle bundle or "muscle" is made up of a plurality of muscle 
fibers), by way of self-attaching electrodes. Preferably, two such 
self-attaching electrodes are used, one extending from each end of the 
microdevice's housing. Advantageously, by using self-attaching electrodes, 
suturing of the electrodes to the nerve is not required. 
It is noted that any type of self-attaching electrode may be used with the 
microdevice in accordance with the present invention. Self-attaching 
electrodes are described, e.g., in U.S. Pat. Nos. 4,920,979 (helical 
electrodes); 4,934,368 (cuff electrodes); or 4,573,481 (helical electrode 
arrays). Additionally, sutured electrodes or electrode arrays affixed to 
substrates that are sutured may also be used, such as is shown in U.S. 
Pat. Nos. 4,026,300 (woven sheet material coupling) or 4,590,946 
(electrodes helically wound and secured to a sutured substrate); although 
using a sutured electrode configuration defeats one of the advantages of 
using self-attaching electrodes--ease of implantation. The '979, '368, 
'481, '300 and '946 patents are all incorporated herein by reference. 
The basic invention is illustrated in FIG. 1A, where there is shown a 
schematic representation of a microdevice 102 attached to a nerve 100 by 
two opposing helical electrodes 104 and 106. As described more fully 
below, the microdevice 102 is housed within a sealed housing, typically an 
elongated housing that has a generally tubular shape. One of the helical 
electrodes 104 extends from one end thereof and wraps around the nerve or 
muscle 100. (Hereafter, where reference is made to a "nerve", "nerve 
fiber" or "nerve bundle", it is to be understood that such reference is 
also intended to include reference to a "muscle", "muscle fiber" or 
"muscle bundle", as appropriate In other words, hereafter the term 
"nerve", including its various forms as a noun or adjective, is used as a 
shorthand notation for "nerve or muscle", including their various forms as 
a noun or adjective.) The other helical electrode 106 extends from the 
other end of the tubular housing and likewise wraps around the nerve 100. 
Preferably, the direction of the helical turns of the electrode 104 is 
opposite that of the helical turns of the electrode 106, which makes it 
easier to implant and attach the electrodes. Because the tubular housing 
is supported between the two helical electrodes 104 and 106, which 
electrodes firmly grasp onto the nerve 100 as their multiple turns wrap 
around the nerve, the microdevice 102 is effectively attached to the 
nerve, and "floats" with the nerve. That is, as the nerve moves, e.g., 
with the motion of a limb or body organ associated with the nerve, the 
microdevice also moves, thereby preventing the nerve from being tugged or 
tethered in any way by the electrode. 
FIG. 1B schematically shows a microdevice 102 attached to a nerve 108 by 
two cuff electrodes 110 and 112, each being attached to respective ends of 
the housing of the microdevice 102. FIG. 1B also illustrates that the 
nerve 108 typically comprises a bundle of individual nerve fibers 114a, 
114b, . . . 114n, which individual nerve fibers are twisted and 
intermingled along the length of the nerve bundle 108. Thus, the 
population of nerve fibers that make physical and/or electrical contact 
with the electrode 110 may not necessarily be the same population of nerve 
fibers that make physical and/or electrical contact with the electrode 
112. Thus, by employing two spaced-apart electrodes as shown in FIG. 1B, 
whether such electrodes are cuff electrodes as shown in FIG. 1B, or 
helical electrodes as shown in FIG. 1A, or other equivalent electrodes, 
the electrodes are advantageously able to interface with different 
populations of nerve fibers. Hence, the same nerve bundle may be 
stimulated the same in two different locations in order to stimulate more 
than one population of nerve fibers within the bundle without any 
mechanical or electrical interaction between the two stimulation sites. 
FIG. 1C depicts the microdevice 102 having opposing helical electrodes 104' 
and 106' where each helical electrode is configured to have only a few 
loose turns. In contrast, FIG. 1D depicts the microdevice 102 having 
opposing helical electrodes 104' and 106', wherein each helical electrode 
104' and 106' is configured to have a multiplicity of tight turns. Here, 
the terms "loose" and "tight" are relative terms, referring to the number 
of turns and/or the spacing between the turns. In general, a loose helical 
electrode is one having 1-2 turns, and a tight helical electrode is one 
having 3 or more turns. The type of helical electrode to be used depends 
upon the location of the implant and the size of the nerve. If the nerve 
is in a location where there is a significant amount of body motion, e.g., 
in a leg or arm, then a larger number of turns are desired to better hold 
the electrode in place around the nerve and prevent the microdevice from 
slipping. If the nerve is in a location where there is little motion, 
e.g., in the trunk of the patient's body, then a lesser number of turns 
are needed. In all situations, however, it is important that there be 
sufficient turns, or other attachment means, to assure good electrical and 
physical contact with the nerve. 
Advantageously, the microdevice of the present invention may be implanted 
by making very small incisions or puncture holes in the patient's skin. 
Typically, the microdevice as described in the '539 and '540 patents, 
referenced above, has dimensions of the order of 10 mm long by 2 mm in 
diameter. Thus, an incision on the order of about 3 mm to 10 mm is all 
that is needed to longitudinally insert the microdevice under the skin. In 
some instances, as indicated in the referenced patents, the microdevice 
may even be implanted through the lumen of a needle. 
Implantation of the microdevice may also be facilitated through the use of 
a fiber optic probe. A suitable saline solution flows through the fiber 
optic probe to keep its lens, as well as the area being observed, clear. 
The surgeon inserts the fiber optic probe under the skin, using 
conventional techniques, to locate a suitable implant site. Then, using a 
hollow needle, about 10 gauge, with a stylet attached to the microdevice, 
the microdevice is implanted at the implant location. The stylet is used 
to not only help maneuver the microdevice into the desired implant 
location, but also to help position the helical electrodes (or other 
self-attaching electrodes) around the nerve or muscle. In some instances, 
if needle electrodes are used (which also comprise a type of 
self-attaching electrodes), such needle electrodes may be pushed through 
the nerve or muscle using the stylet. Once the electrodes are in position, 
the needle and fiber optic probe can be removed, leaving the patient with 
as few puncture wounds following the procedure as possible. 
When the above implant procedure is performed correctly, there is no need 
to puncture the epineurium, or equivalent protective tissue. (The 
epineurium is the outer sheath of connective tissue that encloses the 
bundles of fibers that made up a nerve.) Hence, the nerve is maintained 
protected within its natural sheath, without external penetration. Such 
protection minimizes the likelihood of infection at the nerve. Further, 
even if infection should occur, it will not likely spread to other 
attachment sites because there is no connection between the attachment 
sites. Thus, even in the event of an isolated infection, a massive explant 
of the microdevices should not be needed. 
Advantageously, when two helical electrodes are used, one extending from 
each end of the microdevice as shown in FIGS. 1A, 1C or 1D, and where each 
electrode spirals in the proper direction (with one electrode spiraling in 
one direction, and the other electrode spiraling in the other direction), 
the above-described implant procedure may be used to position both 
electrodes with a minimal number of puncture wounds. 
Further, it is noted that the helical electrode(s) can be positioned 
longitudinally and/or rotationally to optimize the stimulation or sensing 
points so as to activate the optimal family of neurons associated with the 
nerve, or so as to sense a desired signal, e.g., biopotential signal, 
associated with an optimal family of nerve fibers. 
For some applications, e.g., where the microdevice is utilized as a 
microsensor and where one or more parameters are sensed that do not 
require the use of an electrode to perform the sensing function, such as 
is the case for sensing magnetic fields, body position, body acceleration, 
saturated oxygen, etc., the helical electrodes 104 and/or 106, or 
equivalent self-attaching electrodes shown in FIGS. 1A-1E, may simply 
comprise a helical wire(s) that is bonded to the housing of the 
microdevice and that is used to anchor the microdevice in a desired 
implant location relative to the nerve or muscle 100. 
After implantation, it is best if the limb (or other body part) wherein the 
implant was placed can be immobilized for a few days. Such immobilization 
advantageously allows a fibrous capsule to form around the microdevice, 
which fibrous capsule locks the device in its implant position adjacent 
the nerve. Further, because the helix is a loosely open structure, the 
attachment of a helical electrode to a nerve does not constrict the nerve 
and its blood supply. Thus, the fibrous capsule that is formed locks the 
entire implant in place, with the nerve and blood supplies remaining in 
their natural, non-constricted, condition. 
FIG. 1E shows a microdevice 116 made in accordance with the invention that 
is attached to a nerve 100 by a single helical electrode 118. In such 
instance, the return electrical path from the electrode 118 to the 
microdevice 116 is through the nerve 118 and body fluids to an indifferent 
electrode 120, typically located at the opposite end of the microdevice 
housing. 
Referring next to FIG. 2, there is shown a block diagram illustrating the 
transcutaneous transmission of power and information to one or more 
implanted microdevices that are used as microstimulators. In particular, 
as seen in FIG. 2, power and information are coupled to implanted 
microdevices 9 and 10 by an oscillator 46, driven by a stimulation 
controller 47. A coil 40 is driven by the modulated oscillator 46, which 
in turn is driven by the stimulation controller 47. Underneath (shown to 
the right of) skin 48 are implanted microdevices 9 and 10. (While only two 
such microdevices are shown, it is to be understood that any number of 
microdevices may be used.) Microdevice 9 is shown in greater detail. 
Secondary coil 11, within microdevice 9 receives energy and control 
information from the modulated, alternating magnetic field provided by 
coil 40 and passes such energy and information to power supply and data 
detector 12 which, in turn, provides power through an electrode recharge 
current controller 13 to stimulating electrodes 14 and 15. While 
electrodes 14 and 15 are drawn in FIG. 2 as being a "ball" and 
"rectangle", respectively, it is to be understood that such representation 
is only symbolic. For purposes of the present invention, at least one of 
the electrodes 14 or 15, and typically both electrodes, is a 
self-attaching electrode, as described above. That is, typically at least 
electrode 14 will be a helical electrode or cuff electrode (or other 
self-attaching electrode) that attaches to the nerve. 
FIG. 2 shows secondary coil 11 at or near the surface of the skin 48. Such 
is for illustration only. The microdevice 9 or 10 may be much deeper, if 
desired, or at any location within the body of the patient, i.e., within 
an arm or leg. The transmitting coil 40 need not be directly aligned with 
the receiving coil 11, but the receiving coil 11 may be anywhere along the 
length of the transmitting coil 40, and even for some distance beyond the 
ends of the coil 40. In one experimental determination, it was found that 
the microdevices may lie as far as about 5 cm outside the volume 
encompassed by coil 40. The two coils 40 and 11 thus function like the 
windings of a transformer, with one coil being inductively coupled to the 
other. 
The power supply portion of 12 provides the operating and stimulating 
voltages for the microdevice, with the energy being derived from the 
signal received through the coil 11 as coupled from the coil 40. The 
operating voltage may be at two levels, for example, approximately -7 to 
-15 volts, for providing stimulating pulse energy storage; and -2 to -4 
volts for providing operating power for digital logic 16. Data detector 12 
also provides clock and digital data information to logic 16 which decodes 
the control information contained within the modulated, alternating magnet 
field. Such decoded information is used by the logic 16 to control switch 
17 which controls the charge stored on the capacitor 20, connected between 
electrodes 14 and 15. Capacitor 20 is located inside the hermetically 
sealed tube that comprises the housing of the microdevice 9. In some 
embodiments, the capacitor 20 may actually be found outside of the housing 
using the electrodes 14 and 15, but still between the electrodes 14 and 
15, as described in the '539 and '540 patents cited above. Logic 16, which 
is preferably high speed, low current, silicon gate CMOS, also controls 
switch 18 (which may be a transistor switch), which switch 18 controls the 
stimulating pulse current (which is a discharge of the stored charge on 
the capacitor 20). The discharge current flows between electrodes 14 and 
15 through the nerve 100 (represented in FIG. 2 by a resistor drawn with a 
dashed line). Logic 16 also controls current amplitude buffer 19. The 
buffer 19, which may be realized by an adjustable or programmable 
resistor, controls the amount of current allowed to flow in each 
stimulating pulse. 
Turning next to FIG. 3, it is seen that electrode 14 includes a distal tip 
portion 50, that may be wound in the shape of a helix (or otherwise 
attached to a self-attaching electrode), and a stem portion 23 that 
extends into the microdevice. In a preferred embodiment, the electrode 14, 
including the distal tip portion 50 and stem portion 23, is made from 
tantalum, platinum, iridium, or equivalent metal conductor that is 
compatible with body fluids. The electrode 14 is formed, e.g., from a wire 
that has been formed and processed so as to assume the desired helix shape 
at the tip portion 50. 
As further seen in FIG. 3, electrode 15 is placed at the opposite end of 
the microdevice from electrode 14. Only a stem portion 25 of the electrode 
15 is shown in FIG. 3, but it is to be understood that the electrode 15 
may be formed and shaped in the same manner as the electrode 14 when two 
self-attaching electrodes are used. Electrode 15 may be made, e.g., from 
anodized, sintered tantalum, or other suitable metal that is compatible 
with body fluids. The stem portion 25 extends into the microdevice. 
If only one self-attaching electrode is used (as seen in FIG. 1E), then the 
electrode 15 may include a pellet of tantalum (or other suitable metal) 
that is exposed outside the stimulator, connected to the stem portion 25. 
For example, in one configuration, when electrode 14 comprises the only 
self-attaching electrode, then electrode 15 may be constructed of powdered 
tantalum metal molded and sintered into a pellet on the end of a 0.25 mm 
diameter wire, tantalum stem. It is then anodized, to form a thin anodized 
layer 15A, and the tantalum stem is threaded through a glass bead of N51A 
soda-lime glass and the portion of the stem protruding inside the glass 
bead is gold plated (plating not shown). The anodization may be left until 
after the housing is sealed to the glass bead because the heat may affect 
the anodization. The glass bead is preferably of the size of the tantalum 
pellet, approximately 1.5 mm in diameter and 1 mm in width. The entire 
length of the tantalum electrode is approximately 2.8 mm. The porous 
nature of the pellet allows intimate relationship with the body fluids, 
but is of sufficiently small cellular structure that fibrous growth does 
not occur within the cells. The pellet is the outer, exposed portion of 
the electrode and is formed as a cylindrical section approximately less 
than 2 mm long and 2 mm in diameter (approximately 6 or 7 mm.sup.3). The 
outer exposed pellet thus comprises, by its porous structure and anodized 
layer, an electrolytic capacitor, which may be used in lieu of the 
capacitor 20. The capacitance of such an external electrolytic capacitor, 
provided by a tantalum electrode 15 as described above, coupled with an 
iridium counter electrode 14, can be significant, being on the order of 2 
to 30 microfarads. For greater capacitance, the outer cylindrical section 
of tantalum electrode 15 can be larger, but it is noted that sufficient 
capacitance can be achieved by a volume of only 7 mm.sup.3. It has been 
found that anodized tantalum has a very low DC leakage level when biased 
up to 80% of the anodization voltage and tends to self-heal in body 
fluids. 
As indicated above, when two self-attaching electrodes are utilized, as 
shown, e.g., in FIGS. 1A-1D, then a discrete capacitor 20 is placed within 
the microdevice. When the microdevice is used as a stimulator, the 
capacitor 20 is placed in series circuit with electrodes 14 and 15. (When 
the microdevice is used as a sensor, the capacitor 20 may be used in the 
power supply circuit 12 in order to store energy received through the coil 
40 to provide operating power for the sensing circuits, and particularly 
the telemetry circuits, described below.) Such discrete capacitor, 
constructed in accordance with integrated circuit fabrication techniques 
known in the art, occupies a substantial amount of space within the 
microdevice. 
Advantageously, all of the elements needed to receive and store modulated, 
electrical energy and to decode and use the modulating information to 
cause, e.g., stimulating pulses, or to sense biomedical parameters and 
telemeter signals representative of such parameters, are provided within 
the microdevice. All elements are housed within the housing of the 
microdevice except for the exposed electrodes. 
Thus, a preferred embodiment is one in which one or both of the electrodes 
14 and 15 are formed in the shape of a single or plural nerve cuffs, as 
taught in U.S. Pat. No. 4,934,368, or in the shape of helical electrodes, 
in order to attach to a desired nerve. Platinum wires, for example, 
extending out of each end of the microdevice may be connected to the 
appropriate nerve cuff. Alternatively, the distal ends of platinum wires, 
extending out from each end of the microdevice, may be formed in the shape 
of the helical electrodes. With the electrodes in direct contact with the 
nerve, the stimulating pulse does not need to be as large as it would if 
such direct contact did not exist. Hence, in the case of a 
microstimulator, the size of the storage capacitor 20 need not be large. 
Although the size is miniature, when nerve cuffs are used, as shown in 
FIG. 1B, the device will normally have to be surgically implanted, as 
opposed to implanted through the lumen of a needle. When helical 
electrodes are used, as shown in FIGS. 1A, 1C and 1D, the device may be 
surgically implanted, or implanted through the lumen of a needle, as 
described above. Indeed, that is one of the advantages of using helical 
electrodes--plantation of the device is achievable with minimal punctures 
or incisions in the patient. 
As seen in FIG. 3, which shows a cross-sectional side view of the 
microdevice 9, a housing 22 encloses the microdevice. In a preferred 
embodiment, the housing 22 comprises glass capillary tubing approximately 
10 mm long and having an outer diameter of approximately 2 mm. Such glass 
capillary tubing is preferably a biocompatible, lime glass or borosilicate 
glass and is commonly available from or through glass fabrication houses 
such as Kimbel Glass or Corning Glass. 
Alternatively, the housing may be a ceramic, cast or molded epoxy or 
silicon rubber, or other material which is hermetically-sealable, inert 
and suitable for implantation. 
At one end, the glass tube is hermetically-sealed to the electrode 14, 
which electrode comprises an iridium, tantalum, or platinum wire, 
including the stem 23 that extends into the microdevice 9. A wire of, 
e.g., 0.15 mm to 0.25 mm be used, with one end cold-formed to provide a 
flat for bonding a wire thereto, to make electrical connection to the IC 
chip 28 within the microdevice. 
It is important to select a glass for the housing 22 which is stable in 
body fluids and which matches pretty well the coefficient of thermal 
expansion of the material from which the electrodes are made, e.g., 
tantalum, iridium or platinum, because of the heating operations involved 
in fusing the electrodes to the glass housing. Glass capillary tubing, 
N51A, has a coefficient of thermal expansion similar to tantalum and 
iridium and thus may be sealed thereto. The tubing is cut off square about 
2 mm beyond the end of the ferrite core 24. 
In operation of the microdevice as a microstimulator, the storage capacitor 
20 is charged to a suitable stimulating voltage. Upon discharge, or 
partial discharge of the charge, as controlled by the closing of the 
switch 18 and by the setting of the current amplitude limiter 19 (FIG. 2), 
an electrical current pulse flows between the two electrodes 14 and 15, 
thereby stimulating the nerve 100. 
At the other end of the microdevice from electrode 14 is the electrode 15. 
Such electrode 15 also has a stem 25 extending into the microdevice. The 
stem 25 and electrode 15 are preferably made from the same wire, e.g., 
iridium, tantalum or platinum wire. In some instances, e.g., as indicated 
in the '540 patent cited above, it may be desirable to anodize the stem 25 
with an anodized layer 15A. The process for such anodizing is described in 
the '540 patent. 
There are various methods of assembly associated with the microdevice 9. In 
the preferred method, the entire internal assembly is put together and 
inserted into the housing from one end of the housing or the other. Prior 
to inserting the assembly, a glass bead 26 is threaded onto the stem 25 
and fused thereto. The inner end of the stem is gold-plated. A metallized 
film 29 is deposited on the bottom ferrite shelf. The IC electronics chip 
28 is adhered to the metallic film 29 on ferrite shelf 27 by silver epoxy, 
silver solder, an indium-based solder, or other suitable conductive 
adhesive. Two metallized pads 32 and 33 are created on the top half of the 
ferrite core. A polyamide, solder resist line, or barrier 38, is added. 
The tantalum stem 25 is resistance welded or soldered to the weld shim 30. 
An alternate method of connection of the stem 25 to electronic chip 28, 
rather than by means of metallized film 29 and the substrate of the 
electronic chip 28, is to replace the shim 30 and the metallized film 29 
with a small metallized pad disposed on the ferrite shelf 27 to which both 
stem 25 and electronic chip 28 are connected by flying wire bonds, or 
other means. 
The stem 23 of electrode 14 is inserted through the ferrite channel of the 
bottom half of the ferrite core and is connected electrically to the 
electronic chip 28 by electrical conductor 31. A silver epoxy may be used 
to reinforce such electrical connection. Additional silver epoxy may be 
used to fill up the channel and provide a heat sink for the electrode 14. 
The top half of the ferrite core is placed over the bottom half of the 
ferrite core and one end of the coil wire is soldered to a metallized pad, 
32, for example, and the coil is wound on the ferrite and the other end is 
soldered to the other metallized pad 33. Gold wires are bonded between the 
metallized pads 32 and 33 and the electronic chip pads 36 and 37. A 
junction coat is applied. 
The electrode 14, including its stem 23, along with the entire inner 
assembly, are then inserted into one end of the glass capillary tube 22. 
The glass is sealed to the smooth surface of the stem 23, by bringing the 
glass and stem into an oxy-acetylene flame and rotating them within the 
flame. The sealing operation may be viewed under a microscope. It will be 
noted that the glass will shrink backward during melting. 
The glass bead 26 on the stem 25 of electrode 15 on the other end of the 
microdevice is flame-sealed, or fused, to the glass tubing, housing 22. 
The outwardly exposed portions of the electrode 15 may then be anodized, as 
explained previously, if necessary to provide additional external storage 
capacitance. 
The metallized pads 32 and 33 on the top half of the ferrite core 24 may be 
made of indium solder and no barrier 38 is then required. Metallized pads 
32 and 33 may be created of palladium, silver, indium, or solder, or 
mixtures thereof. The flying, gold bond wires may be attached directly 
from such pads to the electronic chip 28. 
Other means may also be used to make the electrical connections within the 
microdevice. For example, a polyamide cap (Kapton) may be used. It is 
placed on the electronic chip 28 and provides solder pads on the top for 
connecting to the electrodes and the coil and on the bottom for connecting 
to the electronics chip 29. Thru-hole connections, in the cap itself, make 
connections between the top and bottom of the cap. 
Testing for hermeticity may be done by helium, but the helium may leak out 
before the test can be made. Finished devices are best tested by soaking 
in a dye solution and rejecting those parts that exhibit streams of 
bubbles or internal dye droplets. 
The microdevice shown in FIGS. 3 and 4 illustrates the coil 11 which, 
depending on the particular application, has approximately 200 turns or 
more, to provide the necessary induction for the coupling of the magnetic 
flux associated with the alternating magnetic field. (Where telemetry is 
also provided within the microdevice, an additional coil is also provided, 
as indicated below.) In one preferred embodiment, approximately 250 turns 
of 51 AWG, (0.00102" diameter or smaller) insulated, copper wire is wound 
in two layers on the ferrite core 24, having a diameter of approximately 
0.050". Such construction will by its own distributed capacitance be 
resonant at approximately 2 MHz. Although an air core and other cores of 
high-permeability and low losses could be made to work, a ferrite core is 
preferred. A particular core material which was used and found 
satisfactory was a low conductivity, high permeability, nickel-zinc 
ferrite stock, having a permeability of 800. It was formed by cutting and 
grinding two half cylinders, to the shape shown in FIGS. 3 and 4, with a 
groove in each, to form a hollow core when the two half cylinders were 
placed together. 
The bottom half of ferrite core 24 is longer than the top half and provides 
a shelf 27 on which to mount the electronic chip 28 (a custom, integrated, 
microcircuit chip) for the microdevice. It is noted that the top half of 
ferrite core 24 extends over electronic chip 28 and on the top surface of 
ferrite core 24 are disposed the metallic pads 32 and 33, FIG. 4 to which 
are connected the ends of the coil. In a preferred embodiment, electronic 
chip 28 is a double-poly P-well CMOS (3 micron) process so that the 
substrate is at the V+ supply rail to which the tantalum stem of electrode 
15 is connected. It is noted that both ends of the coil 11 are 
electrically connected to provide input to the electronic chip 28, 
providing the energy (for powering the microdevice) and the modulation 
(control) information to such electronic chip 28. 
One output of electronic chip 28 is to the electrode 15, and is shown in 
FIG. 3 as being through the substrate (base) of the electronic chip 28 to 
a thick, conductive film 29 which may be plated or adhered to ferrite 
shelf. Electrical connection between the electronic chip 28 and the film 
29 may be accomplished by a silver-filled conductive epoxy or other 
electrically conductive means. The preferred thick, conductive film is 
screenable or imageable (by screen printing or photolithography or other 
imaging method). An alloy of the platinum group and gold (specifically, 
Pt/Pd/Au) in a fritted paste is preferred. Such is then fired for about 60 
minutes, being raised evenly, 50 degrees Centigrade per minute, to 
approximately 850 to 1050 degrees centigrade in 30 minutes and cooling at 
the same rate. Such film shows good weldability and good solderability. 
Weld shim 30, which is conductive, is also bonded or otherwise adhered to 
conductive film 29 and is resistance welded, or otherwise electrically 
connected to tantalum stem 25. Stem 25 comprises part of electrode 15 and 
extends through glass bead 26 to the exposed pellet of tantalum electrode 
15. 
Electrical connection between the stem 25 and the electronic chip 28 may 
also be made by a wire-bond between them or by a flying wire bond from 
each of them to a small metal pad (not shown) on ferrite shelf 24. Such 
connection may also be made as described in connection with FIG. 5, 
hereafter. 
The other output of electronic chip 28 is connected to stem 23 by means of 
wire 31. 
FIG. 4 is a top view of the microdevice 9 with the housing shown in 
cross-section. The ends of coil 11 are connected to two metallized pads 32 
and 33 (of palladium-silver, for example) plated on ferrite 24, by means 
of conductive epoxy or soldering. Such pads 32 and 33 are connected by 
flying, gold wires 34 and 35 which are bonded to aluminized pads 36 and 37 
on electronic chip 28 and protected with a junction coat. Barrier 38, 
which may, for example, be polyamide isolates the conductive epoxy and 
solder from flowing to undesired areas. 
The microdevice 9 may be filled with a harmless, inert gas which is also 
compatible with the internal structure of the microdevice. Prior to fusing 
of the second electrode to the housing, the inert gas may be introduced 
into the microdevice, or the microdevice may be assembled in an inert gas 
atmosphere. The inert gas may be 10% helium and 90% argon or krypton or 
other commonly-used, suitable, biologically-compatible gas. Assembly in a 
dry, relatively clean atmosphere has been found suitable. All epoxy inside 
the microdevice must be allowed to fully cure before sealing, otherwise 
undesired by-products are generated within the microdevice as the epoxy 
cures. 
Referring next to FIG. 5, a block diagram of a microdevice 102 is shown 
that includes circuitry for sensing a desired parameter, e.g., a 
biomedical parameter, and telemetering a signal representative of the 
sensed parameter to an external source or location. The microdevice 102 
includes a power supply and data detector 12' that receives power signals 
and information through a coil as described above in connection with FIGS. 
2-4. Also included within the device 102 is a sensing circuit 130. The 
sensing circuit 130 may comprise any type of sensor circuit known in the 
art, or yet to be developed, such as a circuit to sense voltage; body 
position; pressure; magnetic field from a nearby magnet (to obtain an 
angle); chemical parameters, such as pH, oxygen, salinity, glucose 
concentration, or the like. For sensing some parameters, such a 
biopotential voltages, the sensor circuit 130 is connected to a pair of 
terminals 132 and 134, and the helical electrodes 104 and 106 are 
connected to such terminals. In such instances, the parameter that is 
sensed is thus sensed through the electrodes 104 and/or 106. 
For sensing other parameters, such as body movement, acceleration, or 
certain chemical parameters, the electrodes 104 and 106 may not be needed 
to sense the desired biomedical parameter. In such instances, the desired 
parameter is either sensed through circuitry or elements included within 
the sensing circuitry 130, as is the case for sensing body movement or 
acceleration, see, e.g., U.S. Pat. Nos. 4,940,052 or 5,010,893; or is 
sensed through another type of parameter interface, e.g., an optical 
interface used to measure oxygen saturation based on reflected spectral 
components of incident light, see, e.g., U.S. Pat. No. 4,815,469. The 
'052, '893 and '469 patents are incorporated herein by reference. Where 
the electrodes 104 and 106 are not needed to sense the desired parameter, 
they still may be used solely for anchoring purposes. Further, instead of 
or in addition to the electrodes 104 and 106, which electrodes 104 and/or 
106 are electrically connected to the sensing circuitry 130 through the 
terminals 132 and 134, anchoring "electrodes" 136 and/or 138 (which are 
not electrodes in the classical sense, but are simply wires formed in the 
shape of a helix) may be bonded to the housing of the microdevice 102 at 
one end and be utilized to help anchor the microdevice 102 into a desired 
implant position. 
Still referring to FIG. 5, the sensing circuit 130 generates a sensor 
output signal, appearing on signal line 140, representative of the 
parameter that is sensed. (Note a signal appearing on a referenced signal 
line may also be referred to by the same reference numeral as is used for 
the signal line, e.g., the "sensor output signal 130.") This sensor output 
signal is directed to an oscillator circuit 142, or equivalent, where it 
modulates an oscillator signal. Alternatively, a clock signal 144, 
obtained from the power supply and data detector circuit 12' may be used 
as an oscillator signal (or may be used to derive an oscillator signal) 
that is modulated by the sensor output signal 140. In either event, the 
modulated oscillator or clock signal is directed to a telemetry circuit 
146. The telemetry circuit 146, is coupled to a coil 148. The coil 148 
receives the output of the telemetry circuit 146 and transmits it through 
the coil 148 so that it can be received by an external receiving circuit 
(not shown in FIG. 5). Thus, in this manner the external receiving circuit 
is able to monitor various parameters sensed by the sensing circuit 130. 
Note that information signals received by the power supply and data 
detector circuit 12' are used as control signals 143, 145 and 147 to 
control the operation of the sensing circuit 130, the oscillator 142 and 
telemetry circuit 146 in accordance with a specified mode of operation. 
Thus, in operation, the microdevice 102 shown in FIG. 5 receives power and 
control signals 141 from an external source, senses a specified parameter 
or parameters through sensing circuit 130, and returns a sensed 
information signal 149 to the external source. In this manner, the 
external source may, in effect, function as a recording device that 
records, or otherwise stores, various parameters that are sensed at the 
specific sensing locations that are at or near the electrodes 104 or 106, 
or otherwise near the implant location of the microdevice 102. 
Turning next to FIG. 6, a block diagram is shown of a microdevice 102' that 
includes both sensing and stimulating circuitry. Hence, the microdevice 
102' is able to stimulate a nerve or muscle, as well as sense a specified 
biomedical parameter. The power supply and data detector 12" included in 
the microdevice 102' is substantially as described previously in 
connection with FIGS. 3 and 4. The stimulating function is provided by 
logic circuit 16' current charge regulator 13, current discharge regulator 
19, capacitor 20, and switches 17 and 18, as described above. The current 
stimulation is provided between helical electrodes 104 and 106. 
The sensing function provided by the microdevice 102' is aimed at sensing a 
biopotential signal associated with a contracting muscle, or a neural 
impulse associated with a nerve, and such signals are sensed through the 
same electrodes 104 and 106 as are used for stimulation. A sense amplifier 
150 amplifies and filters the signals sensed through the electrodes 106 
and 108. The amplified and filtered signal is then sent to a data 
modulator 152, where the signal modulates a clock signal obtained from the 
power supply and data detector circuit 12". The modulated clock signal is 
then sent to a telemetry circuit 146. The telemetry circuit 146 transmits 
the signal through the antenna coil 148. Transmission is preferably 
accomplished via a radio frequency (RF) carrier signal having an 
appropriate carrier frequency. Inductive coupling may also be used in some 
embodiments, the same as is used to couple power and information into the 
circuit 102'. 
Control signals obtained from the logic circuit 16' control the operation 
of the sense amplifier 150, the data modulator 152 and the telemetry 
circuit 146. For most applications, operation of the telemetry and sensing 
circuits is done on a sampled basis, with a telemetry pulse being 
generated at a specified rate, e.g., 0.5-10 pulses per second. When not 
used, the sense amplifier 150, data modulator 152 and telemetry circuit 
146 may be turned OFF. 
Referring next to FIG. 7, a block diagram of an implantable microdevice 
102, having a sensing portion 156 (or microsensor 156) and a stimulator 
portion 158 (or microstimulator 158), and an external controller 160 is 
shown. FIG. 7 thus illustrates the concept of using feedback information 
sensed by the microsensor portion 156 of the microdevice 102, telemetered 
to the external controller 160, to control the microstimulator portion 158 
of the microdevice 102. As shown in FIG. 7, the external controller 160 
includes an oscillator 164 for driving the coil 40 with a power signal 
that is modulated with control information. The oscillator 164 is 
modulated by a control signal that is generated by stimulation/sensor 
processing circuitry 170. Such circuitry 170 may take various forms, but 
is preferably realized using a processor circuit that may be readily 
programmed to operate in a desired mode of operation. 
On the receiving side, the controller 160 includes a receiving coil 162 
coupled to a receiving circuit 166. The signal received by the receiving 
circuit is demodulated by a demodulator circuit 168, with a resultant data 
signal 169 being directed to the processing circuitry 170. Based on the 
contents of the data signal 169, the type of information sent to the 
microdevice 102 via the coil 40 may be adjusted in a desired fashion. 
For example, assume that the microdevice 102 is one of a plurality of such 
devices that are implanted in a patient's arm to selectively stimulate an 
arm muscle or nerve 100. Assume further that the microsensor portion 156 
of the microdevice 102 senses motion of the arm and/or voltage signals or 
neuron impulses indicative of the depolarization and/or movement of the 
arm muscle tissue. Thus, the feedback provided by the microsensor portion 
156, received through antenna coil 162, and manifest in the data signal 
169 generated at the controller 160, provides confirmation as to whether a 
given stimulation pulse, or sequence of stimulation pulses, generated by 
the microstimulator portion 158 of the microdevice 102, has achieved a 
desired objective of moving the patient's arm a desired increment. If so, 
then the sequence of stimulation can move to an adjacent microdevice. If 
not, then the magnitude, or some other parameter, associated with the 
microstimulator 158, can be adjusted, e.g., increased in amplitude and/or 
width, in order to achieve the desired stimulation, and hence movement of 
the arm. In this manner, then, movement of the arm can be selectively 
controlled, using the body's own muscle tissue to effectuate the movement, 
but controlling the movement in a desired manner by virtue of the 
stimulation pulses that are generated and the feedback signals that are 
sensed. 
Alternatively, control signals can be generated by the controller 160 to 
activate the microsensor 156 of the microdevice 102 so as to cause the 
microsensor 156 to sense the impedance between of the electrodes 104 and 
106. (Such impedance can be readily checked by monitoring the amount of 
current that flows between the electrodes when a stimulation pulse of a 
given voltage amplitude is applied between the electrode terminals.) The 
impedance measurement thus made is then telemetered back to the controller 
160, where the processing circuitry can readily determine if such 
impedance is within an acceptable range. If not, then that is an 
indication that either one of the electrodes has broken (impedance very 
high), or that there is an electrical short (impedance very low). In 
either event, an out-of-range impedance is an indication of a malfunction, 
and appropriate corrective action can be taken. 
In some applications of the invention, more than one electrode pair may be 
used with the same microdevice. In such instances, a first pair of 
electrodes are used for stimulation, and a second and subsequent pair(s) 
of electrodes are used for sensing. Where multiple (more than two) sensing 
electrodes are used, sensing can be performed, as needed, between any 
selected combinations of the electrodes, as controlled by the control 
signals received from the external controller. 
It is noted that rather than using a single microdevice 102' (as shown in 
FIG. 6) that provides both sensing and stimulating functions, some 
embodiments of the invention contemplate using a desired combination of 
inexpensive, microstimulators and microsensors, controlled by the same 
external controller. Thus, for example, a multiplicity of microstimulators 
may be implanted to stimulate a nerve or muscle for a desired purpose, and 
only one or two microsensors need be implanted, to sense whether the 
desired purpose is achieved. 
It is noted that a microsensor device made in accordance with the present 
invention as shown in FIG. 5, or a combination microsensor/microstimulator 
device as shown in FIG. 6, may be fabricated in a tiny microdevice package 
using the same techniques as described above relative to the 
microstimulator device shown in FIGS. 2-4. 
Advantageously, the integrated stimulator/electrode structure described 
above eliminates the failure mode associated with leaded helical 
electrodes. That is, tethered electrodes can be pulled from their 
implanted position by forces applied by the tether when joint or other 
motions occur. Therefore, since no tether is present in the 
microdevice/electrode design described herein, this failure mode is 
eliminated. 
Further, as seen above, the microdevice with helical electrodes comprises a 
complete unit. Thus, when implanted, there is no stress on the electrodes 
or the housing (e.g., glass) of the microdevice. Rather, the microdevice 
becomes, as it were, an integral part of the nerve to which it is 
attached, without any external tethering or pulling on the nerve. 
While the invention herein disclosed has been described by means of 
specific embodiments and applications thereof, numerous modifications and 
variations could be made thereto by those skilled in the art without 
departing from the scope of the invention set forth in the claims.