[ieee 2008 5th international conference on electrical engineering, computing science and automatic...

An Easy Wireless Multi-Waveform Urinary Electrical Stimulator “UES”

Ernesto Paredes Martínez, Daniel Robles Camarillo, Luís Niño de Rivera Y.O. National Polytechnic Institute (IPN), ESIME Culhuacan, Mexico D.F.

Abstract- This paper proposes a simple wireless multi-waveform Urinary Electrical Stimulator (UES) to stimulate electrically patients with urinary incontinence. This system can generate a set of different programmable bipolar and monopolar waveforms, since pulse generator systems most provide different waveforms suitable for each individual patient [1]. This application discloses 6 distinct types of programmable waveforms. The waveform parameters can be modified by physician changing easy instructions with a software interface (SI). The proposed system lets long distance manipulation of the waveform generator by sending codes that change the characteristics of the waveforms even when the stimulator is implanted in the patient’s body. The waveforms used in this work can be applied in other electrical-stimulations in body or tissues. We will show that a multi-waveform stimulator can be built with common electronic circuits. The paper discusses the waveforms code generator in UES consisting on a Radio Frequency device connected between a multi-waveform stimulator and the nerves.

I. INTRODUCTION

Electrical stimulation can be used to reduce stress

incontinence, urgent incontinence, and could be used to stimulate sacral nerves [1]. The real problem is not the electronic technology used to stimulate, send or receive instructions to generate the waveforms, but in the field of biocompatibility and interconnection between the organs, axons or tissues and the electric stimulator. The present work shows how to build the codes to generate waveforms for the UES which is desirable to be implanted on Polymetil Metacrilate substrate (PMMA) as shown in figure 1.

Fig. 1. Polymethyl-Methacrylate Capsule (PMMA)

The electronics used for the waveform generator in UES is common and inexpensive; however the interconnection

between a Very Low Scale Integrity VLSI-UES system and axons and nerves is a major problem. The maturity of microelectronics technology lets get on hands any waveform required to stimulate axons, this assumption is not new, but the big challenge is how to use that technology on biocompatible substrates to interact with human body. The present work helps anyone to generate in an easy way whatever waveform as desire, and shows an alternative to communicate a stimulator with integral complex bio-systems inside the body. Integral solutions to the UES are still waiting for new solutions with micro actuators, manipulators, micro antennas or micro coils.

We showed in figure 1, a 6 mm PMMA substrate where

the whole UES indicated in figure 3 must be contained. The PMMA must integrate not only the electronics circuits indicated in figure 3, but also the micro needles required, or micro hooks like shown in figure 2, or what ever we need to connect the VLSI-UES circuit to any axon or nerve. The PMMA for biomedical applications has demonstrated excellent biocompatibility properties with human tissues [2].

Fig. 2. Micro hooks

The pretended design of UES is presented in figure 3 on a PMMA substrate [3]. The VLSI circuit is deposited on it and the coil antenna around the VLSI system. The high-tech challenges are mainly in the design and coupling of the antenna MEM’s system on the PMMA and the manufacture of the micro needles. The VLSI -UES circuit is in the core of the MEM’s antenna (Blue spiral). The spiral inductor can be built on a silicon substrate by using the multilevel interconnects through the medium of silicon fabrication processes [4]. We have to be careful about antenna’s geometry since it has to provide a high Quality “Q” [5]. Under PMMA we can see micro needles which have to be connected over the sacral

1 (cm)

2008 5th International Conference on Electrical Engineering, Computing Science and Automatic Control (CCE 2008)

IEEE Catalog Number: CFP08827-CDR ISBN: 978-1-4244-2499-3 Library of Congress: 2008903800 978-1-4244-2499-3/08/$25.00 ©2008 IEEE

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nerves. Reducing the UES’s size avoids surgical complexity and even medical complications.

Fig. 3. UES VLSI circuit on PMMA We describe some characteristics about discrete UES:

1. The wireless system lets the physician to design and

control the waveform that is required to stimulate the patient.

2. The physician from his computer can change the characteristics of the waveforms of the system that has been implanted over the sacral nerve of the patient.

3. Microcontroller’s receiver can contain many pre-charged waveforms

4. Different kind of waveforms can be programmed from the transmitter (SI or MC).

5. In VLSI-UES version, a powerless system is needed to transmit data and power energy.

II. METHOD

One way to generate bipolar waveforms is by using of

adaptive filters [6]; however, this paper reports an empirical method to generate any desired waveforms, without any technological complication. We saw a desire waveform on an oscilloscope or on a paper, and just taking the amplitude values from it; we reproduced the original waveform through hexadecimal values which correspond to analog waveforms. We program the desire waveform in the SI, so user can change waveforms parameters, which can be sending to the receiver inside the human body.

As we can see in figure 4, discrete UES system has in the transmitter a microcontroller (MC) and a modulator block. The SI is used when the physician needs to see what kind of waveform he is generating to stimulate a patient with. When the electrical stimulation treatment is well know by the physician, the SI is not required to control the UES, because UES can work in stand alone mode, due to MC can generate waveform by itself.

Receiver has 3 main blocks; a demodulator is used to obtain the hexadecimal information which will be sent to a MC due to we can convert binary values into analog ones (D/A converter).

Fig. 4. Blocks of UES

III. TRANSMITTER

This proposal involves a wireless sending codes system

from a PC or a microcontroller to an electro-stimulator’s receiver. Once patient is on-line with the UES, physician can program it with a particular waveform (or many as required) according patient’s treatment. We used a TWS-434 transmitter to send hexadecimal words from a MC (ATMEL AT90S2313 MC) to a RWS-434 receiver module with 10 meters of distance. We used MC’s PD1/TXD UART terminal (Figure 5). It has to be supplied with +5VCD power source, and has only one data-in terminal where is connected to an UART-serial data-out (from the MC).

XTL1

4 MHZ

RESET

C222p

C122p

R14.7K

GN

DD

AT

A_I

NV

CC

RF

-OU

T

U1

TWS-434

RESET1XTAL24 XTAL1

5

GND10VCC

20

PB0/AIN012

PB1/AIN113

PB214

PB3/OC1 15

PB4 16

PB5/MOSI 17

PB6/MISO18

PB7/SCK19

PD0/RXD2

PD1/TXD3

PD2/INT06

PD3/INT17

PD4/T08

PD5/T19

PD6/ICP11

U2

AT90S2313

DATA_OUT

E1

ANTENNA

+5VCD

+5VCD

Fig. 5. 433 MHz Wireless transmitter with a MC AT90S2313

MICROCONTROLLER

DEMOD

MODULATOR

DATA

DATA

DATA

DATA

CONVERTER

E1

E2

MICROCONTROLLER

RECEIVER

TRANSMITTER

1 (cm)

Must be microneedles



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It is possible to connect directly the TWS-434 module to RS-232 PC interface. This is an advantage, when we want to the PC controls and supervises constantly the amplitude, frequency, waveform shape, and others patterns of the signal to be transmitted, by a friendly SI as shown in figure 6.

Fig. 6. Software interface “SI” build-up in Matlab 7.0. Symmetric waveform 1

Fig. 7. Symmetric waveform 1 with other values

In figure 6, letter “K” let to select 6 different programmable bipolar and monopolar waveforms UES-SI can generate. We attached 2 rectangular symmetric waveform options (Figure 7) where are preprogrammed the segment’s values (letter “M”). Segment’s values can be written in 4 different blocks called “A”, “B”, “C”, and “D”. For example, in block “A” we see “V=1”, which means voltage “+1 volt and -1 volt” in waveform window (letter “L”) from 0 to 2 milliseconds; block “A…T=2” means the time of section “A” in the graphic; block “B…V=2” means “+2 volts” with “-“1 volt from the “A” section, block “B…T=2” means the time (2 ms) of section “B” in the graphic; block “C…V=1” means “+1 volts” with “-“1 volt from the “A” section, block “C…T=2” means the time (2 ms) of section “C” in the graphic; block “D…V=0” means “0 volts”, block “D…T=2” means the delay time to start another waveform. Letter “N” represents START, RESET AND CANCEL buttons to generate or stop waveform output.

Figure 7 shows the same Rectangular “A” waveform with

V(A)=5, T(A)=2, V(B)=20, T(B)=2, V(C)=5, T(C)=2, V(D)=0, T(D)=3.

IV. RECEIVER

We used a discrete electronic receiver (DER) to create the desire waveforms UES shown in this paper, because the VLSI receiver designed is not implanted yet on PMMA substrate. The DER involves a RWS-434 module, MC AT90S2313, DAC 0800 converter, and an OPAMP LM741. We see in Figure 8 a version about 433 MHz wireless receivers. Figures 12 and 16, show a low-bypass 1st order filter as an output circuit with a capacitor and a silicon diode used to control manually the waveforms’ characteristics (amplitude, frequency, waveform, bipolar voltages); when we saw the exactly patterns desired, we programmed those patterns into the UES.

The electronic used to build waveforms shown in this

work, is not the real problem, but to develop a VLSI circuit implanted on PMMA which holds every part used to create these waveforms, is the main proposal of this work.

DER has 2 modes of operation; mode “A” searches

subroutines pre-charged in the MC´s flash memory. In mode “B”, the transmitter sends full code instructions to the receiver to develop new algorisms waveforms in it. Mode “B” is very useful when we want to generate any waveform which is not pre-charged in the MC receiver’s memory. VLSI-UES design has to send preprogrammed waveforms.

Actually there are 5 pre-charged subroutines in DER-

MC´s flash memory (SI produces rectangular “A” and rectangular “B” with the same subroutine-symmetry but with different values). Each subroutine generates bit frames, which are converter by the DAC 0800 to analog bipolar voltages (see figures 9, 10, 11, 13, 14, 15 and 17).

K

L

M

N



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The receiver’s MC AT90S2313 compares the hexadecimal word transmitted with the header of the 8 previous pre-charged subroutines, and when they match, waveform subroutine is generated and sends it in the input of the DAC 0800, in order to get an analog bipolar voltage output.

XTL1

4 MHZ

C50.1u

R35K

R25K

C4 0.01u

RESET

C222p

R45K

R6

5K

3

26

7145

-

+

U5

LM741

C122p

R14.7K

VLC1

Iout-NEG2

V-3

Iout4

MSB-B15

B26

B37

B48 B5 9B6 10B7 11LSB-B8 12V+ 13Vref (+) 14Vref (-) 15COMPENSATION 16

U4

DAC0800-DIP

RESET1XTAL2

4 XTAL15

GND10VCC20

PB0/AIN0 12

PB1/AIN1 13

PB2 14

PB3/OC1 15

PB416

PB5/MOSI 17

PB6/MISO 18

PB7/SCK 19

PD0/RXD2

PD1/TXD3

PD2/INT06

PD3/INT17

PD4/T08

PD5/T19

PD6/ICP11

U3

AT90S2313

C30.1u

R55K

DATA_IN

E1

ANTENNA

+9VCD -9VCD

+9VCD

+5VCD

-9VCD

+9VCD

-9VCD

GN

DD

IG_D

ATA_

OU

TLI

NEA

R_O

UT

VCC

VCC

GN

DG

ND

ANT

U1 RWS-434

+5VCD

TO WAVEFORM MAKER

1 21U2A

74LS14

Fig. 8. 433 MHz Wireless receiver with a MC AT90S2313 and a DAC 0800

converter

V. RESULTS

In order to use DAC 0800, we divided the 256 decimal values from $00 to $FF hexadecimal (we used the symbol “$” to express a “hexadecimal word”) of one 8-bit register in two portions, the first, includes negatives values (0 to 128), and the second (129 to 255), includes positives values. This convention can vary depending on the application. The 0 Volt reference, is the hexadecimal word $80, and the highest positive voltage is $ FF. The middle values from 0 to 128, and 129 to 255, correspond to values of middle voltages. In figures 9 and 10, we can see squared waveforms signals. The process to generate the waveform in figure 9 is the next:

• The MC´s transmitter generates the hexadecimal word

$BC which correspond to (+) 1 Volt. • 1-milisecond delay subroutine starts. • MC´s transmitter generates a hexadecimal word $4B,

which correspond to (–) 1 Volt. • 1-milisecond delay subroutine starts again. • Is generated the word $FF, which correspond to (+)2

Volts, and so on.

Fig. 9. Symmetric waveform 1

In figure 10 we can see the process to generate the

waveform number 2: 1-milisecond delay subroutine “A”, “B”, and “C”, where the hexadecimal words sequence are $80, $FF, $80, $00, and $80 which correspond to their voltage values of 0 V, (+)2 VCD, 0 V, (–)2 VCD, and 0 VCD respectively.

Fig. 10. Symmetric waveform 2

Triangular waveform showed in figure 11, is a

hexadecimal incremental/decremental generator which follows conversions in the DAC 0800. This is the procedure to generate waveform in figure 11: the first hexadecimal word to be generated is $80 (0 Analog Volts), then the subroutine increments this value to $81, $82, etc, until the value reaches (+) 1 Volt. Next, the hexadecimal word has been decremented from $BC (+1 Volt) to $4B (– 1 Volt), and so on.

A

B

C



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Fig. 11. Triangular waveform generated by incremental/decremental

hexadecimal words

If we want to the VLSI-UES generates exclusive wavelets in figure 13, we need the circuit in figure 12 has to be implanted on PMMA.

Fig. 12. Output circuit to generate bipolar sinusoidal wavelets

Fig. 13. Bipolar sinusoidal wavelet

In figure 14, we can see the bipolar analog voltage

generated point by point with the UES. Using delay subroutines, the sinusoidal wavelets could be more separated each other. So we can control waveform generator frequency as desire. The finally work frequency can vary since 1 Hertz (or less) to 1 MHz.

Fig. 14. Bipolars analog voltages generated by DAC 0800 In electro-acupuncture and urinary disorders, is used a

wavelet called “Chinese wavelet” (Figure 15) [7] which is built by a squared signal in the positive cycle, and in the negative cycle by an exponential discharge signal. That waveform is a bipolar symmetric AC pulse which produces depolarization in both senses [8].

In figure 16, the resistor’s value increases or decreases the

discharge time in the capacitor. Diode “D1” cuts the signal in the positive cycle. The hexadecimal word which are taken by the RWS-434 module, controls the “ON” positive signal timing, the exponential discharge of the negative signal, and wavelet’s frequency.

Fig. 15. Chinese wavelet

If we want to UES on PMMA generates only a Chinese wavelet, we can implement the circuit in figure 16 (circuit with a low-bypass filter and a diode).

RWS-436

WAVEFORM MAKER

RESISTOR VAR

+ C

WAVE_OUT

D1

Fig. 16. Output Circuit to Generate a Chinese Wavelet (outside the UES)

RWS-437

WAVEFORM MAKER

RESISTOR VAR

+ C

WAVE_OUT

+1 +1

-0.3

+2.4

-0.8t



205

Much other kind of waveforms can be built with UES for other general applications, for example, waveform in figure 17.

Fig. 17. Bipolar saw-tooth waveform

We can use encoders/decoders to reduce noise in the

communications. To reduce undesired interference from another transmitter source, ID headers could be sent from the transmitter.

VI. CONCLUSIONS

This work is an alternative to generate any waveform to be applied to electro-stimulation offering possibility of programming the stimulus parameters such as the frequency, duration, amplitude of the pulses, and different bipolar values [9]. The proposed system can be implemented with a set of commercial circuits, easy programmability, and low cost implementation. Bio-signal stimulation can be applied in different medical applications; we show in this paper the technique used to generate complex waveforms. The technological approach presented in this paper shows that a complex urinary stimulation system can be implemented with ordinary digital technology. PMMA as substrate with known VLSI architectures (digital or analog) is an early solution to integrate VLSI or MEM’s circuits inside the human body. This job concludes we need more effort to develop complex VLSI and MEM’s circuits on PMMA substrates to stimulate and manipulate bio-signals in sacral nerves, or some others bio-applications.

REFERENCES [1] Birinder R. Boveja & Angely Widhany. “US. Patent

Publication No. US 2006/0122660 A1.”, June 8, 2006. [2] Alejandra Alcala, Luis Niño de Rivera and F. Graue-

Wiechers. “Encapsulated Retinal Prosthesis: Biocompatibility and Connectivity”. Investigative Ophthalmology and Visual Science. VIS SCI 2005; 46: E-abstract 1842-B251.

[3] David F. Lozano Salmerón, Luís Niño de Rivera Y. O. “Micro transmitter system implementation to sense intraocular pressure variation using MEMS and VLSI.” 2008.

[4] Joachim N. Burghatz, D. C. Edelstein, Mehmet Soyouer, H. A. Ainspan, Keith A. Jenkins. “RF Circuit Design Aspects of Spiral Inductors on Silicon”. IEEE Journal of Solid-State Circuits, Vol. 33, No. 12, December 1998.

[5] Thomas H. Lee. “The Design of CMOS Radio Frequency Integrated Circuits”. CAMBRIDGE University Press. 1998. Pp 47.

[6] Daniel Robles-Camarillo, Luís Niño de Rivera, H. Quiroz Mercado, M. J. López Miranda,V. Ponomaryov, E. Escamilla, G. Garcia, C. Herrera. “Cornea’s Stimulator Electronic System Biosignal”. 2008.

[7] Angel Regueiro Gómez, Mukoil Romanos Zapata. “Electro-stimulator for Acupuncture”. Umbral científico, June. No. 002. Universitary Foundation Manuela Beltrán. Bogotá, Colombia. 2003.

[8] Erick Mendoza Carrillo, Roberto Vega Serrano, Gildardo Navarro Peña, Néstor Ceballos C. “Electrical Stimulation, Applications and News in Urology”. Urinary Mexican College. Vol. XVII, No. 4. October-December 2002. Pp 207-214.

[9] Jaouhar Mou’ine, Daniel Brunner, and Zied Chtourou. “Design and Implementation of a Multichannel Urinary Incontinence Prosthesis”. Proceedings of the 22nd Annual EMBS International Conference. July 23-28, 2000, Chicago IL. Pp 1100-1103.



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